The effective transverse thermal conductivity of amorphous Si3N4 thin films

Abstract

The effective transverse thermal conductivity of Si3N4 thin films is determined as a function of film thickness. Results indicate that the effective thermal conductivity behavior of Si3N4 thin films is similar to that exhibited by amorphous SiO2 films; that is, there is no significant difference between the thermal conductivity of amorphous Si3N4 and amorphous SiO2 thin films as a function of thickness or temperature. The average effective transverse thermal conductivity decreases drastically as the film thickness is reduced. This strong thickness dependence is ascribed to a thermal resistance that is localized at the amorphous film/Si-substrate interface. Within the narrow temperature range studied, the interfacial thermal resistance and the intrinsic conductivity of amorphous films increase with temperature; however, the interfacial resistance dominates as the film thickness is reduced. In light of the observed similarities between the Si3N4 results and those previously obtained on SiO2, the reduction in the effective thermal conductivity of amorphous thin films with decreasing thickness is discussed in terms of both interfacial thermal resistance and scattering mechanisms in amorphous solids.