Faculty Profiles - OHNO, Yutaka

PMMA/Al<inf>2</inf>O<inf>3</inf>bilayer passivation for suppression of hysteresis in chemically doped carbon nanotube thin-film transistors Reviewed

Tan F.W., Hirotani J., Kishimoto S., Ohno Y.

Japanese Journal of Applied Physics Vol. 61 ( 3 ) 2022.3

Authorship：Last author,　Corresponding author Language：English Publisher：Japanese Journal of Applied Physics

Hysteresis is usually present in carbon nanotube thin-film transistors exposed to air due to adsorbed water and oxygen molecules. Thus, it is desirable to passivate the device from these environmental effects and provide an air-stable platform for chemical doping to tune the threshold voltages. Here, we demonstrate p- and n-doped carbon nanotube transistors with suppressed hysteresis using bilayer stacking of poly(methyl methacrylate) and aluminum oxide (Al2O3) passivation layers using a low-temperature process suitable for flexible substrates. The results show that the bilayer passivation layers achieved reduced hysteresis to be 2.25% of applied gate voltage at low operation voltage as 2 V.

DOI： 10.35848/1347-4065/ac5264

Temperature dependence of Raman shift in defective single-walled carbon nanotubes Reviewed

Endo Masanori, Uchiyama Haruki, Ohno Yutaka, Hirotani Jun

APPLIED PHYSICS EXPRESS Vol. 15 ( 2 ) 2022.2

Authorship：Corresponding author Language：English Publisher：Applied Physics Express

Raman scatterings of both pristine and defective single-walled carbon nanotubes were measured. Defects on carbon nanotubes (CNTs) were induced by UV/O3 treatment, and the correlation between the temperature dependence of the Raman shift of the G-band and the crystallinity of CNTs was investigated. In the temperature range of 250-600 K, a gradual negative change in the slope was observed; the linear shift of the Raman G-band frequency with respect to temperature increased as the crystallinity deteriorated. This phenomenon is attributed to the increase in the fourth-order phonon-phonon scattering interaction resulting from the induced defects.

DOI： 10.35848/1882-0786/ac4678

In-plane dual-electrode triboelectric nanogenerator based on differential surface functionalization Reviewed

Matsunaga M., Hirotani J., Ohno Y.

Applied Physics Express Vol. 15 ( 2 ) 2022.2

Authorship：Last author,　Corresponding author Language：English Publisher：Applied Physics Express

Stretchable triboelectric nanogenerators (s-TENGs) are promising power sources for self-powered wearable electronics. Conventional single-electrode s-TENGs require an external ground electrode to form a closed circuit. We propose an in-plane dual-electrode s-TENG based on differential surface functionalization to eliminate the external ground electrode. The s-TENG comprises fully stretchable materials such as carbon nanotube thin films and elastomers. The top surface of the elastomer was functionalized to produce a difference in electronegativity between the two electrode regions. A high output power density of 3.5 W m-2 was obtained by tapping the two electrode regions by hand.

DOI： 10.35848/1882-0786/ac4d07

Carbon Nanotube-Based Nanomechanical Receiver for Digital Data Transfer Reviewed Open Access

Funayama K., Tanaka H., Hirotani J., Shimaoka K., Ohno Y., Tadokoro Y.

ACS Applied Nano Materials Vol. 4 ( 12 ) 2021.12

Language：English Publisher：ACS Applied Nano Materials

The evolution of carbon nanomaterials can provide tremendous advantages in sensing, computation, and functional materials. A carbon nanotube (CNT) has outstanding thermal and electrical conductivity features and is one of the most promising nanoscale carbon materials. It has a hardness of up to 1 TPa. Exploiting these features, nanomechanical systems with CNTs have been reported to achieve ultrasensitive sensors for mass, force, and electromagnetic waves owing to their outstanding elastic and electric properties. Some research groups have attempted to achieve digital data transfer in potential nanoscale wireless terminals with carbon nanomaterials. Although conceptual demonstrations have been reported, the fundamental capability of the transfer, particularly in the presence of noise, is yet to be explained. Here, we experimentally demonstrate for the first time that an ultrasmall digital receiver with a nanomechanical nanoantenna can transfer a vast amount of digital data, up to 1 Mbit, even in the presence of noise. We successfully transfer a digital image data with 393 216 bits. This demonstration proves that the data-transfer capability is close to the theoretical limit established in information theory and channel capacity. This small but robust nanomechanical receiver will contribute to the forthcoming data-oriented age of Internet of things (IoT)- and artificial intelligence (AI)-based systems.

DOI： 10.1021/acsanm.1c02563

Stretchable triboelectric nanogenerator based on carbon nanotubes Invited Reviewed

MATSUNAGA Masahiro, KAWAGUCHI Atsushi, OHNO Yutaka

Oyo Buturi Vol. 90 ( 11 ) page： 684 - 688 2021.11

Authorship：Last author,　Corresponding author Language：Japanese Publisher：The Japan Society of Applied Physics

Triboelectric energy harvesters are expected as a power source for self-powered wearable devices since they can generate electricity from the low-frequency motion of the human body. For wearable device applications, high stretchability is required to follow the dynamic three-dimensional surface of the human body. We have realized a stretchable sheet-shaped triboelectric energy harvester with a high output and elasticity. The high output has been achieved by a fluorine plasma treatment for the surface of the dielectric layer. We demonstrate a self-powered signal transmitter and LED-embedded gloves, exploiting the characteristics of the harvester. Furthermore, we propose a highly efficient intermittent operation circuit to drive electronic devices, using a small amount of power generated by the harvester. Our study can contribute to solve the problem of power source limitations in wearable electronics.

DOI： 10.11470/oubutsu.90.11_684

Effect of electrochemical functionalization of single-walled carbon nanotube electrodes in flexible enzymatic biofuel cells Reviewed

Dynamic Range Enhancement via Linearized Output in Nanoelectromechanical Systems by Combining High-Order Harmonics Reviewed International journal

K. Funayama, H. Tanaka, J. Hirotani, K. Shimaoka, Y. Ohno, and Y. Tadokoro

IEEE Trans. on Circuits and Systems II Vol. 68 ( 10 ) page： 3251 - 3255 2021.10

Special issue on Carbon-based Electronics Invited Reviewed

Das Saptarshi, Ohno Yutaka, Kawarada Hiroshi

CARBON Vol. 182 page： 856 - 856 2021.9

Tunable carbon nanotube diode with varying asymmetric geometry Reviewed Open Access

K. Funayama, J. Hirotani, A. Miura, H. Tanaka, Y. Ohno, and Y. Tadokoro

AIP Advances Vol. 11 ( 7 ) page： 075212 2021.7

D. Momaya and Y. Ohno

Jpn. J. Appl. Phys. Vol. 60 ( 6 ) page： 068002 2021.6

Simple and highly efficient intermittent operation circuit for triboelectric nanogenerator toward wearable electronic applications Reviewed International journal

A. Kawaguchi, H. Uchiyama, M. Matsunaga, and Y. Ohno

Appl. Phys. Exp. Vol. 14 ( 5 ) 2021.5

Low-voltage carbon nanotube complementary electronics using chemical doping to tune the threshold voltage Reviewed International journal

F. W. Tan, J. Hirotani, Y. Nonoguchi, S. Kishimoto, H. Katsura, and Y. Ohno

Appl. Phys. Exp. Vol. 14 ( 4 ) page： 045002 2021.4

ZnO Nanostructures Application in Electrochemistry: Influence of Morphology Reviewed International coauthorship International journal Open Access

Sulciute Agne, Nishimura Keita, Gilshtein Evgeniia, Cesano Federico, Viscardi Guido, Nasibulin Albert G., Ohno Yutaka, Rackauskas Simas

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 125 ( 2 ) page： 1472 - 1482 2021.1

Cross-linking gelation of isomaltodextrin for the chromatographic separation of semiconducting carbon nanotubes Reviewed International journal

Matsunaga Yuki, Hirotani Jun, Ohno Yutaka, Omachi Haruka

APPLIED PHYSICS EXPRESS Vol. 14 ( 1 ) 2021.1

Low-Voltage Operable and Strain-Insensitive Stretchable All-Carbon Nanotube Integrated Circuits with Local Strain Suppression Layer Reviewed International journal Open Access

Nishio Yuya, Hirotani Jun, Kishimoto Shigeru, Kataura Hiromichi, Ohno Yutaka

ADVANCED ELECTRONIC MATERIALS Vol. 7 ( 1 ) 2021.1

Effect of metal electrodes on optically detected magnetic resonance of nitrogen vacancy centers in diamond Reviewed International journal

Uchiyama Haruki, Kishimoto Shigeru, Ishi-Hayase Junko, Ohno Yutaka

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 59 ( 12 ) 2020.12

Fabrication of Carbon Nanotube Thin Films for Flexible Transistors by Using a Cross-Linked Amine Polymer Reviewed International journal

Matsumoto Kaisei, Ueno Kazuki, Hirotani Jun, Ohno Yutaka, Omachi Haruka

CHEMISTRY-A EUROPEAN JOURNAL Vol. 26 ( 28 ) page： 6118 - 6121 2020.5

High output voltage generation of over 5 V from liquid motion on single-layer MoS2 Reviewed International journal Open Access

Aji Adha Sukma, Nishi Ryohei, Ago Hiroki, Ohno Yutaka

NANO ENERGY Vol. 68 2020.2

High-output, transparent, stretchable triboelectric nanogenerator based on carbon nanotube thin film toward wearable energy harvesters Open Access

Matsunaga Masahiro, Hirotani Jun, Kishimoto Shigeru, Ohno Yutaka

NANO ENERGY Vol. 67 2020.1

Fast and Ultraclean Approach for Measuring the Transport Properties of Carbon Nanotubes Open Access

Wei Nan, Laiho Patrik, Khan Abu Taher, Hussain Aqeel, Lyuleeva Alina, Ahmed Saeed, Zhang Qiang, Liao Yongping, Tian Ying, Ding Er-Xiong, Ohno Yutaka, Kauppinen Esko I.

ADVANCED FUNCTIONAL MATERIALS Vol. 30 ( 5 ) 2020.1

Dependence of enhancement factor on electrode size for field emission current from carbon nanotube on silicon wafer

Funayama Keita, Tanaka Hiroya, Hirotani Jun, Shimaoka Keiichi, Ohno Yutaka, Tadokoro Yukihiro

NANOTECHNOLOGY Vol. 30 ( 42 ) page： 425201 2019.10

Aqueous two-phase extraction of semiconducting single-wall carbon nanotubes with isomaltodextrin and thin-film transistor applications Open Access

Omachi Haruka, Komuro Tomohiko, Matsumoto Kaisei, Nakajima Minako, Watanabe Hikaru, Hirotani Jun, Ohno Yutaka, Shinohara Hisanori

APPLIED PHYSICS EXPRESS Vol. 12 ( 9 ) 2019.9

Effects of HLA mismatch on cytomegalovirus reactivation in cord blood transplantation Open Access

Yokoyama Hisayuki, Kanda Junya, Kato Shunichi, Kondo Eisei, Maeda Yoshinobu, Saji Hiroo, Takahashi Satoshi, Onizuka Makoto, Onishi Yasushi, Ozawa Yukiyasu, Kanamori Heiwa, Ishikawa Jun, Ohno Yuju, Ichinohe Tatsuo, Takanashi Minoko, Kato Koji, Atsuta Yoshiko, Kanda Yoshinobu, Ikegame Kazuhiro, Utsunomiya Atae, Kawase Takakazu, Kim Sung-Won, Kuwatsuka Yachiyo, Kobayashi Takeshi, Takatsuka Yoshifusa, Takahashi Yoshiyuki, Tanaka Junji, Tamaki Hiroya, Tsuji Masanori, Nishida Tetsuya, Masuko Masayoshi, Matsuno Ryosuke, Murata Makoto, Morishima Satoko, Morishima Yasuo, Yokoyama Hisayuki, Wake Atsushi, Watanabe Nobuhiro, Ashida T., Hoshino Takumi, Yabe Toshio, Sakamoto Kana, Fuji Shigeo, Miyamura Koichi, Arima Nobuyoshi, Kondo Eisei, Yoshimitsu Makoto, Kawamura Koji, Kawata Takahito, Kishimoto Kenji, Tatara Raine, Hagino Takeshi, Fujiwara Shin-Ichiro, Shimomura Yoshimitsu, Sakaguchi Hirotoshi, Hirabayashi Shigeki, Ishii Hiroto, Onda Yoshiyuki, Kato Itaru, Kawajiri Akihisa, Shindo Takero, Tokunaga Masahito, Nonami Atsushi, Muranushi Hiroyuki, Yoshinaga Noriyoshi, Kawashima Naomi, Shiratori Souichi, Tada Yuma, Tanoue Sus-Umu, Hirayama Masahiro, Fukunaga Keiko, Ohbiki Marie

BONE MARROW TRANSPLANTATION Vol. 54 ( 7 ) page： 1004 - 1012 2019.7

Electrical property measurement of two-dimensional hole-gas layer on hydrogen-terminated diamond surface in vacuum-gap-gate structure

Inaba Masafumi, Kawarada Hiroshi, Ohno Yutaka

APPLIED PHYSICS LETTERS Vol. 114 ( 25 ) page： 253504 2019.6

Operando Analysis of Electron Devices Using Nanodiamond Thin Films Containing Nitrogen-Vacancy Centers Open Access

Uchiyama Haruki, Saijo Soya, Kishimoto Shigeru, Ishi-Hayase Junko, Ohno Yutaka

ACS OMEGA Vol. 4 ( 4 ) page： 7459 - 7466 2019.4

Language：Japanese Publisher：ACS Omega

Operando analysis of electron devices provides key information regarding their performance enhancement, reliability, thermal management, etc. For versatile operando analysis of devices, the nitrogen-vacancy (NV) centers in diamonds are potentially useful media owing to their excellent sensitivity to multiple physical parameters. However, in single crystal diamond substrates often used for sensing applications, placing NV centers in contiguity with the active channel is difficult. This study proposes an operando analysis method using a nanodiamond thin film that can be directly formed onto various electron devices by a simple solution-based process. The results of noise analysis of luminescence of the NV centers in nanodiamonds show that the signal-to-noise ratio in optically detected magnetic resonance can be drastically improved by excluding the large 1/f noise of nanodiamonds. Consequently, the magnetic field and increase in temperature caused by the device current could be simultaneously measured in a lithographically fabricated metal microwire as a test device. Moreover, the spatial mapping measurement is demonstrated and shows a similar profile with the numerical calculation.

DOI： 10.1021/acsomega.9b00344

Graft-versus-MDS effect after unrelated cord blood transplantation: a retrospective analysis of 752 patients registered at the Japanese Data Center for Hematopoietic Cell Transplantation Open Access

Ishiyama Ken, Aoki Jun, Itonaga Hidehiro, Uchida Naoyuki, Takahashi Satoshi, Ohno Yuju, Matsuhashi Yoshiko, Sakura Toru, Onizuka Makoto, Miyakoshi Shigesaburo, Takanashi Minoko, Fukuda Takahiro, Atsuta Yoshiko, Nakao Shinji, Miyazaki Yasushi

BLOOD CANCER JOURNAL Vol. 9 ( 3 ) 2019.3

Highly Uniform, Flexible Microelectrodes Based on the Clean Single-Walled Carbon Nanotube Thin Film with High Electrochemical Activity

Nguyen Xuan Viet, Kishimoto Shigeru, Ohno Yutaka

ACS APPLIED MATERIALS & INTERFACES Vol. 11 ( 6 ) page： 6389 - 6395 2019.2

Enhancement of the electron transfer rate in carbon nanotube flexible electrochemical sensors by surface functionalization Open Access

Nishimura Keita, Ushiyama Takuya, Viet Nguyen Xuan, Inaba Masafumi, Kishimoto Shigeru, Ohno Yutaka

ELECTROCHIMICA ACTA Vol. 295 page： 157 - 163 2019.2

Origins of the variability of the electrical characteristics of solution-processed carbon nanotube thin-film transistors and integrated circuits Open Access

Hirotani Jun, Kishimoto Shigeru, Ohno Yutaka

NANOSCALE ADVANCES Vol. 1 ( 2 ) page： 636 - 642 2019.2

Language：Japanese Publisher：Nanoscale Advances

Carbon nanotube (CNT) thin-film transistors based on solution processing have great potential for use in future flexible and wearable device technologies. However, the considerable variability of their electrical characteristics remains a significant obstacle to their practical use. In this work, we investigated the origins of the variability of these electrical characteristics by performing statistical analysis based on spatial autocorrelation and Monte Carlo simulation. The spatial autocorrelation of the on-current decreased with increasing distance on the order of millimetres, showing that macroscopic non-uniformity of the CNT density was one of the causes of the characteristic variability. In addition, even in the local regime where the macroscopic variability is negligible, the variability was greater than that expected based on the Monte Carlo simulation. The CNT aggregation could be attributed to microscopic variability. We also investigated the variability of the properties of integrated circuits such as inverters and ring oscillators fabricated on flexible plastic film. All of the inverters worked well, and their threshold voltage variations were fairly small. As the number of stages in the ring oscillator increased, the yield decreased, although the oscillation frequency variability improved.

