研究者詳細 - 大野　雄高

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

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

Japanese Journal of Applied Physics 61 巻 ( 3 ) 2022年3月

担当区分：最終著者,　責任著者記述言語：英語出版者・発行元：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 査読有り

Endo Masanori, Uchiyama Haruki, Ohno Yutaka, Hirotani Jun

APPLIED PHYSICS EXPRESS 15 巻 ( 2 ) 2022年2月

担当区分：責任著者記述言語：英語出版者・発行元：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 査読有り

Matsunaga M., Hirotani J., Ohno Y.

Applied Physics Express 15 巻 ( 2 ) 2022年2月

担当区分：最終著者,　責任著者記述言語：英語出版者・発行元：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 査読有り

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

ACS Applied Nano Materials 4 巻 ( 12 ) 2021年12月

記述言語：英語出版者・発行元：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

カーボンナノチューブを用いた柔軟性に富む摩擦帯電型エネルギーハーベスタ招待有り査読有り

松永正広, 川口敦司, 大野雄高

応用物理 90 巻 ( 11 ) 頁： 684 - 688 2021年11月

担当区分：最終著者,　責任著者記述言語：日本語出版者・発行元：公益社団法人応用物理学会

摩擦帯電型エネルギーハーベスタは人体の動作などの低周波の運動から発電することが可能であり，自己給電型ウェアラブルデバイスの電源として期待されている．ウェアラブルデバイスにおいては人体の動的な3次元表面に追従する必要があり，高い伸縮性が要求される．本研究では，カーボンナノチューブ薄膜電極を用いることにより，高出力（8W/m2）かつ高伸縮性（35%）をもつシート状の摩擦帯電型エネルギーハーベスタを実現している．誘電体層表面にフッ素プラズマ処理を施すことにより高出力を得た．作製したハーベスタの特徴を生かし，自己発電型信号送信デバイスやLEDを埋め込んだ手袋を実証する．さらに，微小な電力を蓄積して機能デバイスの駆動に有効な電力を実現するための高効率な間欠動作回路の提案と実証も行う．本研究はウェアラブルデバイスの課題である電源の問題に解決の糸口を与えると期待される．

DOI： 10.11470/oubutsu.90.11_684

Dynamic Range Enhancement Via Linearized Output in Nanoelectromechanical Systems by Combining High-Order Harmonics 査読有り国際誌

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

IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS II-EXPRESS BRIEFS 68 巻 ( 10 ) 頁： 3251 - 3255 2021年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Transactions on Circuits and Systems II: Express Briefs

There is a strong non-linearity between the field-emission current amplitude and field intensity. This nonlinearity degrades the dynamic range of digital signal processing in a mechanical oscillator composed of a cantilever. To solve this issue, we propose a linearization method by combining the harmonics of the field-emission current. The proposed method significantly increases the dynamic range. The nonlinearity error is 8.94× 10-3 %FS for the proposed method, whereas it is 14.1%FS for the conventional method given by the 2nd harmonic current detection. In addition, the proposed method enables to rake up energy of the higher-order harmonics by utilizing our design framework for combining weights, thereby providing a constant derivative of the output current of the input electric field.

DOI： 10.1109/TCSII.2021.3062390

Special issue on Carbon-based Electronics 招待有り査読有り

Das Saptarshi, Ohno Yutaka, Kawarada Hiroshi

CARBON 182 巻頁： 856 - 856 2021年9月

Tunable carbon nanotube diode with varying asymmetric geometry 査読有り

Funayama Keita, Hirotani Jun, Miura Atsushi, Tanaka Hiroya, Ohno Yutaka, Tadokoro Yukihiro

AIP ADVANCES 11 巻 ( 7 ) 頁： 075212 2021年7月

記述言語：英語出版者・発行元：AIP Advances

We propose and demonstrate a carbon nanotube (CNT)-based field emission nanoscale diode to realize a fully integrated nanoscale system, namely, a true nanosystem. To the best of our knowledge, this is the first time a nanodiode simultaneously achieves ease of fabrication and individual tunability of multiple CNT diodes on the nanoscale on the same substrate in a one-time process. A nanodiode comprises a single-wall CNT cathode placed on a substrate, layered insulator, and metal anode. The proposed nanodiode allows us to adjust the turn-on voltage from 1 to 2.4 V by varying the surface area of the anode. Furthermore, as an example of a basic nano-electronic system, nanodiode-based fundamental logic gates (OR and NAND) are demonstrated on a CNT. We propose a theoretical model that derives the theoretical I-V characteristics based on the image-charge method to design the nanodiode quickly. The results in this study contribute to the development of carbon-based nanoelectronic systems.

DOI： 10.1063/5.0058300

Effect of electrochemical functionalization of single-walled carbon nanotube electrodes in flexible enzymatic biofuel cells 査読有り

Momaya Divyang, Ohno Yutaka

JAPANESE JOURNAL OF APPLIED PHYSICS 60 巻 ( 6 ) 頁： 068002 2021年6月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

We report a flexible enzymatic biofuel cell based on electrochemically functionalized single-walled carbon nanotube (SWNT) electrodes. Comparative studies on the impact of the electrochemical functionalization of the SWNT electrodes on the device performance revealed a 40%-110% increase in power density as compared to that of the device with as-fabricated SWNT electrodes, with an observed maximum power density of 7.2 μW cm-2. This improvement in performance can be attributed to the increase in the amount of enzymes adsorbed on the SWNT surface and the enhanced electron transfer rate owing to the SWNT functionalization. Our findings can aid improve the performance of flexible and high-power-density biofuel cells.

DOI： 10.35848/1347-4065/ac0261

Simple and highly efficient intermittent operation circuit for triboelectric nanogenerator toward wearable electronic applications 査読有り国際誌

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

Applied Physics Express 14 巻 ( 5 ) 2021年5月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Triboelectric nanogenerator (TENG) is a promising power source toward the realization of self-powered wearable electronics. However, because of its pulsed output, a power management circuit, such as an intermittent operation circuit and AC-DC converter, is required to drive electronic devices. In this study, we propose a simple and highly efficient intermittent operation circuit composed of a programmable unijunction transistor. The energy transfer efficiency from the storage capacitor to the load reached 89%. We demonstrated that the intermittent circuit can be used to drive electronic devices such as stopwatches and wristwatches using the electricity generated by a carbon-nanotube-based stretchable TENG. © 2021 The Japan Society of Applied Physics.

DOI： 10.35848/1882-0786/abf405

Low-voltage carbon nanotube complementary electronics using chemical doping to tune the threshold voltage 査読有り国際誌

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

Applied Physics Express 14 巻 ( 4 ) 頁： 045002 2021年4月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Simultaneous controlling of the threshold voltage of both p- and n-type transistors, comprising complementary integrated circuits, is required to develop low-voltage and low-power flexible electronics. In this study, we report tuning the threshold voltage of carbon nanotube thin-film transistors with organic and metal-ion complex salts as dopants, and using device passivation to secure air-stability. Chemical doping affords simple yet precise control of the dopant level and enables the threshold voltages to be finely tuned. Complementary inverters were fabricated on a plastic substrate. Operation at a low supply voltage of 0.5 V was achieved with fairly high gain and noise margins.

