Evaluation of the Reverse Behaviors of the Latest Generations of SiC MOSFET and SiC Schottky Barrier Diode
The performance of the SiC power MOSFET exceeds the Si IGBT with similar voltage ratings and bidirectional conducting capability. Unlike the Schottky Barrier Diode (SBD), the body diode of the MOSFET has a reverse recovery problem due to its P-i-N nature. The MOSFET's body diode reverse recovery issues have been widely studied since the Si MOSFET era. Though the reverse recovery of the SiC MOSFET is better than the Si MOSFET, with 10 times lower reverse-recovery current, SiC MOSFET products pack-aged with SBDs are still being widely developed because a design has not yet been de-veloped that satisfies the reverse recovery problem and high conduction loss of the body diode. CREE's second-generation SiC MOSFET's reverse behaviors have been widely studied, and the necessity of paralleling the SBD to achieve small turn-on switching energy is proven.
In this paper, the record high current-rating of CREE's third-generation discrete SiC MOSFET is evaluated. CREE's 1.2kV SiC SBDs are compared according to its current sharing capabilities in parallel with SiC MOSFETs through conducting and switching characteristics, with load currents ranging from 10A to 95A under both room temperature and high temperatures. Fig. 1 shows the double-pulse test setup for the reverse behavior. The diode in Fig. 1 (a) represents a body diode when testing without a SBD in parallel, while that in Fig. 1(b) represents the body diode and the SBD when testing with a SBD in parallel. The hig- temperature setup of the reverse behavior characterization is shown in Fig. 1 (b), where a bent piece of copper is used to transfer heat to the devices being test-ed from the hot plate. Fans are used to cool down the top-side circuits. Fig. 2 shows the comparison between using the freewheeling diode as a body diode and using the freewheeling diode as a body diode in parallel with the SBD under both room temperature and high temperature. As the reverse-recovery behavior of the third-generation SiC MOSFET's body diode is trivial compared to its reverse behavior caused by the output capacitance, the extra reverse energy introduced by the junction capacitance of the SBD actually compensates the elimination of the reverse recovery energy by the SBD. Also, the reverse-recovery behavior of the third-generation SiC MOSFET shows very little increase under high temperatures, and paralleling the SBD does not show much improve-ment under high temperatures, either. In conclusion, for the third-generation SiC MOSFET, the SBD is not necessary to improve reverse-recovery behavior.