DOI： 10.1039/c8na00184g

Carbon Nanotube Thin Films for High-Performance Flexible Electronics Applications

Hirotani Jun, Ohno Yutaka

TOPICS IN CURRENT CHEMISTRY Vol. 377 ( 1 ) page： 3 2019.2

Noise Modeling in Field Emission and Evaluation of the Nano-Receiver in Terms of Temperature Open Access

Funayama Keita, Tanaka Hiroya, Hirotani Jun, Shimaoka Keiichi, Ohno Yutaka, Tadokoro Yukihiro

IEEE ACCESS Vol. 7 page： 57820 - 57828 2019

Language：Japanese Publisher：IEEE Access

The field-emission phenomenon is exploited in a broad variety of applications and systems. Previous studies have reported that the current induced by field emission strongly and inherently depend on the temperature. This dependence enhances the noise in the current, which results in performance degradation in, for example, signal detection and communications in nanoscale receivers. In this paper, a mathematical model is presented for the suppression of the noise based on its probability density. Our experiment and analysis revealed that the density follows a Gaussian distribution, and the dependence on temperature is observed to be exponential. This result is intriguing because in the field of signal processing and communication, the influence of temperature is often considered with a noiseerature model, namely, linear dependence. Using our derived model, we theoretically evaluated the communication performance of a nanoscale receiver; owing to the exponential dependence on temperature, severe performance degradation was found with increasing temperature. This means that, as field-emission technology continues to be developed, the temperature should be kept low, for example, at room temperature, to secure the reliability of nanoscale communication devices.

DOI： 10.1109/ACCESS.2019.2913692

Stochastic Optimal Control to Minimize the Impact of Manufacturing Variations on Nanomechanical Systems Open Access

Ito Yuji, Funayama Keita, Hirotani Jun, Ohno Yutaka, Tadokoro Yukihiro

IEEE ACCESS Vol. 7 page： 171195 - 171205 2019

Language：Japanese Publisher：IEEE Access

This paper presents a control method intended to suppress the effects of manufacturing variations on nanomechanical systems. Often, the resonance characteristics of nanoscale devices are inconsistent, due to unavoidable variations in the fabrication process. This is important because resonant vibrations enhance the sensitivities of the devices. As such, the sensitivities of these systems can be degraded if the device characteristics are not identified. To address this fundamental problem, this paper presents a multidisciplinary method based on control theory, nanotechnology, and communication technology. A stochastic optimal feedback controller is employed to enhance an average sensitivity by regarding the variations as stochastic parameters. This method is applied to nanoscale receivers that detect transmitted binary data based on binary phase-shift keying in communication systems. The proposed method controls the vibrations of carbon nanotubes (CNTs) that serve as the antennas of the receiver. The proposed method is demonstrated via a numerical simulation using nanoscale receivers with the manufacturing variation. The simulation based on experimental data obtained from CNTs shows that the average performance of the devices is enhanced.

DOI： 10.1109/ACCESS.2019.2955697

An interdigitated electrode with dense carbon nanotube forests on conductive supports for electrochemical biosensors Open Access

Sugime Hisashi, Ushiyama Takuya, Nishimura Keita, Ohno Yutaka, Noda Suguru

ANALYST Vol. 143 ( 15 ) page： 3635 - 3642 2018.8

Non-coherent detection of digitally phase-modulated signals with carbon nanotube cantilever vibration Open Access

Tadokoro Y., Ohno Y., Tanaka H.

ELECTRONICS LETTERS Vol. 54 ( 13 ) page： 840 - + 2018.6

Language：Japanese Publisher：Electronics Letters

Towards the realisation of reliable communication systems using simple nanoscale transceivers, this Letter presents a method for the non-coherent detection of digitally phase-modulated signals. Without the synchronisation of the phases of the transmitted and received carrier signals, data transmission cannot be reliably achieved. To address this issue, the proposed method is developed using a nanoscale receiver that receives the binary phase-modulated signal through the mechanical vibration of a carbon nanotube cantilever. The present analysis reveals that this receiver has an interesting characteristic: the two decision statistics available in the receiver have a phase difference of p/2, which means that at least one of the statistics is fairly reliable regardless of the synchronisation error. Through the selection of the more reliable of the two statistics, the proposed method achieves low error in the estimation of the transmitted data even without carrier phase synchronisation. This Letter presents the derivation of the proposed rule for selecting the statistic and numerical results that demonstrate the effectiveness of the proposed method. This Letter is expected to contribute to the realisation of future communication applications using nanoscale transceivers.

DOI： 10.1049/el.2018.0475

Detection of Digitally Phase-Modulated Signals Utilizing Mechanical Vibration of CNT Cantilever

Tadokoro Yukihiro, Ohno Yutaka, Tanaka Hiroya

IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. 17 ( 1 ) page： 84 - 92 2018.1

Phase shifter tuned by varying the spring constant of a nanomechanical cantilever

Tanaka H., Ozaki T., Ohno Y., Tadokoro Y.

JOURNAL OF APPLIED PHYSICS Vol. 122 ( 23 ) 2017.12

Language：Japanese Publisher：Journal of Applied Physics

This paper presents a theoretical study of an adaptive microwave phase shifter based on a nanomechanical resonator. The phase shifter can be tuned to provide an arbitrary phase rotation in the range between -90° and 90° by adjusting the bias voltage applied to the resonator. An analytical model is developed to reveal the underlying mechanism of the phase shifter. It is also analytically demonstrated that the operating frequency can be selected by adjusting the bias voltage. In addition, it is found that the bandwidth is tunable via the quality factor for the cantilever.

DOI： 10.1063/1.4992040

Dry and Direct Deposition of Aerosol-Synthesized Single-Walled Carbon Nanotubes by Thermophoresis

Laiho Patrik, Mustonen Kimmo, Ohno Yutaka, Maruyama Shigeo, Kauppinen Esko I.

ACS APPLIED MATERIALS & INTERFACES Vol. 9 ( 24 ) page： 20738 - 20747 2017.6

Purification of 1.9-nm-diameter semiconducting single-wall carbon nanotubes by temperature-controlled gel-column chromatography and its application to thin-film transistor devices Open Access

Thendie Boanerges, Omachi Haruka, Hirotani Jun, Ohno Yutaka, Miyata Yasumitsu, Shinohara Hisanori

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 56 ( 6 ) 2017.6

Adaptive Control of Angular Sensitivity for VHF-Band Nano-Antenna Using CNT Mechanical Resonator

Tanaka H., Ohno Y., Tadokoro Y.

IEEE Transactions on Molecular, Biological, and Multi-Scale Communications Vol. 3 ( 1 ) page： 24 - 32 2017.3

Language：Japanese Publisher：IEEE Transactions on Molecular, Biological, and Multi-Scale Communications

An adaptive control method of angular sensitivity for a VHF-band nano-antenna is presented. This antenna is composed of a single carbon nanotube cantilever immersed in a DC electric field. The behavior of the antenna is analytically described using a singly clamped metallic sphere model and the image charge method. We derive design guidelines for the direction and shape of angular sensitivity; the amplitude of the DC electric field is a key parameter for controlling the sensitivity. The analysis reveals that the most sensitive direction is tunable in the range of -π/2 to π/2. The shape of sensitivity can be manipulated to be omnidirectional or to correspond to a Hertzian-dipole-like antenna. This investigation is useful for adaptive control to suppress interference signals in nanoscale communication systems.

DOI： 10.1109/TMBMC.2016.2640282

Angular Sensitivity Steering in CNT Electromagnetic Wave Detector

Nobunaga Tatsuya, Tadokoro Yukihiro, Ohno Yutaka, Tanaka Hiroya

IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS Vol. 16 page： 1405 - 1408 2017

Origin of residual particles on transferred graphene grown by CVD Reviewed

Yasunishi Tomohiro, Takabayashi Yuya, Kishimoto Shigeru, Kitaura Ryo, Shinohara Hisanori, Ohno Yutaka

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 55 ( 8 ) 2016.8

Highly individual SWCNTs for high performance thin film electronics Open Access

Kaskela Antti, Laiho Patrik, Fukaya Norihiro, Mustonen Kimmo, Susi Toma, Jiang Hua, Houbenov Nikolay, Ohno Yutaka, Kauppinen Esko I.

CARBON Vol. 103 page： 228 - 234 2016.7

Language：Japanese Publisher：Carbon

We report a continuous floating catalyst chemical vapor deposition synthesis of highly individual single-walled carbon nanotubes (SWCNT) for high performance transparent conducting films (TCF). Active feedback dilution of ferrocene-based catalyst vapor leads to an almost complete elimination of SWCNT bundling and a substantial increase in SWCNT lengths via the suppression of bundling-induced growth termination. The fabricated uniform TCFs exhibit sheet resistances of 89 Ω/sq. at 90% transmittance. This was further improved by micro-patterning, resulting in a sheet resistance of 69 Ω/sq. at 97% transmittance - the highest reported for any carbon nanotube TCF - and highly competitive with commercial indium-tin-oxide-TCFs. Furthermore, we demonstrate that thin film transistors fabricated from these highly individual SWCNTs reach charge carrier mobilities up to 100 cm2 V-1s-1 and ON/OFF-ratios up to 106.

DOI： 10.1016/j.carbon.2016.02.099

Highly stable perovskite solar cells with an all-carbon hole transport layer

Wang Feijiu, Endo Masaru, Mouri Shinichiro, Miyauchi Yuhei, Ohno Yutaka, Wakamiya Atsushi, Murata Yasujiro, Matsuda Kazunari

NANOSCALE Vol. 8 ( 23 ) page： 11882 - 11888 2016

Language：Japanese Publisher：Nanoscale

Nano-carbon materials (carbon nanotubes, graphene, and graphene oxide) have potential application for photovoltaics because of their excellent optical and electronic properties. Here, we demonstrate that a single-walled carbon nanotubes/graphene oxide buffer layer greatly improves the photovoltaic performance of organo-lead iodide perovskite solar cells. The carbon nanotubes/graphene oxide buffer layer works as an efficient hole transport/electron blocking layer. The photovoltaic conversion efficiency of 13.3% was achieved in the organo-lead iodide perovskite solar cell due to the complementary properties of carbon nanotubes and graphene oxide. Furthermore, the great improvement of photovoltaic performance stability in the perovskite solar cells using carbon nanotubes/graphene oxide/polymethyl methacrylate was demonstrated in comparison with that using a typical organic hole transport layer of 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene.

DOI： 10.1039/c6nr01152g

Toward the Limits of Uniformity of Mixed Metallicity SWCNT TFT Arrays with Spark-Synthesized and Surface-Density-Controlled Nanotube Networks Reviewed

Kaskela Antti, Mustonen Kimmo, Laiho Patrik, Ohno Yutaka, Kauppinen Esko I.

ACS APPLIED MATERIALS & INTERFACES Vol. 7 ( 51 ) page： 28134 - 28141 2015.12

Angular Sensitivity of VHF-Band CNT Antenna Reviewed

Tanaka Hiroya, Ohno Yutaka, Tadokoro Yukihiro

IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol. 14 ( 6 ) page： 1112 - 1116 2015.11

Overcoming the quality-quantity tradeoff in dispersion and printing of carbon nanotubes by a repetitive dispersion-extraction process Reviewed Open Access

Shirae Hiroyuki, Kim Dong Young, Hasegawa Kei, Takenobu Taishi, Ohno Yutaka, Noda Suguru

CARBON Vol. 91 page： 20 - 29 2015.9

Printed, short-channel, top-gate carbon nanotube thin-film transistors on flexible plastic film

Maeda Michihiko, Hirotani Jun, Matsui Ryotaro, Higuchi Kentaro, Kishimoto Shigeru, Tomura Takuya, Takesue Masafumi, Hata Katsuhiko, Ohno Yutaka

APPLIED PHYSICS EXPRESS Vol. 8 ( 4 ) 2015.4

Transparent, flexible all-carbon electron devices Reviewed

OHNO Yutaka

Oyo Buturi Vol. 84 ( 2 ) page： 142 - 145 2015.2

Language：Japanese Publisher：The Japan Society of Applied Physics

Carbon nanotube (CNT) thin films are rare materials with multi-functionality in addition to superior electric, optical and mechanical characteristics. This article introduces all-carbon devices having a semiconductor layer and electrodes, with wiring made of a CNT thin film. They are flexible and transparent as well as having the ability to be thermoformed into a variety of 3D shapes. Taking advantage of these characteristics allows the realization of unobservable devices or 3D or highly designable devices.

DOI： 10.11470/oubutsu.84.2_142

Electroluminescence from an Electrostatically Doped Carbon Nanotube Field-Effect Transistor Open Access

Hughes M. A., Ohno Y., Mizutani T.

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 6 ( 10 ) page： 881 - 886 2014.10

Language：Japanese Publisher：Nanoscience and Nanotechnology Letters

We report electroluminescence (EL) from a carbon nanotube field-effect transistor with split-gates. EL is generated by the electrostatic doping technique. Six EL bands could be observed, with the strongest band peaking between 0.867 and 0.850 eV with a full width at half maximum (FWHM) of 64 to 120 meV, depending on the bias conditions. From the EL peak position we estimate a CNT diameter of ∼ 1.05 nm. We also estimate the power and quantum efficiency of the EL to be around 1 × 10-6and 1 × 10-5 respectively. With a fixed drain voltage, increasing the opposite split gate bias caused the EL to increase monotonically from zero, indicating an ambipolar emission mechanism. With a fixed opposite split gate bias the dependence of EL on drain voltage displays a threshold. Drain current is significantly higher when using equal, rather than opposite split gate biases, which we attribute to the trapping of carries by band bending when using opposite split gate bias.

DOI： 10.1166/nnl.2014.1831

Photocurrent from a carbon nanotube diode with split-gate and asymmetric contact geometry Open Access

Hughes M. A., Homewood K. P., Curry R. J., Ohno Y., Mizutani T.

MATERIALS RESEARCH EXPRESS Vol. 1 ( 2 ) 2014.6

Language：Japanese Publisher：Materials Research Express

We fabricated a Ti/Pd asymmetrically contacted single carbon nanotube (CNT) field-effect transistor (FET) with split-gates. Transfer characteristics can be explained if the Schottky barrier for electrons is lower at the Pd contact than it is at the Ti contact. Strong rectification is observed when the gates are unbiased, and the rectification direction can be inverted with the appropriate gate bias. When operated as an FET the device has an on/off ratio of 1 × 107. Under illumination, photocurrent can only be observed with opposite split-gate bias. Open circuit voltage (VOC) and short circuit current (ISC) increase with increasing opposite polarity split-gate bias, representing the first demonstration of the modulation of VOC and ISC in an asymmetric contact CNT FET.

