Study of assembly processes for Liquid Crystal on Silicon (LCoS) microdisplays

This paper involves the development of several assembly processes for Liquid Crystal on Silicon (LCoS) microdisplays. The critical processes that were investigated include lamination of cover glass on silicon and a liquid crystal filling process. For the lamination process, a tool and process was designed and developed. The critical objective behind the development of the lamination process was to attach cover glass on silicon tile and to achieve a cell gap of 3 μm between them. The gap was achieved and verified with various measurement techniques. The lamination process is similar to the fluids problem of flow between parallel plates. An analytical model was developed to estimate the time needed to achieve a 3 μm cell gap by applying different pressures on the cover glass. The analytical model proved to be a guideline in developing the lamination process. The next process in the assembly is filling of liquid crystal (LC) material in the cavity between the cover glass and silicon. For the LC filling, a tool and process was designed and developed. The process works on the principle of flow of fluid in a capillary. The flow rate was enhanced by applying vacuum in the cavity by the designed filling process. To estimate the time needed to fill a cavity by applying a certain vacuum pressure an analytical model was developed. From the model it was observed that the fill time is a function of gap between glass and silicon, vacuum pressure applied, cavity length and the viscosity of material being used for filling.