Improved liquid crystal pretilt angles by patterned dual alignment coating structures.

The pretilt angles for the optically compensated bend (OCB) mode liquid crystals have been improved using novel patterned dual alignment coating structures in this study. The transition from the splay configuration to the bend configuration can thus be effectively reduced. The dual alignment coating structures consisted of a horizontal alignment polyimide (PI) and a patterned vertical alignment liquid crystal polymer (LCP). Three patterning masks were designed for the photolithography process. The pretilt angles were demonstrated to be increased to 34 degrees for the triangle lattice array-patterned cells. It became 31 degrees for the square lattice array-patterned cells, and 24 degrees for the honeycomb lattice array-patterned cells. The improved pretilt angles were illustrated by the force balance model that can be predicted by the LCP area ratio. The effective control over the pretilt angle could improve the response time to 2 ms when the voltage was ramped up to 5.5 V for the OCB mode liquid crystal devices.

Intermediate pre-tilt angle control by a composite alignment thin film structure for liquid crystal displays.

We designed a patterned composite alignment thin film structure using a horizontal alignment polyimide (PI) layer and vertical alignment liquid crystal polymer (LCP) pillars. The LCP polymer precursor concentration was varied at 0-10% and the pillars were introduced by a photolithography process. Both single-sided and double-sided liquid crystal display cells were assembled for a series of electro-optical characterization techniques. The horizontal PI alignment layer alone had a designated control of the pre-tilt angle of 7 degrees after the prescribed mechanical rubbing process. The pre-tilt angle was improved to 24 degrees when the LCP precursor concentration was 5%. It was further increased to 61 degrees at the concentration of 10%. In addition, the study on the electrical response time and gray level variation demonstrated promising results for potential applications. The field-on response time was only 2.79 ms and the field-off response time was 0.35 ms for the double-sided liquid crystal display cells using a ramping voltage of 5.5 V. The effective control of the cell pre-tilt angle suggested that the display power consumption and response time would be greatly improved.