Third Quadrant Operation of 1.2 kV-10 kV SiC Planar MOSFETs: New Device Findings and Converter Validation

This work presents the first comparative study on the third quadrant behavior of 1.2 kV to 10 kV SiC planar MOSFETs. New findings are demonstrated on the competing current sharing between the metal-oxide-semiconductor (MOS) channel and the body diode: in high-voltage MOSFETs, if the MOS channel is on, the body diode turn-on voltage is much higher than the built-in potential of the PN junction. Theoretical explanations are developed and validated by TCAD simulation. This device finding suggests that, for high-voltage SiC planar MOSFETs, turning on the MOS channel may lead to a purely unipolar third-quadrant conduction and the corresponding voltage drop could be higher than that of the bipolar body diode, particularly at high junction temperatures. To understand the implication of this finding on device applications, a DC-DC buck converter was built using a 10 kV SiC MOSFET half-bridge power module. In the high-temperature converter test, the third-quadrant voltage drop was found to be lowest with a negative gate bias control. This work illustrates that the optimal gate bias control for third-quadrant conduction of 10 kV SiC MOSFETs could be different from the one for 1.2 kV SiC MOSFETs.