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KANASHIMA Takeshi

    Department of Electric and Electronic Engineering　Professor
Last Updated :2024/05/19

Researcher Information

Degree

  • Dr. of Engineering（1996/03 Osaka University）

Research funding number

  • 30283732

J-Global ID

Research Interests

  • high-Kゲート   放射光による電子材料の作製及びエッチング   Si/SiO界面の評価   Si酸化膜   high-K gate.   Preparation and Etching of Electrical Materials by Synchro-Radiation   characterization of SiO2 thin fims and Si/SiO2 interface   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electric/electronic material engineering
  • Nanotechnology/Materials / Thin-film surfaces and interfaces

Academic & Professional Experience

  • 2022/04 - Today  Kindai UniversityFaculty of Humanity-Oriented Science and Engineering Department of Electric and Electronic EngineeringProfessor
  • 2007/07 - 2022/03  Osaka UniversityGraduate School of Engineering Science准教授
  • 2007/04 - 2007/06  Osaka UniversityGraduate School of Engineering Science助教
  • 1996/04 - 2007/03  Osaka UniversityFaculty of Engineering Science助手

Education

  • 1993/04 - 1996/03  Osaka University  Graduate School of Engineering Science  Area of Materials and Device Physics, Department of Physical Science
  • 1991/04 - 1993/03  Osaka University  Graduate School of Engineering Science  Area of Materials and Device Physics, Department of Physical Science
  • 1987/04 - 1991/03  Osaka University  Faculty of Engineering Science  Department of Electrical Engineering

Association Memberships

  • 新無機膜研究会   放射光学会   応用物理学会   shinmukimaku kenkyukai   

Published Papers

  • Y. Murakami; T. Usami; R. Watarai; Y. Shiratsuchi; T. Kanashima; R. Nakatani; Y. Gohda; K. Hamaya
    Journal of Applied Physics AIP Publishing 134 (22) 0021-8979 2023/12 
    Using a molecular beam epitaxy technique, we experimentally demonstrate a multiferroic heterostructure consisting of metastable ferromagnetic Co3Mn on piezoelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT). Inserting a 2-nm-thick Fe layer between Co3Mn and PMN-PT(001) allows the formation of bcc Co3Mn layers even at an extremely low growth temperature of ∼80°C. Upon increasing this temperature to 200 °C, a bcc Co3Mn/Fe/PMN-PT(001) multiferroic heterostructure with a relatively large saturation magnetization of ∼1680 kA/m and an atomically flat interface is obtained, resulting in an obvious converse magnetoelectric (CME) effect. The large CME effect originates mainly from the strain-induced modulation of the magnetic anisotropy energy, supported by the first-principles calculations.
  • T. Usami; Y. Sanada; Y. Shiratsuchi; S. Yamada; T. Kanashima; R. Nakatani; K. Hamaya
    Journal of Magnetism and Magnetic Materials Elsevier BV 570 (15) 170532 - 170532 0304-8853 2023/03 [Refereed]
  • Shumpei Fujii; Takamasa Usami; Yu Shiratsuchi; Adam M. Kerrigan; Amran Mahfudh Yatmeidhy; Shinya Yamada; Takeshi Kanashima; Ryoichi Nakatani; Vlado K. Lazarov; Tamio Oguchi; Yoshihiro Gohda; Kohei Hamaya
    NPG Asia Materials Springer Science and Business Media LLC 14 (1) 1884-4049 2022/12 
    Abstract To overcome a bottleneck in spintronic applications such as those of ultralow-power magnetoresistive random-access memory devices, the electric-field control of magnetization vectors in ferromagnetic electrodes has shown much promise. Here, we show the giant converse magnetoelectric (CME) effect in a multiferroic heterostructure consisting of the ferromagnetic Heusler alloy Co2FeSi and ferroelectric-oxide Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) for electric-field control of magnetization vectors. Using an in-plane uniaxial magnetic anisotropy of polycrystalline Co2FeSi film grown on PMN-PT(011), the nonvolatile and repeatable magnetization vector switchings in remanent states are demonstrated. The CME coupling coefficient of the polycrystalline Co2FeSi/PMN-PT(011) is over 1.0 × 10−5 s/m at room temperature, comparable to those of single-crystalline Fe1-xGax/PMN-PT systems. The giant CME effect has been demonstrated by the strain-induced variation in the magnetic anisotropy energy of Co2FeSi with an L21-ordered structure. This approach can lead to a new solution to the reduction in the write power in spintronic memory architectures at room temperature.
  • Takamasa Usami; Shumpei Fujii; Shinya Yamada; Yu Shiratsuchi; Takeshi Kanashima; Ryoichi Nakatani; Kohei Hamaya
    IEEE Transactions on Magnetics 58 (8) 0018-9464 2022 
    We experimentally study a strain-meditated converse magnetoelectric (CME) effect in multiferroic heterostructures consisting of Co2MnSi and Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT). To investigate the CME effect, Co2MnSi films are grown on PMN-PT(001) at various growth temperatures by molecular beam epitaxy. Using magneto-optical Kerr-effect and strain measurements, we find that the remanent magnetization state only for the L21-ordered Co2MnSi/PMN-PT is modulated by the application of the lattice strain while that for the B2-ordered Co2MnSi/PMN-PT is insensitive to the strain. We conclude that the formation of L21-ordered structure is needed to obtain effective CME effect in the Co2MnSi/PMN-PT multiferroic heterostructure.
  • Takahiro Naito; Michihiro Yamada; Shinya Yamada; Takeshi Kanashima; Kentarou Sawano; Kohei Hamaya
    Materials Science in Semiconductor Processing ELSEVIER SCI LTD 113 1369-8001 2020/07 [Refereed]
     
    © 2020 Elsevier Ltd We find relatively large inverse local two-terminal magnetoresistance (MR) effect in ferromagnet (FM)/semiconductor (SC) lateral spin-valve devices. The local MR as a function of the bias voltage applied between two FM/SC contacts shows nonlinear variation, including sign inversion in high bias-voltage conditions. The inverse local MR can be observed up to room temperature, while conventional positive local MR disappears at around 225 K. To consider the origin of the large inverse MR effect, the influence of the nonlinear spin-detection efficiency at a biased FM/SC contact and the spin-drift effect in the SC channel are discussed.
  • Shinya Yamada; Hidenori Higashi; Takeshi Kanashima; Kohei Hamaya
    Materials Science in Semiconductor Processing ELSEVIER SCI LTD 112 1369-8001 2020/06 [Refereed]
     
    © 2020 Elsevier Ltd For flexible semiconductor spintronic devices, we explore the growth of one of the ferromagnetic full-Heusler alloys, Co2FeSi, on a (111)-oriented pseudo-single-crystalline Ge/polyimide flexible template. Using a low-temperature molecular beam epitaxy (MBE) technique, crystalline Co2FeSi films are obtained on the flexible Ge at less than 80 °C. An MBE-grown Ge layer on the flexible Ge enables to improve magnetic properties of the Co2FeSi films. This work is an important step of high-performance flexible spintronics with ferromagnetic full-Heusler alloys.
  • Takeshi Kanashima; Masanori Okuyama
    FERROELECTRIC-GATE FIELD EFFECT TRANSISTOR MEMORIES: DEVICE PHYSICS AND APPLICATIONS, 2ND EDITION SPRINGER-VERLAG SINGAPORE PTE LTD 131 225 - 239 0303-4216 2020 
    Organic ferroelectric-gate field-effect transistor (FET) memories were fabricated using pentacene and rubrene thin films as the semiconductors and a poly(vinylidene fluoride-tetrafluoroethylene) [P(VDF-TeFE)] thin film as the ferroelectric gate. The P(VDF-TeFE) film was prepared by spin-coating and annealing at 170 degrees C for 2.5 h, and the pentacene was prepared by vacuum evaporation. In contrast, the rubrene thin film sheet was grown by physical vapor transport and placed onto a spin-coated P(VDF-TeFE) thin film layer. The polarization-electric field hysteresis of the P(VDF-TeFE) thin film was observed, and the obtained remanent polarization of 3.9 mu C/cm(2) was sufficient for controlling the surface potential of pentacene or rubrene. A hysteresis loop was clearly observed in the drain current-gate voltage behavior of the ferroelectric-gate FET. In the case of the ferroelectric-gate FET with P(VDF-TeFE)/pentacene, the ON/OFF ratio of drain current was 830, and the carrier mobility was 0.11 cm(2)/Vs. On the other hand, the maximum drain current of the FET with P(VDF-TeFE)/rubrene was 1.6x10(-6) A, which is about two orders of magnitude larger than that of the P(VDF-TeFE)-gate FET using the pentacene thin film. The mobility of the organic ferroelectric-gate FET using the rubrene thin film was 0.71 cm(2)/Vs, which is 6.5 times larger than that of the FET with pentacene thin film.
  • H. Higashi; K. Kudo; K. Yamamoto; S. Yamada; T. Kanashima; I. Tsunoda; H. Nakashima; K. Hamaya
    Journal of Applied Physics AIP Publishing 123 (21) 215704 - 215704 0021-8979 2018/06 [Refereed]
     
    We study the electrical properties of pseudo-single-crystalline Ge (PSC-Ge) films grown by a Auinduced layer exchange crystallization method at 250 degrees C. By inserting the SiNx layer between PSC-Ge and SiO2, we initiatively suppress the influence of the Ge/SiO2 interfacial defective layers, which have been reported in our previous works, on the electrical properties of the PSC-Ge layers. As a result, we can detect the influence of the ionized Authorn donors on the temperature-dependent hole concentration and Hall mobility. To further examine their electrical properties in detail, we also fabricate p-thin-film transistors (TFTs) with the PSC-Ge layer. Although the off-state leakage currents are suppressed by inserting the SiNx layer, the value of on/off ratio remains poor (<10(2)). Even after the post-annealing at 400 degrees C for the TFTs, the on/off ratio is still poor (similar to 10(2)) because of the gate-induced drain leakage current although a nominal field effect mobility is enhanced up to similar to 25 cm(2)/V s. Considering these features, we conclude that the Au contaminations into the PSC-Ge layer can affect the electrical properties and device performances despite a low-growth temperature of 250 degrees C. To achieve further high-performance p-TFTs, we have to suppress the Au contaminations into PSC-Ge during the Au-induced crystallization growth. Published by AIP Publishing.
  • T. Kanashima; R. Yamashiro; M. Zenitaka; K. Yamamoto; D. Wang; J. Tadano; S. Yamada; H. Nohira; H. Nakashima; K. Hamaya
    MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING ELSEVIER SCI LTD 70 260 - 264 1369-8001 2017/11 
    Electrical properties of epitaxial La2O3/germanium (Ge) structures can be significantly improved by using epitaxially grown Lutetium(Lu)- or Yttrium(Y)-doped La2O3 passivation layers. For the metal-insulator semiconductor (MIS) devices, hysteretic nature of capacitance-voltage (C-V) characteristics becomes negligibly small and the interface trap density (D-it) is estimated to be less than 10(12) cm(-2) eV(-1) at around the midgap. We discuss a possible mechanism of the improvement of the electrical properties.
  • H. Higashi; M. Nakano; K. Kudo; Y. Fujita; S. Yamada; T. Kanashima; I. Tsunoda; H. Nakashima; K. Hamaya
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 111 (22) 222105-1 - 222105-4 0003-6951 2017/11 [Refereed]
     
    We experimentally demonstrate a flexible thin-film transistor (TFT) with (111)-oriented crystalline germanium (Ge) layers grown by a gold-induced crystallization method. Accumulation-mode metal source/drain p-channel Ge TFTs are fabricated on a polyimide film at <= 400 degrees C. A field-effect mobility (mu(FE)) of 10.7 cm(2)/Vs is obtained, meaning the highest mu(FE) in the p-TFTs fabricated at <= 400 degrees C on flexible plastic substrates. This study will lead to high-performance flexible electronics based on an inorganic-semiconductor channel. Published by AIP Publishing.
  • Michihiro Yamada; Yuichi Fujita; Shinya Yamada; Takeshi Kanashima; Ientarou Sawano; Kohei Hamaya
    MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING ELSEVIER SCI LTD 70 83 - 85 1369-8001 2017/11 [Refereed]
     
    We experimentally demonstrate the control of electrical properties of Heusler-alloy/Ge contacts by phosphorous (P) delta-doping techniques with Si-layer insertion. Low-temperature molecular beam epitaxy methods enable us to obtain the high quality Heusler-alloy/Ge heterointerfaces with P delta-doped layers. Although the resistance area product (RA) values are scattered in the Heusler-alloy/Ge interfaces with conventional delta-doping techniques, we precisely adjust the RA values in the newly developed interface with Si-layer insertion. This method will open a way for developing source and drain structures in Ge-based spintronics devices. (C) 2016 Elsevier Ltd. All rights reserved.
  • Y. Fujita; M. Yamada; M. Tsukahara; T. Oka; S. Yamada; T. Kanashima; K. Sawano; K. Hamaya
    PHYSICAL REVIEW APPLIED AMER PHYSICAL SOC 8 (1) 014007-1 - 014007-9 2331-7019 2017/07 [Refereed]
     
    To achieve spin transport in heavily doped n-type Ge (n(+)-type Ge) in the high-temperature range (T >= 130 K), we examine the growth of highly spin-polarized Co2FeAl0.5Si0.5 (CFAS) films on Ge(111). Using lateral spin valves with the CFAS/Ge Schottky-tunnel contacts, we can observe giant enhancement in the nonlocal spin signals at low temperatures and get a spin signal of approximately 1 m ohm at room temperature. Since nonlocal Hanle-effect curves can be seen up to about 250 K, we experimentally clarify that the spin-relaxation mechanism in n(+)-type Ge in 8 K <= T <= 250 K is attributed to impurity- and phonon-induced spin-flip scatterings. This study experimentally shows the availability of the CFAS spin injector and detector for getting important factors of the spin relaxation up to near room temperature, even in Ge.
  • M. Ikawa; M. Kawano; S. Sakai; S. Yamada; T. Kanashima; K. Hamaya
    JOURNAL OF CRYSTAL GROWTH ELSEVIER SCIENCE BV 468 676 - 679 0022-0248 2017/06 
    We study epitaxial growth and magnetic properties of ferromagnetic alloys, Fe3Si and CoFe, on low-temperature-grown germanium (LT-Ge) layers. Despite high-quality epitaxial growth of Fe3Si and CoFe layers on Ge substrates, the structural and magnetic characteristics of Fe3Si layers are significantly degraded only when the growth is conducted on LT-Ge. We clarify that the degradation is induced by the diffusion of Ge atoms into Fe3Si. Since high-quality CoFe layers can be obtained even on LT-Ge, there is no Ge diffusion into CoFe. It is important for vertical Ge spintronics devices to understand the mechanism of the suppression of the Ge diffusion into the ferromagnetic materials.
  • S. Oki; T. Kurokawa; S. Honda; S. Yamada; T. Kanashima; H. Itoh; K. Hamaya
    AIP ADVANCES AMER INST PHYSICS 7 (5) 2158-3226 2017/05 
    We demonstrate generation and detection of pure spin currents by combining a two-terminal spin-injection technique and Co2FeSi (CFS) spin injectors in lateral spin valves (LSVs). We find that the two-terminal spin injection with CFS has the robust dependence of the nonlocal spin signals on the applied bias currents, markedly superior to the four-terminal spin injection with permalloy reported previously. In our LSVs, since the spin transfer torque from one CFS injector to another CFS one is large, the nonlocal magnetoresistance with respect to applied magnetic fields shows large asymmetry in high bias-current conditions. For utilizing multi-terminal spin injection with CFS as a method for magnetization reversals, the terminal arrangement of CFS spin injectors should be taken into account. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
  • Y. Fujita; M. Yamada; S. Yamada; T. Kanashima; K. Sawano; K. Hamaya
    PHYSICAL REVIEW B AMER PHYSICAL SOC 94 (24) 2469-9950 2016/12 [Refereed]
     
    We experimentally study the spin relaxation mechanism in heavily doped n-type germanium (Ge) layers by electrically detecting pure spin current transport. The spin diffusion length (lambda(Ge)) in heavily doped n-type Ge layers at 125 K is less than 0.7 mu m, much shorter than that expected in the recent study by Dushenko et al. We find that the spin relaxation time tau(s) is independent of temperature in the range of 8 to 125 K, which can be interpreted by the recent theory by Song et al. This study clarifies that the spin-relaxation mechanism at low temperatures in degenerate Ge is dominated by extrinsic scattering with impurities.
  • K. Hamaya; T. Kurokawa; S. Oki; S. Yamada; T. Kanashima; T. Taniyama
    PHYSICAL REVIEW B AMER PHYSICAL SOC 94 (14) 140401(R)-1 - 140401(R)-5 2469-9950 2016/10 [Refereed]
     
    We study the effect of a pure spin current on the Kondo singlet in a dilutedmagnetic alloy using nonlocal lateral spin valve structures with highly spin polarized Co2FeSi electrodes. Temperature dependence of the nonlocal spin signals shows a sharp reduction with decreasing temperature, followed by a plateau corresponding to the low temperature Fermi liquid regime below the Kondo temperature (TK). The spin diffusion length of the Kondo alloy is found to increase with increasing spin accumulation. The results are in agreement with the intuitive description that the Kondo singlet cannot survive any more in sufficiently large spin accumulation even below TK.
  • S. Yamada; S. Honda; J. Hirayama; M. Kawano; K. Santo; K. Tanikawa; T. Kanashima; H. Itoh; K. Hamaya
    PHYSICAL REVIEW B AMER PHYSICAL SOC 94 (9) 094435-1 - 094435-7 2469-9950 2016/09 [Refereed]
     
