Plasma‐beam alignment technique for ferroelectric liquid crystals

Abstract— The plasma‐beam alignment procedure earlier developed for the alignment of nematic liquid crystals is successfully extended to ferroelectric liquid crystals (FLC). The highly uniform alignment of the “chevron” structure (before electrical treatment of FLC cells) and “quasi bookshelf” structure (after the electrical treatment) are realized. The contrast of bistable switching larger than 350:1 is achieved. This makes the non‐contact plasma‐beam alignment procedure especially attractive for high‐contrast bistable LCDs on an LCOS base, particularly used in PDA and e‐books. Fast switching and realization of gray scale in the plasma‐beam aligned FLC cells makes this technique also promising for full‐color displays including color LCD TV.     

Defect‐free half‐V‐mode ferroelectric liquid‐crystal device

Abstract— The horizontal chevron defect found in a half‐V‐mode ferroelectric‐liquid‐crystal (HV‐FLC) device can be suppressed by lowering the FLC's total free energy. The energy levels between spontaneous polarization (PS) up and down domains were degenerated by asymmetrical‐alignment treatments. The difference in the polar surface coefficient (γ²) was the key to suppressing the alignment defect. Alignment layers with opposite surface polarities and different anchoring energies were applied to control the sign and value of γ². The asymmetric cells of PIrub ‐ PIplasma (rubbed polyimide and plasma‐treated polyimide surfaces), PVArub ‐ PIplasma (rubbed polyvinyl alcohol and plasma‐treated polyimide surfaces), and PVArub ‐ PIplasma (both rubbed PI and PVA) alignment conditions presented defect‐free alignment textures under a slow‐cooling process. Among these different alignment treatments, the PVArub ‐ PIrub treated cell demonstrated the best alignment result, benefited by the largest difference in polar surface coefficient.     

Field‐induced photo‐reactive alignment technology for the vertical‐alignment liquid‐crystal mode

Abstract— An advanced vertical‐alignment liquid‐crystal (VA‐LC) technology based on field‐induced photo‐reactive alignment (FPA) as an advanced alignment mode for VA is proposed. FPA realizes uniform alignment and a faster rising response time, especially at high voltage. This technology can generate a pre‐tilt angle only by using photo‐reactive alignment material so that the tact time is shorter and the long‐term reliability is higher than that of conventional photo‐reactive processes, which require additional photo‐reactive monomers. The advanced hybrid FPA was developed by adopting both the tilted alignment with a pre‐tilt angle and conventional vertical alignment. By using an advanced hybrid structure, the response time and contrast ratio can be further improved.     

Plasma beam alignment for the large‐area substrates: Equipment and process

Abstract— We have developed an effective method for liquid‐crystal alignment of the large‐area substrates. This method is based on the oblique treatment of the alignment substrates with a “sheet” of accelerated plasma generated by the anode layer source of the “race track” geometry. During this treatment, the substrate or source is cyclically translated in the direction perpendicular to the plasma “sheet.” This method provides planar, tilted, and vertical liquid‐crystal alignment with excellent uniformity and reproducibility and easy axis control in the azimuthal and polar planes.     

Polymer‐stabilized pretilt angle on the surface of nanoparticle‐induced vertical‐alignment surface for multi‐domain vertical‐alignment liquid‐crystal display

Abstract— By introducing polyhedral oligomeric silsesquioxane (POSS) nanoparticles along with a controlled amount of UV‐curable reactive mesogen (RM) into a liquid‐crystalline (LC) medium, a multi‐domain vertical‐alignment LC device was successfully demonstrated. The device, possessing a vertically aligned LC director in four different azimuthal directions, exhibited a fast response time and wide‐viewing‐angle characteristics, in the absence of conventional polymer‐type vertical‐alignment layers. Electro‐optic characteristics of the fabricated device, before and after UV curing of the cell, were studied. The surface morphology of the substrate surfaces were analyzed by using field‐emission scanning electron microscopy (FESEM). The experimental results show that the technology will possibly be applicable to cost‐effective vertical‐alignment liquid‐crystal devices and is suitable for green‐technology liquid‐crystal displays.     

