Cell Retardation Value Research Articles

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

Abstract— A single‐cel l‐gap transflective liquid‐crystal display with two types of liquid‐crystal alignment based on an in‐plane‐switching structure is proposed. The transmissive region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the reflective region has a homeotropic liquid‐crystal alignment. For every driving voltage for a positive‐dielectric‐anisotropy nematic liquid crystal, the effective cell‐retardation value in the transmissive region becomes larger than that in the reflective region because of optical compensation film which is generated by low‐pretilt‐angle liquid crystal in the transmissive region. Under the optimization of the liquid‐crystal cell and alignment used in the transmissive and reflective areas, the transmissive and reflective parts have similar gamma curves. An identical response time in both the transmissive and reflective regions and a desirable viewing angle for personal portable displays can also be obtained.

Low Voltage and High Transmittance Transflective Display Using Polymer-Stabilized Blue-Phase Liquid Crystal

A fast response time, wide viewing angle, and single-cell-gap transflective display using polymer-stabilized blue-phase liquid crystal is proposed. The transmissive region has an in-plane wall-shaped electrode while the reflective region has an in-plane trapezoid electrode. Both of the electrodes generate a strong horizontal field, resulting in a low operating voltage and high transmittance and reflectance. In every driving voltage, the effective cell retardation value in the transmissive region is larger than that in the reflective region, so that the transmissive and reflective regions have similar gamma curves.

P‐143: Transflective Liquid Crystal Display Using UV Curable Reactive Mesogen

AbstractA single gap transflective liquid crystal display driven by fringe electric field in the transmissive (T) region and vertical electric field in the reflective (R) region was designed with formation of high pretilt angle larger than 45°through polymerization of an UV curable reactive mesogen monomer at the surface in the R region, the effective cell retardation value becomes half of that in the T region where the LCs are homogenously aligned. Consequently, a transflective display driven by a vertical and fringe electric field with a single cell gap and single gamma curves is realized.

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

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.

Optimal Cell Retardation Value of a Fringe-Field Switching Mode Using a Liquid Crystal with Negative Dielectric Anisotropy

ABSTRACT Optimal cell retardation value at which the maximum transmittance occur in a fringe-field switching (FFS) mode is analyzed theoretically and experimentally. In the device, the rotation angle of liquid crystal (LC) director is dependent on electrode position. Nevertheless, the transmittance can be described using a uniaxial medium model within a certain cell retardation value like in the in-plane switching (IPS) mode, where the effective birefringence was reduced to about 76% of the original value.

Cell Gap-Dependent Transmittance Characteristic in a Fringe Field-Driven Homogeneously Aligned Liquid Crystal Cell with Positive Dielectric Anisotropy

Transmittance characteristic in a homogeneously aligned liquid crystal (LC) cell driven by a fringe-electric field is investigated as a function of cell gap using the LC with positive dielectric anisotropy. In this device, the fringe-electric field drives the LCs to rotate so that the dielectric torque is electrode-positional dependent, which results in electrode-position dependency in the LC's rotating angle. As the cell gap decreases to 2 µm, more LCs are affected by surface anchoring, and the LCs above the center of electrodes, in which the LCs are twisted by elastic force between neighboring molecules, are less twisted compared to the 4 µm cell. Consequently, when the cell gap decreases from 4 to 2 µm, the transmittance also decreases even though the cell retardation value remains the same.

Electro-optic characteristics and switching principle of a single-cell-gap transflective liquid-crystal display associated with in-plane rotation of liquid crystal driven by a fringe-field

A single-gap transflective liquid-crystal (LC) display associated with in-plane rotation of the LC director was designed. In the device, a fringe electric field drives to rotate a homogeneously aligned LC in plane to optimize polarization efficiency. Rotating degrees of the LC director, 22.5° and 45° were required in both reflective and transmissive regions, respectively. In the device, the cell gap was the same for both regions, and a dark state was irrespective of the cell retardation value at normal direction, which was highly important in massive fabrications. The switching principle and electro-optic characteristics of the device are reported herein.

Film Compensation of the Optically Compensated Splay Liquid Crystal Device

ABSTRACT Optically compensated splay (OCS) mode, where the LCs are almost homeotropically aligned with a rubbed parallel at both surfaces, and where a mid-director orients itself parallel to the substrate, is known to show a wide-viewing-angle, due to self-compensation effect. Since a cell retardation value exists in the presence of an electric field, film compensation is necessary to realize a wide-viewing-angle and high contrast ratio. In this paper, we show various electro-optic characteristics, depending on cell configurations with optical compensation films.

