Cell gap optimization and alignment effects in reflective PDLC microdisplays

In general this reduction of the cell gap improves the electro-optic proper ties of a polymer dispersed liquid crystal (PDLC) in reflective microdispla ys. At the interface between the PDLC film and the silicon backplane or cov er glass, the LC molecules have a different alignment from those in the dro plets in the interior of the PDLC film. This is shown by microscopic observ ations and the temperature dependency of the brightness and capacitance of the displays. The influence of this alignment effect increases for smaller cell gaps and has an impact on the properties of the PDLC. During and after the filling of the displays, a compression and expansion of the cell gap t akes place, respectively. If the curing of the PDLC takes place before the expansion of the cell gap has stopped, transparent areas in the PDLC film m ay occur some time after curing. This effect is caused by the expansion of the cell gap after curing resulting in the vertical alignment of LC molecul es. This can be concluded from microscopic observations and from measuremen ts of the refractive index and cell gap.