Plasma‐beam alignment of passive liquid crystals (Invited Paper)

Abstract— A plasma‐beam process, developed for the alignment of liquid crystals (LC) in electro‐optic applications, has been successfully applied to align “non‐standard” LC, such as crystalline materials with LC phases at elevated temperatures and reactive mesogenes. In addition to the high alignment quality of the materials, there is no need for an intermediate layer between the substrate and the LC layer. Furthermore, the construction of our source simplifies the alignment procedure of large‐area rigid substrates and the roll‐to‐roll processing of flexible films. This method opens new horizons for optical retarders and polarizers, as well as anisotropic semiconducting films for organic electronics.     

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

Abstract— 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.     

Novel application of ink‐jet‐printing technology in multi‐domain alignment liquid‐crystal displays

Abstract— Based on the drop‐on‐demand characteristics of ink‐jet printing, the multi‐domain alignment liquid‐crystal display (LCD) could be achieved by using patterned polyimide materials. These polyimide ink locations with different alignment procedures could be defined in a single pixel, depending on the designer 's setting. In this paper, we combined the electro‐optical design, polyimide ink formulation, and ink‐jetting technology to demonstrate the application of multi‐domain alignment liquid‐crystal display manufactory. The first one was a multi‐domain vertical‐alignment LCD. After the horizontal alignment material pattern on the vertical alignment film, the viewing angle would reach 150° without compensation film. The second one was a single‐cell‐gap transflective LCD within integrating the horizontal alignment in the transmissive region and hybrid alignment in the reflective one in the same pixel. In addition, this transflective LCD was also demonstrated in the form of a 2.4‐in. 170‐ppi prototype.     

Optical rewritable liquid‐crystal‐alignment technology

Abstract— A new optical rewritable (ORW) liquid‐crystal‐alignment technology has been developed to create a display and to demonstrate its maturity and potential. ORW displays have no electrodes and use polarizers as substrates. The display requires no photolithography on plastic. Its simple construction secures durability and low cost for mass production. The on‐screen information is optically changed in a writing unit that consists of an LCD mask and an exposure source that is based on LEDs, low power, and low cost in comparison with Hg lamps or lasers. A high contrast image can be easily written, viewed, and rewritten through a polarizer, while the multi‐stable gray‐level image requires zero power to maintain the image. Reconfigurable LC alignment using ORW technology best suits plastic‐card displays as well as for LC photonics and various one‐mask processes of patterned LC‐alignment applications.     

Electro‐optical characteristics of ion‐beam‐aligned FFS‐LCDs on diamond‐like‐carbon thin film

Abstract— A fringe‐field‐switching (FFS) mode cell having LC alignment has been developed by using a non‐rubbing method, a ion‐beam‐alignment method on a‐C:H thin film, to analyze the electro‐optical characteristics of this cell. The suitable inorganic thin film for FFS‐LCDs and the alignment capabilities of nematic liquid crystal (NLC) have been studied. An excellent voltage‐transmittance (V‐T) and response‐time curve for the ion‐beam‐aligned FFS‐LCDs were observed using oblique ion‐beam exposure on DLC thin films.     

Electro‐optical characteristics and optimization of vertically aligned STN‐LCDs

A new LCD for high‐duty passive‐matrix driving, referred to as a vertically aligned (VA) STN‐LCD, characterized by high transmittance and a high contrast ratio, has been developed. This LCD can display black‐and‐white images by using crossed polarizers without the use of a color compensator because the LCD has almost zero retardation at the initial alignment state. A fabricated black‐and‐white VA‐STN‐LCD without a black matrix shows high transmittance (>15%) and contrast (CR > 100) under 1/240‐duty direct‐multiplex driving.     

