Showing papers by "Seung Hee Lee published in 2008"

Liquid crystal display using combined fringe and in-plane electric fields

Abstract: A high performance liquid crystal display using combined fringe and in-plane horizontal electric fields is proposed. The strong electric fields cause more liquid crystals to reorient almost in plane above and between the pixel electrodes. As a result, the operation voltage is lower and transmittance is higher than those of fringe field switching and in-plane switching modes, while preserving a wide viewing angle. Such a high performance device is particularly attractive for large panel liquid crystal displays.

Thin cell fringe-field-switching liquid crystal display with a chiral dopant

Abstract: A fringe-field-switching (FFS) liquid crystal display (LCD) using a thin cell doped with a reverse-handed chiral compound is proposed. Such a FFS LCD exhibits a fast response time (∼8ms), high transmittance (>90%), low operating voltage (5Vrms), and intrinsically wide viewing angle. Its application for LCD televisions in order to reduce image blurring is emphasized.

Effect of magnitude of dielectric anisotropy of a liquid crystal on light efficiency in the fringe‐field switching nematic liquid crystal cell

Abstract: The light efficiency of most well‐known nematic liquid crystal (LC) modes, such as twisted nematic and in‐plane switching, depends only on the cell retardation value, irrespective of the cell gap and dielectric anisotropy of the LC. Interestingly, the light efficiency of a homogenously aligned nematic LC cell driven by a fringe electric field, termed the fringe‐field switching (FFS) mode, is found to be dependent on the magnitude of dielectric anisotropy, such that an LC with high dielectric anisotropy results in lower light efficiency than that of an LC with low dielectric anisotropy.

Viewing angle switching of patterned vertical alignment liquid crystal display

Abstract: Viewing angle control of a patterned vertical alignment (PVA) liquid crystal display using only one panel is investigated. In conventional PVA modes, a vertically aligned liquid crystal (LC) director tilts down in four directions making 45° with respect to crossed polarizers to exhibit a wide viewing angle. In the viewing angle control device, one pixel was divided into two sub-pixels such that the LC director in the main pixel is controlled to be tilted down in multiple directions making an angle with the polarizer, playing the role of main display with the wide viewing angle, while the LC director in the sub-pixel is controlled to be tilted down to the polarizer axis, playing the role of sub-pixel to the viewing angle control for the narrow viewing angle. Using sub-pixel control, light leakage or any type of information such as characters and image can be generated in oblique viewing directions without distorting the image quality in the normal direction, which will prevent others from peeping at the displayed image by overlapping the displayed image with the made image.

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

Abstract: 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.

Viewing-angle controllable liquid crystal display using a fringe-and vertical-field driven hybrid aligned nematic liquid crystal

Abstract: Viewing-angle controllable liquid crystal display (LCD) without using an additional panel or pixel division is proposed. In the device, hybrid aligned nematic liquid crystal using a liquid crystal with negative dielectric anisotropy is used. The device shows narrow viewing angle when it is driven only by fringe-electric field, however, it exhibits wide viewing angle if driven by vertical- as well as fringe-electric field. With the approach, the viewing angle of the LCD can be controlled from 120° to 20° in horizontal direction.

Viewing Angle Switching in Fringe-Field Switching Liquid Crystal Display

Abstract: We propose a pixel structure of viewing angle switchable liquid crystal display (LCD) associated with fringe-field switching (FFS) mode using one panel. In the device, one pixel is composed of main- and sub-pixel, in which the former has a role of image expression using the FFS mode and the latter has a role of viewing angle switching using the electrically controllable birefringence (ECB) mode. Consequently, before applying voltage to the sub-pixel, the device shows wide viewing angle, however, when the proper voltage is applied to the sub pixel, the displayed image is blocked in an oblique viewing angle.

Wide-view and sunlight readable transflective liquid-crystal display for mobile applications.

Abstract: A wide-view single cell gap transflective liquid-crystal display (TR-LCD) using the fringe field switching effect is proposed by incorporating a quarter-wave in-cell-retarder below the liquid-crystal (LC) cell in the reflective part. By optimizing the angle between the electrode stripes and the LC rubbing direction in the transmissive and the reflective regions, this TR-LCD exhibits a high optical efficiency and good match between the voltage-dependent transmittance and reflectance curves. Without using any phase compensation films, this TR-LCD exhibits a wide view with 10:1 contrast ratio over a 60° viewing cone in the transmissive mode and over a 40° cone in the reflective mode, which is adequate for mobile displays.