DOI： 10.35848/1882-0786/abe8aa

ZnO Nanostructures Application in Electrochemistry: Influence of Morphology 査読有り国際共著国際誌

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

JOURNAL OF PHYSICAL CHEMISTRY C 125 巻 ( 2 ) 頁： 1472 - 1482 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

The aim of this work was to investigate the influence of morphology on its electrochemical properties by comparing ZnO nanostructures in the forms of tetrapods of different sizes, nanorods, and nanoparticles. ZnO tetrapods were prepared by the combustion method and separated into two fractions by size, ruling out the influence of synthesis conditions. Structural and morphological properties of different ZnO nanostructure morphologies were identified by using various characterization techniques: scanning and transmission electron microscopies (SEM and TEM), X-ray powder diffraction (XRD), nitrogen adsorption/desorption measurements at 77 K, and UV-vis spectroscopy (UV-vis). Analysis of electrochemical properties showed the highest active surface area of 0.095 cm2 and the lowest peak separation value of 61.7 mV for large ZnO tetrapods, which are close to the theoretical values. The correlation between the pore size in different ZnO nanostructures because of packing and their electrochemical properties is established. We expect that the detailed analysis of ZnO nanostructures conducted in this study will be advantageous for future electrochemical and biosensing applications of these materials.

DOI： 10.1021/acs.jpcc.0c08459

Cross-linking gelation of isomaltodextrin for the chromatographic separation of semiconducting carbon nanotubes 査読有り国際誌

Matsunaga Y., Hirotani J., Ohno Y., Omachi H.

Applied Physics Express 14 巻 ( 1 ) 2021年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

The gel column chromatographic separation technique is one of the most rapid and reliable methods to prepare high-purity semiconducting single-wall carbon nanotubes (SWCNTs). However, the use of the expensive dextran-based gels limits the utility and scalability of this technique. Herein, we report the cross-linking gelation of a cost-efficient polysaccharide isomaltodextrin (IMD) for the high-purity separation of s-SWCNTs by column chromatography. The cross-linking reaction with epichlorohydrin under precisely controlled basic conditions gave the sub-micrometer porous IMD gels, which was important for achieving gel chromatographic SWCNT separation. Furthermore, the thin-film transistors prepared from the separated s-SWCNTs exhibited excellent on/off ratios.

DOI： 10.35848/1882-0786/abd28b

Low-Voltage Operable and Strain-Insensitive Stretchable All-Carbon Nanotube Integrated Circuits with Local Strain Suppression Layer 査読有り国際誌

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

ADVANCED ELECTRONIC MATERIALS 7 巻 ( 1 ) 2021年1月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Electronic Materials

Stretchable devices, which can intimately contact dynamic free-form surfaces, show great promise for wearable and implantable devices for human beings and multifunctional electronic skins for soft robotics. Although some successful stretchable devices have been reported, there are still remaining issues; in particular, the fundamental requirements for wearable devices, including low-voltage operation, operation speed, mechanical stretchability and robustness, and easy circuit design, are needed to be satisfied simultaneously. Here, a local strain suppression layer (L-SSL) is introduced into all-carbon nanotube (CNT) stretchable thin-film transistors (TFTs) and integrated circuits (ICs) to address these issues. The L-SSL, which has a high Young's modulus, is placed on top of the active channel region to suppress the induced local strain. The resulting CNT TFTs show no drain current degradation under externally applied tensile strain of up to 35%. Furthermore, stretchable all-CNT ICs, such as inverters and ring oscillators, can operate at low supply voltage as 0.7 V, because high-k material can be used underneath the L-SSL. Biaxial stretching, an indispensable ability for wearable devices on 3D deformable surfaces such as the human body, is also achieved. The all-CNT devices, equipped with an L-SSL, demonstrate potential for strain-insensitive stretchable devices with low-voltage operation.

DOI： 10.1002/aelm.202000674

Effect of metal electrodes on optically detected magnetic resonance of nitrogen vacancy centers in diamond 査読有り国際誌

Uchiyama H., Kishimoto S., Ishi-Hayase J., Ohno Y.

Japanese Journal of Applied Physics 59 巻 ( 12 ) 2020年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Operando detection of various physical quantities in electronic devices under operation has been demonstrated by optically detected magnetic resonance (ODMR) using nitrogen vacancy (NV) centers in diamond. However, the ODMR spectrum may also be affected by the existence of the metal electrodes and wirings of the electronic device, which limits the accurate measurement of the objective physical quantity. In this paper, we report the effect of metal electrodes on the ODMR spectrum of NV centers. It was found that the ODMR contrast increased in the vicinity of the metal electrode fabricated on diamond with NV centers. The microwave concentration at the edge of the metal electrode is a plausible cause for the increase in the ODMR contrast. Our results suggest that it is necessary to recognize that the ODMR spectrum may change near the metal electrode and wirings in the ODMR-based operand analysis of electronic devices.

DOI： 10.35848/1347-4065/abc3d7

Fabrication of Carbon Nanotube Thin Films for Flexible Transistors by Using a Cross-Linked Amine Polymer 査読有り国際誌

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

CHEMISTRY-A EUROPEAN JOURNAL 26 巻 ( 28 ) 頁： 6118 - 6121 2020年5月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Chemistry - A European Journal

Owing to their remarkable properties, single-walled carbon nanotube thin-film transistors (SWCNT-TFTs) are expected to be used in various flexible electronics applications. To fabricate SWCNT channel layers for TFTs, solution-based film formation on a self-assembled monolayer (SAM) covered with amino groups is commonly used. However, this method uses highly oxidized surfaces, which is not suitable for flexible polymeric substrates. In this work, a solution-based SWCNT film fabrication using methoxycarbonyl polyallylamine (Moc-PAA) is reported. The NH2-terminated surface of the cross-linked Moc-PAA layer enables the formation of highly dense and uniform SWCNT networks on both rigid and flexible substrates. TFTs that use the fabricated SWCNT thin film exhibited excellent performance with small variations. The presented simple method to access SWCNT thin film accelerates the realization of flexible nanoelectronics.

DOI： 10.1002/chem.202000228

High output voltage generation of over 5 V from liquid motion on single-layer MoS2 査読有り国際誌

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

NANO ENERGY 68 巻 2020年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Nano Energy

Water stores a large amount of clean energy in its dynamic forms. Owing to the wide availability of water and the rising demand for clean energy sources, the direct electricity generation from liquid motion by low-dimensional materials such as graphene has gained much interest. Electricity generation is induced by the motion of an electric double layer at the interface between the liquid droplet and solid surface. However, the output voltage with materials such as graphene is still limited to several hundred millivolts. In this report, we present a large-area single-layer MoS2 film grown by chemical vapor deposition as a nanogenerator, which is capable of generating a large output voltage of more than 5 V from the motion of an aqueous NaCl droplet. Our findings indicate that the high shunt resistance of MoS2 results in a large generated voltage. Furthermore, we demonstrate the possibility to scale up the MoS2 nanogenerator by arranging them in series and parallel connections, which respectively increase the output voltage and current, with a three-times increase with an array of three MoS2 nanogenerators. Our work opens the application of single-layer MoS2 for harvesting electricity from the dynamic movement of liquid, such as the capability to harvest ocean wave energy, which is also demonstrated here.

DOI： 10.1016/j.nanoen.2019.104370

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

Matsunaga Masahiro, Hirotani Jun, Kishimoto Shigeru, Ohno Yutaka

NANO ENERGY 67 巻 2020年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Nano Energy

Self-powered electronics can improve wearable health monitoring systems. Triboelectric generation, a type of energy harvesting technology, is a promising candidate as power source for wearable devices by generating electricity from body motion. For wearable energy harvesters, stretching is required for adaptation to dynamic three-dimensional body motions, and sufficient output power should be delivered for driving electronic devices. However, the currently demonstrated output power remains insufficient for using stretchable triboelectric generation in practice. We propose high-output (8 W/m2), stretchable triboelectric generators based on transparent carbon nanotube thin films. We realize high output by the surface treatment with fluorine plasma as well as stretchability by scalable and cost-effective spray coated carbon nanotube thin films. The carbon nanotube films also provide excellent scalability, optical transparency (95% transmittance), and durability under large deformations of tensile strain up to 80%. We also demonstrate applications to self-powered optical wireless communication sheets and gloves, where blue light emitting diodes are embedded in the triboelectric nanogenerator sheet and wired using stretchable carbon nanotube films. Our stretchable energy harvesting sheets can contribute to solve major problems in wearable electronics (i.e., power source limitations) at low cost.

