单极正负偏压应力下Ga₂O₃-on-SiC MOSFET阈值电压独特的单调正向漂移

In this study, the instability of heterogeneous Ga2O3-on-SiC (GaOSiC) MOSFETs under unipolar positive/negative bias stress (UPBS/UNBS) was investigated systematically. By adjusting key parameters of stress voltage waveform, including frequency (f), holding time ( t _ h ), rising time ( t _ r ), and falling time ( t _ f ), a two-phase shift in threshold voltage ( V _ T ) with cycle number ( C _n ) was observed in the UPBS measurement. The UPBS-induced positive V _ T shift is primarily attributed to electron trapping by traps at/near the Al2O3/ -Ga2O3 interface during the t _ r transient. At the beginning of UPBS test (first phase of degradation), most trap states are unoccupied and the electron trapping is predominant, leading to similar V _ T shifts in different stress conditions. With C _n further increasing (second phase of degradation), deeper level traps begin trapping electrons due to the accumulation effect, which has been found to have a strong correlation with t _ f . Notably, a monotonic positive shift in V _ T was also observed in the UNBS measurement. This V _ T shift under UNBS was modeled using a stretched exponential equation. Parameters of this equation were used to characterize the rate and magnitude of V _ T degradation under various stress conditions, elucidating the significant role of f and t _ r in the V _ T degradation of GaOSiC MOSFET. TCAD simulations suggest that the monotonic positive shift in V _ T under UNBS is caused by electron trapping at the -Ga2O3/SiC interfacial layer, which contains a high density of traps.