Compared with that in a Si device, the area of near interface oxide traps in a SiC MOSFET is wider, and the corresponding density of traps is two orders of magnitude higher. A lot of traps which are continuously capturing or releasing charges will cause the threshold voltage(Vth) to fluctuate with time, leading to the difficulty in accurately and repeatedly measuring the value of Vth. In the standard method, the value of Vth is measured using a preprocessing method to ensure the consistence in measuring the trap charge state in each time. However, the preprocessed trap state which is affected by drain-source voltages is not taken into account in the standard method, which will bring errors to the Vth test. Aimed at this problem, the transfer curves under the influences of different drain-source voltage pulses were measured at first, which show the effects of different drain-source voltages on Vth. Second, the influence of drain-source voltage on the trap charge state was analyzed based on the transient current method, thus clarifying the mechanism of the influence of drain-source voltage on traps. Finally, the influences of different drain-source voltages on Vth measurement were com-pared. Results indicate that the drain-source voltage affects the positive and negative electric field between the gate and drain, thereby affecting the trap charge state and causing the Vth drift. It is suggested that a smaller drain-source voltage should be used when measuring Vth to improve the measurement accuracy and reduce errors caused by testing factors in reliability experiments.
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