DOI： 10.1016/j.nanoen.2019.104297

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

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 30 巻 ( 5 ) 2020年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Advanced Functional Materials

In this work, a fast approach for the fabrication of hundreds of ultraclean field-effect transistors (FETs) is introduced, using single-walled carbon nanotubes (SWCNTs). The synthesis of the nanomaterial is performed by floating-catalyst chemical vapor deposition, which is employed to fabricate high-performance thin-film transistors. Combined with palladium metal bottom contacts, the transport properties of individual SWCNTs are directly unveiled. The resulting SWCNT-based FETs exhibit a mean field-effect mobility, which is 3.3 times higher than that of high-quality solution-processed CNTs. This demonstrates that the hereby used SWCNTs are superior to comparable materials in terms of their transport properties. In particular, the on–off current ratios reach over 30 million. Thus, this method enables a fast, detailed, and reliable characterization of intrinsic properties of nanomaterials. The obtained ultraclean SWCNT-based FETs shed light on further study of contamination-free SWCNTs on various metal contacts and substrates.

DOI： 10.1002/adfm.201907150

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 30 巻 ( 42 ) 頁： 425201 2019年10月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Nanotechnology

This work studies the enhancement factor associated with a current emitted from a multi-wall carbon nanotube to an extremely small counter electrode. The experimental data show that the field enhancement factor increases by 1.15 times when the width of the counter electrode increases from 50 to 200 nm. To better understand this enhancement effect, field intensities at the emitter surface are numerically simulated. The experimental work and simulations demonstrate that the observed field enhancement results from increases in the capacitance between the emitter and counter electrode. In addition, corrugated counter electrodes are found to greatly affect both the capacitance and enhancement factor. This is because the corrugation of the anode surface raises the capacitance and thus provides a higher current. We experimentally show that an effective surface area enlargement of 1.67 times due to the corrugation provides a 1.06-fold increase of the enhancement factor. These results should assist in the future development of field emission devices based on semiconductor fabrication processes.

DOI： 10.1088/1361-6528/ab33c8

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

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

APPLIED PHYSICS EXPRESS 12 巻 ( 9 ) 2019年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Semiconducting single-wall carbon nanotubes (s-SWCNTs) are promising materials with potential applications in thin-film transistors (TFTs). However, separation techniques are required to obtain highly enriched s-SWCNTs since conventional as-grown SWCNTs are a mixture of 70% semiconducting and 30% metallic SWCNTs. Here, we developed a rapid single-step aqueous two-phase extraction of high-purity s-SWCNTs using isomaltodextrin, which is a cost-effective polysaccharide that contains a large amount of α-1,6-glucosidic linkages. We also succeeded in fabricating high-density uniform films directly from the high-purity s-SWCNT extract. Fabricated TFTs exhibited an excellent on/off ratio, carrier mobility, and on-current density.

DOI： 10.7567/1882-0786/ab369e

Effects of HLA mismatch on cytomegalovirus reactivation in cord blood transplantation

Yokoyama H., Kanda J., Kato S., Kondo E., Maeda Y., Saji H., Takahashi S., Onizuka M., Onishi Y., Ozawa Y., Kanamori H., Ishikawa J., Ohno Y., Ichinohe T., Takanashi M., Kato K., Atsuta Y., Kanda Y.

Bone Marrow Transplantation 54 巻 ( 7 ) 頁： 1004 - 1012 2019年7月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Bone Marrow Transplantation

Although human leukocyte antigen (HLA) mismatch is often thought to be associated with a high incidence of cytomegalovirus (CMV) reactivation, it is not clear whether this process is mediated by HLA mismatch or other factors, such as acute graft-versus-host disease (aGVHD). Here we focused on cord blood transplantation (CBT) and examined the effects of HLA mismatch on the incidence of CMV reactivation while minimizing the effects of aGVHD. In a multivariate analysis considering aGVHD as a time-dependent covariate, a significant effect on the incidence of CMV reactivation was noted for HLA disparity (hazard ratio [HR]: 0.54 for 8/8 match compared with 3-allele mismatch) and development of aGVHD (HR: 1.26). Next, in an analysis excluding cases that developed aGVHD, the incidences of CMV reactivation for 8/8 match and 1-allele mismatch were low compared with those for other mismatches. These findings were supported by the multivariate analysis (HR: 0.49 for 8/8 match and 0.64 for 1-allele mismatch compared with 3-allele mismatch). Together, these results suggested that HLA mismatch was involved in CMV reactivation and was associated with high morbidity of opportunistic infection after CBT.

DOI： 10.1038/s41409-018-0369-0

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 114 巻 ( 25 ) 頁： 253504 2019年6月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：AIP Publishing

Hydrogen-terminated diamond metal-insulator-semiconductor field-effect transistors are candidates for power devices that require a high breakdown field and stable, high-frequency operation. A two-dimensional hole-gas layer can form on H-terminated diamond surfaces. To understand the electrical properties of bare H-terminated diamond surfaces, we investigate the surface impurities on a H-terminated diamond surface in a vacuum-gap gate structure, which uses a H-terminated diamond channel and a vacuum gap as gate dielectrics. To obtain a bare surface without surface adsorbate, the device is annealed in a vacuum. The transconductance is increased by removing adsorbates. The mobility and interface-state density at the H-terminated diamond surface with no adsorbates are 25 cm2 V-1 s-1 and 1 × 1012 cm-2 eV-1, respectively.

DOI： 10.1063/1.5099395

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

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

ACS OMEGA 4 巻 ( 4 ) 頁： 7459 - 7466 2019年4月

記述言語：日本語出版者・発行元：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

Ishiyama K., Aoki J., Itonaga H., Uchida N., Takahashi S., Ohno Y., Matsuhashi Y., Sakura T., Onizuka M., Miyakoshi S., Takanashi M., Fukuda T., Atsuta Y., Nakao S., Miyazaki Y.

Blood Cancer Journal 9 巻 ( 3 ) 2019年3月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Blood Cancer Journal

Allogeneic hematopoietic stem cell transplantation is the sole curative therapy for myelodysplastic syndrome (MDS). However, there is concern regarding graft failure and relapse in patients who undergo cord blood transplantation (CBT). We conducted a retrospective study of the CBT outcomes in MDS patients using the Japanese Data Center for Hematopoietic Cell Transplantation database. Seven hundred fifty-two de novo MDS patients of ≥18 years of age (median, 58 years) undergoing their first CBT between 2001 and 2015 were examined. Two-thirds of the patients were male, and were RAEB. The cumulative incidences of neutrophil and platelet engraftment at day 100 were 77 and 59%, respectively. The 3-year overall survival (OS) was 41% and the median survival of the patients was 1.25 years. A multivariate analysis of pre-transplant variables showed that the age, gender, cytogenetic subgroups, number of RBC transfusions, HCT-CI and year of CBT significantly influenced the outcome. The cumulative incidence of acute graft-versus-host disease (aGVHD) and chronic GVHD (cGVHD) was 32 and 21%, respectively. A survival benefit was observed in patients who developed cGVHD, but not aGVHD. Our results suggest that CBT is an acceptable alternative graft and that a graft-versus-MDS effect can be expected, especially in patients who develop cGVHD.

