Static and Dynamic Characteristics of a 1200-V/22 -mΩ Normally-Off SiC/GaN Cascode Device Built With Parallel-Connected SiC JFETs Controlled by a Single GaN HEMT

A silicon carbide junction field effect transistors (SiC-JFETs) /gallium-nitride high electron mobility transistor (GaN-HEMT) hybrid power switch is proposed with scaled-up current rating enabled by parallel-connected high-voltage (HV, i.e., 1200 V) SiC-JFETs controlled by a single low-voltage enhanced-mode GaN-HEMT in a cascode configuration. Only one set of gate driver (for the GaN HEMT) is required by the cascode device and therewith higher efficiency is achieved regarding the gate-driver loss compared with a board-level parallel connection of several standalone devices (e.g., SiC MOSFETs or SiC/Si cascode devices). Key factors that affect the current-sharing balance between the parallel-connected SiC JFETs and associated matching method are systematically investigated by taking into account the specific transient behaviors of the cascode device. It is found that the variation in SiC JFETs’ threshold voltages plays the most important role in current balancing when the GaN HEMT drives the SiC JFETs internally with superior fast speed. A 1200-V/22-mΩ proof-of-concept prototype of the proposed device with two SiC JFETs in parallel is demonstrated and characterized in a comparative study considering the matching of JFETs. By matching the SiC JFETs according to their transfer curves, the current-sharing imbalance among the SiC JFETs can be limited to be less than 1.5%. This all-wide-bandgap device exhibits high-temperature stability of threshold voltage, extremely small gate-driver loss, and low interelectrode capacitances, of which features are promising for high-frequency applications.