Masataka Inoue

Osaka Institute of Technology, Ōsaka, Ōsaka, Japan

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Publications (83)70.65 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the fabrication and characterization on high-performance ZnO based TFTs on unheated plastic substrate. ZnO films were grown by pulsed laser deposition (PLD) on polyethylene napthalate (PEN) substrates. Top-gate ZnO-TFTs were fabricated by photolithography and wet chemical etching. The source and drain contacts were formed by lift-off of e-beam deposited Ti(20 nm)/Au(200 nm). An HfO2 with thickness 100 nm was selected as the gate insulator, and top gate electrode Ti(20 nm)/Au(200 nm) was deposited by e-beam evaporation. We prepared a set of the structure with SiO2/TiO2 to investigate the characteristic changes that appear in the film characteristics in response to bending. From the ID-VDS and the transfer characteristics which are affected by bending and return for the ZnO-TFT with SiO2/TiO2 buffers, the TFTs were bent to a curvature radius of 8.5 mm. The transconductance, gm is obtained 1.7 mS/mm on flat, 1.4 mS/mm on bending and 1.3 mS/mm on returning the film, respectively. The ID-VDS characteristics were therefore not changed by bending. All of the devices exhibited a clear pinch-off behavior and a high on/off current ratio of ˜10^6. The threshold voltages, Vth were not changed drastically. Furthermore, TFT structures were changed from a conventional top-gate type to a bottom-gate type. A high transconductance of 95.8 mS/mm was achieved in the bottom-gate type TFT by using Al2O3 oxide buffer.
    02/2012;
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    ABSTRACT: Ultra-fast novel nanodevices, namely the self-switching diode (SSD) were fabricated from the InAs/AlGaSb heterostructures grown by solid-source molecular beam epitaxy on a semi-insulating GaAs (100) substrate. The two lines were etched thorough the 2DEG layer and become insulating. The effective channel width was actually smaller because of the depletion layer at the etched boundaries. Depending on the sign of the applied voltage the effective channel width will increase or reduce, giving rise to the diode-like characteristics. The diode-like characteristics were clearly observed for the InAs SSDs at 300K, and turn on voltage is strongly dependent on the channel width of the SSDs. In the SSD with W = 460 nm, the InAs channel of was fully pinched of under the equilibrium condition, and positive voltage of 1.46 V was needed to drive a current thorough the InAs channel. On the other hand, the positive voltage of 2.32 V was needed to drive a current in the SSD with W = 230 nm. We found to need the higher the turn-on voltage in the SSD of the narrower channel width. Furthermore, multi-channel SSDs were fabricated. I-V characteristics and the AFM images of the SSD array of the symmetric nanowires, which are 1.5 μm long and approximately W = 170 nm. The current densities were clearly increased with increasing the number of the nano-wires. The clear diode-like nonlinear behavior and rectification reflected ballistic nature of electrons in InAs-based SSD were observed.
    02/2012;
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    ABSTRACT: Electric properties of aqueous grown ZnO nanorods were investigated. Vertical current measurement through the top 20-nm-thick Au electrode/ZnO nanorods/bottom Au film structure showed asymmetric I-V properties and was discussed in terms of different interface properties between ZnO nanorods and Au. Schottky barrier height in top Au electrode and ZnO nanorods was estimated to be 0.22eV based on core level X-ray photoelectron spectroscopy (XPS) spectra. XPS experiment also suggests that aqueous grown ZnO nanorods have Zn-polarity and that might be one of the reasons of lower barrier height. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 02/2011; 8(2):522-524.
