Showing papers by "Seung Hee Lee published in 2005"
TL;DR: In this article, twisted nematic cells doped by carbon nanotubes (CNTs) were fabricated and the CNTs with a minute amount of doping did not perturb the liquid crystal orientation in the off and on state.
Abstract: We have fabricated twisted nematic cells doped by carbon nanotubes (CNTs). The CNTs with a minute amount of doping did not perturb the liquid crystal orientation in the off and on state. The hysteresis studies of voltage-dependent transmittance and capacitance under ac and dc electric field showed that the residual dc, which is related to an image sticking problem in liquid crystal displays, was greatly reduced due to the ion trapping by CNTs.
197 citations
TL;DR: In this article, the authors investigated the transmittance characteristics of a homogeneously aligned liquid crystal (LC) cell driven by a fringe-electric field and found that the dielectric torque is electrode-positional dependent, which results in electrode position dependency in the LC's rotating angle.
Abstract: 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 ?m, 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 ?m cell. Consequently, when the cell gap decreases from 4 to 2 ?m, the transmittance also decreases even though the cell retardation value remains the same.
32 citations
TL;DR: In this article, the authors proposed a novel fringe field switching (FFS) liquid crystal (LC) mode with a 3-partition pixel slit, where a pixel branch is partitioned into three areas, namely, two edges and a center, where the edge slit angle is larger than the center slit angle.
Abstract: We proposed a novel fringe field switching (FFS) liquid crystal (LC) mode with a 3-partition pixel slit. In this mode, a pixel branch is partitioned into 3 areas, namely, two edges and a center, where the edge slit angle is larger than the center slit angle. Thus the reverse twist region in the pixel edge is reduced and the LC dynamics in this region becomes very stable. Also, when an external pressure is applied to the panel at the operating voltage, the disclination line is barely extended into the active area. Consequently, this mode exhibits a high external pressure resistance with a wide viewing angle and is attractive for pen-based touch panels such as personal digital assistants (PDAs) and tablet personal computers (PCs).
14 citations
TL;DR: In this paper, the optimization of an angle of the electrode used in the transmissive and reflective area solved the problem so that the transflective display with a single gamma curve for reflective and transmissive region is possible.
Abstract: The single-gap transflective liquid crystal display utilizing the fringe-field switching mode has a problem such that the voltage–dependent transmittance and reflectance curves do not match each other and thus a dual driving circuit is required. This study shows that the optimization of an angle of the electrode used in the transmissive and reflective area solves this problem so that the transflective display with a single gamma curve for reflective and transmissive region is possible.
11 citations
TL;DR: In this paper, a thermocurable transparent polyimide having acrylate side groups was prepared from chloromethylated polyimides, a useful starting material for modification of aromatic poly-imides.
Abstract: From chloromethylated polyimide, a useful starting material for modification of aromatic polyimides, a thermocurable transparent polyimide having acrylate side groups was prepared. In the presence of 1,8-diazabicyclo[5,4,0]undec-7-ene, chloromethylated polyimide was esterified with acrylic acid to synthesize poly(imide methylene acrylate). The polymer was soluble in organic solvent, which makes it possible to prepare a planar film by spin coating. The polymer film became insoluble after thermal treatment at 230 °C for 30 min. Optical transparency of the film at 400 nm (for 1 µm thickness) was higher than 98 % and not affected by further heating at 230 °C for 250 min. Adhesion properties measured by the ASTM D3359-B method ranged from 4B to 5B. Preliminary results of planarization testing showed a high degree of planarization (DOP) value (>0.53). These properties demonstrate that poly(imide methylene acrylate) could be utilized as a thermocurable transparent material in fabricating display devices such as TFT-LCD. Copyright © 2004 Society of Chemical Industry
10 citations
TL;DR: In this article, a liquid-crystal (LC) photoalignment material with a high photosensitivity based on the fluorinated poly(arylene ether) containing a chalcone unit in the main chain was reported.
Abstract: We report a liquid-crystal (LC) photoalignment material with a high photosensitivity based on the fluorinated poly(arylene ether) containing a chalcone unit in the main chain. The fluorinated poly(arylene ether) exhibited defect-free homogeneous alignment of LCs upon irradiation of linearly polarized UV light for 10s. Spectroscopic analyses revealed that [2+2] cycloaddition between the chalcone moieties generated the surface anisotropy to induce an efficient alignment of LCs.
