Performance of wide-bandgap discrete and module cascodes at sub-1 kV: GaN vs. SiC

Wide-bandgap (WBG) based cascode devices combine the advantages of the gate driveability and reliability of silicon MOSFETs with the power conversion efficiency and switching rate of wide bandgap devices. A low voltage (rated at ~20–30 V) silicon MOSFET drives a vertical JFET for the SiC cascode whereas for the GaN cascode, it drives a lateral GaN HEMT. This paper presents the first systematic comparison of the WBG discrete and module cascodes considering conduction losses, 3rd quadrant operation, switching performance, unclamped switching performance, spontaneous switchings, crosstalk as well as the temperature sensitivities. The results show that the GaN cascode outperforms the SiC cascode considerably in switching performance, however, demonstrates higher conduction losses with more temperature sensitivity in GaN. In this paper, it is also shown experimentally and theoretically that the switching rate in the GaN cascode is more sensitive to the gate resistance compared to the SiC cascode. While turn-ON dI_DS/dt and dV_DS/dt have positive temperature coefficients in the SiC cascode and negative coefficients in the GaN cascode, the SiC cascode is shown to be more UIS rugged, whereas the GaN cascode is incapable of unclamped inductive switching. The impact of unwanted switching on both GaN and SiC cascodes are also shown, indicating that there is a range of optimum gate resistances where un-wanted turn-on and turn-off switchings can be avoided, with the GaN cascode experiencing a higher crosstalk-induced gate voltage due to its higher switching rates.