Bias-Temperature Instabilities and Radiation Effects on SiC MOSFETs

Abstract

Bias-temperature-instabilities (BTIs) are investigated for 4H-SiC based nMOSFETs before and after total ionizing dose irradiation. We find that the threshold voltage shifts of unirradiated devices decrease significantly with elevated-temperature stress under accumulation bias; in contrast, devices stressed under inversion bias do not exhibit significant threshold voltage shifts. Threshold voltage shifts due to BTI for unirradiated devices stressed under accumulation bias may well be enhanced significantly as a result of the additional ionization of deep dopants in SiC at elevated temperatures. The BTIs are caused by charge carriers are captured by deep interface traps (more than 0.6 eV away from the SiC conduction or valence bands) and O vacancies in the SiO2. Hole trapping at O vacancies dominates the ionizing radiation response. The magnitudes of the changes in threshold voltage shifts increase with switched bias-temperature stress after irradiation, relative to those in unirradiated devices.