SiC JFET: Currently the Best Solution for an Unipolar SiC High Power Switch

Abstract:

Today a main focus in high efficiency power electronics based on silicon carbide (SiC) lies on the development of an unipolar SiC switch. This paper comments on the advantages of SiC switching devices in comparison to silicon (Si) switches, the decision for the SiC JFET against the SiC MOSFET, and will show new experimental results on SiC JFETs with focus on the production related topics like process window and parameter homogeneity which can be achieved with the presented device concept. Due to material properties unipolar SiC switches have, other than their Si high voltage counterparts, very low gate charge, good body diode performance, and reduced switching losses because of the potential of lower in- and output capacitances. The most common unipolar switch is the MOSFET. However, the big challenge in the case of a SiC MOSFET is the gate oxide. A gate oxide on SiC that provides adequate performance and reliability is missing until now. An alternative unipolar switching device is a normally-on JFET. The normally-on behavior is a benefit for current driven applications. If a normally-off behavior is necessary the JFET can be used together with a low voltage Si MOSFET in a cascode arrangement. Recently manufactured SiC JFETs show results in very good accordance to device simulation and demonstrate the possibility to fabricate a SiC JFET within a mass production. A growing market opportunity for such a SiC switch becomes visible.