Researcher Database

Researcher Profile and Settings

Master

Affiliation (Master)

  • Faculty of Information Science and Technology Electronics for Informatics Advanced Electronics

Affiliation (Master)

  • Faculty of Information Science and Technology Electronics for Informatics Advanced Electronics

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Profile and Settings

Affiliation

  • Hokkaido University, Graduate School of Information Science and Technology Division of Electronics for Informatics, Professor

Degree

  • Ph. D.(Toyohashi University of Technology)

Profile and Settings

  • Contact Point

    takeiist.hokudai.ac.jp
  • Name (Japanese)

    Takei
  • Name (Kana)

    Kuniharu
  • Name

    201701001234812650

Alternate Names

Affiliation

  • Hokkaido University, Graduate School of Information Science and Technology Division of Electronics for Informatics, Professor

Achievement

Research Interests

  • 常時生体計測   Nano materials   Nano devices   Printed electronics   Flexible electronics   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electronic devices and equipment

Research Experience

  • 2023/04 - Today Hokkaido University Graduate School of Information Science and Technology Division of Electronics for Informatics Professor
  • 2022/04 - 2023/03 Osaka Metropolitan University Department of Physics and Electronics Professor
  • 2019/04 - 2022/03 Osaka Prefecture University Department of Physics and Electronics Professor
  • 2017/10 - 2021/03 JST PRESTO Researcher
  • 2017/04 - 2019/03 Osaka Prefecture University Department of Physics and Electronics Associate Professor
  • 2013/04 - 2017/03 Osaka Prefecture University Department of Physics and Electronics Assistant Professor
  • 2009/04 - 2013/02 Lawrence Berkeley National Laboratory Material Science Division Postdoctoral scholar
  • 2009/04 - 2013/02 University of California, Berkeley EECS Postdoctoral scholar

Education

  • 2003/04 - 2009/03  豊橋技術科学大学 大学院
  • 2001/04 - 2003/03  Toyohashi University of Technology
  • 1996/04 - 2001/03  National Institute of Technology, Asahikawa College

Awards

  • 2021/03 一般財団法人丸文財団 丸文学術賞
     無機ナノ材料を用いたフレキシブル集積化センサシステムの開発 
    受賞者: 竹井邦晴
  • 2020/04 FFIT FFIT award
  • 2020/02 NEDO NEDO-TCP 2019
  • 2018/11 Clarivate Analytics Highly Cited Researchers 2018
     
    受賞者: TAKEI, Kuniharu
  • 2018/04 文部科学省 文部科学大臣表彰 若手科学者賞
     
    受賞者: 竹井 邦晴
  • 2016/07 電子材料シンポジウム EMS賞
     
    受賞者: 竹井 邦晴
  • 2015/12 MEXT NISTEP Researcher 2015
     
    受賞者: TAKEI, Kuniharu
  • 2015/07 ATI 研究奨励賞
     
    受賞者: 竹井 邦晴
  • 2013/11 ネイチャー・インダストリー・アワード 特別賞
     
    受賞者: 竹井 邦晴
  • 2013/08 MIT Technology Review 35 Top Young Innovators under 35
     
    受賞者: TAKEI, Kuniharu

Published Papers

  • Stretchable Electronic Skin Using Laser-Induced Graphene and Liquid Metal With an Action Recognition System Powered by Machine Learning
    Y. Li, G. Matsumura, Y. Xuan, S. Honda, K. Takei
    Advanced Functional Materials 2024/04 [Refereed][Not invited]
  • Mitsuo Asai, Satoko Honda, Nobuyuki Isshiki, Masahumi Takesue, Atsushi Hiraishi, Mayu Yamada, Kuniharu Takei
    Advanced Materials Technologies 8 (21) 2300842  2365-709X 2023/08/29 [Refereed][Not invited]
     
    Flexible sensors enable the gathering of information from nonplanar surfaces, which facilitates huge data collection tasks. Monitoring of pH levels in industrial wastewater is one example. For this purpose, stable, reliable flexible pH sensors are required to monitor pH in pipes or containers. Carbon nanotube field‐effect transistors (CNT‐FETs) are attractive transducers for flexible sensors because of their multiple functionalities, such as good electrical properties and mechanical flexibility. However, semiconducting single‐walled carbon nanotubes (s‐SWNTs) must be separated from metallic SWNTs of high purity for channel materials to be used in CNT‐FETs. Herein, a simple method to sort s‐SWNTs in an aqueous system using only dispersion and centrifugation is developed. This sorting method is much less expensive than other techniques, such as density gradient ultracentrifugation, agarose‐gel chromatography, or selective sorting by conjugated polymers. These sorted s‐SWNTs result in high‐performance CNT‐FETs with electrical hysteresis reduced to almost zero and improved bias stability. This method demonstrates the importance of the solubility parameter between polymers and water for CNT‐FET hysteresis. The resulting carbon nanotubes also have high uniformity of characteristics, making them valuable as transducers for flexible sensors. Furthermore, real‐time pH monitoring using ion‐sensitive, field‐effect transistors (ISFETs) based on CNT‐FET is demonstrated.
  • Satoko Honda, Ryuki Tanaka, Guren Matsumura, Naruhito Seimiya, Kuniharu Takei
    Advanced Functional Materials 33 (44) 2306516  1616-301X 2023/08/22 [Refereed][Not invited]
     
    Abstract Flexible sensors that can be attached to the body to collect vital data wirelessly enable real‐time, early‐stage diagnosis for human health management. Wearable sweat sensors have received considerable attention for real‐time physiological monitoring. Unlike conventional methods that require blood‐drawing in a clinic, sweat analyses may enable noninvasive tracking of health conditions for early‐stage diagnosis. Even though a variety of studies to monitor metabolites and other substances have been conducted, automatic, continuous, long‐term, simultaneous monitoring of perspiration rate and electrolytes, which are important parameters in dehydration, has yet to be achieved because of challenges related to sensor design. Here a wireless, wearable, integrated, microfluidic sensor system that can continuously measure these parameters in real‐time for prolonged periods are presented. The proposed sensors are systematically characterized, and machine learning is used to predict device tilt angle to calibrate sensor output signals. Using the sensor design to form a water droplet in a fluidic channel, high‐volume perspiration rate is continuously monitored for more than 7000 s (total sweat volume >170 µL). By testing 10 subjects, physiological responses to ingestion of a sports drink are confirmed by measuring perspiration rhythm changes extracted from real‐time, continuous sweat impedance and rate.
  • Junjun Zhang, Cu Dang Van, Kuniharu Takei, Min Hyung Lee
    Journal of Industrial and Engineering Chemistry 124 550 - 557 1226-086X 2023/08 [Refereed][Not invited]
  • Akito Fukui, Keigo Matsuyama, Hiroaki Onoe, Shun Itai, Hidekazu Ikeno, Shunsuke Hiraoka, Kousei Hiura, Yuh Hijikata, Jenny Pirillo, Takahiro Nagata, Kuniharu Takei, Takeshi Yoshimura, Norifumi Fujimura, Daisuke Kiriya
    ACS Nano 1936-0851 2023/07/17
  • Yifei Luo, Mohammad Reza Abidian, Jong-Hyun Ahn, Deji Akinwande, Anne M. Andrews, Markus Antonietti, Zhenan Bao, Magnus Berggren, Christopher A. Berkey, Christopher John Bettinger, Jun Chen, Peng Chen, Wenlong Cheng, Xu Cheng, Seon-Jin Choi, Alex Chortos, Canan Dagdeviren, Reinhold H. Dauskardt, Chong-an Di, Michael D. Dickey, Xiangfeng Duan, Antonio Facchetti, Zhiyong Fan, Yin Fang, Jianyou Feng, Xue Feng, Huajian Gao, Wei Gao, Xiwen Gong, Chuan Fei Guo, Xiaojun Guo, Martin C. Hartel, Zihan He, John S. Ho, Youfan Hu, Qiyao Huang, Yu Huang, Fengwei Huo, Muhammad M. Hussain, Ali Javey, Unyong Jeong, Chen Jiang, Xingyu Jiang, Jiheong Kang, Daniil Karnaushenko, Ali Khademhosseini, Dae-Hyeong Kim, Il-Doo Kim, Dmitry Kireev, Lingxuan Kong, Chengkuo Lee, Nae-Eung Lee, Pooi See Lee, Tae-Woo Lee, Fengyu Li, Jinxing Li, Cuiyuan Liang, Chwee Teck Lim, Yuanjing Lin, Darren J. Lipomi, Jia Liu, Kai Liu, Nan Liu, Ren Liu, Yuxin Liu, Yuxuan Liu, Zhiyuan Liu, Zhuangjian Liu, Xian Jun Loh, Nanshu Lu, Zhisheng Lv, Shlomo Magdassi, George G. Malliaras, Naoji Matsuhisa, Arokia Nathan, Simiao Niu, Jieming Pan, Changhyun Pang, Qibing Pei, Huisheng Peng, Dianpeng Qi, Huaying Ren, John A. Rogers, Aaron Rowe, Oliver G. Schmidt, Tsuyoshi Sekitani, Dae-Gyo Seo, Guozhen Shen, Xing Sheng, Qiongfeng Shi, Takao Someya, Yanlin Song, Eleni Stavrinidou, Meng Su, Xuemei Sun, Kuniharu Takei, Xiao-Ming Tao, Benjamin C. K. Tee, Aaron Voon-Yew Thean, Tran Quang Trung, Changjin Wan, Huiliang Wang, Joseph Wang, Ming Wang, Sihong Wang, Ting Wang, Zhong Lin Wang, Paul S. Weiss, Hanqi Wen, Sheng Xu, Tailin Xu, Hongping Yan, Xuzhou Yan, Hui Yang, Le Yang, Shuaijian Yang, Lan Yin, Cunjiang Yu, Guihua Yu, Jing Yu, Shu-Hong Yu, Xinge Yu, Evgeny Zamburg, Haixia Zhang, Xiangyu Zhang, Xiaosheng Zhang, Xueji Zhang, Yihui Zhang, Yu Zhang, Siyuan Zhao, Xuanhe Zhao, Yuanjin Zheng, Yu-Qing Zheng, Zijian Zheng, Tao Zhou, Bowen Zhu, Ming Zhu, Rong Zhu, Yangzhi Zhu, Yong Zhu, Guijin Zou, Xiaodong Chen
    ACS Nano 17 (6) 5211 - 5295 1936-0851 2023/03/09 [Refereed][Not invited]
  • Seiji Wakabayashi, Takayuki Arie, Seiji Akita, Kohei Nakajima, Kuniharu Takei
    Advanced Materials 34 2201663 - 2201663 0935-9648 2022/07/01 [Refereed][Not invited]
  • L. Liu, P. M. Pancorbo, T.-H. Xiao, S. Noguchi, M. Marumi, H. Segawa, S. Karhadkar, J. G. Pable, K. Hiramatsu, T. Itoh, J. Qu, K. Takei, K. Goda
    Advanced Optical Materials 10 (17) 2022/06 [Refereed][Invited]
     
    The last two decades have witnessed a dramatic growth of wearable sensor technology, mainly represented by flexible, stretchable, on-skin electronic sensors that provide rich information of the wearer's health conditions and surroundings. A recent breakthrough in the field is the development of wearable chemical sensors based on surface-enhanced Raman spectroscopy (SERS) that can detect molecular fingerprints universally, sensitively, and noninvasively. However, while their sensing properties are excellent, these sensors are not scalable for widespread use beyond small-scale human health monitoring due to their cumbersome fabrication process and limited multifunctional sensing capabilities. Here, a highly scalable, wearable SERS sensor is demonstrated based on an easy-to-fabricate, low-cost, ultrathin, flexible, stretchable, adhesive, and biointegratable gold nanomesh. It can be fabricated in any shape and worn on virtually any surface for label-free, large-scale, in situ sensing of diverse analytes from low to high concentrations (10–106 × 10−9 m). To show the practical utility of the wearable SERS sensor, the sensor is tested for the detection of sweat biomarkers, drugs of abuse, and microplastics. This wearable SERS sensor represents a significant step toward the generalizability and practicality of wearable sensing technology.
  • Satoko Honda, Hyuga Hara, Takayuki Arie, Seiji Akita, Kuniharu Takei
    iScience 25 (4) 104163 - 104163 2589-0042 2022/04 [Refereed][Invited]
  • Kazutoshi Tanaka, Yuji Tokudome, Yuna Minami, Satoko Honda, Toshiki Nakajima, Kuniharu Takei, Kohei Nakajima
    Advanced Intelligent Systems 4 (3) 2100166 - 2100166 2640-4567 2022/03 [Refereed][Not invited]
  • Wireless, minimized, stretchable, and breathable electrocardiogram sensor system
    Y. Xuan, H. Hara, S. Honda, Y. Li, Y. Fujita, T. Arie, S. Akita, K. Takei
    Applied Physics Reviews 9 011425  2022/03 [Refereed][Not invited]
  • Akito Fukui, Yuki Aoki, Keigo Matsuyama, Hisashi Ichimiya, Ryo Nouchi, Kuniharu Takei, Atsushi Ashida, Takeshi Yoshimura, Norifumi Fujimura, Daisuke Kiriya
    Nanotechnology 33 (7) 075602  0957-4484 2022/02/12 [Refereed][Not invited]
     
    Abstract Graphene nanoribbon (GNR)-based materials are a promising device material because of their potential high carrier mobility and atomically thin structure. Various approaches have been reported for preparing the GNR-based materials, from bottom-up chemical synthetic procedures to top-down fabrication techniques using lithography of graphene. However, it is still difficult to prepare a large-scale GNR-based material. Here, we develop a procedure to prepare a large-scale GNR network using networked single-layer inorganic nanowires. Vanadium pentoxide (V2O5) nanowires were assembled on graphene with an interfacial layer of a cationic polymer via electrostatic interaction. A large-scale nanowire network can be prepared on graphene and is stable enough for applying an oxygen plasma. Using plasma etching, a networked graphene structure can be generated. Removing the nanowires results in a networked flat structure whose both surface morphology and Raman spectrum indicate a GNR networked structure. The field-effect device indicates the semiconducting character of the GNR networked structure. This work would be useful for fabricating a large-scale GNR-based material as a platform for GNR junctions for physics and electronic circuits.
  • K. Nakagawa, K. Satoh, S. Murakami, K. Takei, S. Akita, T. Arie
    Scientific Reports 11 (1) 19533 - 19533 2021/10 [Refereed][Not invited]
     
    Straintronics is a new concept to enhance electronic device performances by strain for next-generation information sensors and energy-saving technologies. The lattice deformation in graphene can modulate the thermal conductivity because phonons are the main heat carriers. However, the device fabrication process affects graphene's heat transport properties due to its high stretchability. This study experimentally investigates the change in the thermal conductivity when biaxial tensile strain is applied to graphene. To eliminate non-strain factors, two mechanisms are considered: pressure-induced and electrostatic attraction-induced strain. Raman spectroscopy and atomic force microscopy precisely estimate the strain. The thermal conductivity of graphene decreases by approximately 70% with a strain of only 0.1%. Such thermal conductivity controllability paves the way for applying graphene as high-efficiency thermal switches and diodes in future thermal management devices.
  • Wireless and flexible skin moisture and temperature sensor sheets toward the study of thermoregulator center
    Y. Lu, Y. Fujita, S. Honda, S.-H. Yang, Y. Xuan, K. Xu, T. Arie, S. Akita, K. Takei
    Advanced Healthcare Materials 10 202100130  2021/09 [Refereed][Invited]
  • Y. Xuan, Y. Lu, S. Honda, T. Arie, S. Akita, K. Takei
    Advanced Materials Technologies 6 (9) 2100259  2021/09 [Refereed][Not invited]
     
    Owing to the demand for the development of Internet of things devices, multiple sensor platforms are of great interest to society and its future electronics. One of these emerging devices is a mechanically flexible sensor system that can attach and conform to nonplanar surfaces, unlike conventional inflexible sensor chips. To realize this concept, a variety of flexible sensor systems must be developed from materials to system integrations. This study proposes a flexible sensor system as one of the candidates: an active-matrix-based flexible optical image sensor that uses a stacked nanosheet film formed by a solution process and transistors. The results show that the sensor can be utilized as an optical imager because it detects enough optical stimuli. In addition to the sensitivity, the mechanical flexibility of the active-matrix optical sensor is tested, and the results exhibit good electrical stability even after 1000 bending cycles and 0.85 cm bending radius. The mapping of light distribution is successfully demonstrated under both flat and curved conditions. This flexible optical sensor array shows the high possibility to image the light distribution for high-resolution and low power mapping realized by active matrix circuit integration.
  • Flexible hybrid sensor systems with feedback functions
    Kaichen Xu, Yuyao Lu, Kuniharu Takei
    Advanced Functional Materials 31 2007436  2021/09 [Refereed][Invited]
  • Multimodal wearable sensor sheet for health-related chemical and physical monitoring
    S. Hozumi, S. Honda, T. Arie, S. Akita, K. Takei
    ACS Sensors 6 1918 - 1924 2021/04 [Refereed][Not invited]
  • Taichi Inoue, Tetsuki Saito, Kuniharu Takei, Takayuki Arie, Yasumitsu Miyata, Seiji Akita
    Applied Physics Express 14 (3) 1882-0778 2021/03 
    We investigate light-induced persistent resonance frequency shift on MoS2 mechanical resonators towards optically tunable nano-electro-mechanical systems with optical memory function. After the termination of light irradiation, the resonance frequency shifts downwards and the downshift is maintained for more than 20 min. This behavior is induced by trapped photogenerated holes at defects or contamination on MoS2 similar to the persistent photoconductivity. The trapped holes screen the electrostatic force acting on MoS2, which results in the reduction of the tension of MoS2. The downshift can be eliminated by applying the excess voltage pulse to MoS2 to induce Joule heating.
  • K. Xu, Y. Fujita, Y. Lu, S. Honda, M. Shiomi, T. Arie, S. Akita, K. Takei
    Advanced Materials 33 (18) 2008701  0935-9648 2021 [Refereed]
     
    Emerging feedback systems based on tracking body conditions can save human lives. In particular, vulnerable populations such as disabled people, elderly, and infants often require special care. For example, the high global mortality of infants primarily owing to sudden infant death syndrome while sleeping makes request for extraordinary attentions in neonatal intensive care units or daily lives. Here, a versatile laser-induced graphene (LIG)-based integrated flexible sensor system, which can wirelessly monitor the sleeping postures, respiration rate, and diaper moisture with feedback alarm notifications, is reported. A tilt sensor based on confining a liquid metal droplet inside a cavity can track at least 18 slanting orientations. A rapid and scalable laser direct writing method realizes LIG patterning in both the in-plane and out-of-plane configurations as well as the formation of nonstick conductive structures to the liquid metal. By rationally merging the LIG-based tilt, strain, and humidity sensors on a thin flexible film, the multimodal sensor device is applied to a diaper as a real-time feedback tracking system of the sleeping posture, respiration, and wetness toward secure and comfortable lives. User-friendly interfaces, which incorporate alarming functions, provide timely feedback for caregivers tending to vulnerable populations with limited self-care capabilities.
  • Yuyao Lu, Kaichen Xu, Min-Quan Yang, Shin-Yi Tang, Tzu-Yi Yang, Yusuke Fujita, Satoko Honda, Takayuki Arie, Seiji Akita, Yu-Lun Chueh, Kuniharu Takei
    Nanoscale Horizons 6 (3) 260 - 270 2055-6756 2021/01 [Refereed][Not invited]
     

    A Pd/HNb3O8 flexible humidity sensor is developed with long-term stability at a high humidity level (∼90% RH). Using the sensor, wireless monitoring of human respirations and finger moisture variation under exercise is successfully demonstrated.

