H. Iwai

NIMS Medicity, Neyattinkara, Kerala, India

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Publications (368)330.62 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A study of the gate oxide/channel interface quality in ultra-scaled SOI omega-gate nanowire NMOS FETs with cross-section as small as 10 nm × 10 nm is experimentally presented by low-frequency noise measurements. The noise study has been efficiently applied for the characterization of various technological parameters, including strained channel, additional hydrogen anneal, or channel orientation difference. A method for rigorous contribution assessment of the two oxide/channel interfaces (top surface vs. side-walls) is also demonstrated. Quality of the interface is slightly altered among the 4-types of technological parameters and the structural variety down to nanowire. However, an excellent quality of Hf-based high-k/metal gate stack is observed and sustained in all the devices. In particular, efficient tensile strain stressor is demonstrated with high enhancement of the NMOS FET performance and preserved 1/f noise performance fulfilling the requirement for future CMOS logic node stated in the international technology roadmap for semiconductors.
    Solid-State Electronics. 02/2015;
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    ABSTRACT: Bipolar resistive switching characteristics of CeOx layer on Si-based bottom electrodes (BE) are presented. Owing to the formation and the presence of a thin SiO2 interfacial layer (SiO2-IL) between the CeOx layer and BE, the set process is triggered by a local breakdown at the thin SiO2-IL due to large differences in dielectric constants. Reset process, on the other hand, is obtained by local anodic oxidation to the breakdown spots by the high oxygen ion conductivity of the CeOx layer. High insulating properties of SiO2-IL enables obtaining a resistance ratio of over 105 at high-resistive-state to low-resistive-state. A model to explain the resistance ratio has been proposed using initial trap density of SiO2-IL. Moreover, forming-free feature can be achieved with NiSi2 BE.
    Semiconductor Science and Technology 10/2014; 29(11):115030. · 2.21 Impact Factor
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    ABSTRACT: Although several high-k insulators have been deposited on the diamond for metal-insulator-semiconductor field effect transistors (MISFETs) fabrication, the k values and current output are still not fully satisfactory. Here, we present a high-k ZrO2 layer on the diamond for the MISFETs. The k value for ZrO2 is determined by capacitance-voltage characteristic to be 15.4. The leakage current density is smaller than 4.8 × 10(-5) A·cm(-2) for the gate voltage ranging from -4.0 to 2.0 V. The low on-resistance MISFET is obtained by eliminating source/drain-channel interspaces, which shows a large current output and a high extrinsic transconductance. The high-performance diamond MISFET fabrication will push forward the development of power devices.
    Scientific Reports 09/2014; 4:6395. · 5.08 Impact Factor
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    ABSTRACT: In this paper, a detailed 3-D numerical analysis is carried out to study and evaluate CMOS logic device and circuit performance of gate-all-around (GAA) Si nanowire (NW) field-effect transistors (FETs) operating in sub-22-nm CMOS technologies. Employing a coupled drift-diffusion room temperature carrier transport formulation, with 2-D quantum confinement effects, we numerically simulate Si GAA NWFET electrical characteristics. The simulation predictions, on the device performance, short channel effects, and their dependence on NW geometry scaling, are in good agreement with the Si NWFET experimental data reported in literature. Superior electrostatic integrity, OFF-state device performance, lower circuit delays, and faster switching in the Si GAA NWFET-based CMOS circuits are numerically demonstrated in comparison with an Si-on-insulator FinFET. The mixed-mode numerical simulations also predict low supply voltage operations for the Si NWFET-based logic circuits.
    IEEE Transactions on Electron Devices 09/2014; 61(9):3066-3074. · 2.36 Impact Factor
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    ABSTRACT: The photothermal conversion of CO2 provides a straightforward and effective method for the highly efficient production of solar fuels with high solar-light utilization efficiency. This is due to several crucial features of the Group VIII nanocatalysts, including effective energy utilization over the whole range of the solar spectrum, excellent photothermal performance, and unique activation abilities. Photothermal CO2 reaction rates (mol h−1 g−1) that are several orders of magnitude larger than those obtained with photocatalytic methods (μmol h−1 g−1) were thus achieved. It is proposed that the overall water-based CO2 conversion process can be achieved by combining light-driven H2 production from water and photothermal CO2 conversion with H2. More generally, this work suggests that traditional catalysts that are characterized by intense photoabsorption will find new applications in photo-induced green-chemistry processes.
