High-power 4H-SiC JBS rectifiers

This paper reports the detailed design, fabrication, and characterization of two sets of high-power 4H-SiIicon Carbide (4H-SiC) Junction Barrier Schottky (JBS) diodes-one with a 1500-V, 4-A capability and another with 1410-V, 20-A capability. Two-dimensional (2-D) device simulations show that a grid spacing of 4 pm results in the most optimum trade-off between the on-state and off-state characteristics for these device ratings. JBS diodes with linear and honeycombed p(+) grids, Schottky diodes and implanted p-i-n diodes fabricated alongside show that while 4H-SiC JBS diodes behave similar to Schottky diodes in the on-state and switching characteristics, they show reverse characteristics similar to p-i-n diodes. Measurements on 4H-SiC JBS diodes indicate that the reverse-recovery time (tau(rr)) and associated losses are near-zero even at a high reverse dI/dt of 75 A/mus. A dc/dc converter efficiency improvement of 3-6% was obtained over the fastest, lower blocking voltage silicon (Si) diode when operated in the 100-200 kHz range. The 1410-V/20-A JBS diodes were evaluated for both hard- and soft-switching applications. Experimental results indicate that their conduction characteristics are comparable with the Si diode counterpart, but the switching characteristics are far superior. When applied to hard-switching choppers, it reduces not only the reverse-recovery loss, but also the main switch turn-on loss. Using the MOSFET as the main switching device, the combination of switch turn-on loss and diode reverse-recovery loss shows more than a 60 % reduction. When applied to soft-switching choppers, the SiC JBS diode is used as the auxiliary diode to avoid the voltage spike during auxiliary branch turn-off. With the conventional ultrafast reverse-recovery Si diode, a voltage spike exceeds the switched-voltage transition by 100% and the auxiliary circuit requires additional voltage clamping or snubbing to avoid over-voltage failure. With the SiC JBS diode, however, the voltage spike is reduced to less than 50% of the switched-voltage transition and the additional voltage clamping circuit can be eliminated. Savings in soft-switching choppers using SiC JBS diodes can be realized in size and weight reduction, energy loss reduction, and reduced packaging complexity.