Role of Oxygen Vacancies in Short- and Long-Term Instability of Negative Bias-Temperature Stressed SiC MOSFETs

We use hybrid-functional density functional theory to study the role of oxygen vacancies in negative bias-and-temperature stress-induced threshold voltage instability in 4H-silicon carbide power MOSFETs. According to our model, certain originally electrically “inactive” oxygen vacancies are structurally transformed into electrically “active” defects in the presence of strong negative bias and temperature. These newly generated defect configurations function as short-lived or long-lived switching oxide hole traps. The transients of their generation process are shown to correlate well with the measured “short-term” threshold voltage instability. Additionally, we show that the long-lived defects continue to degrade the room-temperature reliability of these devices even after stress removal.