DOI： 10.1088/2053-1591/1/2/026304

Effect of ambient air on n-type carbon nanotube thin-film transistors chemically doped with poly(ethylene imine)

Yasunishi Tomohiro, Kishimoto Shigeru, Ohno Yutaka

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 53 ( 5 ) 2014.5

Fabrication of Single-Walled Carbon Nanotube/Si Heterojunction Solar Cells with High Photovoltaic Performance

Wang Feijiu, Kozawa Daichi, Miyauchi Yuhei, Hiraoka Kazushi, Mouri Shinichiro, Ohno Yutaka, Matsuda Kazunari

ACS PHOTONICS Vol. 1 ( 4 ) page： 360 - 364 2014.4

One-Step Sub-10 mu m patterning of Carbon-Nanotube Thin Films for Transparent Conductor Applications

Fukaya Norihiro, Kim Dong Young, Kishimoto Shigeru, Noda Suguru, Ohno Yutaka

ACS NANO Vol. 8 ( 4 ) page： 3285 - 3293 2014.4

Split gate and asymmetric contact carbon nanotube optical devices Open Access

Hughes M. A., Homewood K. P., Curry R. J., Ohno Y., Mizutani T.

OPTICAL COMPONENTS AND MATERIALS XI Vol. 8982 2014

Language：Japanese Publisher：Proceedings of SPIE - The International Society for Optical Engineering

Asymmetric contacts or split gate geometries can be used to obtain rectification, electroluminescence (EL) and photocurrent from carbon nanotube field effect transistors. Here, we report devices with both split gates and asymmetric contacts and show that device parameters can be optimised with an appropriate split gate bias, giving the ability to select the rectification direction, modify the reverse bias saturation current and the ideality factor. When operated as a photodiode, the short circuit current and open circuit voltage can be modified by the split gate bias, and the estimated power conversion efficiency was 1×10-6. When using split gates and symmetric contacts, strong EL peaking at 0.86 eV was observed with a full width at half maximum varying between 64 and 120 meV, depending on the bias configuration. The power and quantum efficiency of the EL was estimated to be around 1×10-6 and 1×10-5 respectively.

DOI： 10.1117/12.2036962

Carbon nanotube-based thin-film transistors on plastic film

True Nanoの世界：カーボンナノチューブ：特異な物性を活かした電子デバイス Reviewed

大野雄高

パリティ Vol. 29 page： 18 - 21 2014

Ohno Y.

Proceedings of the 20th International Workshop on Active-Matrix Flatpanel Displays and Devices: TFT Technologies and FPD Materials, AM-FPD 2013 page： 243 - 246 2013.11

Language：Japanese Publisher：Proceedings of the 20th International Workshop on Active-Matrix Flatpanel Displays and Devices: TFT Technologies and FPD Materials, AM-FPD 2013

Among various kinds of semiconductor materials, carbon nanotubes can provide high-mobility, low-operation voltage, flexible devices on plastic films at low cost. High-mobility thin-film transistors (TFTs) and functional integrated circuits (ICs) have been fabricated by simple transfer process on a transparent plastic substrate. All-carbon ICs have also been realized for the first time, which has better transparency, flexibility, and stretchability. We also demonstrate high-throughput printing fabrication of high-mobility TFT arrays with flexographic printing technique. © 2013 JSAP.

An ultra-low leakage current single carbon nanotube diode with split-gate and asymmetric contact geometry Open Access

Hughes M. A., Homewood K. P., Curry R. J., Ohno Y., Mizutani T.

APPLIED PHYSICS LETTERS Vol. 103 ( 13 ) 2013.9

Language：Japanese Publisher：Applied Physics Letters

A single carbon nanotube diode is reported, with Ti and Pd contacts, and split gates. Without gate bias the device displays strong rectification, with a leakage current (I0) of 6 × 10-16 A, and an ideality factor (η) of 1.38. When the gate above the Ti contact is biased negatively the diode inverts. When positive bias is then applied to the gate above the Pd contact minority carrier injection is suppressed. Configured such I0 and η were 2 × 10-14 A and 2.01, respectively. Electrical characterization indicates that the Schottky barrier height for electrons is lower for the Pd contact than the Ti contact. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4823602

High-Mobility, Flexible Carbon Nanotube Thin-Film Transistors Fabricated by Transfer and High-Speed Flexographic Printing Techniques

Higuchi Kentaro, Kishimoto Shigeru, Nakajima Yuta, Tomura Takuya, Takesue Masafumi, Hata Katsuhiko, Kauppinen Esko I., Ohno Yutaka

APPLIED PHYSICS EXPRESS Vol. 6 ( 8 ) 2013.8

Language：Japanese Publisher：Applied Physics Express

A lack of high-mobility transistors has been one of the most crucial challenges facing the development of printable electronics. In this work, we report on the fabrication of high-mobility carbon nanotube thin-film transistors using a combination of transfer and high-speed flexographic printing techniques. Based on lithography-free nonvacuum processes, a high mobility of 157 cm2 V-1 s-1 with an ON/OFF ratio of 104 was achieved. Our ambient fabrication technique provides not only a promising platform for printed flexible devices but also demonstrates the realistic potential of low-cost manufacturing technology. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.085101

Mouldable all-carbon integrated circuits Open Access

Sun Dong-Ming, Timmermans Marina Y., Kaskela Antti, Nasibulin Albert G., Kishimoto Shigeru, Mizutani Takashi, Kauppinen Esko I., Ohno Yutaka

NATURE COMMUNICATIONS Vol. 4 page： 2302 2013.8

Language：Japanese Publisher：Nature Communications

A variety of plastic products, ranging from those for daily necessities to electronics products and medical devices, are produced by moulding techniques. The incorporation of electronic circuits into various plastic products is limited by the brittle nature of silicon wafers. Here we report mouldable integrated circuits for the first time. The devices are composed entirely of carbon-based materials, that is, their active channels and passive elements are all fabricated from stretchable and thermostable assemblies of carbon nanotubes, with plastic polymer dielectric layers and substrates. The all-carbon thin-film transistors exhibit a mobility of 1,027 cm 2 V -1 s -1 and an ON/OFF ratio of 10 5. The devices also exhibit extreme biaxial stretchability of up to 18% when subjected to thermopressure forming. We demonstrate functional integrated circuits that can be moulded into a three-dimensional dome. Such mouldable electronics open new possibilities by allowing for the addition of electronic/plastic-like functionalities to plastic/electronic products, improving their designability. © 2013 Macmillan Publishers Limited.

DOI： 10.1038/ncomms3302

Spatially Resolved Transport Properties of Pristine and Doped Single-Walled Carbon Nanotube Networks

Znidarsic Andrej, Kaskela Antti, Laiho Patrik, Gaberscek Miran, Ohno Yutaka, Nasibulin Albert G., Kauppinen Esko I., Hassanien Abdou

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 117 ( 25 ) page： 13324 - 13330 2013.6

Language：Japanese Publisher：Journal of Physical Chemistry C

We use noninvasive atomic force microscopy to probe the spatial electrical conductivity of isolated junctions of pristine and nitric acid treated single-walled carbon nanotube networks (SWCNT-N). By analyzing the local IV curves of SWCNTs and bundles with various diameters, the resistance per unit length and the contact resistance of their junctions are estimated to be 3-16 kΩ/μm and 29-532 kΩ, respectively. We find that the contact resistance decreases with increasing SWCNT or bundle diameter and depends on the contact morphology, reaching a value of 29 kΩ at a diameter of 10 nm. A nitric acid treatment moderately dopes SWCNTs and reduces their average contact resistance by a factor of 3 while the resistance of the nanotubes remains largely unaltered. Remarkably, the same treatment on an SWCNT-N shows similar reduction in the sheet resistance by a factor of 4. These results suggest that the resistance reduction mechanism is related to the contact modulation with no major impact on conductance of SWCNTs. © 2013 American Chemical Society.

DOI： 10.1021/jp403983y

Investigation of Interface Charges of High-k Gate Dielectrics and Their Effects on Carbon Nanotube Field-Effect Transistors

Suzuki Kosuke, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

APPLIED PHYSICS EXPRESS Vol. 6 ( 2 ) 2013.2

Language：Japanese Publisher：Applied Physics Express

We have investigated the interface charges generated at the interfaces of the high-k gate insulator by Kelvin probe force microscopy, as well as their effects on the properties of carbon nanotube field-effect transistors (CNFETs). It was found that positive charges are concentrated near the interfaces of the gate insulator with Au electrodes and a SiO2 substrate. The device simulation results show that the charges at the interfaces of the gate insulator with the Au electrodes are responsible for the change in the polarity of the conduction carriers in the CNFETs. Copyright © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/APEX.6.024002

Fabrication of high-mobility n-type carbon nanotube thin-film transistors on plastic film

Carbon nanotube-based thin-film transistors on plastic film

Ohno Yutaka

PROCEEDINGS OF 2013 TWENTIETH INTERNATIONAL WORKSHOP ON ACTIVE-MATRIX FLATPANEL DISPLAYS AND DEVICES (AM-FPD 13): TFT TECHNOLOGIES AND FPD MATERIALS page： 243 - 246 2013

Yasunishi Tomohiro, Kishimoto Shigeru, Kauppinen Esko I., Ohno Yutaka

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 10, NO 11 Vol. 10 ( 11 ) page： 1612 - 1615 2013

Language：Japanese Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics

We fabricated flexible n -type carbon nanotube thin-film transistors on a plastic film by a simple transfer process and a solution-based chemical doping technique with polyethyleneimine (PEI). There exists an optimal PEI concentration, which is determined by doping level and charge accumulation in the PEI layer. A high electron mobility of 70 cm2/Vs was achieved with an on/off ratio of 105 in ambient air. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201300231

Effect of Air on Metal Contact of Carbon Nanotube Field-Effect Transistors

カーボンナノチューブ薄膜のフレキシブルエレクトロニクス応用

大野雄高

バンドーテクニカルレポート(特別寄稿) Vol. 17 page： 41680 2013

Ishii Satoshi, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

Materia Japan Vol. 52 ( 6 ) page： 266 - 272 2013

Electrical properties of the graphitic carbon contacts on carbon nanotube field effect transistors

Tamaoki Masato, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

APPLIED PHYSICS LETTERS Vol. 101 ( 3 ) 2012.7

Language：Japanese Publisher：Applied Physics Letters

Carbon nanotube field effect transistors (CNT-FETs) with graphitic carbon (G-C) contacts were fabricated and the electrical properties of the G-C contacts were studied. The CNT-FETs showed p-type conduction in air. However, the conduction type has changed to ambipolar in vacuum after annealing at 200 °C. This suggests that the p-type conduction in air is attributed to the adsorbed oxygen. The barrier heights at the G-C/CNT contacts in vacuum were ∼400 meV for electrons and ∼310 meV for holes. These values suggest that the Fermi level of G-C contacts is located at slightly below the midgap of the CNTs in vacuum. © 2012 American Institute of Physics.

DOI： 10.1063/1.4737169

Effect of Carbon Nanotube Network Morphology on Thin Film Transistor Performance

Timmermans Marina Y., Estrada David, Nasibulin Albert G., Wood Joshua D., Behnam Ashkan, Sun Dong-ming, Ohno Yutaka, Lyding Joseph W., Hassanien Abdou, Pop Eric, Kauppinen Esko I.

NANO RESEARCH Vol. 5 ( 5 ) page： 307 - 319 2012.5

Language：Japanese Publisher：Nano Research

The properties of electronic devices based on carbon nanotube networks (CNTNs) depend on the carbon nanotube (CNT) deposition method used, which can yield a range of network morphologies. Here, we synthesize single-walled CNTs using an aerosol (floating catalyst) chemical vapor deposition process and deposit CNTs at room temperature onto substrates as random networks with various morphologies. We use four CNT deposition techniques: electrostatic or thermal precipitation, and filtration through a filter followed by press transfer or dissolving the filter. We study the mobility using pulsed measurements to avoid hysteresis, the on/off ratio, and the electrical noise properties of the CNTNs, and correlate them to the network morphology through careful imaging. Among the four deposition methods thermal precipitation is found to be a novel approach to prepare high-performance, partially aligned CNTNs that are dry-deposited directly after their synthesis. Our results provide new insight into the role of the network morphologies and offer paths towards tunable transport properties in CNT thin film transistors. © 2012 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

DOI： 10.1007/s12274-012-0211-8

Estimation of Height of Barrier Formed in Metallic Carbon Nanotube

Okigawa Yuki, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 51 ( 2 ) 2012.2

Language：Japanese Publisher：Japanese Journal of Applied Physics

We have estimated the height of barriers against carriers formed in the metallic carbon nanotube (m-CNT) grown by plasma-enhanced chemical vapor deposition. The result shows that the heights of the barriers against both electrons and holes are about 300 meV. The existence of the barrier in the m-CNT was confirmed by local current modulation using scanning gate microscopy and by the potential drop obtained by Kelvin probe force microscopy. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.02BN01

Observation of n-Type Conduction in Carbon Nanotube Field-Effect Transistors with Au Contacts in Vacuum

Imaeda Hideki, Ishii Satoshi, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 51 ( 2 ) 2012.2

Language：Japanese Publisher：Japanese Journal of Applied Physics

The change in the conduction type of carbon nanotube field-effect transistors (CNT-FETs) with Au contacts from p-type to n-type by annealing in vacuum was observed. The result was explained by the local work function change of the Au contacts based on the measurement of the surface potential of the Au/CNT contact by Kelvin probe force microscopy (KFM). This work function change became prominent due to the desorption of oxygen by annealing. The degree of the conduction-type change was found to be dependent on the devices. The CNT-FETs with small OFF current showed clear conduction-type change. However, the devices with large OFF current did not show clear conduction-type change. This device dependent behavior was explained by the energy gap difference among devices, in which suppression of OFF current is not sufficient for the devices with thick CNTs with small bandgap. © 2012 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.51.02BN06

Air-Free Fabrication and Investigation of Effect of Air Exposure on Carbon Nanotube Field-Effect Transistors

Ishii Satoshi, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

MATERIALS EXPRESS Vol. 1 ( 4 ) page： 285 - 290 2011.12

Language：Japanese Publisher：Materials Express

An air-free system which enables experiments from carbon nanotube (CNT) growth to device characterization without an effect of ambient air was constructed. It was clarified by using the system that an origin of instability of n-type conduction of carbon nanotube field-effect transistors (CNTFETs) with Al contacts in air was not attributed to oxidation of the Al contacts, but attributed to adsorption of oxygen. The present system was shown to be useful for investigating the effect of air on intrinsic electrical properties of CNTFETs with Al contacts, investigating the effect of passivation, and fabricating CNT p-n junction with Au(p)/Al(n) asymmetric electrodes. © 2011 by American Scientific Publishers.

DOI： 10.1166/mex.2011.1037

Length-Sorted Semiconducting Carbon Nanotubes for High-Mobility Thin Film Transistors

Miyata Yasumitsu, Shiozawa Kazunari, Asada Yuki, Ohno Yutaka, Kitaura Ryo, Mizutani Takashi, Shinohara Hisanori

NANO RESEARCH Vol. 4 ( 10 ) page： 963 - 970 2011.10

Language：Japanese Publisher：Nano Research

We have developed a process for chemical purification of carbon nanotubes for solution-processable thin-film transistors (TFTs) having high mobility. Films of the purified carbon nanotubes fabricated by simple drop coating showed carrier mobilities as high as 164 cm2V-1s-1, normalized transconductances of 0.78 Sm-1, and on/off current ratios of 106. Such high performance requires the preparation of a suspension of micrometer-long and highly purified semiconducting single-walled carbon nanotubes (SWCNTs). Our purification process includes length and electronic-type selective trapping of SWCNTs using recycling gel filtration with a mixture of surfactants. The results provide an important milestone toward printed high-speed and large-area electronics with roll-to-roll and ink-jet device fabrication. © 2011 Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

DOI： 10.1007/s12274-011-0152-7

Carbon nanotubes for VLSI: Interconnect and transistor applications

Awano Y., Sato S., Nihei M., Sakai T., Ohno Y., Mizutani T.

International Symposium on VLSI Technology, Systems, and Applications, Proceedings page： 10 - 11 2011.7

Language：Japanese Publisher：International Symposium on VLSI Technology, Systems, and Applications, Proceedings

We report the present status of Carbon Nanotube (CNT) CVD material technologies and their applications for via interconnects and FETs for VLSI. We succeeded in growing multi-walled CNTs (MWNTs) with the highest shell density (as high as 1013/cm2) and in fabricating via interconnects with high robustness against a high current density. We also report a Si-process compatible technique to control carrier polarity of Single-walled CNT (SWNT) FETs by utilizing fixed charges introduced by the gate oxide. High-performance p- and n-type CNT-FETs and CMOS inverters with stability in air have been realized. © 2011 IEEE.