    We study magnetic properties and interfacial characteristics of all-epitaxial D0(3)-Fe3Si/L2(1)-Fe3-xMnxSi/L2(1)-Co2FeSi Heusler-compound trilayers grown on Ge(111) by room-temperature molecular beam epitaxy. We find that the magnetization reversal processes can be intentionally designed by changing the chemical composition of the intermediate Fe3-xMnxSi layers because of their tunable ferromagnetic-paramagnetic phase-transition temperature. From first-principles calculations, interfacial half metallicity in the Co2FeSi layer is nearly expected when the sequence of stacking layers along < 111 > of the Fe2MnSi/Co2FeSi interface includes the atomic row of L2(1)- or B2-ordered structures. We believe that Co2FeSi/Fe2MnSi/Co2FeSi trilayer systems stacked along < 111 > will open a new avenue for high-performance current-perpendicular-to-plane giant magnetoresistive devices with Heusler compounds.
  • M. Kawano; K. Santo; M. Ikawa; S. Yamada; T. Kanashima; K. Hamaya
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 109 (2) 022406-1 - 022406-4 0003-6951 2016/07 [Refereed]
     
    We experimentally show spin transport up to 125 K in a similar to 40-nm-thick p-Ge(111) layer, epitaxially grown on a ferromagnetic Fe3Si. From the magnitude of the spin signals, the spin diffusion length of the p-Ge(111) layer at 10K can be estimated to be approximately 50 nm. To understand the detectable spin transport in the p-Ge(111), we should consider the energy splitting between heavy-hole and light-hole bands at the L point. Published by AIP Publishing.
  • Yuichi Fujita; Michihiro Yamada; Yuta Nagatomi; Keisuke Yamamoto; Shinya Yamada; Kentarou Sawano; Takeshi Kanashima; Hiroshi Nakashima; Kohei Hamaya
    JAPANESE JOURNAL OF APPLIED PHYSICS IOP PUBLISHING LTD 55 (6) 0021-4922 2016/06 [Refereed]
     
    A possible low-temperature fabrication process of a gate-stack for Ge-based spin metal-oxide-semiconductor field-effect transistor (MOSFET) is investigated. First, since we use epitaxial ferromagnetic Heusler alloys on top of the phosphorous doped Ge epilayer as spin injector and detector, we need a dry etching process to form Heusler-alloy/n(+)- Ge Schottky-tunnel contacts. Next, to remove the Ge epilayers damaged by the dry etching process, the fabricated structures are dipped in a 0.03% diluted H2O2 solution. Finally, Al/SiO2/GeO2/Ge gate-stack structures are fabricated at 300 degrees C as a top gate-stack structure. As a result, the currents in the Ge-MOSFET fabricated here can be modulated by applying gate voltages even by using the low-temperature formed gate-stack structures. This low-temperature fabrication process can be utilized for operating Ge spin MOSFETs with a top gate electrode. (C) 2016 The Japan Society of Applied Physics
  • S. Yamada; K. Tanikawa; J. Hirayama; T. Kanashima; T. Taniyama; K. Hamaya
    AIP Advances American Institute of Physics Inc. 6 (5) 056115/1 - 6 2158-3226 2016/05 [Refereed]
     
    We study magnetic properties of metallic multilayers with FeRh/ferromagnet interfaces grown by low-temperature molecular beam epitaxy. Room-temperature coercivity of the ferromagnetic layers is significantly enhanced after the growth of FeRh, proving the existence of the exchange coupling between the antiferromagnetic FeRh layer and the ferromagnetic layer. However, exchange bias is not clearly observed probably due to the presence of disordered structures, which result from the lattice strain at the FeRh/ferromagnet interfaces due to the lattice mismatch. We infer that the lattice matched interface between FeRh and ferromagnetic layers is a key parameter for controlling magnetic switching fields in such multilayer systems.
  • K. Hamaya; S. Yamada; K. Kasahara; T. Kanashima
    ECS Transactions Electrochemical Society Inc. 75 (8) 651 - 659 1938-6737 2016 [Refereed]
     
    Heteroepitaxial growth of bcc metallic alloys or a high-k insulator on Ge(111) has been explored for next generation Ge-based devices. First, we introduce a finely controlled crystal growth technique of bcc-type ferromagnetic alloys on Ge(111). Next, we show that the Fermi level pinning is significantly suppressed at the high-quality bcc-alloys/Ge heterointerfaces. Using these kinds of structures, we can achieve spin injection and detection in n-Ge. Finally, we present a new approach to gate-stack structures for Ge- MOSFET. Even a crystalline high-k insulator can be grown epitaxially on Ge(111) and a high-quality heterointerface can be achieved. Also, reasonable electrical characteristics are obtained. These finely controlled heterointerfaces will open a way for developing new technologies in next generation Ge-based devices with low power consumption.
  • Takeshi Kanashima; Masanori Okuyama
    FERROELECTRIC-GATE FIELD EFFECT TRANSISTOR MEMORIES: DEVICE PHYSICS AND APPLICATIONS SPRINGER-VERLAG BERLIN 131 187 - 201 0303-4216 2016 [Refereed]
     
    Organic ferroelectric-gate field-effect transistor (FET) memories were fabricated using pentacene and rubrene thin films as the semiconductors and a poly (vinylidene fluoride-tetrafluoroethylene) [P(VDF-TeFE)] thin film as the ferroelectric gate. The P(VDF-TeFE) film was prepared by spin coating and annealing at 170 degrees C for 2.5 h, and the pentacene was prepared by vacuum evaporation. In contrast, the rubrene thin film sheet was grown by physical vapor transport and placed onto a spin-coated P(VDF-TeFE) thin film layer. The polarization-electric field hysteresis of the P(VDF-TeFE) thin film was observed, and the obtained remanent polarization of 3.9 mu C/cm(2) was sufficient for controlling the surface potential of pentacene or rubrene. A hysteresis loop was clearly observed in the drain current-gate voltage behavior of the ferroelectric-gate FET. In the case of the ferroelectric-gate FET with P(VDF-TeFE)/pentacene, the ON/OFF ratio of drain current was 830, and the carrier mobility was 0.11 cm(2)/Vs. On the other hand, the maximum drain current of the FET with P(VDF-TeFE)/rubrene was 1.6 x 10(-6) A, which is about two orders of magnitude larger than that of the P(VDF-TeFE)-gate FET using the pentacene thin film. The mobility of the organic ferroelectric-gate FET using the rubrene thin film was 0.71 cm(2)/Vs, which is 6.5 times larger than that of the FET with pentacene thin film.
  • M. Kawano; M. Ikawa; K. Arima; S. Yamada; T. Kanashima; K. Hamaya
    JOURNAL OF APPLIED PHYSICS AMER INST PHYSICS 119 (4) 045302-1 - 045302-6 0021-8979 2016/01 [Refereed]
     
    We demonstrate low-temperature growth of all-epitaxial Co2FeSi/Ge/Co2FeSi trilayer structures by developing Sn-induced surfactant-mediated molecular beam epitaxy (SMBE) of Ge on Co2FeSi. Despite the growth of a semiconductor on a metal, we verify that the inserted Sn monolayers between Ge and Co2FeSi enable to promote the 2D epitaxial growth of Ge up to 5 nm at a T-G of 250 degrees C. An understanding of the mechanism of the Sn-induced SMBE leads to the achievement of all-epitaxial Co2FeSi/Ge/Co2FeSi trilayer structures with spin-valve-like magnetization reversals. This study will open a way for vertical-type and high-performance sGe-based spintronics devices. (C) 2016 AIP Publishing LLC.
  • T. Kanashima; H. Nohira; M. Zenitaka; Y. Kajihara; S. Yamada; K. Hamaya
    JOURNAL OF APPLIED PHYSICS AMER INST PHYSICS 118 (22) 0021-8979 2015/12 
    We demonstrate a high-quality La2O3 layer on germanium (Ge) as an epitaxial high-k-gate-insulator, where there is an atomic-arrangement matching condition between La2O3(001) and Ge(111). Structural analyses reveal that (001)-oriented La2O3 layers were grown epitaxially only when we used Ge(111) despite low growth temperatures less than 300 degrees C. The permittivity (k) of the La2O3 layer is roughly estimated to be similar to 19 from capacitance-voltage (C-V) analyses in Au/La2O3/Ge structures after post-metallization-annealing treatments, although the C-V curve indicates the presence of carrier traps near the interface. By using X-ray photoelectron spectroscopy analyses, we find that only Ge-O-La bonds are formed at the interface, and the thickness of the equivalent interfacial Ge oxide layer is much smaller than that of GeO2 monolayer. We discuss a model of the interfacial structure between La2O3 and Ge(111) and comment on the C-V characteristics. (C) 2015 AIP Publishing LLC.
  • S. Yamada; K. Tanikawa; J. Hirayama; T. Kanashima; T. Taniyama; K. Hamaya
    PHYSICAL REVIEW B AMER PHYSICAL SOC 92 (9) 094416-1 - 094416-7 1098-0121 2015/09 [Refereed]
     
    B2-ordered Fe100-xRhx alloys, which exhibit a first-order magnetic phase transition from an antiferromagnetic state to a ferromagnetic one at around 350 K, have so far been formed by high-temperature heat treatments above 600 degrees C. Here we demonstrate low-temperature (200 degrees C) growth of B2-ordered Fe100-xRhx films on body-centered-cubic (bcc) alloys. By using molecular beam epitaxy with an insertion of D0(3)-ordered Fe3Si buffer layers, which have good atomic arrangement matching with Fe100-xRhx along < 111 >, B2-ordered Fe100-xRhx films having a sharp magnetic phase transition can be obtained at 200 degrees C even in as-grown conditions. We find that the disordered structures are mainly derived from the lattice strain in the Fe100-xRhx films due to the lattice mismatch between Fe100-xRhx and the buffer layers. We discuss the role of heat treatments and other buffer structures on the B2-ordering and magnetic properties for Fe100-xRhx films.
  • Bu-Sang Cha; Takeshi Kanashima; Seung-Mok Lee; Masanori Okuyama
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 67 (3) 486 - 495 0374-4884 2015/08 [Refereed]
     
    The vibration amplitude, damping ratio and viscous damping force in capacitive micromachinedultrasonic transducers (CMUTs) with a perforated membrane have been calculated theoretically and compared with the experimental data on its vibration behavior. The electrical bias of the DC and the AC voltages and the operation frequency conditions influence the damping effect because leads to variations in the gap height and the vibration velocity of the membrane. We propose a new estimation method to determine the damping ratio by the decay rate of the vibration amplitudes of the perforated membrane plate are measured using a laser vibrometer at each frequency, and the damping ratios were calculated from those results. The influences of the vibration frequency and the electrostatic force on the damping effect under the various operation conditions have been studied.
  • Kento Yamasaki; Soichiro Oki; Shinya Yamada; Takeshi Kanashima; Kohei Hamaya
    APPLIED PHYSICS EXPRESS IOP PUBLISHING LTD 8 (4) 1882-0778 2015/04 [Refereed]
     
    We demonstrate the conversion between a heat current and a spin current in Cu-based lateral spin valves (LSVs) with single-crystalline Co2FeSi (CFS) electrodes. We can observe the thermally induced spin injection from CFS into Cu resulting from the spin-dependent Seebeck effect, and the heat current generated by the spin-dependent Peltier effect can be detected even in the LSV structures. This study is an important step toward understanding heat-spin conversion in single-crystalline materials with various electronic band structures. (C) 2015 The Japan Society of Applied Physics
  • H. Higashi; K. Kasahara; K. Kudo; H. Okamoto; K. Moto; J. -H. Park; S. Yamada; T. Kanashima; M. Miyao; I. Tsunoda; K. Hamaya
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 106 (4) 041902-1 - 041902-5 0003-6951 2015/01 [Refereed]
     
    We demonstrate large-area (similar to 600 mu m), (111)-oriented, and high-crystallinity, i.e., pseudo-single-crystalline, germanium (Ge) films at 275 degrees C, where the temperature is lower than the softening temperature of a flexible substrate. A modulated gold-induced layer exchange crystallization method with an atomic-layer deposited Al2O3 barrier and amorphous-Ge/Au multilayers is established. From the Raman measurements, we can judge that the crystallinity of the obtained Ge films is higher than those grown by aluminum-induced-crystallization methods. Even on a flexible substrate, the pseudo-single-crystalline Ge films for the circuit with thin-film transistor arrays can be achieved, leading to high-performance flexible electronics based on an inorganic-semiconductor channel. (C) 2015 AIP Publishing LLC.
  • Masayuki Sohgawa; Akito Nozawa; Hokuto Yokoyama; Takeshi Kanashima; Masanori Okuyama; Takashi Abe; Haruo Noma; Teruaki Azuma
    Proceedings of IEEE Sensors Institute of Electrical and Electronics Engineers Inc. 2014- (December) 1749 - 1752 2168-9229 2014/12 [Refereed]
     
    A multimodal sensor with Si micro-cantilever embedded in PDMS elastomer for measurement of proximity and touch forces has been fabricated and characterized. DC resistance of the strain gauge on the cantilever changes in proportion to the indentation depth of the object. On the other hand, the AC (> 0:5 MHz) impedance including photo-sensitive component of Si increases with increase of distance between the sensor surface and the object because of decrease of light intensity reflected on the object surface. Moreover, the AC impedance is different between grounding and floating of the proximate object because of difference of distribution of electrostatic field between electrodes, so that it is suggested that proximity can be detected as the impedance change by light as well as the electric field.
  • Masayuki Sohgawa; Kosuke Watanabe; Takeshi Kanashima; Masanori Okuyama; Takashi Abe; Haruo Noma; Teruaki Azuma
    Proceedings of IEEE Sensors Institute of Electrical and Electronics Engineers Inc. 2014- (December) 1706 - 1709 2168-9229 2014/12 [Refereed]
     
    The surface texture of various materials has been characterized by tactile sensor with a micro-cantilever embedded in the PDMS elastomer. The maximum output (resistance of strain gauge on the cantilever) change of the sensor by indentation of the object on the sensor surface depends on the hardness or thickness of the object. Moreover, output change is asymmetric in a back-and-forth indentation test because of relaxation of deformation. On the other hand, the output increases rapidly at beginning of stepwise sliding of the sensor at the object surface because of static friction, and changes periodically corresponding to stick-slip oscillation or surface roughness after slipping. It is demonstrated that about 30 materials of papers, clothes, leathers, and plastic sheets, have been classified into 5 clusters by the principal component analysis using feature quantities extracted from the sensor outputs.
  • Seiji Nakashima; Taiki Ito; Hironori Fujisawa; Takeshi Kanashima; Masanori Okuyama; Masafumi Kobune; Masaru Shimizu
    Japanese Journal of Applied Physics IOP PUBLISHING LTD 53 (8 SPEC. ISSUE 3) 0021-4922 2014/08 [Refereed]
     
    Recently, the semiconducting characteristics of BiFeO3 thin films such as the photovoltaic effect or diode characteristics have been extensively investigated. However, the current conduction mechanism has not been completely clarified yet. In this study, the current conduction mechanism of the ideal BFO thin film, which has a single domain without conduction domain walls, such as 71 and 109° domain walls, has been investigated. The current density-electric field (J-E) characteristics of 100- to 1000-nm-thick BFO thin films and their temperature dependence in the range of 100-260K have been carefully investigated. From these thickness and temperature dependences of the J-E characteristics, it can be concluded that the most probable mechanism of current conduction in the single-domain BFO thin film is space-charge-limited current (SCLC) with a shallow trap. © 2014 The Japan Society of Applied Physics.
  • T. Kanashima; J. M. Park; D. Ricinschi; M. Okuyama
    FERROELECTRICS TAYLOR & FRANCIS LTD 466 (1) 63 - 73 0015-0193 2014/07 [Refereed]
     
    Polycrystalline BiFeO3 (BFO) films have been prepared by using magnetic-field-assisted pulsed laser deposition (PLD), and the microstructure and ferroelectric properties have been investigated. A high deposition rate has been achieved, and a columnar structure has been observed in comparison with that of a BFO thin film prepared without a magnetic field. Trajectories of the charged particles in the plume under a magnetic field have been calculated. As a result, the angle between the substrate normal and the incident particle on the substrate becomes large in magnetic-field-assisted PLD. The evolution of film growth in PLD under a magnetic field has been analyzed by the calculation using the facet growth model. The calculation results show the film with the columnar structure normal to the substrate is obtained. In the experiments, the plume is confined by a magnetic field, and its emission intensity becomes high in PLD under a magnetic field. Moreover, the evaporated ions are excited more strongly under a magnetic field than without a magnetic field. The BFO films show the columnar structure that coincides well with the calculated image, and the deposition rate is enhanced. The polarization versus electric field (P - E) hysteresis loops of BFO films is obtained at room temperature (RT), and the polarization is reduced in the film deposited under a magnetic field.
  • Takeshi Kanashima; Yuu Katsura; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS IOP PUBLISHING LTD 53 (4) 0021-4922 2014/04 [Refereed]
     
    An organic ferroelectric gate field-effect transistor (FET) memory has been fabricated using an organic semiconductor of rubrene thin film with a high mobility and a gate insulating layer of poly(vinylidene fluoride-tetrafluoroethylene) [P(VDF-TeFE)] thin film. A rubrene thin-film sheet was grown by physical vapor transport (PVT), and placed onto a spin-coated P(VDF-TeFE) thin-film layer, and Au source and drain electrodes were formed on this rubrene thin film. A hysteresis loop of the drain current-gate voltage (I-D-V-G) characteristic has been clearly observed in the ferroelectric gate FET, and is caused by the ferroelectricity. The maximum drain current is 1.5 x 10(-6) A, which is about two orders of magnitude larger than that of the P(VDF-TeFE) gate FET using a pentacene thin film. Moreover, the mobility of this organic ferroelectric gate FET using rubrene thin film is 0.71cm(2)V(-1)s(-1), which is 35 times larger than that of the FET with pentacene thin film. (C) 2014 The Japan Society of Applied Physics
  • Dan Ricinschi; Takeshi Kanashima; Masanori Okuyama
    ELECTROCERAMICS XIV CONFERENCE AMER INST PHYSICS 1627 87 - 91 0094-243X 2014 [Refereed]
     
