Hitoshi Hatoh

Invited Lecture. Matrix liquid-crystal display device technologies

Abstract Our recent studies of ferroelectric chiral smectic and super-twisted nematic (ST) multiplexed-matrix liquid-crystal displays (LCDs) and a thin-film-transistor (TFT) active-matrix twisted nematic (TN) LCD are presented, mainly in terms of liquid-crystal material and cell optimization. This is based on a consideration of their electro-optical characteristics. In addition the matrix LCD devices developed through these studies are introduced, including a 12-inch-diagonal video-rate multicolour ferroelectric LCD, a highly multiplexed genuine achromatic ST LCD with a single cell and a 4-inch-diagonal full-colour a-Si TFT-addressed TN LCD for a video display.

Improvement of viewing angle characteristics in a twisted‐nematic liquid‐crystal display by using a cholesteric liquid‐crystal compensation layer

Viewing angle characteristics of a twisted nematic (TN) liquid‐crystal display (LCD) have been improved by inserting a planar aligned cholesteric liquid crystal compensating layer between the TN cell and a polarizer. Dependencies of the electro‐optical characteristics of the novel LCD on the retardation, ratio of thickness to the pitch (dc/p) and twist‐sense in the cholesteric layer are discussed. A thin‐film transistor addressed LCD with a wide viewing angle has been developed based on this novel cell construction and its display performance is reported.

Molecular tilt direction in a slightly tilted homeotropic aligned liquid crystal cell

The influence of hardness and topology of substrate surface on the pretilt angle were investigated for a slightly tilted homeotropic alignment achieved by the rubbing technique. On a soft surface, the grooves are produced which align in the same direction as the rubbing direction while the liquid crystal molecules tilt in the direction opposite to the rubbing direction. On a hard surface, no grooves are observed and the molecules tilt in the same direction as the rubbing direction. These results were applied to the fabrication of a two‐domain vertically aligned nematic liquid crystal display.

Plasma-Polymerized Films as Orientating Layers for Liquid Crystals

Many experimental studies on plasma-polymerized films have been carried out recently. If plasma-polymerized films can be used as an orientating layer for a liquid crystal, they will enlarge application of the liquid crystal. Although there have been some papers concerning a plasma-polymerized orientatig layer for a liquid crystal,(1) there are still many problems left to be solved. The effects of the surface properties of a plasma-polymerized film on liquid crystal alignment are discussed in this paper.

Multiplexed ferroelectric liquid crystal display

Abstract The studies on the fundamental requirements for realization of a multiplexed ferroelectric liquid crystal (FLC) display have been presented as follows: (1) The new classes of 2,5-diphenylpyrimidine FLCs are useful as a blending component for broadening the Sc temperature range and improving the switching response time. (2) A FLC material with the Iso-N-SA-Sc phase transition sequence as well as the long Sc and N helical pitches is required to achieve the homogeneous alignment in a Sc phase. (3) Among the FLC cells with various alignment layers, the PI/PI coated cell exhibits the symmetric and steep bistability threshold behavior. (4) The parameters to evaluate the multiplexing capability of a FLC cell are introduced and applied to select a suitable combination of alignment layers for highly multiplexing. (5) The parameters are also used to evaluate a favorable drive method among the drive schemes proposed so far for multiplexing a FLC cell. On the basis of the above studies, a multicolor ferroele...

Dopant Effects on Electro-Thermo-Optical Characteristics in Matrix-addressed Smectic-A Liquid Crystal Displays

Abstract Liquid crystal (LC) materials doped with non-mesomorphic or chiral substances are used for the matrix-addressed LC displays based on electro-thermo-optical effect. The influence of phase-transition temerature on driving condition and contrast ratio is investigated. Non-mesomorphic dopants which decrease greatly the thermal stability of LC phase expands the allowance of the driving condition and increases the contrast ratio. The chiral dopants also cause similar effects. However, the effects are not caused by the decrease of the thermal stability but by the twist force of chiral dopants. The minimum signal voltage to make a transparent state is not changed by non-mesomorphic dopant, whereas it increases with increasing the concentration of the chiral dopant. On the basis of our investigation, LC blends with the non-mesomorphic or chiral dopants have been developed. They have not only a wide allowance of driving condition and a high contrast ratio but also a high writing speed.

Dependence of pretilt angle on the topography of substrate in liquid crystal alignment brought about by rubbing technique

It was found that the pretilt angle of a liquid crystal alignment brought about using the rubbing technique depends upon the surface topography of substrate. The presence of small projections on the substrate was found to increase the pretilt angle of a liquid crystal alignment. It was found that the pretilt angle depends upon the projection shape and its relationship with the rubbing direction.

Pretilt-angle control of liquid-crystal alignment by using projections on substrate surfaces for dual-domain TN-LCD

— It was found that the value of the pretilt angle of liquid-crystal alignment achieved by a rubbing technique increases when small projections are present on the substrate surface. A dual-domain TN-LCD with very small dc offset voltage across the LC layer was realized by utilizing triangular-shaped projections.

Psychophysical evaluation of viewing-angle characteristics of liquid-crystal displays

— The viewing-angle characteristics of liquid-crystal displays (LCDs) were evaluated using calculated psychophysical metrics related to luminance and color. The results were compared with the results obtained from subjective estimation. The results of psychophysical evaluations agreed better with subjective estimation in the bright state than in the dark state. In addition, it was found that subjective estimates of LCD quality are better correlated with changes in calculated psychophysical values with viewing angle than with the absolute values themselves. It was also found that the iso-curves for different hue angles are useful in evaluating the viewing-angle characteristics of LCDs.

Viewing-angle evaluation method for LCDs with gray-scale images

— A new evaluation method of viewing-angle characteristics for liquid-crystal displays (LCDs) with gray-scale images has been studied. In this method, reverse images, excessively dark images, and excessively bright images, which are a serious problem while displaying gray-scale images, are evaluated quantitatively along with the display contrast ratio. The viewing-angle characteristics of several types of LCDs are compared using this method.