The low-temperature thermal conduction and millimeter-wave dielectric properties of β-Si3N4 as a heat-dissipation substrate

Abstract

Increasing operating frequency is required in wireless communication systems. In use, this generates heat, which results in serious problems for semiconductor devices. Silicon nitride (Si3N4) has high thermal conductivity and fracture strength. Therefore, it is expected to be suitable for heat dissipation in active circuit substrates for wireless communication. In this study, Si3N4 with varying thermal conductivities were prepared by controlling starting material and sintering conditions and their low-temperature thermal conductivities were measured. The mean free path of phonons in β-Si3N4 influences its thermal conductivity. The temperature dependence of the Debye–Waller factor obtained by synchrotron radiation scattering supported the high thermal conductivity of the β-Si3N4. The degradation of thermal conductivity was interpreted in terms of the full width at half maximum of Raman spectra. Further, infrared reflectivity and first-principles calculation for β-Si3N4 confirmed their superior dielectric properties compared with other high thermal conductive materials.