Solution processed SiNxCyOz thin films thermally transformed from silicon oxide/melamine hybrid system

•A solution-processable dielectric layer was fabricated through sol–gel process.•A fabricated hybrid film has an excellent optical transmittance and hardness.•The hybrid film was converted into an inorganic compound in the form of SiNxCyOz.•The dielectric constant of heat-treated specimen was measured lower than 2.0.

In this study, a solution-processable precursor of melamine and silicon oxide, was prepared and thermally converted into inorganic thin films of SiNxCyOz. Using tetra-ethoxysilane and hydroxyl-methyl-melamine, a transparent coating with a high loading content of silica of up to 50% was achieved through the hydrolysis/condensation reactions, which provided a transmittance of 85.1% (thickness of 1.5 ± 0.2 μm) and hard coating grade of 4H pencil test. When the silica/melamine coating was further heat-treated up to 900 °C in an inert environment, the organic melamine was converted into an inorganic compound composed of Si, N, C, and O atoms in the form of SiNxCyOz. The relative compositions of films varied with the heat-treatment temperature, e.g., providing SiN0.03C0.59O1.87 for the thin film heat-treated at 700 °C. The resulting inorganic thin films were mechanically strong and optically shiny with a low root mean square of roughness (< 1.0 nm) giving dielectric constants varying from 2.75 to 1.82 with heat treatment temperature that could be used as low-k materials in commercialized optoelectronic devices.