Impact of Thin Film Thermophysical Properties on Thermal Management of Wide Bandgap Solid-State Transistors

Abstract

Wide bandgap semiconductor solid-state transistors continue to have a wide array of applications that include power supplies, communications, electronic warfare, and multifunctional RF systems. Two viable wide bandgap semiconductor materials currently under investigation are silicon carbide (SiC) and gallium nitride (GaN). One interesting aspect of these devices is their ability to operate at elevated temperatures on the order of 500°C. At higher temperatures the heat capacity of semiconductors is constant, while the phonon mean free path is inversely proportional to the lattice temperature. This causes a significant reduction in the thermal conductivity over the operating temperature range. The submicron-scale conducting channels and junctions of wide bandgap devices can create highly localized heat fluxes on the order of several hundred kilowatts per square centimeter. Since these heat fluxes lead to localized hot spots within the electrically critical regions of the transistors, they can have a strong impact on device gain, power capability, and reliability. Quantifying the thermophysical properties of the underlying thin film materials is of critical importance for the accurate prediction of these localized temperature extremes.