Ray Hasegawa

Alignment Technology and Applications of Liquid Crystal Devices

Contents Preface Overview, Kohki Takatoh Development of the LCD Market Improvement of Viewing Angle Dependence of the Contrast Ratio Ferroelectric and Antiferroelectric Liquid Crystals Development of Novel Alignment Method The Characteristics of this Book RubbingTechnologies: Mechanisms and Applications, Masaki Hasegawa Introduction Rubbing Mechanisms Applications Non-rubbing Methods Introduction, Masaki Hasegawa Photoalignment, Masaki Hasegawa Oblique Evaporation Method, Masanori Sakamoto Liquid Crystal Alignment on Microgroove Surfaces, Kohki Takatoh LB Membranes for the Alignment Layer, Kohki Takatoh PTFE Drawn Films for Alignment Layers, Kohki Takatoh Liquid Crystalline Alignment on Chemically Treated Surfaces, Kohki Takatoh Applications of Nematic Liquid Crystals Summary of Molecular Alignment and Device Applications, Ray Hasegawa Twisted Nematic (TN), Ray Hasegawa Super Twisted Nematic (STN), Nobuyuki Itoh The IPS (In-Plane Switching) Mode, Mitsuhiro Koden Vertical Alignment (VA) Mode and Multi-domain Vertical Alignment (MVA) Mode, Kohki Takatoh Pi Cell, Masaki Hasegawa Multi-domain Mode, Kohki Takatoh Polymer Dispersed Liquid Crystals (PDLC), Ray Hasegawa Alignment Phenomena of Smectic Liquid Crystals Layer Structure and Molecular Orientation of Ferroelectric Liquid Crystals, Nobuyuki Itoh Alignment and Bistability of Ferroelectric Liquid Crystals, Kohki Takatoh Applications of Ferroelectric and Antiferroelectric Liquid Crystals Molecular Orientations and Display Performance in FLC Displays, Mitsuhiro Koden Alignment and Performance of AFLCD, Kohki Takatoh Application of FLC/AFLC Materials to Active-matrix Devices, Kohki Takatoh Index

Dynamic Analysis of Polymer-Dispersed Liquid Crystal by Infrared Spectroscopy

The dynamic behavior of a polymer-dispersed liquid crystal (PDLC) under an electric field has been studied by static and two-dimensional infrared spectroscopy. The PDLC sample was prepared by polymerization-induced phase separation of a mixture of nematic liquid crystal E7 and acrylate. 2D IR correlation analysis indicates that the rigid core of the liquid crystal molecules reorients as a unit, and suggests that the polymer side chain existing in the interface between the polymer and the liquid crystals may reorient in phase with the liquid crystal reorientation by interaction with the liquid crystal molecules.

Analysis of rubbed polyimide films by polarized infrared spectroscopy : Effects of immersion in organic solvents

We applied polarized infrared (IR) spectroscopy to the analysis of rubbed polyimide (PI) films and evaluated the PI orientation induced by rubbing by measuring the dichroic difference. The IR dichroic difference and liquid crystal (LC) alignment were analyzed for rubbed PI films that were immersed in various organic solvents. The solvents which reduced the dichroic difference and pretilt angle of LC molecules could be characterized in terms of their solubility parameters. When the dichroic difference of the PI films was greatly reduced by the immersion in the solvents, a correlation between the LC pretilt angle and the dichroic difference (i.e. the in-plane orientation of the PI molecules) was observed.

Effect of Non-DC Voltage Applied during N*–SmC* Phase Transition on Alignment of Half-V-Shaped Switching Ferroelectric Liquid Crystal

In a half-V-shaped switching ferroelectric liquid crystal (half-V FLC), a liquid crystal material with N*?SmC* phase transition is used. When the material is cooled from N* phase to SmC* phase without an applied electric field, two types of domain with spontaneous polarization (Ps) in the upward or downward direction to the substrate plane are formed. In the conventional half-V FLC, a DC voltage is applied to the liquid crystal during the phase transition to form either type of domain selectively. Is the DC voltage application indispensable for selecting one domain? To clarify this point and to reduce the expected residual charge due to the application of the DC voltage, various waveforms of non-DC voltage were studied. We achieved the formation of one type of domain by applying an asymmetric rectangular waveform adjusted to cancel the effective DC component, and the generation of residual charge was avoided. The obtained half-V FLC alignment showed desirable black appearance in the crossed polarizers.

Analysis of Rubbed Polyimide Films by Polarized Infrared Spectroscopy

Abstract Polarized infrared spectroscopy was applied to the analysis of rubbed polyimide films. N2 purge of a sample chamber and increased substrate thickness enhanced the detection sensitivity. Dichroic differences were measured for the rubbed polyimide films at varied translating speed of the rubbing roller and at varied substrate temperature. The results suggest that the orientation of the polyimide was enhanced by increased polyimide surface temperature brought about by the heat of friction or the external heat. Moreover, a correlation between the LC alignment and the orientation of the polyimide chains was revealed by the analysis of the dichroic difference of the rubbed polyimide films immersed in organic solvents and the LC alignment on the films.

