Preparation and characterization of nanoporous silica film

Crack-free homogeneous nanoporous silica films on a silicon wafer have been synthesized via supercritical drying of wet gel films that were obtained by spin coating the polymeric silica sol, followed by aging in isopropanol(IPA) solution. Polymeric silica sol was prepared using an acid/base two-step procedure with tetraethoxysilane (TEOS) as precursor. The optimized viscosity of silica sol for spinning coating was in the range of 9～15mPa·s. Thickness of the nanoporous silica films was 400～1000nm; The refractive index was 1.09～(1.24) and the dielectric constant was 1.5～2.5. The nanoporous silica films show three-dimensioned network, cross-linked by the primary particles which sizes distribute between 10～20nm.