Investigating the reliability of SiC MOSFET body diodes using Fourier series modelling

Abstract

Using the Fourier series solution to the ambipolar diffusion equation, the robustness of the body diodes of SiC MOSFETs during reverse recovery has been studied. Parasitic bipolar latch-up during the reverse recovery of the body diode is a possible if there is sufficient base current and voltage drop across the body resistance to forward bias the parasitic BJT. SiC MOSFETs have very low carrier lifetime and thin epitaxial drift layers, which means that the dV/dt during the recovery of the body diode can be quite high. This dV/dt coupled with the parasitic drain-to-body capacitance can cause a body current. The paper introduces a new way of assessing the reliability of SiC MOSFETs during the reverse recovery of the body diode. The impact of switching rates, parasitic inductances and carrier lifetime on the activation of the parasitic BJT has been studied.