Both Bias Temperature stress (BTS) and γ-ray irradiation can break Si
Si bonds in the oxide of SiC MOSFETs, generating traps and consequently causing a variation of threshold voltage (VTH). This study investigates the correlation between the defects induced by γ-ray irradiation and BTS. Commercial SiC MOSFETs rated at 1200 V / 80 mΩ from three manufacturers were subjected to 1 Mrad(Si) 60Co-γ irradiation, followed by 168 h of annealing. Devices from the same batch were also tested under negative bias temperature stress (NBTS), positive bias temperature stress (PBTS), and long-term HTGB stress (VGS = 20 V, T = 150 °C for 3200 h) experiment. Results show that the trends of threshold voltage shift (ΔVTH) caused by γ-ray irradiation and BTS stress are consistent across all three devices. The changes follow the order of C > > A > B by extracting the ΔVTH and the density of oxide trapped charges.
γ-ray irradiation and NBTS stress induced a negative shift of the VTH. By separating the changes in oxide trapped charges during the two processes, it was found that the ratio of parameters related to the oxide trapped charge generation rate is around 50, demonstrating a correlation between γ-ray irradiation and NBTS. Furthermore, it was found that the ratio of ΔVTH after 1 Mrad(Si) irradiation and 120 h annealing(ΔVTH-An120h) to that after 2000 h of HTGB stress(ΔVTH-2000h) is around 0.5 for all three devices. This indicates that the TID and PBTS may share a similar correlation. Analysis indicates that ΔVTH induced by γ-ray irradiation and BTS is correlated with oxygen vacancy defects in the gate oxide. Specifically, radiation and NBTS are associated with puckered structures, while PBTS relates to Si5–Si4 structures. Among the three devices, the correlation between the generation rate of trapped charges under radiation and BTS in the three devices can establish the basis for the equivalence between the two methods.
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