A novel GaN HEMT degradation mechanism observed during HTST test

The maximum drain current (Imax) reduction after high temperature short term (HTST) tests in RF-GaN HEMT was investigated. A “critical-voltage” like degradation was observed with voltage levels correlated with the pinch-off voltage of the MIS structure formed by the device field-plate terminal (FP). The recoverable nature of the observed phenomena and the positive temperature dependence of both the Imax reduction and leakage currents within the passivation layer allowed us to propose a novel interpretation based on a charge-injection process from the FP into SiN/AlGaN electrons trap within the device gate-drain access region.