Bias-temperature instabilities and radiation effects on SiC MOSFETs

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 negative bias (accumulation); in contrast devices stressed under positive bias (inversion) do not exhibit significant threshold voltage shifts. Threshold voltage shifts due to BTI for unirradiated devices stressed under negative bias correlate strongly with the additional ionization of deep dopants in SiC at elevated temperatures. The charge that leads to BTI lies in 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. ©The Electrochemical Society