Gak Seok Lee

Direct confirmation of biaxiality in a bent-core mesogen through the measurement of electro-optic characteristics

We propose a method to confirm the biaxial phase in thermotropic nematic liquid crystals from measurement of the electro-optic characteristics. The electro-optic transmittance curve shows monotonic decrease to zero in the uniaxial phase but the curve shows a U-shaped behavior (or a monotonic decrease to nonzero transmittance) in the biaxial phase. In a bent-core mesogen 4,4′(1,3,4oxadiazole2,5diyl)dipheptylbenzoate (ODBP-Ph-C7), known to be in the nematic phase at temperatures between 173 and 222 °C, it has been found that its electro-optic curve at 190 °C shows a U-shaped behavior, while the curve at 210 °C shows a monotonic decrease to zero transmittance. We believe that these experimental results confirm the biaxial nature of ODBP-Ph-C7.

Electrode structure for color shift reduction in fringe-field switching mode

We propose a new electrode structure for the fringe-field switching mode, which not only has a smaller color shift but also transmits more light than the chevron-type structure. While the chevron-type electrode structure mainly uses the different directions of the electric field, the proposed structure makes use of position-dependent strengths as well as different directions of the electric field. Position-dependent electric field strengths bring about rotation of LCs different from position to position in a pixel, which further reduce the color shift by using the multi-domain effect.

Optimization of Electrode Structure and Rubbing Angle in In-Plane-Switching Liquid Crystal Cell for Single-Gamma Transflective Display

We studied the effects of the electrode structure and rubbing angle on the electro-optic characteristics of an in-plane switching (IPS) cell. We found that the threshold voltage and the steepness of the voltage–transmittance (reflectance) [V–T(R)] curve for an IPS cell can be controlled separately by varying the distance between electrodes and the rubbing angle, respectively. We applied these results to realize a single gamma in a transflective IPS cell.

Horizontal switching of double-cellgap liquid crystal cell for superachromatic transflective display

We propose optical configurations of a double-cellgap liquid crystal cell for transflective displays that show achromatic properties. The reflective part is designed in a wide-band quarter-wave structure to achieve a dispersion-free dark state. For the transmissive part, a compensation method is introduced to achieve a superachromatic dark state. To achieve a bright state, horizontal switching as well as vertical switching can be used.

Single cellgap transflective liquid crystal cell with high contrast and high cellgap tolerance.

In this paper an optical configuration of a transflective liquid crystal (LC) cell driven by a horizontal electric field is proposed, which shows high contrast, high cellgap tolerance, and single gamma, simultaneously. The dark state of the reflective part is realized by a polarizer (0 degrees), a half-wave plate (15 degrees), LC layer (120 degrees), and a quarter-wave layer (-15 degrees), while a wide-band quarter-wave plate (45 degrees) and a polarizer (90 degrees) are added for the dark state of the transmissive part. Since the optic axis of the homogeneously aligned LC layer is set to be parallel to the polarization direction of the light passed through the half-wave plate, the dark state is rarely affected by the cellgap of the LC layer. Due to the different directions of the electric fields, LCs are rotated to 97.5 degrees for the bright state of the reflective part, but to 75 degrees for that of the transmissive part. With the proposed configuration, a high contrast single-gamma transflective display with high cellgap tolerance can be realized in a single-cellgap structure.

Nanoparticle Doped In-Cell Retarder for Low Operating Voltage in Transflective Liquid Crystal Displays

In this paper, we propose a method of suppressing the increase in operating voltage caused by the in-cell retarder in transflective liquid crystal displays (LCDs), by doping nanoparticles with a high dielectric constant in the in-cell material. Doping with nano-particles increases the dielectric constant of the in-cell material by more than 5 times that of a pure in-cell material. The in-cell material with a high dielectric constant reduces the magnitude of the electric field, within the volume of the in-cell retarder, to decrease the operating voltages of a transflective LCD with an in-cell retarder. It is confirmed that the increase in operating voltage, in a transflective vertical alignment (VA) cell with an in-cell retarder, can be suppressed, from 3.8 to 0.7 V, by doping an in-cell material with 5 wt % TiO2.

Fringe field switching of a twisted nematic liquid crystal device for a single-cell-gap transflective display

We propose an optical configuration of a twisted nematic liquid crystal device driven by a fringe field for a single-cell-gap transflective display. The dark state of the reflective part is realized by a nematic liquid crystal layer with a twist angle of 63.6 degrees and retardation of 194 nm, while a quarter-wave plate is inserted for the dark state of the transmissive part. Wavelength dispersion of the liquid crystal layer is suppressed by introducing a half-wave plate. Different directions of electric fields rotate liquid crystals to 15 degrees for the bright state of the reflective part, but to -30 degrees for that of the transmissive part. With the proposed configuration, we can realize a high-brightness single-gamma transflective display in a single-cell-gap structure without any in-cell retardation layers.

Electro-optical properties of the nematic phase in V-shaped molecules with a 2,3-naphthalene central unit

So far there is little understanding of the physicochemical properties of the nematic phase of V-shaped bent-core liquid crystalline (VBLC) molecules. We have synthesized VBLC molecules based on a 2,3-naphthalene central unit, varying the carbon number of the flexible alkyl chains (n = 2, 6 or 12) to extend the nematic range. We examined the polar and biaxial properties of the nematic phases for two homologous molecules with n = 6 and 12.

Vertically Aligned Liquid Crystal Cell with Image-Enhanced Reflector for High-Contrast Transflective Displays

We propose vertically aligned liquid crystal cell structures with image-enhanced reflectors for transflective displays. Liquid crystal (LC) molecules are aligned vertically so that an excellent dark state can be achieved. Wide-band quarter-wave design is employed to realize broad spectral characteristics over the entire range of visible wavelengths. The display performance in the transmissive mode can be markedly improved compared with that of homogeneous cells.

P-115: Optimization of Electrode Structure for Single Gamma in a Transflective IPS LCD

In this paper we report the optimization of the electrode structure for a single gamma curve in a single-cellgap transflective IPS LCD. We optimized the distances between electrodes and the angles between LC directors and electrodes to achieve a single gamma curve.