論文 - 田中　貴久

Modulation of VO2 Metal–Insulator Transition by Ferroelectric HfO2 Gate Insulator

T. Yajima, T. Nishimura, T. Tanaka, K. Uchida, A. Toriumi

Advanced Electronic Materials （Wiley）  6 （ 5 ） 1901356 - 1901356 2020年03月

査読有り,  ISSN  2199-160X

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Co-porphyrin functionalized CVD graphene ammonia sensor with high selectivityto disturbing gases: hydrogen and humidity

K. Sawada, T. Tanaka, T. Yokoyama, R. Yamachi, Y. Chiba, H. Masai, J. Terao, K. Uchida

Jpn. J. Appl. Phys （IOP Publishing）  59 （ SG ） SGGG09 - SGGG09 2020年02月

査読有り,  ISSN  0021-4922

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Low-Power and ppm-Level Multimolecule Detection by Integration of Self-Heated Metal Nanosheet Sensors

T. Tanaka, K. Tabuchi, K. Tatehora, Y. Shiiki, S. Nakagawa, T. Takahashi, R. Shimizu, H. Ishikuro, T. Kuroda, T. Yanagida, K. Uchida

IEEE Trans. Electron Devices （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  66 （ 12 ） 5393 - 5398 2019年10月

筆頭著者, 査読有り,  ISSN  0018-9383

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H-2 and NH3 detection with low power consumption was demonstrated by integrated chemiresistive Pt and PtRh nanosheet sensors on glass substrates. The self-heating effects realized low power and local heating of metal nanosheet sensors, enabling the integration of sensors with different operating temperatures. Based on different resistance changes in Pt and PtRh nanosheets toward H-2 and NH3, the concentration of each gas was detected from a gas mixture by consuming around 1-mW power. For decreasing the power consumption and further integration of sensors, sensor scaling and pulsed operations were numerically and experimentally studied. In addition to good connectivity of metal nanosheet sensors to large-scale integration (LSI) circuits, improvements of the power consumption by sensor scaling were proven. The pulsed operations required for integrated sensor arrays maintained a sensor response, or a resistance change, of approximately 60, even when the power consumption was reduced by 20.

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Nanoscale, low-energy molecular sensors for health care and environmental monitoring

K. Uchida, T. Tanaka

AAPPS Bulletin 29   16 - 20 2019年06月

Enhancement of sensor response in graphene gas sensors by gate-induced field

T. Tanaka, T. Yokoyama, K. Uchida

IEEE Electron Device Lett. 39   1924 - 1927 2018年10月

筆頭著者, 査読有り

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Pd-functionalized, suspended graphene nanosheet for fast, low-energy multimolecular sensors

T. Yokoyama, T. Tanaka, Y. Shimokawa, R. Yamachi, Y. Saito, K. Uchida

ACS Appl. Nano Mater. 1   3886 - 3894 2018年07月

査読有り

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Numerical analysis of band tails in nanowires and their effects on the performance of tunneling field-effect transistors

Takahisa Tanaka, Ken Uchida

Japanese Journal of Applied Physics （Japan Society of Applied Physics）  57 （ 6 ） 06HC04 2018年06月

筆頭著者, 査読有り,  ISSN  1347-4065

　概要を見る

Band tails in heavily doped semiconductors are one of the important parameters that determine transfer characteristics of tunneling field-effect transistors. In this study, doping concentration and doing profile dependences of band tails in heavily doped Si nanowires were analyzed by a nonequilibrium Green function method. From the calculated band tails, transfer characteristics of nanowire tunnel field-effect transistors were numerically analyzed by Wentzel-Kramer-Brillouin approximation with exponential barriers. The calculated transfer characteristics demonstrate that the band tails induced by dopants degrade the subthreshold slopes of Si nanowires from 5 to 56mV/dec in the worst case. On the other hand, surface doping leads to a high drain current while maintaining a small subthreshold slope.