DOI： 10.1038/s41408-019-0192-x

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 11 巻 ( 6 ) 頁： 6389 - 6395 2019年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

Electrochemical sensors based on carbon nanotubes (CNTs) have great potential for use in wearable or implantable biomedical sensor applications because of their excellent mechanical flexibility and biocompatibility. However, the main challenge associated with CNT-based sensors is their uniform and reproducible fabrication on the flexible plastic film. Here, we introduce and demonstrate a highly reliable technique to fabricate flexible CNT microelectrodes on a plastic film. The technique involves a process whereby the CNT film is formed by the dry transfer process based on the floating-catalyst chemical vapor deposition. An oxide protection layer, which is used to cover the CNT thin film during the fabrication process, minimizes contamination of the surface. The fabricated flexible CNT microelectrodes show almost ideal electrochemical characteristics for microelectrodes with the average value of the quartile potentials, ΔE = |E 3/4 - E 1/4 |, being 60.4 ± 2.9 mV for the 28 electrodes, while the ideal value of ΔE = 56.4 mV. The CNT microelectrodes also showed enhanced resistance to surface fouling during dopamine oxidation in comparison to carbon fiber and gold microelectrodes; the degradation of the oxidation current after 10 consecutive cycles were 1.8, 8.3, and 13.9% for CNT, carbon fiber, and gold microelectrodes, respectively. The high-sensitivity detection of dopamine is also demonstrated with differential-pulse voltammetry, with a resulting limit of detection of ∼50 nM. The reliability, uniformity, and sensitivity of the present CNT microelectrodes provide a platform for flexible electrochemical sensors.

DOI： 10.1021/acsami.8b19252

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

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

ELECTROCHIMICA ACTA 295 巻頁： 157 - 163 2019年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Electrochimica Acta

Thin films of single-walled carbon nanotubes (SWNTs) possess high potential for use in flexible electrochemical sensors in wearable medical devices. However, the electrochemical activity of such materials is not yet fully understood. We studied the enhancement in electrochemical activity of SWNT-based flexible electrochemical sensors. To exclude the effect of surface contaminations from the fabrication processes on the electrochemical activity, we introduced the dry process for high-quality and clean SWNT film formation and the clean device fabrication process with a protective layer. So-fabricated SWNT electrodes exhibited a low electron transfer rate. Electrochemical functionalization with an H2SO4 solution successfully enhanced the electrochemical activity of the SWNT electrode for the inner sphere probes such as [Fe(CN)6]4−/3−. This method is quite gentle and controllable, but also effective at increasing the electron transfer rate without either degrading the potential window. We found out that there was a correlation between the electron transfer rate and the amount of defects evaluated from Raman scattering spectroscopy. XPS analysis showed that the functionalization process introduced C–O and C[dbnd]O species, suggesting that these species constituted active sites for inner sphere probes. The electrochemical functionalization was also effective for enhancing the limit of detection in dopamine detection with the flexible SWNT electrode. The limit of detection was ∼100 nM for functionalized electrode whereas it was ∼1 μM for as-fabricated electrodes.

DOI： 10.1016/j.electacta.2018.10.147

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

Hirotani Jun, Kishimoto Shigeru, Ohno Yutaka

NANOSCALE ADVANCES 1 巻 ( 2 ) 頁： 636 - 642 2019年2月

記述言語：日本語出版者・発行元：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 377 巻 ( 1 ) 頁： 3 2019年2月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Topics in Current Chemistry

Carbon nanotube thin films have attracted considerable attention because of their potential use in flexible/stretchable electronics applications, such as flexible displays and wearable health monitoring devices. Due to recent progress in the post-purification processes of carbon nanotubes, high-purity semiconducting carbon nanotubes can be obtained for thin-film transistor applications. One of the key challenges for the practical use of carbon nanotube thin-film transistors is the thin-film formation technology, which is required for achieving not only high performance but also uniform device characteristics. In this paper, after describing the fundamental thin-film formation techniques, we review the recent progress of thin-film formation technologies for carbon nanotube-based flexible electronics.

DOI： 10.1007/s41061-018-0227-y

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

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

IEEE ACCESS 7 巻頁： 57820 - 57828 2019年

記述言語：日本語出版者・発行元：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

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

IEEE ACCESS 7 巻頁： 171195 - 171205 2019年

記述言語：日本語出版者・発行元：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

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

ANALYST 143 巻 ( 15 ) 頁： 3635 - 3642 2018年8月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Analyst

A highly sensitive interdigitated electrode (IDE) with vertically aligned dense carbon nanotube forests directly grown on conductive supports was demonstrated by combining UV lithography and a low temperature chemical vapor deposition process (470 °C). The cyclic voltammetry (CV) measurements of K4[Fe(CN)6] showed that the redox current of the IDE with CNT forests (CNTF-IDE) reached the steady state much more quickly compared to that of conventional gold IDE (Au-IDE). The performance of the CNTF-IDE largely depended on the geometry of the electrodes (e.g. width and gap). With the optimum three-dimensional electrode structure, the anodic current was amplified by a factor of ∼18 and ∼67 in the CV and the chronoamperometry measurements, respectively. The collection efficiency, defined as the ratio of the cathodic current to the anodic current at steady state, was improved up to 97.3%. The selective detection of dopamine (DA) under the coexistence of l-ascorbic acid with high concentration (100 μM) was achieved with a linear range of 100 nM-100 μM, a sensitivity of 14.3 mA mol-1 L, and a limit of detection (LOD, S/N = 3) of 42 nM. Compared to the conventional carbon electrodes, the CNTF-IDE showed superior anti-fouling property, which is of significant importance for practical applications, with a negligible shift of the half-wave potential (ΔE1/2 < 1.4 mV) for repeated CV measurements of DA at high concentration (100 μM).

DOI： 10.1039/c8an00528a

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

Tadokoro Y., Ohno Y., Tanaka H.

ELECTRONICS LETTERS 54 巻 ( 13 ) 頁： 840 - + 2018年6月

記述言語：日本語出版者・発行元：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 17 巻 ( 1 ) 頁： 84 - 92 2018年1月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Transactions on Nanotechnology

Communication between tiny sensor nodes is an important function in future sensing applications and services. This paper contributes to the design of both the front end and the demodulator of nanoscale receivers. A nanoscale phase detector is proposed that provides two important functions at nanoscale: Reception of an incoming carrier signal in the megahertz band, and detection of the carrier phase which contains the information of the transmitted digital data. These two functions are achieved by the mechanical vibration of the tip of a carbon nanotube. The proposed detector was theoretically analyzed in terms of its communication aspects; although a digitally phase-modulated signal could be detected in nanoscale, the effective received signal power showed to be strongly reduced in a key performance measure in communication systems, bit error rate. However, the present analysis reveals that the output of the proposed detector has two frequency components, which describe the transmitted data. To take the advantage of this characteristic, a demodulator using maximum-ratio combining is introduced in this paper. The optimal weights used to combine the components were analytically derived to improve the bit error rate performance. The effectiveness of the nanoscale phase detector is numerically demonstrated, and the gain relative to the demodulation achieved using a conventional simple correlator is established.

DOI： 10.1109/TNANO.2017.2765310

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

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

JOURNAL OF APPLIED PHYSICS 122 巻 ( 23 ) 2017年12月

記述言語：日本語出版者・発行元：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 9 巻 ( 24 ) 頁： 20738 - 20747 2017年6月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

Single-walled carbon nanotubes (SWCNTs) show great potential as an active material in electronic and photonic devices, but their applicability is currently limited by shortcomings in existing deposition methods. SWCNTs can be dispersed from liquid solutions; however, their poor solubility requires the use of surfactants and ultrasonication, causing defects and degradation in device performance. Likewise, the high temperatures required by their chemical vapor deposition growth limit substrates on which SWCNTs can be directly grown. Here, we present a systematic study of the direct deposition of pristine, aerosol-synthesized SWCNTs by thermophoresis. The density of the deposited nanotube film can be continuously adjusted from individual, separated nanotubes to multilayer thin films by changing the deposition time. Depending on the lateral flow inside the thermophoretic precipitator, the angular distribution of the deposited SWCNT film can be changed from uniform to nonuniform. Because the substrate is kept at nearly ambient temperature, deposition can be thus carried out on practically any flat substrate with high efficiencies close to unity. The thermophoretic terminal velocity of SWCNTs, determined by aerosol loss measurements, is found to be approximately one-third of the usual prediction in the free molecular regime and shows a weak dependence on the nanotube diameter. As a demonstration of the applicability of our technique, we have used thermophoretic deposition in the fabrication of carbon nanotube thin-film transistors with uniform electrical properties and a high, over 99.5%, yield.