DOI： 10.1109/VTSA.2011.5872210

Electrical properties of carbon nanotube thin-film transistors fabricated using plasma-enhanced chemical vapor deposition measured by scanning probe microscopy

Okigawa Yuki, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

NANOTECHNOLOGY Vol. 22 ( 19 ) page： 195202 2011.5

Language：Japanese Publisher：Nanotechnology

The electrical properties of carbon nanotube thin-film transistors (CNT-FETs) fabricated using plasma-enhanced chemical vapor deposition (PECVD) were studied by scanning probe microscopy. The measured results suggest the formation of an island structure in the subthreshold regime and the disappearance of the island structure at the ON state. These results were explained by the change in the effective number of CNTs that contributed to the electrical conduction due to the gate-bias-dependent resistance of the semiconducting CNTs. The results obtained by Monte Carlo simulation revealed similar results. The effects of metallic CNTs with defects and the scatter of the drain current in the subthreshold regime were also examined. © 2011 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/22/19/195202

Flexible high-performance carbon nanotube integrated circuits

Sun Dong-ming, Timmermans Marina Y., Tian Ying, Nasibulin Albert G., Kauppinen Esko I., Kishimoto Shigeru, Mizutani Takashi, Ohno Yutaka

NATURE NANOTECHNOLOGY Vol. 6 ( 3 ) page： 156 - 161 2011.3

Language：Japanese Publisher：Nature Nanotechnology

Carbon nanotube thin-film transistors are expected to enable the fabrication of high-performance, flexible and transparent devices using relatively simple techniques. However, as-grown nanotube networks usually contain both metallic and semiconducting nanotubes, which leads to a trade-off between charge-carrier mobility (which increases with greater metallic tube content) and on/off ratio (which decreases). Many approaches to separating metallic nanotubes from semiconducting nanotubes have been investigated, but most lead to contamination and shortening of the nanotubes, thus reducing performance. Here, we report the fabrication of high-performance thin-film transistors and integrated circuits on flexible and transparent substrates using floating-catalyst chemical vapour deposition followed by a simple gas-phase filtration and transfer process. The resulting nanotube network has a well-controlled density and a unique morphology, consisting of long (∼10 μm) nanotubes connected by low-resistance Y-shaped junctions. The transistors simultaneously demonstrate a mobility of 35 cm 2 V-1 s-1 and an on/off ratio of 6 × 106. We also demonstrate flexible integrated circuits, including a 21-stage ring oscillator and master-slave delay flip-flops that are capable of sequential logic. Our fabrication procedure should prove to be scalable, for example, by using high-throughput printing techniques. © 2011 Macmillan Publishers Limited. All rights reserved.

DOI： 10.1038/NNANO.2011.1

Thin-Film Transistors with Length-Sorted DNA-Wrapped Single-Wall Carbon Nanotubes

Asada Yuki, Miyata Yasumitsu, Shiozawa Kazunari, Ohno Yutaka, Kitaura Ryo, Mizutani Takashi, Shinohara Hisanori

JOURNAL OF PHYSICAL CHEMISTRY C Vol. 115 ( 1 ) page： 270 - 273 2011.1

Language：Japanese Publisher：Journal of Physical Chemistry C

The present experimental study provides a detailed characterization of the single-wall carbon nanotube (SWNT) length effect on the device characteristics of DNA-wrapped SWNT-network thin-film transistors (TFTs). DNA-assisted dispersion and length separation by high-performance liquid chromatography are used to prepare the SWNTs with average lengths of 400 and 200 nm. The TFTs of both SWNTs exhibit high on/off current ratios of 104-106 and mobilities of 0.4-1.3 cm2/(V s) by optimizing the film density of SWNTs. The optimized density of 200 nm SWNTs is found to be higher than that of 400 nm SWNTs as expected by the percolation theory of two-dimensional random networks, where shorter length SWNTs can maintain high on current despite increasing in the number of SWNT junctions. The present result is an important indicator for realizing high-performance TFTs constructed from SWNTs having desired length. © 2010 American Chemical Society.

DOI： 10.1021/jp107361n

Thin Single-Walled Carbon Nanotubes with Narrow Diameter Distribution Grown by Cold-Wall Chemical Vapor Deposition Combined with Co Nanoparticle Deposition

Ishii Satoshi, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 50 ( 1 ) 2011.1

Language：Japanese Publisher：Japanese Journal of Applied Physics

We have grown thin single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution using the arc-discharge plasma (ADP) technique for Co catalyst metal deposition and a cold-wall chemical vapor deposition (CVD) system for SWNT growth. The diameters of the SWNTs ranged from 0.79 to 1.07 nm. In addition to depositing small and uniform-sized metal catalyst nanoparticles by the ADP technique, decreasing the growth temperature using the cold-wall CVD system seemed to suppress the aggregation of the metal catalyst nanoparitcles leading to SWNTs with small diameters of narrow distribution. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.015102

Impact of fixed charges at interfaces on the operation of top-gate carbon nanotube field-effect transistors

Ohno Yutaka, Moriyama Naoki, Kishimoto Shigeru, Mizutani Takashi

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 Vol. 8 ( 2 ) page： 567 - 569 2011

Language：Japanese Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics

To control the properties of carbon nanotube field-effect transistors (CNFETs), it is important to understand the properties of various interfaces in the devices and their effects on device characteristics. Here, we studied the influence of interface fixed charges introduced between the gate insulator and the substrate on the operation of a top-gate CNFET, using device simulation. The simulation results suggest that with the existence of interface charges, the current modulation mechanism of the CNFET changes from Schottky barrier modulation to channel potential modulation. The minority carrier injection in the OFF state is suppressed by the high-potential region formed near the contact electrodes by the interface charges. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201000571

Improvement in alignment of single-walled carbon nanotubes grown on quartz substrate

Hata Kensuke, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2 Vol. 8 ( 2 ) page： 561 - 563 2011

Language：Japanese Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics

Aligned growth of single-walled carbon nanotubes (SWNTs), which can be realized on a quartz substrate, is important for electron device applications such as high-frequency transistors. In order to improve the alignment of the SWNTs, we studied pretreatments of the substrate before SWNT growth. When the surface of the quartz substrate was etched using hydrofluoric acid, the alignment and linearity of the grown SWNTs improved. This suggests that it is important to remove the uppermost layer on the surface of as-received substrates, which is damaged due to the polishing process. We also studied an etching process to remove the damaged layer without increasing surface roughness. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201000551

Carbon Nanotubes for VLSI: Interconnect and Transistor Applications

Awano Yuji, Sato Shintaro, Nihei Mizuhisa, Sakai Tadashi, Ohno Yutaka, Mizutani Takashi

PROCEEDINGS OF THE IEEE Vol. 98 ( 12 ) page： 2015 - 2031 2010.12

Language：Japanese Publisher：Proceedings of the IEEE

Carbon nanotubes (CNTs) offer unique properties such as the highest current density, ballistic transport, ultrahigh thermal conductivity, and extremely high mechanical strength. Because of these remarkable properties, they have been expected for use as wiring materials and as alternate channel materials for extending complementary metal oxide semiconductor (CMOS) performance in future very large scale integration (VLSI) technologies. In this paper, we report the present status of CNT growth technologies and the applications for via interconnects (vertical wiring) and field-effect transistors (FETs). We fabricated CNT via and evaluated its robustness over a high-density current. In our technology, multiwalled carbon nanotubes (MWNTs) were successfully grown at temperatures as low as 365 C using Co catalyst nanoparticles, which were formed and deposited by a custom-designed particle generation and deposition system. The density of MWNTs grown at 450 C reaches more than MWNTs were grown in via holes with a diameter as small as 40 nm. The resistance of CNT vias with a diameter of 160 nm was found to be of the same order as that of tungsten plugs. The CNT via was able to sustain a current density as high as at 105 C for 100 h without any deterioration in its properties. We propose a Si-process compatible technique to control carrier polarity of CNFETs by utilizing fixed charges introduced by the gate oxide. High-performance - and type CNFETs and CMOS inverters with stability in air have been realized. © 2006 IEEE.

DOI： 10.1109/JPROC.2010.2068030

High-Performance Thin-Film Transistors with DNA-Assisted Solution Processing of Isolated Single-Walled Carbon Nanotubes

Electrical breakdown of individual Si nanochains and silicide nanochains.

Kohno H, Nogami T, Takeda S, Ohno Y, Yonenaga I, Ichikawa S

Journal of nanoscience and nanotechnology Vol. 10 ( 10 ) page： 6655 - 8 2010.10

Asada Yuki, Miyata Yasumitsu, Ohno Yutaka, Kitaura Ryo, Sugai Toshiki, Mizutani Takashi, Shinohara Hisanori

ADVANCED MATERIALS Vol. 22 ( 24 ) page： 2698 - + 2010.6

Language：Japanese Publisher：Advanced Materials

[Figure Presented] Controlling the morphology of single-walled carbon nanotubes (SWNTs) is essential to realize their excellent device characteristics in electronics. DNA-wrapped SWNTs provides an effective, scalable way to fabricate the super-uniform networks of highly isolated, structure-sorted SWNTs for thin-film transistors (TFTs). The DNASWNTs are easily formed into uniform, desired-density networks of individual nanotubes. © 2010 WILEY-VCH Verlag GmbH &, Co. KCaA, Weinheim.

DOI： 10.1002/adma.200904006

Fabrication Process of Carbon Nanotube Field Effect Transistors Using Atomic Layer Deposition Passivation for Biosensors

Nakashima Yasuhiro, Ohno Yutaka, Kishimoto Shigeru, Okochi Mina, Honda Hiroyuki, Mizutani Takashi

JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY Vol. 10 ( 6 ) page： 3805 - 3809 2010.6

Language：Japanese Publisher：Journal of Nanoscience and Nanotechnology

Fabrication process of the carbon nanotube (CNT) field effect transistors (FETs) for biosensors was studied. Atomic layer deposition (ALD) of HfO 2 was applied to the deposition of the passivation/gate insulator film. The CNT-FETs did not show the drain current degradation after ALD passivation even though the passivation by Si 3N 4 deposited by plasma-enhanced chemical vapor deposition (PECVD) resulted in a significant drain current decrease. This indicates the advantage of the present ALD technique in terms of the damage suppression. The biosensing operation was confirmed using thus fabricated CNT-FETs. Copyright © 2010 American Scientific Publishers All rights reserved.

DOI： 10.1166/jnn.2010.1983

Thin film transistors using PECVD-grown carbon nanotubes

Ono Yuki, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

NANOTECHNOLOGY Vol. 21 ( 20 ) page： 205202 2010.5

Language：Japanese Publisher：Nanotechnology

Thin film transistors with a carbon nanotube(CNT) network as a channel have been fabricated using grid-inserted plasma-enhanced chemical vapor deposition(PECVD) which has the advantage of preferential growth of the CNTs with semiconducting behavior in the I-V characteristics of CNT field effect transistors (CNT-FETs). Taking advantage of the preferential growth and suppression of bundle formation, a large ON current of 170 μ Amm -1, which is among the largest in these kinds of devices with a large ON/OFF current ratio of about 105, has been realized in the relatively short channel length of 10μm. The field effect mobility of the device was 5.8cm2V-1s-1. © 2010 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/21/20/205202

Change in carrier type in high-k gate carbon nanotube field-effect transistors by interface fixed charges

Moriyama N., Ohno Y., Kitamura T., Kishimoto S., Mizutani T.

NANOTECHNOLOGY Vol. 21 ( 16 ) 2010.4

Language：Japanese Publisher：Nanotechnology

We study the phenomenon of change in carrier type in carbon nanotube field-effect transistors (CNFETs) caused by the atomic layer deposition (ALD) of a HfO2 gate insulator. When a HfO2 layer is deposited on a CNFET, the type of carrier changes from p-type to n-type. The so-obtained n-type device has good performance and stability in air. The conductivity of such a device with a channel length of 0.7νm is 11% of the quantum conductance 4e2/h. The contact resistance for electron current is estimated to be 14 kΩ. The n-type conduction of this CNFET is maintained for more than 100 days. The change in carrier type is attributed to positive fixed charges introduced at the interface between the HfO2 and SiO2 layers. We also propose a novel technique to control the type of conduction by utilizing interface fixed charges; this technique is compatible with Si CMOS process technology. © 2010 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/21/16/165201

Electrical Properties of Carbon Nanotube Field-Effect Transistors with Multiple Channels Measured by Scanning Gate Microscopy

Okigawa Yuki, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 49 ( 2 ) 2010

Language：Japanese Publisher：Japanese Journal of Applied Physics

Electrical properties of a carbon nanotube field-effect transistor (CNT-FET) with multiple CNT channels were studied by scanning gate microscopy (SGM), in which the scanning probe tip was used as a local gate. It was possible to distinguish the difference in electrical properties of individual CNT channels by SGM. Spot like SGM images were attributed to the barrier against carriers formed in the metallic CNT, resulting in a current modulation of the CNT-FET. It has also been shown that the barrier in the metallic CNT results in an ambipolar behavior of the CNTFETs. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.49.02BD02

High-Performance Top-Gate Carbon Nanotube Field-Effect Transistors and Complementary Metal-Oxide-Semiconductor Inverters Realized by Controlling Interface Charges

Moriyama Naoki, Ohno Yutaka, Suzuki Kosuke, Kishimoto Shigeru, Mizutani Takashi

APPLIED PHYSICS EXPRESS Vol. 3 ( 10 ) 2010

Language：Japanese Publisher：Applied Physics Express

We have realized high-performance p- and n-type top-gate carbon nanotube field-effect transistors (CNFETs) by controlling the charges introduced at the interface between the gate insulator and the substrate. We also fabricated a complementary metal-oxide-semiconductor (CMOS) inverter on an individual single-walled carbon nanotube (SWNT). This CMOS inverter exhibited a high voltage gain of 26 and a large noise margin of ̃70% of Vdd=2. The proposed technique provides air-stable and high-performance carbon nanotube CMOS devices that are compatible with the Si CMOS process. The effects of interface charges on the mechanisms of CNFET operation have also been investigated on the basis of potential calculations. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.3.105102

Medium Scale Integrated Circuits Using Carbon Nanotube Thin Film Transistors

Environmental effects on photoluminescence of single-walled carbon nanotubes

Ohno Yutaka, Maruyama Shigeo, Mizutani Takashi

CARBON NANOTUBES page： 109 - 121 2010

Mizutani Takashi, Okigawa Yuki, Ono Yuki, Kishimoto Shigeru, Ohno Yutaka

APPLIED PHYSICS EXPRESS Vol. 3 ( 11 ) 2010

Language：Japanese Publisher：Applied Physics Express

Medium scale integrated circuits with more than 100 carbon nanotube (CNT) thin-film transistors (TFTs) have been successfully fabricated. These are the largest CNT-based integrated circuits reported so far. Our fabrication technology features a buried back-gate architecture made by CNT growth using plasma-enhanced chemical vapor deposition, chemical doping and enhancement/depletion mode logic gates. High-speed operation with a switching time of 0.51 μs/gate demonstrated by a 53-stage ring oscillator, which has about two orders of magnitude higher switching speed than previous TFT integrated circuits, confirms the suitability of the present TFT technology for implementing CNT-TFT integrated circuits with various functions. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.3.115101

Carrier type conversion in carbon nanotube field-effect transistors caused by interface fixed charges

Ohno Y., Moriyama N., Kitamura T., Suzuki K., Kishimoto S., Mizutani T.