Switching of off-axis viewing quality in twisted nematic liquid crystal display by controlling phase retardation of additional liquid crystal layers

Abstract: This study examined the viewing angle control of twisted nematic liquid crystal displays (TN-LCDs). Conventional TN mode has intrinsic characteristics, such as a narrow viewing angle along the vertical direction and a relatively wide viewing angle along the horizontal and diagonal directions. Our study shows that the viewing angle of the TN-LCD can be made wider and smaller than that of a normal TN cell by adding one or two homogeneously aligned liquid crystal layers between the TN cell and polarizers, and controlling their retardation with an applied voltage.

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

Abstract: 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).

Synthesis and Characterizations of Positive-Working Photosensitive Polyimides Having 4,5-Dimethoxy-o-Nitrobenzyl Side Group

Abstract: To synthesize a new positive-working photosensitive polyimide, alkali-soluble polyimide containing carbox-ylic acid side group was synthesized, and parts of its carboxylic acid groups were esterified with 4,5-dimethoxy-2-nitrobenzyl bromide. The chemical structure of the resulting polymer was characterized by

Reduction of Viewing-Angle Dependent Color Shift in a Reflective Type Cholesteric Liquid Crystal Color Filter

Abstract: The reflective type color filter for the liquid crystal displays (LCDs) was produced using cholesteric liquid crystal monomers whose phase is characterized by the unique optical features of selective reflection. Periodic micrometer scale hemi-spherical photoresist (PR) patterns were formed on glass substrates by thermal reflow method after photolithography. Cholesteric color filter films for red, green, and blue light reflections were then produced and the viewing angle dependence was investigated and compared with that of reflected light on the non-patterned substrates. Computer simulations using "LightTools" were also carried out, and it was confirmed that the color shifts were much smaller on the patterned substrates by bare eyes and Commission Internationale de'Eclairage (CIE) chromaticity coordination analysis qualitatively.

Electrophysical Properties of an Antiferroelectric Liquid Crystal MOPB(H)PBC

Abstract: Spontaneous polarization (P s ), rotational viscosity (η) and response time (τ) have been determined as a function of temperature at different electric fields for an antiferroelectric liquid crystal [4,4-(1-methyloctyloxycarbonyl)phenyl]-4′-[3-(butanoiloxy)prop-1-oxy]biphenyl carboxylate (MOPB(H)PBC). Spontaneous polarization, rotational viscosity and response time increase with decrease in temperature. Critical electric field (the field at which the spontaneous polarization saturates) was found to be increased with decrease in temperature.

Electrokinetic elongation and subsequent dispersion of carbon nanotubes in liquid crystal medium

Abstract: This work reports the elongation and subsequent dispersion of carbon nano tube (CNT) aggregates driven by the electric field in a liquid crystal (LC) medium. Longitudinal and cross sectional views of CNT aggregates were investigated in homogeneously aligned cell driven by in-plane field and homeotropic aligned cell, respectively. CNT aggregates firstly were aligned toward field line by dielectrophoretic torque and secondly they were elongated above a certain threshold field due to interaction between induced dipole moment and electric field. The CNTs aggregates elongated linearly with varying electric fields. The original morphology of the CNT aggregates was restored after the removal of the field. The evidence of a complete restoration indicated that the elasticity of CNT aggregates obeyed Hooke's Law. The elongation was fully reversible only below a certain breakdown field. Above breakdown electric field, CNT aggregates were ruptured and fragmented into small pieces and consequently CNTs got dispersed in LC medium.

