Time Dependence of Bias-Stress-Induced SiC MOSFET Threshold-Voltage Instability Measurements

We have observed significant instability in the threshold voltage of 4H-SiC metal-oxide-semiconductor field-effect transistors due to gate-bias stressing. This effect has a strong measurement time dependence. For example, a 20-mus-long gate ramp used to measure the I-V characteristic and extract a threshold voltage was found to result in a instability three to four times greater than that measured with a 1-s-long gate ramp. The V_T instability was three times greater in devices that did not receive a NO postoxidation anneal compared with those that did. This instability effect is consistent with electrons directly tunneling in and out of near-interfacial oxide traps, which in irradiated Si MOS was attributed to border traps.