  • K. Tanaka, S.-H. Yang, Y. Tokudome, Y. Minami, Y. Lu, T. Arie, S. Akita, K. Takei, T. Nakajima
    Advanced Intelligent Systems 3 2000174 - 2000174 2640-4567 2020/11 [Refereed][Not invited]
  • Kuniharu Takei
    Journal of The Japan Institute of Electronics Packaging 23 (5) 347 - 352 1343-9677 2020/08/01 [Refereed][Invited]
  • Detachable flexible ISFET-based pH sensor array with a flexible connector
    Satoko Honda, Mao Shiomi, Takafumi Yamaguchi, Yusuke Fujita, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Advanced Electronic Materials 6 2000583  2020/08 [Refereed][Not invited]
  • Yuyao Lu, Kaichen Xu, Lishu Zhang, Minako Deguchi, Hiroaki Shishido, Takayuki Arie, Ruihua Pan, Akitoshi Hayashi, Lei Shen, Seiji Akita, Kuniharu Takei
    ACS Nano 14 10966 - 10975 1936-0851 2020/07/28 [Refereed][Not invited]
  • Seiji Wakabayashi, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ACS Omega 5 (28) 17721 - 17725 2470-1343 2020/07/09 [Refereed][Not invited]
  • Yuki Yamada, Keisuke Shinokita, Yasuo Okajima, Sakura N Takeda, Yuji Matsushita, Kuniharu Takei, Takeshi Yoshimura, Atsushi Ashida, Norifumi Fujimura, Kazunari Matsuda, Daisuke Kiriya
    ACS Applied Materials & Interfaces 12 (32) 36496 - 36504 1944-8244 2020/07/07 [Refereed][Not invited]
     
    © 2020 American Chemical Society. To advance the development of atomically thin optoelectronics using two-dimensional (2D) materials, engineering strong luminescence with a physicochemical basis is crucial. Semiconducting monolayer transition-metal dichalcogenides (TMDCs) are candidates for this, but their quantum yield (QY) is known to be poor. Recently, a molecular superacid treatment of bis(trifluoromethane)sulfonimide (TFSI) generated unambiguously bright monolayer TMDCs and a high QY. However, this method is highly dependent on the processing conditions and therefore has not been generalized. Here, we shed light on environmental factors to activate the photoluminescence (PL) intensity of the TFSI-treated monolayer MoS2, with a factor of more than 2 orders of magnitude greater than the original by photoactivation. The method is useful for both mechanically exfoliated and chemically deposited samples. The existence of photoirradiation larger than the band gap demonstrates enhancement of the PL of MoS2; on the other hand, activation by thermal annealing, as demonstrated in the previous report, is less effective for enhancing the PL intensity. The photoactivated monolayer MoS2 shows a long lifetime of ∼1.35 ns, more than a 30-fold improvement over the original as exfoliated. The consistent realization of the bright monolayer MoS2 reveals that air exposure is an essential factor in the process. TFSI treatment in a N2 environment was not effective for achieving a strong PL, even after the photoactivation. These findings can serve as a basis for engineering the bright atomically thin materials for 2D optoelectronics.
  • Toshiki Nakajima, Takafumi Yamaguchi, Seiji Wakabayashi, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Advanced Materials Technologies 5 (7) 2000201 - 2000201 2365-709X 2020/07 [Refereed][Not invited]
  • Takafumi Yamaguchi, Daisuke Yamamoto, Takayuki Arie, Seiji Akita, Kuniharu Takei
    RSC Advances 10 (29) 17353 - 17358 2020/05 [Refereed][Not invited]
     
    To monitor health and diagnose disease in the early stage, future healthcare standards will likely include the continuous monitoring of various vital data. One approach to collect such information is a wearable and flexible device, which detects information from the skin surface. An important dataset is heart pulse information. Herein a method to monitor the detailed pulse signal from a wrist stably and reliably is proposed. Specifically, a soft pneumatic balloon operated by a soft pump applies the appropriate pressure over a tactile sensor onto the radial artery of the wrist to detect detailed heart pulse waves. The soft pump, pneumatic balloon, and flexible tactile pressure sensor are characterized as a fundamental study. Additionally, a proof-of-concept of this integrated device platform is demonstrated by monitoring the heart pulse from a wrist with and without the soft pump functions.
  • Out-of-plane electric whiskers based on nanocarbon strain sensors for multi-directional detection
    S. Wakabayashi, T. Yamaguchi, T. Arie, S. Akita, K. Takei
    Carbon 158 698 - 703 2020/01 [Refereed][Invited]
  • Takafumi Yamaguchi, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS) 2020- 881 - 884 1084-6999 2020/01/01 
    This study proposes a wearable and flexible heart pulse sensor detected from a wrist using the tactile pressure sensor film. In general, it is difficult to monitor heart pulse stably under movement of wrist due to the change of position and pressure of the sensors on a wrist. To address this issue, soft pneumatic pump and actuator are integrated to fix the sensor on a wrist even under movement of body. Fundamental properties of pneumatic pump and tactile pressure sensor are studied in addition to the heart pulse monitoring.
  • Seiji Wakabayashi, Takafumi Yamaguchi, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS) 2020- 235 - 238 1084-6999 2020/01/01 
    This study proposes an out-of-plane electronic whisker (e-whisker) array that integrates a three-dimension whisker structure using polydimethylsiloxane (PDMS) and nanocarbon-based strain sensors. The strain sensor is fabricated by a laser-induced graphene from polyimide film and transfer process from polyimide to the PDMS. Fundamental characteristics of an out-of-plane electronic whisker such as sensitivity and response time are studied as well as the demonstration of e-whisker array. By considering the device structure, multiple directional force detection is realized for the first time. Based on the properties of the sensors, simple and low-cost three-dimensional device fabrication process works well for the e-whisker application.
  • K. Xu, Y. Lu, T. Yamaguchi, T. Arie, S. Akita, K. Takei
    ACS Nano 13 (12) 14348 - 14356 1936-0851 2019/12 [Refereed][Not invited]
     
    Elaborate manipulation of heat transfer renders proper operation of diverse thermal-related technologies. However, accurate implementation of thermal-based or transduction sensing on a thin flexible film over unusual surfaces remains challenging. Herein, efficient thermal management realizes highly accurate flexible multifunctional sensor sheets using a low thermal conductive medium as a thermal barrier. An approximately 50-fold enhancement in the thermal sensing accuracy, which is nearly independent of the changes in the external surroundings, is achieved. Such rational control of heat convection and conduction allows to not only dynamically monitor air flow, but also sight the large-scale air flow distribution on curved surfaces using a flexible thermal flow sensor array. Additionally, accurate wearable skin temperature monitoring independent of the sudden surrounding variations is achieved. This work addresses the formidable challenge of untethered heat transfer induced imprecise thermal related sensing, which universally exists in skin-inspired Internet of Things (IoT) applications.
  • Yoshikawa Daiki, Takei Kuniharu, Arie Takayuki, Akita Seiji
    APPLIED PHYSICS EXPRESS 12 (10) 1882-0778 2019/10/01 [Refereed][Not invited]
     
    Hexagonal boron nitride (h-BN) is an emergent material for single photon emitters that are ultrabright and stable under ambient conditions. To realize h-BN nano-electromechanical resonators (NEMRs) with quantum effects, the oscillation would be electrically controlled without unexpected photothermal effects. This study investigates the mechanical resonance of an optically transparent and electrically insulating h-BN NEMR, which was actuated by an electrostatic force based on the dielectric effect. Under light irradiation, resonance properties show no significant light intensity or wavelength dependence, which indicates that the photothermal effect is well eliminated because of optically transparent h-BN NEMR.
  • Takafumi Yamaguchi, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems and Eurosensors XXXIII, TRANSDUCERS 2019 and EUROSENSORS XXXIII 543 - 546 2019/06/01 
    For comfortable and convenient human life, human-interactive and communicative robot has attractive attention from industrial to home-use applications. One of human-friendly robotic structures is pneumatic balloon type soft robots using mainly silicone rubber operated by compressed air. In this study, we develop a tactile pressure sensor array integrated with pneumatic soft robotic hand to monitor tactile pressure like a human skin. The important advance of this study is to integrate flexible sensors embedded in soft robotic hand without sacrificing softness and flexibility.
  • Mao Shiomi, Shogo Nakata, Yusuke Fujita, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems and Eurosensors XXXIII, TRANSDUCERS 2019 and EUROSENSORS XXXIII 370 - 373 2019/06/01 
    This study reports a highly sensitivity wearable flexible pH sensor using a charge-couple device (CCD) structure. Multi-cycle charge transfer and accumulation depending on pH value realize higher sensitivity than that of the Nernst theory (i.e. 59 mV/pH at room temperature (R.T.)). One difficulty to form the CCD structure on a flexible film is the semiconductor junction due to thermal budget issue for doping injection into semiconductor films. To address this, Schottky junction controlled by an external gate bias is proposed. By optimizing the structure and fabrication process, flexible CCD-based pH sensor is successfully demonstrated. In addition to the study of its fundamental characteristics, real-time sweat pH monitoring is carried out as the first proof-of-concept by attaching the device on an arm. The results show that this flexible pH sensor would be helpful to detect a biological information from sweat.
  • Graphene and carbon nanotube heterojunction transistors with individual gate control
    M. Shiomi, Y. Mochizuki, Y. Imakita, T. Arie, S. Akita, K. Takei
    ACS Nano 13 4771 - 4777 2019/04 [Refereed][Not invited]
  • Human-like electronic skin-integrated soft robotic hand
    T. Yamaguchi, T. Kashiwagi, T. Arie, S. Akita, K. Takei
    Advanced Intelligent Systems 1 1900018  2019/04 [Refereed][Not invited]
  • W. Gao, H. Ota, D. Kiriya, K. Takei, A. Javey
    Accounts of Chemical Research 52 (3) 523 - 533 0001-4842 2019/03 [Refereed][Invited]
     
    © 2019 American Chemical Society. ConspectusWearable sensors play a crucial role in realizing personalized medicine, as they can continuously collect data from the human body to capture meaningful health status changes in time for preventive intervention. However, motion artifacts and mechanical mismatches between conventional rigid electronic materials and soft skin often lead to substantial sensor errors during epidermal measurement. Because of its unique properties such as high flexibility and conformability, flexible electronics enables a natural interaction between electronics and the human body. In this Account, we summarize our recent studies on the design of flexible electronic devices and systems for physical and chemical monitoring. Material innovation, sensor design, device fabrication, system integration, and human studies employed toward continuous and noninvasive wearable sensing are discussed.A flexible electronic device typically contains several key components, including the substrate, the active layer, and the interface layer. The inorganic-nanomaterials-based active layer (prepared by a physical transfer or solution process) is shown to have good physicochemical properties, electron/hole mobility, and mechanical strength. Flexible electronics based on the printed and transferred active materials has shown great promise for physical sensing. For example, integrating a nanowire transistor array for the active matrix and a conductive pressure-sensitive rubber enables tactile pressure mapping; tactile-pressure-sensitive e-skin and organic light-emitting diodes can be integrated for instantaneous pressure visualization. Such printed sensors have been applied as wearable patches to monitor skin temperature, electrocardiograms, and human activities. In addition, liquid metals could serve as an attractive candidate for flexible electronics because of their excellent conductivity, flexibility, and stretchability. Liquid-metal-enabled electronics (based on liquid-liquid heterojunctions and embedded microchannels) have been utilized to monitor a wide range of physiological parameters (e.g., pulse and temperature).Despite the rapid growth in wearable sensing technologies, there is an urgent need for the development of flexible devices that can capture molecular data from the human body to retrieve more insightful health information. We have developed a wearable and flexible sweat-sensing platform toward real-time multiplexed perspiration analysis. An integrated iontophoresis module on a wearable sweat sensor could enable autonomous and programmed sweat extraction. A microfluidics-based sensing system was demonstrated for sweat sampling, sensing, and sweat rate analysis. Roll-to-roll gravure printing allows for mass production of high-performance flexible chemical sensors at low cost. These wearable and flexible sweat sensors have shown great promise in dehydration monitoring, cystic fibrosis diagnosis, drug monitoring, and noninvasive glucose monitoring.Future work in this field should focus on designing robust wearable sensing systems to accurately collect data from the human body and on large-scale human studies to determine how the measured physical and chemical information relates to the individual's specific health conditions. Further research in these directions, along with the large sets of data collected via these wearable and flexible sensing technologies, will have a significant impact on future personalized healthcare.
  • Toward flexible surface-enhanced Raman scattering (SERS) sensors for point-of-care diagnostics
    K. Xu, R. Zhou, K. Takei, M. Hong
    Advanced Science 6 1900925  2019 [Refereed][Not invited]
  • Highly stable kirigami-structured stretchable strain sensors for perdurable wearable electronics
    K. Xu, Y. Lu, S. Honda, T. Arie, S. Akita, K. Takei
    Journal of Materials Chemistry C 7 9609 - 9617 2019 [Refereed][Not invited]
  • Physical and chemical sensing with electronic skin
    K. Takei, W. Gao, C. Wang, A. Javey
    Proceedings of the IEEE 107 2155 - 2167 2019 [Refereed][Invited]
  • Textile-based flexible tactile force sensor sheet
    Honda, S, Zhu, Q, Satoh, S, Arie, T, Akita, S, Takei, K
    Advanced Functional Materials 29 1807957  2019 [Refereed][Not invited]
  • Multifunctional skin-inspired flexible sensor systems for wearable electronics
    Xu, K, Lu, Y, Takei, K
    Advanced Materials Technologies 4 1800628  2019 [Refereed][Invited]
  • All solution-based heterogeneous material formation for p-n junction diode
    Yamamoto, D, Shiomi, M, Arie, T, Akita, S, Takei, K
    ACS Applied Materials & Interfaces 11 1021 - 1025 2019/01 [Refereed][Not invited]
  • Sang Hwa Lee, Sung-Ho Shin, Morten Madsen, Kuniharu Takei, Junghyo Nah, Min Hyung Lee
    Scientific Reports 8 (1) 2045-2322 2018/12/01 [Refereed][Not invited]
     
    The epitaxial layer transfer process was previously introduced to integrate high-quality and ultrathin III-V compound semiconductor layers on any substrate. However, this technique has limitation for fabrication of sub-micron nanoribbons due to the diffraction limit of photolithography. In order to overcome this limitation and scale down its width to sub-50 nm, we need either a costly short wavelength lithography system or a non-optical patterning method. In this work, high-quality III-V compound semiconductor nanowires were fabricated and integrated onto a Si/SiO2 substrate by a soft-lithography top-down approach and an epitaxial layer transfer process, using MBE-grown ultrathin InAs as a source wafer. The width of the InAs nanowires was controlled using solvent-assisted nanoscale embossing (SANE), descumming, and etching processes. By optimizing these processes, NWs with a width less than 50 nm were readily obtained. The InAs NWFETs prepared by our method demonstrate peak electron mobility of ∼1600 cm2/Vs, indicating negligible material degradation during the SANE process.
  • Shiho Kobayashi, Yuki Anno, Kuniharu Takei, Takayuki Arie, Seiji Akita
    Scientific Reports 8 (1) 2045-2322 2018/12/01 [Not refereed][Not invited]
     
    Graphene/semiconductor Schottky junctions are an emerging field for high-performance optoelectronic devices. This study investigates not only the steady state but also the transient photoresponse of graphene field-effect transistor (G-FET) of which gate bias is applied through the Schottky barrier formed at an n-type Si/graphene interface with a thin oxide layer, where the oxide thickness is sufficiently thin for tunneling of the charge carrier. To analyze the photoresponse, we formulate the charge accumulation process at the n-Si/graphene interface, where the tunneling process through the SiOx layer to graphene occurs along with recombination of the accumulated holes and the electrons in the graphene at the surface states on the SiOx layer. Numerical calculations show good qualitative agreement with the experimentally obtained results for the photoresponse of G-FET.
  • A wearable pH sensor with high sensitivity based on a flexible charge-coupled device
    Nakata, S, Shiomi, M, Fujita, Y, Arie, T, Akita, S, Takei, K
    Nature Electronics 1 596 - 603 2018/11 [Refereed][Not invited]
  • Taichi Inoue, Yuta Mochizuki, Kuniharu Takei, Takayuki Arie, Seiji Akita
    2D Materials 5 2018/09/03 [Not refereed][Not invited]
     
    © 2018 IOP Publishing Ltd. Atomically thin two-dimensional (2D) mechanical resonators should realize highly sensitive force sensors and high performance nano-electro-mechanical systems due to their excellent electrical and mechanical properties. However, practical applications require stability of the resonance frequencies against temperature. Here, we demonstrate the manipulation of the thermal expansion coefficients (TECs) by creating a van der Waals heterojunction using graphene and MoS2, which have opposite signs of TECs. Our method greatly suppresses the apparent TEC of the 2D heterojunction to 1/3 of the monolayer graphene without the detraction of the tunability of the resonance frequency by electrostatic attraction.
  • Yuga Miyamoto, Daiki Yoshikawa, Kuniharu Takei, Takayuki Arie, Seiji Akita
    Japanese Journal of Applied Physics 57 (6) 1347-4065 2018/06/01 [Not refereed][Not invited]
     
    An atomically thin MoS2 field-effect transistor (FET) is expected as an ultrathin photosensor with high sensitivity. However, a persistent photoconductivity phenomenon prevents high-speed photoresponse. Here, we investigate the photoresponse of a MoS2 FET with a thin Al2O3 buffer layer on a SiO2 gate insulator. The application of a 2-nm-thick Al2O3 buffer layer greatly improves not only the steady state properties but also the response speed from 1700 to 0.2 s. These experimental results are well explained by the random localized potential fluctuation model combined with the model based on the recombination of the bounded electrons around the trapped hole.
  • Shogo Nakata, Kenichiro Kanao, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS) 2018- 1096 - 1099 1084-6999 2018/04/24 [Refereed][Not invited]
     
    This study proposes an electronic wallpaper (e-wallpaper) integrated with tactile memorable sensor and temperature sensor to use it as electrical message board and to monitor an environmental temperature for a smart house concept. To realize this, a mechanically flexible nonvolatile floating gate random access memory (FGRAM) array integrated with tactile sensors and temperature sensors are successfully fabricated as a first proof-of-concept. In addition to the device demonstrations, the flexible FGRAM is systematically studied as the fundamental properties such as program voltage and time dependences, retention time, cycle test, and mechanical flexibility. This new device platform may open a door to realize a new class of 'Internet of Things (IoT)' concept.
  • Planar-type printed flexible mechanical switch
    Y. Hasuike, T. Arie, S. Akita, K. Takei
    Advanced Electronic Materials 4 1800134  2018 [Refereed][Not invited]
  • Taichi Inoue, Yuki Anno, Yuki Imakita, Kuniharu Takei, Takayuki Arie, Seiji Akita
    Proceedings of SPIE - The International Society for Optical Engineering 10712 1996-756X 2018 [Refereed][Not invited]
     
    We demonstrate manipulation of nonlinear vibration of graphene mechanical resonator (G-MR) optically by photothermal effects of laser. Different photothermal effects are induced by combining of scattering light and different standing waves of light, which have different effects on nonlinear vibration. Experimental results indicate that nonlinearity is suppressed or promoted for each photothermal effects without almost changing its amplitude. These changes cannot be explained by conventional nonlinear vibration that the nonlinearity increases with increasing amplitude. To reveal the principle of the modulation, we proposed novel vibration model including photothermal effects in nonlinear vibration. Numerical calculation from the model well fits experimental results and revealed the principle. We believe that these technics of controlling nonlinear vibration open the further applications of G-MR.
  • Daiki Yoshikawa, Yuga Miyamoto, Kuniharu Takei, Takayuki Arie, Seiji Akita
    Proceedings of SPIE - The International Society for Optical Engineering 10712 1996-756X 2018 [Refereed][Not invited]
     
    Transition metal dichalcogenide such as MoS2 is expected as high performance nano-electro-mechanical devices due to their unique electrical, optical and mechanical properties. One can expect that the combination of these properties are efficient to develop the novel functional devices. Here, we demonstrates the amplitude control of resonance characteristics of a cantilevered MoS2 on the planar substrate, which is actuated by electrostatically. The AC and DC bias voltage dependences of the vibration amplitudes are well explained by the simplified model under linear elastic regime. Moreover, we demonstrate the optical manipulation of the vibration amplitude at the resonance. Under the irradiation of strongly absorbed light by MoS2, the vibration amplitude is successfully manipulated by the laser intensity change.
  • Masaaki Yasuda, Kuniharu Takei, Takayuki Arie, Seiji Akita
    Scientific Reports 7 (1) 2045-2322 2017/12/01 [Not refereed][Not invited]
     
    Optical tweezers based on optical radiation pressure are widely used to manipulate nanoscale to microscale particles. This study demonstrates direct measurement of the optical force gradient distribution acting on a polystyrene (PS) microsphere using a carbon nanotube (CNT) mechanical resonator, where a PS microsphere with 3 μm diameter is welded at the CNT tip using laser heating. With the CNT mechanical resonator with PS microsphere, we measured the distribution of optical force gradient with resolution near the thermal noise limit of 0.02 pN/μm in vacuum, in which condition enables us to high accuracy measurement using the CNT mechanical resonator because of reduced mechanical damping from surrounding fluid. The obtained force gradient and the force gradient distribution agree well with theoretical values calculated using Lorenz-Mie theory.
  • Kenichiro Kanao, Shogo Nakata, Takayuki Arie, Seiji Akita, Kuniharu Takei
    MATERIALS HORIZONS 4 (6) 1079 - 1084 2051-6347 2017/11 [Refereed][Not invited]
     
    The internet of things concept has promoted research on humaninteractive electronics for wearable devices and robotic applications. One interesting application is wallpaper to monitor a room environment and to act as an electronic message board. To demonstrate the potenital of electronic wallpaper (e-wallpaper), this study prepares a flexible nonvolatile floating gate random access memory (FGRAM) array integrated with a tactile touch sensor array as the message board. Additionally, a temperature sensor array is also laminated to monitor the room temperature. Besides the mechanical flexibility, the fundamental properties of flexible FGRAMs, including the tunneling dielectric thickness, program voltage, and program time dependencies, are characterized. Finally, e-wallpaper is demonstrated as a first proof-of-concept to show a possible platform for future macroscale flexible electronics.
  • Taichi Inoue, Yuki Anno, Yuki Imakita, Kuniharu Takei, Takayuki Arie, Seiji Akita
    ACS Omega American Chemical Society ({ACS}) 2 (9) 5792  2017/09 [Refereed][Not invited]
  • Yuki Yamamoto, Daisuke Yamamoto, Makoto Takada, Hiroyoshi Naito, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ADVANCED HEALTHCARE MATERIALS 6 (17) 1700495  2192-2640 2017/09 [Refereed][Invited]
     
