Faculty Profiles - OHNO, Yutaka

Papers - OHNO, Yutaka

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

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

APPLIED PHYSICS LETTERS Vol. 103 ( 13 ) 2013.9

Language：Japanese Publisher：Applied Physics Letters

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

DOI： 10.1063/1.4823602

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

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

APPLIED PHYSICS EXPRESS Vol. 6 ( 8 ) 2013.8

Language：Japanese Publisher：Applied Physics Express

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

DOI： 10.7567/APEX.6.085101

Mouldable all-carbon integrated circuits Open Access

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

NATURE COMMUNICATIONS Vol. 4 page： 2302 2013.8

Language：Japanese Publisher：Nature Communications

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

DOI： 10.1038/ncomms3302

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

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

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

Language：Japanese Publisher：Journal of Physical Chemistry C

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

DOI： 10.1021/jp403983y

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

Suzuki Kosuke, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

APPLIED PHYSICS EXPRESS Vol. 6 ( 2 ) 2013.2

Language：Japanese Publisher：Applied Physics Express

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

DOI： 10.7567/APEX.6.024002

Carbon nanotube-based thin-film transistors on plastic film

Ohno Yutaka

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

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

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

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

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

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

DOI： 10.1002/pssc.201300231

カーボンナノチューブ薄膜のフレキシブルエレクトロニクス応用

大野雄高

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

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

Ishii Satoshi, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

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

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

Tamaoki Masato, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

APPLIED PHYSICS LETTERS Vol. 101 ( 3 ) 2012.7

Language：Japanese Publisher：Applied Physics Letters

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

DOI： 10.1063/1.4737169

Effect of Carbon Nanotube Network Morphology on Thin Film Transistor Performance

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

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

Language：Japanese Publisher：Nano Research

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

DOI： 10.1007/s12274-012-0211-8

Estimation of Height of Barrier Formed in Metallic Carbon Nanotube

Okigawa Yuki, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

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

Language：Japanese Publisher：Japanese Journal of Applied Physics

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

DOI： 10.1143/JJAP.51.02BN01

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

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

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

Language：Japanese Publisher：Japanese Journal of Applied Physics

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

DOI： 10.1143/JJAP.51.02BN06

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

Ishii Satoshi, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

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

Language：Japanese Publisher：Materials Express

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

DOI： 10.1166/mex.2011.1037

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

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

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

Language：Japanese Publisher：Nano Research

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

DOI： 10.1007/s12274-011-0152-7

Carbon nanotubes for VLSI: Interconnect and transistor applications

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

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

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

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

DOI： 10.1109/VTSA.2011.5872210

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

Okigawa Yuki, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

NANOTECHNOLOGY Vol. 22 ( 19 ) page： 195202 2011.5

Language：Japanese Publisher：Nanotechnology

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

DOI： 10.1088/0957-4484/22/19/195202

Flexible high-performance carbon nanotube integrated circuits

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

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

Language：Japanese Publisher：Nature Nanotechnology

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

DOI： 10.1038/NNANO.2011.1

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

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

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

Language：Japanese Publisher：Journal of Physical Chemistry C

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

DOI： 10.1021/jp107361n

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

Ishii Satoshi, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

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

Language：Japanese Publisher：Japanese Journal of Applied Physics

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

DOI： 10.1143/JJAP.50.015102

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