    Here we use density functional theory calculations to study the impact of various spin configurations of magnetic ions on structure and properties of BiFeO3 (BFO). Low-spin and intermediate-spin electronic configurations of Fe in tetragonal BFO impact on the c/a ratio according to the way the t(2g)/e(g) orbitals are filled. Such metastable structures could enhance the magnetization in BFO and couple the ferroelectric and magnetic degrees of freedom in novel ways.
  • Hokuto Yokoyama; Takeshi Kanashima; Masanori Okuyama; Takashi Abe; Haruo Noma; Teruaki Azuma; Masayuki Sohgawa
    IEEJ Transactions on Sensors and Micromachines 134 (3) 58 - 63 1341-8939 2014 [Refereed]
     
    A tactile sensing system that measures normal and shear (triaxial) forces has been developed, and its characteristics such as linearity and crosstalk have been evaluated. Triaxial forces are estimated from the resistance changes of NiCr thin film strain gauge attached to three microcantilevers. The output voltage of the Wheatstone bridge that comprises a gauge film and three reference resistances is acquired using an A/D converter after amplification. Triaxial forces are calculated from the output voltages of three microcantilevers by simple matrix multiplication. Nonlinearity and crosstalk are less than 4% when the normal force applied is up to 1N and less than 10% when the shear force applied is up to 0.2N. Active touch sensing was demonstrated using an object having a striped profile measuring 0.1mm in height and 1mm in width. © 2014 The Institute of Electrical Engineers of Japan.
  • Hokuto Yokoyama; Takeshi Kanashima; Masanori Okuyama; Takashi Abe; Haruo Noma; Teruaki Azuma; Masayuki Sohgawa
    IEEJ Transactions on Sensors and Micromachines Institute of Electrical Engineers of Japan 134 (7) 229 - 234 1347-5525 2014 [Refereed]
     
    A novel method has been proposed to detect proximity and tactile information using a single MEMS sensor. Tactile information is obtained from DC resistance change of NiCr strain gauge film. In contrast, proximity information is obtained from AC impedance change, which is caused by photo-absorption of Si wafer irradiated by a neighboring LED. Therefore, selection of the information to be acquired is performed by switching the DC and AC measurement system. Experimental results show almost linear tactile output to indentation of 0 to 0.5mm and non-linear proximity output to distance of 0 to 50 mm, respectively. Moreover, the sensor is able to acquire rough shape of a toroidal object by proximity measurement. © 2014 The Institute of Electrical Engineers of Japan.
  • Hokuto Yokoyama; Masayuki Sohgawa; Takeshi Kanashima; Teruaki Azuma; Masanori Okuyama; Haruo Noma
    Japanese Journal of Applied Physics IOP PUBLISHING LTD 52 (6) 06GL08  0021-4922 2013/06 [Refereed]
     
    A miniature tactile sensor has been fabricated by connecting stress-sensitive part with an amplifier of integrated circuit through through-silicon-via (TSV) electrically. The sensitive part consists of three warped cantilevers with piezoresistive NiCr thin film which are prepared on a silicon-oninsulator wafer by the surface micromachining technique. The TSV connection can reduce noise of detected change of the piezoresistive output induced by wire between the sensitive part and the amplifier. Fabricated tactile sensor of 5 μ 5mm2 size has linear dependence of the output on both normal and shear forces. The output noise has been successfully decreased by 14 and 34% in the sensor using the TSVs compared with that using wires of 3 and 6mm lengths, respectively. © 2013 The Japan Society of Applied Physics.
  • Hokuto Yokoyama; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama; Takashi Abe; Haruo Noma; Teruaki Azuma
    2013 IEEE SENSORS IEEE 1090 - 1093 1930-0395 2013 [Refereed]
     
    Intensity and direction of normal and shear (3-axial) forces have been measured by using a tactile sensor with NiCr strain gauge film on 3 microcantilevers. Output voltage of the Wheatstone bridge which includes a gauge film is measured as digital signal after amplification. 3-axial forces are calculated from the output voltages of 3 microcantilevers every 100 ms. When normal force is applied from 0 to 1 N, the measurement errors of normal and shear forces are less than 50 mN and 10 mN, respectively. When shear force of 0.1 and 0.2 N is applied, the angle error of evaluated direction is less than 10 degrees.
  • Masayuki Sohgawa; Kosuke Watanabe; Takeshi Kanashima; Masanori Okuyama; Haruo Noma; Teruaki Azuma
    IEEJ Transactions on Sensors and Micromachines The Institute of Electrical Engineers of Japan 133 (5) 4 - 154 1341-8939 2013 [Refereed]
     
    A measurement method of surface texture of objects using active touching of a tactile sensor which has inclined micro-cantilevers with strain gauge film on Si has been reviewed. The fabricated tactile sensors have an ability of detecting roughness of more than ∼20 μm, and they can detect striped pattern on the Japanese banknote. Various kinds of blank paper which have different properties including hardness, friction coefficient, and surface roughness were identified using output from the fabricated tactile sensor. The feature quantities which depend on paper properties were defined from the resistance change by pushing, moving, and stopping of the sensor. The papers were classified in four clusters by principal component analysis of defined feature quantities. © 2013 The Institute of Electrical Engineers of Japan.
  • K. Watanabe; M. Sohgawa; T. Kanashima; M. Okuyama; H. Noma; T. Azuma
    2013 Transducers and Eurosensors XXVII: The 17th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS and EUROSENSORS 2013 1012 - 1015 2013 [Refereed]
     
    We have fabricated the multi-axial tactile sensor which has micro-cantilevers with strain gauge film on Si embedded in hemispherical elastomer, and various kinds of papers have been identified by active touch. Transient responses of the resistance change have been obtained when the sensor was pushed and moved on various kinds of blank papers successively. Some features are extracted from the response by a principal component analysis and the papers are classified in several clusters. © 2013 IEEE.
  • Kosuke Watanabe; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    2013 WORLD HAPTICS CONFERENCE (WHC) IEEE 139 - 144 2013 
    Various kinds of papers have been identified by active touch of a multi-axial tactile sensor which has micro-cantilevers with strain gauge film on Si. When fine surface of the standard surface roughness scale and the printed stripe pattern on a banknote have been scanned by the tactile sensor, it allows to measure such fine roughness as a resistance change of the gauge film, and the triangular unevenness could be obtained down to 20 mu m. Transient responses of the resistance change have been obtained when the sensor was pushed and moved on various kinds of blank papers successively. Some features are extracted from the response by a principal component analysis and the papers are classified in four clusters.
  • Jung Min Park; Seiji Nakashima; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama
    Ferroelectrics TAYLOR & FRANCIS LTD 453 (1) 1 - 7 0015-0193 2013/01 [Refereed]
     
    Polycrystalline BiFeO3 (BFO) films on Pt/TiO2/ SiO2/Si substrate have been prepared by a pulsed laser deposition (PLD) method with various repetition rates. The X-ray diffraction (XRD) pattern observes single-phase perovskite structure with a small secondary phase. While the film-thickness is increased with increasing repetition rates, the grain size increases, and the leakage current reduces. Also, good polarization versus electric field (P-E) hysteresis loops of all polycrystalline BFO films were obtained at room temperature (RT). It is seen that the polarization value (Pr) practically remains almost constant for all the BFO films, and the coercive field (Ec) decreases with increasing the film thickness. © 2013 Copyright Taylor and Francis Group, LLC.
  • Jung Min Park; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama; Seiji Nakashima
    Journal of the Korean Physical Society KOREAN PHYSICAL SOC 62 (7) 1041 - 1045 0374-4884 2013 [Refereed]
     
    Epitaxial BiFeO3 (BFO) thin films have been prepared on La-doped (001) SrTiO3 substrates (La-STO) by using magnetic-field-assisted pulsed laser deposition. X-ray diffraction patterns of the epitaxial BFO thin films prepared under magnetic fields of 0, 0. 1, and 0. 4 T show only (00ℓ) diffraction peaks without secondary phases. From the results of reciprocal space mapping for all epitaxial BFO thin films, (003) reflections show splitting spots, and asymmetric spots of (-103) and (103) reflections exhibit a rhombohedral structure. The microstructure of the epitaxial thin films was modified by the strength of magnetic field, and a columnar structure was shown in the film prepared under a high deposition rate for a magnetic field of 0. 4 T. The polarization versus electric field hysteresis loops were obtained at room temperature (RT) in all the epitaxial films; in particular, the remanent polarization for the epitaxial film prepared under a magnetic field of 0. 1 T was 46 μC/cm2 at RT while the current density was reduced in comparison with those of other epitaxial films. © 2013 The Korean Physical Society.
  • Masayuki Sohgawa; Daiki Hirashima; Yusuke Moriguchi; Tatsuya Uematsu; Wataru Mito; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    SENSORS AND ACTUATORS A-PHYSICAL ELSEVIER SCIENCE SA 186 32 - 37 0924-4247 2012/10 [Refereed]
     
    A tactile sensor consisting of microcantilevers has been fabricated using the NiCr-thin-film strain gauge with low noise by surface micromachining and the slippage has been detected by using the fabricated tactile sensor array. The NiCr alloy thin film of Cr: 75 wt% has very low temperature coefficient of resistance (TCR) and is employed to suppress the temperature noise and drift. The fabricated tactile sensor with the NiCr thin film (Cr: 75 wt%) has linear dependencies of the resistance on normal and shear forces, and shows lower noise and temperature drift than that with conventional NiCr (Cr: 20 wt%) film. Normal and shear forces measured by fabricated sensor well coincide with applied forces with errors of 3-3.5 kPa. Moreover, the gripping status of the robotic hand was detected by using fabricated tactile sensor array, and the slipping condition can be judged at the rate of 76.5%. A (C) 2012 Elsevier B.V. All rights reserved.
  • Jung Min Park; Seiji Nakashima; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama
    Japanese Journal of Applied Physics IOP PUBLISHING LTD 51 (9S2) 09MD05  1347-4065 2012/09 [Refereed]
     
    Polycrystalline BiFeO3 (BFO) thin films have been prepared on Pt/TiO2/SiO2/Si substrates by using a pulsed laser deposition (PLD) method under a magnetic field. The X-ray diffraction (XRD) pattern shows a single-phase perovskite structure with no secondary phases, and (010) and (020) peaks slightly shift to lower angles in comparison with those of a BFO thin film prepared without a magnetic field. A columnar structure and small grain size were observed and the leakage current is slightly high in comparison with that of a BFO thin film prepared without a magnetic field. A polarization versus electric field (P–E) hysteresis loop was obtained at RT and the polarization at zero electric field is 50 µC/cm2. Ferroelectric domain switching corresponding to up and down polarization states was confirmed. An enhanced piezoelectric coefficient (d33) of about 100 pm/V has been obtained at a certain point. Ferroelectric and piezoelectric properties were affected by a columnar microstructure formed by magnetic field application.
  • Jung Min Park; Seiji Nakashima; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama
    Japanese Journal of Applied Physics 51 (9 PART3) 0021-4922 2012/09 [Refereed]
     
    Polycrystalline BiFeO 3 (BFO) thin films have been prepared on Pt/TiO 2/SiO 2/Si substrates by using a pulsed laser deposition (PLD) method under a magnetic field. The X-ray diffraction (XRD) pattern shows a single-phase perovskite structure with no secondary phases, and (010) and (020) peaks slightly shift to lower angles in comparison with those of a BFO thin film prepared without a magnetic field. A columnar structure and small grain size were observed and the leakage current is slightly high in comparison with that of a BFO thin film prepared without a magnetic field. A polarization versus electric field (P-E) hysteresis loop was obtained at RT and the polarization at zero electric field is 50 μC/cm 2. Ferroelectric domain switching corresponding to up and down polarization states was confirmed. An enhanced piezoelectric coefficient (d 33) of about 100 pm/V has been obtained at a certain point. Ferroelectric and piezoelectric properties were affected by a columnar microstructure formed by magnetic field application. © 2012 The Japan Society of Applied Physics.
  • Masayuki Sohgawa; Tatsuya Uematsu; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    Technical Meeting on Sensors and Micromachines 2012 (8) 1 - 6 2012/06
  • DongHun Lee; Kazuki Kubo; Takeshi Kanashima; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS IOP PUBLISHING LTD 51 (4) 0021-4922 2012/04 [Refereed]
     
    The passivation of the Ge surface is an important issue for a high-performance transistor. Therefore, we carried out the theoretical and experimental analyses to search for alternative terminal materials on the Ge surface. First, the chemical reactivities of various nonmetal elements on the Ge surface were simulated by the semi empirical molecular orbital method to passivate the Ge(100) and (111) surface dangling bonds. The simulations showed that F, Cl, and Se are more useful for the treatment of the Ge(100) surface and that F, Cl, S, and Se are more stable on the Ge(111) surface than H. In particular, S is more effective in terminating the dangling bonds by forming a bridge bond (Ge-S-Ge) and more stable on the Ge(111) surface than on the Ge(100) surface. Next, for experimental confirmation, we performed an (NH4)(2)S solution treatment method on the p-type Ge(100) and (111) substrates, and fabricated HfO2/p-Ge metal-insulator-semiconductor (MIS) devices by photo assisted metal organic chemical vapor deposition (MOCVD). As a result, the S-treatment using (NH4)(2)S solution improved more the electrical properties of the HfO2/p-Ge(111) MIS capacitor than those of the capacitor on the Ge(100) substrate. Recently, the sulfur treatment of the Ge surface has been mainly focused on the Ge(100) substrate. However, the results of this study show that the sulfur treatment method using (NH4)(2)S solution is more useful on the Ge(111) surface than on the Ge(100) surface. (C) 2012 The Japan Society of Applied Physics
  • Masayuki Sohgawa; Hokuto Yokoyama; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    Material Research Society Symposium Proceedings 1427 1946-4274 2012/04 [Refereed]
     
    We have developed the tactile sensor using the microcantilevers with strain gauge film which can detect normal and shear forces simultaneously. In this work, the tactile sensor and the IC amplifier have been integrated heterogeneously to shorten the wire length by chip-on-chip stacking and reduce the noise in the output voltage. Standard deviation of the noise can be reduced from 27.6 mV to 3.3 mV by heterogeneous integration of the tactile sensor and the IC amplifier using Au wire bonding. By this heterogeneous integration, the device size and wiring numbers can be reduced, and installation of more sensors is allowed on fingertips of the robot. Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC amplifier on the backside of the sensor chip, instead of using Au wires. Although TSV can be fabricated successfully, resistance to sacrificial etching process is problem. As a result, Si3N4 used instead of SiO2 has improved insulation between TSVs.
  • Takeshi Kanashima; Kazuki Yabe; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS IOP PUBLISHING LTD 51 (2) 0021-4922 2012/02 [Refereed]
     
    Organic ferroelectric field-effect transistor (FET) memories have been fabricated using pentacene as the semiconductor and a flat poly(vinylidene fluoride-tetrafluoroethylene) [P(VDF-TeFE)] thin film as the ferroelectric gate. The P(VDF-TeFE) film is prepared by spin coating, and it was cooled slowly with a flattening process after annealing. The polarization-electric field (P-E) hysteresis of the P(VDF-TeFE) thin film prepared by slow cooling is larger than that in the case of quick cooling. Moreover, the flattening process does not have a negative effect on ferroelectric properties. The obtained remanent polarization (P-r) of 5.2 mu C/cm(2) is sufficient for controlling the pentacene surface potential. Good memory characteristics are obtained in the P(VDF-TeFE) gate FET with pentacene deposited on the flat P(VDF-TeFE). The maximum drain current is about twice larger than that deposited on the rough P(VDF-TeFE) prepared by quick cooling, and the memory retention is over 1 week. (C) 2012 The Japan Society of Applied Physics
  • Masayuki Sohgawa; Hokuto Yokoyama; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    Materials Research Society Symposium Proceedings 1427 14 - 19 0272-9172 2012 [Refereed]
     
    We have developed the tactile sensor using the microcantilevers with strain gauge film which can detect normal and shear forces simultaneously. In this work, the tactile sensor and the IC amplifier have been integrated heterogeneously to shorten the wire length by chip-on-chip stacking and reduce the noise in the output voltage. Standard deviation of the noise can be reduced from 27.6 mV to 3.3 mV by heterogeneous integration of the tactile sensor and the IC amplifier using Au wire bonding. By this heterogeneous integration, the device size and wiring numbers can be reduced, and installation of more sensors is allowed on fingertips of the robot. Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC amplifier on the backside of the sensor chip, instead of using Au wires. Although TSV can be fabricated successfully, resistance to sacrificial etching process is problem. As a result, Si 3N4 used instead of SiO2 has improved insulation between TSVs. © 2012 Materials Research Society.
  • Masanori Okuyama; Kaoru Yamashita; Minoru Noda; Masayuki Sohgawa; Takeshi Kanashima; Haruo Noma
    Transactions on Electrical and Electronic Materials Korean Institute of Electrical and Electronic Material Engineers 13 (5) 215 - 220 2092-7592 2012 
    Miniature ultrasonic and tactile sensors on Si substrate have been proposed, fabricated and characterized to detect objects for a dexterous robot. The ultrasonic sensor consists of piezoelectric PZT thin film on a Pt/Ti/SiO< inf> 2< /inf> and/or Si diaphragm fabricated using a micromachining technique the ultrasonic sensor detects the piezoelectric voltage as an ultrasonic wave. The sensitivity has been enhanced by improving the device structure, and the resonant frequency in the array sensor has been equalized. Position detection has been carried out by using a sensor array with high sensitivity and uniform resonant frequency. The tactile sensor consists of four or three warped cantilevers which have NiCr or Si:B piezoresistive layer for stress detection. Normal and shear stresses can be estimated by calculation using resistance changes of the piezoresitive layers on the cantilevers. Gripping state has been identified by using the tactile sensor which is installed on finger of a robot hand, and friction of objects has been measured by slipping the sensor. © 2012 KIEEME.
  • Bu-Sang Cha; Seung-Mok Lee; Takeshi Kanashima; Masanori Okuyama; Tsunehisa Tanaka
    SENSORS AND ACTUATORS A-PHYSICAL ELSEVIER SCIENCE SA 171 (2) 191 - 198 0924-4247 2011/11 [Refereed]
     