    Wearable, flexible healthcare devices, which can monitor health data to predict and diagnose disease in advance, benefit society. Toward this future, various flexible and stretchable sensors as well as other components are demonstrated by arranging materials, structures, and processes. Although there are many sensor demonstrations, the fundamental characteristics such as the dependence of a temperature sensor on film thickness and the impact of adhesive for an electrocardiogram (ECG) sensor are yet to be explored in detail. In this study, the effect of film thickness for skin temperature measurements, adhesive force, and reliability of gel-less ECG sensors as well as an integrated real-time demonstration is reported. Depending on the ambient conditions, film thickness strongly affects the precision of skin temperature measurements, resulting in a thin flexible film suitable for a temperature sensor in wearable device applications. Furthermore, by arranging the material composition, stable gel-less sticky ECG electrodes are realized. Finally, real-time simultaneous skin temperature and ECG signal recordings are demonstrated by attaching an optimized device onto a volunteer's chest.
  • Shogo Nakata, Takayuki Arie, Seiji Akita, Kuniharu Takei
    TRANSDUCERS 2017 - 19th International Conference on Solid-State Sensors, Actuators and Microsystems 1688 - 1691 2017/07/26 [Refereed][Not invited]
     
    We developed a wearable flexible chemical pH sensor consisted of ion sensitive field effect transistor (ISFET) integrated with a printed flexible physical temperature sensor by developing material systems and optimizing the fabrication process as the first proof-of-concept. A major role of flexible ISFET is to measure pH value of sweat by putting it on a skin. The integrated temperature sensor is used to monitor skin temperature as health condition and to compensate pH value measured by ISFET because the characteristics of ISFET is changed by temperature. By analyzing temperature sensor and ISFET including temperature effect, we could successfully measure real-time pH value and skin temperature. The results show that this flexible integrated device has a high potential to be wearable chemical sensing from sweat in addition to physical health conditions.
  • Daisuke Yamamoto, Shogo Nakata, Kenichiro Kanao, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ADVANCED MATERIALS TECHNOLOGIES 2 (7) 1700057  2365-709X 2017/07 [Refereed][Not invited]
     
    Flexible healthcare devices attract much research attention due to their potential application in everyday health monitoring and data acquisition. In order to precisely monitor changes in health data, simultaneous recording of motion data is of vital importance, as different modes of human activity have a strong influence on a person's vital signs. However, human motion detection has received comparatively little attention in flexible electronics, even though flexible health monitoring sensors are well-studied and researched by many groups. In this study, a planar-type, multifunctional health sensor sheet integrated with acceleration, temperature, and electrocardiogram sensors, fabricated completely by printing methods is proposed and demonstrated. A vibrational space for the acceleration sensor is created by using a kirigami structure for the electrodes, allowing it to be pushed out of plane without affecting the resistance. The acceleration sensor's sensitivity is investigated experimentally by changing the dimensions of its beam structure, after which we are able to optimize the sensor such that it would be able to detect light human activity. Finally, as a proof of concept, the device is successfully demonstrated to be able to detect human motion, skin temperature, and electrocardiogram signals simultaneously when attached to the chest of a test subject.
  • Yuki Anno, Masato Takeuchi, Masaya Matsuoka, Kuniharu Takei, Seiji Akita, Takayuki Arie
    APPLIED PHYSICS LETTERS 110 (26) 0003-6951 2017/06 [Not refereed][Not invited]
     
    The thermoelectric properties of graphene are strongly related to the defect density, and as such, these can be used to investigate carrier scattering. In this study, the defect density was controlled by the use of oxygen plasma treatment. Oxygen plasma introduces structural defects into graphene, initially introducing sp(3) defects that transform into vacancy-type defects with further exposure, as indicated by XPS analysis, and these transitions cause substantial changes in both the electrical and thermoelectric properties of graphene. In this work, we estimate the effects of both defect density and species, analyzed by Raman spectroscopy, on the thermoelectric power of graphene, and find that the maximum thermoelectric power decreases with increasing defect density. We also find, from Ioffe's semiclassical approximation, that at the lower defect densities, phonons are the predominant source of carrier scattering, while at higher defect densities, the scattering is mainly caused by charged impurities, which corresponds to a change in defect population from the sp(3)-type to vacancies. Published by AIP Publishing.
  • Yuki Anno, Yuki Imakita, Kuniharu Takei, Seiji Akita, Takayuki Arie
    2D Materials 4 (2) 2053-1583 2017/06/01 [Not refereed][Not invited]
     
    Thermoelectric properties of materials are typically evaluated using the figure of merit, ZT, which relies on both the electrical and thermal properties of the materials. Although graphene has a high thermoelectric power factor, its overall ZT value is quite low as it possesses extremely high thermal conductivity. Phonons are the main heat carrier in graphene, and therefore propagation of heat in the material may be modulated by introducing defects into the structure, resulting in reduced thermal conductivity. In this study, we investigate the effect of graphene defect density on the thermoelectric performance of graphene. The defects introduced into graphene by oxygen plasma treatment reduce its Seebeck coefficient as well as its electrical conductivity as a result, the thermoelectric power factor declines with increasing defect density. However, at higher defect densities, the reduction in thermal conductivity dominates over the reduction in electrical conductivity and, consequently, graphene treated in this way is observed to possess ZT values of up to three times that of pristine graphene. Therefore, it may be concluded that introducing controlled amount of defects into graphene is an effective way of reducing its thermal conductivity, thereby enhancing the performance of graphene-based thermoelectric devices.
  • Shogo Nakata, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ACS SENSORS 2 (3) 443 - 448 2379-3694 2017/03 [Refereed][Not invited]
     
    Real-time daily healthcare monitoring may increase the chances of predicting and diagnosing diseases in their early stages which, currently, occurs most frequently during medical check-ups. Next-generation noninvasive healthcare devices, such as flexible multifunctional sensor sheets designed to be worn on skin, are considered to be highly suitable candidates for continuous real-time health monitoring. For healthcare applications, acquiring data on the chemical state of the body, alongside physical characteristics such as body temperature and activity, are extremely important for predicting and identifying potential health conditions. To record these data, in this study, we developed a wearable, flexible sweat chemical sensor sheet for pH measurement, consisting of an ion-sensitive field-effect transistor (ISFET) integrated with a flexible temperature sensor: we intend to use this device as the foundation of a fully integrated, wearable healthcare patch in the future. After characterizing the performance, mechanical flexibility, and stability of the sensor, real-time measurements of sweat pH and skin temperature are successfully conducted through skin contact. This flexible integrated device has the potential to be developed into a chemical sensor for sweat for applications in healthcare and sports.
  • Rehan Kapadia, Kuniharu Takei, Hui Fang
    Micro- and Nanoelectronics: Emerging Device Challenges and Solutions 185 - 198 2017/01/01 
    As transistor channel lengths have scaled down, significant electrostatic control challenges have arisen. Initially, these challenges were met by replacing silicon dioxide (SiO2) via high-? dielectrics, improving gate capacitance, and reducing gate leakage currents simultaneously. However, further scaling of the channel lengths required changes to the structure of the transistor, moving from bulk devices to FinFET and silicon (Si) on insulator (SOI) transistor structures. The key advantage of such structures is the improved electrostatics, ensuring that all parts of the channel are more strongly controlled by the gate as compared with the drain.
  • TAKEI, Kuniharu
    Journal of the Imaging Society of Japan 一般社団法人 日本画像学会 56 (6) 589 - 600 2017 [Refereed][Invited]
     

    Flexible printed electronics is of great interest in the next class of device platform to detect multiple information from macroscale non-planar surfaces. As a contribution to this field, in this review, printed flexible sensors and their applications are introduced. Especially, strain, temperature, electrocardiogram, and ultraviolet light sensors on flexible sheets are discussed based on experimental results. Furthermore, by arranging the device structures and integrating the sensors, electronic skin/whisker and healthcare patch applications are demonstrated as the first proof-of-concepts. Although there are still a lot of challenges such as stability, reliability, and more functionalities for a variety of applications to move forward to realizing practical printed electronics, these developments may be able to help the future progress for flexible printed electronics. This review follows these to guide the readers to develop the system further.

  • D. Yamamoto, S. Nakata, K. Kanao, T. Arie, S. Akita, K. Takei
    30TH IEEE INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS 2017) 239 - 242 1084-6999 2017 [Refereed][Not invited]
     
    This study proposes a new structure and fabrication technique to realize a planar-type multi-functional flexible patch integrated with acceleration sensor for motion detection, skin temperature sensor, and electrocardiogram (ECG) sensor formed by all printing methods. Especially, by studying a strain engineering and proposing a new fabrication process and structure using kirigami concept, all sensors are successfully integrated and demonstrated in an in-plane polyethylene terephthalate (PET) film as the first proof-of-concept for human activity and health condition monitoring. This study may lead the Internet of Things concepts to realize not only multi-functional health monitoring patch, but also low-cost sensor sheets.
  • Yuki Yamamoto, Shingo Harada, Daisuke Yamamoto, Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    SCIENCE ADVANCES 2 (11) e1601473  2375-2548 2016/11 [Refereed][Not invited]
     
    Real-time health care monitoring may enable prediction and prevention of disease or improve treatment by diagnosing illnesses in the early stages. Wearable, comfortable, sensing devices are required to allow continuous monitoring of a person's health; other important considerations for this technology are device flexibility, low-cost components and processing, and multifunctionality. To address these criteria, we present a flexible, multifunctional printed health care sensor equipped with a three-axis acceleration sensor to monitor physical movement and motion. Because the device is designed to be attached directly onto the skin, it has a modular design with two detachable components: One device component is nondisposable, whereas the other one is disposable and designed to be worn in contact with the skin. The design of this disposable sensing sheet takes into account hygiene concerns and low-cost materials and fabrication methods as well as features integrated, printed sensors to monitor for temperature, acceleration, electrocardiograms, and a kirigami structure, which allows for stretching on skin. The reusable component of the device contains more expensive device components, features an ultraviolet light sensor that is controlled by carbon nanotube thin-film transistors, and has a mechanically flexible and stable liquid metal contact for connection to the disposable sensing sheet. After characterizing the electrical properties of the transistors and flexible sensors, we demonstrate a proof-of-concept device that is capable of health care monitoring combined with detection of physical activity, showing that this device provides an excellent platform for the development of commercially viable, wearable health care monitors.
  • Kenichiro Kanao, Takayuki Arie, Seiji Akita, Kuniharu Takei
    JOURNAL OF MATERIALS CHEMISTRY C 4 (39) 9261 - 9265 2050-7526 2016/10 [Refereed][Not invited]
     
    Flexible electronics have great potential as the next class of macroscale multi-sensing devices capable of collecting a variety of information from diverse surfaces. A platform to integrate different electric components on a flexible substrate for macroscale electronics without increasing device fabrication costs needs to be explored. To address this requirement, we demonstrate an all-solution-processed tactile touch memory flexible device integrated with a NiO ReRAM, a tactile touch sensor, and resistors. The function of the solution-processed NiO ReRAM is attributed to a threshold switching mechanism due to the charge trap in the NiO film and the trap-controlled space-charge-limited current. In terms of device operations, the NiO ReRAM is mechanically stable with an on/off current ratio more than 10(3) while bending the substrate with a radius up to 6.1 mm. As a proof-of-concept for device applications, a tactile touch memory device, which has functions of writing and erasing tactile touch information by applying a tactile touch and SET/RESET voltage, respectively, is successfully operated. The results are promising to advance all-solution-based macroscale flexible electronics.
  • Shogo Nakata, Kenichiro Kanao, Shingo Harada, Takayuki Arie, Seiji Akita, Kuniharu Takei
    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 213 (9) 2345 - 2351 1862-6300 2016/09 [Refereed][Not invited]
     
    One of the major challenges toward widespread application of flexible tactile pressure sensors lies in the distinction between tactile pressure stimuli and contributions from substrate bending. To this point, this issue has been a bottleneck in further advancement of this class of devices. To address this issue, we demonstrate a flexible tactile pressure sensor sheet with extremely high selectivity between tactile pressure and substrate bending: these devices are designed with strain engineering with the goal of incorporation into artificial skin applications. In addition to characterizing the mechanical and electrical performance of the sensor, a first proof of concept for tactile pressure mapping at several mechanical flex states is conducted, demonstrating that these devices are highly compliant tactile pressure sensors well-suited to robotic skin and prosthesis applications. [GRAPHICS] (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Yukiko Wada, Koji Kita, Kuniharu Takei, Takayuki Arie, Seiji Akita
    APPLIED PHYSICS EXPRESS 9 (8) 1882-0778 2016/08 [Not refereed][Not invited]
     
    We investigate the pressure dependence of heat transfer to ambient gases for a suspended carbon nanotube yarn. The heat transport of the yarn including the heat exchange with surrounding gases is investigated using a simple one-dimensional heat transport model under Joule heating of the yarn. It is revealed that the effective diameter of the yarn for heat exchange is much smaller than the geometrical diameter of the yarn. This smaller effective diameter for heat exchange should contribute to realizing higher sensitivity and sensing over a wider range of pressures for heat-exchange-type vacuum gauges and flow sensors. (C) 2016 The Japan Society of Applied Physics
  • Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ADVANCED MATERIALS TECHNOLOGIES 1 (5) 1600058  2365-709X 2016/08 [Refereed][Not invited]
     
    Flexible electronics is now one of key technologies for electronic devices that collect information from nonplanar surfaces, ultimately enabling the realization of the trillion sensor concept and the internet of things. Both flexible discrete devices and sensors are required for integration of digital and analog circuits for signal processing. In this study, flexible, energy efficient, complementary metal-oxide-semiconductor (CMOS) digital and analog circuits, monolithically integrated with a temperature sensor are reported: This is achieved by developing the process of p-type and n-type transistors on a flexible substrate. For the digital circuits, CMOS-based J-K flip-flop circuits are fabricated on a polyimide substrate, and testing confirms that they can be operated under mechanical bending without malfunction. Furthermore, the fabrication of a flexible analog differential amplifier is demonstrated, with the device successfully amplifying the output of an integrated temperature sensor by approximate to 38 times. Although these demonstrations are still at the proof-of-concept stage for flexible signal processing circuits, these achievements are a key step toward the next level of device integration, thereby enabling the development of viable flexible electronic devices.
  • Kevin Chen, Wei Gao, Sam Emaminejad, Daisuke Kiriya, Hiroki Ota, Hnin Yin Yin Nyein, Kuniharu Takei, Ali Javey
    Advanced Materials 28 (22) 4396  1521-4095 2016/06/08 [Refereed][Not invited]
  • Kevin Chen, Wei Gao, Sam Emaminejad, Daisuke Kiriya, Hiroki Ota, Hnin Yin Yin Nyein, Kuniharu Takei, Ali Javey
    ADVANCED MATERIALS 28 (22) 4397 - 4414 0935-9648 2016/06 [Refereed][Not invited]
     
    Printing technologies offer large-area, high-throughput production capabilities for electronics and sensors on mechanically flexible substrates that can conformally cover different surfaces. These capabilities enable a wide range of new applications such as low-cost disposable electronics for health monitoring and wearables, extremely large format electronic displays, interactive wallpapers, and sensing arrays. Solution-processed carbon nanotubes have been shown to be a promising candidate for such printing processes, offering stable devices with high performance. Here, recent progress made in printed carbon nanotube electronics is discussed in terms of materials, processing, devices, and applications. Research challenges and opportunities moving forward from processing and system-level integration points of view are also discussed for enabling practical applications.
  • Masaaki Yasuda, Kuniharu Takei, Takayuki Arie, Seiji Akita
    SCIENTIFIC REPORTS 6 2045-2322 2016/03 [Not refereed][Not invited]
     
    Despite the superb intrinsic properties of carbon nanotube mechanical resonators, the quality factors at room temperature are 1,000 or less, even in vacuum, which is much lower than that of mechanical resonators fabricated using a top-down approach. This study demonstrates the improvement of the quality factor and the control of nonlinearity of the mechanical resonance of the cantilevered nanotube by electrostatic interaction. The apparent quality factor of the nanotube supported by insulator is improved drastically from approximately 630 to 3200 at room temperature. Results show that retardation of the electrostatic force induced by the contact resistance between the nanotube and the insulator support improves the quality factor. Finite element method calculation reveals that the nonuniform pileup charge on the insulator support strongly influences the nonlinearity of the resonance.
  • Flexible and wearable health monitoring devices
    Yuki Yamamoto, Shingo Harada, Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    20th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2016 1374 - 1375 2016 
    Flexible and wearable electronics enables to monitor real-time health condition that allows us to eventually predict and diagnose the disease in advance if the device can be attached comfortably on skin without awareness1. A bandage-type health monitoring patch is integrated with an acceleration (human motion) sensor, a temperature sensor, an ultraviolet (UV) sensor, and an electrocardiogram (ECG) sensor on a flexible substrate. All sensors were fabricated by using macroscale and low-cost printing methods. Furthermore, multi-layered, detachable sheet structure is proposed to separate a low-cost disposal sensor sheet and an expensive flexible circuit reusable sheet for the low-cost practical device application.
  • Kenshi Inotani, Kuniharu Takei, Takayuki Arie, Seiji Akita
    2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016 [Refereed][Not invited]
  • Kuniharu Takei
    2016 23RD INTERNATIONAL WORKSHOP ON ACTIVE-MATRIX FLATPANEL DISPLAYS AND DEVICES (AM-FPD) 9 - 10 2016 [Refereed][Not invited]
     
    Macroscale and multi-functional flexible sensor networks have been widely proposed for the Internet of Things (IoT) and the trillion sensor networks. In this report, our recent progress of flexible sensors fabricated by some printing methods on user-defined non-planer substrates is presented. Especially, flexible strain sensor and temperature sensors are discussed to monitor human condition as a health monitoring device and to detect an object for a robotic prosthesis skin. In addition, flexible digital and analog circuits for the future fully integrated flexible device system are introduced.
  • Yuki Anno, Kuniharu Takei, Seiji Akita, Takayuki Arie
    2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016 [Refereed][Not invited]
  • Yuki Imakita, Yuki Anno, Kuniharu Takei, Seiji Akita, Takayuki Arie
    2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016 [Refereed][Not invited]
  • Kenichiro Kanao, Shogo Nakata, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2016 IEEE 29TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS) 435 - 438 1084-6999 2016 [Refereed][Not invited]
     
    This study demonstrates a tactile pressure-memorized functional flexible device integrated with a tactile pressure sensor and a resistive random access memory (ReRAM) using all solution-based fabrication process toward low-cost and macroscale flexible electronics. Solution-processed NiO ReRAM shows a stable switching operation with >3 orders-ON/OFF resistance ratio without being affected by bending of the substrate up to 5.6 mm radius. As the first proof-of-concept, carbon black (CB) and polydimethylsiloxane (PDMS)-based tactile pressure sensor is integrated with the ReRAM. The integrated device can successfully memorize tactile information by ReRAM. This demonstration eventually allows us to apply for flexible human-interactive tactile array devices by memorizing tactile or other sensing information.
  • Shogo Nakata, Kenichiro Kanao, Shingo Harada, Takaynki Arie, Seiji Akita, Kuniharu Takei
    2016 IEEE 29TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS) 873 - 876 1084-6999 2016 [Refereed][Not invited]
     
    This study proposes and demonstrates a multi-layered pillar-like, carbon black (CB)/polydimethylsiloxane (PDMS)-based pressure sensor embedded in silicone rubbers to realize high selectivity of tactile pressure against bending of substrate based on a strain engineering. This device is fabricated by all solution-based process that is eventually applied to all-printing technique. Furthermore. as the first proof-of-concept, real-time tactile sensing is demonstrated for several applications such as wearable devices and robotic artificial skin (e-skin). This finding and demonstration eventually can be applied to the low-cost, high precise tactile sensor that can be conformally covered over any surfaces.
  • Kenichiro Kanao, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Journal of Materials Chemistry C 4 (39) 9261 - 9265 2050-7526 2016 [Not refereed][Not invited]
     
    Flexible electronics have great potential as the next class of macroscale multi-sensing devices capable of collecting a variety of information from diverse surfaces. A platform to integrate different electric components on a flexible substrate for macroscale electronics without increasing device fabrication costs needs to be explored. To address this requirement, we demonstrate an all-solution-processed tactile touch memory flexible device integrated with a NiO ReRAM, a tactile touch sensor, and resistors. The function of the solution-processed NiO ReRAM is attributed to a threshold switching mechanism due to the charge trap in the NiO film and the trap-controlled space-charge-limited current. In terms of device operations, the NiO ReRAM is mechanically stable with an on/off current ratio more than 103 while bending the substrate with a radius up to 6.1 mm. As a proof-of-concept for device applications, a tactile touch memory device, which has functions of writing and erasing tactile touch information by applying a tactile touch and SET/RESET voltage, respectively, is successfully operated. The results are promising to advance all-solution-based macroscale flexible electronics.
  • Shohei Ishida, Yuki Anno, Masato Takeuchi, Masaya Matsuoka, Kuniharu Takei, Takayuki Arie, Seiji Akita
    SCIENTIFIC REPORTS 5 2045-2322 2015/10 [Not refereed][Not invited]
     