2009 International Semiconductor Device Research Symposium, ISDRS '09 2009.12

A study of preferential growth of carbon nanotubes with semiconducting behavior grown by plasma-enhanced chemical vapor deposition

Mizutani Takashi, Ohnaka Hirofumi, Okigawa Yuki, Kishimoto Shigeru, Ohno Yutaka

JOURNAL OF APPLIED PHYSICS Vol. 106 ( 7 ) 2009.10

Language：Japanese Publisher：Journal of Applied Physics

The electrical properties of carbon nanotubes (CNTs) grown by plasma-enhanced chemical vapor deposition (PECVD) have been studied by measuring the I-V characteristics of many CNT-field effect transistors. The ratio of modulation current to total current was as high as 97%, with a small nondepletable OFF current component. This suggests that CNTs with semiconducting behavior were preferentially grown in the PECVD process. Raman scattering spectroscopy of the PECVD-grown CNTs, however, revealed several peaks of the radial breezing mode, which correspond to the presence of metallic CNTs. Scanning gate microscopy measurement of the CNT-FET with an ON/OFF ratio of 100 revealed the existence of a potential barrier in the metallic CNTs. These results suggest that observation of the preferential growth of CNTs with semiconducting behavior in the CNT-FETs fabricated via the present PECVD process results from the opening of the band gap due to defects caused by irradiation damage during the PECVD growth. © 2009 American Institute of Physics.

DOI： 10.1063/1.3234389

Is vacuum annealing converts p-type single wall carbon nanotube field effect transistor (in air) to n-type (in vacuum) is universally true (?)

Somani P., Kobayashi A., Ohno Y., Kishimoto S., Mizutani T.

Carbon - Science and Technology Vol. 2 ( 2 ) page： 98 - 102 2009.7

Language：Japanese Publisher：Carbon - Science and Technology

Our study on nickel silicide and gold contacted single-wall-carbon-nanotube field effect transistors (SWCN-FETs) is in sharp contrast to earlier published reports of type conversion in SWCN-FETs (from p- to n-) when cycled between air and vacuum, and indicates that (1) band gap of SWCN (2) the extent to which Fermi level of the metal contact gets shifted due to adsorption/desorption of oxygen and (3) relative position of the Fermi level of the metal contact with respect to the top of the valance band of SWCN (in an oxygen-free environment) are some of the important factors that governs such phenomena. © Applied Science Innovations Pvt. Ltd., India.

Electrical properties of carbon nanotube FETs

Mizutani T., Ohno Y., Kishimoto S.

ASDAM 2008 - Conference Proceedings of the 7th International Conference on Advanced Semiconductor Devices and Microsystems page： 1 - 8 2008.12

Language：Japanese Publisher：ASDAM 2008 - Conference Proceedings of the 7th International Conference on Advanced Semiconductor Devices and Microsystems

DOI： 10.1109/ASDAM.2008.4743290

Electrical properties of carbon nanotube FETs

Mizutani T., Ohno Y., Kishimoto S.

Proceedings of SPIE - The International Society for Optical Engineering Vol. 7037 2008.11

Language：Japanese Publisher：Proceedings of SPIE - The International Society for Optical Engineering

The electrical properties of carbon nanotube FETs (CNTFETs) have been studied in detail. The conduction type of the CNTFETs was dependent on the work function of the contact metal, which suggests that Fermi level pinning at the metal/nanotube interface is not strong. Based on the two-probe and four-probe resistance measurements, it has been shown that the carrier transport at the contact is explained by the edge contact model even in the diffusive regime. The chemical doping using F4TCNQ was effective in reducing not only the channel resistance but also the contact resistance. In the CNTFETs fabricated using plasma-enhanced (PE) CVD-grown nanotubes, the drain current of the most of the devices could be modulated by the gate voltage with small OFF current suggesting the preferential growth of the nanotubes with semiconducting behavior. Multichannel top-gate CNTFETs with horizontally-aligned nanotubes as channels have been successfully fabricated using CNT growth on the ST-cut quartz substrate, arc-discharge plasma deposition of the catalyst metal, and ALD gate insulator deposition. The devices show normally-on and n-type conduction property with a relatively-high ON current of 13 mA/mm. CNTFETs with nanotube network have also been fabricated by direct growth on the SiO2/Si substrate using grid-inserted PECVD and using catalyst formed on the channel area of the FETs. The uniformity of the electrical properties of the network channel CNTFETs were very good. Finally, it has been shown that the surface potential profile measurement based on the electrostatic force detection in the scanning probe microscopy was effective in studying the behavior of the CNTFETs such as the transient behavior and the effect of the defects.

DOI： 10.1117/12.794695

High-density horizontally aligned growth of carbon nanotubes with Co nanoparticles deposited by arc-discharge plasma method Open Access

Phokharatkul D., Ohno Y., Nakano H., Kishimoto S., Mizutani T.

APPLIED PHYSICS LETTERS Vol. 93 ( 5 ) 2008.8

Language：Japanese Publisher：Applied Physics Letters

High-density horizontally aligned single-walled carbon nanotubes are grown on a quartz substrate using Co nanoparticles deposited by arc-discharge plasma method. The Co nanoparticles with a density as high as 6.0× 1010 cm-2 are formed by a single pulse of arc discharge at room temperature. The density of the aligned nanotubes is ∼8 μ m-1 in average. Multichannel nanotube field-effect transistors with a high- k top-gate structure are fabricated with aligned nanotubes. The devices show high-performance, normally on, and n -type conduction property without any doping process. A high on current of 1.3 mA and a large transconductance of 0.23 mS for a channel width of 100 μm are obtained. The normally on and n -type property is attributed to fixed positive charges in the Hf O2 gate insulator and at the interfaces. © 2008 American Institute of Physics.

DOI： 10.1063/1.2969290

Fabrication of carbon nanotubes by slot-excited microwave plasma-enhanced chemical vapor deposition

Il Shim Gyu, Kojima Yoshihiro, Kono Satoshi, Ohno Yutaka, Ishijima Tatsuo

JAPANESE JOURNAL OF APPLIED PHYSICS Vol. 47 ( 7 ) page： 5652 - 5655 2008.7

Language：Japanese Publisher：Japanese Journal of Applied Physics

Carbon nanotubes (CNTs) are fabricated by adopting plasma-enhanced chemical vapor deposition (PECVD) with a planar microwave plasma source. Plasma is produced by a slot antenna at 2.45-GHz microwave injection in CH 4/H2 mixture. In this study, it is shown that avoiding the exposure of the substrate to the plasma drastically improves the CNT growth. Furthermore, it is found that the CNT quality can be controlled with the optimization of one of the steps in the catalyst treatment, such as the preheating procedure; the treated catalyst is considered to be unaffected by the heating in the high-density microwave plasma treatment during the CNT growth. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.5652

Photoluminescence in carbon nanotubes : exciton transitions and environmental effects Reviewed Open Access

OHNO Yutaka

Oyo Buturi Vol. 77 ( 6 ) page： 656 - 661 2008.6

Language：Japanese Publisher：The Japan Society of Applied Physics

Carbon nanotubes are promising materials for various applications from electron devices to medical equipment. It is necessary to establish a characterization method for the nanotube materials as well as large scale synthesis technique for stable quality. Photoluminescence (PL) spectroscopy of carbon nanotubes is an important technique in addition to Raman scattering spectroscopy for characterizing nanotube materials. Since the optical properties of nanotubes are strongly affected by environmental conditions around them, it is necessary to understand the environmental effects to establish PL spectroscopy as a useful characterization tool. The environmental effects are mainly caused by the dielectric screening of inter-carrier Coulomb interactions. In addition, mechanical interactions with surrounding materials and the interfacial properties are also involved. Utilizing its sensitivity to the environment, PL is also of interest as a nano-scale sensing tool.

DOI： 10.11470/oubutsu.77.6_656

Electrical properties of carbon nanotube FETs Open Access

Mizutani T., Nosho Y., Ohno Y.

Journal of Physics: Conference Series Vol. 109 ( 1 ) 2008.3

Language：Japanese Publisher：Journal of Physics: Conference Series

DOI： 10.1088/1742-6596/109/1/012002

Potential profile measurement of carbon nanotube FETs based on the electrostatic force detection

Potential profile measurement of carbon nanotube FETs based on the electrostatic force detection

Okigawa Yuki, Umesaka Takeo, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

NANO Vol. 3 ( 1 ) page： 51 - 54 2008.2

Okigawa Y., Umesaka T., Ohno Y., Kishimoto S., Mizutani T.

Nano Vol. 3 ( 1 ) page： 51 - 54 2008.2

Language：Japanese Publisher：Nano

We have measured the potential distribution on carbon nanotube (CNT) field-effect transistors (FETs) using electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KFM). Clearer potential profiles were obtained by EFM than by KFM. When the CNT-FET is in the ON state, the EFM image shows uniform potential distribution along the CNT. In contrast, when the CNT-FET is in the OFF state, nonuniform potential image with dark spots are obtained. The dark spots can be attributed to the defects in the CNTs. © 2008 World Scientific Publishing Company.

DOI： 10.1142/S1793292008000812

AlGaN/GaN MIS-HEMTs with HfO<inf>2</inf> gate insulator

Electrical properties of carbon nanotube FETs

Mizutania T., Ohno Y., Kishimoto S.

ASDAM 2008, CONFERENCE PROCEEDINGS page： 1 - 8 2008

Kawano A., Kishimoto S., Ohno Y., Maezawa K., Mizutani T., Ueno H., Ueda T., Tanaka T.

Physica Status Solidi (C) Current Topics in Solid State Physics Vol. 4 ( 7 ) page： 2700 - 2703 2007.12

Language：Japanese Publisher：Physica Status Solidi (C) Current Topics in Solid State Physics

AlGaN/GaN MIS-HEMTs using HfO2 gate insulator with a large dielectric constant have been fabricated. HfO2 gate insulator was deposited by pulsed laser deposition at room temperature. It has been demonstrated that the HfO2 gate insulator is effective in suppressing the gate leakage current keeping a large transconductance. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssc.200674769

Enhanced 1520 nm photoluminescence from Er3+ ions in di-erbium-carbide metallofullerenes (Er2C2)@C-82 (isomers I, II, and III)

Ito Yasuhiro, Okazaki Toshiya, Okubo Shingo, Akachi Masahiro, Ohno Yutaka, Mizutani Takashi, Nakamura Tetsuya, Kitaura Ryo, Sugai Toshiki, Shinohara Hisanori

ACS NANO Vol. 1 ( 5 ) page： 456 - 462 2007.12

Language：Japanese Publisher：ACS Nano

Di-erbium and di-erbium-carbide endohedral metallofullerenes with a C 82 cage such as Er2@C82 (isomers I, II, and III) and (Er2C2)@C82 (isomers I, II, and III) have been synthesized and chromatographically isolated (99%). The structures of Er2@C82 (I, II, III) and (Er2C 2)@C82 (I, II, III) metallofullerenes are characterized by comparison with the UV-vis-NIR absorption spectra of (Y2C 2)@C82 (I, II, III), where molecular symmetries of the structures are determined to be Cs, C2v and C 3v, respectively. Furthermore, enhanced near-infrared photoluminescence (PL) at 1520 nm from Er3+ ions in Er 2@C82 (I, III) and (Er2C2)@C 82 (I, III) have been observed at room temperature. The PL intensities have been shown to depend on the symmetry of the C82 cage. In particular, the PL intensity of (Er2C2)@C 82 (III) has been the strongest among the isomers of Er 2@C82 and (Er2C2)@C82. Optical measurements indicate that the PL properties of Er2@C 82 (I, II, III) and (Er2C2)@C82 (I, II, III) correlate strongly with the absorbance at 1520 nm and the HOMO-LUMO energy gap of the C82 cage. © 2007 American Chemical Society.

DOI： 10.1021/nn700235z

Excitonic transition energies in single-walled carbon nanotubes: Dependence on environmental dielectric constant

Ohno Yutaka, Iwasaki Shinya, Murakami Yoichi, Kishimoto Shigeru, Maruyama Shigeo, Mizutani Takashi

PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS Vol. 244 ( 11 ) page： 4002 - 4005 2007.11

Language：Japanese Publisher：Physica Status Solidi (B) Basic Research

The dependence of optical transition energies in single-walled carbon nanotubes (SWNTs) on environmental dielectric constant (εenv) have been investigated in the range of εenv from 1.0 to 37, by immersing SWNTs bridged overtrenches in various organic solvents by means of photoluminescence (PL) and the excitation spectroscopies. With increasing εenv, both E11 and E22 exhibited a redshift by several tens meV and a tendency to saturate at a εenv ∼ 5 without an indication of significant (n,m) dependence. The redshifts can be explained by dielectric screening of the repulsive electron-electron interaction. We have also investigated the time-resolved PL in air and in solvent, respectively, utilizing the excitation intensity correlation technique. When the sample was immersed in solvent, the correlation signal collapsed, and the decay time decrease as compared to in air. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/pssb.200776124

The effects of chemical doping with F(4)TCNQ in carbon nanotube field-effect transistors studied by the transmission-line-model technique

Nosho Y., Ohno Y., Kishimoto S., Mizutani T.

NANOTECHNOLOGY Vol. 18 ( 41 ) 2007.10

Language：Japanese Publisher：Nanotechnology

We have studied the effects of p-type chemical doping with F 4TCNQ (tetrafluorotetracyano-p-quinodimethane) in carbon nanotube field-effect transistors (CNFETs). The transmission-line-model technique using multi-probe CNFETs has been employed to investigate the effects of chemical doping on the channel resistance and contact resistance. It has been found that chemical doping is effective in the reduction of the contact resistance as well as the channel resistance. The device performances of top-gate CNFETs such as transconductance, on-resistance, and on/off ratio were improved by the F 4TCNQ chemical doping on the access regions. © IOP Publishing Ltd.

DOI： 10.1088/0957-4484/18/41/415202

Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials Open Access

Miyauchi Y., Saito R., Sato K., Ohno Y., Iwasaki S., Mizutani T., Jiang J., Maruyama S.

CHEMICAL PHYSICS LETTERS Vol. 442 ( 4-6 ) page： 394 - 399 2007.7

Language：Japanese Publisher：Chemical Physics Letters

We theoretically investigate the environmental effect for optical transition energies of single-walled carbon nanotubes (SWNTs), by calculating the exciton transition energies of SWNTs. The static dielectric constants used in the exciton calculation can be expressed as a function of the dielectric constants of the surrounding material and that of the SWNT, in which the static and dynamic dielectric constants of the SWNT represent the screening effect of core electrons and the valence π electrons, respectively. The calculated results reproduce the environmental effect of the experimental transition energies for various surrounding materials and for various diameters of SWNTs. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.cplett.2007.06.018

Evidence of edge conduction at nanotube/metal contact in carbon nanotube devices

Nosho Yosuke, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 46 ( 17-19 ) page： L474 - L476 2007.5

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 2: Letters

We have investigated the current flow path between the nanotube and the contact electrode in carbon nanotube devices using multiprobe devices. The contact and channel resistances have been evaluated by two methods; transmission-line-model technique and four-probe measurement. By comparing the results, we have found that channel resistance evaluated by the four-probe measurement includes contact resistance. This indicates that the widely used four-probe measurement is not applicable to nanotube devices for the evaluation of channel resistance excluding contact resistance. This finding also implies that electron transport between the nanotube and the contact metal occurs at the edge of the contact electrode. ©2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.L474

Surface potential measurement of carbon nanotube field-effect transistors using Kelvin probe force microscopy

Umesaka Takeo, Ohnaka Hirofumi, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 46 ( 4B ) page： 2496 - 2500 2007.4

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

The surface potential of carbon nanotube field-effect transistors (CNT-FETs) was measured using Kelvin probe force microscopy (KFM). A clear potential image of the CNT channel with a diameter of 1.1 nm was obtained by measurement in air. The measured potential image was dependent on the sequence of the gate bias, and showed transient behavior with a time constant of several tens of minutes. These behaviors were consistent with the drain current transient and the hysteresis of the current-voltage characteristic of the CNT-FETs. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.2496

Interfacial Property of Metal/Nanotube Contacts in Carbon Nanotube Transistors

(解説)カーボンナノチューブの光電子機能デバイス応用

大野雄高

マテリアルステージ 7 page： 33 2007

(解説)カーボンナノチューブトランジスタにおける電極界面の特性 Reviewed

大野雄高

表面科学 28 page： 40 2007

Fabrication process of carbon nanotube FETs using ALD passivation for biosensors

Nakashima Y., Ohno Y., Kishimoto S., Okochi M., Honda H., Mizutani T.