    Capacitive micromachined ultrasonic transducers (CMUTs) with a perforated membrane have been fabricated and characterized in air. Two types of CMUT device have been fabricated having perforation ratio (area ratio of holes = AR) of 10% and 20%, and analyzed about electrical and mechanical characteristics. The perforation ratio (AR) of membrane substantially influences on the electrostatic force and mechanical restoring force of the device since it leads to the area variation of electrode and membrane, it subsequently influences on the sensitivity and frequency response of the CMUT device. The electrostatic force and mechanical restoring force were improved by decreasing the AR and increasing the DC bias voltage. The open-circuit sensitivity of a CMUT having AR 10% membrane, 8.45 mu V/Pa, is larger than that of AR 20%, 4.07 mu V/Pa at DC 15 V. Furthermore, the resonance behaviors were observed in the range of 60-80 kHz, and the resonance frequency could be changed by varying the applied DC voltage and AR. (C) 2011 Elsevier B.V. All rights reserved.
  • Park Jung Min; Gotoda Fumiya; Nakashima Seiji; Sohgawa Masayuki; Kanashima Takeshi; Okuyama Masanori
    Jpn J Appl Phys The Japan Society of Applied Physics 50 (9) 09NB03 - 09NB03-5 0021-4922 2011/09 
    BiFe0.9Co0.1O3(BFCO) films have been prepared on Pt/TiO2/SiO2/Si substrates with a magnetic field of 0.4 T by pulsed laser deposition. BFCO films prepared under magnetic field show a single-phase perovskite structure with a little secondary phase, and their (010) and (020) peaks shift to lower angles than those of the film prepared without magnetic field. The BFCO film of about 1 μm thickness shows a columnar structure, although the BFCO film of about 350 nm prepared without magnetic field shows a grain like structure. The leakage current density of the BFCO film prepared under magnetic field is much lower than that of the BFCO film prepared without magnetic field. The saturated $P$--$E$ hysteresis loops of both BFCO films are obtained at 80 K, and the $M$--$H$ hysteresis loops of both BFCO films show a weak ferromagnetism behavior at room temperature.
  • Nakashima Seiji; Fujisawa Hironori; Suminaga Hiroyuki; Park Jung Min; Nishioka Hiroshi; Kobune Masafumi; Kanashima Takeshi; Okuyama Masanori; Shimizu Masaru
    Jpn J Appl Phys The Japan Society of Applied Physics 50 (9) 09NB01 - 09NB01-4 0021-4922 2011/09 
    BiFeO3(BFO) thin films with various Bi/Fe ratios have been deposited on SrRuO3/SrTiO3(001) substrates by dual ion beam sputtering. A Bi2O3ceramic disk and an $\alpha$-Fe2O3powder disk were used as targets, and simultaneously sputtered using a dual ion beam. Bi/Fe ratio has been controlled by adjusting the beam current ratio on the Bi2O3- and $\alpha$-Fe2O3-side ion sources. Even a BFO thin film with a Bi/Fe ratio of 0.95 and a smooth surface shows a slightly leaky characteristic. $[\text{Fe$^{2+}$}]/([\text{Fe$^{3+}$}]+[\text{Fe$^{2+}$}])$ ratio has been estimated by Auger electron spectroscopy (AES). From the AES profiles, the $[\text{Fe$^{2+}$}]/([\text{Fe$^{3+}$}]+[\text{Fe$^{2+}$}])$ ratio of the BFO thin film with a Bi/Fe ratio of 0.95 is estimated to be 0.14. It is considered that not only improving surface roughness but also enhancing oxidization is important for reduction in leakage current.
  • Seiji Nakashima; Hironori Fujisawa; Masaru Shimizu; Osami Sakata; Tomoaki Yamada; Hiroshi Funakubo; Jung Min Park; Takeshi Kanashima; Masanori Okuyama
    Journal of the Korean Physical Society KOREAN PHYSICAL SOC 59 (31) 2556 - 2559 0374-4884 2011/09 [Refereed]
     
    An electric-field-induced strain at 80 K in a 350-nm-thick BiFeO3 (BFO) thin film deposited by pulsed laser deposition has been investigated by using time-resolved X-ray diffraction with synchrotron radiation under an electric field. 300-nsec-wide and 804.09-nsec-period voltage pulses were applied to the BFO thin film during the measurements. The time-resolved X-ray diffraction profile around the BFO (001) diffraction peak indicates that the BFO (001) diffraction peak shifts to lower angle when the voltage is applied. The strain estimated from the peak shift increases lineally with increasing amplitude of the voltage pulses. The piezoelectric constant (d33) of the (001)-oriented domains in the polycrystalline BFO thin film at 80 K is 20.2 pm/V. This value is smaller than that measured at RT of 27.8 pm/V in our previous report.
  • Jung Min Park; Fumiya Gotoda; Takeshi Kanashima; Masanori Okuyama; Seiji Nakashima
    Journal of the Korean Physical Society KOREAN PHYSICAL SOC 59 (31) 2537 - 2541 0374-4884 2011/09 [Refereed]
     
    Polycrystalline BiFeO3 thin films were prepared on indium-tin-oxide (ITO)-coated glass substrates by using pulsed laser deposition (PLD). The X-ray diffraction (XRD) pattern showed a polycrystalline perovskite phase and a (010) preferred orientation. A higher deposition temperature was required to crystallize for the BFO thin film on an ITO substrate compared to the BFO thin film grown on a Pt substrate, the grain size was smaller than that of the BFO thin film on Pt substrate, and the leakage current density was less. The optical transmittance was about 80% around 780 nm, and the direct band gap (Eg) was 2.72 ± 0.03 eV. The P - E hysteresis loop of the BFO thin film on an ITO substrate was obtained at RT, and the polarization difference at zero electric field (2Pro), corresponding to the double remanent polarization was 140 μC/cm. The M - H hysteresis loop was obtained at RT, and the antiferromagnetic behavior was little affected by using different substrates.
  • Jung Min Park; Fumiya Gotoda; Seiji Nakashima; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama
    Japanese Journal of Applied Physics IOP PUBLISHING LTD 50 (9S2) 09NB03  1347-4065 2011/09 [Refereed]
     
    BiFe0.9Co0.1O3 (BFCO) films have been prepared on Pt/TiO2/SiO2/Si substrates with a magnetic field of 0.4 T by pulsed laser deposition. BFCO films prepared under magnetic field show a single-phase perovskite structure with a little secondary phase, and their (010) and (020) peaks shift to lower angles than those of the film prepared without magnetic field. The BFCO film of about 1 µm thickness shows a columnar structure, although the BFCO film of about 350 nm prepared without magnetic field shows a grain like structure. The leakage current density of the BFCO film prepared under magnetic field is much lower than that of the BFCO film prepared without magnetic field. The saturated P–E hysteresis loops of both BFCO films are obtained at 80 K, and the M–H hysteresis loops of both BFCO films show a weak ferromagnetism behavior at room temperature.
  • Seiji Nakashima; Hironori Fujisawa; Hiroyuki Suminaga; Jung Min Park; Hiroshi Nishioka; Masafumi Kobune; Takeshi Kanashima; Masanori Okuyama; Masaru Shimizu
    Japanese Journal of Applied Physics JAPAN SOC APPLIED PHYSICS 50 (9 PART 3) 0021-4922 2011/09 [Refereed]
     
    BiFeO3 (BFO) thin films with various Bi/Fe ratios have been deposited on SrRuO3/SrTiO3/SrTiO3(001) substrates by dual ion beam sputtering. A Bi2O3 ceramic disk and an α-Fe2O3 powder disk were used as targets, and simultaneously sputtered using a dual ion beam. Bi/Fe ratio has been controlled by adjusting the beam current ratio on the Bi2O 3- and α-Fe2O3-side ion sources. Even a BFO thin film with a Bi/Fe ratio of 0.95 and a smooth surface shows a slightly leaky characteristic. [Fe2+]/(Fe3+]+ [Fe2+]) ratio has been estimated by Auger electron spectroscopy (AES). From the AES profiles, the [Fe2+]/(Fe3+]+ [Fe2+]) ratio of the BFO thin film with a Bi/Fe ratio of 0.95 is estimated to be 0.14. It is considered that not only improving surface roughness but also enhancing oxidization is important for reduction in leakage current. © 2011 The Japan Society of Applied Physics.
  • Jung Min Park; Fumiya Gotoda; Seiji Nakashima; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama
    Japanese Journal of Applied Physics 50 (9 PART 3) 0021-4922 2011/09 [Refereed]
     
    BiFe0.9Co0.1O3 (BFCO) films have been prepared on Pt/TiO2/SiO2/Si substrates with a magnetic field of 0.4 T by pulsed laser deposition. BFCO films prepared under magnetic field show a single-phase perovskite structure with a little secondary phase, and their (010) and (020) peaks shift to lower angles than those of the film prepared without magnetic field. The BFCO film of about 1 μm thickness shows a columnar structure, although the BFCO film of about 350nm prepared without magnetic field shows a grain like structure. The leakage current density of the BFCO film prepared under magnetic field is much lower than that of the BFCO film prepared without magnetic field. The saturated P-E hysteresis loops of both BFCO films are obtained at 80 K, and the M-H hysteresis loops of both BFCO films show a weak ferromagnetism behavior at room temperature. © 2011 The Japan Society of Applied Physics.
  • DongHun Lee; Hyun Lee; Hideto Imajo; Yuichi Yoshioka; Takeshi Kanashima; Masanori Okuyama
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 59 (3) 2503 - 2508 0374-4884 2011/09 [Refereed]
     
    The electrical property of the interfacial layer is improved by fluorine treatment on a HfO2/Ge metal-insulator-semiconductor (MIS) device. The thin HfO2 dielectric was prepared using a photo-assisted metal-organic chemical vapor deposition (MOCVD) system. However, the fluorine was easily out-diffused after post metallization annealing (PMA) at high temperature. In this study, the post nitridation of the fluorinated HfO2/Ge gate stack was carried out by using a nitrogen (N) radical treatment at high temperature (200 degrees C) to prevent the fluorine (F) diffusion. Interface traps, such as poorly passivated dangling bonds and oxygen vacancies (V-0), near the interface were passivated by co-doping of F and N. Consequently, the dielectric property of the HfO2/Ge gate stack was improved to hamper F out-diffusion. Therefore, we suggest that N radical treatment following F-2-treatment is a very useful solution for improving the dielectric property of a HfO2/Ge gate stack.
  • Jung Min Park; Fumiya Gotoda; Seiji Nakashima; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama
    Japanese Journal of Applied Physics 50 (9 PART 3) 0021-4922 2011/09 [Refereed]
     
    BiFe0.9Co0.1O3 (BFCO) films have been prepared on Pt/TiO2/SiO2/Si substrates with a magnetic field of 0.4 T by pulsed laser deposition. BFCO films prepared under magnetic field show a single-phase perovskite structure with a little secondary phase, and their (010) and (020) peaks shift to lower angles than those of the film prepared without magnetic field. The BFCO film of about 1 μm thickness shows a columnar structure, although the BFCO film of about 350nm prepared without magnetic field shows a grain like structure. The leakage current density of the BFCO film prepared under magnetic field is much lower than that of the BFCO film prepared without magnetic field. The saturated P-E hysteresis loops of both BFCO films are obtained at 80 K, and the M-H hysteresis loops of both BFCO films show a weak ferromagnetism behavior at room temperature. © 2011 The Japan Society of Applied Physics.
  • Masayuki Sohgawa; Tatsuya Uematsu; Wataru Mito; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    JAPANESE JOURNAL OF APPLIED PHYSICS IOP PUBLISHING LTD 50 (6) 0021-4922 2011/06 
    A tactile sensor array covered by a projected cylindrical elastomer has been designed and fabricated for crosstalk reduction among sensor elements caused by the lateral deformation of the elastomer. The analysis of elastomer deformation by the finite element method showed that the optimal thickness of the flat elastomer between cylinders and the substrate is 50-100 mu m, because the sensor structure has not only a low crosstalk but also a high robustness. A tactile sensor array having the flat elastomer of 70 mu m thickness has little crosstalk and high robustness. (c) 2011 The Japan Society of Applied Physics
  • Daiki Hirashima; Tatsuya Uematsu; Masayuki Sohgawa; Wataru Mito; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 50 (6) 0021-4922 2011/06 [Refereed]
     
    A Tactile sensor system consisting of elements with three microcantilevers embedded in a cylindrical elastomer has been fabricated by micro electromechanical systems (MEMS) technology. These sensor small size (3 x 4 mm(2)) chips are mounted on a flexible sheet, and thus the fabricated sensor array can be set even on a curved surface. In addition, the spacial distribution of normal and shear forces is obtained when two kinds of objects (an acrylic hemisphere and a brass cylinder) come in contact with the fabricated sensor shifted laterally. The distribution results appropriately reflect the surface shape of the object and give the behavior of the forces vector. (c) 2011 The Japan Society of Applied Physics
  • Daiki Hirashima; Tatsuya Uematsu; Masayuki Sohgawa; Wataru Mito; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    Japanese Journal of Applied Physics IOP PUBLISHING LTD 50 (6) 06GM02  0021-4922 2011/06 [Refereed]
     
    A Tactile sensor system consisting of elements with three microcantilevers embedded in a cylindrical elastomer has been fabricated by micro electromechanical systems (MEMS) technology. These sensor small size (3 × 4mm2) chips are mounted on a flexible sheet, and thus the fabricated sensor array can be set even on a curved surface. In addition, the spacial distribution of normal and shear forces is obtained when two kinds of objects (an acrylic hemisphere and a brass cylinder) come in contact with the fabricated sensor shifted laterally. The distribution results appropriately reflect the surface shape of the object and give the behavior of the forces vector. © 2011 The Japan Society of Applied Physics.
  • Jung Min Park; Fumiya Gotoda; Seiji Nakashima; Takeshi Kanashima; Masanori Okuyama
    Current Applied Physics ELSEVIER SCIENCE BV 11 (3 SUPPL.) S270 - S273 1567-1739 2011/05 [Refereed]
     
    BiFe1-xZnxO3 (BFZO) thin films (x = 0, 0.05, and 0.1) have been prepared on Pt/TiO2/SiO 2/Si substrate by pulsed laser deposition and their multiferoic properties have been investigated. BFZO thin films shows polycrystalline perovskite single phase. The grains become small with increasing the substitution of Zn, and leakage current of BFZO thin film for x = 0.05 was lower than that of BiFeO3 thin film. The dielectric constant of BFZO thin films for x = 0, 0.05, and 0.1 are 107, 146, and 170 at room temperature, respectively. P-E hysteresis loops were obtained at room temperature and 80 K, and Pr slightly increases at low frequency from 500 Hz to 20 kHz. M-H hysteresis loops show weak ferromagnetic properties at 300 K and 80 K by substitution of Zn. © 2011 Elsevier B.V. All rights reserved.
  • Seiji Nakashima; Yosuke Tsujita; Hironori Fujisawa; Jung Min Park; Takeshi Kanashima; Masanori Okuyama; Masaru Shimizu
    Current Applied Physics ELSEVIER SCIENCE BV 11 (3 SUPPL.) S244 - S246 1567-1739 2011/05 [Refereed]
     
    We report on deposition of epitaxial BiFeO3 (BFO) thin films on SrRuO3-buffered SrTiO3 (001) substrate by using ion beam sputtering process. An X-ray diffraction analysis indicate that the BFO thin film deposited at 500 °C using a target with Bi/Fe ratio of 1.05 is perovskite single phase and is epitaxially grown on the substrate. The BFO thin film show saturated D-E hysteresis loops and the double remanent polarization (2Pr) of 100 μC/cm2 without measurement frequency dependence. © 2011 Elsevier B.V. All rights reserved.
  • DongHun Lee; Hideto Imajo; Takeshi Kanashima; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS IOP PUBLISHING LTD 50 (4) 0021-4922 2011/04 [Refereed]
     
    We have fabricated Ge-based p-channel metal-insulator-semiconductor field effect transistor (p-MISFET) devices using a hafnium oxide (HfO2) gate film prepared by photoassisted metal organic chemical vapor deposition (MOCVD). To reduce the interface state of a HfO2/Ge gate stack, we performed a new F-2 treatment method on a Ge surface. Before the deposition of HfO2 insulation thin films on n-type Ge(100), Ge surfaces were treated in fluorine (F-2) gas ambient under various conditions. Experimental results show that F is densely distributed at the interface of the HfO2/Ge gate stack with the F-2 treatment of the HfO2 bottom layers. Poorly passivated dangling bonds and oxygen vacancies (V-o) near the interface between HfO2 and Ge were stabilized by chemically active F. Consequently, the interface state density (D-it) of the HfO2/Ge gate stack was reduced and the electrical characteristics of the HfO2/Ge p-MISFETs were improved. Therefore, the new F-2 treatment method is very useful for fabricating a good HfO2/Ge p-MISFET device. (C) 2011 The Japan Society of Applied Physics
  • Jung Min Park; Takeshi Kanashima; Masanori Okuyama; Seiji Nakashima; Kyung Man Kim; Jai-Yeoul Lee; Hee Young Lee
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 58 (3) 674 - 677 0374-4884 2011/03 [Refereed]
     
    Epitaxial 0.7BiFeO(3)-0.3.BaTiO3 solid solution thin films were grown on La doped SrTiO3 (001) substrates by using pulsed laser deposition (PLD). The XRD pattern and the pole figure showed peaks corresponding to (001) planes. The capacitance-voltage (C-V) measurement showed dielectric constant and loss values of 70 and 0.07, respectively. The polarization hysteresis (P-E) was obtained at room temperature with remnant polarization (2P(r)) and coercive field (2E(c)) values of 23 mu C/cm(2) and 508 kV/cm, respectively. The magnetization hysteresis (M-H) loop showed a linear behavior of a typical paramagnetic nature.
  • Wataru Mito; Tatsuya Mima; Hirotake Yamazoe; Shunsuke Yoshida; Masahiro Tada; Masayuki Sohgawa; Takeshi Kanashima; Masanori Okuyama; Haruo Noma
    Transactions of the Society of Instrument and Control Engineers 計測自動制御学会 47 (1) 40 - 42 0453-4654 2011/01 [Refereed]
     
