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 ( ${\rm {V_T}})$ , maximum transconductance ( ${\rm {g_{m,max}}})$ , and subthreshold swing (S). Our results show a universal continuous, symmetrical, and reversible ${\rm {V_T}}$ shift and ${\rm {g_{m, max}}}$ change as gate stress voltage ( $\text {V}_{{{\text {GS},\text {stress}}}})$ increases from −5 to 5V at room temperature. The time evolution of ${\rm {V_T}}$ 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 defect band very close to the GaN/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.