Takeshi Togano

NOVEL FERROELECTRIC LIQUID CRYSTAL MODE FOR ACTIVE MATRIX LIQUID CRYSTAL DISPLAY USING CHOLESTERIC-CHIRAL SMECTIC C PHASE TRANSITION MATERIAL

We propose a novel ferroelectric liquid crystal (FLC) mode which is capable of gray-scale display with an active device such as a thin-film transistor (TFT). This technology is based on the monostable FLC mode, which is obtained from a material with cholesteric–chiral smectic C (Ch–SmC*) phase transition sequences and by applying a low DC voltage only near the phase transition temperature from Ch to SmC* for making the layer normal direction uniform. The electrooptical response of liquid crystal molecules under AC voltage is asymmetric between plus and minus voltages. It shows characteristics such as low spontaneous polarization (PS) value, short response time, small temperature dependence and wide tolerance to cell gap nonuniformity. Furthermore, we made TFT prototype panels using this mode. We could confirm this mode, realizing high-quality moving pictures without blurring based on the nonholding display and good color reproducibility based on the field sequential color method.

Local Layer Structures in Ferroelectric Liquid Crystal Cells Filled with a Material Which Exhibits Cholesteric-Chiral Smectic C Phase Transition

We investigated the local layer structures in ferroelectric liquid crystal (FLC) cells which have a monostable switching mode using synchrotron X-ray micro diffraction. The monostable switching mode is realized by the FLC cells filled with a material which has cholesteric–chiral smectic C (Ch–SmC*) phase transition sequences. On cooling these cells from the isotropic phase to the SmC* phase, the texture of domains and stripes was observed. The X-ray micro diffraction study revealed that the smectic layer bending with the layer shrinkage generate the texture.

Dot Inversion Spontaneous Polarization Structure in the Half-V-shaped Switching Ferroelectric Liquid Crystal Mode

The half-V shaped switching ferroelectric liquid crystal mode (half-V FLC mode) can easily yield excellent moving pictures based on the nonholding display by simple AC driving. However, the AC driving in the entire area of the liquid crystal display (LCD) panel (i.e. the field-inversion drive method) raises a concern of the cross talk problem in large-size LCD panels. In this paper, we propose a novel alignment method that is controlled to yield alternating layer directions between neighboring pixels. Such layer structures correspond to the structure of dot inversion spontaneous polarization, and a nonholding display can be realized by the dot-inversion drive method. By this method, we can simultaneously obtain a cross-talk-free display, excellent moving pictures and wider viewing angle. The contrast ratio is expected to be improved by further liquid crystal development and/or the multi-domain process technology.

X-RAY MICRODIFFRACTION STUDY OF THE HALF-V SHAPED SWITCHING LIQUID CRYSTAL

Local layer structures and their formation process in a half-V-shaped switching ferroelectric liquid crystal (HV-FLC) were investigated by means of synchrotron X-ray microdiffraction. The HV-FLC is a FLC that has a cholesteric–chiral smectic C (Ch–SmC * ) phase transition sequences. X-ray microdiffraction measurements revealed that the SmC * phase in the HV-FLC was composed of asymmetric chevron and inclined-bookshelf structures. In addition, temperature-controlled X-ray diffraction measurements showed that the transient layer structures appeared during the Ch to SmC * phase transition.

Pretilt Angle Dependence of the Switching Behavior in the Intrinsic Half-V-Shaped Switching Ferroelectric Liquid Crystal Mode

The intrinsic half-V-shaped switching ferroelectric liquid crystal mode (iHV-FLC mode) which is obtained from a material with isotropic (Iso.), cholesteric (Ch) and chiral smectic C (SmC*) phase transition sequences can easily yield excellent moving pictures. There are very few reports of liquid crystal (LC) molecular alignment during the Ch–SmC* phase transition sequence although it is important to clarify the molecular alignment and switching behavior in order to improve device characteristics such as the contrast ratio. We have conducted a detailed observation of the switching behavior of a cell with a striped texture and examined the pretilt angle dependence of the alignment state.

Analysis of the Hysteresis Phenomenon in the Intrinsic Half-V-Shaped Switching Ferroelectric Liquid Crystal Mode

The intrinsic half-V-shaped switching ferroelectric liquid crystal mode (iHV-FLC mode) is known to be able to easily yield excellent moving pictures without blurring, based on the nonholding display by simple AC driving in the ideal condition. However, we have sometimes observed the blurred moving pictures even in the iHV-FLC mode with very short response time. We have conducted the detailed measurement of the electrooptical response. The protracted hysteresis phenomenon could be observed in some cells. This phenomenon had a strong relationship with the internal ionic impurity density. The 1st frame hysteresis phenomenon could be observed even in the purest cells. It is considered to be caused by the c-director position at zero field and its driving scheme.