    We have designed and fabricated a tactile array sensors with three inclined micro-cantilevers embedded in elastomer, which can detect both normal and shear stresses. In this paper, we confirmed gripping status classification using sensor output. Using our sensor, four gripping status (free, grasping, holding and slipping) could be classified significantly.
  • Jung Min Park; Fumiya Gotoda; Seiji Nakashima; Takeshi Kanashima; Masanori Okuyama
    Ferroelectrics TAYLOR & FRANCIS LTD 416 (1) 119 - 124 0015-0193 2011 [Refereed]
     
    Sr-substituted BiFeO3 thin films (BSFO) have been prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition using 15% Bi-excess targets (Bi1.15(1-x)SrxFeO3). Some XRD peaks shift to low angle with increasing Sr, and grain sizes decrease. Leakage current densities of BSFO thin films are almost same or a little larger compared to that of BiFeO3 thin film, but P-E hysteresis loops were obtained at RT and 80 K. M-H hysteresis loops of BSFO thin films show weak ferromagnetism at RT and 80 K. BSFO thin film for x = 0.05 shows good multiferroic properties including ferroelectricity and ferromagnetism. Copyright © Taylor & Francis Group, LLC.
  • DongHun Lee; Hyun Lee; Takeshi Kanashima; Masanori Okuyama
    APPLIED SURFACE SCIENCE ELSEVIER SCIENCE BV 257 (3) 917 - 920 0169-4332 2010/11 [Refereed]
     
    Energy state and coordination of fluorine (F)-passivated Ge surface have been theoretically analyzed by semi-empirical molecular orbital method in comparison with hydrogen-passivated Ge surface to predict usefulness of F for passivation element and surface stabilization. Heat of formation for the reaction of F atoms and Ge layer system decreased simultaneously without energy barrier. Resultantly, F-Ge bonds were formed on Ge layer system and Ge surface dangling bonds were passivated by F dissimilar to the reaction of H atoms and Ge layer system. Furthermore, it was confirmed experimentally that the electrical properties of HfO(2)/Ge gate stack were improved by F(2)-ambient treatment of Ge substrate prior to HfO(2) deposition. It is concluded that F-passivation of Ge surface is useful in making stable and low-defective Ge substrate for high-k dielectric layer deposition. (C) 2010 Elsevier B.V. All rights reserved.
  • Seiji Nakashima; Hironori Fujisawa; Satoshi Ichikawa; Jung Min Park; Takeshi Kanashima; Masanori Okuyama; Masaru Shimizu
    Journal of Applied Physics AMER INST PHYSICS 108 (7) 0021-8979 2010/10 [Refereed]
     
    Bismuth-layer-structured multiferroic Bi5Ti3FeO 15 (BTFO15) (number of pseudoperovskite blocks, m=4) and natural-superlattice-structured Bi4Ti3O 12-Bi5Ti3FeO15 (BIT-BTFO15) (m=3 or 4) thin films were prepared on (001)-oriented and (110)-oriented La-doped (3.73 wt %) SrTiO3 (La-STO) single-crystal substrates using pulsed laser deposition. X-ray diffraction patterns of these thin films on (001) La-STO single crystals indicated that the obtained thin films were single-phase (00l) -oriented layered perovskite, and that the BIT-BTFO15 (m=3 or 4) natural-superlattice structure was also obtained. On (110) La-STO single crystal, layered perovskite (11l) -oriented thin films were also obtained. Moreover, cross-sectional transmission electron microscope images of these thin films revealed four pseudoperovskite blocks (m=4) in the BTFO15 thin films, and an intergrowth structure of three and four pseudoperovskite blocks (m=3 or 4) in BIT-BTFO15 sandwiched by two (Bi2O2)2+ layers. In ferroelectric D-E hysteresis loop measurements, BTFO15 (m=4) and BIT-BTFO15 (m=3 or 4) thin films on (110) La-doped STO single crystals produced clear ferroelectric hysteresis loops with double remanent polarizations (2 P r) of 49 μC/cm2 and 44 μC/cm2, respectively. However, BTFO15 and BIT-BTFO15 thin films on (001) La-doped STO single crystals had paraelectric characteristics. These results demonstrate that the spontaneous polarization vectors of the BTFO15 and BIT-BTFO15 thin films were parallel to the a axis of their unit cells. © 2010 American Institute of Physics.
  • MITO Wataru; YAMAZOE Hirotake; YOSHIDA Shunsuke; TADA Masahiro; SOHGAWA Masayuki; KANASHIMA Takeshi; OKUYAMA Masanor; NOMA Haruo
    ITE Technical Report 一般社団法人映像情報メディア学会 34 (18) 39 - 42 1342-6893 2010/05 
    We have designed and fabricated a tactile sensors array with three inclined micro-cantilevers on a single sensor embedded in elastomer. Each sensor element can detect both normal and shear stresses. In this paper, we propose classification method of gripping status using sensor array and machine learning algorithm based on hidden marcov model. By integrating multiple sensor data using machine learning algorithm using hidden marcov model, our method allows to detect partial contact status such as non-contact, three types of partial contact, full-contact. Through experiments, we confirmed tha...
  • Mito Wataru; Yamazoe Hirotake; Yoshida Shunsuke; Tada Masahiro; Sohgawa Masayuki; Kanashima Takeshi; Okuyama Masanori; Noma Haruo
    The Abstracts of the international conference on advanced mechatronics : toward evolutionary fusion of IT and mechatronics : ICAM The Japan Society of Mechanical Engineers 2010 351 - 354 1348-8961 2010 
    We have designed and fabricated a tactile sensors array with three inclined micro-cantilevers on a single sensor embedded in elastomer. Each sensor element can detect both normal and shear stress. In this paper, we propose classification method of gripping status using sensor array and a machine learning algorithm. By integrating multiple sensor data using machine learning algorithm, our method allows to detect partial slipping on contact surface as an initial sign of slipping. Through experiments, we confirmed that our method achieves better classification ratio than existing methods using single sensor data.
  • T. Kanashima; Y. Yoshioka; D. H. Lee; M. Okuyama
    SIGE, GE, AND RELATED COMPOUNDS 4: MATERIALS, PROCESSING, AND DEVICES ELECTROCHEMICAL SOC INC 33 (6) 235 - 241 1938-5862 2010 [Refereed]
     
    Deep level transient spectroscopy (DLTS) technique that has some merits such as no assumption of leakage mechanism and characterization of both majority and minority carrier traps is applied for characterization of interface state density to HfO2/Ge gate stack. DLTS and isothermal capacitance transient spectroscopy (ICTS) signals of HfO2/Ge gate stack can be detected, and the results of these measurements show that interface state densities of majority and minority carriers can be reduced by fluorine treatment, and no new traps are created by this treatment. So, fluorine treatment is useful to improve the device performance. Moreover, DLTS and ICTS signals can be simultaneously obtained, and capture cross-section can be estimated by using these results.
  • Nguyen Truong Tho; Takeshi Kanashima; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 49 (9) 0021-4922 2010 [Refereed]
     
    Ferroelectric Bi1.1Fe0.9Co0.1O3 (BFCO) thin films of 100 nm thickness have been prepared on Pt/TiO2/SiO2/Si substrates by chemical solution deposition (CSD) using iterative rapid thermal annealing (RTA) at 510-560 degrees C. A thin film prepared at 520 degrees C shows low leakage currents of about 6 x 10(-3) and 2 x 10(-2) A/cm(2) at 80 K and room temperature (RT) at a high electric field of 2 MV/cm, respectively. However, the leakage current is above 10(-2) A/cm(2) at high applied electric fields from 1 to 2 MV/cm so that P-E hysteresis loops of the thin film seem to be unsaturated at RT. As a result, the difference in polarizations at the zero field of the BFCO film prepared at 520 degrees C is 150 mC/cm(2) at an applied electric field of 3 MV/cm and RT, which is larger than that of 120 mC/cm(2) at an applied electric field of 4 MV/cm and 80 K. (C) 2010 The Japan Society of Applied Physics
  • Nguyen Truong Tho; Takeshi Kanashima; Masayuki Sohgawa; Dan Ricinschi; Minoru Noda; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 49 (9) 0021-4922 2010 [Refereed]
     
    Ferroelectric Bi1.1Fe1-xCoxO3 (BFCO) thin films with x = 0-0.3 have been prepared on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) using iterative rapid thermal annealing (RTA) in nitrogen and oxygen. The crystallization of the rhombohedral structure of BiFeO3 (BFO) is observed clearly in all thin films, and a monoclinic Bi2O3 phase is also observed and is markedly larger in Co-doped BFO thin films than in BFO thin films. An electric field of 2 MV/cm is applied to the Bi1.1Fe0.9Co0.1O3 thin film annealed in nitrogen at 520 degrees C without dielectric breakdown, but its polarization versus electric field (P-E) hysteresis loops are not saturated owing to its high leakage current density. The Bi1.1Fe0.8Co0.2O3 thin film prepared at 520 degrees C in oxygen shows a very good saturation of P-E hysteresis loops at room temperature (RT) at the low leakage current of about 8.7 x 10(-3) A/cm(2) under a high electric field of 1.5 MV/cm. The leakage current at a low electric field may be Ohmic emission at any temperature; however at a high electric field, it may be attributed to tunnel emission at 80 K and Schottky emission at RT. (C) 2010 The Japan Society of Applied Physics
  • Tomohiro Watanabe; Hiroyuki Miyashita; Takeshi Kanashima; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 49 (4) 0021-4922 2010 [Refereed]
     
    Organic ferroelectric gate field-effect transistor (FET) memories have been fabricated using pentacene as the semiconductor and a poly(vinylidene fluoride-tetrafluoroethylene) [P(VDF-TeFE)] thin film as the ferroelectric gate. The P(VDF-TeFE) film is prepared by spin coating and annealing at 170 degrees C for 2.5 h, and pentacene is prepared by vacuum evaporation. The polarization-electric field (P-E) hysteresis of the P(VDF-TeFE) thin film is observed and enhanced by poling treatment. The obtained P-r of 4 mu C/cm(2) is sufficient for controlling pentacene surface potential. Good memory characteristics are obtained in the P(VDF-TeFE) gate FET. For such a FET, the ON/OFF ratio of drain current is 830, the carrier mobility is 0.11 cm(2) V-1 s(-1), and the memory retention is over 16 h. (C) 2010 The Japan Society of Applied Physics
  • Le Van Hai; Takeshi Kanashima; Masanori Okuyama
    Journal of the Korean Physical Society 55 (2 PART 1) 884 - 887 0374-4884 2009/08 
    Fast annealing was used to improve the electronic properties of ferroelectric and buffer layers in Pt/SrBi2Ta2Og(SBT)/ SiO2/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structures. Damage of the SiO2 layer due to SBT constituent diffusion was reduced significantly as annealing time at high temperature of the ferroelectric SBT can be reduced from 1-2 hours to few minutes. Leakage currents through both the SiO2 buffer and the SBT ferroelectric layers were decreased in the sample prepared by using fast annealing. The C-V and the.
  • SOHGAWA Masayuki; KANASHIMA Takeshi; YAMASHITA Kaoru; NODA Minoru; OKUYAMA Masanori; NOMA Haruo
    IEICE technical report. Electron devices 一般社団法人電子情報通信学会 109 (157) 41 - 46 0913-5685 2009/07 
    Tactile array sensors with macro-cantilevers embedded in elastomer which can detect both normal and shear stresses have been designed and fabricated. Inclined cantilevers sensitive to normal and shear stresses can be obtained by using Cr/Si bilayer structure. These cantilevers can be successfully embedded in the elastomer without their destruction. The outputs from opposite cantilevers are same signs in the case of normal stress application, but the outputs are opposite signs in the case of shear stress. So, normal and shear stresses can be distinguished by summation and difference of outpu...
  • TACHIBANA H; KAMANARU S; MATSUURA H; SOHGAWA M; KANASHIMA T; OKUYAMA M; YAMASHITA K; NODA M; NOMA M
    電気学会研究会資料. PHS, フィジカルセンサ研究会 2009 (16) 97 - 102 2009/07 
    触覚センサの出力安定性はスパッタリングで成膜したNiCrを用いることで大きく改善できたが、さらなる安定化を目指してNiCrの組成比をコントロールすることで抵抗温度係数の低減を試みた。NiとCrのターゲットの面積比を変えることで様々な組成の薄膜を作製し、温度特性や結晶性等を調べた結果、Crの量が40～60%のときに温度係数が小さくなることが分かった。
  • Masayuki Sohgawa; Tatsuya Mima; Hiroyuki Onishi; Takeshi Kanashima; Masanori Okuyama; Kaoru Yamashita; Minoru Noda; Masayoshi Higuchi; Haruo Noma
    The 15th International Conference on Solid-State Sensors, Actuators and Microsystems 284 - 287 2009/06 [Refereed]
     
    Tactile array sensor of the micro-cantilevers embedded in the elastomer has been fabricated to detect normal and 2-axes shear stresses. It is demonstrated that tactile array sensor with 3 times 3 detective elements can be fabricated with excellent yield. The sensor element is sensitive to both normal and shear stresses applied on entire sensor surface. Moreover, it has good directional characteristics so that it is shown that magnitude and direction of shear stress can be obtained by difference of output voltages of adjacent sensor cantilevers. The sensor output has good reproducibility for multiple measurement. The output from sensor element drastically changes with shifting applying position of force. It is considered that we can obtain pressed position from distribution of output from sensor element array.
  • Hiroyuki Onishi; Masayuki Sohgawa; Hiroto Tachibana; Yu Ming Huang; Takeshi Kanashima; Masanori Okuyama; Kaoru Yamashita; Minoru Noda; Haruo Noma
    IEEJ Transactions on Sensors and Micromachines 129 (11) 7 - 416 1341-8939 2009 [Refereed]
     
    Tactile sensor consisted of micro-cantilevers has been developed to detect both normal and shear stresses, and have human-friendly surface. NiCr thin film is used as strain gauge having low resistance drift, although Si piezo-resistance gauge shows the large resistance drift induced by large temperature coefficient of resistance (TCR) and its output is unstable. TCRs of NiCr films prepared by vacuum evaporation and sputtering (at RT and 600°C) are 0.054%, 0.082%, and 0.0065%, respectively, and are much lower than that of Si, 0.25%. As a result, reduction of resistance drift and stabilization of the sensor have been obtained by using NiCr thin gauge. © 2009 The Institute of Electrical Engineers of Japan.
  • Seiji Nakashima; Dan Ricinschi; Jung Min Park; Takeshi Kanashima; Hironori Fujisawa; Masaru Shimizu; Masanori Okuyama
    Journal of Applied Physics AMER INST PHYSICS 105 (6) 061617  0021-8979 2009 [Refereed]
     
    The stress influence of the structural and ferroelectric properties of polycrystalline BiFeO3 (BFO) thin films has been investigated using a membrane substrate for relaxing stress. Reciprocal space mapping (RSM) measurement has been performed to confirm the stress dependence of the crystal structure of polycrystalline BFO thin films on the Pt (200 nm) / TiO2 (50 nm) / SiO2 (600 nm) / Si (625 μm) substrate (stress-constrained BFO film) and the Pt (200 nm) / TiO2 (50 nm) / SiO2 (600 nm) /Si (15 μm) membrane substrate (stress-relaxed BFO film). The BFO thin films prepared by pulsed laser deposition were polycrystalline and mainly exhibit a texture with (001) and (110) plane orientations. From the RSM results, the crystal structure of the (001)-oriented domain changes from Pm monoclinic to Cm monoclinic or to R3c rhombohedral due to stress relaxation. Moreover, at room temperature as well as at 150 K, remanent polarization (Pr) increases and double coercive field (2E c) decreases (in the latter case from 88 to 94 μC/ cm2 and from 532 to 457 kV/cm, respectively) due to relaxing stress. The enhancement of ferroelectricity is attributed to the crystal structural deformation and/or transition and angle change between the polarization direction and film plane. © 2009 American Institute of Physics.
  • Minoru Noda; Shigeyuki Watanabe; Kousuke Seki; Takeshi Kanashima; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 47 (9) 7500 - 7504 0021-4922 2008/09 [Refereed]
     
    A flew coplanar waveguide (Ba,Sr)TiO3/Au/Cr/(Ba,Sr)TiO3 sandwich structure was designed and fabricated as a microwave tunable device. (Ba,Sr)TiO3 (BST) (60/40) thin films were prepared on (100) MgO substrate by metal-organic-decomposition (MOD). The tunability increased from 10.4 to 13.3% with the addition of sandwich structure (upper BST films thickness, 600 nm) at 1 MHz, while the dielectric loss in the structure was 0.006. The microwave propagation characteristics of the sandwich structure and the conventional single BST film coplanar waveguide (CPW) tunable transmission lines were evaluated. The differential phase shift increased from 4.4 to 16 at 20 GHz with the sandwich structure (upper BST film thickness, 600 nm. CPW line gap, 5 mu m and length, 2500 mu m) with an insertion loss of 5.5 dB, when a dc bias voltage from 0 to 30 V was applied. The figure-of-merit improved front the single BST him (1.0 degrees/dB) to the sandwich (2.9 degrees/dB) structure at 20 GHz. Finally, it was confirmed that the sandwich structure is a good Candidate for improving the Characteristics of microwave tunable devices.
  • HUANG Yu-Ming; SOHGAWA Masayuki; ONISHI Hiroyuki; KANASHIMA Takeshi; OKUYAMA Masanori; YAMASHITA Kaoru; NODA Minoru; NOMA Haruo
    電気学会研究会資料. PHS, フィジカルセンサ研究会 2008 (7) 31 - 34 2008/06 
    これまでポリマー/Siカンチレバー型触覚センサの検知部としてはPtひずみゲージを用いていたが、抵抗の温度依存性が大きく出力に大きなドリフトが表れていた。そこで温度係数の小さいNiCr薄膜を用いて温度特性を改善し高分解能化を試みた。真空蒸着により作製したNiCrひずみゲージはバルク材料に比べれば大きいものの、Ptに比較すれば温度係数を1/3に低減できた。
  • Masayuki Sohgawa; Yu-Ming Huang; Minoru Noda; Takeshi Kanashima; Kaoru Yamashita; Masanori Okuyama; Masaaki Ikeda; Haruo Noma
    MICROELECTROMECHANICAL SYSTEMS - MATERIALS AND DEVICES MATERIALS RESEARCH SOC 1052 151 - + 0272-9172 2008 [Refereed]
     
