Alex Man Ho Kwan

Improved Designs for an Electrothermal In-Plane Microactuator

Reported presently are two design approaches to improve the performance of an electrothermal in-plane microactuator with “chevron” beams. One incorporates beams with uniform cross sections but nonuniform lengths or tilt angles to accommodate the thermally induced expansion of the “shuttle”; the other incorporates beams with nonuniform cross sections to widen the high-temperature “expansion” zones. It is derived analytically, verified using finite-element simulations, and tested by microfabricating actuators occupying a constrained device area that the incorporation of one or the other proposed features leads to an improved performance figure-of-merit, defined to be the product of the actuation displacement and force. An increase in the figure-of-merit by up to 65% per beam has been measured.

Integrated gate-protected HEMTs and mixed-signal functional blocks for GaN smart power ICs

On a GaN smart power IC platform, a robust GaN high electron mobility transistor (HEMT) with integrated gate protection is demonstrated by embedding a depletion-mode HEMT (D-HEMT) into the gate electrode of an enhancement-mode HEMT (E-HEMT). This protection scheme allows large input bias (e.g. 20 V) without gate-overdrive-induced reliability issues, and yields no penalties on the ON-state current and OFF-state breakdown voltage. Mixed-signal functional blocks, such as a 2-level quantizer circuit and a set/reset flip-flop, are demonstrated with operation up to 250°C to expand the design library for implementation of GaN smart power ICs.

A GaN Pulse Width Modulation Integrated Circuit for GaN Power Converters

We report the first gallium nitride (GaN)-based pulse width modulation (PWM) integrated circuit (IC) featuring monolithically integrated enhancement- and depletion-mode high electron mobility transistors and lateral field-effect rectifiers on the GaN smart power technology platform. The PWM IC is able to generate 1-MHz PWM signal with its duty cycle modulated effectively by a reference voltage (Vc) over a wide range with good linearity. It features a 5 V supply voltage and is composed of a sawtooth generator and a comparator, both of which can be operated at 1 MHz and exhibit proper functionality over a wide temperature range (from 25 °C to 250 °C). This circuit demonstration further proves the feasibility of an all-GaN solution that features monolithically integrated peripheral gate control circuits and power switches for GaN power converters. An all-GaN solution would lead to a compact system with improved efficiency and enhanced reliability.

High-Gain and High-Bandwidth AlGaN/GaN High Electron Mobility Transistor Comparator with High-Temperature Operation

This paper presents the dc and dynamic characterizations of a GaN-based voltage comparator, fabricated with monolithic integration of enhancement-mode (E-mode) and depletion-mode (D-mode) AlGaN/GaN high electron mobility transistors (HEMTs). The comparator features high gain (>31 dB) and wide bandwidth (>4 MHz), and small propagation delay time (<20 ns) over a wide temperature range up to 250 °C. Its dc gain is still 27.1 dB at 400 °C. These results demonstrate the potential of the AlGaN/GaN HEMT technology for mixed-signal integrated circuits used in GaN power electronics that promises high-voltage, high-current, and high-temperature operation.

A Highly Linear Integrated Temperature Sensor on a GaN Smart Power IC Platform

On a GaN smart power integrated circuit (IC) platform, a highly linear (i.e., proportional to absolute temperature) temperature sensor IC is demonstrated for building voltage references as well as temperature compensation functional blocks. The circuit is designed based on the temperature-dependent characteristics of GaN-based peripheral devices (e.g., heterojunction Schottky barrier diode, enhancement-/depletion-mode high electron mobility transistors, and lateral field-effect rectifiers) that are monolithically integrated with high-voltage power devices. This monolithic integration scheme facilitates the design efforts in taking full advantages of GaNs superior capability to operate at high temperatures. Proper circuit operation was demonstrated at 275 °C.

Integrated Over-Temperature Protection Circuit for GaN Smart Power ICs

As a thermal sensing and protection module on a GaN smart power IC platform, the first GaN over-temperature protection (OTP) circuit is demonstrated to deliver a desirable triggering signal at the critical temperature. The integrated OTP circuit is realized based on monolithic integration of enhancement-/depletion-mode high electron mobility transistors (HEMT) and HEMT-compatible lateral field effect rectifiers on a baseline AlGaN/GaN-on-Si wafer. The circuit effectively indicates the over-temperature up to 250 ?C, and has a power supply rejection radio well above 35 dB. This sensing/protection circuit is expected to provide enhanced reliability to the high-voltage GaN power devices.

A Gate Overdrive Protection Technique for Improved Reliability in AlGaN/GaN Enhancement-Mode HEMTs

On a GaN smart power integrated-circuit platform, a monolithically integrated gate-protected high-voltage AlGaN/GaN enhancement-/depletion-mode high-electron mobility transistor (HEMT) has been proposed. It can sustain large input gate voltage swing (>; 20 V) with enhanced safety (no gate failure observed) and improved reliability (no observable shifting of the threshold voltage), and the breakdown voltage is not sacrificed. Such a protection scheme with a wide input gate bias range also facilitates simple and reliable connections between the gate driver circuits and the power switches without the level shifter circuits for conventional GaN Schottky gate power HEMTs.

Designs for improving the performance of an electro-thermal in-plane actuator

Reported presently are two designs to improve the performance of a “chevron” electro-thermal in-plane actuator. One incorporates beams with uniform cross-sections but nonuniform lengths and tilt angles to accommodate the thermally induced expansion of the “shuttle”; the other incorporates beams with non-uniform cross-sections to achieve a wider spread of the high temperature “expansion” regions of the beams. With the product of the actuation force and displacement defined as a figure-of-merit, it is verified using finite-element simulation that the incorporation of non-uniform lengths and tilt angles, and non-uniform beam cross-sections leads to respective improvement of 10 and 65% in the figure-of-merit. The effectiveness of these designs was also tested by micro-fabricating actuators occupying fixed device areas.

Device Technology for GaN Mixed-Signal Integrated Circuits

A device technology platform for implementing GaN mixed-signal integrated circuits is presented. High-performance GaN enhancement-/depletion-mode (E/D-mode) high electron mobility transistors (HEMTs) are the key devices for implementing digital/analog functional blocks, while Schottky diodes and lateral field-effect rectifiers provide useful components for sensing circuits. As a case study, a GaN 2-bit quantizer circuit fabricated on that platform is demonstrated, leading a way to highly integrated system-on-chip solutions for protection/sense/control applications.

High-Gain and High-Bandwidth AlGaN/GaN HEMT Comparator

Alex Man Ho Kwan, King Yuen Wong, Xiaosen Liu and Kevin J. Chen Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, CHINA * Phone: +852-23588530 E-mail: alexmhkwan@ust.hk