Kunio Tsuda

Bio: Kunio Tsuda is an academic researcher from Toshiba. The author has contributed to research in topics: High-electron-mobility transistor & High voltage. The author has an hindex of 22, co-authored 66 publications receiving 2315 citations.

Recessed-gate structure approach toward normally off high-Voltage AlGaN/GaN HEMT for power electronics applications

Abstract: 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 increased with the reduction of two-dimensional electron gas (2DEG) density only under the gate electrode without reduction of 2DEG density in the other channel regions such as the channel between drain and gate. The threshold-voltage increase was experimentally demonstrated. The threshold voltage of fabricated recessed-gate device increased to -0.14 V while the threshold voltage without the recessed-gate structure was about -4 V. The specific on-resistance of the device was maintained as low as 4 m/spl Omega//spl middot/cm/sup 2/ and the breakdown voltage was 435 V. The on-resistance and the breakdown voltage tradeoff characteristics were the same as those of normally on devices. From the viewpoint of device design, the on-resistance for the normally off device was modeled using the relationship between the AlGaN layer thickness under the gate electrode and the 2DEG density. It is found that the MIS gate structure and the recess etching without the offset region between recess edge and gate electrode will further improve the on-resistance. The simulation results show the possibility of the on-resistance below 1 m/spl Omega//spl middot/cm/sup 2/ for normally off AlGaN/GaN HEMTs operating at several hundred volts with threshold voltage up to +1 V.

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

Abstract: 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.

Suppression of Dynamic On-Resistance Increase and Gate Charge Measurements in High-Voltage GaN-HEMTs With Optimized Field-Plate Structure

Abstract: 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 electric-field uniformity between the gate and drain as a result of using the dual FP. The gate-drain charge Q gd for the fabricated devices has also been measured to provide a basis for discussion of the ability of high-speed switching operation. Although Q gd /A (A: active device area) was almost the same as that of the conventional Si-power MOSFETs, R on A was dramatically reduced to about a seventh of the reported 600-V Si-MOSFET value. Therefore, R on Q gd for 600-V device was reduced to 0.32 OmeganC, which was approximately a sixth of that for the Si-power MOSFETs. The high-voltage GaN-HEMTs have significant advantages over silicon-power MOSFETs in terms of both the reduced on-resistance and the high-speed switching capability.

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

Abstract: 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.

A 120-W Boost Converter Operation Using a High-Voltage GaN-HEMT

Abstract: 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 increase of the current collapse phenomena.

A Survey of Wide Bandgap Power Semiconductor Devices

Abstract: Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

Gate Injection Transistor (GIT)—A Normally-Off AlGaN/GaN Power Transistor Using Conductivity Modulation

Abstract: We have developed a normally-off GaN-based transistor using conductivity modulation, which we call a gate injection transistor (GIT). This new device principle utilizes hole-injection from the p-AlGaN to the AlGaN/GaN heterojunction, which simultaneously increases the electron density in the channel, resulting in a dramatic increase of the drain current owing to the conductivity modulation. The fabricated GIT exhibits a threshold voltage of 1.0 V with a maximum drain current of 200 mA/mm, in which a forward gate voltage of up to 6 V can be applied. The obtained specific ON-state resistance (RON . A) and the OFF-state breakdown voltage (BV ds) are 2.6 mOmega . cm2 and 800 V, respectively. The developed GIT is advantageous for power switching applications.

High-performance enhancement-mode AlGaN/GaN HEMTs using fluoride-based plasma treatment

Abstract: We report a novel approach in fabricating high-performance enhancement mode (E-mode) AlGaN/GaN HEMTs. The fabrication technique is based on fluoride-based plasma treatment of the gate region in AlGaN/GaN HEMTs and post-gate rapid thermal annealing with an annealing temperature lower than 500/spl deg/C. Starting with a conventional depletion-mode HEMT sample, we found that fluoride-based plasma treatment can effectively shift the threshold voltage from -4.0 to 0.9 V. Most importantly, a zero transconductance (g/sub m/) was obtained at V/sub gs/=0 V, demonstrating for the first time true E-mode operation in an AlGaN/GaN HEMT. At V/sub gs/=0 V, the off-state drain leakage current is 28 /spl mu/A/mm at a drain-source bias of 6 V. The fabricated E-mode AlGaN/GaN HEMTs with 1 /spl mu/m-long gate exhibit a maximum drain current density of 310 mA/mm, a peak g/sub m/ of 148 mS/mm, a current gain cutoff frequency f/sub T/ of 10.1 GHz and a maximum oscillation frequency f/sub max/ of 34.3 GHz.

Recessed-gate structure approach toward normally off high-Voltage AlGaN/GaN HEMT for power electronics applications

Abstract: 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 increased with the reduction of two-dimensional electron gas (2DEG) density only under the gate electrode without reduction of 2DEG density in the other channel regions such as the channel between drain and gate. The threshold-voltage increase was experimentally demonstrated. The threshold voltage of fabricated recessed-gate device increased to -0.14 V while the threshold voltage without the recessed-gate structure was about -4 V. The specific on-resistance of the device was maintained as low as 4 m/spl Omega//spl middot/cm/sup 2/ and the breakdown voltage was 435 V. The on-resistance and the breakdown voltage tradeoff characteristics were the same as those of normally on devices. From the viewpoint of device design, the on-resistance for the normally off device was modeled using the relationship between the AlGaN layer thickness under the gate electrode and the 2DEG density. It is found that the MIS gate structure and the recess etching without the offset region between recess edge and gate electrode will further improve the on-resistance. The simulation results show the possibility of the on-resistance below 1 m/spl Omega//spl middot/cm/sup 2/ for normally off AlGaN/GaN HEMTs operating at several hundred volts with threshold voltage up to +1 V.

GaN Power Transistors on Si Substrates for Switching Applications

Abstract: In this paper, GaN power transistors on Si substrates for power switching application are reported. GaN heterojunction field-effect transistor (HFET) structure on Si is an important configuration in order to realize a low loss and high power devices as well as one of the cost-effective solutions. Current collapse phenomena are discussed for GaN-HFETs on Si substrate, resulting in suppression of the current collapse due to using the conducting Si substrate. Furthermore, attempts for normally off GaN-FETs were examined. A hybrid metal-oxide-semiconductor HFET structure is a promising candidate for obtaining devices with a lower on-resistance (Ron) and a high breakdown voltage (Vb).