Tsuneo Ogura

High breakdown voltage AlGaN-GaN power-HEMT design and high current density switching behavior

AlGaN-GaN power high-electron mobility transistors (HEMTs) with 600-V breakdown voltage are fabricated and demonstrated as switching power devices for motor drive and power supply applications. The fabricated power HEMT realized the high breakdown voltage by optimized field plate technique and the low on-state resistance of 3.3 m/spl Omega/cm/sup 2/, which is 20 times lower than that or silicon MOSFETs, thanks to the high critical field of GaN material and the high mobility in 2DEG channel. The fabricated devices also demonstrated the high current density switching of 850 A/cm/sup 2/ turn-off. These results show that AlGaN-GaN power-HEMTs are one of the most promising candidates for future switching power device for power electronics applications.

Influence of surface defect charge at AlGaN-GaN-HEMT upon Schottky gate leakage current and breakdown voltage

The relation between Schottky gate leakage current and the breakdown voltage of AlGaN-GaN high-electron mobility transistors (HEMTs) is discussed based on the newly introduced simple, yet useful, surface defect charge model. This model represents the leakage current caused by the positive charge in the surface portion of AlGaN layer induced by process damage such as nitrogen vacancies. The new model has been implemented into a two-dimensional device simulator, and the relationship between the gate leakage current and the breakdown voltage was simulated. The simulation results reproduced the relationship obtained experimentally between the leakage current and the breakdown voltage. Further simulation and experiment results show that the breakdown voltage is maintained even if the defect charge exists up to the defect charge density of 2.5/spl times/10/sup 12/ cm/sup -2/, provided the field plate structure is adopted, while the breakdown voltage shows a sudden drop for the defect density over 5/spl times/10/sup 11/ cm/sup -2/ without the field plate. This result shows that the field plate structure is effective for suppressing the surface charge influence on breakdown voltage due to the relaxation of the electric field concentration in the surface portion of the AlGaN layer.

High breakdown Voltage undoped AlGaN-GaN power HEMT on sapphire substrate and its demonstration for DC-DC converter application

Undoped AlGaN-GaN power high electron mobility transistors (HEMTs) on sapphire substrate with 470-V breakdown voltage were fabricated and demonstrated as a main switching device for a high-voltage dc-dc converter. The fabricated power HEMT realized a high breakdown voltage with a field plate structure and a low on-state resistance of 3.9 m/spl Omega//spl middot/cm/sup 2/, which is 10 /spl times/ lower than that of conventional Si MOSFETs. The dc-dc converter operation of a down chopper circuit was demonstrated using the fabricated device at the input voltage of 300 V. These results show the promising possibilities of the AlGaN-GaN power HEMTs on sapphire substrate for future switching power devices.

Design optimization of high breakdown voltage AlGaN-GaN power HEMT on an insulating substrate for R/sub ON/A-V/sub B/ tradeoff characteristics

High breakdown voltage AlGaN-GaN power high-electron mobility transistors (HEMTs) on an insulating substrate were designed for the power electronics application. The field plate structure was employed for high breakdown voltage. The field plate length, the insulator thickness and AlGaN layer doping concentration were design parameters for the breakdown voltage. The optimization of the contact length and contact resistivity reduction were effective to reduce the specific on-resistance. The tradeoff characteristics between the on-resistance and the breakdown voltage can be improved by the optimization of the above design parameters, and the on-resistance can be estimated to be about 0.6 m/spl Omega//spl middot/cm/sup 2/ for the breakdown voltage of 600 V. This on-resistance is almost the same as that for the device on a conductive substrate.

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.

Design and Demonstration of High Breakdown Voltage GaN High Electron Mobility Transistor (HEMT) Using Field Plate Structure for Power Electronics Applications

AlGaN/GaN power high electron mobility transistors (HEMTs) with a breakdown voltage of 600 V are fabricated and demonstrated as switching power devices for motor drive and power supply applications. A high breakdown voltage was realized in the fabricated power-HEMT by the field plate technique and an ultra low on-state resistance of 3.3 mΩcm2, which is 20 times lower than the silicon limit, due to the high critical field of the GaN material and the high mobility in a two-dimensional electron gas channel. A device with the double-field plate structure was also designed using two-dimensional device simulation to increase the breakdown voltage without any increase of the GaN layer thickness.

Turn-off switching analysis considering dynamic avalanche effect for low turn-off loss high-voltage IGBTs

An avalanche generation phenomenon has a large influence on turn-off switching loss and reverse-biased safe operating area of high-voltage insulated gate bipolar transistors (IGBTs). The purpose of this paper is to clarify the correlation between the avalanche multiplication phenomenon and the turn-off characteristics. We introduce a turn-off switching analytical model of IGBTs that considers the avalanche multiplication effect. It is concluded that the criterion of dynamic avalanche depends on the gate resistance. In the case of 4.5-kV IGBTs, the gate resistance of more than 200 /spl Omega//spl middot/cm/sup 2/ is needed to suppress the dynamic avalanche generation under a clumped inductive load circuit. On the contrary, the turn-off switching loss increases in the case that the gate resistance R/sub G/ is increased to more than approximately 100 /spl Omega//spl middot/cm/sup 2/. Theses results show that to realize low turn-off switching loss, it is necessary to ensure that the gate resistance is below a constant value, such as 100 /spl Omega//spl middot/cm/sup 2/. However, at high current density, such as 80 A/cm/sup 2/, the dynamic avalanche will generate under such small gate resistance condition. Therefore, it is important to develop IGBTs without destruction even under the condition of dynamic avalanche generation.

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.