Impacts of gate bias and its variation on gamma-ray irradiation resistance of SiC MOSFETs

Gamma-ray irradiation into vertical type n-channel hexagonal (4H)-silicon carbide (SiC) metal-oxide-semiconductor field effect transistors (MOSFETs) was performed under various gate biases. The threshold voltage for the MOSFETs irradiated with a constant positive gate bias showed a large negative shift, and the shift slightly recovered above 100 kGy. For MOSFETs with non- and a negative constant biases, no significant change in threshold voltage, Vth, was observed up to 400 kGy. By changing the gate bias from positive bias to either negative or non-bias, the Vth significantly recovered from the large negative voltage shift induced by 50 kGy irradiation with positive gate bias after only 10 kGy irradiation with either negative or zero bias. It indicates that the positive charges generated in the gate oxide near the oxide–SiC interface due to irradiation were removed or recombined instantly by the irradiation under zero or negative biases.