Kyung Su Ha

P-132: Blue Phases Liquid Crystal Cell Driven by Strong In-Plane Electric Field

The polymer-stabilized blue phase liquid crystals are in the limelight of liquid crystal display area because of its fast response and wide viewing angle with alignment layer free. The conventional device is driven by in-plane field, which has thin electrodes only on bottom substrate and also due to low Kerr constant of LC, the driving voltage of the device is very high. We propose improved electrode structure which has partition-wall shaped electrodes. The proposed device has maximized horizontal electric field so that the driving voltage is decreased. Further, adoption of two transistors can lower driving voltage.

Analysis of optical bounce associated with two-step molecular reorientation in the fringe-field switching mode

The dynamic electro-optic response of liquid crystals (LCs) having positive dielectric anisotropy has been investigated in the fringe-field switching device. Simulation and experimental results show a huge optical bounce near the centre of the pixel electrodes of the device during decaying time of the LC director from an operating voltage. The causality of the said behaviour has been detected as two-step molecular relaxation, first tilt down and then rotating of the LC, which is associated with splay/bend and then twist relaxation, respectively. Reduction of dielectric anisotropy of the used LC material in the device has been suggested as a remedy of reducing optical bounce. The reduction of rotational viscosity also produces optical bounce of lesser duration; however, the intensity of the bounce remains invariant.

High performance low-cost polarizer using depolarization of a polarized light by reactive mesogen

Currently, the polyethlene terephthalate (PET) film challenges to substitute Tri-acetyl cellulouse (TAC) film which is a protection film in a polarizer layer, because of low cost of PET film. On the contrary, the PET film shows an optical problem such that color shift or interference optical pattern in oblique direction can occur because the film is made with the lamination process, which induces high phase retardation. In this paper, we propose a color shift free low cost polarizer by polymerization of random oriented reactive mesogen (RM) on the PET film. We calculate the viewing angle performance of the polarizer with the conventional PET film, with the TAC film and with the proposed PET film. As a result, we confirm that the proposed optical configuration can satisfy the optical performance equivalent to that of conventional TAC film uses in addition to the cost-down.

Surface Polymer Stabilization by Reactive Mesogen in Optically Compensated Splay Mode

We have studied the optically compensated splay (OCS) mode applied to polymer stabilization technique using polymerization of reactive mesogen (RM) to reduce or eliminate critical voltage, setting voltage, and phase transition time from bend to splay state. The pretilt angle of almost vertically aligned liquid crystal directors could be lowered through the polymerization of UV-curable RM and applied voltage, at surfaces of vertical alignment layers. To confirm initial stable splay state, we investigated electro-optic characteristics according to concentration of RM in this paper.

Abnormal behaviour in colour tracking characteristics of the fringe-field switching liquid crystal display

Colour tracking behaviour is observed in most liquid crystal displays. In in-plane switching and vertical alignment devices, the colour chromaticity in the normal direction changes linearly from bluish- to yellowish-white as the grey level is increased from the dark to white state. Interestingly, abnormal behaviour in colour tracking is observed in fringe-field switching devices using a liquid crystal with positive dielectric anisotropy, such that the colour chromaticity changes from bluish to yellowish up to a certain grey level, then turns around and becomes bluish-white as the grey level is further increased to the fully white state. According to our theoretical and experimental results, this ‘turn around’ effect in the colour tracking of the fringe-field switching mode is associated with the generation of a tilt angle of the liquid crystal molecules with increasing voltage in the electrode position where the light modulation is associated with the polarisation rotation.

Study of Optical Bounce According to Electrode Structure in the Fringe-Field Switching Mode Using the Negative Liquid Crystal

The switching response behavior of negative dielectric anisotropic liquid crystal in the fringe-field switching (FFS) mode was investigated with respect to the pixel electrode positions. When the applied voltage relaxes to lower voltage, optical bounce was observed at the edge region of pixel electrode. Based on the simulation results, we have proposed a promising molecular behavior associated with optical bounce, which originates from the reorientation process of LC director that is in over-twist state associated with tilt angle. Experimental results also show the optical bounce during switching-off time.

P‐129: Study on Electro‐Optic Characteristics According to Length between Pixel Electrodes in the Fringe and In‐Plane Field Switching Mode

We have studied electro-optic characteristics of high performance liquid crystal display using combined fringe and in-plane horizontal electric fields, named as fringe and In-plane switching (FIS). The strong electric fields cause more liquid crystals to reorient above and between the pixel electrodes. Moreover, the operating voltage of FIS mode was decreased by using two thin film transistors (TFTs). To suggest novel structure of FIS mode, electro optic characteristics are analyzed as a function of length between pixel electrodes compared to IPS and FFS mode. Consequently FIS mode shows not only higher transmittance but also lower operating voltage than those of IPS and FFS mode while keeping wide viewing angle.

Study of Optimal Phase Retardation According to Electrode Structure in the Fringe-Field Switching Mode Using the Negative Liquid Crystal

The fringe-field switching (FFS) mode has unique characteristics such as high transmittance and wide viewing angle and its electro-optic characteristics strongly depend on pixel electrode width (w) and distance (l) between them. In this study, optimal phase retardation of the FFS mode using a liquid crystal (LC) with negative dielectric anisotropy depending on pixel electrode structure was investigated based on the simulation. The results shows that when the width of the pixel electrode and distance between electrodes are 3 μm and 4.5 μm, respectively, the cell shows transmittance 0.87 with optimal phase retardation value of LC cell 0.36 μ. As w and l are decreased to 1 μ and 1.5 μ, the cell shows transmittance of 0.90 with optimal phase retardation of LC cell 0.40 μ, indicating that the light modulation method is changed according to electrode structure.