Optical And Surface Properties Of Arc Ion Plating Aluminum Nitride Thin Films

AlN has been studied for more than half a century.With the development of material fabrication techniques,AlN thin films are used more and more widely.Since AlN film has wide bandgaps,high heat resistance and good optical properties,it is often used as optical material to make various optical devices.AlN thin film is an excellent insulating film with excellent dielectric properties,especially suitable for high temperature insulation.In addition,AlN thin films have excellent piezoelectric properties and are ideal candidate materials for piezoelectric devices.It is also the preferred material for surface acoustic wave(SAW)devices.High-quality AlN has unique advantages as an optical material.Therefore,it is significant to study transmittance,optical constants,hydrophobicity and corrosion-resistance of AlN films.In this work,AlN thin films were prepared on silicon,stainless steel and glass by arc ion plating by changing deposition parameters such as time,nitrogen content,oxygen doping,substrate temperature and working pressure,and optical properties,surface hydrophobicity and corrosion resistance of the films were studied.It is found that post-annealing and aging-in-air play profound roles on the properties of the AlN films.The results show that a large number of metal particles are formed on the surface of AlN thin films prepared by arc ion plating.Both size and quantity of the macro-particles on surface of the AlN thin films increase with increasing deposition time.The larger the surface roughness,the larger the surface contact angle is,resulting in the better the hydrophobicity.In addition,as the film was aged in air,it was found that the metal content in the film was reduced.As a result,the surface energy was reduced,and the contact angle was larger,showing more hydrophobicity when compared with the as-deposited state.At the same time,the corrosion resistance of the film is enhanced.It is indicated that a better hydrophobicity is accompanied with a better corrosion resistance.AlN samples were prepared by setting different deposition time.The study has obtained the following results.(1)Less transmittance of the AlN films is presented as deposition time is increased.Reduction of transmittance is due to the coarse surface and the existence of the macro-particles,which are mainly formed by metallic Al.Therefore,one may elevate transmittance of AlN fims either by reducing Al content within the films through nitriding or oxidation.(2)The nitrogen content is another key parameter.High transmittance of the AlN film can be obtained at high the nitrogen contents.(3)Substrate temperature can enhance reaction between Al and N₂.Transmittance of the AlN films increases with increasing substrate temperature,but further increase of temperature results decreasing transmittance.(4)During the film deposition,pressure is an important parameter determining the mean-free-path of gas molecules and thus controlling the film quality.The transmissivity of the films increase with increasing deposition pressure.(5)Oxygen doping is an important parameter which affects the optical properties of the AlN films,too.In the experiments,oxygen was inlet together with nitrogen during deposition.Through the studies above,the following conclusions can be drawn out:Reducing the content of metallic Al on the surface either by nitriding or by oxidation may enhance light transmittance of the AlN thin films.Meaning while,hydrophobicity and corrosion-resistance of the films can be elevated since the surface energy is reduced.