Reliability Evaluation of p-GaN Gate HEMTs in Bootstrap Circuit

On GaN power IC platform, the lateral p-GaN gate high-electron-mobility transistors (HEMTs) can be reconfigured as diodes in a bootstrap circuit by shorting the gate and source as the anode terminal. In the initial forward charging period, the gate-to-drain junction of the device would withstand a large forward voltage that causes reliability concerns but remains unclear. In this work, a comprehensive reliability evaluation of 650-V p-GaN gate HEMTs is conducted in the forward charging mode. The root cause of device degradation is found to lie in the gate-metal/p-GaN Schottky junction at the drain-side gate edge that degrades to exhibit an ohmic-like gate behavior. TCAD device simulation also reveals that the supply bias of around 15 V is a safe operating voltage for the studied device. A promising solution to boost device reliability in bootstrap circuits is to deploy a larger gate-to-drain distance.