Papers by Author: Kazu Kojima

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Authors: Satoshi Tanimoto, Kenichi Ueoka, Takaya Fujita, Sawa Araki, Kazu Kojima, Toshiharu Makino, Satoshi Yamasaki
Abstract: A new rectifier, called SPND or SNPD (Schottky-PN or -NP junction diode) and inherently showing low on-resistance and unipolar operation, was experimentally demonstrated for the first time on 4H-SiC. It is structured with an n or a p region of very low doping that is sandwiched and completely depleted between a Schottky junction and a one-sided PN junction. Either electrons or holes, but not both, contribute to the current conduction process. Clear and sharp rectifying properties are observed over the entire range of applied voltage.
Authors: Kenji Fukuda, Shinsuke Harada, Junji Senzaki, Mitsuo Okamoto, Yasunori Tanaka, Akimasa Kinoshita, Ryouji Kosugi, Kazu Kojima, Makoto Kato, Atsushi Shimozato, Kenji Suzuki, Yusuke Hayashi, Kazuto Takao, Tomohisa Kato, Shin Ichi Nishizawa, Tsutomu Yatsuo, Hajime Okumura, Hiromichi Ohashi, Kazuo Arai
Abstract: The C(000-1) face of 4H-SiC has a lot of advantages for the power device fabrication such as the highest oxidation ratio and a smooth surface. However, the DMOS type power MOSFETs on the C(000-1) face have not been realized because of the difficulty of epitaxial growth and of high quality MOS interface formation. We have systematically investigated the device fabrication techniques for power MOSFETs on the C(000-1) face, and succeeded with the IEMOS which have blocking voltage of 660V and an on-resistance of 1.8mΩcm2 and excellent dynamic characteristics.
Authors: Shinobu Onoda, Naoya Iwamoto, Makoto Murakami, Takeshi Ohshima, Toshio Hirao, Kazu Kojima, K. Kawano, I. Nakano
Abstract: We investigated the energy spectra in p+n 6H-SiC diodes by a wide variety of charged particles with energies up to several hundred MeV. Though Pulse Height Defect (PHD) was detected when the samples were irradiated with high energy heavy ions (322MeV-Kr and 454MeV-Xe), linearity between pulse height (peak channel) and ion energy up to 150MeV was observed.
Authors: Chiharu Ota, Johji Nishio, Kazuto Takao, Tetsuo Hatakeyama, Takashi Shinohe, Kazu Kojima, Shin Ichi Nishizawa, Hiromichi Ohashi
Abstract: Previous simulation works and experiments on the loss of 4H-SiC floating junction Schottky barrier diodes (Super-SBDs) show that the loss is related to the doping concentration in the drift region and the pattern of the floating layer. The effect of the doping concentration for lowering the loss is characterized the breakdown voltage (Vbd) and the on-state resistances (RonS) of the Super-SBDs based on Baliga’s figure of Merit (BFOM). Experimental devices with two doping concentrations in the drift region are fabricated to investigate the static characteristics: Vbd and RonS. The Vbd of the Super-SBDs is close to the simulation result, near 3000 V. However the tendency of the Vbd by the doping concentration is not similar to the simulation result. And the RonS are about 3.22 mcm2 which is higher than that of simulation result. The doping concentration optimized in this study does not show significant lowering loss and the design of the floating layer in the termination region affect the low-loss static characteristics of the Super-SBD. In addition, adopting PiN structure with floating layer (Super-PiN) affects the low-loss dynamic characteristics, optimizing the doping concentration in the drift region. We conclude that the fabricated Super-SBDs with the floating layer in the termination region, the drift region with a doping concentration of 1.01016 cm-3 and mesa-shaped termination structure, have excellent Vbd of 2990 V which is almost same as that of simulation result and RonS of 3.22 mcm2.
Authors: Shigeomi Hishiki, Naoya Iwamoto, Takeshi Ohshima, Hisayoshi Itoh, Kazu Kojima, K. Kawano
Abstract: The effect of the fabrication process of n-channel 6H-SiC MOSFETs on their radiation resistance is investigated. MOSFETs that post implantation annealing for source and drain was carried out with carbon coating on the sample surface are compared to MOSFETs that post implantation annealing was carried out without carbon coating. The radiation resistance (gamma-rays) of the carbon-coated MOSFETs is higher than that of non-coated ones. The channel mobility for MOSFETs whose gate oxide was formed using pyrogenic or dry oxidation process dose not change by gamma-ray irradiation below 1x105 Gy. The value of channel mobility slightly increases with increasing dose above 1x105 Gy. No significant increase in irradiation induced interface traps is observed.
Authors: Shinobu Onoda, Takeshi Ohshima, Toshio Hirao, Shigeomi Hishiki, Naoya Iwamoto, Kazu Kojima, K. Kawano
Abstract: Transient currents in 6H-SiC n+p diodes and those in Si PIN diodes are compared, and the carrier dynamic response to a heavy ion collision is analyzed using Technology Computer Aided Design (TCAD). In case of 6H-SiC n+p diodes, it is found that the contribution of the ambipolar-diffusion current to total transient current is extremely weak compared to that in Si PIN diodes, since plasma disruption is accelerated by the Auger recombination process in the former.
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