    Graphene is a promising material for use in photodetectors for the ultrawide wavelength region: from ultraviolet to terahertz. Nevertheless, only the 2.3% light absorption of monolayer graphene and fast recombination time of photo-excited charge restrict its sensitivity. To enhance the photosensitivity, hybridization of photosensitive material and graphene has been widely studied, where the accumulated photo-excited charge adjacent to the graphene channel modifies the Fermi level of graphene. However, the charge accumulation process slows the response to around a few tens of seconds to minutes. In contrast, a charge accumulation at the contact would induce the efficient light-induced modification of the contact resistance, which would enhance its photosensitivity. Herein, we demonstrate a highly photosensitive graphene field-effect transistor with noise-equivalent power of -3 x 10(-15) W/Hz(1/2) and with response time within milliseconds at room temperature, where the Au oxide on Au electrodes modulates the contact resistance because of the light-assisted relaxation of the trapped charge at the contact. Additionally, this light-induced relaxation imparts an optical memory function with retention time of -5s. These findings are expected to open avenues to realization of graphene photodetectors with high sensitivity toward single photon detection with optical memory function.
  • Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    SCIENTIFIC REPORTS 5 15099  2045-2322 2015/10 [Refereed][Not invited]
     
    Low-power flexible logic circuits are key components required by the next generation of flexible electronic devices. For stable device operation, such components require a high degree of mechanical flexibility and reliability. Here, the mechanical properties of low-power flexible complementary metal-oxide-semiconductor (CMOS) logic circuits including inverter, NAND, and NOR are investigated. To fabricate CMOS circuits on flexible polyimide substrates, carbon nanotube (CNT) network films are used for p-type transistors, whereas amorphous InGaZnO films are used for the n-type transistors. The power consumption and voltage gain of CMOS inverters are <500 pW/mm at V-in = 0V (<7.5 nW/mm at V-in = 5V) and >45, respectively. Importantly, bending of the substrate is not found to cause significant changes in the device characteristics. This is also observed to be the case for more complex flexible NAND and NOR logic circuits for bending states with a curvature radius of 2.6 mm. The mechanical stability of these CMOS logic circuits makes them ideal candidates for use in flexible integrated devices.
  • Yuki Anno, Kuniharu Takei, Seiji Akita, Takayuki Arie
    ADVANCED ELECTRONIC MATERIALS 1 (9) 2199-160X 2015/09 [Not refereed][Not invited]
     
    The thermoelectric properties of various graphene samples, including isotopically modified heterostructures grown by chemical vapor deposition, are investigated from the viewpoint of thermoelectric device applications. The thermoelectric power of graphene varies from -80 to 90 mu V K-1, depending on the applied gate voltage. Similar to typical metals and semiconductors, the thermoelectric power of graphene decreases as the electrical conductivity increases, regardless if isotopes are present. The results follow a line with a slope of -198 mu V K-1 in the Jonker plot, indicating that the maximum power factor is 5.29 x 10(-3) W m(-1) K-2 irrespective of carbon isotope modulation in graphene. Because limiting phonon propagation independent of the electric properties can reduce the thermal conductivity of graphene containing carbon isotopes and isotopic heterojunctions, introducing carbon isotopes into the graphene structure improves the thermoelectric figure of merit without affecting the power factor.
  • Takehiro Gohara, Kuniharu Takei, Takayuki Arie, Seiji Akita
    CARBON 89 225 - 231 0008-6223 2015/08 [Not refereed][Not invited]
     
    Carbon nanocoils (CNC) are promising nanocarbon materials for application as functional composites such as electromagnetic wave absorbers. However, the suppression of carbon byproducts during CNC growth is necessary to obtain high purity CNCs with high yield. Here, we demonstrate a simple but efficient method for the reduction of carbon byproducts using a patterned thin film catalyst. Results show that the collision of tip catalysts of growing CNCs to the substrate or other CNCs inhibits the smooth growth of CNCs because of the deactivation of the catalyst. The collision also stimulates the formation of a carbon byproduct layer underneath the CNC layer. The well-controlled thin film catalyst with checkerboard pattern brings us four-times-higher efficiency of the catalyst and suppresses the carbon byproduct layer to similar to 1/3. (C) 2015 Elsevier Ltd. All rights reserved.
  • Atsuko Nagataki, Kuniharu Takei, Takayuki Arie, Seiji Akita
    APPLIED PHYSICS EXPRESS 8 (8) 1882-0778 2015/08 [Not refereed][Not invited]
     
    We demonstrate the control of a cantilever-type carbon-nanotube mechanical resonator in a potential well induced by van der Waals interaction with a graphene flake using molecular dynamics simulations. The energy potential profile for the resonator is successfully modulated by changing the graphene width. As a result of the potential profile modification, the resonance frequency can be markedly changed from the original value of 18.2 to 55 GHz by reducing the graphene width. Additionally, the nonlinear effect is easily developed even under the small amplitude regime around thermal vibration using a narrow graphene layer with a width of 10 angstrom. (C) 2015 The Japan Society of Applied Physics
  • Wataru Honda, Shingo Harada, Shohei Ishida, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ADVANCED MATERIALS 27 (32) 4674 - 4680 0935-9648 2015/08 [Refereed][Not invited]
  • Shingo Harada, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ADVANCED ELECTRONIC MATERIALS 1 (7) 1500080  2199-160X 2015/07 [Refereed][Not invited]
     
    A liquid-solid metal contact for a multilayer detachable flexible device is proposed. The structure shows a low-contact resistance, high stability, and high reliability compared to conventional a solid-solid contact. As a proof-of-concept, a flexible device integrated with a light-emitting diode array is demonstrated by attaching to human skin.
  • Yukiko Wada, Yoshihiro Fujita, Kuniharu Takei, Takayuki Arie, Seiji Akita
    JAPANESE JOURNAL OF APPLIED PHYSICS 54 (6) 0021-4922 2015/06 [Not refereed][Not invited]
     
    We investigate the pressure dependence of transfer characteristics of suspended single-walled carbon-nanotube field-effect transistors. We find that the gate bias around the charge neutral point with low drain current is appropriate for gas sensing application, while the high gate bias condition with high drain current that induces Joule heating in the suspended region for the desorption of the adsorbed molecules is preferable for the vacuum gauge application based on the heat exchange surrounding gas molecules, where the temperature at the suspended channel is investigated based on the simple one-dimensional heat transport model. We also revealed that the pressure dependence of the channel conductance at the gate bias around the charge neutral point can be explained by the Langmuir isotherm. (C) 2015 The Japan Society of Applied Physics
  • Yuki Yamamoto, Kenichiro Kanao, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ACS APPLIED MATERIALS & INTERFACES 7 (20) 11002 - 11006 1944-8244 2015/05 [Refereed][Not invited]
     
    Harnessing a natural power source such as the human body temperature or sunlight should realize ultimate low-power devices. In particular, macroscale and flexible actuators that do not require an artificial power source have tremendous potential. Here we propose and demonstrate electrically powerless polymer-based actuators operated at ambient conditions using a packaging technique in which the stimulating power source is produced by heat from the human body or sunlight. The actuating angle, force, and reliability are discussed as functions of temperature and exposure to sunlight. Furthermore, a wearable device platform and a smart curtain actuated by the temperature of human skin and sunlight, respectively, are demonstrated as the first proof-of-concepts. These nature-powered actuators should realize a new class of ultimate low-power devices.
  • Kuniharu Takei, Wataru Honda, Shingo Harada, Takayuki Arie, Seiji Akita
    ADVANCED HEALTHCARE MATERIALS 4 (4) 487 - 500 2192-2640 2015/03 [Refereed][Invited]
     
    This Progress Report introduces flexible wearable health-monitoring devices that interact with a person by detecting from and stimulating the body. Interactive health-monitoring devices should be highly flexible and attach to the body without awareness like a bandage. This type of wearable health-monitoring device will realize a new class of electronics, which will be applicable not only to health monitoring, but also to other electrical devices. However, to realize wearable health-monitoring devices, many obstacles must be overcome to economically form the active electrical components on a flexible substrate using macroscale fabrication processes. In particular, health-monitoring sensors and curing functions need to be integrated. Here recent developments and advancements toward flexible health-monitoring devices are presented, including conceptual designs of human-interactive devices.
  • Kuniharu Takei, Shingo Harada, Wataru Honda, Yuki Yamamoto, Kenichiro Kanao, Takayuki Arie, Seiji Akita
    Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 9187 675 - 684 1611-3349 2015 [Refereed][Not invited]
     
    Wearable devices using solid device components have recently been released to purchase for different kinds of applications. However, ideal “wear- able” devices should be like a cloth, so that they can be attached on a human skin or cloth without awareness. To realize flexible and wearable electronics, a challenge is how to form mechanically flexible electrical materials on a flexible substrate. To address this requirement, we here propose and develop nanoma- terial film formations on a macroscale flexible substrate using printing methods. As examples, we present an artificial electronic skin (e-skin) for robotic/prosthesis and a wearable device. By considering strain engineering, composition of materials into the film, and surface interaction to form uniform printing films, a variety of flexible devices can be readily fabricated without using an expensive tool such as a vacuum system.
  • Yuki Yamamoto, Kenichiro Kanao, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2015 TRANSDUCERS - 2015 18TH INTERNATIONAL CONFERENCE ON SOLID-STATE SENSORS, ACTUATORS AND MICROSYSTEMS (TRANSDUCERS) 2129 - 2131 2015 [Refereed][Not invited]
     
    This study demonstrates thermal and optical responsive actuator operated by skin temperature and sunlight without using electrical power supply. Different types of thermal and optical responsive actuators have been reported to date. However, actuator stimulated by both skin temperature and sunlight has yet to be demonstrated, although these are a high potential as the next class of power sources for devices. To realize an actuation using these stimuli, we propose to use a mixture of poly(N-isopropylacrylamide) (pNIPAM) as a thermal actuation material and carbon nanotubes (CNTs) as a light absorber to convert into heat on a polyethylene terephthalate (PET) substrate. By considering a packaging technique of the pNIPAM film, a human body temperature-and the sunlight-stimulated actuator is successfully demonstrated in air ambient.
  • Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2015 TRANSDUCERS - 2015 18TH INTERNATIONAL CONFERENCE ON SOLID-STATE SENSORS, ACTUATORS AND MICROSYSTEMS (TRANSDUCERS) 1433 - 1435 2015 [Refereed][Not invited]
     
    A mechanically flexible complementary metal-oxide-semiconductor (CMOS) inverter and optical sensor are developed by integrating p-type carbon nanotubes (CNTs) network thin-film transistors (TFTs) and n-type InGaZnO TFTs on a polyimide substrate. Although a flexible CMOS circuitry has been reported [1], mechanical reliability and its sensor application have yet to be demonstrated. Here, we demonstrate a flexible CMOS inverter and an optical sensor using CNT and InGaZnO with relatively high field-effect mobility. Furthermore, we experimentally confirmed that these devices are mechanically stable by comparing electrical properties under flat and bending states.
  • Shingo Harada, Kenichiro Kanao, Yuki Yamamoto, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2015 TRANSDUCERS - 2015 18TH INTERNATIONAL CONFERENCE ON SOLID-STATE SENSORS, ACTUATORS AND MICROSYSTEMS (TRANSDUCERS) 164 - 167 2015 [Refereed][Not invited]
     
    This paper describes printed, flexible, tactile, friction, and temperature sensors for the applications of an artificial electronic skin (e-skin). Conventional e-skin reported previously does not have the capability to detect friction in addition to tactile and temperature that allows us to imitate human functionalities and hold an object without dropping and/or breaking. This is due to difficulty of device fabrication on a flexible substrate. Furthermore, a printing technique is required to realize macroscale and low-cost flexible devices for the practical application. Here, we address these two challenges by arranging the structure of devices and developing the inks and printing technique.
  • Kenichiro Kanao, Shingo Harada, Yuki Yamamoto, Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2015 28TH IEEE INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS 2015) 756 - 759 1084-6999 2015 [Refereed][Not invited]
     
    Flexible electronics are of great interest in a future electric device such as artificial electronic devices. Especially, artificial electronic skin (e-skin) is widely studied by developing a tactile pressure sensor on a flexible substrate. However, conventional flexible tactile sensors also detect the bending of substrate without applying a tactile pressure, and that is the one of bottlenecks to realize stable operation of a flexible device. This study demonstrates the high selectivity of tactile pressure and temperature sensors against bending based on strain engineering. To achieve high selectivity, a cantilever type strain sensor in a flexible substrate is developed. In addition, the temperature sensor is also mechanically stable. It should be worth to note that these sensors are fabricated by a fully printing method using a screen printer. This finding and demonstration eventually allow us to apply the flexible devices on versatile surfaces with accurate sensing.
  • Shingo Harada, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2015 TRANSDUCERS - 2015 18TH INTERNATIONAL CONFERENCE ON SOLID-STATE SENSORS, ACTUATORS AND MICROSYSTEMS (TRANSDUCERS) 761 - 763 2015 [Refereed][Not invited]
     
    This report describes a flexible and stretchable superhydrophobic surface on an elastomer silicone rubber by one-step laser treatment for the future flexible and wearable electronics. Previously, there are some studies about the fabrication of superhydrophobic surface on silicone rubber by forming micro-or nanostructure. However, the superhydrophobicity and self-cleaning under bending/stretching and time reliability have yet to be demonstrated. Here, we conduct a systematic study of superhydrophobicity and self-cleaning surface under applying a tensile stress and its application of microfluidic valve.
  • Kenichiro Kanao, Shingo Harada, Yuki Yamamoto, Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    RSC ADVANCES 5 (38) 30170 - 30174 2046-2069 2015 [Refereed][Not invited]
     
    Flexible devices can conformally cover any surfaces and interact with different stimuli such as human touch. Although a flexible tactile sensor has been reported as an artificial skin application, distinguishing between a tactile force and strain due to substrate bending remains challenging. Here we report a highly selective tactile force sensor against bending on the basis of strain engineering by fabricating a cantilever structure. The proposed device achieves a 4-23 times improvement in selectivity compared to conventional pressure sensitive rubber. As a proof-of-concept for e-skin, an array composed of highly selective tactile force sensors and temperature sensors is successfully demonstrated to imitate human skin.
  • Wataru Honda, Shingo Harada, Takayuki Arie, Seiji Akita, Kuniharu Takei
    Proceedings of IEEE Sensors 2014- (December) 2227 - 2229 2168-9229 2014/12/12 [Refereed][Not invited]
     
    We developed a printed high sensitive temperature sensor by synthesizing poly (3, 4-ethlenedioxythiophene) poly (styrenesulfonate) (PEDOT:PSS) and carbon nanotubes (CNTs) composition ink on a flexible substrate. There are two advantages of this flexible temperature sensor, which are (1) high sensitivity (∼0.6%/°C) compared to other reported flexible temperature sensors, (2) fully-printable low-cost process on macroscale flexible substrates due to solution-based process. The key point to achieve the high sensitivity was a mixture of PEDOT:PSS and CNTs for the temperature sensor material. Based on the analyses, the mechanism of this high sensitivity is most likely due to electron hopping at the interface of PEDOT:PSS and CNTs. In addition to the sensor analyses, real-time human skin temperature was monitored by attaching on a human skin like a bandage as a proof-of-concept, and it was successfully conducted to observe small skin temperature change during activities.
  • Shingo Harada, Kenichiro Kanao, Yuki Yamamoto, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ACS NANO 8 (12) 12851 - 12857 1936-0851 2014/12 [Refereed][Not invited]
     
    A three-axis tactile force sensor that determines the touch and slip/friction force may advance artificial skin and robotic applications by fully imitating human skin. The ability to detect slip/friction and tactile forces simultaneously allows unknown objects to be held in robotic applications. However, the functionalities of flexible devices have been limited to a tactile force in one direction due to difficulties fabricating devices on flexible substrates. Here we demonstrate a fully printed fingerprint-like three-axis tactile force and temperature sensor for artificial skin applications. To achieve economic macroscale devices, these sensors are fabricated and integrated using only printing methods. Strain engineering enables the strain distribution to be detected upon applying a slip/friction force. By reading the strain difference at four integrated force sensors for a pixel, both the tactile and slip/friction forces can be analyzed simultaneously. As a proof of concept, the high sensitivity and selectivity for both force and temperature are demonstrated using a 3 x 3 array artificial skin that senses tactile, slip/friction, and temperature. Multifunctional sensing components for a flexible device are important advances for both practical applications and basic research in flexible electronics.
  • Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE 211 (11) 2631 - 2634 1862-6300 2014/11 [Refereed][Not invited]
     
    Foldable components such as electrodes, transistors, and sensors are necessary to realize wearable electronics to be reliable use. In this paper, we propose a printable and foldable electrode using a composite ink of carbon nanotubes and polymer. Relative resistance change corresponding to the foldability by folding the electrode up to 1000 times is relatively small similar to 9.9 and similar to 1.7% for the folding directions of tensile and compressive stress in the electrodes, respectively. As a proof-of-concepts, a foldable calculator is demonstrated without malfunction. This electrode may lead to develop foldable electronics furthermore and can be applied to a wide range of applications.
  • Yuki Anno, Kuniharu Takei, Seiji Akita, Takayuki Arie
    PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 8 (8) 692 - 697 1862-6254 2014/08 [Not refereed][Not invited]
     
    Because phonons are the main carriers for graphene heat transfer, modifying the dynamic properties of the crystal lattice by isotopes modulates the phonon behavior and alters the thermal properties. Here we demonstrate an artificially controlled texture synthesis of C-12-graphene/C-13-graphene heterostructures via chemical vapor deposition and an O-2 plasma etching. The electrical and thermal properties of the graphene across the heterojunction show that C-12-graphene and C-13-graphene are electronically connected as resistors in series, while the thermal conductivity across the junction is dramatically reduced due to the suppressed phonon propagation, which causes the conductivity across the junction to be lower than that of graphene sheets with randomly mixed isotopes. These findings should help realize novel two-dimensional graphene thermoelectric devices where phonon modulation controls the electrons and heat transport independently. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
  • Wataru Honda, Shingo Harada, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ADVANCED FUNCTIONAL MATERIALS 24 (22) 3299 - 3304 1616-301X 2014/06 [Refereed][Not invited]
     
    Wearable human-interactive devices are advanced technologies that will improve the comfort, convenience, and security of humans, and have a wide range of applications from robotics to clinical health monitoring. In this study, a fully printed wearable human-interactive device called a smart bandage is proposed as the first proof of concept. The device incorporates touch and temperature sensors to monitor health, a drug-delivery system to improve health, and a wireless coil to detect touch. The sensors, microelectromechanical systems (MEMS) structure, and wireless coil are monolithically integrated onto flexible substrates. A smart bandage is demonstrated on a human arm. These types of wearable human-interactive devices represent a promising platform not only for interactive devices, but also for flexible MEMS technology.
  • Takehiro Gohara, Kuniharu Takei, Takayuki Arie, Seiji Akita
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 32 (3) 1071-1023 2014/05 [Not refereed][Not invited]
     
    The authors investigate individual carbon nanocoil (CNC) growth by in-situ observations using optical microscopy. From the temperature dependence of growth rate, the activation energy for CNC growth was found to be 0.5 eV. A higher activation energy of 1.1 eV was required to form noncoiled fibers. Comparing these activation energies indicated that incorporating Sn within the Fe matrix lowered the activation energy for carbon diffusion, within or on catalyst particles. The authors also found that the smooth growth of some CNCs was inhibited by the collision of catalyst particles at the tips of the CNCs. (C) 2014 American Vacuum Society.
  • Toshinori Kuroyanagi, Yuki Terada, Kuniharu Takei, Seiji Akita, Takayuki Arie
    APPLIED PHYSICS LETTERS 104 (19) 0003-6951 2014/05 [Not refereed][Not invited]
     
    We investigate the effects of humidity on the vibrations of carbon nanotubes (CNTs) using two types of CNT cantilevers: open-ended and close-ended CNT cantilevers. As the humidity increases, the resonant frequency of the open-ended CNT cantilever decreases due to the adsorption of water molecules onto the CNT tip, whereas that of the close-ended CNT cantilever increases probably due to the change in the viscosity of the air surrounding the CNT cantilever, which is negatively correlated with the humidity of air. Our findings suggest that a close-ended CNT cantilever is more suitable for a quick-response and ultrasensitive hygrometer because it continuously reads the viscosity change of moist air in the vicinity of the CNT. (C) 2014 AIP Publishing LLC.
  • Shingo Harada, Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    ACS NANO 8 (4) 3921 - 3927 1936-0851 2014/04 [Refereed][Not invited]
     