    Angewandte Chemie International Edition 07/2014; · 11.34 Impact Factor
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    [Show abstract] [Hide abstract]
    ABSTRACT: The photothermal conversion of CO2 provides a straightforward and effective method for the highly efficient production of solar fuels with high solar-light utilization efficiency. This is due to several crucial features of the Group VIII nanocatalysts, including effective energy utilization over the whole range of the solar spectrum, excellent photothermal performance, and unique activation abilities. Photothermal CO2 reaction rates (mol h−1 g−1) that are several orders of magnitude larger than those obtained with photocatalytic methods (μmol h−1 g−1) were thus achieved. It is proposed that the overall water-based CO2 conversion process can be achieved by combining light-driven H2 production from water and photothermal CO2 conversion with H2. More generally, this work suggests that traditional catalysts that are characterized by intense photoabsorption will find new applications in photo-induced green-chemistry processes.
    Angewandte Chemie 07/2014;
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    ABSTRACT: It was found that the electrical properties of CeO2/La2O3 stack are much better than a single layer La2O3 film. A thin CeO2 capping layer can effectively suppress the oxygen vacancy formation in the La2O3 film. This work further investigates the current conduction mechanisms of the CeO2 (1 nm thick)/La2O3 (4 nm thick) stack. Results show that this thin stacked dielectric film still has a large leakage current density; the typical 1−V leakage can exceed 1 mA/cm2 at room temperature. The large leakage current should be due to both the oxide defect centers as well as the film structure. Results show that at low electric field (<0.2 MV/cm), the thermionic emission induced current conduction in this stacked structure is quite pronounced as a result of interface barrier lowering due to the capping CeO2 film which has a higher k value than that of the La2O3 film. At higher electric fields, the current conduction is governed by Poole–Frenkel (PF) emission via defect centers with an effective energy level of 0.119 eV. The temperature dependent current–voltage characteristics further indicate that the dielectric defects may be regenerated as a result of the change of the thermal equilibrium of the redox reaction in CeO2 film at high temperature and the drift of oxygen under the applied electric field.
    Microelectronics Reliability 06/2014; · 1.21 Impact Factor
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    ABSTRACT: The thermopowers of single-crystalline anilinium tetrathiafulvalene-2-carboxylate (TTFCOONH3Ph) and its deuteriated form (TTFCOOND3Ph) have been examined at room temperature, and a significant isotope effect was found: 102 μV/K for TTFCOONH3Ph, and 48 μV/K for TTFCOOND3Ph, which amounts to a difference of a factor of around two. The origin of the difference, for example, X-ray crystal structure and doping level, was examined based on chemical and physical characterizations, and it was found that very low ion transport drastically enhances the thermopower of holes, giving rise to the large isotope effect.
    Berichte der deutschen chemischen Gesellschaft 05/2014; · 2.97 Impact Factor
  • ECS Transactions 05/2014; 61(4):265-270.
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    ABSTRACT: A study of the interface quality in ultra-scaled omega-gate nanowire NMOSFETs, with variant technological boosters, is presented by low-frequency noise (LFN) measurements. Excellent quality of the interfaces has been achieved down to narrow width (10nm), and whatever the technological splits. In particular, efficient tensile stressor has been demonstrated with high performance enhancement and preserved noise performance fulfilling the ITRS 1/f LFN road map.
    2014 International Symposium on VLSI Technology, Systems and Application (VLSI-TSA); 04/2014
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    ABSTRACT: We report an experimental investigation of oxide/channel interface quality in SOI omega-gate nanowire NMOS FETs with cross-section as small as 10nm×10nm by low-frequency noise measurements. The noise study has been efficiently applied for the characterization of various technological parameters, including strained channel, H2 anneal, or channel orientation. A method for rigorous contribution assessment of the two interfaces (top surface vs. side-walls) is also demonstrated. Excellent quality of the interfaces is extracted for all our technological and structural parameters.