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Nanoscale Pt thin film sensor for accurate detection of ppm level hydrogen in air at high humidity

Takahisa Tanaka, Shinsuke Hoshino, Tsunaki Takahashi, Ken Uchida

Sensors and Actuators, B: Chemical （Elsevier B.V.）  258   913 - 919 2018年04月

筆頭著者, 査読有り,  ISSN  0925-4005

　概要を見る

Hydrogen is an important biomarker for the human digestive system. However, accurate detection of ppm-level hydrogen in breath is difficult due to the competing detection of high concentration water. We fabricated Pt thin films that respond to hydrogen in air at concentrations as low as 500 ppb. In both dry and humid air, these films have almost identical response to hydrogen, i.e., their resistance decreases linearly with increasing hydrogen concentration regardless of relative humidity. Even at high relative humidity, these Pt thin films can detect ppm-level hydrogen. Furthermore, it was strongly suggested that these films can be applied to low-level hydrogen in the air expired by a healthy human. Based on the chemical kinetics, namely the adsorption and desorption of hydrogen and oxygen, the sensor response is quantitatively described by relating the hydrogen surface coverage to the magnitude of electron scattering at the Pt surface. The proposed model successfully reproduces the effects of hydrogen concentration and time on the sensor response, particularly at hydrogen concentrations below 20 ppm. Based on this model, these Pt thin film sensors have the potential to detect 1 ppm hydrogen in expired air within 30 s.

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Experimental Study on Deformation Potential (D-ac) in MOSFETs: Demonstration of Increased D-ac at MOS Interfaces and Its Impact on Electron Mobility

Teruyuki Ohashi, Takahisa Tanaka, Tsunaki Takahashi, Shunri Oda, Ken Uchida

IEEE JOURNAL OF THE ELECTRON DEVICES SOCIETY （IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC）  4 （ 5 ） 278 - 285 2016年09月

査読有り,  ISSN  2168-6734

　概要を見る

Deformation potential (D-ac), which is one of the most important parameters determining the rate of electron-acoustic phonon scattering, in Si around MOS interfaces is thoroughly studied with regard to the dependences on surface carrier densities, back-gate biases, and device structures. It is demonstrated that D-ac increases sharply at the MOS interface. To investigate the impact of the increased D-ac on mu(e), thick body-channel SOI MOSFETs, where drain current flows in the entire SOI layers, was fabricated. The carrier transport experiments reveal that mu(e) of greater than 1100 cm(2) V-1 s(-1) is obtained in body-channel SOI MOSFETs with the SOI thickness of greater than 70 nm. By taking into account the D-ac profile around the MOS interface, experimental mu(e) of SOI MOSFETs is numerically reproduced over a wide range of SOI thicknesses. mu(e) of the body-channel SOI MOSFETs is also well reproduced using the same D-ac profile. Thus, it is concluded that D-ac increases sharply at the Si/SiO2 interface. The accurate modeling of the increased D-ac around the Si/SiO2 interface is indispensable for designing high-performance and/or low-power 3-D MOSFETs including FinFETs, extremely thin SOI MOSFETs, and nanowire MOSFETs, because these types of MOSFETs have greater interface-to-volume ratios.

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Deionization of Dopants in Silicon Nanofilms Even with Donor Concentration of Greater than 10(19) cm(-3)

Takahisa Tanaka, Yuya Kurosawa, Naotoshi Kadotani, Tsunaki Takahashi, Shunri Oda, Ken Uchida

NANO LETTERS （AMER CHEMICAL SOC）  16 （ 2 ） 1143 - 1149 2016年02月

筆頭著者, 査読有り,  ISSN  1530-6984

　概要を見る

Understanding the dopant properties in heavily doped nanoscale semiconductors is essential to design nanoscale devices. We report the deionization or finite ionization energy of dopants in silicon (Si) nanofilms with dopant concentration (N-D) of greater than 10(19) cm(-3), which is in contrast to the zero ionization energy (E-D) in bulk Si at the same N-D. From the comparison of experimentally observed and theoretically calculated E-D, we attribute the deionization to the suppression of metal-insulator transition in highly doped nanoscale semiconductors in addition to the quantum confinement and the dielectric mismatch, which greatly increase E-D in low-doped nanoscale semiconductors. Thus, for nanoscale transistors, N-D should be higher than that estimated from bulk Si dopant properties in order to reduce their resistivity by the metal insulator transition.