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    ABSTRACT: Terahertz (THz) radiation from InAs thin films grown by molecular-beam epitaxy on closely lattice-matched p-type GaSb (100) substrates and lattice-mismatched semi-insulating GaAs (100) substrates was investigated. The THz radiation intensity was measured from InAs films with thicknesses between 100nm and 1.5μm excited by a femtosecond laser pulse with a wavelength of approximately 780nm. The radiation intensity increased as the InAs film thickness increased and it exceeded that from a bulk n-type InAs substrate with an electron concentration of 2.3 × 1016cm−3 when the InAs film thickness was greater than about 500nm. In addition, the THz intensity from a 1-μm-thick InAs film was greater than that from a bulk p-type InAs substrate. We ascribe this enhanced THz intensity to the wave reflected from the lower interface between the InAs film and the layer grown beneath it. We confirmed this by observing an increased pulse width due to constructive overlap of the reflected wave. The results demonstrate that InAs thin films are promising materials for THz emitting devices. KeywordsTHz radiation–InAs–Thin films–MBE
    Journal of infrared, millimeter and terahertz waves 01/2011; 32(5):646-654. · 1.12 Impact Factor
  • Physica Status Solidi (A) Applications and Materials 10/2010; 208(2):449 - 452. · 1.53 Impact Factor
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    ABSTRACT: Aiming at stable biosensing operation, aqueous-grown ZnO nanorods on sapphire substrates were examined their chemical stability against the immersion in HCl solution. Density and diameter of the ZnO nanorods were remained but their height was shortened when immersed with aminosilane modification while bare ZnO nanorods were completely disappeared after 5 min immersion, indicating that the aminosilane modification is useful to improve the chemical stability of ZnO nanolods even though the membrane by the silanezation process is not fully stable to HCl solution. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 03/2010; 7(6):1562 - 1564.
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    ABSTRACT: ZnO nanorods were grown on a -, c - and r -plane sapphire substrates using aqueous solution with microwave irradiation heating. ZnO nanorods about 200 nm diameter with c-axis orientation were grown independently on the orientation of the substrates. Photoluminescence (PL) spectrum at 6 K showed a dominant peak at 3.3609 eV (I6) with the width as narrow as 2.2 meV comparable to that of epitaxially grown single-crystalline ZnO films. The PL properties were improved by thermal annealing process without generating structural defects. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 01/2010; 7(6):1592-1594.
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    ABSTRACT: We report on the fabrication and characterization of top-gate ZnO thin film transistors (TFTs) using glass substrates. High quality ZnO epitaxial films were grown on glass substrates (Corning #1737) by pulsed laser deposition. The thickness of the films was in the range of 50-100 nm. The growth temperature was set to 380^oC. These films were characterized by x-ray diffraction, and Hall effects measurements. Highly c-axis oriented ZnO(0002) reflections corresponding to the wurtzite-phase were observed for all the films, indicating that these films grow epitaxially as a crystalline single phase on a glass substrate. The Hall effects measurements show that we have succeeded in fabricating a ZnO film with an electron mobility of 36 cm^2/Vs on a glass substrate. Top-gate ZnO TFTs were fabricated by photolithography and wet chemical etching. The ohmic contact metal Ti/Au was deposited by electron beam evaporation. The top gate electrodes and the gate insulator SiO2 were finally deposited by electron beam evaporation. A room temperature characteristic of ZnO TFT with 50 μm gate length was an n-channel depletion type with a transconductance of 5.4 mS/mm. The off current was less than 10-9 A and the on/off current ratio was about 10^6 at VDS=5V.
    03/2009;
  • Japanese Journal of Applied Physics 01/2009; 48. · 1.07 Impact Factor
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    ABSTRACT: Characteristics of ion-sensitive operation of electrolyte-solution-gate field-effect transistors (ESG-FETs) are reported with implications for the development of healthcare chips. ZnO-based polycrystalline films grown on glass substrates by sputtering were used for the ESG-FETs with the modification of the gate electrode by amino groups. The equilibrium proton transfer to/from the amino groups was found to change the gate electrode potential at a constant rate of 58 mV/pH, which successfully modulated the current flow in transistors in accordance with a conventional FET theory. A typical pH sensitivity of -0.8 muA/pH with a small time-constant of 5 s was obtained for the ESG-FET operation with 3× 5 mm2 gate area.
    Applied Physics Express - APPL PHYS EXPRESS. 01/2009; 2.
  • Journal of the Society of Materials Science Japan 01/2009; 58(3):243-250.
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    ABSTRACT: ZnO nanorod arrays were grown directly on n-Si (111) substrates using an aqueous solution method aiming at integration with Si-based device technology. The growth of the ZnO nanorod arrays was found to be influenced by the thickness of the native oxide layer on Si substrates. A dense array of about 200 nm diameter nanorods was obtained from the thick equimolar aqueous solution containing 100 mM of zinc nitrate hexahydrate and hexamethylenetetramine, while the solution with lower concentrations resulted in scattered corn-shaped ones. Electrochemical potential in electrolyte of the ZnO nanorod arrays on Si (111) substrates was studied and found to have a slope of -50 mV/pH, suggesting a potential application to future sensing nanosystems.
    Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures 01/2009; 27(3):1684-. · 1.36 Impact Factor
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    ABSTRACT: We report on the fabrication and the DC characterization of InAs/AlGaSb three-terminal ballistic junctions consisting of three quantum-wire T-shaped structures. InAs/AlGaSb quantum wells were grown by molecular beam epitaxy, and the three-terminal ballistic junctions were defined using electron beam lithography. Typical electron mobility of 80,000 -- 200,000 cm^2/Vs and sheet carrier density of 1.0 -- 2.0 x 10^12 cm-2 were observed at 77K. Ballistic electron transport properties are due to the one-dimensional (1D) nature of electrons in InAs and dramatic changes in scattering probability from the 2D electron system, which are expected to occur at higher temperatures. We measured the rectified output voltage, VC at the central branch of the devices at various temperatures. Nonlinearity and negative voltages at the central branch, regardless the polarities of the source-drain (left and right branch) voltage, were observed at each temperature. Clear rectification effects were observed in the ballistic junctions even at room temperature. Details of the triode characteristics in the InAs/AlGaSb ballistic devices will be discussed at the conference.
    03/2008;
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    ABSTRACT: We report on the fabrication and characterization of InAs/AlGaSb high electron mobility transistors (HEMTs) with high-k gate insulators (Al2O3 and HfO2). InAs/AlGaSb quantum well structures were grown by molecular beam epitaxy on a semi-insulating GaAs substrate [1]. From Hall measurements at room temperature, the as-grown wafer showed an electron mobility of 20,000-25,000 cm^2/Vs and a sheet carrier density of 1.0-2.0x10^12 cm-2. InAs/AlGaSb HEMTs have demonstrated a maximum extrinsic transconductance of 181mS/mm at room temperature. The gate leakage current has been markedly decreased by using thin high-k gate insulators. A typical gate current density of less than 1 nA/mm at room temperature was achieved by inserting the high-k gate insulator. We also found that the leakage current density was smaller than for other experimental results on InAs HEMTs with a Shottky gate [2]. In addition, we evaluated the electron motility and drift velocity by increasing the electronic field between the sources and the drain. [1] T. Maemoto et al., Journal of Physics: Conference Series 38, 112 (2006). [2] J. Bergman et al., 61th Device Research Conference, June 23-25 (2003).
    03/2008;
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    ABSTRACT: We studied the structures of ZnO/ZnMgO heterostructure field-effect transistors (FETs) to achieve high performance and stability in these devices. Two types of heterostructure were examined. One consisted of a ZnO channel layer and a thin ZnMgO cap layer to form a hetero-metal-insulator-semiconductor (hetero-MIS) structure, and the other had formed a conventional MIS structure. Both Al2O3 and HfO2 were examined as high-k gate dielectrics. The results indicate that high-performance FETs can be obtained using a hetero-MIS structure and that the reduction in access resistance is crucial for further improvements in FET performance. In addition, both an increase in transconductance and a stable FET operation were realized for the hetero-MIS structure by replacing the Al2O3 gate dielectric with a HfO2 gate dielectric. Stable operation was verified from the observation of a markedly reduced hysteresis less than 0.1 V for HfO2, which was lower than that for Al2O3.
