Investigation of Repetitive Short Circuit Stress as a Degradation Metric in Symmetrical and Asymmetrical Double-Trench SiC Power MOSFETs

Abstract

In this paper, the reliability of planar, symmetrical, and asymmetrical SiC MOSFET is compared under repetitive short circuit shocks. Both static and dynamic parameters are tested after certain cycles to investigate the degradation pattern of the devices. It has been found out that the planar device has the highest reliability and is barely degraded for almost all parameters after 5000 cycles. The symmetrical device has the lowest reliability, which shows degradation after 50 cycles and ultimately fails after 141 cycles. The asymmetrical device shows significant degradation after 100 cycles and fails to turnon/off after 1000 cycles. For both symmetrical and asymmetrical devices, the degradation is directly linked to the damage of the gate oxide.

Measurements and Review of Failure Mechanisms and Reliability Constraints of 4H-SiC Power MOSFETs Under Short Circuit Events

“…This phenomenon is because a more negative V gs can suppress the current density and lower the lattice temperature, proven by simulation results in [24], [66]. In [67], researchers discovered that after the device was turned-off in the short circuit event, the residual high temperature combined with negative V gs could provide enough energy for holes to inject and accumulate within the gate oxide, and mitigate the shift of parameters compared with the condition of the applied V gs of 0 V. In [58], similar phenomena was also reported, but different from the positive V th shift in most papers, radical negative drifts for both symmetrical and asymmetrical trench SiC MOSFETs were observed, as shown in Fig 21 . The reason behind was because of the negative V gs between short circuit intervals. The residual high temperature right after the short circuit caused energized holes to overcome the barrier and inject into the gate oxide, which not only counteracted but also outweighed the effect of injected electrons.…”

“…The only reported degradation of dv/dt and di/dt under short circuit event was in [58]. However, the fluctuation was rather large.…”

“…Results showed that the long-term reliability of planar devices was five times higher in contrast with trench devices. The repetitive short circuit reliability of planar, symmetrical, and asymmetrical trench SiC MOSFETs was also compared at different temperatures by authors [87]. The same test conditions (V ds =400 V, V gs =+17/-5 V, t sc =10 µs) were applied on three types of devices with similar power rating.…”