Liquid crystal flow control using microfabrication techniques

One of the more critical parts of the fabrication of high quality liquid cr ystal over silicon (LCOS) devices is a controlled means of introducing the liquid crystal (LC) into the gap formed between the silicon backplane and t he coverglass. Existing backplane fabrication techniques leave the mirror e lements standing proud of the silicon die, causing a disruption to the LC f low-front due to capillary pinning. If the LC flow is not uniform in its sp atial extent and the filling speed not tightly controlled, LC alignment def ects 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 dielect ric 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 interpixel trenches, thus producing a smooth planar surface. Different sur face preparation processes are compared and it is demonstrated that this ne w SIFT process leads to even LC spreading, uniform LC alignment and a compl ete elimination of capillary pinning. The process also provides some insigh t into the nature of LC surface interactions.