Study On Antireflection And Selfcleaning Of Sapphire For Intelligent Terminal Window Appliations

Sapphire has became the development trend of optical materials, especially for moving window. Sapphire has a lot of advantages, such as high hardness, corrosion resistance, and strong ability to resist radiation. But it cannot meet the requirement of high transmittance, and the wettability of sapphire is also poor. SiO₂ film as one of antireflection materials was always used for sapphire optical window, but because the thermal expansion coefficient between SiO₂ and sapphire are different, that will lead the film be falling off easily. In order to overcome the problem, HfO₂/ SiO₂ double layer antireflection coating were prepared on sapphire. At the same time, on the other side of sapphire the subwavelength structure is epitaxial grown on sapphire surface to improve the performance of sapphire optical window.The theoretical calculation results by Essential Macleod showed that SiO₂ / HfO₂ layer can be used to improve the transmittance of sapphire in the visible band. And the film refractive index change will also have a certain impact on the transmittance of sapphire. At the same time, the transmittance of subwavelength structure was also simulated by Rsoft CAD software, the result showed that the transmittance determined by the parameters of the structure（filling factor, depth, period）.The performance characterization result of sample showed that the middle layer obviously enhance the combining ability of the film, and also can obviously improve the transmittance in the visible band.The AAO mask was preparaed by the method of anodic oxidation, and then we use the inductively coupled plasma etching（ICP） equipment to make the Aluminum graphics, and also researched the etch process. The best process of etching Aluminum is that, gas pressure 3mTorr, etching power 100 W, gas flow ratio of Cl2 and Ar is 1:1. And finally use the method of solid phase epitaxy to change it into the subwavelength structure of sapphire.Sapphire double-sided anti-reflection structure makes the transmittance in the visible band of the sapphire relative increase by 9.1%. At the same time we also measured the influence on the subwavelength structure’s wettability. The result showed that subwavelength structure can greatly change the wettability of sapphire, it can change the wetting angle of sapphire from 60.9 ° to 125.4°.