Kohki Takatoh

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

Reduction of the threshold voltages of nematic liquid crystal electrooptical devices by doping inorganic nanoparticles

We report the reduction of threshold voltage, Vth, of twisted nematic liquid crystal devices by doping the nanoparticles of MgO and SiO2. The results are well explained by inserting the experimentally determined values of elastic constants and dielectric anisotropy in the formula Vth = π√Keff/e0Δe, where both of these quantities decrease due to the existence of these nanoparticles. The Vth decrease approximately as √S, where S being the order parameter. The S is also shown to decrease by doping nanoparticles.

Enhancement of Contrast Ratio by Using Ferroelectric Nanoparticles in the Alignment Layer of Liquid Crystal Display

We demonstrate the effect of the ferroelectric nanoparticles dispersed in the alignment layer of a twisted nematic (TN) liquid crystal (LC) panel. In comparison to a conventional TN LC panel with a conventional polymide layer, the TN LC panel with an alignment layer doped with ferroelectric nanoparticles shows a much higher contrast ratio. The effects of barium titanate nanoparticles at several different concentrations have been studied, among which 2.5 and 5 wt % barium titanate nanoparticles mixtures show better performances. The surface texture of the alignment layers has also been studied by atomic force microscopy (AFM).

32.3: New Peeping Prevention Technology to Control Viewing Angle Properties of TFT-LCDs

New peeping prevention technology to control the viewing angle properties of TFT-LCDs has been developed. This technology can be applied to all kinds of LCDs, especially to the ones for PCs, cellular phones, ATMs and so on. In this technology, an additional LC panel in which the whole area is divided into two kinds of small visible domains of different LC alignment directions is used. The products, named VAC Filter™ or VACF™, have been put on sale in 2003 and have been applied to TOSHIBA TECRA M3 and so on.

P-132: Enhancement of the Performance of LCDs by Doping Inorganic Nanoparticles: The Reduction of Operating Voltage and Response Time and the Increase of the Optical Throughput at Low Temperature

We have conducted an investigation into the possibility of realizing the enhancement of the performance of TN-LCDs by doping the nanoparticles of an inorganic compound, MgO, and it is shown that there occur the reduction of operating voltage; and also the reduction of response times both for the rising process and the decaying process, particularly at low temperature, say at −5°C and at −10°C; and the increase of the optical throughput, particularly at low temperature at −10°C.

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.

Improvement of Electro-Optical Characteristics of Liquid Crystal Display by Nanoparticle-Embedded Alignment Layers

The effect of various metal-oxide nanoparticles embedded in the alignment layer of a liquid crystal (LC) display is experimentally investigated. The study mainly focuses on the electro-optical properties of a twisted-nematic LC display. It is confirmed that a certain type of nanoparticles contribute to the enhancement of contrast ratio. In addition, it is observed that for almost all types of nanoparticles used in the present study, the statistical error of electro-optical properties of LC test cells reduces as compared to that of cells without nanoparticles, indicating the improvement of LC molecular alignment. For a further clarification, AFM study and other related measurements are performed.

Physical interpretation of the characteristics of LCDs embedded with MgO and SiO2 nanoparticles

— The electro-optical characteristics of TN-LCD and ECB-LCD cells, both of which were embedded with of MgO and SiO2 nanoparticles at a low concentration of about or below 1 wt.%, were investigated. The threshold voltage and operating voltage of these LCD cells were found to decrease by 5–16%, depending on the materials and the concentration of nanoparticles. Measurements of the physical properties of nanoparticle-embedded NLCs, such as the order parameter, clearing point, birefringence, dielectric anisotropy, elastic constants, and rotational viscosity on the nanoparticle-doped NLC sample cells, were performed. Through these measurements, it is shown that the decrease in the threshold voltage and the operating voltage may be attributed to the decrease in the order parameter by 10–30% due to the existence of these nanoparticles.

Electro-Optical Properties of LCD Doped with Nanoparticles and with Optical Compensators: Ways for Fast Response

This paper consists of two Parts. In the Part 1, we report the experimental results and considerations of the reduction of operation voltage and response time of narrow-gap TN(NTN)-LCDs embedded with the nanoparticles of hydrophobic Aerosil silica. While, in the Part 2, we give a report of the reduction of response time, especially τoff for the decay process of optically compensated tunable birefringence (OCTB)-mode LCD.

Fast-response twisted nematic liquid crystal displays with ultrashort pitch liquid crystalline materials

A new method to improve the response time of twisted nematic (TN) liquid crystal displays (LCDs) with liquid crystalline (LC) materials of pitch length shorter than twice the cell gap is proposed. It was known that by using LC materials possessing shorter pitch length, the response time could be improved. However, in previous studies, the pitch length p was limited to values larger than the twice of the cell gap d. This is because 90° TN arrangements become unstable and transform into a 270° super-twisted nematic (STN) arrangement for p < 2d. It was found that by applying voltage to 270° STN arrangement, the 90° TN arrangement could be formed and the obtained TN-LCDs could be stabilised by photopolymerisation. This is because the 270° STN arrangement contains splay deformation. The obtained TN-LCDs exhibit a fast response. By using this method, fast-response TN-LCDs could be realised maintaining moderate driving voltage.