Thermal Optimization of Rectilinear Gate Multi-Finger GaN HEMTs for Maximum Temperature Reduction and Improved Reliability

This paper presents an optimization methodology for rectilinear-gate Gallium Nitride High Electron Mobility Transistors (HEMTs) that enhances thermal performance while not increasing manufacturing complexity and without compromising high-frequency operation. Conventional rectilinear gates with uniform spacing produce significant temperature non-uniformity which degrades device reliability. Previous gate-temperature minimization methods reduced device temperature but required larger uniform gate separations, thereby increasing device area, gate inductance, and phase mismatch, while only providing marginal improvements in temperature uniformity. To address these trade-offs and substantially reduce temperature non-uniformity beneath the gates of a multi-finger HEMT, a rigorous geometrically driven optimization methodology is proposed which systematically optimizes individual gate spacings. A coupled MATLAB–COMSOL Multiphysics co-simulation framework validated the proposed methodology and demonstrated that it redistributes heat more effectively without requiring large inter-gate separation. Simulation results demonstrate device temperature reduction of up to 52°C and temperature-uniformity improvement of up to 7°C, and an active-area penalty by up to 13% compared with conventional rectilinear uniform-spacing HEMTs. The optimized geometry also reduces gate-feed path-length differences, improving phase coherence among the gate fingers. A first-order phase-mismatch analysis estimates an increase in the phase-coherent frequency range to 3–9 GHz. The proposed approach therefore provides a fabrication-efficient and scalable strategy for reliable, high-power, high-frequency GaN HEMTs.