    Tactile sensors of Si microcantilevers with a piezoresistive layer have been proposed for detection of both normal and shear stresses. Micro-cantilevers were fabricated by the surface micromachining of SOI wafers and were adequately inclined by controlling deflection with a Cr layer. The cantilevers were embedded in the PDMS elastomer to create a human-friendly surface. When a stress is applied to the surface of elastomer, the deformation of the cantilevers along with the elastomer is detected as a resistance change in the piezoresistive layer of the cantilevers. The piezoresistive response of the cantilever was analyzed by FEM calculations. The fabricated tactile sensor is sensitive to both normal and longitudinal shear stresses and its responses agree closely with the calculated value. Moreover, it has little sensitivity to shear stress in the transverse direction to the cantilever, which means that the tactile sensor can. distinguish the direction of shear stress. This sensor can be utilized for tactile sensing in human support robots.
  • Yu Ming Huang; Masayuki Sohgawa; Kaoru Yamashita; Takeshi Kanashima; Masanori Okuyama; Minoru Noda; Haruo Noma
    IEEJ Transactions on Sensors and Micromachines 128 (5) 193 - 197 1341-8939 2008 [Refereed]
     
    Cantilever-type tactile sensors of silicon-polymer beam structures were fabricated by surface micromachining and covering with elastomers. Two kinds of elastomers with different Young's modulus PDMS and urethane gel have been used to control deflection of the cantilevers and adjust the sensitivity cantilever-type tactile sensors. The resistance change of the sensor with PDMS has linear dependence on normal and shear stresses, but that of the sensor with urethane gel is nonliner to normal and shear stresses. However, the sensitivity of urethane gel type sensor is about 30 times larger than PDMS type sensor. © 2008 The Institute of Electrical Engineers of Japan.
  • Masayuki Sohgawa; Yu-Ming Huang; Minoru Noda; Takeshi Kanashima; Kaoru Yamashita; Masanori Okuyama; Masaaki Ikeda; Haruo Noma
    Material Research Society Symposium Proceedings 1052 151 - 156 1946-4274 2007/12 [Refereed]
     
    The tactile sensors for human support robots which can detect both normal stress and shear stress and have human-friendly surface have been proposed. Micro-cantilevers adequately inclined by Cr deflection control layer were fabricated by the surface micromachining on SOI wafer. The cantilevers were covered with the PDMS elastomer for human-friendly surface. When the stress is added to the surface of elastomer, the deformation of cantilevers along with elastomer is detected as piezoresistive layer in the cantilevers. The piezoresistive response of the cantilever is analyzed by FEM calculation. The response of the fabricated tactile sensor to normal stress and shear stress was measured by output from this resistance. The tactile sensor with PDMS elastomer can detect both normal stress and shear stress. On the other hand, it hardly has sensitivity to shear stress of orthogonal direction to the cantilever. It means that the tactile sensor can distinguish the direction of shear stress. The sensitivity of tactile sensor vary widely with cantilever pattern and relation between direction of cantilever and crystallite orientation of Si. It is suggested that the sensitivity of tactile sensor can be improved by using FEM estimation and selective ion implantation.
  • SOHGAWA Masayuki; HUANG Yu-Ming; KANASHIMA Takeshi; YAMASHITA Kaoru; OKUYAMA Masanori; NODA Minoru; IKEDA Masaaki; NOMA Haruo
    電気学会研究会資料. PHS, フィジカルセンサ研究会 2007 (14) 47 - 50 2007/07 
    ロボット用多軸触覚センサを試作し評価した。有限要素法による解析に基づき、力検知用のSiピエゾ抵抗を設けたCr/Siカンチレバー構造を最適な傾斜形状に作製し、これをエラストマ中に埋め込むことでセンサ素子を完成した。作製したセンサ表面に垂直力と剪断力を印加したところ、どちらに対しても感度が得られ、多軸触覚センサが実現可能であることを示した。
  • Bong Yeon Lee; Takaki Minami; Takeshi Kanashima; Masanori Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS INST PURE APPLIED PHYSICS 45 (11) 8608 - 8610 0021-4922 2006/11 [Refereed]
     
    A new type of ferroelectric gate field-effect transistor (FET) using ferroelectric-insulator interface conduction has been proposed. Drain current flows along the interface between the ferroelectric and insulator layers and requires no semiconductor. The channel region of the FET is composed of a Pt/insulator HfO2/ferroelectric Pb(Zr0.52Ti0.48)O-3 (PZT)/Pt/TiO2/SiO2/Si multilayer, and the source and drain areas are formed at the interface of the PZT and HfO2 films. Drain current versus gate voltage characteristics show a clockwise hysteresis loop similar to that for a conventional p-channel transistor. The FET shows that the on/off ratio of the conduction current is within 10(5) to 10(6) and that the off-state current is about 10(-10) A.
  • Kwi Young Yun; Dan Ricinschi; Takeshi Kanashima; Masanori Okuyama
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 89 (19) 0003-6951 2006/11 [Refereed]
     
    Ferroelectric BiFeO3 thin films were grown on Pt/TiO2/SiO2/Si substrates by pulsed-laser deposition. From the x-ray diffraction analysis, the BiFeO3 thin films consist of perovskite single phase, and the crystal structure shows the tetragonal structure with a space group P4mm. The BiFeO3 thin films show enhanced electrical properties with low leakage current density value of similar to 10(-4) A/cm(2) at a maximum applied voltage of 31 V. This enhanced electrical resistivity allowed the authors to obtain giant ferroelectric polarization values such as saturation polarizations of 110 and 166 mu C/cm(2) at room temperature and 80 K, respectively.
  • Le Van Hai; Takeshi Kanashima; Masanori Okuyama
    INTEGRATED FERROELECTRICS TAYLOR & FRANCIS LTD 84 (1) 179 - 188 1058-4587 2006 [Refereed]
     
    APt/SrBi2Ta2O9( SBT)/SiO2/n-Si metal-ferroelectric-insulator-semiconductor (MFIS) structure has been prepared with SrBi2Ta2O9 thin film whose surface was modified by irradiation of nitrogen or oxygen radical. The leakage current is reduced by irradiation treatment and C-V characteristic shows clear memory window and sharp slopes corresponding to good interface layer. It is estimated from X-ray Photoelectron Spectroscopy and Ultraviolet Photoyield Spectroscopy that the SBT thin films with nitrogen treatment have exhibited the higher threshold energy than that without the irradiation. Memory window of the MFIS structures are in the range of 1-2 V when the gate voltage is varied from 3-6 V. Retention time of ON and OFF states is 1 week in the structure irradiated with oxygen radical and 12 days in that with nitrogen radical although that without the irradiation is only 3 hours.
  • M. Sohgawa; M. Yoshida; T. Kanashima; M. Okuyama; A. Fujimoto
    Journal of the Korean Physical Society 46 (1) 262 - 264 0374-4884 2005/01 
    SrBi2Ta2O9 (SBT)/SiO2/Si structures have been characterized by photoreflectance spectroscopy (PRS) without electrode formation. SBT film was deposited on SiO2/n-Si by the metal-organic decomposition (MOD) method and annealed in O2 atmosphere at 600°C. The voltage was applied by attaching ITO transparent electrodes during PRS measurement. The PRS spectral intensity of SBT/SiO 2/Si structure has hysteresis characteristics as well as a C-V curve. Additionally, the spectral intensity gradually decreases with time, in a similar way to reduction of the capacitance. These results mean that the spectral intensity indicates the ferroelectricity of SBT film in SBT/SiO 2/Si structure, so that it is considered that characterization of MFIS structure without electrode can be measured by PRS.
  • Masayuki Sohgawa; Masato Yoshida; Takeshi Kanashima; Akira Fujimoto; Masanori Okuyama
    Journal of Korean Physical Society 46 (1) 262 - 264 1976-8524 2005/01 [Refereed]
     
    SrBi2Ta2O9 (SBT)/SiO2/Si structures have been characterized by photoreflectance spectroscopy (PRS) without electrode formation. SBT film was deposited on SiO2/n-Si by the metal-organic decomposition (MOD) method and annealed in O2 atmosphere at 600 C. The voltage was applied by attaching ITO transparent electrodes during PRS measurement. The PRS spectral intensity of SBT/SiO2/Si structure has hysteresis characteristics as well as a C-V curve. Additionally, the spectral intensity gradually decreases with time, in a similar way to reduction of the capacitance. These results mean that the spectral intensity indicates the ferroelectricity of SBT film in SBT/SiO2/Si structure, so that it is considered that characterization of MFIS structure without electrode can be measured by PRS.
  • T Kanashima; K Ikeda; T Tada; M Sohgawa; M Okuyama
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 46 (1) 258 - 261 0374-4884 2005/01 
    High-k HfO2 thin films have been prepared mainly at 400degreesC in O-2 atmosphere by pulsed laser deposition (PLD), and defects in the film have been characterized by electron spin resonance (ESR). Two ESR peaks are found at 9 similar or equal to 2.003 and 2.006. The g similar or equal to 2.006 peak intensity is higher in the sample deposited at target-sample distance of 45 mm than in that deposited at 60 mm. This is because part of the substrate and the film are exposed to high-energy particles ablated during deposition and are hence damaged. Moreover, the peak at g similar or equal to 2.006 is related to the interface state density calculated from the high-frequency C - V curve. On the other hand, the peak at g similar or equal to 2.003 is related to the thickness of the interfacial layer, and thus may be attributed to defects in the interfacial layer.
  • Takeshi Kanashima; Masayuki Sohgawa; Koji Ikeda; Masato Yoshida; Masanori Okuyama
    Technical report of IEICE. SDM 一般社団法人電子情報通信学会 103 (533) 51 - 56 0913-5685 2003/12 
    HfO_2 thin films have been prepared on Si(100) wafer by pulsed laser deposition (PLD) method, and characterized by electrical and optical techniques. The samples were deposited at various temperature in O_2. From the results of I-V and C-V characteristics, the sample deposited at 400℃ at pressure of 0.2 Torr, shows relatively small interface state and fiat-band shift. Moreover, the sample is grown in O_2 and N_2 mixture ambient to reduce the interfacial layer. The film whose interfacial layer is relatively small is obtained, but an interface trap is increased. It needs to optimize the deposition conditions. Interface strain of Si and insulator is characterized by photoreflectance spectroscopy (PRS). PRS intensity increases with increasing growth temperature, and an interfacial layer increases with increasing growth temperature. The strain on the Si surface also increases. Moreover, PRS spectrum is not observed in the sample deposited at the O_2 pressure of 0.05 Torr. This suggests that the interfacial layer is small.
  • T Kanashima; O Maida; N Kohma; M Okumoto; M Ueno; S Kitai; M Okuyama; H Ohashi
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS INST PURE APPLIED PHYSICS 42 (6A) L603 - L606 0021-4922 2003/06 [Refereed]
     
    Fluorocarbon films have been deposited by soft X-ray ablation of polytetrafluoroethylene (PTFE) and characterized as low-dielectric-constant interlayer dielectrics. Very rapid deposition of such films at about 1500 nm/min could be achieved at room temperature, and the dielectric constant of the deposited films is about 2.1. Fourier transform infrared spectroscopy (FT-IR) measurement results suggest that the deposited films are formed primarily as one-dimensional chains of (-CF2-)(n) which are cross-linked partially. The cross-link density increases with increasing deposition temperature, and their thermal stability improves. However, the dielectric constant of the films increased abruptly above 300degreesC.
  • T Kanashima; M Sohgawa; H Kanda; K Ikeda; M Okuyama
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 42 (SUPPL.) S1357 - S1361 0374-4884 2003/04 [Refereed]
     
    High-k thin films of ZrO2, PrOx of similar to10 nm thickness have been prepared by pulsed laser deposition, and characterized in microscopic structure and electrical properties. Crystallization is promoted in ZrO2 films deposited above 400 degreesC, but a significant XRD peak was not observed in the ZrO2 film grown below 400 degreesC. The leakage current is decreased by increasing growth temperature, but all equivalent-oxide thickness (EOT) obtained from accumulation capacitance of C-V characteristics becomes large. The films deposited at 400 degreesC were annealed at 400 degreesC in O-2 gas to reduce the leakage. The leakage current change to be small, but the EOTs become large. Oxygen radical annealing is carried out to reduced the leakage, and is effective for ZrO2 thin film. Oil the other hand. only small improvement is observed ill the PrOx films.
  • H Kanda; M Sohgawa; Y Toyoshima; T Kanashima; M Okuyama; A Fujimoto
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 42 (SUPPL.) S1072 - S1075 0374-4884 2003/04 [Refereed]
     
    SrBi2Ta2O9(SBT) thin film grown on SiO2/Si by a pulsed laser deposition was evaluated by photoreflectance spectroscopy (PRS) which is one of the non-destructive techniques to characterize an interface. The stress of a SiO2/Si interface of ferroelectric-insulator-semiconductor (FIS) structure has been evaluated by using this method. As a result, there is a tensile stress which is larger than that before deposition, and the stress becomes large according to increasing SBT thickness. Moreover, when ferroelectric thin film is poled, the stress becomes small with increase of the voltage.
  • Hirofumi Kanda; Masayuki Sohgawa; Yoshihide Toyoshima; Takeshi Kanashima; Masanori Okuyama; Akira Fujimoto
    Journal of Korean Physical Society 42 1072 - 1075 1976-8524 2003/04 [Refereed]
     
    SrBi2Ta2O9(SBT) thin film grown on SiO2/Si by a pulsed laser deposition was evaluated by photoreflectance spectroscopy (PRS) which is one of the non-destructive techniques to characterize an interface. The stress of a SiO2/Si interface of ferroelectric-insulator-semiconductor (FIS) structure has been evaluated by using this method. As a result, there is a tensile stress which is larger than that before deposition, and the stress becomes large according to increasing SBT thickness. Moreover, when ferroelectric thin film is poled, the stress becomes small with increase of the voltage.
  • Takeshi Kanashima; Masayuki Sohgawa; Hirofumi Kanda; Koji Ikeda; Masanori Okuyama
    Journal of Korean Physical Society 42 1357 - 1361 1976-8524 2003/04 [Refereed]
     
    High-k thin films of ZrO2, PrOx of ~ 10 nm thickness have been prepared by pulsed laser deposition, and characterized in microscopic structure and electrical properties. Crystallization is promoted in ZrO2 films deposited above 400C, but a significant XRD peak was not observed in the ZrO2 film grown below 400C. The leakage current is decreased by increasing growth temperature, but an equivalent-oxide thickness (EOT) obtained from accumulation capacitance of CV characteristics becomes large. The films deposited at 400C were annealed at 400C in O2 gas to reduce the leakage. The leakage current change to be small, but the EOTs become large. Oxygen radical annealing is carried out to reduced the leakage, and is effective for ZrO2 thin film. On the other hand, only small improvement is observed in the PrOx films.
  • A Fujimoto; T Kanashima; M Okuyama
    BOSTON TRANSDUCERS'03: DIGEST OF TECHNICAL PAPERS, VOLS 1 AND 2 IEEE 1 540 - 543 2003 [Refereed]
     
    Surface reactions of SnO2 gas sensor for aminic molecules such as methyl and ethyl amine and for carboxylic molecules such as forming and acetic acid have been simulated by molecular orbital calculation and compared with experimental results. The calculated results show that forming acid molecule is adsorbed closer to SnO2 cluster surface than methylamine molecule. Experimental results showed the SnO2 gas sensor had higher sensitivity for forming acid gas than methylamine gas. These results support that the sensitivity of SnO2 gas sensor may be affected for the adsorbed position of gas molecule from the sensor surface.
  • Takeshi Kanashima; Masayuki Sohgawa; Koji Ikeda; Hirofumi Kanda; Masanori Okuyama
    Technical report of IEICE. SDM 一般社団法人電子情報通信学会 102 (540) 45 - 49 0913-5685 2002/12 
    PrOx thin films have been prepared on Si(100) wafer by pulsed laser deposition (PLD) method, and characterized by electrical and optical techniques. The samples were deposited at 400℃ in O_2 at pressure of 0.2 Torr and post-annealed by RTA. Accumulate capacitance shown in C-V curve is increased by low-temperature and short-time annealing, but is decreased by high-temperature and long-time annealing. Moreover, interfacial layer is grown for high-temperature annealing for 60s. The fixed charge in the film is decreased by RTA at 400℃ for 20s and 60s, but interface trap is increased. Interface ...
  • T Kanashima; S Kitai; M Sohgawa; H Kanda; M Okuyama
    ISAF 2002: PROCEEDINGS OF THE 13TH IEEE INTERNATIONAL SYMPOSIUM ON APPLICATIONS OF FERROELECTRICS IEEE 199 - 202 1099-4734 2002 
    High-k thin films of ZrO2, HfO2 PrOx, of similar to10 nm thickness have been prepared by pulsed laser deposition (PLD), and characterized in microscopic structure and electrical properties. Crystallization is promoted in ZrO2 films deposited above 400degreesC, but a significant XRD peak was not observed in the ZrO2 film grown below 400degreesC. Moreover, density of the film is confirmed to saturate above 400degreesC by grazing incident angle X-ray reflectance. The leakage current is decreased by increasing growth temperature, but an equivalent-oxide thickness (EOT) obtained from accumulation capacitance of C - V characteristics becomes large. HfO2 films show the similar behaviors to ZrO2 films. The films deposited at 400degreesC were annealed at 400degreesC in O-2 gas to reduce the leakage, but the EOTs become large. So, these films were irradiated with oxygen radical at the pressure of 10(-3) Pa both to prevent the growth of interfacial layer and to enhance the oxidation of only the films. Although the leakage of ZrO2 films can be reduced by oxygen radical irradiation, only small improvement is observed in the PrOx films.
  • Satoshi Kitai; Masayuki Sohgawa; Hirofumi Kanda; Takeshi Kanashima; Masanori Okuyama
    Technical report of IEICE. SDM 一般社団法人電子情報通信学会 101 (515) 11 - 16 0913-5685 2001/12 
    PrO_x thin films have been prepared on Si(100)wafer by pulsed laser deposition method. It is shown from XPS spectra and TEM image of PrO_x film that the deposition in O_2 ambient of 0.2 Torr produces an interfacial silicate layer. Deposition in high vacuum at RT has only an ultra-thin interfacial layer, but both hysteresis in C-V characteristic and leakage current are large. After an O_2 annealing, the accumulation capacitance has increased, and the hysteresis and the leakage current have been improved, but the interfacial layer was grown. In deposition method using shadow mask, thin films ...
  • 藤本晶; 寒川雅之; 金島岳; 奥山雅則
    和歌山工業高等専門学校研究紀要 和歌山工業高等専門学校 (36) 15 - 19 0287-5381 2001/10
  • 北井聡; 寒川雅之; 神田浩文; 金島岳; 奥山雅則
    電気学会電子材料研究会資料 EFM-01 (6-13) 43 - 47 2001/09
  • S Miura; N Kihara; K Mashima; A Miyaji; E Ishiguro; H Ohashi; Y Tamenori; H Okumura; T Kanashima; T Ishikawa
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT ELSEVIER SCIENCE BV 467 287 - 290 0168-9002 2001/07 [Refereed]
     
