Experimental Investigations Of Ultra-precision Grinding And Polishing Of Soft-brittle HgCdTe Single Crystals

Mercury cadmium telluride (HgCdTe or MCT) is an outstanding representative of II-VI compounds, and becomes the most important materials for the applications of infrared (IR) devices. This is due to the unique optical and electrical properties of MCT, such as high absorption coefficient, quantum efficiency, wide band gap, as well as fast responses. MCT has been the most significant materials for the IR optoelectronic devices and new-generation IR focus plane arrays (FPA). MCT-based high performance IR devices are widely used in the fields of aeronautics, astronautics, IR remote controls, economies and defenses. MCT is a kind of soft-brittle, as well as hard to machine materials. At present, the machining on MCT wafers is mainly depending on the traditional ultra-precision processes, resulting in low machining accuracy induced by defects, such as micro scratches, embedding, etc. The traditional machining processes are difficult to meet the stringent standards of MCT based high performance IR devices. It is therefore necessary to develop novel ultra-precision machining processes. MCT is selected as the object of this study, owing to the wide applications of MCT in the IR devices, as well as the significance of soft-brittle crystals in ultra-precision machining.Nanoindentation and nanoscratching were conducted on MCT wafers using an in-situ Triboldenter nanoindenter. Machinability at nano-scale of MCT wafers were investigated by the nanoindenter. Nanohardness, elastic modulus, and friction coefficient were obtained under nanoindentation and nanoscratching. Soft-plastic characteristics of MCT wafers were observed under nanoindentation and nanoscratching, which is different from the soft-brittle nature at macro-scale. These benefit for the development of novel ultra-precision machining processes.A novel ceramic bond ultrafine diamond wheel was developed, and nanogrinding was carried out on MCT wafers using the developed diamond wheel. The ultrafine diamond wheel exhibits unique grinding characteristics, and ultra-smooth ground surfaces free of any crack, embedding, and burn damage, were achieved.The chemical mechanical polishing (CMP) slurry used consists of nanometer silica sol and hydrogen peroxide. Systematic CMP experiments of MCT wafers were performed on a ZYP200precision polisher. The effects of mesh size of abrasives, concentration of slurry, pressure, and rotation of CMP plate on the surface roughness and removal rate were studied, and the optimal CMP parameters were achieved.