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Dive into the research topics where Toyokazu Ohnishi is active.

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Featured researches published by Toyokazu Ohnishi.


the international power electronics conference - ecce asia | 2010

Neutron induced single-event burnout of IGBT

Tomoyuki Shoji; Shuichi Nishida; Toyokazu Ohnishi; Touma Fujikawa; Noboru Nose; Masayasu Ishiko; Kimimori Hamada

Cosmic-ray neutrons can trigger a single-event burnout (SEB), which is a catastrophic failure mode in power semiconductor devices. It was found experimentally that the incident neutron induced SEB failure rate increases as a function of the applied collector voltage in an insulated gate bipolar transistor (IGBT). Moreover, the failure rate increased sharply with an increase in the applied collector voltage when the voltage exceeded a certain threshold value. Transient device simulation showed that the onset of impact ionization at the n− drift/n+ buffer junction (nn+ junction) can trigger turning-on of the inherent parasitic thyristor, and then SEB subsequently occurs. In addition, it was analytically derived that reducing the current gain of the parasitic transistor was effective in increasing the SEB threshold voltage. Furthermore, ‘white’ neutron-irradiation experiments demonstrated that suppressing the inherent parasitic thyristor action leads to an improvement of the SEB threshold voltage.


Materials Science Forum | 2011

Reverse Electrical Characteristics of 4H-SiC JBS Diodes Fabricated on In-House Substrate with Low Threading Dislocation Density

Fujiwara Hirokazu; Masaki Konishi; Toyokazu Ohnishi; Tutomu Nakamura; Kimimori Hamada; Takashi Katsuno; Yukihiko Watanabe; Takeshi Endo; Takeo Yamamoto; Kazuhiro Tsuruta; Shoichi Onda

The impacts of threading dislocations, surface defects, donor concentration, and schottky Schottky barrier height on the reverse IV characteristic of silicon carbide (SiC) junction barrier schottky Schottky (JBS) diodes were investigated. The 100 A JBS diodes were fabricated on 4H-SiC 3-inch N-type wafers with two types of threading dislocation density. The typical densities are were 0.2×104 and 3.8×104 cm-2, respectively. The improvement of vIt was found that variations in the leakage current and the high yield of large area JBS diodes werecould be were obtained improved by using a wafer with a low threading dislocation density. In the range of low leakage current, the investigation shows showed a correlation between leakage current and threading dislocation density.


international symposium on power semiconductor devices and ic s | 2003

A PT-IGBT with a p-/n+ buffer layer

Masayasu Ishiko; Sachiko Kawaji; Katsuhiko Nishiwaki; Toyokazu Ohnishi

A novel punch-through insulated gate bipolar transistor with a p-/n+ buffer layer was proposed to improve the characteristics of conventional high power IGBT used in motor control inverters at high voltages operation. The new structure with p-floating layer inserted between n- epi and n+ buffer layer shows higher breakdown voltage than that of conventional IGBT structures. We also demonstrate, for the first time, the performance of 900V-200A class IGBTs using this p- floating/n+ buffer structure. As a result of the measurements, the IGBT proposed here shows an on-state voltage of 1.9V at 250A/cm/sup 2/ and the fall time of 350 nsec.


Archive | 1994

Semiconductor laser stack with lens and method of manufacturing the same

Akinori Seki; Toyokazu Ohnishi; Jiro Nakano


international symposium on power semiconductor devices and ic's | 2010

Cosmic ray ruggedness of IGBTs for hybrid vehicles

Shuichi Nishida; Tomoyuki Shoji; Toyokazu Ohnishi; Touma Fujikawa; Noboru Nose; Masayasu Ishiko; Kimimori Hamada


Archive | 1994

Layered semiconductor laser having solder laminations and method of making same

Akinori Seki; Toyokazu Ohnishi; Jiro Nakano; Takahide Sugiyama; Kazuyoshi Tomita; Hiroyuki Kano


Ieej Transactions on Industry Applications | 2011

Reliability Design for Neutron Induced Single-Event Burnout of IGBT

Tomoyuki Shoji; Shuichi Nishida; Toyokazu Ohnishi; Touma Fujikawa; Noboru Nose; Kimimori Hamada; Masayasu Ishiko


Archive | 2003

A Novel PT-IGBT with a p-/n+ Buffer Layer

Masayasu Ishiko; Sachiko Kawaji; Katsuhiko Nishiwaki; Toyokazu Ohnishi; Toyota Central


Archive | 1994

Semiconductor laser having stacked active layers with reduced drive voltage

Akinori Seki; Toyokazu Ohnishi; Jiro Nakano


Archive | 1995

Field-effect transistor and method of producing same

Toyokazu Ohnishi

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