Al-Si-N/a-SiN:H thin-film coating for polycarbonate glazing applications

To improve the scratch resistance and UV weatherability of polycarbonate (PC), a protective layer consisting of a transparent Al-Si-N thin film of high hardness and a UV-blocking a-SiN:H (hydrogenated amorphous Si-N) thin film was studied using inductively coupled plasma-assisted reactive magnetron sputtering at room temperature. Transparent and hard Al-Si-N thin films with Si contents of 5-45 at% were deposited and characterized. Further, to protect PC from UV radiation below 300 nm in wavelength, UV-blocking a-SiN:H thin films were deposited at different H₂ flow rates ranging from 2 to 8 sccm. The average transmittance of 460 nm thick Al-Si-N thin films was measured to be greater than 80% in the visible spectral range, and the maximum hardness of 31 GPa was obtained at 24 at% Si content. The UV transmittance of 140 nm thick a-SiN:H thin films was found to be less than 3% at wavelengths shorter than 300 nm. The double-layer structure of Al-Si-N (460 nm)/a-SiN:H (140 nm) showed a hardness of 29 GPa and an average transmittance of 78% for visible light along with a UV transmittance of less than 3%. In this study, the protective coating layer deposition for PC glazing applications was developed and characterized.