Compared deep class-AB and class-B ageing on AlGaN/GaN HEMT in S-Band pulsed-RF operating life

AlGaN/GaN HEMTs are on the way to lead the RF-power amplification field according to their outstanding performances. However, due to its relative youth, reliability studies in several types of operating conditions allow to understand mechanisms peculiar to this technology and responsible for the wearing out of devices. This paper reports the reliability study on two power amplifiers using AlGaN/GaN HEMT. Based on results of a previous study of 1280 h in standard operating conditions wherein no evolution of electrical parameters have been observed, two ageing tests in deep class-AB (432 h) and class-B (795 h) are performed under pulsed-RF operating life at high drain bias voltages and saturated operation. This study shows a drift in RF performances which is linked with the evolution of electrical parameters (RDSON, gm and VP). Similar kinetics and amplitude of degradations are observed revealing quasi-similar contribution of thermal effects in both cases. Degradations are supposed to be related to trapped charges phenomena induced by high voltage operating conditions. Although, several results attest to this hypothesis, a part of the evolutions seems to be linked with structural changes.