Investigation of the Dynamic On-State Resistance of 600 V Normally-Off and Normally-On GaN HEMTs

In this paper, current collapse phenomena and thermal effects in normally-off and normally-on GaN HEMTs are investigated. The experimental results show that a high-off-state voltage and high-switched drain current at high junction temperature cause an increase of the on-state resistance RDSON. Varying the switching frequency from 50 to 400 kHz, an increase of the onstate resistance is further observed for both types of GaN devices. It is evident from these experiments that the number of switching transients significantly influences the increase of the RDSO N, suggesting that this increase is due to a current collapse in GaN HEMTs. A detailed comparison of the evaluated RDSO N between GaN transistors and the high-speed CoolMOS-C7 transistor is presented.