DOI： 10.1021/acsami.7b03151

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

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

JAPANESE JOURNAL OF APPLIED PHYSICS 56 巻 ( 6 ) 2017年6月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Large-diameter semiconductor single-wall carbon nanotubes (s-SWCNTs) have superior mobility and conductivity to small-diameter s-SWCNTs. However, the purification of s-SWCNTs with diameters larger than 1.6 nm by gel filtration has been difficult owing to the low selectivity of the conventional purification method in these large-diameter regions. We report a combination of temperature-controlled gel filtration and the gradient elution technique that we developed to enrich a high-purity s-SWCNT with a diameter as large as 1.9nm. The thin-film transistor (TFT) device using the 1.9-nm-diameter SWCNT shows an average channel mobility of 23.7 cm2V%1 s%1, which is much higher than those of conventional SWCNTTFTs with smaller-diameters of 1.5 and 1.4 nm.

DOI： 10.7567/JJAP.56.065102

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 3 巻 ( 1 ) 頁： 24 - 32 2017年3月

記述言語：日本語出版者・発行元：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 16 巻頁： 1405 - 1408 2017年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Antennas and Wireless Propagation Letters

Angular sensitivity steering is demonstrated using the mechanical vibration of a carbon nanotube (CNT) cantilever. We propose a linear array of electromagnetic wave detectors based on the mechanical CNT resonator. The proposed linear array allows angular sensitivity design in terms of the geometrical properties of the cantilevers, i.e., the array factor is tuned using the resonant frequency of the cantilever and the distance between the electrode and the tip of the cantilever. We analytically investigate the underlying mechanism of the linear array and provide clear design guidelines for the array factor.

DOI： 10.1109/LAWP.2016.2640272

Origin of residual particles on transferred graphene grown by CVD 査読有り

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

JAPANESE JOURNAL OF APPLIED PHYSICS 55 巻 ( 8 ) 2016年8月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Large-area single-layer graphene can be grown on Cu foil by CVD, but for device applications, the layer must to be transferred onto an insulating substrate. As residual particles are often observed on transferred graphene, we investigated their origin using scanning electron microscopy and energy-dispersive X-ray spectrometry (EDX). The results show that these residual particles are composed either of silicon or an alloy of a few metals, and hence, likely originate from the quartz tube of the CVD furnace and the impurities contained in the Cu foil.

DOI： 10.7567/JJAP.55.080305

Highly individual SWCNTs for high performance thin film electronics

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

CARBON 103 巻頁： 228 - 234 2016年7月

記述言語：日本語出版者・発行元：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 8 巻 ( 23 ) 頁： 11882 - 11888 2016年

記述言語：日本語出版者・発行元：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 査読有り

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

ACS APPLIED MATERIALS & INTERFACES 7 巻 ( 51 ) 頁： 28134 - 28141 2015年12月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

We report the fabrication of thin film transistors (TFTs) from networks of nonbundled single-walled carbon nanotubes with controlled surface densities. Individual nanotubes were synthesized by using a spark generator-based floating catalyst CVD process. High uniformity and the control of SWCNT surface density were realized by mixing of the SWCNT aerosol in a turbulent flow mixer and monitoring the online number concentration with a condensation particle counter at the reactor outlet in real time. The networks consist of predominantly nonbundled SWCNTs with diameters of 1.0-1.3 nm, mean length of 3.97 μm, and metallic to semiconducting tube ratio of 1:2. The ON/OFF ratio and charge carrier mobility of SWCNT TFTs were simultaneously optimized through fabrication of devices with SWCNT surface densities ranging from 0.36 to 1.8 μm-2 and channel lengths and widths from 5 to 100 μm and from 100 to 500 μm, respectively. The density optimized TFTs exhibited excellent performance figures with charge carrier mobilities up to 100 cm2 V-1 s-1 and ON/OFF current ratios exceeding 1 × 106, combined with high uniformity and more than 99% of devices working as theoretically expected.

DOI： 10.1021/acsami.5b10439

Angular Sensitivity of VHF-Band CNT Antenna 査読有り

Tanaka Hiroya, Ohno Yutaka, Tadokoro Yukihiro

IEEE TRANSACTIONS ON NANOTECHNOLOGY 14 巻 ( 6 ) 頁： 1112 - 1116 2015年11月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：IEEE Transactions on Nanotechnology

A carbon nanotube (CNT)-based antenna detects incoming electromagnetic waves based on electrically induced mechanical vibration. In this study, we perform an analysis of the angular sensitivity of a CNT-based antenna. To analyze the mechanical vibration, we introduce a simple model using the image charge method. The analysis shows that the angular sensitivity depends on |sin2 θ|, where θ is the angle of arrival. This is clearly different from the traditional Hertzian dipole detector, whose sensitivity varies with |sinθ|. In addition, the full width at half maximum of the angular sensitivity distribution for the CNT-based antenna is 0.36 π, which is smaller than the value of 0.5 π for a Hertzian dipole detector.

DOI： 10.1109/TNANO.2015.2477813

Overcoming the quality-quantity tradeoff in dispersion and printing of carbon nanotubes by a repetitive dispersion-extraction process 査読有り

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

CARBON 91 巻頁： 20 - 29 2015年9月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Carbon

Dispersion-printing processes are essential for the fabrication of various devices using carbon nanotubes (CNTs). Insufficient dispersion results in CNT aggregates, while excessive dispersion results in the shortening of individual CNTs. To overcome this tradeoff, we propose here a repetitive dispersion-extraction process for CNTs. Long-duration ultrasonication (for 100 min) produced an aqueous dispersion of CNTs with sodium dodecylbenzene sulfonate with a high yield of 64%, but with short CNT lengths (a few μm), and poor conductivity in the printed films (∼450 S cm-1). Short-duration ultrasonication (for 3 min) yielded a CNT dispersion with a very small yield of 2.4%, but with long CNTs (up to 20-40 μm), and improved conductivity in the printed films (2200 S cm-1). The remaining sediment was used for the next cycle after the addition of the surfactant solution. 90% of the CNT aggregates were converted into conductive CNT films within 13 cycles (i.e., within 39 min), demonstrating the improved conductivity and reduced energy/time requirements for ultrasonication. CNT lines with conductivities of 1400-2300 S cm-1 without doping and sub-100 μm width, and uniform CNT films with 80% optical transmittance and 50 Ω/sq sheet resistance with nitric acid doping were obtained on polyethylene terephthalate films.

DOI： 10.1016/j.carbon.2015.04.033

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 8 巻 ( 4 ) 2015年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

We fabricated sub-10-μm-class short-channel, top-gate carbon nanotube thin-film transistors using a flexographic printing technique, which is a high-speed printing technique that uses a flexible polymer plate. This device fabrication process is completely photolithography-free and vacuum-free as a result of the printing technique. The printing resolution was improved by using micro-flexo plates fabricated by a microprocessing technique. The fabricated device, with a channel length of 9.5 μm, exhibited a high on-current of 0.94 mA/mm. Hysteresis was suppressed by introducing a top-gate structure.

