Papers by Author: Takashi Tsuji

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Authors: Takashi Tsuji, T. Tawara, Ryohei Tanuma, Yoshiyuki Yonezawa, Noriyuki Iwamuro, K. Kosaka, H. Yurimoto, S. Kobayashi, Hirofumi Matsuhata, Kenji Fukuda, Hajime Okumura, Kazuo Arai
Abstract: The authors fabricated pn diodes with Al+ implantation in p-type epitaxial layers, and investigated the influence of the implantation dose on reverse leakage currents. Only in the highest dose with the Al concentration of 2x1020cm-3, more than 90% of the devices showed high leakage currents above 10-4A at the maximum electric field of 3MV/cm. In such devices, almost all of the emissive spots corresponded to threading screw dislocations (TSDs) by the analysis of emission microscopy and X-ray topography. These TSDs were defined as killer defects with the estimated density of 500cm-2 in the case of the highest dose. The emissions were supposed to be due to microplasmas, since the spectra of the emissions were different from those of heat radiation. Condensation of Al atoms, nitrogen atoms and DI defects were excluded as the origin of the emissions by secondary ion mass spectrometry and low temperature photoluminescence analyses.
Authors: Takashi Tsuji, Akimasa Kinoshita, Noriyuki Iwamuro, Kenji Fukuda, Kazuo Tezuka, Tatsuro Tsuyuki, Hiroshi Kimura
Abstract: The 1200V class silicon carbide Schottky barrier diodes were designed and fabricated. The drift layer resistance was reduced in order to realize low forward voltage drops. Since the low drift layer resistance led to the low breakdown voltage, the avalanche withstanding capability should be enhanced not to cause the destructive breakdown. By means of the optimized device design, we succeeded to realize the low forward voltage drop while maintaining the high avalanche withstanding capability. The forward voltage drops at 200A/cm2 were 1.35V at 25°C and 1.63V at 175°C, respectively. The avalanche withstanding capability was more than 3500mJ/cm2 at 25°C. By substituting SiC-SBDs for Si-pin diodes, the estimated total power loss of the module comprised by Si-IGBTs and the diodes was reduced by 35%. We could also confirm that no failures happened after long term reliability tests.
Authors: Shinsuke Harada, Yasuyuki Hoshi, Yuichi Harada, Takashi Tsuji, Akimasa Kinoshita, Mitsuo Okamoto, Youichi Makifuchi, Yasuyuki Kawada, Kouji Imamura, Masahide Gotoh, Takeshi Tawara, Shinichi Nakamata, T. Sakai, Fumikazu Imai, Naoyuki Ohse, Mina Ryo, Atsushi Tanaka, Kazuo Tezuka, Tatsurou Tsuyuki, Saburou Shimizu, Noriyuki Iwamuro, Yoshiyuki Sakai, Hiroshi Kimura, Kenji Fukuda, Hajime Okumura
Abstract: SiC power module with low loss and high reliability was developed by utilizing IEMOSFET and SBD. The IEMOSFET is the SiC MOSFET with high channel mobility in which the channel region is the p-type carbon-face epitaxial layer with low acceptor concentration. Elemental technologies for the high channel mobility and the high reliability of the gate oxide have been developed to realize the excellent characteristics by the IEMOSFET. The SBD was designed so as to minimize the forward voltage drops and the reverse leakage current. For the fabrication of these SiC power devices, the mass production technology such as gate oxidation, ion implantation and following activation annealing have been also developed.
Authors: Kazuo Tezuka, Tatsurou Tsuyuki, Saburou Shimizu, Shinichi Nakamata, Takashi Tsuji, Noriyuki Iwamuro, Shinsuke Harada, Kenji Fukuda, Hiroshi Kimura
Abstract: In this paper, we demonstrate the fabrication of SBD utilizing SiC process line specially designed for mass production of SiC power device. In SiC power device process, ion implantation and activation annealing are key technologies. Details of ion implantation system and activation annealing system designed for SiC power device production are shown. Further, device characteristics of SBD fabricated using this production line is also shown briefly.
Authors: Takashi Tsuji, H. Irihama, T. Mihara, Kazushi Yamanaka
Abstract: Evaluation method of nano-scale internal cracks by ultrasonic atomic force microscopy (UAFM) is proposed based on two approaches. The first one is a linear vibration analysis of the contact stiffness calculated from a finite element method analysis of a model including a subsurface gap. The second one is a nonlinear vibration analysis of a stiffening or softening spring representing the opening-and-closing behavior of the gap. These methods were verified by obtaining the resonance frequency mapping, the load dependence of the resonance frequency and the resonance spectra in UAFM on a subsurface gap in highly oriented pyrolytic graphite. As a result, it was proved that the proposed method is useful for evaluating the opening-and-closing behavior of the gap. Although the present study is focused on a nano-scale gap, this method is applicable to larger scale cracks using a larger tip and more stiff support than those used in AFM.
Authors: Hiromu Shiomi, Takashi Tsuji, Naoyuki Ohse, Yasuhiko Onishi, Kenji Fukuda
Abstract: Impact ionization coefficients are important material properties that determine the breakdown voltage and safe operating area of power devices. This paper presents an anisotropy breakdown model with modified parameters that reproduces well experimental results for both peak breakdown voltages and sharp drops in breakdown voltage at high junction–termination–extension (JTE) acceptor concentrations. Using a newly developed simulation model, we optimized the edge termination and current-spreading layers (CSLs) and obtained a low specific on-resistance (RONA) of 11.6 mΩcm2 for a breakdown voltage (BVDSS) of approximately 4 kV and a high-avalanche-withstanding energy robustness of 4.6 Jcm-2.
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