The Impact of Temperature and Switching Rate on Dynamic Transients of High Voltage Silicon and 4H-SiC NPN BJTs: A Technology Evaluation

This paper reports the application of silicon BJT modelling techniques to the modelling of dynamic behaviour of high-voltage 4H-SiC BJTs, and the experimental validation thereof. High voltage silicon BJTs are impractical due to their low current gain which requires a bulky base driver. Emergence of high voltage 4H-SiC vertical NPN BJTs with a tenfold higher gain enables the application of efficient drivers, with ratings close to those of IGBTs. This paper demonstrates the advantages offered by 4H-SiC BJTs by means of wide-scale measurements at 800 V and 10 A in a range of temperatures up to 175◦C and adjusted base driver switching rates. The paper shows that the turn-off storage delay in the SiC BJT is two orders of magnitude lower than that of the silicon device. It also shows that the turn-on switching transients of SiC device are by an order of magnitude and the turn-off transients are by two orders of magnitude faster than that of its silicon counterpart, resulting in a tenfold reduction of the switching energy. It also demonstrates the temperature dependency of switching transients of the silicon BJT, and the relative temperature-invariance of the SiC device’s performance. The paper concludes with validation of the transient models for the 4H-SiC NPN BJT, showing that the model is sufficiently accurate for transient switching and loss calculations.