Surface topography and alignment effects in UV-modified polyimide films with micron size patterns

Abstract

The characteristics of UV-modified polyimide CBDA-BAPP films for liquid crystal (LC) alignment have been investigated. Linearly polarized ultra-violet laser light (lambda = 325 nm) was used to expose the film. The LC direction of this film tends to be oriented parallel to the surface and perpendicular to the polarization direction of the laser light. The uniformity of the LC direction stabilizes when the exposure time exceeds a certain length. From the atomic force microscope investigation, we find that the films have been dented at the places exposed to the laser light. When a mask with striped pattern was used during exposure, we observed grooves in the exposed regions. The grooved patterns agree well with the calculated diffraction patterns caused by the mask, however, the groove direction has no effect on the alignment of the LCs. In our experiments, we also achieved LC alignment patterns as small as 2 mum using UV exposure with a mask.