Investigations on the Degradations of Double-Trench SiC Power MOSFETs Under Repetitive Avalanche Stress

The degradations of electrical parameters for double-trench silicon carbide (SiC) power metal-oxidesemiconductor field-effect transistors (MOSFETs) under repetitive avalanche stress are investigated in this paper. The injection of hot holes into the bottom oxide of the gate trench during avalanche process is demonstrated to be the dominant degradation mechanism, while the channel is rarely influenced by the stress. The injected holes attract extra electrons in the SiC layer along the SiC/SiO2interface, decreasing the ON-state drain-source resistance (Rdson). Due to this reason, the threshold voltage (Vth) of the device also reduces slightly. Moreover, other than static electrical parameters, dynamic characteristics including the gate-drain capacitance (Cgd) and the switching characteristics of the device also degrade. After being stressed by repetitive avalanche stress, the depletion region beneath the bottom of the gate trench gets thinner, leading to the increase in Cgd, which further influences the switching behaviors. The turn-ON and turn-OFF switching times of the device are calculated. It illustrates that the repetitive avalanche stress results in an obvious delay in the turn-OFF procedure, but hardly influences the turn-ON behaviors of the double-trench SiC MOSFET.