Analysis of electro-optical properties of polymer-stabilized OCB and the application to TFT-LCDs

— A 9-in. full-color polymer-stabilized OCB TFT-LCD with stable bend alignment in the absence of an electric field was developed. The condition of the polymer stabilization, the characteristics of UV-curable monomers, and their influence on the configurations of the polymer network in the cell were studied. Possible models of the configuration were proposed and their relationship to the electro-optical properties was analyzed using a novel simulation method considering the distribution of anchoring effects from both alignment surfaces and the polymer network. It was suggested that a good performance such as high contrast ratio and fast response could be expected in the polymer network originating from newly developed monomers composed of multifunctional LC acrylates due to a relatively weak-anchoring effect and presumably its localization near the alignment surfaces. By using the newly developed monomers under the optimized polymer-stabilizing process, a high contrast ratio of 250:1 and fast response nearly equal to that of a conventional OCB cell were achieved.

17.3: Electro‐Optical Properties of Polymer‐Stabilized OCB and Its Application to TFT‐LCD

To eliminate an initial transition from splay to bend alignment, polymer-stabilized OCB was developed. The influences of the monomer concentration and the applied voltage during UV irradiation were studied, and stable bend alignment in the absence of electric field was obtained. The large retardation change and the fast response were achieved by using a mixture of multifunctional LC acrylate monomers, and a 9-inch full-color polymer-stabilized OCB TFT-LCD with initial bend alignment and the contrast ratio of 250:1 was successfully developed.

A 15‐in. XGA thresholdless antiferroelectric LCD addressed by TFTs and using the quasi‐dc driving method

— A 15-in. TFT-LCD with XGA resolution using thresholdless antiferroelectric liquid crystal (TLAF) has been developed. TLAF materials show V-shaped switching and enable display of analog gray scale, wide viewing angle, and fast response. However, in the case that high-resolution TFT-LCDs using materials with large spontaneous polarization such as TLAF were driven by the conventional method, alternating current (ac) driving, the obtained contrast ratio was limited because of a sharp decline of holding voltage due to the growth of a depolarization field. In order to enhance the contrast ratio, a novel driving method referred to as quasi-dc driving was proposed. In the quasi-dc driving, the polarity of the applied voltage to liquid crystals inverts at certain intervals of several seconds. Moreover, the applied voltage and the charging time at the time of polarity inversion are increased more than the intended signals. By this method, the 15-in. TFT-LCD using TLAF with high contrast ratio (more than 100:1) and wide viewing angle was realized.

Application of FLC/AFLC materials to active-matrix devices

The market of TFT-LCDs has been enlarged during the last 10 years. Notebook computers have been the main application. For this application, twisted nematic mode has been used and demands for other modes has been limited. However, larger size of LCDs for monitors or TV are expected to be the next most promising market. Drawbacks of the twisted nematic (TN) mode for this market were narrow viewing angle and slow switching speed. The viewing angle dependence was overcome by using compensation film or by using new LCD modes, for example in-plane switching mode. The slow response is the last drawback to be overcome to realize excellent moving pictures which will be seriously requested in the near future. Several methods have been proposed for fast response of LCDs. However, the applications of ferroelectric liquid crystalline or antiferroelectric liquid crystalline (AFLC) (FLC) materials to TFT-LCDs should be the most promising one. In this article, the authors will review the application of FLC/AFLC materials to TFT-LCDs, such as deformed helix ferroelectric (DHF) mode, twisted FLC mode, monostable FLC mode, APD mode and the application of frustrated phase. Next, the problems to be solved for the application of these materials to TFT devices will be discussed. Finally, the authors will demonstrate the 15″ XGA TFT-LCD using liquid crystalline material showing frustoelectric LC state, which is driven by newly developed driving technologies. Copyright

Electro-optical properties of thresholdless antiferroelectric liquid crystal and its application to high-resolution TFT-LCD

Abstract Thresholdless antiferroelectric liquid crystal (TLAF) characterized by V-shaped switching in a smectic liquid crystal is very attractive for active matrix driving, but the switching mechanism is not fully understood. We have studied electro-optical properties of the TLAF material MLC-0071, and developed a 15-inch TFT-LCD with XGA resolution using the material. Temperature-dependence of relative permittivity suggested the presence of a Goldstone mode. This result implies the V-shaped switching of MLC-0071 is based on a smectic C*-like phase. From the measurements of optical anisotropy etc., it was found that the TLAF had a chevron structure and the molecules oriented parallel to the substrate plane when gray-level voltage was applied. The 15-inch TLAF-TFT-LCD provided wide viewing angle, high contrast ratio and small color shift.