Jae-jin Lyu

Stabilization of the liquid crystal director in the patterned vertical alignment mode through formation of pretilt angle by reactive mesogen

In the patterned vertical alignment (PVA) cell in which multidomains are formed from the perfect vertical alignment through an oblique field only, the formation of disclinations between liquid crystal (LC) molecules is inevitable in the presence of an electric field, which lowers transmittance and the response time. In the proposed PVA device, the pretilt angle is formed in four different directions through the polymerization of an UV curable reactive mesogen monomer at the surface. In this way, the reorientation of LC responding to an electric field is well defined, and thus the device shows reduced threshold voltage and much improved response time in all gray scales.

Recent Trends on Patterned Vertical Alignment (PVA) and Fringe-Field Switching (FFS) Liquid Crystal Displays for Liquid Crystal Television Applications

This paper reviews the recent trends on super-patterned vertical alignment (S-PVA) and fringe-field switching (FFS) technologies for liquid crystal display (LCD)-television (TV) applications. For PVA mode, Samsung originally announced S-PVA technology in 2004 to enhance off-axis viewing quality of conventional PVA mode. S-PVA is a new technology which enables screen quality advantages over super-in plane switching (S-IPS) and multi-domain VA (MVA), including high transmittance, >2300:1 contrast ratio, and wide viewing angle with no off-axis image inversion. This paper explores and updates Samsungs latest developments toward its goal of ultimate LCD-TV performance. For FFS mode, the technology appeared in 1998 by HYDIS and now it has been commercialized in all kinds of display applications, implying its technical importance. This paper reviews recent developments and performance of LCD-TV using the FFS mode based on published papers and our knowledge.

Surface-Modification on Vertical Alignment Layer Using UV-Curable Reactive Mesogens

The patterned vertical alignment (PVA) liquid crystal (LC) mode shows a wide viewing angle and a perfect dark state at a normal direction. However, it is inevitable to avoid the formation of disclinations and the movement of defect points during stabilization of LCs reorientation. It is due to fact that the LC directors tilt downward in different directions with collisions between them by the fringe-electric field. Consequently, the transmittance decreases and the response time gets slower. In order to overcome this barrier, the pretilt angles in four different directions are introduced on the substrates utilizing UV-curable reactive mesogen (RM) monomers. According to our studies, concentration of RM, UV curing condition, and applied voltage to the cell are critical to achieve an optimized surface-modified PVA mode which provides the well-defined reorientation of the LCs with respect to an electric field. Moreover, morphological behaviors on surface of substrate depending on curing conditions were investigated in order to confirm the existence of the stabilized polymer.

Trapping of defect point to improve response time via controlled azimuthal anchoring in a vertically aligned liquid crystal cell with polymer wall

Conventional multi-domain vertically aligned liquid crystal (LC) cells have defect points due to the collision of LC directors during the formation of multiple domains. In addition, the location of defects changes with time resulting in a slow response time. This paper proposes a robust vertically aligned LC cell, where the LCs are locked by polymer walls, and the azimuthal anchoring on the surface of the alignment layer is controlled by the polymerization of a UV curable reactive mesogen monomer. As a result, the defect points are trapped at a single position, resulting in a greatly improved response time.

34.3: A Novel Charge-Shared S-PVA Technology

A charge-shared super patterned-ITO vertical alignment (CS S-PVA) LCD mode is proposed. CS S-PVA controls the voltage ratio between two sub-pixels by a unique charge-sharing topology, resulting in improved off-axis image quality and transmittance increase without any side effects. Moreover, the new S-PVA LCD mode is free of image-sticking. Operating schemes and display performance of CS S-PVA are presented.

P-93: High Performance 17.0″ SVGA OCB Panel with Fast Initial Bend Transition

Recently, the vigorous researches on the moving picture quality of TFT-LCDs have been made to overcome their drawbacks in replacing CRTs for TV application. Among them, the fast response OCB mode is thought to have the highest potential for TV application, even though its image quality still needs to be improved. In this regard, we have optimized the cell parameters of OCB mode to get wide viewing angle, high contrast ratio and transmittance as well as the fast response time. Based on these parameters, we have improved image qualities remarkably by adopting these to 17.0″ SVGA proto-panel, which shows the contrast ratio over 250, viewing angle over 80 degree for all direction except rubbing direction, response time under 7 ms including inter-gray scale and the transmittance of 90% of TN mode. Especially, by adopting new driving scheme, we considerably reduced the initial bend transition time, which is known as one of drawbacks in OCB mode. We are continuing further research to get the competitive image quality and good reliability, which is comparable to commercially used PVA or IPS mode.

Surface Polymer-Stabilized Vertically Aligned Liquid Crystal Cells with Various Polymer Wall Structures

Vertically aligned liquid crystal (LC) surrounded by polymer wall, which is also known as locked-super homeotropic (LSH) mode has several advantages such as rubbing- and spacer-free, wide-viewing angle and stable LC dynamics against external pressure. However, the LSH mode shows slow response time due to the instantaneous collision between the LC molecules when a vertical electric field is applied, because the reorientation of chiral doped vertically aligned LC is only determined by the polymer wall. We found that the slow response time can be improved by surface polymer-stabilized technique where surface pretilt angle is defined on alignment layers. This technology can be used in any shape of polymer wall. (PACS 42.79.Kr, 85.60.-q).

38.3: Top-COM-Based PLS Mode for Embedded Touch Screen Applications

We have successfully demonstrated a top-com based PLS (plane to line switching) LCD mode by adopting a low-temperature passivation layer above the organic layer. The top-com based PLS mode increased the panel transmission by 60% compared to the conventional bottom-com PLS structure. A digital switching-type touch screen function has been embedded inside the panel, showing excellent sensitivity of 20gf. These results were achieved by a new additional column spacer layer and a passivation trench structure. This technology can be applied to wide angle of view hand-held phones, personal digital assistants (PDAs), and tablet PCs.

Electro-Optic Characteristics of the Fringe Field Switching (FFS) Mode Depending on Thickness of Passivation Layer between Pixel and Common Electrodes

We have studied electro-optic characteristics as a function of passivation thickness existing between common electrode and pixel electrodes in the fringe-field switching (FFS) mode using the LC with positive dielectric anisotropy. A steep increase in the transmission is observed with increase in the passivation layer from to and thereafter it almost saturates over the of passivation layer. This saturation is mainly associated with correlation between transmittance at the center region of pixel electrode and at the center region between pixel electrodes. From the results, optimal thickness of passivation layer can be defined.

P‐197: Improved Patterned VA Mode for Fast Response Time by Using Strong Fringe‐Field Effect

We propose an improved pattern structure that can reduce the response time by using strong fringe field in the pattern vertical alignment LCD. We applied an additional buried electrode in the PVA LCD so that we could increase the fringe field on the edge of the electrode. The strong fringe field on the edge of the electrode helps the liquid crystal director in the bulk area to have an appropriate orientation quickly when the voltage is applied. As a result, we could improve the response time effectively. We used the software TechWiz LCD in order to calculate the director configuration and the response time. From the simulation results, we have found that the proposed structure exhibited 74.2% improvement in response time compared to the conventional structure in calculation.