MICROPROCESSES AND NANOTECHNOLOGY 2007, DIGEST OF PAPERS page： 488 - + 2007

OHNO Yutaka, NOSHO Yosuke, MIZUTANI Takashi

Hyomen Kagaku Vol. 28 ( 1 ) page： 40 - 45 2007

Language：Japanese Publisher：The Surface Science Society of Japan

It is important to understand the interfacial properties of the nanotube/metal contacts because, in the case of carbon nanotube field-effect transistors (NT-FETs), the FET action is dominated by the Schottky barrier formed at the interface of the source contact. In this study, we have studied the interfacial properties from the electrical characterization of NT-FETs. First, the conduction pass in the vicinity of the contact electrodes has been investigated using a multi-terminal device. Then, the relation between conduction property of NT-FETs and work function of the contact metals has been investigated. The interfacial band structure has been discussed in terms of the temperature dependence of the drain current.

DOI： 10.1380/jsssj.28.40

Relation between conduction property and work function of contact metal in carbon nanotube field-effect transistors

Nosho Y., Ohno Y., Kishimoto S., Mizutani T.

NANOTECHNOLOGY Vol. 17 ( 14 ) page： 3412 - 3415 2006.7

Language：Japanese Publisher：Nanotechnology

We have investigated the relation between the conduction property and the work function of the contact metal in carbon nanotube field-effect transistors (NTFETs). The conduction type and the drain current are dependent on the work function. In contrast to NTFETs with Ti and Pd contact electrodes, which showed p-type conduction behaviour, devices with Mg contact electrodes showed ambipolar characteristics and most of the devices with Ca contact electrodes showed n-type conduction behaviour. This indicates that the barrier height of the metal/nanotube contact is dependent on the work function of the contact metal, which suggests that the Fermi-level pinning is weak at the interface, in contrast to conventional semiconductors such as Si and GaAs. We have also demonstrated nonlinear rectification current-voltage characteristics in a nanotube quasi-pn diode with no impurity doping, in which different contact metals with different work functions are used for the anode and the cathode. © 2006 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/17/14/011

Chirality-dependent environmental effects in photoluminescence of single-walled carbon nanotubes

Ohno Yutaka, Iwasaki Shinya, Murakami Yoichi, Kishimoto Shigeru, Maruyama Shigeo, Mizutani Takashi

PHYSICAL REVIEW B Vol. 73 ( 23 ) 2006.6

Language：Japanese Publisher：Physical Review B - Condensed Matter and Materials Physics

The optical transition energies, E11 and E22, of single-walled carbon nanotubes (SWNTs) suspended in air have been investigated for 20 species by photoluminescence and excitation spectroscopies. We have studied the environmental effects in photoluminescence by comparing our results with those for the SWNTs wrapped by sodium-dodecyl-sulfate (SDS), as reported by Weisman and Bachilo [Nano Lett. 3, 1235 (2003)]. The energy differences between air-suspended and SDS-wrapped SWNTs, Δ Eii = E ii air - E ii SDS, depends on the chiral vector (n,m), specifically on the chiral angle and type of SWNT (type I or type II). The Δ E11 and Δ E22 mostly blueshifted, with the exception of the Δ E22 of some type II SWNTs (that have a small chiral angle), which redshifted. With an increase in the chiral angle, the Δ E11 increased in type I SWNTs and decreased in type II SWNTs. In contrast, the Δ E22 demonstrated opposite dependence on the chiral angle. The differences in Δ E11 and Δ E22 between type I and type II disappeared in the SWNTs with chiral angles close to 30° (near armchair). The (n,m) dependence of the environmental effect on the transition energies can be explained by the difference in the effective mass, which contributes to the energy of Coulomb interactions between carriers. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevB.73.235427

Fabrication of carbon nanotube field effect transistors using plasma-enhanced chemical vapor deposition grown nanotubes

Ohnaka Hirofumi, Kojima Yoshihiro, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 6B ) page： 5485 - 5489 2006.6

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

Single-walled carbon nanotubes are grown using grid-inserted plasma-enhanced chemical vapor deposition (PECVD). The field effect transistor operation was confirmed using the PECVD grown carbon nanotubes (CNTs). The preferential growth of the semiconducting nanotubes was confirmed in the grid-inserted PECVD by measuring current-voltage (1-V) characteristics of the devices. Based on the measurement of the electrical breakdown of the metallic CNTs, the probability of growing the semiconducting nanotubes has been estimated to be more than 90%. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.5485

Fabrication of antigen sensors using carbon nanotube field effect transistors

Tani Kentaro, Ito Hiroshi, Ohno Yutaka, Kishimoto Shigeru, Okochi Mina, Honda Hiroyuki, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 6B ) page： 5481 - 5484 2006.6

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

Antigen sensors using carbon nanotube field effect transistors (CNT-FETs) were fabricated. In order to avoid the problem of exposing source and drain electrodes directly to the phosphate buffered saline (PBS) solution, source and drain electrodes were covered with evaporated SiO film. The immobilization of antibodies on the device surface was confirmed by the observation of fluorescence. Drain current in the sensor device was decreased by the antibody-antigen binding, which suggests a potential use of CNT-FETs as antigen sensors. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.5481

Suppression of hysteresis in carbon nanotube field-effect transistors: Effect of contamination induced by device fabrication process

Shimauchi Hideki, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 6B ) page： 5501 - 5503 2006.6

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

We have statistically studied the suppression of hysteresis in carbon nanotube field-effect transistors. The effect of the device fabrication process on the hysteresis has been investigated. The results show that contamination induced by the fabrication process impedes the suppression of hysteresis in device passivation. To remove the contamination, we have introduced a cleaning process as a treatment before passivation. The effectiveness of passivation with polymethylmetacrylate has been improved by the cleaning process using H 2SO4/H2O2 solution. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.5501

AIGaN/GaN high electron mobility transistors with inclined-gate-recess structure

Aoi Y., Ohno Y., Kishimoto S., Maezawa K., Mizutani T.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers Vol. 45 ( 4 B ) page： 3368 - 3371 2006.4

Language：Japanese Publisher：Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers

We have studied an inclined-gate-recess structure in order to clarify the effect of increasing the electric field in the channel. Two-dimensional device simulation has revealed that the electric field and the electron velocity in the channel have increased by the inclined-gate-recess structure, which leads to an improvement of gm. AlGaN/GaN high electron mobility transistors (HEMTs) with inclined-gate-recess have been fabricated. Improved gm and fT have been obtained, which confirms the importance of increasing the electric field in the channel. © 2006 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.45.3368

Photoluminescence of single-walled carbon nanotubes in field-effect transistors

AlGaN/GaN high electron mobility transistors with inclined-gate-recess structure

Aoi Yuma, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 45 ( 4B ) page： 3368 - 3371 2006.4

Ohno Y, Kishimoto S, Mizutani T

NANOTECHNOLOGY Vol. 17 ( 2 ) page： 549 - 555 2006.1

Language：Japanese Publisher：Nanotechnology

We have studied the photoluminescence (PL) of individual single-walled carbon nanotubes (SWNTs) placed in field-effect transistor structures. The SWNTs were suspended in the air so that strong PL was obtained. When an external bias voltage was applied to the device, no spectral changes could be detected, but the intensity drastically increased or decreased. This behaviour is explained by the injection/extraction of carriers from/to the electrodes by the electric field. In the case of p-type FETs in the air, PL intensity increased due to hole injection by applying a small negative gate bias. After the device was heated in vacuum, the maximum PL intensity was obtained at zero gate bias. This can be explained by the change in the interface between the SWNT and contact electrodes. The drain field dependence of the PL intensity shows a monotonic decrease, which is explained by a competition between the recombination lifetime and transit time of photo-excited carriers in the SWNT. Using analytical steady-state rate equations on carrier density in the SWNT, the relation between the recombination lifetime and carrier transit time has been evaluated. The carrier saturation velocity has also been estimated. © 2006 IOP Publishing Ltd.

DOI： 10.1088/0957-4484/17/2/035

AlGaN/GaN MIS-HEMTs with ZrO<inf>2</inf> gate insulator

(解説)カーボンナノチューブのフォトルミネッセンス

大野雄高

ナノ学会会報 4 page： 67 2006

27aUA-1 Chirality-dependent environmental effect on photoluminescence in carbon nanotubes Open Access

Ohno Y., Iwasaki S., Murakami Y., Kishimoto S., Maruyama S., Mizutani T.

Meeting Abstracts of the Physical Society of Japan Vol. 61.1.4 ( 0 ) page： 805 2006

Sugimoto T., Ohno Y., Kishimoto S., Maezawa K., Osaka J., Mizutani T.

Institute of Physics Conference Series Vol. 184 page： 279 - 282 2005.12

Language：Japanese Publisher：Institute of Physics Conference Series

AlGaN/GaN MIS-HEMTs using ZrO2 gate insulator with a large dielectric constant have been successfully fabricated. The gate leakage current decreased by more than three orders of magnitude compared to that of the conventional AlGaN/GaN HEMTs without the ZrO2 gate insulator. Current collapse has also been suppressed in the MIS-HEMTs. The decrease in g mmax, which was observed in the case of Si3N4 MIS-HEMTs, was suppressed in the present MIS-HEMTs demonstrating the effectiveness of the ZrO2 gate insulator. © 2005 IOP Publishing Ltd.

Electron traps in AlGaN/GaN MIS-HEMTs observed by drain current DLTS

Okino T., Ohno Y., Kishimoto S., Maezawa K., Osaka J., Mizutani T.

Institute of Physics Conference Series Vol. 184 page： 271 - 274 2005.12

Surface potential transient of AlGaN/GaN HEMTs measured by Kelvin probe force microscopy

Nakagami K., Ohno Y., Kishimoto S., Maezawa K., Mizutani T.

Institute of Physics Conference Series Vol. 184 page： 275 - 278 2005.12

Language：Japanese Publisher：Institute of Physics Conference Series

Surface potential of the AlGaN/GaN high-electron-mobility transistors was measured by Kelvin probe force microscopy to study the mechanism of the drain current collapse. The potential after the gate bias stress increased due to the emission of trapped electrons from the surface states. The time constant of the potential increase was 75 s, which was comparable to that of the drain current recovery from the collapsed level. © 2005 IOP Publishing Ltd.

Deep levels in n-type AlGaN grown by hydride vapor-phase epitaxy on sapphire characterized by deep-level transient spectroscopy

Osaka J, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

APPLIED PHYSICS LETTERS Vol. 87 ( 22 ) page： 1 - 3 2005.11

Language：Japanese Publisher：Applied Physics Letters

Deep levels in unintentionally doped n -type Al0.09 Ga0.91 N and Al0.17 Ga0.83 N films grown on sapphire by hydride vapor-phase epitaxy were characterized using capacitance deep-level transient spectroscopy and were compared to the reported electron traps in GaN grown by various techniques. It was shown that at least three dominant deep levels exist in each sample. The Al mole fraction dependence of their activation energy suggested that each of these three levels has the same origin as the three dominant well known point-defect-related deep levels in GaN, respectively. It is thought that deep levels in GaN change their electric characteristics in low Al content AlGaN. © 2005 American Institute of Physics.

DOI： 10.1063/1.2137901

Direct integration of GaAsHEMTs on AlN ceramic substrates using fluidic self-assembly

Soga I, Hayashi S, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

ELECTRONICS LETTERS Vol. 41 ( 23 ) page： 1275 - 1276 2005.11

Language：Japanese Publisher：Electronics Letters

Direct integration of AlGaAs/GaAs HEMTs on AlN ceramic substrates has been demonstrated based on the fluidic self-assembly (FSA) technology. The FSA is a unique technology to arrange small device blocks (around a few tens of microns) onto the other substrates. With this technology the core part of the HEMT having no pad can be mounted on the ceramic substrate. The HEMT core can then be connected electrically with the circuit on a ceramic substrate using a planar wiring process. This eliminates large stray capacitance and inductance in the conventional technology. It has been demonstrated that the good FET characteristics are obtained even after FSA process. © IEE 2005.

DOI： 10.1049/el:20052840

Metamorphic Resonant Tunneling Diodes and Its Application to Chaos Generator ICs

Maezawa Koichi, Iwase Takashi, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi, Sano Kimikazu, Takakusaki Misao, Nakata Hirofumi

Japanese Journal of Applied Physics Vol. 44 ( 7A ) page： 4790 - 4794 2005.7

Language：Japanese Publisher：The Japan Society of Applied Physics

In this paper we discuss the properties of InGaAs/AlAs metamorphic resonant tunneling diodes (RTDs) on GaAs substrates. The current–voltage, surface roughness, and low-frequency noise characteristics were investigated to clarify the effect of step-grading buffer layers. No degradation of the current–voltage characteristics were observed despite the large surface roughness due to a lattice mismatch. Moreover, low-frequency noise measurements showed only 1⁄f noise without special peak structures, and the amplitudes of which were comparable to those of the lattice-matched ones. Next, we fabricated resonant tunneling frequency divider ICs, which is based on the bifurcation phenomenon in a chaos system, on metamorphic substrates. A maximum operation frequency of 88 GHz and good phase noise properties were obtained, which are similar to those of the lattice-matched ones. These results demonstrate the effectiveness of the step-grading buffer layers even for the RTDs that consist of very thin layers and are sensitive to crystal qualities.

DOI： 10.1143/JJAP.44.4790

Effects of Fabrication Process on Current-Voltage Characteristics of Carbon Nanotube Field Effect Transistors

Mizutani Takashi, Iwatsuki Shinya, Ohno Yutaka, Kishimoto Shigeru

Japanese Journal of Applied Physics Vol. 44 ( 4A ) page： 1599 - 1602 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

The effects of the fabrication process on the current–voltage (I–V) characteristics of carbon nanotube field effect transistors (CNT-FETs) were studied in detail. A large hysteresis observed in the I–V characteristics of the CNT-FETs having no passivation film became small by passivating the device surface with a SiNx film. The conduction behaivior of the CNT-FETs changed from p-type to ambipolar characteristics by SiNx passivation. Ambipolar characteristics were also observed in the top-gate CNT-FETs with a gate-source spacing of 2 μm.

DOI： 10.1143/JJAP.44.1599

Growth of mm-Long Carbon Nanotubes by Grid-Inserted Plasma-Enhanced Chemical Vapor Deposition Open Access

Kishimoto Shigeru, Kojima Yoshihiro, Ohno Yutaka, Sugai Toshiki, Shinohara Hisanori, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 4A ) page： 1554 - 1557 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Vertically aligned long multi-walled carbon nanotubes (MWNTs) have been successfully grown by grid-inserted plasma-enhanced chemical vapor deposition (PECVD). A thin Fe (1 nm)/Ti (1 nm) double-layer catalyst was effective in growing the long MWNTs. The length of the MWNTs increased to 1 mm for the growth time of 120 min without growth termination. A thick Fe catalyst or thick Ti underlayer resulted in a low growth rate. Transmission electron microscopy, energy-dispersive X-ray analysis and thermo-gravimetric analysis (TGA) measurements suggest that the MWNTs were grown in a root growth mode. Moreover, the TGA measurements suggest that MWNTs of high quality/purity were successfully grown by grid-inserted PECVD with a double-layer catalyst.

DOI： 10.1143/JJAP.44.1554

Growth of High-Quality Carbon Nanotubes by Grid-Inserted Plasma-Enhanced Chemical Vapor Deposition for Field Emitters

Kojima Yoshihiro, Kishimoto Shigeru, Ohno Yutaka, Sakai Akira, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 4B ) page： 2600 - 2603 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

The effect of a grid inserted between the anode and the cathode in plasma-enhanced chemical vapor deposition (PECVD) on carbon nanotube (CNT) growth was studied. The optimum grid-cathode distance and grid-cathode voltage were 4 mm and 2–10 V, respectively. Long small-diameter nanotubes were grown under these conditions. The smallest nanotube diameter obtained was 3 nm. However, when the grid-cathode voltage was higher than 10 V, short large-diameter nanotubes were grown. The field emission characteristics of CNTs with a low ON voltage and a high current density were explained by Fowler-Nordheim (FN) tunneling.