    Mammalian-mimicking functional electrical devices have tremendous potential in robotics, wearable and health monitoring systems, and human interfaces. The keys to achieve these devices are (1) highly sensitive sensors, (2) economically fabricated macroscale devices on flexible substrates, and (3) multifunctions beyond mammalian functions. Although highly sensitive artificial electronic devices have been reported, none have been fabricated using cost-effective macroscale printing methods and demonstrate multifunctionalities of artificial electronics. Herein we report fully printed high-sensitivity multifunctional artificial electronic whiskers (e-whisker) integrated with strain and temperature sensors using printable nanocomposite inks. Importantly, changing the composition ratio tunes the sensitivity of strain. Additionally, the printed temperature sensor array can be incorporated with the strain sensor array beyond mammalian whisker functionalities. The sensitivity for the strain sensor is impressively high (similar to 59%/Pa), which is the best sensitivity reported to date (>7 x improvement). As the proof-of-concept for a truly printable multifunctional artificial e-whisker array, two- and three-dimensional space and temperature distribution mapping are demonstrated. This fully printable flexible sensor array should be applicable to a wide range of low-cost macroscale electrical applications.
  • Kuniharu Takei, Zhibin Yu, Maxwell Zheng, Hiroki Ota, Toshitake Takahashi, Ali Javey
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 111 (5) 1703 - 1707 0027-8424 2014/02 [Refereed][Not invited]
     
    Mammalian whiskers present an important class of tactile sensors that complement the functionalities of skin for detecting wind with high sensitivity and navigation around local obstacles. Here, we report electronic whiskers based on highly tunable composite films of carbon nanotubes and silver nanoparticles that are patterned on high-aspect-ratio elastic fibers. The nanotubes form a conductive network matrix with excellent bendability, and nanoparticle loading enhances the conductivity and endows the composite with high strain sensitivity. The resistivity of the composites is highly sensitive to strain with a pressure sensitivity of up to similar to 8%/Pa for the whiskers, which is > 10x higher than all previously reported capacitive or resistive pressure sensors. It is notable that the resistivity and sensitivity of the composite films can be readily modulated by a few orders of magnitude by changing the composition ratio of the components, thereby allowing for exploration of whisker sensors with excellent performance. Systems consisting of whisker arrays are fabricated, and as a proof of concept, real-time two-and three-dimensional gas-flow mapping is demonstrated. The ultrahigh sensitivity and ease of fabrication of the demonstrated whiskers may enable a wide range of applications in advanced robotics and human-machine interfacing.
  • Shingo Harada, Wataru Honda, Takayuki Arie, Seiji Akita, Kuniharu Takei
    2014 IEEE 27TH INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS) 737 - 740 2014 [Refereed][Not invited]
     
    We demonstrate a macroscale sensor sheet by fabricating the fully printed, large-scale, and high sensitive strain sensor array on mechanically flexible substrates. This sensor sheet can conformally cover any surfaces for the application of real-time infrastructure stress monitoring as the first proof-of-concept. To realize this concept, a screen printing method is proposed to use by developing an ink for strain sensor. Printed strain sensor array exhibits impressively high sensitivity, and successfully detects two-dimensional strain distribution of small deformation <10 mu m.
  • Kuniharu Takei
    DESIGN, USER EXPERIENCE, AND USABILITY: USER EXPERIENCE DESIGN FOR EVERYDAY LIFE APPLICATIONS AND SERVICES, PT III 8519 710 - 718 0302-9743 2014 [Refereed][Not invited]
     
    Wearable devices have high potentials for a wide range of applications for future electronics. One of the possible applications is human interactive devices for health monitoring system. In this study, we present high performance flexible and stretchable devices for artificial electronic skins and health monitoring system utilizing inorganic nanomaterial films patterned by printing methods as a proof of concepts. Inorganic-based flexible devices realize a low voltage operation <5 V compared to other flexible devices using organic materials. Mechanical flexibility and stretchability are experimentally characterized, and different types of applications are demonstrated. This inorganic-based printing method may lead the field in high performance flexible electronics and open new fields in human interactive wearable devices.
  • Shingo Harada, Takayuki Arie, Seiji Akita, Kuniharu Takei
    BioNanoScience 4 (3) 301 - 305 2191-1649 2014 [Refereed][Not invited]
     
    Biologically inspired superhydrophobic and self-cleaning surfaces similar to a lotus leaf are of great interest for waterproof passivation in electronics as well as the different types of device applications, such as microfluidics and bacteria controls. This study describes quick one-step laser-treated superhydrophobic and self-cleaning surfaces of elastomer silicone rubber and its mechanical flexibility. By studying the contact and sliding angles with different geometries of silicone rubber and tensile strain conditions, models to realize superhydrophobic and self-cleaning surfaces are discussed. Additionally, a microfluidic valve as a proof-of-concept application to a total analysis system is demonstrated in addition to the application of waterproof passivation layer. Because this approach is a simple method, it has great potential for practical applications. © 2014 Springer Science+Business Media New York.
  • Toshitake Takahashi, Zhibin Yu, Kevin Chen, Daisuke Kiriya, Chuan Wang, Kuniharu Takei, Hiroshi Shiraki, Teresa Chen, Biwu Ma, Ali Javey
    Nano Letters 13 (11) 5425 - 5430 1530-6984 2013/11/13 [Refereed][Not invited]
     
    We report visible light and X-ray imagers on lightweight and mechanically flexible plastic substrates. The process involves solution processing of organic photodetectors on top of an active-matrix backplane consisting of carbon nanotube thin-film transistors. The system takes advantage of the high mobility of nanotube transistors for low operating voltages and efficient light absorption of organic bulk-heterojunctions for high imaging sensitivity. With this highly scalable process scheme, 18 × 18 pixel-array flexible imagers (physical size of 2 cm × 1.5 cm) with high performance are successfully demonstrated. In addition, as the absorption peak of the adopted organic photodiodes covers the green band of the light spectrum, X-ray imaging is readily demonstrated by placing a scintillator film on top of the flexible imagers. © 2013 American Chemical Society.
  • Megan L. Hoarfrost, Kuniharu Takei, Victor Ho, Andrew Heitsch, Peter Trefonas, Ali Javey, Rachel A. Segalman
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 4 (21) 3741 - 3746 1948-7185 2013/11 [Refereed][Not invited]
     
    We introduce a new class of spin-on dopants composed of organic, dopant-containing polymers. These new dopants offer a hybrid between conventional inorganic spin-on dopants and a recently developed organic monolayer doping technique that affords unprecedented control and uniformity of doping profiles. We demonstrate the ability of polymer film doping to achieve both p-type and n-type silicon by using boron- and phosphorus-containing polymer films. Different doping mechanisms are observed for boron and phosphorus doping, which could be related to the specific chemistries of the polymers. Thus, there is an opportunity to further control doping in the future by tuning the polymer chemistry.
  • Tatsuya Kagota, Atsuko Nagataki, Kuniharu Takei, Takayuki Arie, Seiji Akita
    APPLIED PHYSICS LETTERS 103 (20) 0003-6951 2013/11 [Not refereed][Not invited]
     
    We investigated the release of a stuck carbon nanotube (CNT) cantilever beam in nanorelay applications using a nano-manipulator. Even with strong adhesion induced by electrostatic attraction that is 100 times stronger than the van der Waals interaction, successful release of a nanotube arm from a stuck state was realized by the application of a resonant vibration to the stuck CNT arm. Furthermore, nonvolatile operation of the nanotube nanorelay was demonstrated by the application of the resonant vibration to the stuck CNT arm. (C) 2013 AIP Publishing LLC.
  • Chuan Wang, David Hwang, Zhibin Yu, Kuniharu Takei, Junwoo Park, Teresa Chen, Biwu Ma, Ali Javey
    NATURE MATERIALS 12 (10) 899 - 904 1476-1122 2013/10 [Refereed][Not invited]
     
    Electronic skin (e-skin) presents a network of mechanically flexible sensors that can conformally wrap irregular surfaces and spatially map and quantify various stimuli(1-12). Previous works on e-skin have focused on the optimization of pressure sensors interfaced with an electronic readout, whereas user interfaces based on a human-readable output were not explored. Here, we report the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels. In this system, organic light-emitting diodes (OLEDs) are turned on locally where the surface is touched, and the intensity of the emitted light quantifies the magnitude of the applied pressure. This work represents a system-on-plastic(4,13-17) demonstration where three distinct electronic components-thin-film transistor, pressure sensor and OLED arrays-are monolithically integrated over large areas on a single plastic substrate. The reported e-skin may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices.
  • Pak Heng Lau, Kuniharu Takei, Chuan Wang, Yeonkyeong Ju, Junseok Kim, Zhibin Yu, Toshitake Takahashi, Gyoujin Cho, Ali Javey
    NANO LETTERS 13 (8) 3864 - 3869 1530-6984 2013/08 [Refereed][Not invited]
     
    Fully printed transistors are a key component of ubiquitous flexible electronics. In this work, the advantages of an inverse gravure printing technique and the solution processing of semiconductor-enriched single-walled carbon nanotubes (SWNTs) are combined to fabricate fully printed thin-film transistors on mechanically flexible substrates. The fully printed transistors are configured in a top-gate device geometry and utilize silver metal electrodes and an inorganic/organic high-kappa (similar to 17) gate dielectric. The devices exhibit excellent performance for a fully printed process, with mobility and on/off current ratio of up to similar to 9 cm(2)/(V s) and 10(5), respectively. Extreme bendability is observed, without measurable change in the electrical performance down to a small radius of curvature of 1 mm. Given the high performance of the transistors, our high-throughput printing process serves as an enabling nanomanufacturing scheme for a wide range of large-area electronic applications based on carbon nanotube networks.
  • Kuniharu Takei, Rehan Kapadia, Yongjun Li, E. Plis, Sanjay Krishna, Ali Javey
    JOURNAL OF PHYSICAL CHEMISTRY C 117 (34) 17845 - 17849 1932-7447 2013/08 [Refereed][Not invited]
     
    Surface charge transfer is presented as an effective doping technique for III-V nanostructures. We generalize that the technique is applicable to nanoscale semiconductors in the limit where carriers are quantum confined. As a proof-of-concept, potassium surface charge transfer doping is carried out for one-dimensional (1D) and two-dimensional (2D) In As on Si/SiO2 substrates. Experiments and simulations show that equivalent dopant areal dose of up to similar to 2 x 10(12) cm(-2) is obtained, which is sufficient for degenerate doping of InAs nanostructures. This work presents a new pathway for controllable doping of inorganic semiconductors with limits fundamentally different from those of substitutional doping.
  • Rehan Kapadia, Zhibin Yu, Hsin Hua H. Wang, Maxwell Zheng, Corsin Battaglia, Mark Hettick, Daisuke Kiriya, Kuniharu Takei, Peter Lobaccaro, Jeffrey W. Beeman, Joel W. Ager, Roya Maboudian, Daryl C. Chrzan, Ali Javey
    Scientific Reports 3 2013/07/24 
    III-V photovoltaics (PVs) have demonstrated the highest power conversion efficiencies for both single-and multi-junction cells. However, expensive epitaxial growth substrates, low precursor utilization rates, long growth times, and large equipment investments restrict applications to concentrated and space photovoltaics (PVs). Here, we demonstrate the first vapor-liquid-solid (VLS) growth of high-quality III-V thin-films on metal foils as a promising platform for large-Area terrestrial PVs overcoming the above obstacles.Wedemonstrate 1-3 mmthick InP thin-films onMofoils withultra-large grain size up to 100 mm, which is,100 times larger than those obtained by conventional growth processes. The films exhibit electron mobilities as high as 500 cm2/V-s and minority carrier lifetimes as long as 2.5 ns. Furthermore, under 1-sun equivalent illumination, photoluminescence efficiency measurements indicate that an open circuit voltage of up to 930 mV can be achieved, only 40 mV lower than measured on a single crystal reference wafer.
  • Ole Waldmann, Arun Persaud, Rehan Kapadia, Kuniharu Takei, Frances I. Allen, Ali Javey, Thomas Schenkel
    THIN SOLID FILMS 534 488 - 491 0040-6090 2013/05 [Refereed][Not invited]
     
    Results from electron field-emission studies using arrays of patterned carbon nanofiber bundles are reported. We find that the desired field-emission characteristics were not compromised when a protective coating consisting of a layer of palladium of 5 and 30 nm thickness was applied. Following exposure to a hydrogen plasma for several hours we find that the coatings impede plasma damage significantly, whereas the field-emission properties of uncoated nanofibers degraded much more rapidly. The results demonstrate that carbon nanofibers with protective conformal metal coatings can be integrated into harsh plasma environments enabling a range of applications such as field-ionization ion sources and advanced (micro)-plasma discharges. (C) 2013 Elsevier B.V. All rights reserved.
  • Hui Fang, Mahmut Tosun, Gyungseon Seol, Ting Chia Chang, Kuniharu Takei, Jing Guo, Ali Javey
    NANO LETTERS 13 (5) 1991 - 1995 1530-6984 2013/05 [Refereed][Not invited]
     
    We report here the first degenerate n-doping of few-layer MoS2 and WSe2 semiconductors by surface charge transfer using potassium. High-electron sheet densities of similar to 1.0 x 10(13) cm(-2) and 2.5 X 10(12) cm(-2) for MoS2 and WSe2 are obtained, respectively. In addition, top-gated WSe2 and MoS2 n-FETs with selective K doping at the metal source/drain contacts are fabricated and shown to exhibit low contact resistances. Uniquely, WSe2 n-FETs are reported for the first time, exhibiting an electron mobility of similar to 110 cm(2)/V.s, which is comparable to the hole mobility of previously reported p-FETs using the same material. Ab initio simulations were performed to understand K doping of MoS2 and WSe2 in comparison with graphene. The results here demonstrate the need of degenerate doping of few-layer chalcogenides to improve the contact resistances and further realize high performance and complementary channel electronics.
  • Kuniharu Takei, Rehan Kapadia, Hui Fang, E. Plis, Sanjay Krishna, Ali Javey
    APPLIED PHYSICS LETTERS 102 (15) 153513  0003-6951 2013/04 [Refereed][Not invited]
     
    Interface quality of InAs-on-insulator (XOI) field-effect transistors (FETs) with a ZrO2 gate dielectric is examined as a function of various chemical treatments. With a forming gas anneal, InAs XOI FETs exhibit a low subthreshold swing of similar to 72 mV/dec with an interface trap density of similar to 1.5 x 10(12) states/cm(2) eV-both of which are comparable to the best reported epitaxially grown III-V devices on III-V substrates. Importantly, the results indicate that the surface properties of InAs are preserved during the layer transfer process, thereby, enabling the realization of high performance III-V FETs on Si substrates using the XOI configuration. (C) 2013 AIP Publishing LLC [http://dx.doi.org/10.1063/1.4802779]
  • Sung-Jin Choi, Patrick Bennett, Kuniharu Takei, Chuan Wang, Cheuk Chi Lo, Ali Javey, Jeffrey Bokor
    ACS NANO 7 (1) 798 - 803 1936-0851 2013/01 [Refereed][Not invited]
     
    We develop short-channel transistors using solution-processed single-walled carbon nanotubes (SWNTs) to evaluate the feasibility of those SWNTs for high-performance applications. Our results show that even though the intrinsic field-effect mobility is lower than the mobility of CVD nanotubes, the electrical contact between the nanotube and metal electrodes is not significantly affected. It is this contact resistance which often limits the performance of ultrascaled transistors. Moreover, we found that the contact resistance is lowered by the introduction of oxygen treatment. Therefore, high-performance solution-processed nanotube transistors with a 15 nm channel length were obtained by combining a top-gate structure and gate insulators made of a high-dielectric-constant ZrO2 film. The combination of these elements yields a performance comparable to that obtained with CVD nanotube transistors, which Indicates the potential for using solution-processed SWNTs for future aggressively scaled transistor technology.
  • Chuan Wang, Kuniharu Takei, Toshitakei Takahashi, Ali Javey
    MICRO- AND NANOTECHNOLOGY SENSORS, SYSTEMS, AND APPLICATIONS V 8725 0277-786X 2013 [Refereed][Not invited]
     
    We report solution-based processing of high-purity semiconducting carbon nanotube networks that has led to low-cost fabrication of large quantity of thin-film transistors (TFTs) with excellent yield and highly uniform, respectable performance on mechanically flexible substrates. Based on the semiconducting carbon nanotube TFTs, a wide range of macro-scale system-level electronics have been demonstrated including flexible integrated circuits, flexible full-color active-matrix organic light-emitting diode display, and smart interactive skin sensor that can simultaneously map and respond to the outside stimulus. Our work shows carbon nanotubes' immense promise as a low-cost and scalable TFT technology for nonconventional electronic systems with excellent performances.
  • Daisuke Kiriya, Maxwell Zheng, Rehan Kapadia, Junjun Zhang, Mark Hettick, Zhibin Yu, Kuniharu Takei, Hsin-Hua Hank Wang, Peter Lobaccaro, Ali Javey
    JOURNAL OF APPLIED PHYSICS 112 (12) 0021-8979 2012/12 [Refereed][Not invited]
     
    Scalable growth of high quality III-V semiconductor thin films on non-epitaxial substrates is of profound interest for photovoltaic applications. Here, we demonstrate growth of indium phosphide (InP) crystals directly on metal foils using closed-space sublimation (CSS) method. CSS allows effective transfer of source material to the substrate due to a small (similar to 2mm gap between source and substrate) sublimation space. The crystallization kinetics are found to be dependent on the substrate temperature and pressure of the system. Importantly, experiments revealed that both InP nanowires and polycrystalline films could be obtained by tuning the growth conditions. Furthermore, utilizing a silicon dioxide mask, selective nucleation of InP on metal substrates was obtained. Photoluminescence measurements depict the high optical quality of the CSS grown InP. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768836]
  • Chuan Wang, Jun-Chau Chien, Hui Fang, Kuniharu Takei, Junghyo Nah, E. Plis, Sanjay Krishna, Ali M. Niknejad, Ali Javey
    NANO LETTERS 12 (8) 4140 - 4145 1530-6984 2012/08 [Refereed][Not invited]
     
    This paper reports the radio frequency (RF) performance of InAs nanomembrane transistors on both mechanically rigid and flexible substrates. We have employed a self-aligned device architecture by using a T-shaped gate structure to fabricate high performance InAs metal-oxide-semiconductor field-effect transistors (MOSFETs) with channel lengths down to 75 nm. RF measurements reveal that the InAs devices made on a silicon substrate exhibit a cutoff frequency (f(t)) of similar to 165 GHz, which is one of the best results achieved in III-V MOSFETs on silicon. Similarly, the devices fabricated on a bendable polyimide substrate provide a f(t) of similar to 105 GHz, representing the best performance achieved for transistors fabricated directly on mechanically flexible substrates. The results demonstrate the potential of III-V-on-insulator platform for extremely high-frequency (EHF) electronics on both conventional silicon and flexible substrates.
  • Hyunhyub Ko, Rehan Kapadia, Kuniharu Takei, Toshitake Takahashi, Xiaobo Zhang, Ali Javey
    NANOTECHNOLOGY 23 (34) 0957-4484 2012/08 [Refereed][Not invited]
     
    The development of flexible electronic systems has been extensively researched in recent years, with the goal of expanding the potential scope and market of modern electronic devices in the areas of computation, communications, displays, sensing and energy. Uniquely, the use of soft polymeric substrates enables the incorporation of advanced features beyond mechanical bendability and stretchability. In this paper, we describe several functionalities which can be achieved using engineered nanostructured materials. In particular, reversible binding, self-cleaning, antireflective and shape-reconfigurable properties are introduced for the realization of multifunctional, flexible electronic devices. Examples of flexible systems capable of spatial mapping and/or responding to external stimuli are also presented as a new class of user-interactive devices.
  • Hui Fang, Steven Chuang, Ting Chia Chang, Kuniharu Takei, Toshitake Takahashi, Ali Javey
    NANO LETTERS 12 (7) 3788 - 3792 1530-6984 2012/07 [Refereed][Not invited]
     
    We report high performance p-type field-effect transistors based on single layered (thickness, similar to 0.7 nm) WSe2 as the active channel with chemically doped source/drain contacts and high-K gate dielectrics. The top-gated monolayer transistors exhibit a high effective hole mobility of "-ISO cm(2)/(V s), perfect subthreshold swing of similar to 60 mV/dec, and I-ON/'OFF of >10(6) at room temperature. Special attention is given to lowering the contact resistance for hole injection by using high work function Pd contacts along with degenerate surface doping of the contacts by patterned NO2 chemisorption on WSe2. The results here present a promising material system and device architecture for p-type monolayer transistors with excellent characteristics.
  • Junghyo Nah, Hui Fang, Chuan Wang, Kuniharu Takei, Min Hyung Lee, E. Plis, Sanjay Krishna, Ali Javey
    NANO LETTERS 12 (7) 3592 - 3595 1530-6984 2012/07 [Refereed][Not invited]
     
