Kahoru Mori

Ferroelectric Liquid Crystal Display Using Tristable Switching

Smectic layer structure and switching behavior in antiferroelectric liquid crystals TFMHPOBC, TFMHPDBC and MHPOBC were studied. At the phase transition point between SmC* and SmCA*, discontinuity in the leaning angle and the layer spacing was observed. In the SmA phase, diffraction peaks attributable to the focal conic texture and the planar layer structure were observed, implying that the bookshelf structure and the focal conic texture coexist. Using the tristable switching, we designed the fundamental waveforms for multiplex driving and constructed a prototype antiferroelectric liquid crystal display which works at room temperature.

Full-color antiferroelectric liquid crystal display

Abstract A 6-in.-diagonal full-color antiferroelectric liquid crystal display with 220 × (320×3) color pixels has been developed. An analogue gray scale was achieved by utilizing in-pixel multidomain switching, and the satisfactory video images were obtained in the prototype display device.

Experimental Studies on Phase Transitions in an Antiferroelectric Liquid Crystal

The effect of optical purity on the antiferroelectric phase transition and the field-induced ferroelectric phase transition in Sm C A * were studied by means of dielectric measurements and observations of D-E hysteresis loops. The Curie-Weiss law was found to hold in Sm A and the Curie-Weiss constant to increase as the optical purity is reduced. Three types of D-E curves were obtained in the Sm C A * phase. It was found that a double hysteresis loop changed into a single one at high frequencies. The results obtained are discussed on the basis of a phenomenological theory

Layer Structure of Antiferroelectric Liquid Crystal MHPOBC Studied by X-Ray Diffraction

The layer structure of the antiferroelectric liquid crystal MHPOBC was studied by X-ray measurements. We observed a thermal hysteresis in the layer structure; i.e., a chevron structure was formed in the cooling process, and a bookshelf structure in the heating process. It was found that the layer spacing decreases discontinuously at the Sm C*-Sm CA* transition point for an enantiomeric mixture in the cooling process. The result is discussed on the basis of a phenomenological theory.

Ferroelectric Liquid Crystal Display with High Contrast Ratio

To obtain zig-zag defect-free liquid crystal cells by means of a standard rubbing technique, the effect of a new polyimide film on pretilt angle at a surface has been investigated. This new polyimide imposes the high pretilt over wide rubbing density, and good orientation of liquid crystals without zig-zag defects can be obtained for rubbing densities higher than 0.5×103. A new driving scheme to realize display devices with a high contrast ratio is proposed. This scheme is devised by utilizing anomalous switching behavior and AC-stabilized effect. The prototype of the ferroelectric liquid crystal display device shows the maximum contrast ratio of 40:1.

Phase Transitions in an Antiferroelectric Liquid Crystal TFMHPOBC

We studied phase transitions in an antiferroelectric liquid crystal TFMHPOBC (C8H17O-b-b-COO-b-*CH(CF3)C6H13) by means of dielectric measurements and microscopic observations. Both a Goldstone mode and a soft mode were observed in the SmC* phase, but only a soft mode in the SmCA* phase. From the temperature dependence of the relaxational frequency, it was clarified that the ferroelectric mode tends to be soft even in the antiferroelectric phase transition. The unwinding process of the helical structure in the SmCA* phase was observed with a reflecting microscope. It was also found that all the transitions, i.e., SmA-SmCA*, SmA-SmC* and SmC*-SmCA*, are of the first order. We present the E(electric field)-T(temperature) phase diagram of the optically pure TFMHPOBC and the mixture of R- and S-enantiomers.

Switching Properties in Antiferroelectric Liquid Crystals

The influences of alignment materials on switching properties in antiferroelectric liquid crystals have been studied by using three kinds of polyimide resins. It has turned out that the threshold voltages of the switching between an antiferroelectric state and a ferroelectric state depend on the alignment materials, and that response times are also affected by the alignment materials.

Multicolor video-rate antiferroelectric LCD with high contrast and wide viewing angle

— A6-in.-diagonal multicolor antiferroelectric liquid-crystal display (AFLC) with 200 × (320 × 3) color pixels has been developed. To obtain high contrast and high-multiplex driving, newly synthesized AFLC materials which show fast response and a good hysteresis loop were mixed into the main component. A new driving scheme, including a reset time in addition to the line time, was designed.

Multiplexing Performance of Antiferroelectric Liquid Crystal Device

A multiplex-driving technique for an antiferroelectric liquid crystal device has been studied. A new driving scheme is proposed, which overcomes the disadvantage of slow switching from a ferroelectric state to an antiferroelectric state. It is confirmed that the antiferroelectric liquid crystal device can be driven at a high duty ratio of 1/500 by using this scheme.

Surface alignment of ferroelectric liquid crystals using polyimide, polyamide-imide and polyamide layers and their effect on pre-tilt angle

Abstract Fluoro and non-fluoro polymer alignment layers of high and low pre-tilt angle were developed for ferroelectric liquid crystal display devices to exploit the effect of rubbed polyimide, polyamide-imide and polyamide alignment layers on pre-tilt angle and other electro-optical properties. Fluorine containing polyimide and polyamide alignment control layers displayed high pre-tilt angle (< 10°) and good alignment of liquid crystal molecules with no zig-zag defects by means of standard rubbing techniques. Non-fluoro polymer alignment layers showed relatively small pre-tilt angle (< 5°) with good or random alignment having some zig-zag defects in the ferroelectric liquid crystal cells. The ferroelectric liquid crystal used in the experiment was CS-1011 having the phase sequences SC*-SA-N*-I. The characteristic changes due to structurally different polymer layers on ferroelectric liquid crystal alignment are described.