Modeling and analyzing near-junction thermal transport in high-heat-flux GaN devices heterogeneously integrated with diamond

Gallium nitride (GaN) electronic devices possess excellent electrical characteristics that make them promising for advanced power and radiofrequency device applications. However, elevated channel temperatures associated with localized Joule heating degrade the device reliability and limit the device performance. To address this, recent intensive efforts have heterogeneously integrated diamond, the best thermal conductor among three-dimensional materials, near the device junction and have fabricated GaN-on-diamond devices. Numerous efforts have also been made to investigate their thermal characteristics via finite element simulations. The majority of these efforts have adopted several simplifying assumptions to facilitate thermal analysis and reduce computational loads. However, few have examined the impact of these assumptions on the device junction temperature. Here, we evaluate this impact by constructing a three-dimensional near-junction thermal transport model for GaN-on-diamond devices and calculating the temperature- and thickness-dependent GaN thermal conductivity utilizing semiclassical phonon transport theory. We further explore the influence of several near-junction thermal design parameters, including GaN layer and diamond substrate thicknesses, GaN/diamond thermal boundary resistance, and gate pitch and width, on the device junction temperature. Overall, this work may provide detailed guidelines and best practices for modeling and analyzing near-junction thermal transport in high-heat-flux GaN devices heterogeneously integrated with diamond.