GaN Power Switching Research Articles

An Ultra Compact GaN 3x3 Matrix Converter

In this paper, we describe compact isolated gated drivers with Drive-by-Microwave (DBM) technology, which can provide isolated gate signal and power all together by a microwave wireless power transmission. The fabricated GaN gate driver successfully drives a GaN power switching device without an isolated voltage source. Furthermore, an ultra-compact GaN 3x3 matrix converter with DBM technology is presented, which is composed of a GaN-GIT (Gate Injection Transistor) bi-directional power switches integration chip, electro-magnetic resonant coupling based isolated dividing couplers in printed circuit board to reduce the complicated gate lines, and an one-chip and low consumption GaN/Si DBM driver chip for 9 bi-directional power switch control. The proposed GaN 3x3 matrix converter for 5.0kW is overwhelmingly compact such as 25mm x 18mm because of GaN power device integration and the DBM technology. Furthermore the power consumption for all divers is very low as 2.0W due to the isolated microwave power source sharing.

Progress in High Voltage SiC and GaN Power Switching Devices

The present status of the development and commercialization of SiC and GaN power devices for power electronics applications is presented. The technology obstacles and needs as well as future trend in these power devices are also discussed.

Methodology for the Study of Dynamic ON-Resistance in High-Voltage GaN Field-Effect Transistors

We have developed a new methodology to investigate the dynamic ON-resistance (RON) of high-voltage GaN field-effect transistors. The new technique allows the study of RON transients after a switching event over an arbitrary length of time. Using this technique, we have investigated dynamic RON transients in AlGaN/GaN high-voltage, high electron-mobility transistors over a time span of ten decades under a variety of conditions. We find that right after an OFF-to-ON switching event, RON can be several times higher under dc conditions. The increase in RON is enhanced as the drain-source voltage in the OFF-state increases. The RON recovery process after an OFF-to-ON switching event is characterized by a fast release of trapped charge through a temperature-independent tunneling process followed by conventional thermally activated detrapping on a longer timescale. After a high-power-to-ON switching event, in contrast, detrapping only takes place through a temperature-independent process. We postulate that the fast temperature-independent detrapping originates from interface states at the AlGaN barrier/AlN spacer interface. The thermally activated detrapping can arise from traps at the surface of the device or inside the AlGaN barrier. These findings are relevant in the quest to engineer a reliable GaN power switch with minimum dynamic RON problems.

Breakdown and dynamic effects in GaN power switching devices

AbstractApproaches towards fast switching GaN devices for applications in power electronics are presented. First, an overview on breakdown mechanisms in GaN power devices is given. Suitable techniques towards devices with high breakdown strength are then discussed and set into relation to their specific dynamic switching properties. It has been found that dynamic switching properties of GaN power devices may be significantly compromised at high drain bias levels. The dynamic effects depend on technological parameters such as epitaxial layer design and crystalline quality of the buffer layer, passivation layers and the lateral device designs (e.g. field plate arrangements). GaN high voltage switching devices therefore require a balanced trade‐off between all these influencing quantities. This paper concentrates on dependencies related to the epitaxial design of the buffer layer(s). (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High-Speed, Enhancement-Mode GaN Power Switch With Regrown ${\rm n}+$ GaN Ohmic Contacts and Staircase Field Plates

We report a novel GaN heterojunction field-effect transistor device that incorporates vertically scaled epilayers, a nanoscale gate with integrated staircase-shaped field plates, and regrown ohmic contacts. This device technology has an unprecedented combination of high breakdown (176 V), low ON-resistance (1.2 Ωmm), enhancement-mode operation (VTH=+0.35 V), and excellent high-frequency performance (fT/fmax=50/120 GHz), which enables new applications as a high-frequency power switch or a microwave power amplifier. The gate design manages the electric field at the drain edge of the gate, which mitigates dynamic ON-resistance degradation.

Device Breakdown and Dynamic effects in GaN Power Switching Devices: Dependencies on Material Properties and Device Design

High voltage GaN based transistors already showed promising de-vice properties which makes them very attractive for future highly efficient power switching application. To further optimize device switching performance at high bias voltages the dependency of de-vice breakdown and dynamic effects on device layer epitaxy and processing has to be analyzed. This paper discusses the dependen-cies of breakdown events, predominantly vertical breakdown be-tween the device on the chip front side and the conductive n-type SiC or Si substrate on various technological parameters. They comprise high voltage buffer design and material quality, SiC sub-strate conductivity as well as metal contact technology of GaN HEMT devices. Furthermore a correlation between many of those parameters and dynamic switching properties has been determined. Physical mechanisms are then proposed to explain the basic inter-dependencies.

Effects of post-oxidation on leakage current of high-voltage AlGaN/GaN Schottky barrier diodes on Si(1 1 1) substrates

The effects of post-oxidation on the leakage current of high-voltage AlGaN/GaN Schottky barrier diodes (SBDs) on Si(111) substrates were investigated. Auger electron spectroscopy was used to study post-oxidation mechanisms. The group-III oxides, AlOx or GaOx, were formed as indicated the oxygen on the AlGaN layer after post-oxidation. The formation of group-III oxides resulted in passivation. The diffusion of Ni into the AlGaN layer was also detected owing to the post-oxidation annealing shallow states near the Schottky contact. When post-oxidation was performed at 600°C, all Ni at the Schottky contact was combined with oxygen. This high post-oxidation temperature was therefore unsuitable because the Schottky interface changed from Ni/AlGaN to Au/AlGaN. Leakage current until breakdown was considerably decreased after post-oxidation at 500°C. The breakdown voltage of GaN SBD was increased from 351 to 524V at a drift length of 20μm by the post-oxidation. The figure-of-merit (BV2/Ron,sp) of identical device was also improved from 29.6 to 53.1 by the post-oxidation. Our results suggest that post-oxidation is suitable for GaN power switch fabrication.

AlGaN/GaN High-Electron-Mobility Transistor Using a Trench Structure for High-Voltage Switching Applications

We proposed a new AlGaN/GaN high-electron-mobility transistor using a trench structure for high-voltage switching applications. The proposed trench structure was designed for the use at the gate edge, which improved the gate leakage current and breakdown voltage. We considered that the thickness of the AlGaN barrier was related to the polarization, surface-state density and leakage current. The surface states at the gate edge were controlled by etching the AlGaN barrier by 22 nm. The gate leakage current of the proposed device was 40 ?A/mm while that of a conventional device was 201 ?A/mm with a reverse gate-drain voltage of 100 V. The suppressed gate leakage current may have been caused by the decrease in the surface states at the gate edge. The breakdown voltage of the proposed device was 762 V while that of the conventional device without a trench structure was 120 V. The forward drain current and transconductance of the proposed device were decreased slightly because the channel resistance was increased in the trench region. The results of this study suggest that the trench structure improves the off-state characteristics of GaN power switches.

Device Breakdown and Dynamic effects in GaN Power Switching Devices: Dependencies on Material Properties and Device Design

not Available.

High-voltage SiC and GaN power devices

The recent progress in the development of high-voltage SiC and GaN power switching devices is reviewed. The experimental performance of various rectifiers and transistors, which have been demonstrated, is discussed. Material and processing challenges and reliability concerns on SiC and GaN power devices are also described. The future trends in device development and commercialization are pointed out.