Ichiro Omura

A 4500 V injection enhanced insulated gate bipolar transistor (IEGT) operating in a mode similar to a thyristor

This paper proposes a new MOS-gate transistor structure (IEGT) for the first time, that realizes enhanced electron injection so that the carrier distribution takes a form similar to that of a thyristor and a low forward voltage drop is attained even for 4500 V devices. A developed simple analytical one dimensional model can predict a sufficiently accurate current voltage curve and clarifies a new design criterion for IEGT operation. A fabricated 4500 V IEGT realized a 2.5 V forward voltage drop at 100 A/cm/sup 2/. The IEGT had a current density over ten times that of conventional trench gate IGBT at 2.5 V forward voltage drop. An operation mode of IEGT has been theoretically and experimentally confirmed.<<ETX>>

Oscillation effects in IGBT's related to negative capacitance phenomena

Insulated gate bipolar transistors (IGBTs) are inherently unstable at high collector voltages due to negative gate capacitance values. We investigate IGBT gate voltage oscillations by experiment and through computer simulation. In addition, we show that under certain gate circuit conditions, gate voltage oscillations can lead to already observed collector current imbalance effects.

600V AlGaN/GaN power-HEMT: design, fabrication and demonstration on high voltage DC-DC converter

A 600 V class AlGaN/GaN power HEMT was designed for high voltage power electronics application such as power supplies and motor drives. The fabricated device was demonstrated in a DC-DC down converter circuit, showing the future possibility of high efficiency and high frequency operations of AlGaN/GaN power HEMTs.

Carrier injection enhancement effect of high voltage MOS devices-device physics and design concept

IEGTs are one of the promising candidates for replacing GTOs in high voltage applications in 4.5 kV range. The injection enhancement effect of IEGT structure with the deep trench MOS gate and/or the wide cell design successfully reduces the voltage drop in the N-base. In this paper, we discuss the device physics and design concept of the injection enhancement effect for not only the trench structure but also the planar structure.

Gallium Nitride power HEMT for high switching frequency power electronics

Very large number of power semiconductor devices (semiconductor power switches) are used in power electronics systems such as AC-DC converter for PCs, DC-DC converters for CPU, motor driver systems and induction heating systems for home appliances, and GaN device is one of a promising candidate for future power devices thanks to the wide band gap semiconductor material property. In GaN base device research, the GaN-HEMT structure is widely investigated than the other device structures specially in RF technology field. This structure also suits to high switching frequency power electronics applications because of the high breakdown voltage and the inherent high speed characteristics of HEMT device. This paper describes the possibility of GaN-HEMT for power electronics applications specially focused on high switching frequency applications comparing the limit of silicon devices such as MOSFETs and IGBTs, and also describes latest research result including demonstration of high switching frequency power electronics circuit.

IGBT negative gate capacitance and related instability effects

For high collector voltages, Insulated Gate Bipolar Transistors (IGBTs) exhibit a negative gate capacitance. In this condition, a p-channel inversion layer is formed on the N-base surface. The positive charges in the p-channel induce negative charges in the MOS gate electrode. This results in a negative gate capacitance. As a consequence of this negative capacitance, IGBT operation is inherently unstable, leading to current redistribution between cells or even chips.

O n -Resistance Modulation of High Voltage GaN HEMT on Sapphire Substrate Under High Applied Voltage

The 620-V/1.4-A GaN high-electron mobility transistors on sapphire substrate were fabricated and the ON-resistance modulations caused by current collapse phenomena were measured under high applied voltage. Since the fabricated devices had insulating substrates, no field-plate (FP) effect was expected and the ON-resistance increases of these devices were larger than those on an n-SiC substrate even with the same source-FP structure. The dual-FP structure, which was a combination of gate FP and source FP, was effective in suppressing the ON -resistance increase due to minimization of the gate-edge electric field concentration. The ON-resistance after the applied voltage of 250 V decreased by twice that at low drain voltage by the dual-FP structure. Gallium nitride (GaN), high-electron mobility transistor (HEMT), high voltage, power semiconductor device.

A novel low on-resistance Schottky-barrier diode with p-buried floating layer structure

A novel low on-resistance Schottky-barrier diode (SBD) structure with a p-buried floating layer is demonstrated by fabricating 300-V SBDs using a buried epitaxial growth technique. The fabricated SBDs realize a 50% reduction of chip area and show a possibility of higher breakdown voltage SBD of over 100 V. In addition, both the low on-resistance and the soft-recovery characteristics can be realized by the p-buried floating layer structure. The demonstrated structure is very attractive for reduction of power dissipation without electromagnetic interference noise increase.

Critical IGBT Design Regarding EMI and Switching Losses

Critical N-base layer design in IGBT is discussed regarding electro-magnetic interference (EMI) and switching losses during turn-off. The newly proposed criteria for oscillation and avalanche induced loss were given by a simple equation model and the validity of the model has been confirmed with experimental results. This paper shows an efficient design method of N-base for EMI-free IGBT with considering the turn-off loss. In addition, EMI reduction structure with partly buried N layer in N-base was proposed for break through the design limit of N-base.

Semisuperjunction MOSFETs: new design concept for lower on-resistance and softer reverse-recovery body diode

A new superjunction (SJ) structure offering remarkable advantages compared with the conventional SJ structure is proposed and demonstrated for a power-switching device. In the proposed structure (semi-SJ structure), an n-doped layer is connected to the bottom of the SJ structure. According to the results of experiment and simulation, the semi-SJ structure has both lower on-resistance and softer recovery of body diode than conventional SJ MOSFETs. The fabricated semi-SJ MOSFETs with breakdown voltage of 690 V realize on-resistance 28% lower than that of the conventional SJ MOSFET with same aspect ratio. The softness factor of the body diode is also improved by a factor of five. The proposed MOSFET is very attractive for H bridge topology applications, such as switching mode power supplies and small inverter systems, thanks to the low on-resistance and the soft recovery body diode.