Thermal Stability of Mid-infrared SiO₂ Thin Films Deposited by Dual Ion Beam Sputtering Method

SiO₂ films are deposited on Si and sapphire (α-Al₂O₃) substrates by Dual Ion beam sputtering method. The microstructure, surface morphology, residual stress and optical stability of SiO₂ coating in the wavelength of 0.4~1.2 μm and 3~5 μm are investigated, systematically. The results indicate that the residual stress goes through a local minimum value at ~400℃. There is a close relationship between the optical constant and the surface conditions, residual stress, microstructure of SiO₂ film. As the temperature increases up to 1 000℃, SiO₂ film can keep well thermal stability without notable damage morphology. The result can give some guidance for designing the optical coatings used in harsh environments.