DOI： 10.7567/APEX.8.045102

透明で柔軟なオールカーボン電子デバイス査読有り

大野雄高

応用物理 84 巻 ( 2 ) 頁： 142 - 145 2015年2月

記述言語：日本語出版者・発行元：公益社団法人応用物理学会

カーボンナノチューブ（CNT）薄膜は優れた電気的・光学的・機械的特性に加え，多機能性を兼ね備えたまれな材料である．本稿では，半導体層と電極・配線をCNT薄膜で実現したオールカーボンデバイスについて紹介する．柔軟性と透明性を併せもち，またさまざまな立体形状に加熱成形することもできる．これらの特長を生かすと，透明で存在を感じさせないデバイスや，立体的でデザイン性に富んだデバイスなどの実現につながる．

DOI： 10.11470/oubutsu.84.2_142

Electroluminescence from an Electrostatically Doped Carbon Nanotube Field-Effect Transistor

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

NANOSCIENCE AND NANOTECHNOLOGY LETTERS 6 巻 ( 10 ) 頁： 881 - 886 2014年10月

記述言語：日本語出版者・発行元：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

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

MATERIALS RESEARCH EXPRESS 1 巻 ( 2 ) 2014年6月

記述言語：日本語出版者・発行元：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 53 巻 ( 5 ) 2014年5月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Japanese Journal of Applied Physics

Chemical doping with poly(ethylene imine) (PEI) is often used to produce n-type carbon nanotube thin-film transistors (CNT TFTs) with stability in air. However, the effect of air on the device characteristics has not yet been fully investigated. In this study, we performed a detailed investigation on how the oxygen and water present in air affect stability issues, including hysteresis, current collapse, and ambipolar properties of PEI-doped n-type CNT TFTs fabricated on a transparent plastic film. We found that current collapse and hysteresis are predominantly caused by the combination of water and oxygen, suggesting that a water/oxygen redox reaction is responsible for the instability of PEI-doped devices. Water vapor has a rather more severe impact in the case of PEI-doped devices than in the case of undoped CNT TFTs because of the hygroscopicity of PEI. Surface passivation with Al2O3, deposited by a low-temperature atomic layer deposition technique, notably improved the stability of the device properties in ambient air. © 2014 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.53.05FD01

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 1 巻 ( 4 ) 頁： 360 - 364 2014年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Photonics

The photovoltaic properties of carbon nanotube/Si heterojunction solar cells were investigated using network films of high-quality single-walled carbon nanotubes (SWNTs) grown by atmospheric-pressure floating-catalyst chemical vapor deposition. Because of the optimization of the device window size and the utilization of SWNT thin films with both low resistivity and high transparency, a high photovoltaic conversion efficiency of greater than 12% was achieved for SWNT/Si heterojunction solar cells without any postprocessing, such as carrier doping treatment. In addition, the high reproducibility of the photovoltaic performance of these devices in air was demonstrated. (Graph Presented).

DOI： 10.1021/ph400133k

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 8 巻 ( 4 ) 頁： 3285 - 3293 2014年4月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Nano

We propose a technique for one-step micropatterning of as-grown carbon-nanotube films on a plastic substrate with sub-10 μm resolution on the basis of the dry transfer process. By utilizing this technique, we demonstrated the novel high-performance flexible carbon-nanotube transparent conductive film with a microgrid structure, which enabled improvement of the performance over the trade-off between the sheet resistance and transmittance of a conventional uniform carbon-nanotube film. The sheet resistance was reduced by 46% at its maximum by adding the microgrid, leading to a value of 53 ω/sq at a transmittance of 80%. We also demonstrated easy fabrication of multitouch projected capacitive sensors with 12 × 12 electrodes. The technique is quite promising for energy-saving production of transparent conductor devices with 100% material utilization. © 2014 American Chemical Society.

DOI： 10.1021/nn4041975

Split gate and asymmetric contact carbon nanotube optical devices

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

OPTICAL COMPONENTS AND MATERIALS XI 8982 巻 2014年

記述言語：日本語出版者・発行元：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査読有り

大野雄高

パリティ 29 巻頁： 18 - 21 2014年

Ohno Y.

Proceedings of the 20th International Workshop on Active-Matrix Flatpanel Displays and Devices: TFT Technologies and FPD Materials, AM-FPD 2013 頁： 243 - 246 2013年11月

記述言語：日本語出版者・発行元：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

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

APPLIED PHYSICS LETTERS 103 巻 ( 13 ) 2013年9月

記述言語：日本語出版者・発行元：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 6 巻 ( 8 ) 2013年8月

記述言語：日本語出版者・発行元：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

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

NATURE COMMUNICATIONS 4 巻頁： 2302 2013年8月

記述言語：日本語出版者・発行元：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 117 巻 ( 25 ) 頁： 13324 - 13330 2013年6月

記述言語：日本語出版者・発行元：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 6 巻 ( 2 ) 2013年2月

記述言語：日本語出版者・発行元：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 頁： 243 - 246 2013年

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

PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 10, NO 11 10 巻 ( 11 ) 頁： 1612 - 1615 2013年

記述言語：日本語出版者・発行元：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

カーボンナノチューブ電界効果型トランジスタの金属電極における大気の影響

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) 17 巻頁： 41680 2013年

石井聡, 岸本茂, 大野雄高, 水谷孝

まてりあ 52 巻 ( 6 ) 頁： 266 - 272 2013年

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

Tamaoki Masato, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

APPLIED PHYSICS LETTERS 101 巻 ( 3 ) 2012年7月

記述言語：日本語出版者・発行元：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 5 巻 ( 5 ) 頁： 307 - 319 2012年5月

記述言語：日本語出版者・発行元：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 51 巻 ( 2 ) 2012年2月

記述言語：日本語出版者・発行元：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 51 巻 ( 2 ) 2012年2月

記述言語：日本語出版者・発行元：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 1 巻 ( 4 ) 頁： 285 - 290 2011年12月

記述言語：日本語出版者・発行元：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 4 巻 ( 10 ) 頁： 963 - 970 2011年10月

記述言語：日本語出版者・発行元：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 頁： 10 - 11 2011年7月

記述言語：日本語出版者・発行元：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 22 巻 ( 19 ) 頁： 195202 2011年5月

記述言語：日本語出版者・発行元：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 6 巻 ( 3 ) 頁： 156 - 161 2011年3月

記述言語：日本語出版者・発行元：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 115 巻 ( 1 ) 頁： 270 - 273 2011年1月

記述言語：日本語出版者・発行元：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 50 巻 ( 1 ) 2011年1月

記述言語：日本語出版者・発行元：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 8 巻 ( 2 ) 頁： 567 - 569 2011年

記述言語：日本語出版者・発行元：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 8 巻 ( 2 ) 頁： 561 - 563 2011年

記述言語：日本語出版者・発行元：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 98 巻 ( 12 ) 頁： 2015 - 2031 2010年12月

記述言語：日本語出版者・発行元：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 10 巻 ( 10 ) 頁： 6655 - 8 2010年10月

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

ADVANCED MATERIALS 22 巻 ( 24 ) 頁： 2698 - + 2010年6月

記述言語：日本語出版者・発行元：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 10 巻 ( 6 ) 頁： 3805 - 3809 2010年6月

記述言語：日本語出版者・発行元：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 21 巻 ( 20 ) 頁： 205202 2010年5月

記述言語：日本語出版者・発行元：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 21 巻 ( 16 ) 2010年4月

記述言語：日本語出版者・発行元：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 49 巻 ( 2 ) 2010年