A Study on Advertising Expressive Factors of Fashion Products on Brand Equity -Focused on Mediate Role of Brand Personality-

Abstract: The purpose of this study was to examine the impact of advertising expressive factors on brand equity and to investigate the role of brand personality as a factor mediate variable. The subject used for this study were 352 female university students. The data was analyzed by descriptive analysis, correlation analysis and confirmatory factor analysis using SPSS program and Amos program. As the result, model fit index showed

Optical design for excellent contrast ratio in a reflective horizontal-switching liquid crystal cell

Abstract: In this paper, we propose an optical configuration for a reflective liquid crystal (LC) cell with a single polarizer that can show an excellent contrast ratio by effectively eliminating phase dispersion. The proposed configuration consists of a half-wave retarder, two A-plates, a quarter-wave LC cell and a reflector; the configuration was designed on a Poincare sphere with the trigonometric method. From the calculation, we confirm that this configuration can show a high contrast ratio as compared with the conventional configuration due to the excellent dark state.

P-194: New 8-Domain MVA LCD with Reduced Color Shift

Abstract: A new MVA LCD is proposed by introducing an electric shielding layer to divide a unit pixel into at least two different regions with different threshold voltages. Such a MVA exhibits a wide view angle and much weaker color shift using only one TFT which is attractive for TV applications.

An application of fashion cycle methodology to change in residential floor coverings, 1950–2000

Abstract: Established research methods for investigating stylistic change were applied to a consumer product category outside the arena of clothing or personal appearance. Residential carpet sales expanded in the United States with the post-1945 growth of tufted carpet manufacturing, but by the 1990s, as consumers and builders made other floor covering choices, carpet sales were suffering. Quantitative content analysis of 1033 pictures in two consumer interior decorating magazines counted depictions (within room types) of single and combined floor covering surfaces (wall-to-wall carpeting, room-sized and area rugs, and wood, ceramic/stone and vinyl floors), as well as visual carpet structures (average cut pile, shag, loop, and sculptured) and colour-differentiated patterns (no pattern, shaded pattern, and pronounced pattern). Graphed results presented some visual patterning that reflected accepted definitions of inclining and declining trends, normal (bell-shaped curve) fashion cycles, and classic (flatten...

39.3: Wide-View Transflective LCD Using Fringe-Field Switching Mode

Abstract: A high optical efficiency and wide-view transflective LCD for mobile displays based on fringing field switching is proposed. The transmissive part uses homogenous alignment while the reflective part uses hybrid alignment with different optic axis orientation. In addition, the transmissive and reflective parts exhibit a similar gamma curve.

The study of physical properties and their effect on electro-optical characteristics of nematic liquid crystal doped with carbon nano tubes

Abstract: The properties of liquid crystal (LCs) can be altered by incorporating guest materials. The physical properties of carbon nano tubes doped liquid crystal (CNTs/LC) and pristine LC have been investigated. The rotational viscosity of CNTs/LC was lower whereas dielectric anisotropy was almost the same as compared to pristine LC. Also the twisted nematic LC cell driven by vertical field and homogeneously aligned nematic LC cells doped with carbon nanotubes (CNTs) driven by an in-plane field were fabricated and their electro-optic characteristics were investigated. The response time of CNTs doped LC was found to be improved due to the decrease in rotational viscosity.

P‐200: Effect of the Magnitude of Dielectric Anisotropy on the Light Efficiency of Fringe‐Field Switching Nematic Liquid Crystal Cell

Abstract: The light efficiency of fringe-field switching (FFS) mode when using a liquid crystal (LC) with positive dielectric anisotropy was found to be dependent on dielectric anisotropy, such that the lower the dielectric anisotropy, it becomes higher. On the contrary, for the LC with negative dielectric anisotropy it is almost independent of magnitude of dielectric anisotropy. This paper investigates light efficiency of FFS mode dependent on the magnitude of dielectric anisotropy of the LC associated with rubbing angle and cell gap.

P‐193: Single Gap and Single Gamma Transflective Display Using Fringe‐Field Switching Mode

Abstract: A new transflective liquid crystal displays associated with fringe field switching (FFS) mode is proposed. The device utilizes unique characteristic of the FFS mode in which the rotation angle of LC director is dependent on electrode position in on state. with optimization of pixel electrode width and distance between them, the LC director could rotate about 22.5° and 45° depending on electrode positions. Consequently, the region with low and high rotation angle could be played as reflective and transmissive regions, respectively, realizing a high image quality transflective display with single gap and single gamma characteristics.