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

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ), maximum transconductance (g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m,max</sub> ), and subthreshold swing (S). Our results show a universal continuous, symmetrical, and reversible VT shift and gm,max change as gate stress voltage (VGS,stress) increases from -5 to 5V at room temperature. The time evolution of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> 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.