    The performance of an elliptically bent cylinder mirror, installed in A-branch of the Soft X-ray photochemistry beamline (BL27SU) at the SPring-8, is described. The aim of this branch beamline is to provide a micro white-beam focusing for a need in photochemistry community. This elastically bent mirror is the key component for the extremely intense micro-beam focusing optics. (C) 2001 Elsevier Science B.V. All rights reserved.
  • Takeshi Kanashima; Osamu Maida; Norinao Kohma; Masashi Agata; Shinji Yudate; Masato Ueno; Masanori Okuyama; Haruhiko Ohashi
    Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 40 (6 A) 4195 - 4196 0021-4922 2001/06 
    Irradiation effects of soft X-rays on Si wafer in O2 and N2 atmospheres have been studied at SPring-8, the synchrotron radiation (SR) facility in Japan. Si wafers were irradiated in O2 and N2 ambients of 3 × 10-3, 0.2 and 12 Pa. The Si surfaces were analyzed by Auger electron spectroscopy to study the changes on the Si surface. In the case where O2 or N2 gas pressure is the order of 10-3 Pa, etching of the native oxide is observed. On the other hand, a Si(92eV) L23 VV peak shift was observed at a pressure of 12 Pa at low temperatures below 150°C. Nitrization and oxidation of the Si surface can be promoted by direct reaction of silicon with nitrogen and oxygen gases at low temperature by soft X-ray irradiation.
  • KITAI Satoshi; SOUGAWA Masayuki; KANDA Hirofumi; KANASHIMA Takeshi; OKUYAMA Masanori
    Technical report of IEICE. SDM 一般社団法人電子情報通信学会 101 (108) 19 - 24 0913-5685 2001/06 
    We have prepared uniform ZrO_2 thin films for high-k gate dielectrics in the next generation ULSI ZrO_2 thin films have been grown on Si(100) wafer by pulsed laser deposition at 400℃. An uniform ZrO_2 thin film (of EOT=2.7 nm) is obtained. Oxygen radical annealing gives little change of EOT, and the leakage current is less than 1x10^<-7 A/cm^2 at 1 MV/cm. Moreover, the interface between high-k material and Si has been characterized by photoreflectance spectroscopy. The stress on Si with ZrO_2 prepared by MOD, is smaller than the case of Si/SiO_2.
  • Masayuki Sohgawa; Masashi Agata; Takeshi Kanashima; Kaoru Yamashita; Koji Eriguchi; Akira Fujimoto; Masanori Okuyama
    Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 40 (4 B) 2844 - 2848 0021-4922 2001/04 
    Strain and stress at the Si surface have been studied by photoreflectance (PR) spectroscopy. A Si diaphragm structure has been fabricated in order to produce the surface strain caused by N2 gas pressure which changes the PR spectra of the Si diaphragm. The transition energy obtained from the PR peak energy of approximately 3.4 eV is proportional to the surface stress, which is calculated by elastic analysis. Additionally, PR spectroscopy was applied to measure stress at the interface between the Si and thermal oxide. As the SiO2 growth temperature increases, the interface stress decreases. From our experimental results, it is considered that PR spectroscopy is effective as a contactless and nondestructive monitoring technique for Si surface stress.
  • O. Maida; N. Kohma; M. Ueno; A. Shibuya; T. Kanashima; M. Okuyama; H. Ohashi
    Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers 40 (4 A) 2435 - 2439 0021-4922 2001/04 
    The effects of soft X-ray irradiation of poly-tetra-fluoro-ethylene (PTFE) have been investigated using a figure-8 undulator. In the case of high-intensity irradiation, the surface temperature of the irradiated region increased and PTFE near the surface was evaporated effectively. In contrast, the PTFE surface swelled by the under low-intensity irradiation with the insertion of Al filters more than 9 μm thick. This reaction was found to be strongly dependent on the flux. The surface profile is largely determined by the relationship between fragment desorption and porous structure generation, and an increase in the surface temperature enhances the fragment desorption and has considerable influence on the surface profile. Al filter insertion decreases the flux and suppresses low-energy photons which are absorbed near the surface. Hence irradiated photons are composed of high-energy photons which penetrate deeply, and the surface temperature is difficult to increase by Al-filter-inserted irradiation.
  • M. Sohgawa; S. Kitai; H. Kanda; T. Kanashima; A. Fujimoto; M. Okuyama
    Extended Abstracts of International Workshop on Gate Insulator, IWGI 2001 Institute of Electrical and Electronics Engineers Inc. 170 - 173 2001 [Refereed]
     
    In this paper, we have prepared ZrO2 and lanthanide oxide thin films by PLD (Pulsed Laser Deposition) method and characterized these electrical properties by using C-V and J-V characteristics and these interfacial properties by using PR spectroscopy.
  • H Wada; M Agata; K Eriguchi; A Fujimoto; T Kanashima; M Okuyama
    JOURNAL OF APPLIED PHYSICS AMER INST PHYSICS 88 (5) 2336 - 2341 0021-8979 2000/09 
    Si surface damage induced during Ar and CHF3/CF4/Ar plasma processing has been characterized by photoreflectance spectroscopy (PRS). The photoreflectance (PR) signal intensity decreases drastically as the rf input power increases in the Si substrate exposed to the plasma. The recovery of the plasma-induced damage is confirmed by PRS after subsequent annealing over 500 degrees C. We found, from the shift of the PR spectra, the strain at the Si surface induced by the plasma treatment might be due to the introduction of the ions, C, F, or H, not to those of Ar. The depth profile of the defect density in the Si substrate is estimated quantitatively by analyzing the depth profile of the PR signal intensities. (C) 2000 American Institute of Physics. [S0021-8979(00)06316-7].
  • T Kanashima; A Fujimoto; M Okuyama
    SENSORS AND ACTUATORS B-CHEMICAL ELSEVIER SCIENCE SA 64 (1-3) 189 - 192 0925-4005 2000/06 
    Adsorptions of methanol and hydrogen molecules on (100) and (001) SnO2 surfaces have been investigated by using molecular orbital (MO) calculation, and compared with experimental data of gas sensing. From MO calculation, adsorption of methanol molecule on SnO2 surface tends to occur compared with H-2 molecule adsorption, in contrast to experimental data. Moreover, methanol can react with adsorbed O-2 molecule on SnO2 surface. So, it is considered that the sensitivity of SnO2 gas sensor is induced by adsorption of hydrogen atom or CH3 species rather than that of hydrogen or methanol molecule. (C) 2000 Elsevier Science S.A. All rights reserved.
  • M Agata; H Wada; O Maida; K Eriguchi; A Fujimoto; T Kanashima; M Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS JAPAN J APPLIED PHYSICS 39 (4B) 2040 - 2044 0021-4922 2000/04 
    Thin gate oxide charging damage induced by plasma exposure in the metal-oxide-semiconductor (MOS) structure has been studied by photoreflectance (PR) spectroscopy. The PR signal intensity around the photon energy of 3.4 eV is found to decrease as the plasma exposure time increases. The capacitance-voltage (C-V) characteristic shows the generation of SiO2/Si interface states as well as that of electron trap sites in the oxides induced by the DC mode Ar plasma exposure. The SiO2/Si interface state plays the role of a recombination center for the photo generated carriers, resulting in the decrease in the surface potential change. On the other hand, the electron trapped in the oxide increases the surface potential. Therefore, the decrement in the PR signal intensity is considered to correspond primarily to the SiO2/Si interface state generation induced by the plasma-process, because the signal intensity decreases with the decrease of the surface potential.
  • M Agata; M Sogawa; O Maida; K Eriguchi; A Fujimoto; T Kanashima; M Okuyama
    2000 5TH INTERNATIONAL SYMPOSIUM ON PLASMA PROCESS-INDUCED DAMAGE AMERICAN VACUUM SOCIETY NORTHERN CALIFORNIA CHAPTER 97 - 100 2000 [Refereed]
     
    Thin gate oxide charging damage has been studied by photoreflectance (PR) spectroscopy in MOS structure samples. Antenna-area-dependent oxide charging damage such as the generation of SiO2/Si interface states as well as that of electron trap sites in the oxides, has been also addressed by the decrease of the PR peak signal intensity from MOS capacitors, and also confirmed by the capacitance-voltage (C-V) characteristics.
  • Masashi Agata; Masayuki Sohgawa; Osamu Maida; Koji Eriguchi; Akira Fujimoto; Takeshi Kanashima; Masanori Okuyama
    Technical report of IEICE. SDM 一般社団法人電子情報通信学会 99 (491) 75 - 80 0913-5685 1999/12 
    Charging damage of metal/Si/SiO2 structure induced by the plasma exposure has been studied by the photoreflectace (PR) spectroscopy. The increase of the SiO2/Si interface states as well as that of the electron trap sites in the oxide is considered to be induced by the Ar plasma exposure. The interface states reduce the surface potential change and the signal intensity. The electron trapped in the oxide increase the surface potential and the signal intensity. The PR signal intensity decreases as the plasma exposure time increases. Therefore, the PR spectrum is considered to give primarily th...
  • T Kanashima; M Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS JAPAN J APPLIED PHYSICS 38 (4A) 2044 - 2048 0021-4922 1999/04 
    Capacitance-voltage (C-V) characteristics of the metal-ferroelectrics-insulator-silicon (MFIS) structure have been calculated by the conventional metal-oxide-silicon (MOS) analysis method. The potential profile is obtained by using the Poisson equation of D-E hysteresis, and its capacitance is estimated as combination of SiO2-Si capacitance and ferroelectric film capacitance obtained fi om dielectric constant corresponding to the internal field. PbZrxTi1-xO3 (PZT) and SrBi2Ta2O9 (SBT) ferroelectrics, SiO2, MgO, SrTiO3 (STO) and CeO2 insulators, and silicon semiconductor, were used as independent parameters for the analyses. The dependence of MFIS C-V characteristics on ferroelectric properties, film thickness and impurity concentration of the semiconductor is calculated. Film thicknesses of ferroelectrics and insulators affect the: memory window width markedly, and have to be optimized in order to obtain a large memory window width. On the other hand, MFIS C-V characteristics and memory window width are not influenced by P-r because the effective P-r is small in the MFIS structure.
  • O Maida; N Okada; T Kanashima; M Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS JAPAN J APPLIED PHYSICS 38 (4B) 2341 - 2344 0021-4922 1999/04 
    The interface transition layer in ultrathin SiO2 film is characterized by analyzing the oscillatory tunneling current. SiO2 thin films are deposited on atomically flat Si at low temperature (300 degrees C) by photo-induced chemical vapor deposition (photo-CVD) and their electrical characteristics are investigated. The electrical characteristics of the SiO2/Si diode are improved by annealing in O-2 atmosphere under ultraviolet irradiation, and the current becomes small and equivalent to that of a thermally grown oxide. Tunneling current through the ultrathin gate oxide is observed to exhibit oscillatory behavior in the Fowler-Nordheim (FN) tunneling region, which results from the interference of the incident and reflected electron waves at the SiO2/Si interface. It is clarified from theoretical calculation of the tunneling current that the amplitude and phase of the oscillatory current are strongly affected by the transition layer thickness. It is concluded that the: interface transition layer of photo-CVD SiO2 film is thinner than that of thermally grown SiO2 film from analysis of the amplitude of the oscillatory profile.
  • T Kanashima; M Okuyama
    JOURNAL OF APPLIED PHYSICS AMER INST PHYSICS 85 (1) 244 - 248 0021-8979 1999/01 
    The atomic bonding of F-2 molecules on Si(111) and Si(100) surfaces has been analyzed by the molecular orbital method. The stable geometry is obtained by minimizing the total energy of a system in which a F-2 molecule approaches the Si surface, and the infrared absorption spectrum characteristic of its atomic bonds is analyzed. Si clusters consisting of 22 and 32 Si atoms for the Si(100) and Si(100) surfaces, respectively, with dangling bonds terminated by H atoms are treated. The F-F bond disappears and a Si-F bond is formed as the F-2 molecule approaches the Si surface. The F-2 molecule reacts with the Si(100) surface more easily than with the Si(111) surface. Moreover, etching of Si by F-2 gas occurs in the case of Si(111), but not in the case of Si(100). The obtained infrared absorption spectra agree qualitatively with experimental data. (C) 1999 American Institute of Physics. [S0021-8979(98)10723-5].
  • O Maida; H Yamamoto; N Okada; T Kanashima; M Okuyama
    APPLIED SURFACE SCIENCE ELSEVIER SCIENCE BV 130 214 - 220 0169-4332 1998/06 
    Micro-morphology of Si surface treated by chemical solution has been observed by atomic force microscope, and its relationship with electronic property of SiO2/Si structure has been investigated. Well-ordered atomic steps and flat terraces were observed on some Si surfaces. SiO2 film has been prepared on the substrates at low temperatures of 300 degrees C by photo-induced chemical vapor deposition (photo-CVD) method. Interface state densities of the SiO2/Si structures become less on the atomically flat Si than those on rough Si. In addition, breakdown voltage of the SiO2 films were measured to clarify the relation of the insulation property with roughness. A and B modes of the breakdown have been observed in as-deposited sample, but is independent on surface roughness. These failures can be reduced by O-2 annealing. (C) 1998 Elsevier Science B.V. All rights reserved.
  • Koyano, I; M Okuyama; E Ishiguro; A Hiraya; H Ohashi; T Kanashima; K Ueda; IH Suzuki; T Ibuki
    JOURNAL OF SYNCHROTRON RADIATION MUNKSGAARD INT PUBL LTD 5 (3) 545 - 547 0909-0495 1998/05 
    Design and construction of a soft X-ray beamline at SPring-8 is reported. The beamline utilizes high-quality linearly polarized soft X-rays obtainable from a figure-8 undulator for the study of photophysical and photochemical processes of atoms, molecules and surfaces in the inner-shell excitation region. It consists of two experimental stations, a photochemistry station and a chemical vapour deposition (CVD) station. A high-resolution grating monochromator is installed at the photochemistry station, while the intense undispersed undulator radiation is used at the CVD station. Unique features of the experimental chambers and of the analysis and characterization systems are described along with those of the monochromator.
  • M Okuyama; Y Oishi; Y Matsumuro; T Kanashima
    JOURNAL OF THE KOREAN PHYSICAL SOCIETY KOREAN PHYSICAL SOC 32 (4 SUPPL.) S1357 - S1360 0374-4884 1998/02 
    Voltage dependence of high-frequency capacitance of metal-ferroelectric-SiO2-Si structure has been analyzed by solving the potential profile. Dielectric polarization required to control Si surface potential is very small in comparison with the conventional remanent polarization. SrBi2Ta2O9/SiO2/Si structure has been prepared by laser ablation of SrBi2Ta2O9 film on SiO2/Si at low temperatures of 400-550 degrees C. SrBi2Ta2O9 films have a good (105) preferential orientation. SrBi2Ta2O9/SiO2/Si structures show good C-V hysteresis curve. Dielectric hysteresis of the SrBi2Ta2O9 film in SrBi2Ta2O9/SiO2/Si structure has been obtained by analyzing the C-V characteristics. MFIS-FET using SrBi2Ta2O9 film has been fabricated and shows good memory characteristic.
  • N Nagai; M Takeuchi; T Kimura; T Kanashima
    HEAT TRANSFER 1998, VOL 4 TAYLOR & FRANCIS LTD 137 - 141 1998 
    In this report, two kinds of experiments to measure contact angles on superheated walls were conducted in order to get useful information for the evaluation of surface wettability in boiling phenomena or the designing of liquid-film evaporation devices. First one is liquid-droplet method in which the temperature of surrounding argon gas or water vapor atmosphere was controlled equal to the solid temperature, and the contact angles of water droplet were measured. The other one is quasi-two-dimensional subcooled boiling method in which the contact angles of quasi-two-dimensional bubbles were measured.As a result of experiments, equilibrium, advancing and receding contact angles of small superheated region could be measured by both liquid-droplet method and quasi-two-dimensional boiling method. The obtained results show that contact angles on superheated walls have little temperature dependence.
  • H Yamamoto; K Okumura; T Kanashima; M Okuyama
    THIRD INTERNATIONAL CONFERENCE ON THIN FILM PHYSICS AND APPLICATIONS SPIE-INT SOC OPTICAL ENGINEERING 3175 161 - 165 0277-786X 1998 [Refereed]
     
