Liquid Crystal Flow Control Using Microfabrication Techniques

One of the more critical parts of the fabrication of high quality liquid crystal over silicon (LCOS) devices is a controlled means of introducing the liquid crystal (LC) into the gap formed between the silicon backplane and the coverglass. Existing backplane fabrication techniques leave the mirror elements standing proud of the silicon die, causing a disruption to the LC flow-front due to capillary pinning. If the LC flow is not uniform in its spatial extent and the filling speed not tightly controlled, LC alignment defects are generated which affect the optical performance of the device in a detrimental way. To gain better control over the LC filling, a process has been developed in which the inter-mirror trenches are filled with a dielectric material. The self-aligning insulator filled trench (SIFT) process is a novel variation on the lift-off process. It has been developed to fill the inter-pixel trenches, thus producing a smooth planar surface. Different surface preparation processes are compared and it is demonstrated that this new SIFT process leads to even LC spreading, uniform LC alignment and a complete elimination of capillary pinning. The process also provides some insight into the nature of LC surface interactions