A New Complete Condition Monitoring Method for SiC Power MOSFETs

This article proposes a new complete condition monitoring method which can independently monitor both the threshold voltage drift and the packaging degradation accurately by monitoring only the reverse body diode voltage drop at different gate bias levels. The SiC MOSFETs are aged through an accelerated aging method and the corresponding changes in electrical parameters are periodically measured to assess their correlation with the state of the device's health. It has been revealed that the on-state resistance reveals the combination of gate oxide and package-related degradation while the threshold voltage mainly depicts gate oxide-related issues. Unlike these two parameters, the body diode voltage drop is found to independently indicate the state of device health both for package and gate oxide. This is caused by a unique secondary conduction mode of SiC MOSFETs in third-quadrant operation which is clearly disclosed with transition boundaries by a proposed body diode transfer characterization curve. In order to have a detailed condition information of the device with a simple circuit, monitoring the reverse body diode voltage drop at 0 and -5 V gate bias is proposed. The proposed condition monitoring method is implemented on a gate drive circuit and experimental results are given for two artificially degraded devices. The experimental results confirm that the proposed method can independently monitor both the gate oxide and packaging degradations accurately by monitoring a single precursor parameter. The proposed method can be integrated into the gate driver or converter itself to monitor SiC devices.