    2014 15th International Conference on Ultimate Integration on Silicon (ULIS); 04/2014
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    ABSTRACT: Contributions of gate metal to electrical characteristics in AlGaN/GaN Schottky HEMT are reported. The focus is on the collapse of drain current associated with Schottky metals. Ni and W gate introduce electrically active defects under the gate metal in AlGaN layer. These electrically active defects induce the current collapse, higher gate leakage current, and frequency dispersion in C-V characteristics. Contrarily, TiN metal seems to mitigate the appearance of such electrically active defects. The observed current collapse is not the permanent but the recoverable degradation by means of light exposure irrespectively of the gate metals, suggesting the involvement of electron trapping on defects, particularly at the gate edge on the drain side where the electric field is the highest. The nitrogen vacancies in the AlGaN layer underneath the Schottky gate are plausible origin that is responsible for the electrically active defects based on the dependence of nitrogen concentration in TiN metal on the current collapse, which can be explained in terms of nitrogen diffusion from the AlGaN layer to the gate metal.
    IEEE Transactions on Electron Devices 03/2014; PP(99):1-1. · 2.36 Impact Factor
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    ABSTRACT: Interface properties of La-silicate gate dielectrics on Si substrates with W or nano-sized grain W2C gate electrodes have been investigated. A low interface state density of 2.5 × 1011 cm−2/eV has been achieved with W2C gate electrodes, which is one third of those with W gate electrode. An interface roughness of 0.33 nm with spatial frequency comparable to the grain size of W gate electrode has been observed. Besides, an atomically flat interface of 0.12 nm has been obtained with W2C gate electrode. The origin of flat interface may be attributed to the elimination of inhomogeneous stress by grains in metal electrode.
    Applied Physics Letters 01/2014; 104(2):021601-021601-4. · 3.52 Impact Factor
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    ABSTRACT: Ultra-thin InGaAs gate stacks with CET= 0.73 nm (EOT<; 0.5 nm), Dit as low as 8.0×1011 (cm-2 eV-1) and thermal stability up to 600°C is demonstrated by using La2O3 as gate dielectric. A silicide/InGaAs junction with excellent controllability at the interface is also proposed. These results promise the integration compatibility of this gate stack for future node 3D device structures.
    2013 IEEE International Electron Devices Meeting (IEDM); 12/2013
  • Diamond and Related Materials 09/2013; · 1.57 Impact Factor
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    ABSTRACT: Metal induced effects on electrical characteristics in AlGaN/GaN Schottky HEMT are reported. Focus is given to the collapse of drain current attributed to Schottky metal. Of particular interest for discussion is that TiN gate can suppresses the collapse of drain current compared with conventional Ni gate. Nitrogen concentrations in TiN gate are found to be correlated to the current collapse, indicating that the nitrogen vacancy is responsible for the traps in AlGaN/GaN HEMT. The reduction in a concentration gradient of nitrogen should be accomplished for preventing the formation of the traps. Because of the metal dependent collapse of the drain current, the traps are considered to be formed under the gate edge on the drain side in AlGaN layer.
    ESSDERC 2013 - 43rd European Solid State Device Research Conference; 09/2013
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    ABSTRACT: In this work, the effects of a gate-to-channel dielectric breakdown on the output characteristics of advanced La2O3-based metal–oxide-semiconductor field-effect transistors (MOSFETs) are investigated. The electrical behaviour is modeled using a potentiometer-like resistor network. It is shown how the relevant features that characterize a breakdown event in an MOS transistor: location of the failure site along the device channel, post-breakdown oxide resistance, and post-breakdown channel resistance, affect the mutual and drain transconductances of the device. The connection with the nonlinear current source model for broken down transistors is also discussed.
    Microelectronic Engineering 09/2013; 109:322–325. · 1.34 Impact Factor
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    ABSTRACT: Low-frequency noise (LFN) has been investigated in tri-gate (TG) Si nanowire (NW) FET. We have carefully measured and analyzed LFN for gate length down to 40 nm and cross-section width down to 10 nm. Drain current noise spectral density has been measured in linear region from weak to strong inversion of transistor operation. In particular, we have shown that the LFN behavior is in good agreement with carrier number fluctuations with correlated mobility fluctuations model in ultra-scaled TGNW FETs. We did not observe large contribution due to surface orientation difference between (100) top and (110) side-wall surfaces of TGNW. Moreover, the extracted oxide trap density is roughly the same for reference wide devices and TGNW FETs without significant impact of channel area downscaling and geometry.
