An Investigation into the Mechanism of AC Bias Temperature Instability in SiC MOSFETs Through Gate Charging Characteristics

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) play a crucial role in the advancement of next-generation power electronics. Nevertheless, their reliability is adversely affected by threshold voltage drift, which is induced by alternating current bias temperature instability (AC BTI) during pulse-width modulation (PWM) operation. To address inconsistencies in AC BTI theories, this study employs an analysis of gate charging characteristics, revealing new phenomena that clarify the degradation mechanism. Degradation tests conducted at 75∘C with 50 kHz PWM signals on both planar and trench gate SiC MOSFETs demonstrate a persistent positive drift in gate charging characteristics across all bias conditions, which contrasts with predictions made by the recombination-enhanced defect reaction (REDR) framework. These findings indicate that additional charges trapped by locally enhanced electric fields primarily drive AC BTI, while the effects of REDR play a secondary role. Post-degradation capacitance-voltage (C-V) and subthreshold swing (SS) measurements further support these observations. This research contributes to a deeper understanding of AC BTI in high-frequency applications and offers valuable insights for enhancing the reliability of SiC MOSFETs.