Nano porous SiO2 has been studied for tens of years,for its promising thermal,optical and electrical usage [1,2].In this work,mesoporous SiO2 film was fabricated by spin-coating through collosol precursor,which was catalyzed by HCl,NH4OH and NH4F respectively.SiO2 films were deposited at different viscosities in the range of 0 cp to 25 cp.Surface morphologies of all samples were measured by SEM(scanning electron microscope).They showed distinct morphologies that as viscosity increased,SiO2 film turned from porous state to network state,which was shown in fig.1(a-f).when viscosity reached a certain value,SiO2 film became dense like.Transmittance and refractive index were measured by ellipsometer.Permittivity was measured by Agilent 4294 Impedance Analyzer.properties.Surface morphology,electrical and optical properties were investigated.Under more precise control,an optimal deposition parameter was found to obtain low-k transparent mesoporous SiO2 film with pores of 300 nm in diameter and 600 nm in thickness,shown in fig.1 g.Structural applications such as template and mask were also investigated.Great progress has been achieved for further attempt to fabricate circular RRAM units under the mask of porous SiO2 film.