Analysis of Dynamic Transients of High Voltage Silicon and 4H-SiC NPN BJTs

Abstract:
4H-SiC vertical NPN BJTs are attractive power devices with potentials to be used as high power switching devices with high voltage ratings in range of 1.7 kV. Compared with silicon power BJTs, they particularly benefit from a large current gain to a factor of ten times higher than silicon counterparts which improves the efficiency of the gate driver. In this paper, the advantages of the 4H-SiC NPN BJTs in terms of switching transients over their silicon counterparts is illustrated by means of extensive experimental measurements and modelling. High level injection, as a common phenomenon among bipolar devices, determines the switching Speed between on-state and off-state. The two device types have been tested at 800 V with maximum temperature of 175degC and maximum collector current of 8 A. The turn-on and turn-off transition in Silicon BJT is seen to be much slower than that of the SiC BJT while the switching time will increase with increasing temperature and decreases with larger collector currents.