記述言語：日本語出版者・発行元：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

Environmental effects on photoluminescence of single-walled carbon nanotubes

Ohno Yutaka, Maruyama Shigeo, Mizutani Takashi

CARBON NANOTUBES 頁： 109 - 121 2010年

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

APPLIED PHYSICS EXPRESS 3 巻 ( 10 ) 2010年

記述言語：日本語出版者・発行元：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

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

APPLIED PHYSICS EXPRESS 3 巻 ( 11 ) 2010年

記述言語：日本語出版者・発行元：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年12月

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 106 巻 ( 7 ) 2009年10月

記述言語：日本語出版者・発行元：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 2 巻 ( 2 ) 頁： 98 - 102 2009年7月

記述言語：日本語出版者・発行元：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 頁： 1 - 8 2008年12月

記述言語：日本語出版者・発行元：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 7037 巻 2008年11月

記述言語：日本語出版者・発行元：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

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

APPLIED PHYSICS LETTERS 93 巻 ( 5 ) 2008年8月

記述言語：日本語出版者・発行元：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 47 巻 ( 7 ) 頁： 5652 - 5655 2008年7月

記述言語：日本語出版者・発行元：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

カーボンナノチューブのフォトルミネッセンスにおける励起子遷移と周辺環境効果査読有り

大野雄高

応用物理 77 巻 ( 6 ) 頁： 656 - 661 2008年6月

記述言語：日本語出版者・発行元：公益社団法人応用物理学会

カーボンナノチューブ（CNT）は電子デバイスから医療器具まで幅広く応用が期待され，安定した品質の得られる大量合成技術とともに，CNT材料の評価技術の確立・標準化が望まれている．フォトルミネッセンス（PL）分光はラマン分光と並んで重要な評価技術である．CNTの光学特性は周辺の環境により敏感に変化する．PL分光法を評価技術として確立するためには，PLの基礎的物理に加え，環境効果を理解する必要がある．この環境効果は，主にキャリア間に働くクーロン相互作用の遮〔しや〕蔽〔へい〕効果に起因する．それに加え，周辺材料との力学的相互作用や界面特性も影響する．環境に敏感なことを利用したナノスケールのセンシング技術も提案され，環境効果は応用面も興味深い．

DOI： 10.11470/oubutsu.77.6_656

Electrical properties of carbon nanotube FETs

Mizutani T., Nosho Y., Ohno Y.

Journal of Physics: Conference Series 109 巻 ( 1 ) 2008年3月

記述言語：日本語出版者・発行元：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 3 巻 ( 1 ) 頁： 51 - 54 2008年2月

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

Nano 3 巻 ( 1 ) 頁： 51 - 54 2008年2月

記述言語：日本語出版者・発行元：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 頁： 1 - 8 2008年

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 4 巻 ( 7 ) 頁： 2700 - 2703 2007年12月

記述言語：日本語出版者・発行元：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 1 巻 ( 5 ) 頁： 456 - 462 2007年12月

記述言語：日本語出版者・発行元：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 244 巻 ( 11 ) 頁： 4002 - 4005 2007年11月

記述言語：日本語出版者・発行元：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 18 巻 ( 41 ) 2007年10月

記述言語：日本語出版者・発行元：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

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

CHEMICAL PHYSICS LETTERS 442 巻 ( 4-6 ) 頁： 394 - 399 2007年7月

記述言語：日本語出版者・発行元：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 46 巻 ( 17-19 ) 頁： L474 - L476 2007年5月

記述言語：日本語出版者・発行元：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 46 巻 ( 4B ) 頁： 2496 - 2500 2007年4月

記述言語：日本語出版者・発行元：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

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

(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 頁： 33 2007年

(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査読有り

大野雄高

表面科学 28 頁： 40 2007年

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 頁： 488 - + 2007年

大野雄高, 能生陽介, 水谷孝

表面科学 28 巻 ( 1 ) 頁： 40 - 45 2007年

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 17 巻 ( 14 ) 頁： 3412 - 3415 2006年7月

記述言語：日本語出版者・発行元：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 73 巻 ( 23 ) 2006年6月

記述言語：日本語出版者・発行元：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 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 45 巻 ( 6B ) 頁： 5481 - 5484 2006年6月

記述言語：日本語出版者・発行元：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 45 巻 ( 6B ) 頁： 5501 - 5503 2006年6月

記述言語：日本語出版者・発行元：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

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 45 巻 ( 6B ) 頁： 5485 - 5489 2006年6月

記述言語：日本語出版者・発行元：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

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 45 巻 ( 4 B ) 頁： 3368 - 3371 2006年4月

記述言語：日本語出版者・発行元：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 45 巻 ( 4B ) 頁： 3368 - 3371 2006年4月

Ohno Y, Kishimoto S, Mizutani T

NANOTECHNOLOGY 17 巻 ( 2 ) 頁： 549 - 555 2006年1月

記述言語：日本語出版者・発行元：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 頁： 67 2006年

27aUA-1 カーボンナノチューブの蛍光の環境効果 : カイラリティ依存性(27aUA ナノチューブ光物性I,領域7(分子性固体・有機導体))

大野雄高, 岩崎慎也, 村上陽一, 岸本茂, 丸山茂夫, 水谷孝

日本物理学会講演概要集 61.1.4 巻 ( 0 ) 頁： 805 2006年

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

Institute of Physics Conference Series 184 巻頁： 279 - 282 2005年12月

記述言語：日本語出版者・発行元：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 184 巻頁： 271 - 274 2005年12月

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 184 巻頁： 275 - 278 2005年12月

記述言語：日本語出版者・発行元：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 87 巻 ( 22 ) 頁： 1 - 3 2005年11月

記述言語：日本語出版者・発行元：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 41 巻 ( 23 ) 頁： 1275 - 1276 2005年11月

記述言語：日本語出版者・発行元：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

Fabrication and characterization of peapod field-effect transistors using peapods synthesized directly on Si substrate

Metamorphic resonant tunneling diodes and its application to chaos generator ICs

Maezawa K, Iwase T, Ohno Y, Kishimoto S, Mizutani T, Sano K, Takakusaki M, Nakata H

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 巻 ( 7A ) 頁： 4790 - 4794 2005年7月

Effects of fabrication process on current-voltage characteristics of carbon nanotube field effect transistors

Mizutani T, Iwatsuki S, Ohno Y, Kishimoto S

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 巻 ( 4A ) 頁： 1599 - 1602 2005年4月

Growth of high-quality carbon nanotubes by grid-inserted plasma-enhanced chemical vapor deposition for field emitters

Kojima Y, Kishimoto S, Ohno Y, Sakai A, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 巻 ( 4B ) 頁： 2600 - 2603 2005年4月

Photoresponse of carbon nanotube field-effect transistors

Ohno Y, Kishimoto S, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 巻 ( 4A ) 頁： 1592 - 1595 2005年4月

Growth of mm-long carbon nanotubes by grid-inserted plasma-enhanced chemical vapor deposition

Kishimoto S, Kojima Y, Ohno Y, Sugai T, Shinohara H, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 巻 ( 4A ) 頁： 1554 - 1557 2005年4月

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

Nosho Y, Ohno Y, Kishimoto S, Mizutani T

APPLIED PHYSICS LETTERS 86 巻 ( 7 ) 2005年2月

Synthesis of carbon nanotube peapods directly on Si substrates

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 86 巻 ( 2 ) 2005年1月

Tunable field-effect transistor device with metallofullerene nanopeapods

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 巻 ( 1A ) 頁： 469 - 472 2005年1月

AlGaN/GaN MIS-HEMTs with ZrO2 gate insulator

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

COMPOUND SEMICONDUCTORS 2004, PROCEEDINGS 184 巻頁： 279 - 282 2005年

Kurokawa Y, Ohno Y, Shimada T, Ishida M, Kishimoto S, Okazaki T, Shinohara H, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 巻 ( 42-45 ) 頁： L1341 - L1343 2005年