Electro-Optic Characteristics of Single Gap Transflective Display Using In-Plane Switching Mode

ABSTRACT We have designed a single gap transflective liquid crystal display (LCD) using an in-plane switching mode, where the rotating angle of the LC director between electrodes, and above electrodes, is 45° and 22.5° in average, respectively. Optimization of the cell structures such as electrode structure, cell structure, physical properties of the LC and the LC cell retardation value have been perform to obtain a low-power transflective LCD with a single gap structure and a single driving circuit.

수직전기장을 이용한 수평배향 단일갭 반투과형 액정 디스플레이

We have designed a novel single cell gap transflective display associated with dual orientation of the liquid crystal. Owing to hybrid alignment in reflective part, the effective cell retardation value becomes half of cell retardation value in transmissive part where the LCs are homogeneously aligned. This study shows the possibility to manufacture the transflective display with a single gamma curve for reflective and transmissive region. The new device shows a high image quality with relatively easy fabrication.

Color Tracking Analysis of the Fringe-Field-Switching Cell Using a Liquid Crystal with Negative Dielectric Anisotropy

Color tracking in a fringe-field driven homogenously aligned nematic liquid crystal cell [named fringe-field switching (FFS)] has been investigated. In the in-plane switching (IPS) device and the FFS device using liquid crystals (LCs) with negative dielectric anisotropy (-LC), the LCs rotate almost in plane except for surfaces where the color tracking occurs for cell retardation value that shows a maximal transmittance. In the IPS device, authentic color appears at a very low cell retardation value that exhibits a low transmittance and bluish white. However, the FFS device shows authentic color even at a relatively high cell retardation value 0.30 µm so that high transmittance and greenish white are kept.

A hybrid aligned nematic reflective liquid crystal display driven by a fringe-field

We have designed a novel reflective nematic liquid crystal (LC) cell driven by a fringe electric field, in which the LCs are hybrid aligned in the initial state. Due to the hybrid alignment of the LC, the effective retardation value of the cell is greatly reduced when viewed in the normal direction and such a cell retardation value of 0.28 µm equals a quarter wave plate viewed in the normal direction. This means that the new reflective device can have a large cell gap of greater than 3 µm, which is advantageous when manufacturing the cell and, in addition, the device shows excellent electro-optic characteristics.

유전율 이방성이 음인 액정을 이용한 Fringe-field Switching Mode의 Authentic-color 특성

We have studied color tracking of a fringe-field driven homogenously aligned nematic liquid crystal (LC) cell with negative dielectric anisotropy and compared it with other devices such as the twisted nematic(TN) and in-plane switching(IPS) modes. According to studies, the TN device shows bluish color at grey scale and even at a low retardation cell it cannot avoid color tracking. The authentic IPS device having cell retardation value of 0.23 also shows bluish white color. However, the FFS device shows excellent color tracking characteristics even at high retardation value of the cell while keeping high transmittance and greenish white.

P‐105: A Single‐Cell‐Gap Transflective Display

AbstractWe propose a novel single cell gap‐transflective display associated with dual orientation of the liquid crystal. Owing to hybrid alignment in reflective part, the effective cell retardation value becomes half of real cell retardation value, allowing having a high cell gap even in the reflective part. In this way, a single cell gap transflective display with a high image quality is realized.

Analysis of Optimal Phase Retardation of a Fringe Field-Driven Homogeneously Aligned Nematic Liquid Crystal Cell

We studied the optimal cell retardation value that shows the maximal transmittance in a fringe-field-driven homogeneously aligned (HA) nematic liquid crystal (LC) cell. When the LC with positive dielectric anisotropy is used, the transmittance is much higher than that of an in-plane-field-driven HA cell. The unexpected electrooptic behaviors are caused because the transmittance of light from a deformed LC in a white state cannot be explained using only the uniaxial medium model that describes an in-plane-field-driven HA cell.

1매의 편광판으로 구성된 반사형 Fringe-field Switching Mode의 전기 광학 특성

We have performed computer simulation to obtain electro-optic chracteristics of reflective liquid crystal display (LCD) using wide viewing angle LC mode, fringe field switching(FFS). Unlike other reflective LCD modes, in the FFS mode, the LC director in plance so an application to reflective display consisted of polarizer, LC layer and reflector is possible. when an incident light is 550mm, the optimal cell retardation value is 0.1365<TEX>${\mu}$</TEX>m and the efficiency of reflectivity is high over 90% with very little wavelength dispersion. Further, we have studied a new reflective display with polarizer, optical compensation film with half plate, LC plus reflector. The display with optimized cell parameters shows high contrast ratio (CR) over 130 with high light efficiency over 90% at normal direction and the CR greater than 5 exists over 60<TEX>$^{\circ}$</TEX> of polar angle in all directions.