    Japanese Journal of Applied Physics 01/2008; 47:2845-2847. · 1.07 Impact Factor
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    ABSTRACT: We report on structural and optical properties for Zn1-xMgxO (ZMO) thin films produced by pulsed laser ablation. ZMO thin films were grown on a-plane Al2O3 substrates at 400°C. In order to efficiently incorporate Mg into ZnO thin films, we used multiple ZnO-MgO ablation targets. Pulses from a Nd:YAG laser (4th harmonic generation: 266 nm) were directed on the ZnO-MgO ablation targets, which consisted of MgO single crystals mounted on ZnO ceramic targets. The ZMO films were characterized by x-ray diffraction, optical transmittance and cathodeluminescence (CL) measurements. Highly c-axis oriented ZMO(0002) reflections corresponding to the wurtzite-phase were observed. The c-axis lattice constants of the films were determined from the ZnMgO(0002) peak. The c-axis length of the ZMO films decreased linearly with Mg content. From the optical transmittance spectra of ZMO films, we observed a blue shift in the absorption edge with increasing Mg content. Band gap energies of ZMO thin films were determined from the optical transmittance and CL spectra. We found that the band gap energy changed from 3.27 eV to 3.95 eV. The Mg content of ZMO films increased monotonically with the number of laser pulses which struck the MgO target. These results show that laser ablation using multiple targets of ZnO and MgO is effective for band engineering of ZMO.
    Journal of Physics Conference Series 05/2007; 59(1):670.
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    ABSTRACT: High‐mobility electrons were successfully formed in a ZnO/ZnMgO heterostructure grown on an a‐surface sapphire substrate by molecular beam epitaxy. A very high low‐temperature mobility of as high as 890 cm2/Vs was observed at 20 K. The observation of Shubnikov‐de Haas (SdH) oscillations at 4.2 K revealed that the high‐density electrons form a two‐dimensional electron gas (2DEG) and the 2DEG is induced by both spontaneous and piezoelectric polarizations in ZnO and ZnMgO layers. The fact that the SdH oscillations contain only one frequency component excludes the existence of 2DEG layers in the ZnO/ZnMgO multiple‐quantum‐well (MQW) buffer layer. Self‐consistent calculations for electronic states in the ZnO/ZnMgO MQW layers also support the experimental observations. © 2007 American Institute of Physics
    AIP Conference Proceedings. 04/2007; 893(1):319-320.
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    ABSTRACT: We report on the fabrication and characterization of InAs/AlGaSb heterojunction field-effect transistors (HFETs) with high-k gate insulators. These HFETs have been operated with a maximum extrinsic transconductance of 180 mS/mm at room temperature. The use of an 80-nm-thick Al2O3 gate insulator greatly lowered the gate leakage. The leakage current density was three orders of magnitude lower compared with other experimental studies of Shottky gate InAs HFETs. In addition, we evaluated the electron motility and drift velocity by increasing the field strength.
    04/2007;
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    ABSTRACT: To achieve a superconducting transition temperature higher than 100 K in the BiSrCaCuO system, the addition of Pb has been known to be effective. This paper points out the problems in forming superconductive thin films using sputtering, and proposes a way to introduce Pb during deposition which cannot be achieved reproducibly by the conventional method.In this method, Pb is deposited on a substrate, followed by sputter-deposition of a BiSrCaCuO thin film and the solid phase reaction of the two films. The characteristics, film composition, crystallinity, and electric conductivity of the film formed by this method will be described. The results indicate that this method is effective in producing superconductive films. The relationship between superconductivity and Pb doping will be also described.
    Electronics and Communications in Japan (Part II Electronics) 03/2007; 73(10):98 - 105. · 0.18 Impact Factor
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    ABSTRACT: We discuss peculiarities of the nonlinear optical processes utilizing intersubband nonlinearities in high band offset heterostructures formed by three nearly lattice matched binaries, InAs, GaSb, AlSb, and their alloys. We show that these materials offer unique benefits for nonlinear optics due to great flexibility in designing optical interaction schemes in a wide frequency range and very large values of the nonlinear susceptibilities even involving short-wavelength transitions. The resulting nonlinear conversion efficiency for the second-harmonic or sum-frequency generation is in the mW/W2 range even for very short coherence lengths of the order of several mum.
    Proc SPIE 03/2007;

Publication Stats

437 Citations
70.65 Total Impact Points

Institutions

  • 1991–2011
    • Osaka Institute of Technology
      Ōsaka, Ōsaka, Japan
  • 2002
    • Australian National University
      • Department of Electronic Materials Engineering (EME)
      Canberra, Australian Capital Territory, Australia
  • 1995
    • Hokkaido University
      • Research Center for Integrated Quantum Electronics
      Sapporo-shi, Hokkaido, Japan
  • 1983
    • Fujitsu Ltd.
      Kawasaki Si, Kanagawa, Japan