Faculty Profiles - OHNO, Yutaka

Papers - OHNO, Yutaka

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

Ohno Yutaka, Moriyama Naoki, Kishimoto Shigeru, Mizutani Takashi

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

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

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

DOI： 10.1002/pssc.201000571

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

Hata Kensuke, Ohno Yutaka, Kishimoto Shigeru, Mizutani Takashi

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

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

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

DOI： 10.1002/pssc.201000551

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Carbon Nanotubes for VLSI: Interconnect and Transistor Applications

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

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

Language：Japanese Publisher：Proceedings of the IEEE

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

DOI： 10.1109/JPROC.2010.2068030

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Electrical breakdown of individual Si nanochains and silicide nanochains.

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

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

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

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

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

Language：Japanese Publisher：Advanced Materials

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

DOI： 10.1002/adma.200904006

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PubMed

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

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

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

Language：Japanese Publisher：Journal of Nanoscience and Nanotechnology

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

DOI： 10.1166/jnn.2010.1983

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PubMed

Thin film transistors using PECVD-grown carbon nanotubes

Ono Yuki, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

NANOTECHNOLOGY Vol. 21 ( 20 ) page： 205202 2010.5

Language：Japanese Publisher：Nanotechnology

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

DOI： 10.1088/0957-4484/21/20/205202

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PubMed

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

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

NANOTECHNOLOGY Vol. 21 ( 16 ) 2010.4

Language：Japanese Publisher：Nanotechnology

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

DOI： 10.1088/0957-4484/21/16/165201

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

Okigawa Yuki, Kishimoto Shigeru, Ohno Yutaka, Mizutani Takashi

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

Language：Japanese Publisher：Japanese Journal of Applied Physics

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

DOI： 10.1143/JJAP.49.02BD02

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Environmental effects on photoluminescence of single-walled carbon nanotubes

Ohno Yutaka, Maruyama Shigeo, Mizutani Takashi

CARBON NANOTUBES page： 109 - 121 2010

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

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

APPLIED PHYSICS EXPRESS Vol. 3 ( 10 ) 2010

Language：Japanese Publisher：Applied Physics Express

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

DOI： 10.1143/APEX.3.105102

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Medium Scale Integrated Circuits Using Carbon Nanotube Thin Film Transistors

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

APPLIED PHYSICS EXPRESS Vol. 3 ( 11 ) 2010

Language：Japanese Publisher：Applied Physics Express

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

DOI： 10.1143/APEX.3.115101

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

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

2009 International Semiconductor Device Research Symposium, ISDRS '09 2009.12

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

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

JOURNAL OF APPLIED PHYSICS Vol. 106 ( 7 ) 2009.10

Language：Japanese Publisher：Journal of Applied Physics

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

DOI： 10.1063/1.3234389

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

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

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

Language：Japanese Publisher：Carbon - Science and Technology

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

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Electrical properties of carbon nanotube FETs

Mizutani T., Ohno Y., Kishimoto S.

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

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

DOI： 10.1109/ASDAM.2008.4743290

Scopus

Electrical properties of carbon nanotube FETs

Mizutani T., Ohno Y., Kishimoto S.

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

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

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

DOI： 10.1117/12.794695

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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 Vol. 93 ( 5 ) 2008.8

Language：Japanese Publisher：Applied Physics Letters

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

DOI： 10.1063/1.2969290

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

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

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

Language：Japanese Publisher：Japanese Journal of Applied Physics

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

DOI： 10.1143/JJAP.47.5652

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Photoluminescence in carbon nanotubes : exciton transitions and environmental effects Reviewed

OHNO Yutaka

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

Language：Japanese Publisher：The Japan Society of Applied Physics

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

DOI： 10.11470/oubutsu.77.6_656

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Papers - OHNO, Yutaka