    Surface treatment effects on microscopic morphology of Si(111) and (100) surfaces have been investigated by atomic force microscope (AFM). Well-ordered atomic steps and flat terraces have been clearly observed on the Si(lll) surfaces treated in 40% NH4F solution. Then, SiO2 films were deposited on these atomically flat substrates at 300 degrees C by photo-CVD method. Interface state density of the Si/SiO2 structure with this flat surface is smaller than that of the substrate with disordered surface. On the other hand, in the case of Si(100) wafers, atomically flat structures have not been observed in the surfaces treated by 1% HF, 40% BHF and HF/H2O2 solutions, and a lot of small and random unevennesses have been observed on each surface. Si/SiO2 interface state density decreases with decreasing average roughness of Si surface.
  • H Wada; K Eriguchi; A Fujimoto; T Kanashima; M Okuyama
    1998 3RD INTERNATIONAL SYMPOSIUM ON PLASMA PROCESS-INDUCED DAMAGE AMERICAN VACUUM SOCIETY NORTHERN CALIFORNIA CHAPTER 152 - 155 1998 [Refereed]
     
    Si substrate damage induced by CHF3/CF4/Ar plasma processing has been characterized by photoreflectance (PR) spectroscopy. Moreover, the damage induced by Ar plasma has been characterized in-situ in the processing chamber. Both of the PR signal intensities decrease with the plasma treatment. The decrease in the PR signal intensity is attributed to the decrease of modulation due to the introduction of the charged defects that changes the space charge density of the depletion layer. We propose a new model for the estimation of the defect density induced by plasma exposure. Using this model based on the PR spectroscopy, the defect density can be quantitatively calculated.
  • M Okuyama; WB Wu; Y Oishi; T Kanashima
    APPLIED SURFACE SCIENCE ELSEVIER SCIENCE BV 117 406 - 412 0169-4332 1997/06 
    The volt-age dependence of the high-frequency capacitance of a metal-ferroelectric-insulator-semiconductor (MFIS) structure is analyzed by relating the potential profile to the dielectric hysteresis of the ferroelectric thin film. About one hundredth of the dielectric polarization of ferroelectric ceramic PZT is enough to control the Si surface potential for ferroelectric gate FET memory, and large coercive force is required to obtain enough voltage window. MFIS structures using Bi-layer-structured ferroelectric thin films are also studied from experimental viewpoint. SrBi2Ta2O9 and Bi4Ti3O12 thin films have been prepared by laser ablation method on both Pt sheet and Si wafers at low temperatures of 400-500 degrees C. SrBi2Ta2O9 thin films have a good (105) preferential orientation. and Bi4Ti3O12 thin films have (117) and c-axis orientations on these substrates. D-E hystereses are obtained in SrBi2Ta2O9 and Bi4Ti3O12 thin films prepared on Pt sheet, and are enough to control the Si surface potential. Ferroelectric film-SiO2-Si structures show good C-V hysteresis curves owing to the Si surface potential controlled by the D-E hysteresis.
  • T Kanashima; Y Kurioka; T Imai; H Yamamoto; M Okuyama
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS JAPAN J APPLIED PHYSICS 36 (4B) 2460 - 2463 0021-4922 1997/04 
    Effects of F-2 treatment on the Si(100) surface have been characterized using infrared reflection absorption spectroscopy (IR-RAS). Hydrogen desorbs first from Si-H, and desorption from Si-H-2 and Si-H-3 follows subsequently, when the n-Si(100) wafer terminated by Si-H, Si-H-2 and Si-H-3 is exposed to F-2 gas. Moreover, the hydrogen of Si-H-2 desorbs faster on a terrace than on an edge. Finally, the Si(100) surface is covered by Si-F and Si-F-2.
  • T Kanashima; M Okuyama; Y Hamakawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS JAPAN J APPLIED PHYSICS 36 (3B) 1448 - 1452 0021-4922 1997/03 
    Energy states of hydrogen-related defects in SiO2 such as Si-H, Si-O-H and Si-O-O-H have been studied by theoretical analysis using molecular orbital (MO) calculation. The theoretical analyses have been carried out using both the semiempirical and ab-initio MO methods, and the ab-initio MO calculation results shows that the transition energy from the excited-singlet state to the ground state is 3.89 eV in a Si-O-O-H cluster. This value is close to that of the photoluminescence peak energy measured in the SiO2 film grown by photo-induced chemical vapor deposition. The strengths of the hydrogen bonds with Si and Si-O have been investigated, and it was found that Si-OH is more stable than Si-H.
  • Optical Properties and Molecular Orbital Analyses of Defects in Photo-CVD SiO2 Thin Films
    Takeshi Kanashima
    1996/03
  • H Yamamoto; S Iwasaki; K Okumura; T Kanashima; M Okuyama; Y Hamakawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS JAPAN SOC APPLIED PHYSICS 35 (2B) 1569 - 1572 0021-4922 1996/02 
    Charged traps near the Si-SiO2 interface in a SiO2 film deposited by photo-induced chemical vapor deposition (photo-CVD) have been analyzed by the photo I-V method. In the as-deposited film, positively charged traps distribute in the region between 2 nm and 10 nm from the Si-SiO2 interface, and their density decreases monotonically with increasing depth. The density of traps in the region between 2 nm and 4 nm is decreased by annealing in N-2 or O-2, and that of traps in the region between 4 nm and 10 nn is decreased only by annealing in O-2. Furthermore, the results of electron spin resonance (ESR) antilysis suggest the possibility that the positively charged traps in the 2-4 nm region are related to the defects observed in ESR.
  • T Kanashima; M Okuyama; Y Hamakawa
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS JAPAN J APPLIED PHYSICS 35 (2B) 1445 - 1449 0021-4922 1996/02 
    Energy states of oxygen-excess defects in SiO2 have been studied by theoretical analyses using molecular orbital calculation and discussed on the basis of comparison with photoluminescence of SiO2 thin films. Theoretical analyses have been carried out using both the semi-empirical and ab-initio methods, and have shown that the transition energy from the excited singlet state to the ground state is 2.32 eV with the STO-3G basis set and 2.40 eV with the 3-21G basis set, which are very close to the 2.4 eV photoluminescence peak measured in the photo induced chemical vapor deposition SiO2 thin film. This analysis and the effects of annealing in O-2 and N-2 atmospheres suggest that origin of the photoluminescence peak at 2.4 eV is oxygen-excess defect.
  • Takeshi Kanashima; Masanori Okuyama; Yoshihiro Hamakawa
    Applied Surface Science 79-80 (C) 321 - 326 0169-4332 1994/05 
    Defects and other imperfections in SiO2 films grown by photo-induced chemical vapor deposition (photo-CVD) have been characterized by optical absorption and photoluminescence excited by ArF and F2 excimer lasers. The absorption peaks at 6.3 and 7.6 eV have been measured in films prepared at growth temperatures between room temperature and 300°C. Photoluminescence peaks have been observed at around 2.7, 3.5 and 4.4 eV. Their dependencies on both the deposition temperatures and excitation energy have been investigated. The origins of these peaks are discussed. © 1994.
  • T KANASHIMA; R NAGAYOSHI; M OKUYAMA; Y HAMAKAWA
    JOURNAL OF APPLIED PHYSICS AMER INST PHYSICS 74 (9) 5742 - 5747 0021-8979 1993/11 
    Photoluminescence and absorption properties of photo-induced chemical vapor deposition produced SiO2 films have been studied to identify the defects and the other imperfections. Two kinds of distinct absorption peak have been found which lie at 6.3 eV for low temperature deposition (around 30-degrees-C), and at 7.6 eV for high temperature deposition (around 300-degrees-C). Photoluminescence peaks at 2.7, 3.6-3.8, and 4.4 eV are found in the film deposited at high temperature, but the 4.4 eV peak is not seen in film deposited at low temperature. Intensity changes of the photoluminescence and absorption peaks have been obtained in various films which were deposited at different gas-flow-rate-ratios of Si2H6/O2 and were annealed in O2 and N2 ambients. It is considered from the treatment dependence of these peaks that the absorption peak at 7.6 eV and photoluminescence peak at 2.7 eV are attributable to oxygen-vacancies, but the absorption peak at 6.3 eV relates to oxygen-excess defects.
  • T KANASHIMA; M OKUYAMA; Y HAMAKAWA
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS JAPAN SOC APPLIED PHYSICS 32 (6B) 3113 - 3119 0021-4922 1993/06 
    Defects and other imperfections in photo-induced chemical vapor deposition (photo-CVD) SiO2 films have been characterized by photoluminescence excited by ArF and F2 excimer lasers. Photoluminescence peaks have been observed at around 2.7, 3.5 and 4.4 eV and are characteristic of both the deposition temperatures of photo-CVD and excitation energy. The intensity of the photoluminescence peak at around 2.7 eV initially increases with ArF excimer laser irradiation but decreases after about 2000 shots. On the other hand, it decreases monotonously with F2 excimer laser irradiation. The origins of these peaks have been discussed in terms of various dependences of photoluminescence and absorption spectra.
  • エキシマレーザ励起フォトルミネッセンスによる光CVD SiO2膜の欠陥評価
    金島 岳
    1993/03

Books etc

  • P(VDF-TeFE)/Organic Semiconductor Structure Ferroelectric-GateFETs
    T. Kanashima; M. Okuyama (Joint work)Springer 2016/01 9789402408416

Works

  • ゲルマニウムベース高移動度トランジスタのための表面修飾と絶縁体／界面改善
    2008
  • ナノ薄膜技術を応用したロボットのための集積多軸触覚センサの開発
    2006
  • ナノ薄膜技術を応用したロボットのための集積多軸触覚センサの開発
    2005

MISC

Industrial Property Rights

  • 強誘電体メモリ及びその製造方法
    特願2006-241846

Awards & Honors

  • 2006 JJAP論文賞

Research Grants & Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2022/03 
    Author : Kanashima Takeshi
     
    Germanium (Ge)-MISFETs using low-temperature growth epitaxial La2O3 as a gate insulating film have been focused. The gate-stack is formed directly on Ge with low interface defects by atomic matching without a GeO2 buffer layer which is thermally unstable and relatively low dielectric constant. Therefore, it can reduce the oxide film equivalent film thickness (EOT) for further miniaturization. In order to improve the interface characteristics, the iodine solution treatment is optimized as surface passivation and the Ge-based transistor fabrication process is optimized. As a result, relatively high mobility of the Ge-MOSFET fabricated at a low temperature of 350 oC is achieved. Moreover, in order to realize a smaller EOT, the interface reaction was suppressed by controlling the oxygen concentration during growth and optimizing the annealing conditions.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009 -2011 
    Author : OKUYAMA Masanori; KANASHIMA Takeshi; SOHGAWA Masayuki; RICINSCHI Dan
     
    Multiferroic BiFeO_3 has giant dielectric hysteresis at room temperature but very small magnetic hysteresis and so little magneto-electric effect. Then, BiFeO_3 and BiFe_<1-x> M_xO_3 thin films are prepared by pulsed laser deposition under magnetic field and/ or annealed under magnetic field. So, magnetic hysteresis of the prepare thin films could be increased by antiparallel arrangement of different spins of adjacent magnetic ions, defect generation and/ or microscopic texture variation, keeping large ferroelectricity and moreover magneto-electric effect is expected to be enhance.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2008 -2011 
    Author : KANASHIMA Takeshi
     
    Germanium has been attracting much attention for high-performance ULSI, because it has higher electron and hole mobilities than Si. However, Ge-based MIS transistors still have the problems such as a high interface state density. So, the passivation of the Ge surface has been studied to reduce the interface state density. The theoretical analysis was carried out to search for alternative terminal materials on the Ge surface, and the passivation effects have been characterized experimentally. As a result, it is shown that F, Cl and S treatments can reduce the interface state density.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2000 -2003 
    Author : 奥山 雅則; 金島 岳; 山下 馨; 野田 実; 上野 智雄; 舟窪 浩
     
    Pulsed Laser Deposition(PLD)法により製膜したSrBi_2Ta_2O_9(SBT)薄膜を用いたMetal-Ferroelectric-Insulator-Semiconductor(MFIS)構造においてRapid Thermal Annealing(RTA)を行うことにより良好な静電容量保持特性が得られており、このゲート形成プロセスを用いたMFIS-FETを新たに考案し試作を行った。 試作したp-Channel FETのId-Vg特性において強誘電体分極ヒステリシスによって制御されたId-Vgヒステリシスが観測され、メモリウインドウは約1.5Vであった。IdのON/OFF比はSBT強誘電体薄膜を形成する以前のMOSFETと同等の7桁以上と非常に良好な特性が得られた。データ保持時間は10^3秒以上が確認された。一方、さらなる特性の向上を目指し、強誘電体膜成長中の拡散バリアとなり良好な表面チャネルキャリア移動度を与えるI層として酸窒化膜を採用し、その最適化を行った。Si基板上に3種類の窒化膜:1)N_2O雰囲気中での熱酸窒化膜、2)Cat-CVD法による表面窒化酸化膜、3)Plasma CVDによる表面窒化酸化膜、を形成し1)SiON/Si,2),3)SiON/SiO_2/Si構造を作製し評価した。その結果、Cat-CVD法による酸窒化膜は表面に窒素が偏在し、拡散バリア性の向上、リーク電流のプールフレンケル成分の低減、等が見られた。また、Plasma窒化法による酸窒化膜は比較的膜内部にも窒素が含有され、膜全体としてバリア性も高いと考察された。また窒化時間により表面付近窒素含有量を制御できた。これら窒化膜をI層として用いる場合のMFIS-FETプロセスフローも提案、検討した。 さらに前年度から強誘電体-絶縁体界面伝導電流を利用した新構造ゲートFETメモリの提案、検討を進めており、強誘電体分極ヒステリシスに対応するId-Vgヒステリシス特性、IdのON/OFF比約2桁が得られた。本構造はSi以外の基板への応用が可能でありPt金属上でのヒステリシスも確認されている。
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2000 -2002 
    Author : 金島 岳
     
    近年、半導体デバイスにおいては非常な集積化が進み、LSIを構成する素子は非常に微細なものとなっている。これらULSIデバイスにおいて、素子の信頼性に重要な位置を占めているFETのゲート絶縁膜は、0. 1μm世代では膜厚が2nm程度(シリコン酸化膜換算)と、原子十数層程度からなるものが必要となってきている。放射光を照射することで、原子レベルで平坦なSi表面が形成できることが報告され、また放射光軟X線励起CVDでは、真空紫外光源励起CVDにくらべ良質の薄膜が得られることが示されている。そこで、放射光からの強い軟X線により選択的な高励起状態を作り出し、絶縁膜・誘電体膜を作製した。 本研究では、放射光を用いSi表面の直接窒化・酸化を行った。窒素または酸素雰囲気中で軟X線アンジュレータからの放射光を直接Si基板へ照射した。光のエネルギ`は0.3、1.9kevとした。AESによる測定で窒素分圧が低いときは、表面に吸着するだけであるが、12Paまで分圧をあげることで表面にSiN結合が形成することを確認した。また基板温度を200℃まで下げても同様の反応が見られ、放射光により基板表面および雰囲気ガスを励起することで反応を促進できることが示された。さらに、他の電子材料への放射光照射を行い、反応性および薄膜作成の可能性について調べた。その結果、高輝度放射光をa-Si : Hへ照射することで、激しい反応が見られ、急激な水素の脱離、体積変化または結晶性の変化が引き起こされると考えられる。またCaF_2へ光照射を行ったところ、放射光誘起蒸発が起こることが分かり、この現象を利用した薄膜作製を行った。その結果、約10nm/分程度の製膜速度が得られ、XPSなどの測定よりCaF_2が形成されたと考えられる。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2000 -2002 
    Author : NODA Minoru; KIJIMA Takeshi; KANASHIMA Takeshi; OKUYAMA Masanori
     
    1. It is suggested that leakage current through layer of ferroelectric such as SrBi_2TaO_9 and Sr_2 (Ta_<1-x>, Nb_x)_2O_7 has a dominant effect on memory retention properties of Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure. Furthermore, it is confirmed especially for the. SBT film that suppression of the leakage improved drastically retention properties, then increased the time by an order of magnitude, more than 2x10^4 s. with some post-oxygen annealing process. 2. We proposed a dynamic model where carriers flow though ferroelectric layer and inject into the interface between ferroelectric and insulator layers, thus electric field imposed on the ferroelectric film gradually cancelled and decreased. As a result, experimental results shown above was qualitatively explained. 3. A new analysis instrument utilizing ionization potential measurement was proposed and fabricated, which enables us to evaluate the SBT sutface with and without post-oxygen annealing, then to consider the band diagram of MFIS structure. It reveals that, before the annealing, hole conduction dominates the leakage through the SBT film, and that, after the annealing, barrier height against hole increases from 1.6 to 2.0 eV. This result agrees well with the mentioned above, where a reduction of leakage by the annealing improves the memory retention characteristics. 4. A Rapid Thermal Annealing process with oxygen atmosphere improved greatly the retention time of MFIS diode. With a very high temperature and short time of 1000℃ and 30 s, the retention time became more than 6x10^5 s (about 1 week), and was extrapolated to about 3x10^7 s (about 1 year). 5. A high pressure (7 atm) oxygen annealing was examined in order to improve the retention properties furthermore: It was found that the annealing is effective to reduce the leakage and estimated that Bi_xO_y layer, different from (Bi_2O_2)^<2+> layer, was fermed and suppress the leakage.
  • 放射光による電子材料のエッチング
  • 分子軌道法による半導体表面の評価
  • High-k膜の成長とその評価
  • Etching of Electrical Materials by SR
  • Characterization of semiconductor surface by molecular orbital calculation
  • characterization of high-k thim film

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