    ESSDERC 2013 - 43rd European Solid State Device Research Conference; 09/2013
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    ABSTRACT: In order to search a gate dielectric with high permittivity on hydrogenated-diamond (H-diamond), LaAlO3 films with thin Al2O3 buffer layers are fabricated on the H-diamond epilayers by sputtering-deposition (SD) and atomic layer deposition (ALD) techniques, respectively. Interfacial band configuration and electrical properties of the SD-LaAlO3/ALD-Al2O3/H-diamond metal-oxide-semiconductor field effect transistors (MOSFETs) with gate lengths of 10, 20, and 30 μm have been investigated. The valence and conduction band offsets of the SD-LaAlO3/ALD-Al2O3 structure are measured by X-ray photoelectron spectroscopy to be 1.1 ± 0.2 and 1.6 ± 0.2 eV, respectively. The valence band discontinuity between H-diamond and LaAlO3 is evaluated to be 4.0 ± 0.2 eV, showing that the MOS structure acts as the gate which controls a hole carrier density. The leakage current density of the SD-LaAlO3/ALD-Al2O3/H-diamond MOS diode is smaller than 10−8 A cm−2 at gate bias from −4 to 2 V. The capacitance-voltage curve in the depletion mode shows sharp dependence, small flat band voltage, and small hysteresis shift, which implies low positive and trapped charge densities. The MOSFETs show p-type channel and complete normally off characteristics with threshold voltages changing from −3.6 ± 0.1 to −5.0 ± 0.1 V dependent on the gate length. The drain current maximum and the extrinsic transconductance of the MOSFET with gate length of 10 μm are −7.5 mA mm−1 and 2.3 ± 0.1 mS mm−1, respectively. The enhancement mode SD-LaAlO3/ALD-Al2O3/H-diamond MOSFET is concluded to be suitable for the applications of high power and high frequency electrical devices.
    Journal of Applied Physics 08/2013; 114(8). · 2.19 Impact Factor
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    ABSTRACT: TTFCOONH3Ph is a recently synthesized open-shell ionic semiconductor, the electronic state of which differs from that of typical organic closed-shell semiconductors. Magnetotransport properties were examined using a single-crystal sample, and found to exhibit small negative magnetoresistance (∼0.2%) for 9 T at room temperature (rt). The magnetization curve verifies the existence of a ferromagnetic (35%) and a paramagnetic (65%) component at rt, which is very similar to that of diluted magnetic semiconductors, despite the absence of any ferromagnetic metal elements. Electron spin resonance reveals weak localization of paramagnetic molecular spins, and moreover, ferromagnetic resonance confirms the existence of magnetically ordered spins in addition to the paramagnetic ones. The origin of the spin-polarized transport is discussed.
    Solid State Communications 07/2013; 165:27–32. · 1.70 Impact Factor

Publication Stats

3k Citations
330.62 Total Impact Points

Institutions

  • 2013–2014
    • NIMS Medicity
      Neyattinkara, Kerala, India
  • 2007–2014
    • National Institute for Materials Science
      • • Materials Analysis Station
      • • Photocatalytic Materials Center
      • • Computational Materials Science Center
      Tsukuba, Ibaraki, Japan
  • 2000–2014
    • Tokyo Institute of Technology
      • • Graduate School of Interdisciplinary Science and Engineering
      • • Frontier Research Center
      Edo, Tōkyō, Japan
  • 2010
    • University of Tsukuba
      • Applied Physics
      Tsukuba, Ibaraki, Japan
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan
  • 2008–2010
    • City University of Hong Kong
      • Department of Electronic Engineering
      Chiu-lung, Kowloon City, Hong Kong
  • 2008–2009
    • Indian Institute of Technology Bombay
      • Department of Electrical Engineering
      Mumbai, Mahārāshtra, India
  • 2006
    • Indian Institute of Technology Ropar
      • Department of Electrical Engineering
      Rūpar, Punjab, India
  • 1988–2002
    • Toshiba Corporation
      Edo, Tōkyō, Japan
  • 1989–2001
    • Stanford University
      • Center for Integrated Systems
      Stanford, CA, United States
  • 1994–1998
    • University of Bologna
      Bolonia, Emilia-Romagna, Italy