記述言語：日本語出版者・発行元：Japanese Journal of Applied Physics, Part 2: Letters

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@C peapod to be ∼100meV from the temperature dependence of the drain current. © 2005 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.44.L1341

Fabricated on a GaAs-based semiconductor-on-insulator substrate using a spin-on-low-k dielectric film

Fabrication and characterization of carbon nanotube FETs

Mizutani T, Ohno Y

QUANTUM SENSING AND NANOPHOTONIC DEVICES II 5732 巻頁： 28 - 36 2005年

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 184 巻頁： 271 - 274 2005年

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 43 巻 ( 5 ) 頁： 1049 - 1054 2005年

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 184 巻頁： 275 - 278 2005年

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 85 巻 ( 24 ) 頁： 6028 - 6029 2004年12月

Fluid dynamic assembly of semiconductor blocks for heterogeneous integration

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 43 巻 ( 9A ) 頁： 5951 - 5954 2004年9月

Direct observation of high-frequency chaos signals from the resonant tunneling chaos generator

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 43 巻 ( 8A ) 頁： 5235 - 5238 2004年8月

Drain current DLTS of AlGaN-GaN MIS-HEMTs

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

IEEE ELECTRON DEVICE LETTERS 25 巻 ( 8 ) 頁： 523 - 525 2004年8月

Fabrication technique for carbon nanotube single-electron transistors using focused ion beam

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 43 巻 ( 8A ) 頁： 5669 - 5670 2004年8月

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

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

APPLIED PHYSICS LETTERS 84 巻 ( 13 ) 頁： 2412 - 2414 2004年3月

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

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

APPLIED PHYSICS LETTERS 84 巻 ( 12 ) 頁： 2184 - 2186 2004年3月

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 21 巻 ( 2-4 ) 頁： 1089 - 1092 2004年3月

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

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

APPLIED PHYSICS LETTERS 84 巻 ( 8 ) 頁： 1368 - 1370 2004年2月

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 200 巻 ( 1 ) 頁： 195 - 198 2003年11月

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 巻 ( 11 ) 頁： 6839 - 6840 2003年11月

Experimental demonstration of capacitor-coupled resonant tunneling logic gates for ultra-short gate-delay operation

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 42 巻 ( 11 ) 頁： 6766 - 6771 2003年11月

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 39 巻 ( 21 ) 頁： 1546 - 1548 2003年10月

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 50 巻 ( 10 ) 頁： 2015 - 2020 2003年10月

Position-controlled carbon nanotube field-effect transistors fabricated by chemical vapor deposition using patterned metal catalyst

Ohno Y, Iwatsuki S, Hiraka T, Okazaki T, Kishimoto S, Maezawa K, Shinohara H, Mizutani T

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 巻 ( 6B ) 頁： 4116 - 4119 2003年6月

AlGaN/GaN heterostructure metal-insulator-semiconductor high-electron-mobility transistors with Si3N4 gate insulator

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 巻 ( 4B ) 頁： 2278 - 2280 2003年4月

Comparison of electrical characteristics of metamorphic HEMTs with InPHEMTs and PHEMTs

Kawada K, Ohno Y, Kishimoto S, Maezawa K, Mizutani T, Takakusaki M, Nakata H

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 42 巻 ( 4B ) 頁： 2219 - 2222 2003年4月

Characterization of electrical properties of micro-Schottky contacts on epitaxial lateral overgrowth GaN

Kumada K, Murata T, Ohno Y, Kishimoto S, Maezawa K, Mizutani T, Sawaki N

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 42 巻 ( 4B ) 頁： 2250 - 2253 2003年4月

Fluidic assembly of thin GaAs blocks on Si substrates

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 42 巻 ( 4B ) 頁： 2226 - 2229 2003年4月

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 76 巻 ( 4 ) 頁： 475 - 478 2003年3月

Measurement of frequency dispersion of AlGaN/GaN high electron mobility transistors

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 42 巻 ( 2A ) 頁： 424 - 425 2003年2月

23aXF-6 カーボンナノチューブ・ナノピーポットにおける輸送特性の温度依存性

嶋田行志, 大野雄高, 岡崎俊也, 菅井俊樹, 岸本茂, 水谷孝, 篠原久典

日本物理学会講演概要集 58.2.4 巻 ( 0 ) 頁： 760 2003年

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 174 巻頁： 243 - 246 2003年

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 0 巻 ( 7 ) 頁： 2335 - 2338 2003年

歴代理事長座談会

大野豊, 片山卓也, 米澤明憲, 武市正人, 阿草清滋

コンピュータソフトウェア 20 巻 ( 6 ) 頁： 537 - 548 2003年

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 194 巻 ( 2 ) 頁： 447 - 451 2002年12月

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

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

APPLIED PHYSICS LETTERS 81 巻 ( 21 ) 頁： 4067 - 4069 2002年11月

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

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

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS 85 巻 ( 10 ) 頁： 1 - 6 2002年10月

Large gate leakage current in AlGaN/GaN high electron mobility transistors

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 巻 ( 8 ) 頁： 5125 - 5126 2002年8月

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 41 巻 ( 4B ) 頁： L452 - L454 2002年4月

Electroluminescence in AlGaN/GaN high electron mobility transistors under high bias voltage

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 41 巻 ( 4A ) 頁： 1990 - 1991 2002年4月

50 GHz frequency divider using resonant tunnelling chaos circuit

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

ELECTRONICS LETTERS 38 巻 ( 7 ) 頁： 305 - 306 2002年3月

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

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

JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS 41 巻 ( 2B ) 頁： 1150 - 1153 2002年2月

Electroluminescence in AlGaN/GaN HEMTS

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

COMPOUND SEMICONDUCTORS 2001 ( 170 ) 頁： 119 - 124 2002年

Low-frequency noise characteristics of AlGaN/GaN HEMT

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

COMPOUND SEMICONDUCTORS 2001 ( 170 ) 頁： 113 - 117 2002年

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

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

Japanese Journal of Applied Physics 41 巻 ( 4B ) 頁： L452 - L454 2002年

記述言語：英語出版者・発行元：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

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 頁： 57 - 60 2002年

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 40 巻 ( 10A ) 頁： L1005 - L1007 2001年10月

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 40 巻 ( 3B ) 頁： 2065 - 2068 2001年3月

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 40 巻 ( 10A ) 頁： L1005 - L1007 2001年

記述言語：英語出版者・発行元：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 頁： 236 - 239 2001年

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 40 巻 ( 3B ) 頁： 2065 - 2068 2001年

記述言語：英語出版者・発行元：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

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

JOURNAL OF APPLIED PHYSICS 87 巻 ( 9 ) 頁： 4332 - 4336 2000年5月

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 39 巻 ( 1 ) 頁： 35 - 40 2000年1月

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

Ohno Yutaka, Kishimoto Shigeru, Maezawa Koichi, Mizutani Takashi

Japanese Journal of Applied Physics 39 巻 ( 1 ) 頁： 35 - 40 2000年

記述言語：英語出版者・発行元：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 38 巻 ( 4B ) 頁： 2586 - 2589 1999年4月

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 38 巻 ( 3A ) 頁： 1363 - 1364 1999年3月

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 38 巻 ( 1B ) 頁： 546 - 549 1999年1月

Photoluminescence intensity enhancement by electron beam irradiation into GaAs quantum wells

Murata T, Ohno Y, Kishimoto S, Mizutani T

SOLID-STATE ELECTRONICS 43 巻 ( 1 ) 頁： 147 - 152 1999年1月

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 38 巻 ( 3A ) 頁： 1363 - 1364 1999年

記述言語：英語出版者・発行元：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 38 巻 ( 4B ) 頁： 2586 - 2589 1999年

記述言語：英語出版者・発行元：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 38 巻 ( 1B ) 頁： 546 - 549 1999年

記述言語：英語出版者・発行元：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