Photoalignment and photo‐patterning of planar and homeotropic liquid‐crystal‐display configurations

Abstract— Optical alignment and micro‐patterning of the alignment of liquid‐crystal displays (LCDs) by linear photopolymerization (LPP) technology renders high‐quality multi‐domain twisted‐nematic (TN) and supertwisted‐nematic (STN) displays with broad fields of view over wide temperature ranges feasible. The prerequisites are the generation of photo‐induced high‐resolution azimuthal alignment patterns with defined bias‐tilt angles 0° ≤ θ ≤ 90°. For the first time, LPP‐aligned single‐ and dual‐domain vertically aligned nematic LCDs (VAN‐LCDs) are presented. Dual‐domain VAN‐LCDs are shown to exhibit broad fields of view which are further broadened by combining the displays with LPP‐aligned optical compensators made of liquid‐crystal polymers.     

Diamond‐like‐carbon LC‐alignment layers for application in LCOS microdisplays

Abstract— To improve the lifetime and yield of LCOS microdisplays, non‐contact LC alignment techniques using inorganic materials are under investigation. This report focuses on oblique ion‐beam treatment of diamond‐like carbon (DLC) layers, and in particular on the influence of the ion dose on the LC alignment on DLC, keeping the ion‐beam angle (40°) and ion‐beam energy (170 eV) the same. LC alignment on ion‐milled DLC layers is uniform if the ion dose is between 3.8 × 10^?4 C/cm² and 5.5 × 10^?3 C/cm². Above and below this ion dose range, non‐uniform alignment is observed. NEXAFS experiments show that this is caused by lack of molecular anisotropy on the surface of the ion‐milled DLC layers. By varying the ion dose between 3.8 × 10^?4 C/cm² and 5.5 × 10^?3 C/cm², LC molecules have an average pre‐tilt between 3° and 5°, which is within the desired range for application in LCOS microdisplays. The lifetime of the LCOS microdisplays with ion‐milled DLC for projection‐TV application is, however, shorter than the lifetime of microdisplays with PI layers. Ion milling probably creates a reactive surface that is unstable under the high light fluxes used in projection TVs. A solution for this problem could be chemical passivation of the ion‐milled alignment layers. Initial experiments with passivation of ion‐milled PI resulted in an increase in lifetime, but the lifetime after passivation was still lower than the lifetime of rubbed PI layers (factor 0.7). Nevertheless, ion‐milling of DLC or PI can be a good alternative LC alignment technique in other LCD applications. LC‐alignment layers based on inorganic layers such as obliquely deposited SiO₂ films would be a better option for application in LCOS microdisplays due to their higher light stability.     

Ferroelectric liquid crystal aligned on SiO2 thin films using ion‐beam deposition

Abstract— Results for a ferroelectric‐liquid‐crystal (FLC) display cell, aligned on inorganic SiO₂ thin‐film surfaces by using oblique ion‐beam sputtering deposition on the substrates, is presented. A large deposition angle from 60° to 80° can be employed for the thin alignment layer, with thicknesses varying from 5 to 40 nm. Two types of uniform alignment, chevron (before electrical treatment) and quazi‐bookshelf (after electrical treatment), were studied. High‐quality alignment on large‐sized substrates was also easily be achieved because of the linear design of the ion‐beam sputtering source, which was previously a significant challenge for FLC on SiO_x layers.     

Properties of azo‐dye alignment layer on plastic substrates

Abstract— The alignment properties of the azo‐dye photo‐alignment material SD‐1/SDA‐2 on plastic substrates are investigated. Important liquid‐crystal cell parameters, such as azimuthal and polar anchoring energy, pretilt angle, voltage holding ratio, and the corresponding electro‐optical properties are presented. Excellent alignment with high anchoring energy can be achieved with a polarized UV dose less than 1.0 J/cm². A reflective six‐digit flexible passive‐matrix‐driven TN‐LCD for smart‐card applications showing excellent electro‐optical properties is demonstrated.     

