Phenomenon of Short-Time Threshold Voltage Shift and Its Application in Junction Temperature Estimation

Silicon carbide (SiC) has seen tremendous advancement in high-efficiency, high-frequency, and high-temperature applications during recent years. However, the gate oxide of SiC MOSFET is reported to be less reliable compared with its Si counterpart, introducing the problem of threshold voltage (Vth) shift. Recent publications have investigated Vth shift which are mainly based on the long-time scale ranging from seconds to several days. However, the Vth shift in a shorter time scale has not been widely discussed and studied due to its high bandwidth requirement in measurement. This paper proposed an investigation into the short-time Vth shift using a developed current-controlled gate driver. The phenomenon of short-time Vth shift is captured and analyzed, which shows that it occurs within the first microsecond of the gate voltage being applied. Moreover, a modelling approach using the logarithm equation is proposed to describe the relationship between the short-time Vth shift and the gate stress time. Experiments are conducted under different temperatures, illustrating the temperature dependency of the short-time Vth shift process.