Third Quadrant Operation of SiC MOSFETs: Comprehensive Analysis and Condition Monitoring Solution

To achieve higher power density at a reduced cost, it is more advantageous to utilize the inherent body diode found in silicon carbide MOSFETs (SiC MOSFETs) rather than relying on an external Schottky barrier diode (SBD). Therefore, it is crucial to investigate the third quadrant operation of SiC MOSFETs and analyze the factors influencing the behavior and reliability of the body diode. By examining the intricate relationship among gate voltage bias, gate-oxide degradation, and third quadrant operation, this study contributes to a comprehensive understanding of the underlying mechanisms and provides insights into optimizing device performance and reliability. First, this article shows that the current flows through both the channel and the p-n junction during the third quadrant operation, which impacts the reverse recovery conduction and power losses. The characteristics of the body diode and technology-computer-aided design (T-CAD) results confirm that the distribution of current between the channel and the p-n junction can be controlled by adjusting the gate voltage bias. Consequently, the gate voltage can partially or fully obstruct the channel during reverse conduction, thereby enabling the regulation of the current flow. Second, the study demonstrates that the degradation of the gate oxide can impact the third quadrant operation and reduce the reverse recovery current. Finally, this article proposes a circuit that can monitor the gate-oxide degradation by monitoring the peak reverse recovery current (PRRC). The results are confirmed experimentally on a double pulse tester (DPT) setup.