Interfacial Thermal Transport in Top-Side Diamond Integrated AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN high electron mobility transistors (HEMTs) are critical components in modern radio frequency (RF) power amplifiers. However, commercial AlGaN/GaN HEMTs often require power derating to maintain safe channel temperatures. Deposition of a polycrystalline diamond heat spreader onto an as-fabricated device offers a means to facilitate efficient top-side heat extraction. However, the dielectric interlayer used for the growth of a diamond heat spreader and the AlGaN barrier introduce interfacial thermal resistances that can limit the heat transfer performance of the diamond. In this work, a polycrystalline diamond heat spreader was deposited on an AlGaN/GaN-on-SiC epitaxial wafer using a 9.7 nm SiO₂ interlayer. The total thermal boundary resistance (TBR) including contributions from the SiO₂ layer and the AlGaN barrier was determined as a function of the temperature using time-domain thermoreflectance (TDTR). A TBR of 15.8 ± 1.44 m²K GW^-1 was measured at room temperature, primarily dominated by the contribution of the SiO₂ interlayer. A notable contribution from the AlGaN barrier was also identified, which is expected to become more significant with further thinning of the interlayer. A slight decrease in the TBR with temperature was observed, consistent with the temperature-dependent increase in the thermal conductivity of the amorphous SiO₂ layer. Thermal modeling of a multifinger AlGaN/GaN HEMT was performed to evaluate the cooling effectiveness of the top-side diamond and provide design guidelines for optimal integration, considering key parameters such as the diamond thermal conductivity, TBR, and film thickness.