Kota Ohi

Latest Technology Trends in Power Semiconductor Devices

Manabu Yoshino, Yujiro Takeuchi, Kota Ohi, Akira Nakajima

Efforts to achieve carbon neutrality are accelerating in order to solve global warming, a worldwide environmental problem. Efficient use of electric energy requires improved performance, higher functionality, and higher quality of power semiconductor devices, which are key components. In recent years, as …

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Hole path concept for low switching loss and low EMI noise with high IE-effect

Mika Sawada, Yusuke Sakurai, Kota Ohi, Yoshihiro Ikura et autres

This paper presents the “Hole Path Concept” in trench gate IGBTs in order to have extended performance in faster switching with balance low switching loss and low ElectroMagnetic Interference (EMI) noise. The hole path IGBT which is utilized narrow hole extraction regions …

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Trench shielded gate concept for improved switching performance with the low miller capacitance

Mika Sawada, Kota Ohi, Yoshihiro Ikura, Yuichi Onozawa et autres

This paper presents the new gate structure concept in trench gate IGBTs in order to have extended performance in faster switching without penalties on the on-state voltage drop (Von). The combination of the trench gate and adjacent emitter-connected trench achieves the dramatic …

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Ultra low miller capacitance trench-gate IGBT with the split gate structure

Kota Ohi, Yoshihiro Ikura, A. Yoshimoto, Kazuyuki Sugimura et autres

This paper presents a newly developed trench gate IGBT which utilizes the split gate structure. It can realize both low Miller capacitance and high Injection Enhancement (IE) effect. The Miller capacitance has been reduced to 1/10 compared to that of the general …

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Improved current stability in multi‐mesa‐channel AlGaN/GaN transistors

Joel Tacla Asubar, Kota Ohi, Kenya Nishiguchi, Tamotsu Hashizume

Abstract We present further experimental results that demonstrate the superior current stability of multi‐mesa‐channel (MMC) AlGaN/GaN HEMTs over their conventional planar counterparts. Pulsed ID‐VDS measurements revealed almost overlapping ID‐VDS curves for the MMC device even with increasing drain‐to‐source quiescent bias VDSq with …

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Current Stability in Multi-Mesa-Channel AlGaN/GaN HEMTs

Kota Ohi, Joel Tacla Asubar, Kenya Nishiguchi, Tamotsu Hashizume

We develop and characterize multi-mesa-channel (MMC) AlGaN/GaN high-electron mobility transistors (HEMTs), in which a periodic trench structure is fabricated only under the gate electrode. A surrounding-field effect in the MMC structure results in a shallower threshold voltage and a smaller subthreshold slope …

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Competitive virus assay method for titration of noncytopathogenic bovine viral diarrhea viruses (END+ and END− viruses)

Mahmod Muhsen, Kota Ohi, Hiroshi Aoki, Hidetoshi Ikeda et autres

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Reduction of current collapse in the multi‐mesa‐channel AlGaN/GaN HEMT

Kota Ohi, Tamotsu Hashizume

Abstract Transport properties and off‐stress‐induced current collapse characteristics of the multi‐mesa‐channel (MMC) AlGaN/GaN HEMTs were investigated. The surrounding field effect in the MMC structure led to a shallower threshold voltage and a smaller subthreshold slope compared to those of the conventional planar …

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Characterization of MOS interfaces and current collapse in AlGaN/GaN HEMTs

Hashizume Tamotsu, Chihoko Mizue, Yujin Hori, Tajima Masafumi et autres

Formation of Recessed-Oxide Gate for Normally-Off AlGaN/GaN High Electron Mobility Transistors Using Selective Electrochemical Oxidation

Naohisa Harada, Yujin Hori, N. Azumaishi, Kota Ohi et autres

A selective electrochemical oxidation has been applied to the AlGaN surface to fabricate a recessed-oxide-gate structure for normally-off AlGaN/GaN high-electron-mobility transistors (HEMTs). We observed bias-dependent oxidation current characteristics peculiar to the AlGaN/GaN heterostructure. A flat interface between the oxide and AlGaN was …

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Trapping effect evaluation of gateless AlGaN/GaN heterojunction field-effect transistors using transmission-line-model method

Cheng-Yu Hu, Tamotsu Hashizume, Kota Ohi, Masafumi Tajima

An electric-field-dependent trapping effect was observed in our AlGaN/GaN transmission-line-model (TLM) structure. Therefore, we adopted a “gradual voltage stress” scheme to induce a similar trapping effect, that is, a similar sheet resistance variation (ΔRSH) for all intervals of our AlGaN/GaN TLM structure. …

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Current control of AlGaN/GaN HEMT with multi-mesa nanochannels

Kota Ohi, Tamotsu Hashizume