Evolution of GaN HEMT Small-Signal Parameters During Semi-on State for RF/MM-Wave Applications

This paper presents a comprehensive reliability study of GaN HEMTs, emphasizing the application of S-parameter analysis to identify degradation mechanisms complementary to conventional DC metrics. By employing small-signal Sparameter analysis, we systematically differentiate degradation effects occurring in different regions of the device. We identify surface trapping, particularly at the drain edge of the gate under semi-on hot carrier stress, as the dominant degradation mechanism. A time-dependent recovery of the degradation is observed, suggesting against permanent hot carrier degradation. This study also highlights differences in dynamic trapping behavior of GaN cap compared to SiN cap, emphasizing the impact of passivation on device reliability.