    One of the major challenges in further advancement of RI V electronics is to integrate high mobility complementary transistors on the same substrate. The difficulty is due to the large lattice mismatch of the optimal p- and n-type III-V semiconductors. In this work, we employ a two-step epitaxial layer transfer process for the heterogeneous assembly of ultrathin membranes of III-V compound semiconductors on Si/SiO2 substrates. In this III-V-on-insulator (XOI) concept, ultrathin-body InAs (thickness, 13 nm) and InGaSb (thickness, 7 nm) layers are used for enhancement-mode n- and p- MOSFETs, respectively. The peak effective mobilities of the complementary devices are similar to 1190 and similar to 370 cm(2)/(V s) for electrons and holes, respectively, both of which are higher than the state-of-the-art Si MOSFETs. We demonstrate the first proof-of-concept III-V CMOS logic operation by fabricating NOT and NAND gates, highlighting the utility of the XOI platform.
  • Maxwell Zheng, Zhibin Yu, Tae Joon Seok, Yu-Ze Chen, Rehan Kapadia, Kuniharu Takei, Shaul Aloni, Joel W. Ager, Ming Wu, Yu-Lun Chueh, Ali Javey
    JOURNAL OF APPLIED PHYSICS 111 (12) 0021-8979 2012/06 [Refereed][Not invited]
     
    III-V semiconductor solar cells have demonstrated the highest power conversion efficiencies to date. However, the cost of III-V solar cells has historically been too high to be practical outside of specialty applications. This stems from the cost of raw materials, need for a lattice-matched substrate for single-crystal growth, and complex epitaxial growth processes. To address these challenges, here, we explore the direct non-epitaxial growth of thin poly-crystalline films of III-Vs on metal substrates by using metalorganic chemical vapor deposition. This method minimizes the amount of raw material used while utilizing a low cost substrate. Specifically, we focus on InP which is known to have a low surface recombination velocity of carriers, thereby, making it an ideal candidate for efficient poly-crystalline cells where surface/interface properties at the grain boundaries are critical. The grown InP films are 1-3 mu m thick and are composed of micron-sized grains that generally extend from the surface to the Mo substrate. They exhibit similar photoluminescence peak widths and positions as single-crystalline InP, as well as excellent crystallinity as examined through TEM and XRD analyses. This work presents poly-InP as a promising absorber layer for future photovoltaics. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730442]
  • Hui Fang, Steven Chuang, Kuniharu Takei, Ha Sul Kim, Elena Plis, Chin-Hung Liu, Sanjay Krishna, Yu-Lun Chueh, Ali Javey
    IEEE ELECTRON DEVICE LETTERS 33 (4) 504 - 506 0741-3106 2012/04 [Refereed][Not invited]
     
    Ultrathin-body InAsSb-on-insulator n-type field-effect transistors (FETs) with ultrahigh electron mobilities are reported. The devices are obtained by the layer transfer of ultrathin InAs0.7Sb0.3 layers (thickness of 7-17 nm) onto Si/SiO2 substrates. InAsSb-on-insulator FETs exhibit an effective mobility of similar to 3400 cm(2)/V . s for a body thickness of 7 nm, which represents similar to 2x enhancement over InAs devices of similar thickness. The top-gated FETs deliver an intrinsic transconductance of similar to 0.56 mS/mu m (gate length of similar to 500 nm) at V-DS = 0.5 V with I-ON/I-OFF of 10(2)-10(3). These results demonstrate the utility of the transfer process for obtaining high-mobility n-FETs on Si substrates by using mixed anion arsenide-antimonide as the active channel material.
  • Kuniharu Takei, Morten Madsen, Hui Fang, Rehan Kapadia, Steven Chuang, Ha Sul Kim, Chin-Hung Liu, E. Plis, Junghyo Nah, Sanjay Krishna, Yu-Lun Chueh, Jing Guo, Ali Javey
    NANO LETTERS 12 (4) 2060 - 2066 2012/04 [Refereed][Not invited]
     
    As of yet, III-V p-type field-effect transistors (p-FETs) on Si have not been reported, due partly to materials and processing challenges, presenting an important bottleneck in the development of complementary III-V electronics. Here, we report the first high-mobility HI-V p-FET on Si, enabled by the epitaxial layer transfer of InGaSb heterostructures with nanoscale thicknesses. Importantly, the use of ultrathin (thickness, similar to 2.5 nm) InAs cladding layers results in drastic performance enhancements arising from (i) surface passivation of the InGaSb channel, (ii) mobility enhancement due to the confinement of holes in InGaSb, and (iii) low-resistance, dopant-free contacts due to the type III band alignment of the heterojunction. The fabricated p-FETs display a peak effective mobility of similar to 820 cm(2)/(V s) for holes with a subthreshold swing of similar to 130 mV/decade. The results present an important advance in the field of III-V electronics.
  • Chuan Wang, Jun-Chau Chien, Kuniharu Takei, Toshitake Takahashi, Junghyo Nah, Ali M. Niknejad, Ali Javey
    NANO LETTERS 12 (3) 1527 - 1533 1530-6984 2012/03 [Refereed][Not invited]
     
    Solution-processed thin-films of semiconducting carbon nanotubes as the channel material for flexible electronics simultaneously offers high performance, low cost, and ambient stability, which significantly outruns the organic semiconductor materials. In this work, we report the use of semiconductor-enriched carbon nanotubes for high-performance integrated circuits on mechanically flexible substrates for digital, analog and radio frequency applications. The as-obtained thin-film transistors (TFTs) exhibit highly uniform device performance with on-current and transconductance up to 15 mu A/mu m and 4 mu S/mu m. By performing capacitance voltage measurements, the gate capacitance of the nanotube TFT is precisely extracted and the corresponding peak effective device mobility is evaluated to be around 50 cm(2)V(-1)s(-1). Wing such devices, digital logic gates including inverters, NAND, and NOR gates with superior bending stability have been demonstrated. Moreover, radio frequency measurements show that cutoff frequency of 170 MHz can be achieved in devices with a relatively long channel length of 4 mu m, which is sufficient for certain wireless communication applications. This proof-of-concept demonstration indicates that our platform can serve as a foundation for scalable, low-cost, high-performance flexible electronics.
  • Arun Persaud, Ole Waldmann, Rehan Kapadia, Kuniharu Takei, Ali Javey, Thomas Schenkel
    REVIEW OF SCIENTIFIC INSTRUMENTS 83 (2) 0034-6748 2012/02 [Refereed][Not invited]
     
    Field ionization as a means to create ions for compact and rugged neutron sources is pursued. Arrays of carbon nano-fibers promise the high field-enhancement factors required for efficient field ionization. We report on the fabrication of arrays of field emitters with a density up to 10(6) tips/cm(2) and measure their performance characteristics using electron field emission. The critical issue of uniformity is discussed, as are efforts towards coating the nano-fibers to enhance their lifetime and surface properties. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3672437]
  • Toshitake Takahashi, Patricia Nichols, Kuniharu Takei, Alexandra C. Ford, Arash Jamshidi, Ming C. Wu, C. Z. Ning, Ali Javey
    NANOTECHNOLOGY 23 (4) 0957-4484 2012/02 [Refereed][Not invited]
     
    Spatially composition-graded CdSxSe1-x (x = 0-1) nanowires are grown and transferred as parallel arrays onto Si/SiO2 substrates by a one-step, directional contact printing process. Upon subsequent device fabrication, an array of tunable-wavelength photodetectors is demonstrated. From the spectral photoconductivity measurements, the cutoff wavelength for the device array, as determined by the bandgap, is shown to cover a significant portion of the visible spectrum. The ability to transfer a collection of crystalline semiconductor nanowires while preserving the spatially graded composition may enable a wide range of applications, such as tunable lasers and photodetectors, efficient photovoltaics, and multiplexed chemical sensors.
  • Min Hyung Lee, Kuniharu Takei, Junjun Zhang, Rehan Kapadia, Maxwell Zheng, Yu-Ze Chen, Junghyo Nah, Tyler S. Matthews, Yu-Lun Chueh, Joel W. Ager, Ali Javey
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 51 (43) 10760 - 10764 1433-7851 2012 [Refereed][Not invited]
  • Yang Chai, Arash Hazeghi, Kuniharu Takei, Hong-Yu Chen, Philip C. H. Chan, Ali Javey, H. -S. Philip Wong
    IEEE TRANSACTIONS ON ELECTRON DEVICES 59 (1) 12 - 19 0018-9383 2012/01 [Refereed][Not invited]
     
    Carbon nanotubes (CNTs) are promising candidates for transistors and interconnects for nanoelectronic circuits. Although CNTs intrinsically have excellent electrical conductivity, the large contact resistance at the interface between CNT and metal hinders its practical application. Here, we show that electrical contact to the CNT is substantially improved using a graphitic interfacial layer catalyzed by a Ni layer. The p-type semiconducting CNT with graphitic contact exhibits high ON-state conductance at room temperature and a steep subthreshold swing in a back-gate configuration. We also show contact improvement to the semiconducting CNTs with different capping metals. To study the role of the graphitic interfacial layer in the contact stack, the capping metal and Ni catalyst were selectively removed and replaced with new metal pads deposited by evaporation and without further annealing. Good electrical contact to the semiconducting CNTs was still preserved after the new metal replacement, indicating that the contact improvement is attributed to the presence of the graphitic interfacial layer.
  • Toshitake Takahashi, Kuniharu Takei, Andrew G. Gillies, Ronald S. Fearing, Ali Javey
    NANO LETTERS 11 (12) 5408 - 5413 1530-6984 2011/12 [Refereed][Not invited]
     
    In this paper, we report a promising approach for fabricating large-scale flexible and stretchable electronics using a semiconductor-enriched carbon nanotube solution. Uniform semiconducting nanotube networks with superb electrical properties (mobility of similar to 20 cm(2) V-1 s(-1) and I-ON/I-OFF of similar to 10(4)) are obtained on polyimide substrates. The substrate is made stretchable by laser cutting a honeycomb mesh structure, which combined with nanotube-network transistors enables highly robust conformal electronic devices with minimal device-to-device stochastic variations. The utility of this device concept is demonstrated by fabricating an active-matrix backplane (12 x 8 pixels, physical size of 6 x 4 cm(2)) for pressure mapping using a pressure sensitive rubber as the sensor element.
  • Cary L. Pint, Kuniharu Takei, Rehan Kapadia, Maxwell Zheng, Alexandra C. Ford, Junjun Zhang, Arash Jamshidi, Rizia Bardhan, Jeffrey J. Urban, Ming Wu, Joel W. Ager, Michael M. Oye, Ali Javey
    ADVANCED ENERGY MATERIALS 1 (6) 1040 - 1045 1614-6832 2011/11 [Refereed][Not invited]
  • Yang Chai, Yi Wu, Kuniharu Takei, Hong-Yu Chen, Shimeng Yu, Philip C. H. Chan, Ali Javey, H. -S. Philip Wong
    IEEE TRANSACTIONS ON ELECTRON DEVICES 58 (11) 3933 - 3939 0018-9383 2011/11 [Refereed][Not invited]
     
    There has been a strong demand for developing an ultradense and low-power nonvolatile memory technology. In this paper, we present a carbon-based resistive random access memory device with a carbon nanotube (CNT) electrode. An amorphous carbon layer is sandwiched between the fast-diffusing top metal electrode and the bottom CNT electrode, exhibiting a bipolar switching behavior. The use of the CNT electrode can substantially reduce the size of the active device area. We also demonstrate a carbon-based complementary resistive switch (CRS) consisting of two back-to-back connected memory cells, providing a route to reduce the sneak current in the cross-point memory. The bit information of the CRS cell is stored in a high-resistance state, thus reducing the power consumption of the CRS memory cell. This paper provides valuable early data on the effect of electrode size scaling down to nanometer size.
  • Kuniharu Takei, Hui Fang, S. Bala Kumar, Rehan Kapadia, Qun Gao, Morten Madsen, Ha Sul Kim, Chin-Hung Liu, Yu-Lun Chueh, Elena Plis, Sanjay Krishna, Hans A. Bechtel, Jing Guo, Ali Javey
    NANO LETTERS 11 (11) 5008 - 5012 2011/11 [Refereed][Not invited]
     
    Nanoscale size effects drastically alter the fundamental properties of semiconductors. Here, we investigate the dominant role of quantum confinement in the field-effect device properties of free-standing InAs nanomembranes with varied thicknesses of 5-50 nm, First, optical absorption studies are performed by transferring InAs "quantum membranes" (QMs) onto transparent substrates; from which the quantized sub-bands are directly visualized. These sub-bands determine the contact resistance of the system with the experimental values consistent with the expected number of quantum transport modes available for a given thickness. Finally, the effective electron mobility of InAs QMs is shown to exhibit anomalous field and thickness dependences that are in distinct contrast to the conventional MOSFET models, arising from the strong quantum confinement of carriers. The results provide an important advance toward establishing the fundamental device physics of two-dimensional semiconductors.
  • Kuniharu Takei, Steven Chuang, Hui Fang, Rehan Kapadia, Chin-Hung Liu, Junghyo Nah, Ha Sul Kim, E. Plis, Sanjay Krishna, Yu-Lun Chueh, Ali Javey
    APPLIED PHYSICS LETTERS 99 (10) 2011/09 [Refereed][Not invited]
     
    The effect of body thickness (5-13 nm) on the leakage currents of top-gated, InAs-on-insulator field-effect-transistors with a channel length of similar to 200 nm is explored. From a combination of experiments and simulation, it is found that the OFF-state currents are primarily dominated by Shockley Read Hall recombination/generation and trap-assisted tunneling. The OFF currents are shown to decrease with thickness reduction, highlighting the importance of the ultrathin body device configuration. The devices exhibit promising performances, with a peak extrinsic and intrinsic transconductances of similar to 1.7 and 2.3 mS/mu m, respectively, at a low source/drain voltage of 0.5 V and a body thickness of similar to 13 nm. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3636110]
  • Min Hyung Lee, Namsoo Lim, Daniel J. Ruebusch, Arash Jamshidi, Rehan Kapadia, Rebecca Lee, Tae Joon Seok, Kuniharu Takei, Kee Young Cho, Zhiyoung Fan, Hwanung Jang, Ming Wu, Gyoujin Cho, Ali Javey
    NANO LETTERS 11 (8) 3425 - 3430 1530-6984 2011/08 [Refereed][Not invited]
     
    A high-throughput process for nanotexturing of hard and soft surfaces based on the roll-to-roll anodization and etching of low-cost aluminum foils is presented. The process enables the precise control of surface topography, feature size, and shape over large areas thereby presenting a highly versatile platform for fabricating substrates with user-defined, functional performance. Specifically, the optical and surface wetting properties of the foil substrates were systematically characterized and tuned through the modulation of the surface texture. In addition, textured aluminum foils with pore and bowl surface features were used as zeptoliter reaction vessels for the well-controlled synthesis of inorganic, organic, and plasmonic nanomaterials, demonstrating yet another powerful potential use of the presented approach.
  • Morten Madsen, Kuniharu Takei, Rehan Kapadia, Hui Fang, Hyunhyub Ko, Toshitake Takahashi, Alexandra C. Ford, Min Hyung Lee, Ali Javey
    ADVANCED MATERIALS 23 (28) 3115 - 3127 0935-9648 2011/07 [Refereed][Not invited]
     
    Recent advancements in the integration of nanoscale, single-crystalline semiconductor 'X' on substrate 'Y' (XoY) for use in transistor and sensor applications are presented. XoY is a generic materials framework for enabling the fabrication of various novel devices, without the constraints of the original growth substrates. Two specific XoY process schemes, along with their associated materials, device and applications are presented. In one example, the layer transfer of ultrathin III-V semiconductors with thicknesses of just a few nanometers on Si substrates is explored for use as energy-efficient electronics, with the fabricated devices exhibiting excellent electrical properties. In the second example, contact printing of nanowire-arrays on thin, bendable substrates for use as artificial electronic-skin is presented. Here, the devices are capable of conformably covering any surface, and providing a real-time, two-dimensional mapping of external stimuli for the realization of smart functional surfaces. This work is an example of the emerging field of "translational nanotechnology" as it bridges basic science of nanomaterials with practical applications.
  • Yaping Dan, Kwanyong Seo, Kuniharu Takei, Jhim H. Meza, Ali Javey, Kenneth B. Crozier
    NANO LETTERS 11 (6) 2527 - 2532 1530-6984 2011/06 [Refereed][Not invited]
     
    Nanowires have unique optical properties(1-4) and are considered as important building blocks for energy harvesting applications such as solar cells.(2,5-8) However, due to their large surface-to-volume ratios, the recombination of charge carriers through surface states reduces the carrier diffusion lengths in nanowires a few orders of magnitude,(9) often resulting in the low efficiency (a few percent or less) of nanowire-based solar cells.(7,8,10,11) Reducing the recombination by surface passivation is crucial for the realization of high-performance nanosized optoelectronic devices but remains largely unexplored.(7,12-14) Here we show that a thin layer of amorphous silicon (a-Si) coated on a single-crystalline silicon nanowire, forming a core shell structure in situ in the vapor-liquid-solid process, reduces the surface recombination nearly 2 orders of magnitude. Under illumination of modulated light, we measure a greater than 90-fold improvement in the photosensitivity of individual core-shell nanowires, compared to regular nanowires without shell. Simulations of the optical absorption of the nanowires indicate that the strong absorption of the a-Si shell contributes to this effect, but we conclude that the effect is mainly due to the enhanced carrier lifetime by surface passivation.
  • Kee Cho, Daniel J. Ruebusch, Min Hyung Lee, Jae Hyun Moon, Alexandra C. Ford, Rehan Kapadia, Kuniharu Takei, Onur Ergen, Ali Javey
    APPLIED PHYSICS LETTERS 98 (20) 0003-6951 2011/05 [Refereed][Not invited]
     
    Semiconductor nanopillar arrays with radially doped junctions have been widely proposed as an attractive device architecture for cost effective and high efficiency solar cells. A challenge in the fabrication of three-dimensional nanopillar devices is the need for highly abrupt and conformal junctions along the radial axes. Here, a sulfur monolayer doping scheme is implemented to achieve conformal ultrashallow junctions with sub-10 nm depths and a high electrically active dopant concentration of 10(19)-10(20) cm(-3) in arrays of InP nanopillars. The enabled solar cells exhibit a respectable conversion efficiency of 8.1% and a short circuit current density of 25 mA/cm(3). The work demonstrates the utility of well-established surface chemistry for fabrication of nonplanar junctions for complex devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3585138]
  • Arun Persaud, Ian Allen, Michael R. Dickinson, Thomas Schenkel, Rehan Kapadia, Kuniharu Takei, Ali Javey
    JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B 29 (2) 1071-1023 2011/03 [Refereed][Not invited]
     
    The authors report on the use of carbon nanofiber nanoemitters to ionize deuterium atoms for the generation of neutrons in a deuterium-deuterium reaction in a preloaded target. Acceleration voltages in the range of 50-80 kV are used. Field emission of electrons is investigated to characterize the emitters. The experimental setup and sample preparation are described and first data of neutron production are presented. Ongoing experiments to increase neutron production yields by optimizing the field emitter geometry and surface conditions are discussed. (c) 2011 American Vacuum Society. [DOI: 10.1116/1.3531929]
  • Hui Fang, Morten Madsen, Carlo Carraro, Kuniharu Takei, Ha Sul Kim, Elena Plis, Szu-Ying Chen, Sanjay Krishna, Yu-Lun Chueh, Roya Maboudian, Ali Javey
    APPLIED PHYSICS LETTERS 98 (1) 0003-6951 2011/01 [Refereed][Not invited]
     
    Strain state of ultrathin InAs-on-insulator layers obtained from an epitaxial transfer process is studied. The as-grown InAs epilayer (10-20 nm thick) on the GaSb/AlGaSb source wafer has the expected similar to 0.62% tensile strain. The strain is found to fully release during the epitaxial transfer of the InAs layer onto a Si/SiO(2) substrate. In order to engineer the strain of the transferred InAs layers, a ZrO(x) cap was used during the transfer process to effectively preserve the strain. The work presents an important advance toward the control of materials properties of III-V on insulator layers. (C) 2011 American Institute of Physics. [doi:10.1063/1.3537963]
  • Tetsuhiro Harimoto, Kuniharu Takei, Takeshi Kawano, Akito Ishihara, Takahiro Kawashima, Hidekazu Kaneko, Makoto Ishida, Shiro Usui
    BIOSENSORS & BIOELECTRONICS 26 (5) 2368 - 2375 0956-5663 2011/01 [Refereed][Not invited]
     
    In order to record multi-site electroretinogram (ERG) responses in isolated carp retinae, we utilized three-dimensional (3D), extracellular, 3.5-mu m-diameter silicon (Si) probe arrays fabricated by the selective vapor-liquid-solid (VLS) growth method. Neural recordings with the Si microprobe exhibit low signal-to-noise (SIN) ratios of recorded responses due to the high-electrical-impedance characteristics of the small recording area at the probe tip. To increase the S/N ratio, we designed and fabricated enlarged gold (Au) tipped Si microprobes (10-mu m-diameter Au tip and 3.5-mu m-diameter probe body). In addition, we demonstrated that the signal attenuation and phase delay of ERG responses recorded via the Si probe can be compensated by the inverse filtering method. We conclude that the reduction of probe impedance and the compensation of recorded signals are useful approaches to obtain distortion-free recording of neural signals with high-impedance microelectrodes. (C) 2010 Elsevier B.V. All rights reserved.
  • Hyunhyub Ko, Kuniharu Takei, Rehan Kapadia, Steven Chuang, Hui Fang, Paul W. Leu, Kartik Ganapathi, Elena Plis, Ha Sul Kim, Szu-Ying Chen, Morten Madsen, Alexandra C. Ford, Yu-Lun Chueh, Sanjay Krishna, Sayeef Salahuddin, Ali Javey
    NATURE 468 (7321) 286 - 289 0028-0836 2010/11 [Refereed][Not invited]
     