Second wind of the oblique deposition method of liquid‐crystal alignment: Ion‐beam sputtering technique

Abstract— Liquid‐crystal (LC) alignment on SiO_x films produced by ion‐beam sputtering deposition was comprehensively studied. The conditions for planar, tilted planar, homeotropic, and tilted homeotropic LC alignment of high uniformity were determined. The alignment photostability and aging issue are discussed. An original sputtering system based on the anode‐layer source excelling in high reliability and quality of sputtered coatings were used. Because this system can be easily scaled up, the alignment treatment of the large‐area alignment substrates, including those used in modern LCD manufacturing, can be realized. The advantages of the sputtering LC alignment technique, in comparison with its vapor‐deposition predecessor, are described.     

Color performance of an MVA‐LCD using an LED backlight

Abstract— The color performance, including color gamut, color shift, and gamma curve, of a multi‐domain vertical‐alignment (MVA) liquid‐crystal display (LCD) using an LED backlight are calculated quantitatively. Simulation results indicate that an LED backlight exhibits better angular color uniformity and smaller color shifts than a CCFL backlight. Color gamut can be further widened and color shift reduced when using a color‐sequential RGB‐LED backlight without color filters, while the angular‐dependent gamma curves are less influenced using different backlights. The obtained quantitative results are useful for optimizing the color performance and color management of high‐end LCD monitors and LCD TVs.     

A single‐cell‐gap transflective LCD using active‐level‐shift technology

Abstract— A single‐cell‐gap transflective LCD using active‐level‐shift (ALS) technology has been developed and is presented. An efficient pixel architecture has recently been designed to apply different voltages on transmissive and reflective subpixels through two separated storage capacitors, formed by a boosting electrode and pixel electrodes. A 2.2‐in. vertical‐alignment‐mode (VA) transflective LCD prototype with a similar gamma for both the transmissive and reflective areas was obtained. Compared to a conventional dual‐cell‐gap design, the new single‐cell‐gap design achieves a 17% higher aperture ratio and the contrast increased from 200:1 to 500:1.     

Tuning the alignment of liquid crystals by means of nano‐structured surfaces (Invited Paper)

Abstract— The solid‐surface/liquid‐crystal interactions, defining the field‐free alignment of the liquid crystal in conventional liquid‐crystal displays, are playing a vital role in their optical appearance and performance. Nano‐scale changes in the solid‐surface structure induced by light have been recently shown to affect the anchoring strength and the easy‐axis direction. Fine tuning of the anchoring strength is also demonstrated by nano‐structuring of the Langmuir‐Blodgett monolayer employed as liquid‐crystal alignment layers promoting homeotropic orientation. On the basis of nano‐engineering of the surface alignment properties, two novel alignment concepts have been introduced: electrically commanded surfaces (ECS) and high‐performance alignment layers (HiPAL). Nano‐structured polymers related to these concepts have been designed, synthesized, and used as materials for alignment layers in LCDs. ECS materials belong to the category of active alignment materials designed to mediate switching of the liquid crystal, whereas the HiPAL materials make possible the control of the molecular tilt angle in a broad range, from 0° to 90°, and they seem to enable the control of the anchoring strength as well. The nano‐structured alignment materials are strong candidates for implementation in a new generation of advanced liquid‐crystal displays and devices.     

A new vertical‐alignment LC mode with high‐transmittance and fast‐response‐time features

Abstract— A novel pixel design for vertical‐alignment LCDs with superior transmittance has been developed. The new liquid‐crystal mode, refered to as the hole‐induced vertical‐alignment mode (Hi‐VA), uses a via hole of an organic layer on a TFT substrate to achieve multi‐domain alignment. Compared to the conventional design, the Hi‐VA mode has a transmittance of up to 135% with a contrast ratio of 2000:1. Moreover, the new structure is free from ITO patterning or protrusion on the color‐filter side, which makes the fabrication process simple and low cost.