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Impact of hydrogen on carrier mobility and concentration in graphene decorated with Pd nanoparticle

Akihito Goto, Go Takeuchi, Ryosuke Yamachi, Takahisa Tanaka, Tsunaki Takahashi, Ken Uchida

ECS Transactions （Electrochemical Society Inc.）  72 （ 14 ） 7 - 12 2016年

査読有り,  ISSN  1938-6737

　概要を見る

As a candidate of highly-sensitive hydrogen sensors, Palladium (Pd)-decorated graphene sensors have been investigated. Thanks to high reactivity of Pd nanoparticles to hydrogen and high surface-tovolume ratio of two-dimensionally layered graphene, graphene decorated with Pd nanoparticles can be used as a highly sensitive hydrogen sensor. Although the conductivity of Pd-graphene sensor is known to be greatly changed in hydrogen atmosphere, the mechanisms of conductivity change have not been fully understood. In this work, both carrier concentration and mobility in hydrogen are investigated using Hall effect measurement. It is shown that relative change of carrier concentration is greater when carrier concentration is lower. On the other hand, mobility is not systematically changed as a function of carrier concentration. This mobility behavior is attributed to the competition between greater effective mass and shorter screening length at higher carrier concentration. Based on these observations, we develop strategy for achieving high sensitivity in Pd graphene hydrogen sensor.

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Upper limit of two-dimensional hole gas mobility in strained Ge/SiGe heterostructures

T. Tanaka, Y. Hoshi, K. Sawano, N. Usami, Y. Shiraki, K. M. Itoh

APPLIED PHYSICS LETTERS （AMER INST PHYSICS）  100 （ 22 ） 222102 2012年05月

筆頭著者, 査読有り,  ISSN  0003-6951

　概要を見る

High two-dimensional hole gas (2DHG) mobility (mu(2DHG) > 10000 cm(2)/Vs at T < 100 K) strained Ge/Si1-xGex structures with x = 0.5 and 0.65 were fabricated, and temperature dependence of their 2DHG mobility was obtained experimentally by the mobility spectrum analysis of the conductivity under magnetic fields. The theoretically calculated 2DHG mobility was compared to experimental data to determine the effective deformation potentials for scattering by acoustic and optical phonons. Using empirically confirmed parameters, the upper theoretical limit of room temperature 2DHG mobility mu(2DHG) in strained Ge as a function of strain was calculated. The possibility to achieve mu(2DHG) > 5000 cm(2)/Vs at room temperature is presented. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723690]

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Experimental and theoretical analysis of the temperature dependence of the two-dimensional electron mobility in a strained Si quantum well

Takahisa Tanaka, Go Tsuchiya, Yusuke Hoshi, Kentarou Sawano, Yasuhiro Shiraki, Kohei M. Itoh

JOURNAL OF APPLIED PHYSICS （AMER INST PHYSICS）  111 （ 7 ） 073715 2012年04月

筆頭著者, 査読有り,  ISSN  0021-8979

　概要を見る

The temperature dependence of the mobility of the two-dimensional electron gas (2DEG) in a silicon quantum well strained by Si0.7Ge0.3 relaxed buffer layer is determined precisely by a mobility spectrum analysis. The 2DEG mobility is 2780 cm(2)/V s at room temperature and, upon cooling, increases continuously to reach mu(2DEG) = 7.4 x 10(4) cm(2)/V s at 7K. A back gate installed on the sample changes the 2DEG concentration n successfully to establish mu(2DEG) alpha n(1.4) at the constant temperature T = 10K, implying that the scattering at such low temperature is limited solely by the remote ionized impurity scattering. Based on this finding, theoretical analysis of the temperature dependence of mu(2DEG) is performed based on the relaxation time approximation using 2DEG wavefunctions and subband structures determined self-consistently and including three major scatterings; by intravalley acoustic phonons, intervalley g-processes of longitudinal optical (LO) phonons, and remote ionized impurities. The calculation included only three fitting parameters, the shear deformation potential (Xi(u) = 9.5 eV), LO phonon deformation potential for g-process scattering (D-0 = 9.0 x 10(8) eV/cm), and sheet density of remote ionized impurities that have been determined by quantitative comparison with our experimental results. The temperature dependence of mu(2DEG) calculated theoretically show excellent agreement with experimentally determined mu(2DEG). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702464]

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