Characterization of Electrical Parameters for Health Monitoring in SiC MOSFETs during AC Power Cycling

In this work, electrical parameters of silicon carbide MOSFETs and their temperature dependency, as well as their electrical behavior over time are investigated. An approach is presented to make assertions about the condition of the transistors during operation through the measurement of multiple temperature and degradation-sensitive electrical parameters. The on-state voltage, peak gate current and quasi-threshold voltage are monitored through dedicated acquisition circuits. An exemplary AC power cycling setup which combines switching and conduction losses while applying nominal DC-link voltage is used to characterize the parameters in operation. The setup consists of two half-bridge modules with measurement circuitry connected directly to the devices under test. Results show the capability of the proposed circuits to measure parameters carrying temperature and health information in normal operation. A high linearity of the quasi-threshold voltage in regards to the junction temperature is found, with a relative temperature sensitivity in the per mille range, comparable to the sensitivity of the on-state resistance. No significant temperature sensitivity is found for the peak gate current, due to the specific gate driver design.