Unified Mechanism for Positive- and Negative-Bias Temperature Instability in GaN MOSFETs

We present a comprehensive study of bias temperature instability (BTI) in GaN MOSFETs under moderate positive and negative gate bias stress. We investigate the evolution of threshold voltage (V-T), maximum transconductance (g(m, max)), and subthreshold swing (S). Our results show a universal continuous, symmetrical, and reversible V-T shift and gm, max change as gate stress voltage (V-GS,V- stress) increasesfrom-5 to 5V at roomtemperature. The time evolution of VT is well described by a power law model. The voltage dependence, time dependence, and temperature dependence of our results suggest that for moderate gate bias stress, positive BTI and negative BTI are due to a single reversible mechanism. This is electron trapping/detrapping in preexisting oxide traps that form a defectband very close to theGaN/oxide interface and extend in energy beyond the conduction band edge of GaN and below the Fermi level at the channel surface at 0 V.