Papers by Author: Kazuo Arai

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Authors: Yasunori Tanaka, Koji Yano, Mitsuo Okamoto, Akio Takatsuka, Kazuo Arai, Tsutomu Yatsuo
Abstract: We have succeeded to fabricate SiC buried gate static induction transistors (BGSITs) with the breakdown voltage VBR of 1270 V at the gate voltage VGS of –12 V and the specific on-resistance RonS of 1.21 mΩ·cm2 at VGS = 2.5 V. The turn-off behaviors of BGSITs strongly depend on the source length WS, which is the distance between the gate electrodes. The rise time tr of BGSIT for WS = 1,070 μm is 395 nsec, while that for WS = 210 μm is 70nsec. From the 3D computer simulations, we confirmed that the difference in turn-off behavior came from the time delay in potential barrier formation in channel region because of high p+ gate resistivity. The turn-off behaviors also depend on the operation temperature, especially for long WS. On the other hand, the turn-on behaviors hardly depend on the WS and temperature.
Authors: Kazutoshi Kojima, Hajime Okumura, Satoshi Kuroda, Kazuo Arai, Akihiko Ohi, Hiroyuki Akinaga
Abstract: Homoepitaxial growth was carried out on 4H-SiC on-axis substrate by horizontal hot wall chemical vapor deposition. By using carbon face substrate, specular surface morphology of a wide area of up to 80% of a 2-inch epitaxial wafer was obtained at a low C/Si ratio growth condition of 0.6. The Micropipe in on-axis substrate was indicated to be filled with spiral growth and to be dissociated into screw dislocations during epitaxial growth. It was found that the appearance of basal plane dislocations on the epitaxial layer surface can be prevented by using an on-axis substrate.
Authors: Akio Takatsuka, Yasunori Tanaka, Koji Yano, Norio Matsumoto, Tsutomu Yatsuo, Kazuo Arai
Abstract: 3 kV normally-off SiC-buried gate static induction transistors (SiC-BGSITs) were fabricated by using an innovative fabrication process that was used by us previously to fabricate 0.7–1.2 kV SiC-BGSITs. The fabricated device shows the lowest specific on-resistance of 9.16 mΩ·cm2, compared to all other devices of the same class. The threshold voltage of this device was 1.4 V at room temperature and was maintained at values more than 1 V with normally-off characteristics at 200 °C. The device can block drain voltage of 3 kV with a leakage current density of 6.9 mA/cm2.
Authors: Shinsuke Harada, Makoto Kato, Mitsuo Okamoto, Tsutomu Yatsuo, Kenji Fukuda, Kazuo Arai
Abstract: The channel mobility in the SiC MOSFET degrades on the rough surface of the p-well formed by ion implantation. Recently, we have developed a double-epitaxial MOSFET (DEMOSFET), in which the p-well comprises two stacked epitaxially grown p-type layers and an n-type region between the p-wells is formed by ion implantation. This device exhibited a low on-resistance of 8.5 mcm2 with a blocking voltage of 600 V. In this study, to further improve the performance, we newly developed a device structure named implantation and epitaxial MOSFET (IEMOSFET). In this device, the p-well is formed by selective high-concentration p+ implantation followed by low-concentration p- epitaxial growth. The fabricated IEMOSFET with a buried channel exhibited superior characteristics to the DEMOSFET. The extremely low specific on-resistance of 4.3 mcm2 was achieved with a blocking voltage of 1100 V. This value is the lowest in the normally-off SiC MOSFETs.
Authors: Hitoshi Habuka, Yusuke Katsumi, Yutaka Miura, Keiko Tanaka, Yasushi Fukai, Takaya Fukae, Yuan Gao, Tomohisa Kato, Hajime Okumura, Kazuo Arai
Abstract: The etching technology for 4H-silicon carbide (SiC) was studied using ClF3 gas at 673-973K, 100 % and atmospheric pressure in a horizontal reactor. The etch rate, greater than 10 um/min, can be obtained for both the C-face and Si-face at substrate temperatures higher than 723 K. The etch rate increases with the increasing ClF3 gas flow rate. The etch rate of the Si-face is smaller than that of the C-face. The etched surface of the Si-face shows many hexagonal-shaped etch pits. The C-face after the etching is very smooth with a very small number of round shaped shallow pits. The average roughness of the etched surface tends to be small at the higher temperatures.
Authors: Kazutoshi Kojima, Tetsuo Takahashi, Yuuki Ishida, Satoshi Kuroda, Hajime Okumura, Kazuo Arai
Authors: Mitsuo Okamoto, Tsutomu Yatsuo, Kenji Fukuda, Hajime Okumura, Kazuo Arai
Abstract: From a viewpoint of device application using p-channel SiC MOSFETs, control of their channel properties is of great importance. We aimed to control the electrical properties of 4H-SiC p-channel MOSFETs through locating the p-type epitaxial layer at the channel area, so called “epi-channel MOSFET” structure. We varied the dopant concentrations and the thickness of the epi-channel layer, and investigated their electrical properties. In case of heavily doped epi-channel samples, the devices indicated “normally-on” characteristics, and their channel mobility decreased slightly in comparison with the inversion-type devices. As for lightly doped epi-channel samples, the subthreshold current increased with thickness of the epi-channel layer keeping their “normally-off” characteristics. Their channel mobility also increased with thickness of the epi-channel layer. The peak value of field effect channel mobility of the sample with 2.5 μm thickness and 5×1015 /cm3 dopant concentration epi-channel was 18.1 cm2/Vs.
Authors: Akio Takatsuka, Yasunori Tanaka, Koji Yano, Tsutomu Yatsuo, Kazuo Arai
Abstract: In this work, we succeeded in developing high performance normally-off SiC buried gate static induction transistors (SiC-BGSITs). To achieve the normally-off characteristics, design parameters around the channel region were optimized and process conditions were improved to realize these parameters. The off-state characteristic of the SiC-BGSIT showed an avalanche breakdown voltage of VBR=980 V at a gate voltage of VG=0 V. Furthermore, the leakage current at VD=950 V is lower than 0.5 μA. These results indicate that the BGSIT has a good normally-off characteristic. At VG=2.5 V, an on-resistance of 28.0 mΩ corresponding to the specific on-resistance of 1.89 mΩ•cm2 was obtained and the current rating was calculated as 33 A at a power density of 200 W/cm2 in the on-state characteristic.
Authors: Kenji Fukuda, Junji Senzaki, Mitsuhiro Kushibe, Kazutoshi Kojima, Ryouji Kosugi, Seiji Suzuki, Shinsuke Harada, Takaya Suzuki, Tomoyuki Tanaka, Kazuo Arai
Authors: Naoki Oyanagi, Shin Ichi Nishizawa, Kazuo Arai
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