Wataru Saito 교수

A recessed-gate structure has been studied with a view to realizing normally off operation of high-voltage AlGaN/GaN high-electron mobility transistors (HEMTs) for power electronics applications. The recessed-gate structure is very attractive for realizing normally off high-voltage AlGaN/GaN HEMTs because the gate threshold voltage can be controlled by the etching depth of the recess without significant increase in on-resistance characteristics. With this structure the threshold voltage can be i

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

The dynamic on-resistance increase associated with the current collapse phenomena in high-voltage GaN high-electron-mobility transistors (HEMTs) has been suppressed by employing an optimized field-plate (FP) structure. The fabricated GaN-HEMTs of 600 V/4.7 A and 940 V/4.4 A for power-electronics applications employ a dual-FP structure consisting of a short-gate FP underneath a long-source FP. The measured on-resistance shows minimal increase during high-voltage switching due to increased electri

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 ga

Four types of the field-plate (FP) structure were fabricated to discuss the relation between the current collapse phenomena and the electric-field peak in high-voltage GaN-HEMTs. The on -resistance increase caused by current collapse phenomena is dramatically reduced by the single-gate-FP and dual-FP structures compared with the source-FP structure, because the gate-edge electric field was reduced by the gate-FP electrode. The dual-FP structure was slightly more effective to suppress the collaps

A boost converter with a 940-V/4.4 A GaN-HEMT as the main switching device was demonstrated to show the possibility of using high-voltage GaN-HEMTs in power electronic applications. The demonstrated circuit achieved an output power of 122 W and a power efficiency of 94.2% under a drain peak voltage as high as 350 V and a switching frequency of 1 MHz. The dual field-plate structure realized high-voltage switching operation with high power efficiency as dynamic on-resistance was suppressed by an i

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 tradeo

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 w

A 13.56-MHz class-E amplifier with a high-voltage GaN HEMT as the main switching device is demonstrated to show the possibility of using GaN HEMTs in high-frequency switching power applications such as RF power-supply applications. The 380-V/1.9-A GaN power HEMT was designed and fabricated for high-voltage power-electronics applications. The demonstrated circuit achieved the output power of 13.4 W and the power efficiency of 91% under a drain-peak voltage as high as 330 V. This result shows that

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 mΩ·cm 2 , 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

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 so

This paper reports device characteristics of superjunction (SJ) MOSFETs employed with platinum (Pt) doping or electron irradiation processes for high speed recovery operation of the internal body diode. For the inverter application, high speed recovery operation of the internal body diode is necessary. 600 V-class SJ-MOSFETs were fabricated with a lifetime control process. In this paper, the influence of the carrier lifetime control process upon the on-resistance, leakage current and withstandin

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 vol

This paper reports that theoretical limits for the superjunction (SJ) and field plate (FP) structures and the optimum application voltage range is discussed with the previous experimental data. The specific on-resistance limit of the SJ structure is as same as that of the FP structure and inverse proportional to the cell aspect ratio γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SJ</sub> and γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML"