Ultrasonic-hydration Polishing Method On Sapphire Optical Micro Cavity

Sapphire is a kind of brittle and hard material, with the capacities of high melting point, high hardness, resistance to electromagnetic interference, stable physical and chemical performance, and working in the bad environment, etc. Sapphire optical microcavity has compacter struture, saves time for assembly, and has no assembly error, which can make the traditional optical system realize miniaturization, integration and array. However, the microcavity structure which is formed by laser etching, which machining accuracy and surface roughness cannot reach the requirements of optical performance. Therefore, a new kind ultra-precision polishing method is needed to realize the super smooth surface. In the view of past researches for sapphire polishing methods, the research object is mainly planar substrate, and there is few studies for polishing method of tiny structures, as well as for surface modification of sapphire, which is to lower surface hardness in order to improve the surface quality and material removal efficiency. Basing on the requirement of the above subject, this paper put forward a kind of non-contact ultrasonic assisting hydration polishing method, which can solve the difficulty of material processing and the problem of low efficiency of polishing. At the same time, it solves the difficulty of polishing microcavity structure. In this paper, the main work and contributions are as follows.Firstly, the paper put forward the plan of surface modification, conducted researches on timeliness of the modification, and study the influence of surface roughness on surface modification. Basing on the chemical properties of sapphire, hydration modification and hydrophilic modification plan were raised to compare the ability of surface modification. When the wafer was placed after a period of time and measured hardness again. The research found that the modification had a certain timeliness. At the same time, in several modification tests on the wafers with different surface roughness, it was found that the rougher the surface is, the easier to modification, and the greater the reduction in hardness.Then, the material removal model was established basing on Contact mechanics. Material removal can be divided into cutting removal and deformation removal. Sapphire, as a kind brittle and hard material, the main means of material removal is deformation removal. Basing on the theory above, a material removal model for one singe abrasive particle was established. The speed of abrasive particle and its size promote material removal. The ultrasonic vibration material removal model was also established, in this circumstance the material removal under the ultrasonic vibration is greater through comparison.Next, ANSYS- Fluent was used to analyze the polishing liquid fluid parameters in the micro cavity. In according to the requirements of project, this paper designed basic shape and structure of micro cavity, created micro cavity model through the Gambit and imported into ANSYS Fluent software setting up the different inlet parameters, getting the results of velocity and pressure distribution. By the numerical simulation of the discrete phase, polishing abrasive movement under different inlet velocity were simulated. At the same time the condition under ultrasonic vibration was investigated, the velocity, pressure and motion trajectory got more uniform, proving that the ultrasonic vibration assisted polishing can gain better polishing quality.Finally, the ultrasonic assisted polishing experiments were conducted. A Two degrees of freedom ultrasonic vibration cutting device was transformed to clamp sapphire wafers. Under different vibration frequency and power, wafers’ displacement were tested. Different modification methods and experimental parameters on the polishing were studied, and the influence of particle size on the polishing quality. At the same time, the polishing quality in the different areas of the microcavity was compared.