Comparison of organic and inorganic alignment layers for low‐power liquid‐crystal devices using low‐frequency applied‐voltage waveforms

Abstract— Bistable displays are known to have low‐power consumption, but they usually lack the ability to display full‐color video‐rate images. Operating active‐matrix liquid‐crystal displays (AMLCDs) with an ultra‐wide refresh‐rate range, down to ～1 Hz, can lower the power consumption to that of bistable devices and offer video rates as well. A SiO^x‐layer‐based liquid‐crystal (LC) alignment technique is studied here to overcome the ion problems typically encountered with low‐refresh‐rate devices. The effect of ions on the voltage‐holding ratio (VHR) and residual DC voltage (RDC) with SiO^x‐based LC alignment is compared with those for polyimide‐based LC alignment. It is found that only SiO^x alignment provides high VHR and small RDC, with good stability over time. Therefore, it is shown that SiO^x alignment is an excellent candidate for low‐power AMLCDs operated with an ultra‐wide refresh‐rate range.     

A polarizer‐free flexible display using dye‐doped liquid‐crystal gels

Abstract— A reflective‐type polarizer‐free flexible display using a dye‐doped liquid‐crystal (LC) gels is demonstrated. Compared to the conventional guest‐host LC mode, it has high contrast ratio and brightness due to the combining of both scattering and absorption. Such a gel‐like flexible display is bendable and trimable. In this paper, a three‐step switch using distinct dye‐doped LC gels is also demonstrated. The potential applications are e‐paper and decorative displays.     

Improvement of off‐axis color shift on hybrid viewing‐angle device using dual γ‐voltage method

We have mass production on one kind of liquid crystal display (LCD) device with hybrid viewing‐angle (HVA), which can be switched between the wide viewing‐angle (WVA) and narrow viewing‐angle (NVA) by one button. This device adopts the single cell design that with lower cost, and utilizes the optical properties of electrically tilted LC to achieve the function of NVA display. An issue has received less attention in the past and been indeed found in the production process. It is that the off‐axis color shift will appear in NVA mode. We put forward one method to improve this issue here, which is combined with the concepts of Gray Frame Insertion (GFI) and Impulse‐type driving. By switching the voltage between two different γ values, the color shift will be perfected on the produce.     

A single‐substrate multicolor cholesteric liquid‐crystal display prepared through ink‐jet printing

Abstract— Ink‐jet printing was used to prepare a single‐substrate multicolor cholesteric liquid‐crystal (Ch‐LC) display incorporating three Ch‐LCs exhibiting different reflective wavelengths. A room‐temperature low‐vacuum chemical‐vapor‐deposition process was developed for coating a thin polymer film onto the Ch‐LC so that the top electrode could be coated onto the Ch‐LC layer. Herein, the successful operation of such a 10.4‐in. QVGA Ch‐LC display at 40 V will be described.     

Electric‐field‐driven LC lens for 3‐D/2‐D autostereoscopic display

Abstract— The use of an electric‐field‐driven liquid‐crystal (ELC) lens cell for switching between a 3‐D and 2‐D display is proposed. Due to the phase retardation of the non‐uniform LC directors, an ELC lens functions the same as a geometric lens. The parameters of an ELC for 3‐D applications are optimized through the simulation of the electrode configuration and voltage levels. A prototype was made where the ELC lens is placed in front of a liquid‐crystal display (LCD) 15 in. on the diagonal with a 99‐μm subpixel pitch. Under zero voltage, the ELC lens is a transparent medium and the users can see a clear 2‐D image. In 3‐D mode, the ELC lens array performs the same as a cylindrical lens array to the incident vertical polarization under suitable driving voltages. Placing a half‐wave plate between the LCD and ELC lens is proposed to change the polarization of the LCD to be parallel with the polarization lens direction of the ELC lens. The measurement of the horizontal luminance profile, performance of the ELC lens, and feasibility for 3‐D/2‐D switching was verified. The fabrication process for the ELC lens is compatible with the current LCD production process and enables the accurate control of the lens pitch of the ELC lens.     

Double‐faced TFT‐LCD having one LC panel and one lighting system

Abstract— We have developed a novel liquid‐crystal‐display (LCD) system referred to as a “Double‐Faced LCD.” It has only one LC panel and one lighting system, but it works not only as a transmissive‐type LCD from one side but also as a reflective‐type LCD from the other side. Therefore, the thickness and the weight of the Double‐Faced LCD can be reduced compared to those of conventional LC modules that have two LC panels and two lighting systems.     

Pixel‐isolated liquid‐crystal mode by using a patterned anisotropic phase separation for flexible LCDs

Abstract— A pixel‐isolated liquid‐crystal (PILC) mode for enhancing the mechanical stability of flexible‐display applications is proposed. Because liquid‐crystal (LC) molecules in this mode are isolated in each pixel by patterned or phase‐separated microstructures, and the two substrates are tightly attached to each other by a solidified polymer layer, the LC alignment is stable against external pressure, and the cell gap of our structure is uniformly preserved against bending deformation of the plastic substrates. The mechanical stability of the PILC structure having plastic substrates was tested for its electro‐optic properties.     

