Threshold Voltage Instability of Commercial 1.2 kV SiC Power MOSFETs

Abstract

This paper presents threshold voltage instability of commercially available 1.2 kV SiC power MOSFETs from multiple vendors. Time-dependent bias-stress measurements are implemented to define the threshold voltage change incurred by near interface oxide traps. Bias-stress on the gate gives rise to injection of carriers into the gate oxide by direct tunneling to the near interface traps. Positive gate bias tends to increase threshold, whereas, negative gate bias tends to decrease threshold voltage. Threshold voltage shifts for various vendors vary from 0.15 V to 0.74 V under bias-stress of +30 V, and -0.05 V to -0.2 V under bias-stress of -10 V for 50 hours. This wide variation in the shifts between vendors indicates the different trap distribution in their oxides. In general, a positive threshold voltage shift decreases current drive, while a negative shift can cause the device to move into an ON state. However, the shift by itself does not represent an operational problem in power electronics but signifies the high density of defects in the gate oxide which may have significance for useful lifetime of gate oxides.