Using triangular voltage sweep to detect mobile ions in silicon carbide MOS

Since power devices such as DMOSFETs will operate at high temperature where mobile ion effects are enhanced, identifying their presence is a key reliability issue for power electronics applications. We have detected the presence of mobile ion contamination in some SiC MOS device sample sets and correlated those results with observed high temperature bias instability. The differing behaviors of these devices to bias stressing as a function of temperature suggests that in some cases mobile ion drift may be counteracting the typical charge trapping effect. Initial triangular voltage sweep (TVS) data indicates the presence of roughly 1-4×10¹² cm^-2 mobile ions in samples where the bias instability significantly decreased with higher temperature, while samples with a nearly flat or positive-trending response showed overall lower ion contaminations of roughly 6-9×10¹¹ cm^-2. These results, although preliminary, support the theory that mobile ion contamination is in some cases masking charge trapping-induced instability. In other cases, mobile ions are dominating the response to bias stressing in SiC MOS, especially at elevated temperature.