T04.5 - Impact of Substrate Bias on the Stability of Bidirectional GaN HEMT in Hard- and Soft-Switching

Many power electronics circuits for DC/AC conversion require power semiconductors with bidirectional voltage-blocking capability, typically achieved by connecting two unidirectional devices in series. Emerging monolithic bidirectional GaN-on-Si HEMTs (MBD-HEMTs) offer a single-device solution, reducing complexity. However, substrate management remains a critical challenge due to the floating substrate, which results in a dynamically changing bias—negative during hard-switching and positive during soft-switching. Adding a substrate management circuit can address this but increases cost and complexity. To optimize substrate management, understanding the impact of dynamic substrate bias on device stability is essential. This work investigates dynamic on-resistance (dyRON) and threshold voltage (Vth) in GaN HEMTs with a floating substrate under hard- and soft-switching. A significant dyRON shift is observed when the substrate is floating or shorted to the drain during hard-switching, while Vth shift remains minimal. The back-gating effect, driven by substrate bias changes, is identified as the primary cause. These findings offer guidance for enhancing MBD-HEMT stability