Instabilities by parasitic substrate-loop of GaN-on-Si HEMTs in half-bridges

The stability of GaN-on-Si HEMTs with substrate to- source termination is analyzed in a high-voltage half-bridge. The work exposes that external substrate termination creates a parasitic substrate loop, which leads to unstable switching behavior under certain conditions. Stability analysis reveals that parasitic inductance in the substrate-loop alone is sufficient for instabilities, even with zero parasitic inductance in the gate- and power-loops. A systematic analytical stability analysis is carried out based on a small-signal equivalent circuit. The theory is verified by measurements using a PCB- embedded 600V GaN HEMT with integrated gate driver Adequate damping of the substrate loop resonance enables stable operation of the halfbridge module.