[IEEE 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Atlanta, GA, USA (2018.10.31-2018.11.2)] 2018 IEEE 6th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Substrate Bias Effect on E-Mode GaN-on-Si HEMT Cos<inf>s</inf> Losses

摘要： Previous work found large COSS losses in GaN-on-Si HEMTs used in soft-switched, MHz-frequency power converters. Here, we use a back-gate bias between the source and Si substrate to investigate the capacitance characteristics of commercially-available GaN HEMTs. The small-signal capacitance is reduced significantly – up to 2× for a 650 V HEMT and 4× for a 100 V HEMT – indicating that the drain-substrate capacitance is a significant portion of the total output capacitance. This portion of the capacitance appears responsible for trapping-detrapping with time constants on the order of seconds. We verify this by testing the 100 V GaN HEMT in the Sawyer-Tower circuit with negative substrate bias, finding that COSS losses are reduced by up to 30% compared to the shorted substrate condition.