Towards Highly-Integrated High-Voltage Multi-MHz GaN-on-Si Power ICs and Modules

This work investigates how integration of half-bridge transistors, drivers and freewheeling-diodes on a conductive Si-substrate influences DC-DC converter performance. Based on a lateral 600 V GaNtechnology, a 300-150V, 750W buck converter is built. Conventional separate substrate-to-source terminations of the high-side and low-side devices resulted in 97.3% maximum efficiency. A common semi-floating substrate termination as applicable to monolithic ICs reduced the maximum efficiency to 96.8%, but improved no-load losses. Capacitance measurements which include the substrate as terminal explain two opposite effects resulting from the common substrate: Increased Miller capacitance slows down hard-switching turn-on transitions; reduced effective switch-node capacitance speeds up resonant transitions. Operating the integrated GaN driver with external Si-CMOS pre-driver in burst operation up to 40MHz at 350 V shows potential for multi-MHz applications. While monolithic integration is beneficial to reduced parasitic inductances and assembly effort, a differentiated analysis considering different switching conditions is required to identify system-level advantages.