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.