Anisotropic thermal conductivity of nano-porous silica film

In this work thermal conductivity of porous silica film was studied comprehensively. Silica films with porosity from 21% to 64% were spin coated. It is observed for the first time that the porous silica material has strong anisotropic characteristic. The pores in the higher porosity silica film tend to distribute horizontally. This distribution of the pores in the dielectric film is the main factor that induces the anisotropic characteristic. We proposed a serial-parallel hybrid model to explain the correlation between porosity and thermal conductivity in both in-plane and cross-plane components. The anisotropic characteristic of the thermal conductivity may be accompanied by the anisotropic dielectric constant, which will greatly complicate the RC delay simulation of the circuits.