Study Of Processing And Properties Of SiO₂ Films Prepared On Sapphire Substrate

Sapphire has such excellent properties that it is superior to other current and emerging materials for window and dome applications. However, the current states of production and process of sapphire are not very well. The c-axis compressive strength of sapphire decreases dramatically at elevated temperature and the optical transmission cannot satisfy the demand of application and design. In order to meet the need for applications of high-speed or high-temperature, the anti-reflective and protective films need to be prepared on the sapphire surface. Silicon dioxide (SiO2) are promising anti-reflective films with good physical, chemical properties and good adhesion to sapphire. Great progress has been made in the researches about SiO2 anti-reflective and protective films overseas. But no domestic work has been done on SiO2 optical and protective films. Researches of the paper mostly concentrate on design and preparation of anti-reflective and protective films of SiO2 on sapphire. What's more, we have studied the properties of the films. The work is base for SiO2 used as anti-reflective and protective coatings on sapphire dome. The main contents and results are listed as follows:With the help of OPFCAD software, anti-reflective and protective films of SiO2 and SiO2/Si are designed on the sapphire substrate and analysis of structure sensitive factor and variation are done. The results of design explain that if SiO2 films deposited on the surfaces of sapphire the average transmittance in 3~5 m waveband can exceed 97%, which can meet the requirements of missile dome in infrared application.SiO2 films are prepared on silicon substrates in order to get the functions of the main experiment parameters such as RF power, gas flow, vacuum gas pressure, target-substrate distance and substrate temperature on deposition rate of films. The optimized parameters ranges are obtained by considering films deposition rate, composition and structure.The designed films of SiO2 and SiO2/Si are prepared on sample and hemisphere dome of sapphire by radio frequency magnetron reactive sputtering method. The average transmittance at a wavelength of 3~5 m of sapphire coated with one layer of SiO2 antireflective films on two sides can reach 96.43%. So as to the transmittanceof coated sapphire can satisfy the demand of window and dome applications.XPS analysis as well as XRD and high temperature heat treatment are made. XPS results confirm the formation of SiO2. XRD results show that deposited SiO2 films are amorphous. Heat treatments explain that films are still amorphous as the temperature of heat treatment reach 800 .