9 citations
TL;DR: In this paper, the electro-optic characteristics of cell configurations with optical compensation films are analyzed. But the authors focus on the optical compensation effect and do not consider the effect of self-compensation.
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.
8 citations
TL;DR: In this paper, the authors studied the dynamic stability of a liquid crystal (LC) in an adjacent active region near the edge of a pixel slit according to the horizontal electric field generated by the data signal for the fringe field switching (FFS) mode.
Abstract: We have studied the dynamic stability of a liquid crystal (LC) in an adjacent active region near the edge of a pixel slit according to the horizontal electric field generated by the data signal for the fringe field switching (FFS) mode. The horizontal component of a fringe electric field becomes strong as the distance between the common electrode and the data bus line decreases. Therefore, the disclination lines (DLs), which are formed near the pixel edge, barely intrude an active region. Moreover, the LC director existing in this region becomes stable and has a large twist angle. This indicates that the LC dynamic stability near the pixel edge is markedly affected by the horizontal electric field of a strong data signal.
7 citations
TL;DR: In this paper, a single gap transflective liquid crystal display (LCD) using an in-plane switching mode was designed, where the rotating angle of the LC director between electrodes, and above electrodes, is 45° and 22.5° in average, respectively.
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.
6 citations
TL;DR: In this article, the authors investigated reflective mode with wide-band property using liquid crystal (LC) cell and inner retarder (λ/4) and found that the maximum contrast ratio increases and viewing angle decreases compared with the case that slow axis of LC and the transmission axis of analyzer coincide.
Abstract: This study investigates reflective mode with wide-band property using liquid crystal (LC) cell (λ/2) and inner retarder (λ/4). In wide-band type, the maximum contrast ratio increases and viewing angle decreases compared with the case that slow axis of LC and the transmission axis of analyzer coincide. However, for perfect dark state, the retardation of LC cell should be kept 0.275 µm. If not, maximum CR decreases from 150 to 100.
5 citations
TL;DR: In this paper, the voltage-dependent liquid crystal (LC) dynamic stability corresponding to the pixel edge shape in the fringe field switching (FFS) mode was studied, and it was shown that the edge shape with no reverse twist region is very stable near the edge of the pixel slit.
Abstract: We studied the voltage–dependent liquid crystal (LC) dynamic stability corresponding to the pixel edge shape in the fringe field switching (FFS) mode. LC dynamics is very unstable near the edge of the pixel slit, where there is a horizontally different field direction compared with the active region, particularly when the slit angle decreases to 3°. Actually, there are strong field competitions near the edge of the pixel slit due to the patterned pixel shape. Also, a dark disclination line (D/L) at the domain boundary is generated with increasing operation voltage and the D/L extends into the active area at a high applied voltage. It is possible to control LC dynamics near the pixel edge by using different pixel edge shapes. In this paper, we propose an advanced edge shape. This shape has no reverse twist region, unlike the conventional structure, and therefore, LC dynamics is very stable near the edge of the pixel slit. This result indicates that a pixel edge shape with no reverse twist is very important in the design of a high-image-quality FFS mode.
TL;DR: In this article, dual domain structure of the FFS and IPS modes could reduce such a voltage-dependent transmittance difference dependent on the position, although 1° of misalignment exists since the LC directors rotate clockwise and anticlockwise.
Abstract: The liquid crystal (LC) modes, in-plane switching (IPS) and fringe-field switching (FFS), associated with a transition from a homogenously aligned to twist deformation require rubbing process. In both devices, 1° of misalignment in azimuthal direction could cause voltage–dependent transmittance (V–T) to be different from that in a normal area and consequently results in a rubbing mura. According to our studies, dual domain structure of the FFS and IPS modes could reduce such a V–T difference dependent on the position although 1° of misalignment exists since the LC directors rotate clockwise and anticlockwise.
TL;DR: In this paper, color tracking in a fringe-field driven homogenously aligned nematic liquid crystal cell was investigated, and the FFS device showed authentic color even at a relatively high cell retardation value 0.30 µm so that high transmittance and greenish white were kept.
Abstract: 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.