Wen-Hao Hsu

Anchoring energy enhancement and pretilt angle control of liquid crystal alignment on polymerized surfaces

We demonstrate enhanced surface anchoring energy and control of pretilt angle in a nematic liquid crystal cell with vertical alignment and polymerized surfaces (PS-VA). The polymerized surfaces are formed by ultraviolet (UV) irradiation-induced phase separation of a minute amount of a reactive monomer in the vertical-aligned nematic liquid crystal. By introducing a bias voltage during UV curing, surface-localized polymer protrusions with a dimension of 100nm and a field-induced pretilt angle are observed. Experimental evidences and theoretical analyses validate that PS-VA has increased surface anchoring strength by two folds and pretilt angle has been changed from 89° to 86° compared to those of a VA cell. The enabling PS-VA cell technique with excel electro-optical properties such as very good dark state, high optical contrast, and fast rise and decay times may lead to development of a wide range of applications.

Vertically Aligned In-Plane-Switching LCD Mode With Novel Pixel Circuits

In this paper, we propose two novel pixel circuits which are able to provide great picture quality at oblique viewing angles. These two pixel circuits are based upon the VA-IPS mode with vertically aligned nematic liquid crystals and in-plane switching electrodes. Comparing to current VA-type LCDs, the VA-IPS mode can be used to improve oblique gamma distortion with its tone rendering distortion index (TRDI) as low as 0.15. With the proposed pixel circuits, we believe the TRDI can be further improved to be less than 0.13. The novel technologies are very likely to be the solution for VA-type LCDs when facing the competition from other display technologies.

Investigation of Response Time of Vertically Aligned In-Plane- Switching LCD Mode

The response time of the vertically aligned in-plane-switching (VA-IPS) mode with respect to different driving voltages is studied. It is found that the rising time, Ton, is highly related to the square of the electric field between the inter-digit electrodes. Since the dielectric torque exerted on the liquid crystal molecules is proportional to the square of the electric field, one can say that it basically dominates the Ton of the VA-IPS mode. However, there’s evidence showing that the total torque perceived by the LC molecules is not simply caused by the voltage applied to the inter-digit electrodes, but also by the flexoelectricity originating from the splay deformation between the electrodes. This leads to the phenomenon that Ton doesn’t monotonically decrease with the increasing dielectric torque.