    Over the past several years, the inherent scaling limitations of silicon (Si) electron devices have fuelled the exploration of alternative semiconductors, with high carrier mobility, to further enhance device performance(1-8). In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied(7,9,10): such devices combine the high mobility of III-V semiconductors and the well established, low-cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored(9,11-13)-but besides complexity, high defect densities and junction leakage currents present limitations in this approach. Motivated by this challenge, here we use an epitaxial transfer method for the integration of ultrathin layers of single-crystal InAs on Si/SiO(2) substrates. As a parallel with silicon-on-insulator (SOI) technology(14), we use 'XOI' to represent our compound semiconductoron-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high-quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsO(x) layer (similar to 1 nm thick). The fabricated field-effect transistors exhibit a peak transconductance of similar to 1.6 mS mu m(-1) at a drain-source voltage of 0.5 V, with an on/off current ratio of greater than 10,000.
  • Zhiyong Fan, Rehan Kapadia, Paul W. Leu, Xiaobo Zhang, Yu-Lun Chueh, Kuniharu Takei, Kyoungsik Yu, Arash Jamshidi, Asghar A. Rathore, Daniel J. Ruebusch, Ming Wu, Ali Javey
    NANO LETTERS 10 (10) 3823 - 3827 1530-6984 2010/10 [Refereed][Not invited]
     
    Optical properties of highly ordered Ge nanopillar arrays are tuned through shape and geometry control to achieve the Optimal absorption efficiency Increasing the Ge materials filling ratio is shown to increase the reflectance while simultaneously decreasing the transmittance. with the absorbance showing a strong diameter dependency To enhance the broad band optical absorption efficiency. a novel dual-diameter nanopillar structure is presented, with a small diameter tip for minimal reflectance and a large diameter base for maximal effective absorption coefficient The enabled single-crystalline absorber material with a thickness of only 2 mu m exhibits an impressive absorbance of similar to 99% over wavelengths, lambda = 300-900 nm These results enable a viable and convenient route toward shape-controlled nanopillar-based high-performance photonic devices
  • Onur Ergen, Daniel J. Ruebusch, Hui Fang, Asghar A. Rathore, Rehan Kapadia, Zhiyong Fan, Kuniharu Takei, Arash Jamshidi, Ming Wu, Ali Javey
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 (40) 13972 - 13974 0002-7863 2010/10 [Refereed][Not invited]
     
    Highly regular, single-crystalline nanopillar arrays with tunable shapes and geometry are synthesized by the template-assisted vapor liquid solid growth mechanism. In this approach, the grown nanopillars faithfully reproduce the shape of the pores because during the growth the liquid catalyst seeds fill the space available, thereby conforming to the pore geometry. The process is highly generic for various material systems, and as an example, CdS and Ge nanopillar arrays with square, rectangular, and circular cross sections are demonstrated. In the future, this technique can be used to engineer the intrinsic properties of NPLs as a function of three independently controlled dimensional parameters - length, width and height.
  • Kuniharu Takei, Toshitake Takahashi, Johnny C. Ho, Hyunhyub Ko, Andrew G. Gillies, Paul W. Leu, Ronald S. Fearing, Ali Javey
    NATURE MATERIALS 9 (10) 821 - 826 1476-1122 2010/10 [Refereed][Not invited]
     
    Large-scale integration of high-performance electronic components on mechanically flexible substrates may enable new applications in electronics, sensing and energy(1-8). Over the past several years, tremendous progress in the printing and transfer of single-crystalline, inorganic micro-and nanostructures on plastic substrates has been achieved through various process schemes(5-10). For instance, contact printing of parallel arrays of semiconductor nanowires (NWs) has been explored as a versatile route to enable fabrication of high-performance, bendable transistors and sensors(11-14). However, truly macroscale integration of ordered NW circuitry has not yet been demonstrated, with the largest-scale active systems being of the order of 1 cm(2) (refs 11,15). This limitation is in part due to assembly-and processing-related obstacles, although larger-scale integration has been demonstrated for randomly oriented NWs (ref. 16). Driven by this challenge, here we demonstrate macroscale (7 x 7 cm(2)) integration of parallel NW arrays as the active-matrix backplane of a flexible pressure-sensor array (18 x 19 pixels). The integrated sensor array effectively functions as an artificial electronic skin(2,17,18), capable of monitoring applied pressure profiles with high spatial resolution. The active-matrix circuitry operates at a low operating voltage of less than 5V and exhibits superb mechanical robustness and reliability, without performance degradation on bending to small radii of curvature (2.5 mm) for over 2,000 bending cycles. This work presents the largest integration of ordered NW-array active components, and demonstrates a model platform for future integration of nanomaterials for practical applications.
  • Toshitake Takahashi, Kuniharu Takei, Ehsan Adabi, Zhiyong Fan, Ali M. Niknejad, Ali Javey
    ACS NANO 4 (10) 5855 - 5860 1936-0851 2010/10 [Refereed][Not invited]
     
    The radio frequency response of InAs nanowire array transistors on mechanically flexible substrates is characterized. For the first time, GHz device operation of nanowire arrays is demonstrated, despite the relatively long channel lengths of similar to 1.5 mu m used in this work. Specifically, the transistors exhibit an impressive maximum frequency of oscillation, f(max) similar to 1.8 GHz, and a cutoff frequency, f(t) similar to 1 GHz. The high-frequency response of the devices is due to the high saturation velocity of electrons in high-mobility InAs nanowires. The work presents a new platform for flexible, ultrahigh frequency devices with potential applications in high-performance digital and analog circuitry.
  • Hyunhyub Ko, Zhenxing Zhang, Kuniharu Takei, Ali Javey
    NANOTECHNOLOGY 21 (29) 0957-4484 2010/07 [Refereed][Not invited]
     
    We introduce a simple and robust method for fabricating hierarchical fibrillar arrays based on polymer micropillar (mu PLR) arrays decorated with ZnO nanowires (NWs) on mechanically flexible substrates. The hierarchical fibrillar arrays are fabricated by replica molding of polymer mu PLR arrays on microfabricated silicon templates and subsequent solution-based growth of ZnO NWs. Fine control over the dimensions and aspect ratios of both the microelements and the nanoelements is demonstrated. The hierarchical mu PLR/NW arrays show superhydrophobic surface properties, with the contact angle higher than that of planar surfaces and mu PLR arrays without nanostructures. The fabrication strategy suggested here may be potentially extended to fabricate other organic/inorganic hierarchical systems for different applications.
  • Takeshi Kawano, Tetsuhiro Harimoto, Akito Ishihara, Kuniharu Takei, Takahiro Kawashima, Shiro Usui, Makoto Ishida
    BIOSENSORS & BIOELECTRONICS 25 (7) 1809 - 1815 0956-5663 2010/03 [Refereed][Not invited]
     
    We report here a technique for use in electrical interfaces between neurons and microelectronics, using vertically integrated silicon probe arrays with diameters of 2-3.5 mu m and lengths of 60-120 mu m. Silicon probe arrays can be fabricated by selective vapor-liquid-solid (VLS) growth. A doped n-type silicon probe with the resistance of 1 k Omega has an electrical impedance of less than 10 M Omega in physiological saline. After inserting the probe arrays into the retina of a carp (Cyrpinus carpio), we conducted electrical recording of neural signals, using the probes to measure light-evoked electrical neural signals. We determined that recorded signals represented local field potentials of the retina (electroretinogram (ERG)). The VLS-probe can provide minimally invasive neural recording/stimulation capabilities at high spatial resolution for fundamental studies of nervous systems. In addition, the probe arrays can be integrated with microelectronics; therefore, these probes make it possible to construct interfaces between neurons and microelectronics in advanced neuroscience applications. (C) 2010 Elsevier B.V. All rights reserved.
  • Yu-Lun Chueh, Zhiyong Fan, Kuniharu Takei, Hyunhyub Ko, Rehan Kapadia, Asghar A. Rathore, Nate Miller, Kyoungsik Yu, Ming Wu, E. E. Haller, Ali Javey
    NANO LETTERS 10 (2) 520 - 523 1530-6984 2010/02 [Refereed][Not invited]
     
    Direct growth of black Ge on low-temperature substrates, including plastics and rubber is reported. The material is based on highly dense, crystalline/amorphous core/shell Ge nanoneedle arrays with ultrasharp tips (similar to 4 nm) enabled by the Ni catalyzed vapor-solid-solid growth process. Ge nanoneedle arrays exhibit remarkable optical properties, Specifically, minimal optical reflectance (<1%) is observed, even for high angles of incidence (similar to 75 degrees) and for relatively short nanoneedle lengths (-1 mu m). Furthermore, the. material exhibits high optical absorption efficiency with an effective band gap of similar to 1 eV. The reported black Ge could potentially have important practical implications For efficient photovoltaic and photodetector applications on nonconventional substrates.
  • Maxwell Zheng, Kuniharu Takei, Benjamin Hsia, Hui Fang, Xiaobo Zhang, Nicola Ferralis, Hyunhyub Ko, Yu-Lun Chueh, Yuegang Zhang, Roya Maboudian, Ali Javey
    APPLIED PHYSICS LETTERS 96 (6) 0003-6951 2010/02 [Refereed][Not invited]
     
    Metal-catalyzed crystallization of amorphous carbon to graphene by thermal annealing is demonstrated. In this "limited source" process scheme, the thickness of the precipitated graphene is directly controlled by the thickness of the initial amorphous carbon layer. This is in contrast to chemical vapor deposition processes, where the carbon source is virtually unlimited and controlling the number of graphene layers depends on the tight control over a number of deposition parameters. Based on the Raman analysis, the quality of graphene is comparable to other synthesis methods found in the literature, such as chemical vapor deposition. The ability to synthesize graphene sheets with tunable thickness over large areas presents an important progress toward their eventual integration for various technological applications.
  • Yu-Lun Chueh, Cosima N. Boswell, Chun-Wei Yuan, Swanee J. Shin, Kuniharu Takei, Johnny C. Ho, Hyunhyub Ko, Zhiyong Fan, E. E. Haller, D. C. Chrzan, Ali Javey
    NANO LETTERS 10 (2) 393 - 397 1530-6984 2010/02 [Refereed][Not invited]
     
    A tunable structural engineering of nanowires based on template-assisted alloying and phase segregation processes is demonstrated. The Au-Ge system, which has a low eutectic temperature and negligible solid solubility (< 10(-3) atom %)of Au in Ge at low temperatures, is utilized. Depending on the Au concentration of the initial nanowires, final structures ranging from nearly periodic nanodisk patterns to core/shell and fully alloyed nanowires are produced. The formation mechanisms are discussed in detail and characterized by in situ transmission electron microscopy and energy-dispersive spectrometry analyses. Electrical measurements illustrate the metallic and semiconducting characteristics of the fully alloyed and alternating Au/Ge nanodisk structures, respectively.
  • Kuniharu Takei, Takeshi Kawano, Takahiro Kawashima, Kazuaki Sawada, Hidekazu Kaneko, Makoto Ishida
    BIOMEDICAL MICRODEVICES 12 (1) 41 - 48 1387-2176 2010/02 [Refereed][Not invited]
     
    We report on the development of a microtube electrode array as a neural interface device. To combine the desired properties for the neural interface device, such as low invasiveness with a small needle and a good signal-to-noise ratio in neural recordings, we applied the structure of a glass pipette electrode to each microtube electrode. The device was fabricated as sub-5-mu m-diameter out-of-plane silicon dioxide microtube arrays using silicon microneedle templates, which are grown by the selective vapor-liquid-solid method. The microtubes had inner diameters of 1.9-6.4 mu m and a length of 25 mu m. Impedances ranged from 220 k Omega to 1.55 M Omega, which are less than those for conventional microneedles. In addition, the microtube electrodes had less signal attenuation than conventional microneedle electrodes. We confirmed that the effects of parasitic capacitances between neighboring microtubes and channels were sufficiently small using a test signal. Finally, neural responses evoked from a rat peripheral nerve were recorded in vivo using a microtube electrode to confirm that this type of electrode can be used for both electrophysiological measurements and as a neural interface device.
  • Hyunhyub Ko, Zhenxing Zhang, Johnny C. Ho, Kuniharu Takei, Rehan Kapadia, Yu-Lun Chueh, Weizhen Cao, Brett A. Cruden, Ali Javey
    SMALL 6 (1) 22 - 26 1613-6810 2010/01 [Refereed][Not invited]
  • Yang Chai, Yi Wu, Kuniharu Takei, Hong-Yu Chen, Shimeng Yu, Philip C. H. Chan, Ali Javey, H. -S. Philip Wong
    2010 INTERNATIONAL ELECTRON DEVICES MEETING - TECHNICAL DIGEST 2010 [Refereed][Not invited]
     
    We demonstrate the nonvolatile resistive switching of an amorphous carbon (a-C) layer with carbon nanotube (CNT) electrodes for ultra-dense memory. The use of CNT as electrode leads to the ultimately scaled cross-point area (similar to 1 nm(2)), and the use of a-C results in an all-carbon memory. Carbon-based complementary resistive switching (CRS) is shown for the first time, enabling cross-point memory without cell selection devices.
  • Yang Chai, Arash Hazeghi, Kuniharu Takei, Hong-Yu Chen, Philip C. H. Chan, Ali Javey, H. -S. Philip Wong
    2010 INTERNATIONAL ELECTRON DEVICES MEETING - TECHNICAL DIGEST 2010 [Refereed][Not invited]
     
    Graphitic interfacial layer is used to wet the surface of carbon nanotube and dramatically lower the contact resistance of metal to metallic single-wall carbon nanotube (m-CNT). Using Ni-catalyzed graphitization of amorphous carbon (a-C), the average resistance of metal/m-CNT is reduced by 7X compared to the same contact without the graphitic layer. Small-signal conductance measurements from 77K to 300K reveal the effective contact improvement.
  • Johnny C. Ho, Alexandra C. Ford, Yu-Lun Chueh, Paul W. Leu, Onur Ergen, Kuniharu Takei, Gregory Smith, Prashant Majhi, Joseph Bennett, Ali Javey
    APPLIED PHYSICS LETTERS 95 (7) 0003-6951 2009/08 [Refereed][Not invited]
     
    One of the challenges for the nanoscale device fabrication of III-V semiconductors is controllable postdeposition doping techniques to create ultrashallow junctions. Here, we demonstrate nanoscale, sulfur doping of InAs planar substrates with high dopant areal dose and uniformity by using a self-limiting monolayer doping approach. From transmission electron microscopy and secondary ion mass spectrometry, a dopant profile abruptness of similar to 3.5 nm/decade is observed without significant defect density. The n(+)/p(+) junctions fabricated by using this doping scheme exhibit negative differential resistance characteristics, further demonstrating the utility of this approach for device fabrication with high electrically active sulfur concentrations of similar to 8x10(18) cm(-3).
  • Tetsuhiro Harimoto, Akito Ishihara, Takeshi Kawano, Kuniharu Takei, Hidekazu Kaneko, Makoto Ishida, Siro Usui
    TRANSDUCERS 2009 - 15th International Conference on Solid-State Sensors, Actuators and Microsystems 1682 - 1685 2009/06 [Refereed][Not invited]
     
    We report in-vitro multisite field potential recordings from fish retina using a vertically integrated silicon (Si) microprobe array. Eight active channels of the enlarged probe-head "Kokeshi (Japanese dolls)" type Si probe enabled multisite electrical recordings of retinal responses (electroretinograms (ERGs)) to white light stimuli. The ERG a- and b-waves were obtained at each probe, and the result suggests the capability of the Si probe array for use in further investigations of spatio-temporal property of ERGs. ©2009 IEEE.
  • Kuniharu Takei, Takahiro Kawashima, Takeshi Kawano, Hidekazu Kaneko, Kazuaki Sawada, Makoto Ishida
    BIOMEDICAL MICRODEVICES 11 (3) 539 - 545 1387-2176 2009/06 [Refereed][Not invited]
     
    We have proposed fabricating very fine out-of-plane silicon-dioxide microtube arrays using a selective vapor-liquid-solid (VLS) growth technique and microfabrication processes. In this study, we elucidated the liquid-flow properties of microtubes with different inner diameters. Our fabricated microtubes were 0.5 mu m in wall thickness; 20 mu m in height; and either 2.5 mu m, 4.1 mu m, 4.6 mu m, or 6.4 mu m in inner diameter. We determined the relationship between the flow pressure and the liquid flow rate through the microtube. We also conducted a nerve block test, in which a microtube with 4.6 mu m inner diameter was used to administer lidocaine solution (Na channel blocker) to the rat sciatic nerve. This successful test represents the first reported use of a microtube for drug delivery to the peripheral nerve of a rat. We conclude that the proposed microtube array and its fabrication process might contribute to developing pharmacological devices.
  • Toshitake Takahashi, Kuniharu Takei, Johnny C. Ho, Yu-Lun Chueh, Zhiyong Fan, Ali Javey
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 131 (6) 2102 - + 0002-7863 2009/02 [Refereed][Not invited]
     
    Large-area, patterned printing of nanowires by using fluorinated self-assembled monolayers as the resist layer is demonstrated. By projecting a light pattern on the surface of the monolayer resist in an oxygen-rich environment, sticky and nonsticky regions on the surface are directly defined in a single-step process which then enables the highly specific and patterned transfer of the nanowires by the contact printing process, without the need for a subsequent lift-off step. This work demonstrates a simple route toward scalable, patterned printing of nanowires on substrates by utilizing light-tunable, nanoscale chemical interactions and demonstrates the versatility of molecular monolayers for use as a resist layer.
  • Akihiro Goryu, Akihito Ikedo, Kuniharu Takei, Kazuaki Sawada, Takeshi Kawano, Makoto Ishida
    2009 IEEE 22nd International Conference on Micro Electro Mechanical Systems 224 - 227 1084-6999 2009/01 [Refereed][Not invited]
  • Kuniharu Takei, Akifumi Fujishiro, Takahiro Kawashima, Kazuaki Sawada, Hidekazu Kaneko, Takeshi Kawano, Makoto Ishida
    TRANSDUCERS 2009 - 15th International Conference on Solid-State Sensors, Actuators and Microsystems 334 - 337 2009 [Refereed][Not invited]
     
    This paper presents a very thin silicon dioxide microtube electrode array, which has sub tenmicrometers in inner diameter, as a neural interface device with high signal-to-noise ratio and low invasiveness. The device was realized by using out-of-plane silicon dioxide microtube arrays fabricated from vapor-liquid-solid growth and microfabrication techniques. Here we report advantages of electrical properties of the microtube electrode such as low electrode impedance and high signal-to-noise ratio, compared to that of previous our silicon microprobebased electrode arrays. In addition to the fundamental properties, we also demonstrated animal experiments to record evoked neural responses from the sciatic nerve of a rat through the microtube electrode. ©2009 IEEE.
  • Kuniharu Takei, Takeshi Kawano, Takahiro Kawashima, Kazuaki Sawada, Hidekazu Kaneko, Makoto Ishida
    IEEE 22ND INTERNATIONAL CONFERENCE ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS 2009) 192 - 195 1084-6999 2009 [Refereed][Not invited]
     
    We report applications of sub-5 mu m diameter silicon microprobes and silicon dioxide microtubes fabricated by vapor-liquid-solid method and microfabrication techniques, to use in in-vivo animal experiments. Before animal experiments, electrical impedance and test signal detection via the microprobe electrode were investigated. According to the results, electrical impedance at 1 kHz is approximately 2 M Omega, and microprobe detected the test signals (80 mu Vp-p at 1kHz) in saline solution. For microtube array, liquid flow through the microtube is confirmed at injection pressures of 25-45 kPa to get sub-mu L/min flow rates. Finally, the microprobe and the microtube were applied to tibial muscle and sciatic nerves of rats, respectively. From these animal experiments, we could observe the electrical and chemical reactions of muscle and nerves using both sub-5 mu m diameter microprobe and microtube successfully.
  • Kuniharu Takei, Takahiro Kawashima, Kazuaki Sawada, Makoto Ishida
    IEEE SENSORS JOURNAL 8 (5-6) 470 - 475 1530-437X 2008/05 [Refereed][Not invited]
     
