Reliability and failure analysis in power GaN-HEMTs: an overview

Power GaN transistors have recently demonstrated to be excellent devices for application in power electronics. The high breakdown field and the superior mobility of the 2-dimensional electron gas allow to fabricate transistors with low resistive and switching losses, that permit to increase the efficiency of switching mode power converters beyond 99 %. GaN-based transistors are currently supposed to be adopted in KW-range power converters; 650 V transistors are already available on the market, and 1200 V devices are currently under development. During operation, GaN power transistors can reach critical conditions, especially in the off-state (with a high V-DS, in excess of 650 V), during hard-switching (where high current and voltage can be simultaneously present), and for high positive gate voltages (in the case of normally-off devices). This paper reports our most recent results on the gradual and catastrophic degradation of GaN-based power HEMTs. We present the results of three different case studies, on: (i) the time-dependent breakdown of power HEMTs submitted to high off-state stress; (ii) the degradation of HEMTs with p-GaN gate submitted to high gate stress; (iii) the hot electron effects in GaN-MISHEMTs submitted to high-temperature source current stress.