Modeling Irradiation-Induced Degradation for 4H-SiC Power MOSFETs

In this article, we proposed a comprehensive model for predicting the degradation of SiC MOSFETs after gamma-ray irradiation. It is experimentally founded that SiC MOSFETs exhibit different degradation behaviors under gate bias (i.e., ${V}_{\text {GS}} =15$ V and ${V}_{\text {DS}} $ = 0 V) and drain bias (i.e., ${V}_{\text {GS}} $ = 0 V and ${V}_{\text {DS}} =400$ V) in terms of threshold voltage ( ${V}_{\text {TH}}$ ) and ON-resistance ( ${R}_{\text {ds}, \text{ON}}$ ). TCAD simulation shows that gate bias causes a high electric field in gate oxide above the MOS channel region, while drain bias generates relatively lower electric field in gate oxide around near-channel region. The differences in electric field under gate bias and drain bias lead to different hole yields and charge accumulation in gate oxide, which is the underlying physical mechanism for their different degradation behaviors. ${V}_{\text {TH}}$ is chosen as the parameter to quantify the accumulated charges in gate oxide and further predict irradiation-induced degradation. The relationship between the variation of threshold voltage ( ${\Delta} {V}_{\text {TH}}$ ) and the total ionizing doses (TIDs) under both gate and drain bias is formulated and validated. Comparison among measured data, TCAD simulation, and model prediction shows that the maximum prediction error is lower than 0.08 V, which proves the rationale and accuracy of the proposed degradation model. In addition, the two submodels for gate bias and drain bias are unified as one according to the time dependence effect (TDE) for TID irradiation. The proposed model could be useful to predict the degradation and/or lifetime of SiC MOSFETs in irradiation environments.