Thermal conduction normal to thin silicon nitride films on diamond and GaN

Self-heating effects severely limit the performance of high-power gallium nitride (GaN) high-electron-mobility transistors (HEMTs). High thermal resistances within micrometers of the transistor junction often dominate the junction temperature rise and fundamentally restrict the device power handling capability. The use of high-thermal-conductivity diamond near the junction can address this thermal limitation, but this approach requires careful attention to the quality of the thermal interface between the GaN and diamond. Here we use time-domain thermoreflectance (TDTR) to measure thermal resistances of thin silicon nitride (SiN) films with varying thicknesses on both diamond and GaN. Measurement of these two sets of samples provides an estimate for the thermal resistance between the GaN and diamond since the SiN film can be used as a bonding layer between the two materials. The effective resistances of the SiN film and bottom interface (SiN/diamond or SiN/GaN) range from 22 to 37 m² K GW^-1 for both sets of samples. Our findings suggest the possibility of achieving 22 m² K GW^-1 as the GaN/diamond thermal interface resistance.