Thermal simulations of three-dimensional integrated multichip module with GaN power amplifier and Si modulator

A finite-element simulation was used to quantitatively estimate the heat transfer in a three-dimensional multichip module (MCM) consisting of a GaN power amplifier with solder-bump-bonded Si modulator and integrated antenna on a high-resistivity SiC substrate under various conditions of power density and substrate and epi thicknesses via wire thickness and effective heat transfer coefficient. The maximum temperature in the integrated-antenna approach occurred in the center of the MCM. At a GaN power amplifier power level of 3W∕mm, a steady-state temperature of ∼125°C was reached in ∼20s. Bulk GaN substrates were also found to provide good thermal transfer characteristics, while sapphire produced an increase in temperature almost a factor of 3 higher than for SiC. At a power density of 10W∕mm, the steady-state operating temperature was ∼400°C even with SiC substrates.