DOI： 10.1143/JJAP.44.2600

Photoresponse of Carbon Nanotube Field-Effect Transistors

Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 4A ) page： 1592 - 1595 2005.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Photoresponse of carbon nanotube field-effect transistors (FETs) is investigated using microscopic measurements. The nanotube FETs, with an isolated single-walled carbon nanotube (SWNT) for the channel, were fabricated by means of the position-controlled nanotube growth technique. An increase in the off-state current and the threshold-voltage shift of the FET were caused by laser illumination. The increase in the off-state current is attributed to photocurrent due to carriers excited in the SWNT channel. The excitation spectrum of the photocurrent had a peak corresponding to optical absorption by the third interband gap of the van Hove singularity of the semiconducting SWNT with a diameter of ∼2 nm. The photocurrent increased in proportion to incident laser power with a dynamic range over four orders of magnitude. The external quantum efficiency was 2×10−7. An inverter action to optical-signal input was observed near the threshold voltage of the FET. The responsivity was as high as 2×10−3 A/W for a single SWNT channel. This high responsivity is explained by the field-effect amplification phenomenon.

DOI： 10.1143/JJAP.44.1592

n-Type carbon nanotube field-effect transistors fabricated by using Ca contact electrodes Open Access

Nosho Y, Ohno Y, Kishimoto S, Mizutani T

APPLIED PHYSICS LETTERS Vol. 86 ( 7 ) 2005.2

Synthesis of carbon nanotube peapods directly on Si substrates Open Access

Ohno Y, Kurokawa Y, Kishimoto S, Mizutani T, Shimada T, Ishida M, Okazaki T, Shinohara H, Murakami Y, Maruyama S, Sakai A, Hiraga K

APPLIED PHYSICS LETTERS Vol. 86 ( 2 ) 2005.1

Tunable Field-Effect Transistor Device with Metallofullerene Nanopeapods

Shimada Takashi, Ohno Yutaka, Suenaga Kazutomo, Okazaki Toshiya, Kishimoto Shigeru, Mizutani Takashi, Taniguchi Risa, Kato Haruhito, Cao Baopeng, Sugai Toshiki, Shinohara Hisanori

Japanese Journal of Applied Physics Vol. 44 ( 1A ) page： 469 - 472 2005.1

Language：Japanese Publisher：The Japan Society of Applied Physics

A fine tuning of the band gap of single-wall carbon nanotubes (SWNTs) has been achieved by filling various types of endohedral metallofullerenes into the SWNTs, the so-called nanopeapods. We report various electronic transport properties of fullerene peapods used as the channels of field-effect transistors (FETs) and demonstrate that the metallofullerene peapods can provide the tunable band gaps of the FET channels depending on the type of metallofullerene inserted in the SWNTs. All of the metallofullerene peapods FETs exhibit p- and n-type, the so-called ambipolar carrier transportation by variable gate bias. The ranges of the off state regions of the FET fabricated highly sensitivity with respect to the amount of charge transfer in metallofullerenes, which results in band-gap engineering. Metallofullerene peapods can be used to manipulate the electronic structure of SWNTs in nanometer scale. In such a highly functionalized SWNT, metallofullerene peapods, might be a key material for fabricating and developing sophisticated electronic devices in the future.

DOI： 10.1143/JJAP.44.469

Fabrication and Characterization of Peapod Field-Effect Transistors Using Peapods Synthesized Directly on Si Substrate

AlGaN/GaN MIS-HEMTs with ZrO2 gate insulator

Sugimoto T, Ohno Y, Kishimoto S, Maezawa K, Osaka J, Mizutani T

COMPOUND SEMICONDUCTORS 2004, PROCEEDINGS Vol. 184 page： 279 - 282 2005

Electron traps in AlGaN/GaN MIS-HEMTs observed by drain current DLTS

Okino T, Ohno Y, Kishimoto S, Maezawa K, Osaka J, Mizutani T

COMPOUND SEMICONDUCTORS 2004, PROCEEDINGS Vol. 184 page： 271 - 274 2005

Kurokawa Yuto, Ohno Yutaka, Shimada Takashi, Ishida Masashi, Kishimoto Shigeru, Okazaki Toshiya, Shinohara Hisanori, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 44 ( 42-45 ) page： L1341 - L1343 2005

Language：Japanese Publisher：The Japan Society of Applied Physics

We have successfully fabricated carbon nanopeapod field-effect transistors (FETs) using peapods synthesized directly on a SiO2/Si substrate. Single-walled carbon nanotubes (SWNTs) for pods were synthesized on the substrate by utilizing position-controlled chemical vapor deposition. The end caps of the SWNTs were removed by oxidation by baking in air. Insertion of fullerenes into the cap-opened SWNTs was performed by the vapor phase doping method. Fabricated Gd@C82 peapod FETs showed ambipolar characteristics. We have estimated the bandgap of the Gd@C82 peapod to be ∼100 meV from the temperature dependence of the drain current.

DOI： 10.1143/JJAP.44.L1341

Fabrication and characterization of carbon nanotube FETs

Mizutani T, Ohno Y

QUANTUM SENSING AND NANOPHOTONIC DEVICES II Vol. 5732 page： 28 - 36 2005

Origin of the 2450 cm(-1) Raman bands in HOPG, single-wall and double-wall carbon nanotubes

Shimada T, Sugai T, Fantini C, Souza M, Cancado LG, Jorio A, Pimenta MA, Salto R, Gruneis A, Dresselhaus G, Dresselhaus MS, Ohno Y, Mizutani T, Shinohara H

CARBON Vol. 43 ( 5 ) page： 1049 - 1054 2005

Surface potential transient of AlGaN/GaN HEMTs measured by Kelvin probe force microscopy

Nakagami K, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

COMPOUND SEMICONDUCTORS 2004, PROCEEDINGS Vol. 184 page： 275 - 278 2005

Surface potential measurements of AlGaN/GaN high-electron-mobility transistors by Kelvin probe force microscopy

Nakagami K, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

APPLIED PHYSICS LETTERS Vol. 85 ( 24 ) page： 6028 - 6029 2004.12

Fluid Dynamic Assembly of Semiconductor Blocks for Heterogeneous Integration

Soga Ikuo, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 43 ( 9A ) page： 5951 - 5954 2004.9

Language：Japanese Publisher：The Japan Society of Applied Physics

We have studied the fluidic assembly (FA) technique for heterogeneous integration. In this technique, device blocks, the size of which ranges from a few tens of microns to a few hundreds of microns, are arranged onto another material substrate in fluid. Here, we propose a novel technique to improve FA, called fluid dynamic assembly (FDA), which employs fluid dynamic effects. In the FDA, a special structure is fabricated on the block, which stabilizes the posture of the blocks falling in the fluid. This can be used to control the face of assembled blocks. In this paper, the feasibility of the FDA is discussed on the basis of fluid dynamic simulation and experiments. The numerical simulations revealed that the face control can be carried out for the block having ringlike (O-type) structures on it. Then we carried out the FDA experiments using thin disk-shaped GaAs blocks with O-type structure, and demonstrated an 87% face control ratio for the blocks with 7.5-μm-thick structure. Moreover, the less symmetric C-type structure was examined, and demonstrated even a high face control ratio of 96%.

DOI： 10.1143/JJAP.43.5951

Direct Observation of High-Frequency Chaos Signals from the Resonant Tunneling Chaos Generator

Maezawa Koichi, Kawano Yoichi, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 43 ( 8A ) page： 5235 - 5238 2004.8

Language：Japanese Publisher：The Japan Society of Applied Physics

The direct observation of the chaos signal patterns in a microwave frequency range was demonstrated on the resonant tunneling chaos generator circuit. It is difficult to observe such high-frequency chaos because one must use a sampling oscilloscope. To overcome this problem, we devised a special circuit controlling the chaos to output identical signals repeatedly. This permits us to observe (seemingly)random patterns. This control scheme may lead to various applications.

DOI： 10.1143/jjap.43.5235

Fabrication Technique for Carbon Nanotube Single-Electron Transistors Using Focused Ion Beam

Kurokawa Yuto, Ohno Yutaka, Kishimoto Shigeru, Okazaki Toshiya, Shinohara Hisanori, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 43 ( 8A ) page： 5669 - 5670 2004.8

Language：Japanese Publisher：The Japan Society of Applied Physics

We have proposed a technique for fabricating carbon nanotube single-electron transistors using a focused ion beam (FIB). Wiring to a multiwalled carbon nanotube was formed by the ion-beam-assisted deposition of tungsten. Tunneling barriers were formed in the nanotube by ion beam etching. A drain current oscillation originating from the Coulomb blockade effect was observed at 23 K.

DOI： 10.1143/JJAP.43.5669

Fabricated on a GaAs-based Semiconductor-on-Insulator Substrate Using a Spin-On Low-k Dielectric Film

Drain current DLTS of AlGaN-GaN MIS-HEMTs

Okino T, Ochiai A, Ohno Y, Kishimoto S, Maezawa K, Mizutani I

IEEE ELECTRON DEVICE LETTERS Vol. 25 ( 8 ) page： 523 - 525 2004.8

Double-wall carbon nanotube field-effect transistors: Ambipolar transport characteristics Open Access

Shimada T, Sugai T, Ohno Y, Kishimoto S, Mizutani T, Yoshida H, Okazaki T, Shinohara H

APPLIED PHYSICS LETTERS Vol. 84 ( 13 ) page： 2412 - 2414 2004.3

Effects of surface passivation on breakdown of AlGaN/GaN high-electron-mobility transistors Open Access

Ohno Y, Nakao T, Kishimoto S, Maezawa K, Mizutani T

APPLIED PHYSICS LETTERS Vol. 84 ( 12 ) page： 2184 - 2186 2004.3

Transport properties of C-78, C-90 and Dy@C-82 fullerenes-nanopeapods by field effect transistors

Shimada T, Ohno Y, Okazaki T, Sugai T, Suenaga K, Kishimoto S, Mizutani T, Inoue T, Taniguchi R, Fukui N, Okubo H, Shinohara H

PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES Vol. 21 ( 2-4 ) page： 1089 - 1092 2004.3

Chirality assignment of individual single-walled carbon nanotubes in carbon nanotube field-effect transistors by micro-photocurrent spectroscopy Open Access

Ohno Y, Kishimoto S, Mizutani T, Okazaki T, Shinohara H

APPLIED PHYSICS LETTERS Vol. 84 ( 8 ) page： 1368 - 1370 2004.2

Drain current DLTS of AlGaN/GaN HEMTs

Mizutani T, Okino T, Kawada K, Ohno Y, Kishimoto S, Maezawa K

PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE Vol. 200 ( 1 ) page： 195 - 198 2003.11

Sato Kuninori, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 42 ( 11 ) page： 6839 - 6840 2003.11

Language：Japanese Publisher：The Japan Society of Applied Physics

We proposed and successfully fabricated a GaAs-based semiconductor-on-insulator (SOI) metal–semiconductor-filed-effect-transistor (MESFET) using a low-temperature wafer-bonding technique with a spin-on low-k dielectric film, FOx, as a bonding layer. In this structure, the channel is isolated from the semi-insulating (SI) GaAs substrate by a FOx layer. The fabricated 1-μm-gate-length SOI MESFETs showed good pinch-off and saturation characteristics. One of the most important improvements expected for this structure is a reduction of the drain-source capacitance, CDS, which dominates the microwave switching property (on/off ratio). It was demonstrated that the CDS of the SOI MESFET is much smaller than that of the conventional GaAs MESFET. It was also confirmed that the drain current of the SOI MESFET is negligibly affected by the side-gate voltage.

DOI： 10.1143/JJAP.42.6839

Experimental Demonstration of Capacitor-Coupled Resonant Tunneling Logic Gates for Ultra-short Gate-delay Operation

Tanaka Tetsuro, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 42 ( 11 ) page： 6766 - 6771 2003.11

Language：Japanese Publisher：The Japan Society of Applied Physics

The capacitor-coupled monostable-bistable transition logic element (C2MOBILE) is an extension of the high-speed logic gate MOBILE based on the negative differential resistance of the resonant tunneling diodes. The C2MOBILE uses a transient current through the coupling capacitor to transmit signals between gates, and is expected to operate with an extremely short gate delay time. In this paper, basic operations of the C2MOBILE are demonstrated with the circuits fabricated on InP substrates. The circuits tested here are the 2- and 3-stage logic circuits and the AND/OR gate. The gate delay time was estimated to be around 1 ps for these circuits. A much shorter gate delay time close to 100 fs should be possible with the sophisticated circuit design and fabrication process.

DOI： 10.1143/JJAP.42.6766

Position-Controlled Carbon Nanotube Field-Effect Transistors Fabricated by Chemical Vapor Deposition Using Patterned Metal Catalyst

88 GHz dynamic 2 : 1 frequency divider using resonant tunnelling chaos circuit

Kawano Y, Ohno Y, Kishimoto S, Maezawa K, Mizutani T, Sano K

ELECTRONICS LETTERS Vol. 39 ( 21 ) page： 1546 - 1548 2003.10

A study on current collapse in AlGaN/GaN HEMTs induced by bias stress

Mizutani T, Ohno Y, Akita M, Kishimoto S, Maezawa K

IEEE TRANSACTIONS ON ELECTRON DEVICES Vol. 50 ( 10 ) page： 2015 - 2020 2003.10

Ohno Yutaka, Iwatsuki Shinya, Hiraoka Tatsuki, Okazaki Toshiya, Kishimoto Shigeru, Maezawa Koichi, Shinohara Hisanori, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 42 ( 6B ) page： 4116 - 4119 2003.6

Language：Japanese Publisher：The Japan Society of Applied Physics

Position-controlled carbon nanotube field effect transistors (FETs) have been fabricated by using patterned catalysts and chemical vapor deposition. A double-layer metal of platinum and cobalt was used as the catalyst. The use of a mixture of ethanol and argon as the source gas was effective for obtaining FETs with good characteristics. Coulomb oscillation was observed at room temperature. 76% of the fabricated devices showed FET operation. The characteristics of FETs with metallic nanotubes were improved by applying a high voltage.

DOI： 10.1143/JJAP.42.4116

AlGaN/GaN Heterostructure Metal-Insulator-Semiconductor High-Electron-Mobility Transistors with Si3N4 Gate Insulator

Ochiai Masaru, Akita Mitsutoshi, Ohno Yutaka, Kishimoto Shigeru, Maezawa Kouichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 42 ( 4B ) page： 2278 - 2280 2003.4

Language：Japanese Publisher：The Japan Society of Applied Physics

AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) using Si3N4 film as a gate insulator have been successfully fabricated. The gate leakage current decreased by about three orders of magnitude compared to that of the conventional AlGaN/GaN HEMTs without the Si3N4 gate insulator. The low-frequency noise of the MIS-HEMTs was smaller than that of the conventional HEMTs. Current collapse has also been suppressed in the MIS-HEMTs.

DOI： 10.1143/JJAP.42.2278

Characterization of Electrical Properties of Micro-Schottky Contacts on Epitaxial Lateral Overgrowth GaN

Kumada Keiichiro, Murata Tomohiro, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi, Sawaki Nobuhiko

Japanese Journal of Applied Physics Vol. 42 ( 4B ) page： 2250 - 2253 2003.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Current-voltage characteristics of micro-Schottky contacts fabricated on Epitaxial lateral overgrowth (ELO) GaN have been measured. The obtained characteristics are classified into two groups; good contacts with small ideality factor (n-value) and poor contacts with large n-value. By comparing the distribution of I-V characteristics of the micro-Schottky contact array with the distribution of dislocations revealed by molten KOH etching, it was concluded that the dislocations are not responsible for the poor I-V characteristics of the Schottky contacts. Regarding the origin of the poor I-V characteristics, the high doping density area formed at the top surface of the as-grown wafer was suggested.

DOI： 10.1143/JJAP.42.2250

Fluidic Assembly of Thin GaAs Blocks on Si Substrates

Soga Ikuo, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 42 ( 4B ) page： 2226 - 2229 2003.4

Language：Japanese Publisher：The Japan Society of Applied Physics

We have studied the fluidic assembly technique for heterogeneous integration. In this technique, small device blocks, the size of which ranges from a few tens of microns to a few hundreds of microns, can be assembled into the recesses formed on the Si substrate. First, we used thin disk-shaped GaAs blocks to study the fundamental process of the fluidic assembly. A 100% yield was achieved with an appropriate strength of sonic vibration. The assembled blocks were confirmed to have no strain by using Raman scattering spectroscopy even if they were annealed at 320°C for 30 min. In addition, the effects of the shape of blocks are discussed based on the experimental results for disk- and square-shaped blocks.