    This paper reports on a novel technique for realizing submicron and micron diameter SiO2 tubes on a Si substrate for biomedical applications such as, for example, patch clamps. The tube arrays have been successfully fabricated on Si substrates using a selective vapor-liquid-solid (VLS) growth method combined with MEMS techniques. The size of the tubes is typically between 0.2 mu m and 2 mu m in diameter and from 8 mu m to 40 mu m in length. The dimensions are controlled by the diameter of a Au pattern and the VLS growth time. The tubes were coated with parylene, a biocompatible material, which makes them stronger. The diameter is such that the array can be used in biomedical applications where insertion of the tubes into tissue is minimally invasive. Water flow experiments through the tubes were carried out successfully without the tubes breaking.
  • Kuniharu Takei, Takahiro Kawashima, Takeshi Kawano, Hidekuni Takao, Kazuaki Sawada, Makoto Ishida
    JOURNAL OF MICROMECHANICS AND MICROENGINEERING 18 (3) 0960-1317 2008/03 [Refereed][Not invited]
     
    Three-dimensional microtubes and microprobes with MOSFET circuits are integrated for use in chemical and electrical neural interface applications with microelectronics. We propose a vapor-liquid-solid (VLS) method to realize both the microtubes and microprobes, which are 2 mu m and 3.6 mu m in diameter, respectively, and can be fabricated after the on-chip MOSFET processes. The on-chip NMOSFET shows electrical characteristics with a threshold voltage of 1.2 V and a subthreshold swing of 145 mV decade(-1), confirming that subsequent fabrications of the tube and probe are compatible with the inclusion of the on-chip circuits. The prototype oxide tube, which has 2.7 mu m inner diameter and 29 mu m height, has a flow rate of 550 nl min(-1) with an external pump pressure of 33.5 kPa. The impedance of the on-chip Si probe, which has 2 mu m diameter and 30 mu m height, measured at 1 kHz in a saline environment is 2 M Omega. Insertion into a gelatin membrane confirms that both the tube and the probe show sufficient penetration capabilities.
  • Kuniharu Takei, Takahiro Kawashima, Kazuaki Sawada, Makoto Ishida
    Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings 179 - 182 0589-1019 2007 [Refereed][Not invited]
     
    This paper describes the fabrication of Si micro probe and SiO2 micro tube array and their mechanical properties. The device is successfully fabricated with high-density array. One of the requirements of the penetrating device is to have the enough mechanical strength to be able to penetrate into the tissue. Hence mechanical properties are investigated and discussed using the results on bending obtained by experiments and simulation of finite element method. The device was penetrated by simple in-vitro experiments using a gelatin. © 2007 IEEE.
  • Kuniharu Takei, Takahiro Kawashima, Hidekuni Takao, Kazuaki Sawada, Makoto Ishida
    TRANSDUCERS '07 & EUROSENSORS XXI, DIGEST OF TECHNICAL PAPERS, VOLS 1 AND 2 2007 [Refereed][Not invited]
     
    This paper describes a device design, fabrication, experimental results, and mechanical strength for a multi functional device of neural behavioral analysis. The device has been fabricated with Si micro probe of 2 mu m in diameter and SiO2 micro tube of 3.6 mu m in outer diameter on circuit of MOSFETs, using standard IC process followed by a selective VLS growth and MEMS techniques. MOSFETs' performance on Si(111) is 150mV/decade of subthreshold factor and 1.2V of threshold voltage after the fabrication process of probes and tubes. Penetration experiment into the gelatin was carried out for an application of neural recording devices.
  • Kuniharu Takei, Takahiro Kawashitna, Kazuaki Sawada, Makoto Ishida
    2007 ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-16 179 - + 1094-687X 2007 [Refereed][Not invited]
     
    This paper describes the fabrication of Si micro wobe and SiO2 micro tube array and their mechanical properties. The device is successfully fabricated with high-density array. One of the requirements of the penetrating device is to have the enough mechanical strength to be able to penetrate into the tissue. Hence mechanical properties are investigated and discussed using the results on bending obtained by experiments and simulation of finite element method. The device was penetrated by simple in-vitro experiments using a gelatin.

MISC

  • 中川魁斗, 佐藤和郎, 村上修一, 竹井邦晴, 秋田成司, 有江隆之  応用物理学会春季学術講演会講演予稿集(CD-ROM)  68th-  2021
  • 中川魁斗, 佐藤和郎, 村上修一, 竹井邦晴, 秋田成司, 有江隆之  応用物理学会春季学術講演会講演予稿集(CD-ROM)  66th-  2019
  • 中川魁斗, 佐藤和郎, 村上修一, 竹井邦晴, 秋田成司, 有江隆之  応用物理学会秋季学術講演会講演予稿集(CD-ROM)  80th-  2019
  • 中田 尚吾, 有江 隆之, 秋田 成司, 竹井 邦晴  「センサ・マイクロマシンと応用システム」シンポジウム論文集 電気学会センサ・マイクロマシン部門 [編]  34-  4p  2017/10/31
  • 山本 大介, 中田 尚吾, 有江 隆之, 秋田 成司, 竹井 邦晴  「センサ・マイクロマシンと応用システム」シンポジウム論文集 電気学会センサ・マイクロマシン部門 [編]  34-  6p  2017/10/31
  • 金尾 顕一朗, 有江 隆之, 秋田 成司, 竹井 邦晴  「センサ・マイクロマシンと応用システム」シンポジウム論文集 電気学会センサ・マイクロマシン部門 [編]  33-  1  -4  2016/10/02
  • 竹井 邦晴  応用物理  84-  (11)  1002  -1007  2015/11
  • 原田 真吾, 有江 隆之, 秋田 成司, 竹井 邦晴  「センサ・マイクロマシンと応用システム」シンポジウム論文集 電気学会センサ・マイクロマシン部門 [編]  32-  1  -4  2015/10/28
  • Chuan Wang, Kuniharu Takei, Toshitake Takahashi, Ali Javey  CHEMICAL SOCIETY REVIEWS  42-  (7)  2592  -2609  2013  [Not refereed][Not invited]
     
    Single-walled carbon nanotubes (SWNTs) possess fascinating electrical properties and offer new entries into a wide range of novel electronic applications that are unattainable with conventional Si-based devices. The field initially focused on the use of individual or parallel arrays of nanotubes as the channel material for ultra-scaled nanoelectronic devices. However, the challenge in the deterministic assembly has proven to be a major technological barrier. In recent years, solution deposition of semiconductor-enriched SWNT networks has been actively explored for high performance and uniform thin-film transistors (TFTs) on mechanically rigid and flexible substrates. This presents a unique niche for nanotube electronics by overcoming their limitations and taking full advantage of their superb chemical and physical properties. This review focuses on the large-area processing and electronic properties of SWNT TFTs. A wide range of applications in conformal integrated circuits, radio-frequency electronics, artificial skin sensors, and displays are discussed - with emphasis on large-area systems where nm-scale accuracy in the assembly of nanotubes is not required. The demonstrations show SWNTs' immense promise as a low-cost and scalable TFT technology for nonconventional electronic systems with excellent device performances.
  • Rehan Kapadia, Zhiyong Fan, Kuniharu Takei, Ali Javey  NANO ENERGY  1-  (1)  132  -144  2012/01  [Not refereed][Not invited]
     
    Nanopillar photovoltaics present significant potential for fabrication of high-efficiency, low-cost solar cells. The advantages over planar cells, including wider materials choice, device geometries, and enhanced optical and electronic properties have been studied in detail over the past decade. Specifically, the 3-D geometry enables optimization of carrier collection and reduction of the material quality constraints. Furthermore, the anti-reflective and light trapping properties enable a drastic reduction in material necessary to absorb the majority of the incident light. Together, the optical and electronic advantages allow solar cell fabrication on low-cost substrates. However, the choice of the material system is important for taking advantage of the unique properties of nanopillar cells, especially given large surface/interface area. This review focuses on the recent work on the optical and electronic properties of nanopillar photovoltaics and the fabrication processes utilizing low-cost substrates. (C) 2011 Elsevier Ltd. All rights reserved.
  • Zhiyong Fan, Johnny C. Ho, Toshitake Takahashi, Roie Yerushalmi, Kuniharu Takei, Alexandra C. Ford, Yu-Lun Chueh, Ali Javey  ADVANCED MATERIALS  21-  (37)  3730  -3743  2009/10  [Not refereed][Not invited]
     
    In recent years, there has been tremendous progress in the research and development of printable electronics on mechanically flexible substrates based on inorganic active components, which provide high performance and stable device operations at low cost. In this regard, various approaches have been developed for the direct transfer or printing of micro- and nanoscale, inorganic semiconductors on substrates. In this review article, we focus on the recent advancements in the large-scale integration of single crystalline, inorganic-nanowire (NW) arrays for electronic and sensor applications, specifically involving the contact printing of NWs at defined locations. We discuss the advantages, limitations, and the state-of-the-art of this technology, and present an integration platform for future printable, heterogeneous-sensor circuitry based on NW parallel arrays.
  • KAWANO Takeshi, TAKEI Kuniharu, IKEDO Akihito, GORYU Akhiro, HARIMOTO Tetsuhiro, FUJISHIRO Akifumi, OKUGAWA Akihiro, KAWASHIMA Takahiro, ISHIDA Makoto  電気学会研究会資料. MBE, 医用・生体工学研究会  2009-  (80)  67  -70  2009/09/24  [Not refereed][Not invited]
  • TAKEI Kuniharu, KAWASHIMA Takahiro, TAKAO Hidekuni, SAWADA Kazuaki, ISHIDA Makoto  電気学会研究会資料. BMS, バイオ・マイクロシステム研究会 = The papers of Technical Meeting on Bio Micro Systems, IEE Japan  2006-  (1)  1  -4  2006/05/15

Books etc

  • Flexible, Wearable, and Stretchable Electronics
    Kuniharu Takei (ContributorFlexible Sensor Sheets for Healthcare Applications)
    CRC Press 2020/10
  • Flexible and Stretchable Medical Devices
    TAKEI, Kuniharu (Editor)
    Wiley-VCH 2018/03
  • Flexible Electronics From Materials to Devices
    TAKEI, Kuniharu (Joint workNanomaterial-based flexible sensors)
    World Scientific 2016
  • Wearable Electronics Sensors for Safe and Healthy Living
    TAKEI, Kuniharu (Joint workWearable and Flexible Sensor Sheets toward Periodic Health Monitoring)
    Springer 2015
  • Micro- and Nanoelectronics: Emerging Device Challenges and Solutions
    R. Kapadia, K. Takei, H. Fang (Joint work2-D InAs XOI FETs: Fabrication and Device Physics)
    CRC Press 2014

Association Memberships

  • Japan Society of Vacuum and Surface Science   ECS   IEEE   IEEJ   JSAP   

Research Projects

  • Electronics with spontaneous phenomena based on circulation
    JST:ALCA-NEXT
    Date (from‐to) : 2023/11 -2027/03
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2022/04 -2026/03 
    Author : 竹井 邦晴, 中嶋 浩平, 渡辺 心
  • 在宅での睡眠時無呼吸症候群の簡易・早期診断に向けたフレキシブルセンサシステム
    村田学術振興財団:研究助成
    Date (from‐to) : 2022/12 -2025/11
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2022/04 -2024/03 
    Author : 竹井 邦晴, MUNEER SAIQA
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2021/11 -2024/03 
    Author : 竹井 邦晴, MUNEER SAIQA
  • 日本学術振興会:科学研究費助成事業
    Date (from‐to) : 2021/09 -2024/03 
    Author : 竹井 邦晴, MUNEER SAIQA
  • Wearable remote monitoring system with feedback functions
    JST:AIP Accelerated Program
    Date (from‐to) : 2021/04 -2024/03 
    Author : 竹井邦晴, 渡辺心
  • 日本学術振興会:科学研究費助成事業 新学術領域研究(研究領域提案型)
    Date (from‐to) : 2018/06 -2023/03 
    Author : 中嶋 浩平, 竹井 邦晴
     
    本年度は、リザバー計算・物理リザバー計算、両方の手法に関して、全般的に進捗があった。特に、リザバーの計算能力を定量する情報処理容量という指標に関しての理論的な知見が多く集まった(特に、時変、時不変の情報処理容量の区別やそれとecho state propertyという概念との関係など)。実装に関しては、まず、通常のリザバー計算に基づいて、これまで、センサーのエミュレーション、つまり、いわゆるindirect sensingを行ってきたが、本年度はこの手法に対して新たにphysics-informed machine learningの手法を導入し、性能向上を実現した。物理リザバー計算に関して、まずopen-loopの設定に関しては、新たな物理リザバー(渦、ウレタン、服、細胞集団など)を複数提案した。渦を用いた物理リザバー計算に関しては、上述した時変の情報処理容量の寄与を議論した。また、フレキシブルセンサーを導入したシリコン角材を用いて、環境中の物体で入力に対して一般化同期するものをad hocに物理リザバーとして活用する手法を提案し、これをremote reservoirと呼び、その計算能力を定量した。ここでも情報処理容量の解析が威力を発揮した。closed-loopの設定に関しては、魚ロボットを構築し、物理リザバーの手法に基づいて自律駆動できることを示した。
  • ウイルスの院内感染予防に向けた遠隔バイタル計測センサシートの開発
    日立財団:倉田奨励金
    Date (from‐to) : 2021/04 -2023/03
  • ナノカーボン接触界面制御による新奇電子デバイスの創製
    東電記念財団:研究助成(ステップアップ助成)
    Date (from‐to) : 2020/04 -2023/03
  • a
    JST:研究成果展開事業 スタートアップ・エコシステム形成支援
    Date (from‐to) : 2021/06 -2022/03
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)
    Date (from‐to) : 2017/04 -2021/03 
    Author : Takei Kuniharu
     
    This study aims to develop a new type of wearable and flexible device to allow continuous and real-time vital signals from skin surface by realizing high performance and high reliable physical and chemical sensors. For a chemical sensor, a charge-coupled device concept was applied to a flexible pH sensor, resulting in that high performance sweat pH detection was realized. In addition to the chemical sensors, electrocardiogram, respiration, and skin temperature sensors were developed as physical sensors with high reliability for a long-time monitoring. After characterizing the sensor performances and optimizing the materials and structures, process development was conducted to integrate all sensors on a flexible film. The multimodal flexible sensor sheet and the wireless circuit system was combined to study the physiological monitoring. By attaching the sensor system, real-time and continuous vital monitoring was successfully realized with stable and reliable data collections.
  • ナノカーボン接触界面制御による新奇電子デバイスの創製
    東電記念財団:研究助成(基礎研究)
    Date (from‐to) : 2017/04 -2020/03
  • 科学技術振興機構:戦略的な研究開発の推進 戦略的創造研究推進事業 さきがけ
    Date (from‐to) : 2017 -2020 
    Author : 竹井 邦晴
     
    本研究では、人の健康状態、室内環境の複数情報を連続的に計測し、それらの相関関係解析及びビッグデータ化による「未病の発見」や「予防医学」への発展を目指す。本実現に向け、全く新しいコンセプトとして、違和感無く装着可能なフレキシブルな環境・健康管理センサシートシステムの開発を行う。本システムのプラットフォーム構築により、幸福で快適、安全・安心な生活が可能になる超スマート社会実現の基礎技術構築を行う。
  • 科学技術振興機構:産学が連携した研究開発成果の展開 研究成果展開事業 大学発新産業創出プログラム(START) 社会還元加速プログラム(SCORE)
    Date (from‐to) : 2019 -2019 
    Author : 竹井 邦晴
     
    フレキシブル温度、圧力、歪み、心電図センサーを無線、信号処理回路と実装したシステムの開発と、それを用いた実証試験と事業化検証を行う。具体的にはフレキシブル圧力分布計測および貼付型ウェアラブル熱中症予防センサーパッチのプロトタイプを試作品とし、ビジネスモデルを検証する。
  • 液体金属とナノカーボンの電気接触機構解明とその高感度センサ応用
    泉科学技術振興財団:研究助成
    Date (from‐to) : 2016/10 -2018/03
  • 生体融和型マルチ健康管理パッチデバイスの開発
    日揮・実吉奨学会:研究助成
    Date (from‐to) : 2016/09 -2017/08
  • フレキシブルCMOS増幅器と温度センサ集積ウェアラブル健康管理デバイスの開発
    村田学術振興財団:研究助成
    Date (from‐to) : 2015/08 -2016/07
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    Date (from‐to) : 2014/04 -2016/03 
    Author : Takei Kuniharu
     
    In this study, we developed an artificial electronic skin that enables to detect “tactile force”, “friction force”, and “temperature” distributions inspired by a human skin for a robotic and a prosthesis applications. In particular, macro-scale printing techniques of strain and temperature sensors were particularly developed for low-cost, multi-functional flexible devices. Based on a strain engineering, simultaneous detections of “tactile” and “friction” forces were realized by integrating with a three-dimensional structure on a flexible substrate. Finally, 3×3 array artificial electronic skin was successfully demonstrated.
  • Japan Society for the Promotion of Science:Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)
    Date (from‐to) : 2014/04 -2016/03 
    Author : Takei Kuniharu
     
    In this study, we aim to develop a flexible low-power, wireless CMOS/MEMS integrated device by developing each device components and integration process on a flexible substrate for the future electronics. In particular, printed strain and temperature sensors are realized by developing the printed sensor inks using mainly inorganic nanomaterials. Furthermore, by optimizing the ink and fabrication process, we could achieve the high sensitivity for strain and temperature detections compared to previous reports. In addition to the sensors, low power and high performance flexible digital and analog circuits are also demonstrated without any malfunction even under mechanical bending conditions. Finally, by applying the developed technologies, flexible and wearable healthcare device are developed as a proof-of-concept.
  • ナノ材料の大面積印刷技術による高性能人工電子ヒゲの開発
    マツダ財団:マツダ研究助成
    Date (from‐to) : 2013/10 -2015/09
  • 日本学術振興会:科学研究費助成事業 研究活動スタート支援
    Date (from‐to) : 2013/08 -2015/03 
    Author : 竹井 邦晴
     
    本研究では、ナノ材料の印刷技術による高感度歪みセンサの開発及び人工電子ヒゲデバイスの開発を目指した。特に(1)ナノ材料のフレキシブルデバイスへの可能性の示唆、(2)新規デバイス(人工電子ヒゲ)による新たな分野の開拓、(3)ナノ材料のパターニング技術の開発、の3点に重点を置き研究を行った。 まず銀ナノ粒子とカーボンナノチューブの混合インクを開発し歪みセンサを作製した。歪みセンサは、スクリーン印刷法を用いることにより、様々なフレキシブル基板上に大面積且つ容易に形成することが可能になった。デバイス作製の最適化を行うことでセンサの超高感度化を実現し、またナノ材料の混合比を制御することにより歪みセンサの感度を調節することが可能であることが明らかになった。これは応用用途に合わせた感度の調整が容易に出来ることを示しており重要な要素となる。このような印刷技術によるフレキシブル基板上でのセンサ応用はほとんど例がなく、本研究の重点課題であった(1)ナノ材料の可能性の示唆について示すことが出来た。 次に、平成26年度達成目標であった人工電子ヒゲアレイの開発も行った。出力信号は、簡単なシステムを用いることでパソコンでのリアルタイム計測を実現した。まず印刷した歪みセンサアレイを、レーザー加工機を用いてフレキシブル基板をヒゲ構造に形成した。そして構築したシステムを用いて3次元構造体の分布計測を試みた。その結果、猫の髭のように高解像度で3次元構造体の形状を検出することが出来ることを確認した。本結果から研究課題であった(2)新規デバイスの開発、(3)ナノ材料のパターニング技術の開発について達成することができた。 当該年度において、本研究課題全てを達成することができ、今後は本技術の応用による様々な分野への貢献が期待できる。
  • 液相―固相混合光励起フレキシブルアクチュエータの開発
    旭硝子財団:研究助成
    Date (from‐to) : 2014/04 -2015/03
  • 異種材料集積化低消費電力CMOS/MEMSウェアラブルデバイスの実現
    国際科学技術財団:研究助成
    Date (from‐to) : 2014/04 -2015/03
  • 会話型ヒューマンインターフェースに向けたナノ材料電子機械フレキシブルデバイス
    立石科学技術振興財団:研究助成
    Date (from‐to) : 2014/04 -2015/03
  • 無機ナノ材料界面の電気的解析とその大面積印刷デバイス
    ATI:研究助成
    Date (from‐to) : 2013/10 -2014/09
  • 日本学術振興会:科学研究費助成事業 特別研究員奨励費
    Date (from‐to) : 2007 -2008 
    Author : 竹井 邦晴
     
    本研究課題では、神経細胞に対して低侵襲であり、電気計測、薬液搬送、刺激、信号処理など多機能を可能とするマイクロセンサチップの実現を目指すものであった。本年度得られた成果は、まずこのスマートセンサ構造を実現し、それらの諸特性を解明したことである。これらの結果は、今後の応用への基礎データとなった。特に今回提案するチューブ構造及びサイズはこれまでに報告されておらず、その特性を明らかにするだけでも十分重要なものであった。さらに実際に動物へ本デバイスを適用し、実際に神経細胞への薬液搬送、神経細胞からの誘発電位計測に成功している。また新たな可能性として、本デバイスを用いた光局所刺激、パッチクランプアレイといった実験も行い、その可能性についても示唆できた。本結果より、本デバイスが目的とする神経電位解析用ツールとして十分応用可能であることを示唆した。また本デバイスはこれまでにないほど、低侵襲性のデバイスであり、また全く新しいコンセプトのもと多機能化を実現したものであることを追記する。


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