Improved Electrothermal Ruggedness in SiC MOSFETs Compared With Silicon IGBTs

A 1.2-kV/24-A SiC-MOSFET and a 1.2-kV/30-A Si-Insulated gate bipolar transistor (IGBT) have been electrothermally stressed in unclamped inductive switching conditions at different ambient temperatures ranging from -25 °C to 125 °C. The devices have been stressed with avalanche currents at their rated currents and 40% higher. The activation of the parasitic bipolar junction transistor (BJT) during avalanche mode conduction results from the increased body resistance causing a voltage drop between the source and body, greater than the emitter-base voltage of the parasitic BJT. Because the BJT current and temperature relate through a positive feedback mechanism, thermal runaway results in the destruction of the device. It is shown that the avalanche power sustained before the destruction of the device increases as the ambient temperature decreases. SiC MOSFETs are shown to be able to withstand avalanche currents equal to the rated forward current at 25 °C, whereas IGBTs cannot sustain the same electrothermal stress. SiC MOSFETs are also shown to be capable of withstanding avalanche currents 40% above the rated forward current though only at reduced temperatures. An electrothermal model has been developed to explain the temperature dependency of the BJT latchup, and the results are supported by finite-element models.