Enhanced Cooling of Multifinger GaN HEMTs via Topside Diamond Integration

Gallium nitride high electron mobility transistors (HEMTs) are key components for today’s 5G power amplifiers. However, device overheating requires commercial devices to operate under derated power levels. This work reports the cooling effectiveness of a top-side diamond heat spreader for a 16-finger GaN/SiC HEMT using gate resistance thermometry. A $2~\mu $ m thick diamond heat spreader was found to reduce the gate temperature rise by ~20% at 12 W/mm. Simulation results indicate that a diamond thickness greater than $1.5~\mu $ m is required to achieve a 10% reduction in the device thermal resistance ( ${\mathrm{R}}_{{\text {Th}}}$ ). To achieve a 10% reduction in the ${\mathrm{R}}_{{\text {Th}}}$ , the thermal conductivity of a $2~\mu $ m thick diamond layer needs to be greater than 450 W/m $\cdot $ K and the SiN protection layer should be thinner than 75 nm. The incorporation of topside diamond combined with replacing the SiC substrate with diamond was shown to reduce the ${\mathrm{R}}_{{\text {Th}}}$ by 42.2% compared to a standard GaN/SiC HEMT in simulation.