Jin Seog Gwag

A Multimode-Type Transflective Liquid Crystal Display Using the Hybrid-Aligned Nematic and Parallel-Rubbed Vertically Aligned Modes

We propose a transflective liquid crystal display (LCD) of the multimode type, which is composed of the hybrid-aligned nematic (HAN) mode in the reflective region and the parallel rubbed vertically aligned (PRVA) mode in the transmissive region. An optimized optical configuration is also proposed. In order to make the reflective and transmissive regions in one pixel independent, an Ar+ ion-beam alignment method was used. We confirmed that the transflective LCD of the proposed multimode type had high reflectance and transmittance, wide-viewing-angle property, and high contrast ratio.

In-plane bistable nematic liquid crystal devices based on nanoimprinted surface relief

The authors present a bistable nematic device, using a fourfold symmetrical bidirection nanometer-scale surface grating fabricated by the nanoimprinting lithography. The bistability is achieved by a composite action between two orthogonal surface undulations, which tend to stabilize the nematic director along either of the two diagonal axes. The switching between the bistable states is easily driven by orthogonal in-plane electric fields. A recent model of groove-induced surface anchoring due to Fukuda et al. [Phys. Rev. Lett. 98, 187803 (2007)] accounts for the azimuthal bistability in the present system.

Surface-controlled patterned vertical alignment mode with reactive mesogen

We proposed a patterned vertical alignment (PVA) mode controlled by a modified surface with ultraviolet (UV) curable reactive mesogen (RM) mixed with vertical alignment material for a liquid crystal display (LCD) with fast response time. In the surface-controlled PVA (SC-PVA) mode, the RM monomers in the alignment layer are polymerized along the LC directors by UV exposure under an applied voltage. The polymerized RMs produce a pretilt against the substrate normal depending on the applied field direction in the patterned electrode configuration. In such SC-PVA mode, fast response time was achieved at whole grey levels with the predetermined rotational preference of the LC directors governed by the pretilt direction.

Control of liquid crystal pretilt angle by anchoring competition of the stacked alignment layers

We proposed a method to control the pretilt angle of liquid crystals by stacking of a vertical alignment layer on a planar alignment layer. The pretilt angle can be controlled over the full range (0°–90°) depending on the thickness of the vertical alignment layer. We also proposed a numerical model to describe the physical mechanism based on the anchoring competition between liquid crystal, planar, and vertical polyimide alignment layers.

Alignment of liquid crystal on a polyimide surface exposed to an Ar ion beam

In this paper properties of nematic liquid crystals aligned on polyimide surfaces exposed to a low-energy Ar ion beam are investigated. We studied how the pretilt angle of a liquid crystal cell is affected by ion-beam conditions, such as the energy of the incident ions, the angle of incidence, and the exposure time. X-ray photoelectron spectroscopy data indicate that ion-beam exposure changes the chemical bonding states of the polyimide surface, which may be one of the main causes of anisotropic liquid crystal alignment. We also found that twisted-nematic cells fabricated by the ion-beam alignment method have the voltage holding time enough for application to thin-film-transistor liquid crystal displays.

Viewing angle control mode using nematic bistability.

As an approach using bistable nematic liquid crystals, we present a liquid crystal display with viewing angle control using two stable states, splay and 180 degrees-twist at pi cell, with three terminal electrode structures. The splay state is controlled by in-plane switching for a wide viewing angle (WVA), while the 180 degrees-twist state is operated by vertical switching for a narrow viewing angle (NVA). With this bistable mode, we fabricated viewing angle-controlled LCDs without additional optical components.

Surface nematic bistability at nanoimprinted topography

The azimuthal nematic bistability was realized by frustration between two azimuthally orthogonal anchoring axes induced by a nanoimprinted groove pattern and mechanical rubbing. The nematic bistability can be explained by the revised Berreman model of groove-induced surface anchoring, recently introduced by Fukuda et al. [Phys. Rev. Lett. 98, 187803 (2007)]. The azimuthal bistability can be tuned in arbitrary direction by changing the groove pitch and rubbing conditions. This simple combinatorial scheme may be considered as a practical candidate for bistable displays with tailored bistable directions required in various liquid crystal device modes.

Simple method for measuring the high pretilt angle of nematic liquid crystals

Pretilt angle measurable by using the conventional crystal rotation method is limited to about 0°–20° and 70°–90°. We propose a method by which we can measure the pretilt angle by using the crystal rotation method even if the pretilt angle is between 20° and 70°. In this method, the determination of a pretilt angle is achieved by finding the rotation angles where transmittances are maximum and minimum in the periodic transmittance characteristics obtained with the variation of rotation angle.

Two-Domain Hybrid-Aligned Nematic Cell Fabricated by Ion Beam Treatment of Vertical Alignment Layer

Organic materials for vertical alignment can be used to align liquid crystals horizontally by irradiating an ion beam on the surface under appropriate conditions. Using this technique, we can achieve easily a multidomain alignment for a hybrid-aligned nematic (HAN) cell. We found that a two-domain HAN cell obtained by ion beam exposure shows excellent electro-optical characteristics. The use of the same alignment material in a HAN cell could reduce the cost of production and generation of DC offset voltage.

Electrically tilted liquid crystal display mode for high speed operation

To develop liquid crystal displays suitable for moving picture, a liquid crystal display mode having an electrically tilted phase is proposed. This is realized by initially having a tilted liquid crystal with low bias voltage. We found that its measured response time is in good agreement with numerical calculation obtained using the Erickson–Leslie equation. The falling times were smaller than 10 ms with conventional driving and 6 ms with overdriving.