DOI： 10.1143/JJAP.42.2226

Comparison of Electrical Characteristics of Metamorphic HEMTs with InP HEMTs and PHEMTs

Kawada Kenji, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi, Takakusaki Misao, Nakata Hirofumi

Japanese Journal of Applied Physics Vol. 42 ( 4B ) page： 2219 - 2222 2003.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors (MHEMTs) were fabricated on GaAs substrates. A step-graded InAlAs buffer layer was used to relax the lattice mismatch between the active layers and the substrates. The electrical characteristics of the MHEMTs were compared with those of HEMTs on InP substrates (InP HEMTs) and pseudomorphic HEMTs (PHEMTs). Present MHEMTs have exhibited superior characteristics in the low-frequency (LF) noise and side-gate effect to InP HEMTs and PHEMTs. A sufficiently high current-gain cutoff frequency of 210 GHz was obtained for the MHEMTs with gate length of 0.1 μm.

DOI： 10.1143/JJAP.42.2219

Measurement of Frequency Dispersion of AlGaN/GaN High Electron Mobility Transistors.

Electronic properties of Gd@C-82 metallofullerene peapods: (Gd @ C-82)(n)@SWNTs

Okazaki T, Shimada T, Suenaga K, Ohno Y, Mizutani T, Lee J, Kuk Y, Shinohara H

APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING Vol. 76 ( 4 ) page： 475 - 478 2003.3

Mizutani Takashi, Makihara Hiroshi, Akita Mitsutoshi, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi

Japanese Journal of Applied Physics Vol. 42 ( 2A ) page： 424 - 425 2003.2

Language：Japanese Publisher：The Japan Society of Applied Physics

Frequency dispersion of the drain conductance was observed in AlGaN/GaN high electron mobility transistors (HEMTs). The transition frequency shifted to higher frequencies with increasing temperature. The activation energy for the change of the transition frequency was 0.47 eV, which was almost the same as that obtained by the measurement of the temperature dependence of the low-frequency noise.

DOI： 10.1143/JJAP.42.424

Large Gate Leakage Current in AlGaN/GaN High Electron Mobility Transistors.

Carrier transport properties of carbonnanotubes and nanopeapods Open Access

Shimada Takashi, Ohno Yutaka, Okazaki Toshiya, Sugai Toshiki, Kishimoto Shigeru, Mizutani Takashi, Shinohara Hisanori

Meeting Abstracts of the Physical Society of Japan Vol. 58.2.4 ( 0 ) page： 760 2003

Experimental demonstration of a resonant tunneling delta-sigma modulator for high-speed, high-resolution analog-to-digital converter

Yokoyama Y, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

COMPOUND SEMICONDUCTORS 2002 Vol. 174 page： 243 - 246 2003

Study on off-state breakdown in AlGaN/GaN HEMTs

Nakao T, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

5TH INTERNATIONAL CONFERENCE ON NITRIDE SEMICONDUCTORS (ICNS-5), PROCEEDINGS Vol. 0 ( 7 ) page： 2335 - 2338 2003

The round table talk of the successive presidents of JSSST

OHNO Yutaka, KATAYAMA Takuya, YONEZAWA Akinori, TAKEICHI Masato, AGUSA Kiyoshi

Computer Software Vol. 20 ( 6 ) page： 537 - 548 2003

Current collapse in AlGaN/GaN HEMTs investigated by electrical and optical characterizations

Mizutani T, Ohno Y, Akita M, Kishimoto S, Maezawa K

PHYSICA STATUS SOLIDI A-APPLIED RESEARCH Vol. 194 ( 2 ) page： 447 - 451 2002.12

Ambipolar field-effect transistor behavior of Gd@C-82 metallofullerene peapods Open Access

Shimada T, Okazaki T, Taniguchi R, Sugai T, Shinohara H, Suenaga K, Ohno Y, Mizuno S, Kishimoto S, Mizutani T

APPLIED PHYSICS LETTERS Vol. 81 ( 21 ) page： 4067 - 4069 2002.11

Effects of the HEMT parameters on the operation frequency of resonant tunneling logic gate MOBILE Open Access

Aoyama T, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS Vol. 85 ( 10 ) page： 1 - 6 2002.10

Mizuno Shinya, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 41 ( 8 ) page： 5125 - 5126 2002.8

Language：Japanese Publisher：The Japan Society of Applied Physics

A large gate leakage current in AlGaN/GaN high electron mobility transistors (HEMTs) was observed. Temperature dependence of Ig-Vg characteristics revealed that tunneling current is dominant in the leakage current. By introducing ECR plasma treatment before the gate metal deposition, the gate leakage current was reduced by two to three orders of magnitude.

DOI： 10.1143/JJAP.41.5125

Electroluminescence in AlGaN/GaN High Electron Mobility Transistors under High Bias Voltage.

Temperature distribution measurement in AlGaN/GaN high-electron-mobility transistors by micro-Raman scattering spectroscopy

Ohno Y, Akita M, Kishimoto S, Maezawa K, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 41 ( 4B ) page： L452 - L454 2002.4

Nakao Takeshi, Ohno Yutaka, Akita Mitsutoshi, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 41 ( 4A ) page： 1990 - 1991 2002.4

Language：Japanese Publisher：The Japan Society of Applied Physics

Electroluminescence (EL) in GaN high electron mobility transistors (HEMTs) biased at high drain-source voltages was investigated. The electroluminescence was observed at the drain edge where the high-field region is formed. This is quite different from the case of GaAs HEMTs where luminescence was observed at the gate edge. EL spectroscopy was also performed. The luminescence with the wavelength of visible to near-infrared light, the energy of which was less than the band gap energy, was observed with polarization in the direction parallel to the drain current.

DOI： 10.1143/JJAP.41.1990

Indium Phosphide & Related Materials. High-Speed Operation of a Novel Frequency Divider Using Resonant Thnneling Chaos Circuit.

50 GHz frequency divider using resonant tunnelling chaos circuit

Kawano Y, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

ELECTRONICS LETTERS Vol. 38 ( 7 ) page： 305 - 306 2002.3

Kawano Yoichi, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 41 ( 2B ) page： 1150 - 1153 2002.2

Language：Japanese Publisher：The Japan Society of Applied Physics

This paper demonstrates high-frequency operations of the frequency divider IC composed of a resonant tunneling diode and a high electron mobility transistor. The maximum frequency dividing operation of 6.3 GHz was confirmed. This circuit is based on the long-period behavior of the nonlinear circuits generating chaos. We investigate the effects of the input frequency, the bias voltage, and the input amplitude on the operation to discuss the operating margins. It is also shown that the dividing ratio can be selected by changing the input amplitude.

DOI： 10.1143/JJAP.41.1150

Temperature Distribution Measurement in AlGaN/GaN High-Electron-Mobility Transistors by Micro-Raman Scattering Spectroscopy.

Electroluminescence in AlGaN/GaN HEMTS

Ohno Y, Nakao T, Akita M, Kishimoto S, Maezawa K, Mizutani T

COMPOUND SEMICONDUCTORS 2001 ( 170 ) page： 119 - 124 2002

Low-frequency noise characteristics of AlGaN/GaN HEMT

Makihara H, Akita M, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

COMPOUND SEMICONDUCTORS 2001 ( 170 ) page： 113 - 117 2002

Temperature distributions in AlGaN/GaN HEMTs measured by micro-Raman scattering spectroscopy

Ohno Y, Akita M, Kishimoto S, Maezawa K, Mizutani T

INTERNATIONAL WORKSHOP ON NITRIDE SEMICONDUCTORS, PROCEEDINGS page： 57 - 60 2002

Ohno Yutaka, Akita Mitsutoshi, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 41 ( 4B ) page： L452 - L454 2002

Language：English Publisher：The Japan Society of Applied Physics

Temperature distributions in AlGaN/GaN high-electron-mobility transistors under bias voltage have been measured by micro-Raman scattering spectroscopy. The temperature was estimated from the Raman shift of E2 phonons of GaN. The spatial and temperature resolutions are 1 μm and 10 K, respectively. When the power dissipation was 248 mW at a drain voltage of 40 V, the peak temperature of 443 K was observed at the gate edge on the drain side at the center of the channel. This position corresponds to the high-field region at the gate edge.

DOI： 10.1143/jjap.41.l452

A delta-sigma analog-to-digital converter using resonant tunneling diodes

Yokoyama Y, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 40 ( 10A ) page： L1005 - L1007 2001.10

Resonant-tunneling-injection photoluminescence of single InAs self-assembled quantum dots embedded in a thin AlGaAs barrier

Ohno Y, Kishimoto S, Maezawa K, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS Vol. 40 ( 3B ) page： 2065 - 2068 2001.3

A Delta-Sigma Analog-to-Digital Converter Using Resonant Tunneling Diodes.

Yokoyama Yuji, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 40 ( 10A ) page： L1005 - L1007 2001

Language：English Publisher：The Japan Society of Applied Physics

A novel delta-sigma (ΔΣ) analog-to-digital converter (ADC) using resonant tunneling diodes (RTDs) is proposed. A ΔΣ modulator circuit, which is the key element of the ΔΣ ADC, can be designed in a very simple form using a monostable-bistable transition logic element (MOBILE). The operation of this ΔΣ modulator circuit is confirmed by numerical simulation.

DOI： 10.1143/jjap.40.l1005

High-speed operation of a novel frequency divider using resonant tunneling chaos circuit

Kawano Y, Ohno Y, Kishimoto S, Maezawa K, Mizutani T

2001 INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS, CONFERENCE PROCEEDINGS page： 236 - 239 2001

Resonant-Tunneling-Injection Photoluminescence of Single InAs Self-Assembled Quantum Dots Embedded in a Thin AlGaAs Barrier.

Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 40 ( 3B ) page： 2065 - 2068 2001

Language：English Publisher：The Japan Society of Applied Physics

We have investigated resonant-tunneling-injection photoluminescence (PL) of single InAs self-assembled quantum dots (QDs) which were embedded in the barrier layer of an n-GaAs/i-AlGaAs/n-GaAs tunneling diode. A triangular structure in the PL intensity-voltage characteristics of a single PL line was observed. This reflects the electron tunneling from a three-dimensional emitter to the zero-dimensional quantum level of the QD. In addition, three subpeaks and a broad bulge of the PL were superimposed on the triangular structure. The subpeaks were ascribed to the resonant tunneling of holes into valence quantum levels of the QD. The origin of the excess PL bulge which is obtained at off-resonance bias condition is also discussed.

DOI： 10.1143/jjap.40.2065

Observation of resonant tunneling through single self-assembled InAs quantum dots using electrophotoluminescence spectroscopy Open Access

Ohno Y, Asaoka K, Kishimoto S, Maezawa K, Mizutani T

JOURNAL OF APPLIED PHYSICS Vol. 87 ( 9 ) page： 4332 - 4336 2000.5

Photoluminescence study of resonant tunneling transistor with p(+)/n-junction gate

Ohno Y, Kishimoto S, Maezawa K, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS Vol. 39 ( 1 ) page： 35 - 40 2000.1

Photoluminescence Study of Resonant Tunneling Teansistor with p+/n-Junction Gate.

Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 39 ( 1 ) page： 35 - 40 2000

Language：English Publisher：The Japan Society of Applied Physics

We studied photoluminescence (PL) of a resonant tunneling transistor with a p+/n-junction gate. The excitation energy was selected to be close to the band-gap energy of the GaAs collector layer 1) so as not to excite the barrier layer and quantum well directly, and 2) in order to obtain a simple luminescence spectrum. The PL signal shows strong correlation with the resonant tunneling current. The PL peak position shows a redshift with increasing collector voltage, indicating the existence of the quantum-confined Stark effect. The collector voltage dependence of the PL linewidth suggests the existence of charge accumulation in the quantum well. The accumulated electron density and the charging time were estimated. It was also shown that the PL intensity could be controlled by the gate voltage without affecting the resonant tunneling behavior of electrons.

DOI： 10.1143/jjap.39.35

Optoelectronic flexible-function logic gate using monostable-bistable transition of serially connected resonant tunneling transistors

Ohno Y, Kishimoto S, Maezawa K, Mizutani T, Akeyoshi T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Vol. 38 ( 4B ) page： 2586 - 2589 1999.4

Measurements of electroluminescence intensity distribution in the direction of gate width of n(+) self-aligned gate GaAs metal-semiconductor field-effect transistors

Niwa H, Ohno Y, Kishimoto S, Maezawa K, Mizutani T, Yamazaki H, Taniguchi T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS Vol. 38 ( 3A ) page： 1363 - 1364 1999.3

Microscopic photoluminescence study of InAs single quantum dots grown on (100) GaAs

Asaoka K, Ohno Y, Kishimoto S, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS Vol. 38 ( 1B ) page： 546 - 549 1999.1

Photoluminescence intensity enhancement by electron beam irradiation into GaAs quantum wells

Murata T, Ohno Y, Kishimoto S, Mizutani T

SOLID-STATE ELECTRONICS Vol. 43 ( 1 ) page： 147 - 152 1999.1

Measurements of Electroluminescence Intensity Distribution in the Direction of Gate Width of n+ Self-Aligned Gate GaAs Metal-Semiconductor Field-Effect Transistors.

Niwa Hiroyuki, Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi, Yamazaki Hajime, Taniguchi Toru

Japanese Journal of Applied Physics Vol. 38 ( 3A ) page： 1363 - 1364 1999

Language：English Publisher：The Japan Society of Applied Physics

We studied electroluminescence (EL) intensity distributions in the direction of gate width of n+ self-aligned gate GaAs metal-semiconductor field-effect transistors (MESFETs). Nonuniform EL was observed along the gate-width direction, suggesting the nonuniform high-field formation in the direction of the gate. It has also been found that the EL at the source side shows gentler distribution than that at the drain side. These features suggest that the nonuniform hole distribution generated by impact ionization at the drain side becomes gradual during the process of their flow into the source and gate electrodes.

DOI： 10.1143/jjap.38.1363

Optoelectronic Flexible-Function Logic Gate Using Monostable-Bistable Transition of Serially Connected Resonant Tanneling Transitors.

Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi, Akeyoshi Tomoyuki

Japanese Journal of Applied Physics Vol. 38 ( 4B ) page： 2586 - 2589 1999

Language：English Publisher：The Japan Society of Applied Physics

A novel optoelectronic resonant tunneling logic gate, OE MOBILE, is proposed and its basic logic functions such as NOT, NOR, NAND, OR, and AND are confirmed for optical inputs. The fundamental idea is to use optical inputs to determine the logic level of the gate which consists of two serially connected resonant tunneling transistors (RTTs) with a p+/n-junction gate. The OE MOBILE is operated by oscillating bias voltage to employ monostable-bistable transition. At the time when the transition occurs, the optical inputs are applied by illuminating the RTTs to control their peak currents and consequently to determine the output logic levels. The power of an optical input for logic operations is as small as 5 µW owing to the operation based on monostable-bistable transition. It should be pointed out that the functions of an OE MOBILE can be changed between NOR and NAND by changing the control terminal voltage.

DOI： 10.1143/jjap.38.2586

Microscopic Photoluminescence Study of InAs Single Quantum Dots Grown on (100) GaAs.

Asaoka Kazuya, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

Japanese Journal of Applied Physics Vol. 38 ( 1B ) page： 546 - 549 1999

Language：English Publisher：The Japan Society of Applied Physics

We report ultranarrow (≤60 µeV) photoluminescence (PL) lines originating from single InAs quantum dots (QDs) sandwiched by Al0.35Ga0.65As barrier layers, demonstrating their δ-function-like density of states (DOS). The temperature dependence of the full-width at half maximum (FWHM) was studied between 10 and 90 K. It linearly increased with increasing temperature from 40 to 80 K (~7 µeV/K), suggesting the existence of an excitonic dephasing mechanism. Pure dephasing of excitons due to exciton-phonon interactions in acoustic phonon mode was suggested as a possible mechanism for the PL line broadening.

DOI： 10.1143/jjap.38.546