Prospects of emerging polymer‐stabilized blue‐phase liquid‐crystal displays

Abstract— The prospects of emerging polymer‐stabilized blue‐phase liquid‐crystal displays, or more generally, Kerr‐effect‐induced isotropic‐to‐anisotropic transition, are analyzed with special emphases on the temperature effects. As the temperature increases, both the Kerr constant, induced birefringence, and response time decrease but at different rates. The proposed physical models fit well with experimental results. Some remaining technical challenges associated with this promising display technology are discussed.     

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.     

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.     

A wide view auto‐stereoscopic 3D display with an eye‐tracking system for enhanced horizontal viewing position and viewing distance

This paper describes the development of auto‐stereoscopic three‐dimensional (3D) display with an eye‐tracking system for not only the X‐axis (right–left) and Y‐axis (up–down) plane directions but also the Z‐axis (forward–backward) direction. In the past, the eye‐tracking 3D system for the XY‐axes plane directions that we had developed had a narrow 3D viewing space in the Z‐axis direction because of occurrence of 3D crosstalk variation on screen. The 3D crosstalk variation on screen was occurred when the viewer's eye position moved back and forth along the Z‐axis direction. The reason was that the liquid crystal (LC) barrier pitch was fixed and the LC barrier was able to control the only barrier aperture position. To solve this problem, we developed the LC barrier that is able to control the barrier pitch as well as the barrier aperture position in real time, corresponding to the viewer's eye position. As a result, the 3D viewing space has achieved to expand up to 320–1016 mm from the display surface in the Z‐axis direction and within a range of ±267 mm in the X‐axis direction. In terms of the Y‐axis direction, the viewing space is not necessary to be considered, because of a stripe‐shaped parallax barrier.     

Liquid‐crystal‐material technologies for advanced display applications

Abstract— Ions were dissolved into the liquid‐crystal (LC) materials from peripheral materials and were also generated by electric dissociation. Moreover, those ions are partly stabilized in the form of hydrated or solvated ions with polar molecules. As the ions in an LC slab of display panel deteriorate the image quality, it is essential that LC materials be free from mobile ions and be resilent to contamination by ions. Studies on the generation and behavior of ions in LC materials and their influence on display image quality were successfully applied to the development of advanced LC materials featuring high reliability and high purity, as well as low operational voltage, resulting in sophisticated LCDs with high image quality.     

Controling color of liquid‐crystal displays

Abstract— Two newly derived characterization models for a liquid‐crystal (LC) display have been tested for five LC‐based displays. Data measured from a series of test colors indicated that all LC‐based displays showed similar characteristics, including an S‐shaped tone curve and poor channel chromaticity constancy. Because they include a hyperbolic function in their definition, the models do not have analytical inverses, and so iterative mathematical techniques are applied. It was shown that a new characterization model based on a hyperbolic function fits the tone curve very accurately with only four coefficients per channel for any type of LCD. In addition, it was also shown that the first derivative of the function provides a means of accurate correction of the chromaticity variation.     

Alignment control technology of liquid crystal molecules

Liquid crystal displays are now indispensable in everyday life. The display characteristics considerably depend on the configuration of liquid crystal (LC) molecules and interactions between the LC molecules and an alignment film surface. In this paper, we introduce various methods to control parameters that dominate the LC alignment. These parameters include order parameters, the pretilt angle, the director direction, and surface anchoring strength. We also introduce their evaluation methods. In particular, recent alignment film‐free technology is explained in detail. In addition, details of how these parameters are related to the display characteristics, particularly wide viewing angles and fast response characteristics, are described primarily with reference to recent technologies.     

A reflective polarizer‐free display using dye‐doped polymer‐stabilized blue‐phase liquid crystals

Abstract— A reflective polarizer‐free display using dye‐doped polymer‐stabilized blue‐phase liquid crystal (DDPSBP‐LC) has been demonstrated. The mechanism is a combination of electrically tunable light absorption and Bragg reflection. In this paper, the influence of light absorption in DDPSBP‐LC by changing the dye concentration and absorption paths has been studied. Increased dye concentration can improve the contrast ratio of DDPSBP‐LC; however, the response time is the tradeoff. Increasing the cell gap can improve the contrast ratio of DDPSBP‐LC; however, the response time remains the same. The study of DDPSBP‐LC can help in shutter‐glass applications of 3‐D displays and electronic paper.     

Fast response fringe‐field switching mode liquid crystal development for shutter glass 3D

A type of fast response time (RT) liquid crystal (LC) was developed to adopt in fringe‐field switching (FFS) mode for shutter glass 3D display device, the average gray to gray level (GTG) RT can reduce from 7.43 ms to 4.48 ms at a refreshing rate of 60 Hz, and the transmittance can increase by 15.4% compared with conventional LC based on the same cell gap. Meanwhile, the correlation among optical efficiency, correlative color temperature (CCT) of module and retardation of LC for FFS mode was studied. Transmittance is proportional to the retardation of LC; however, the CCT is inversely proportional to the retardation. The fast response LC can keep almost the original optical efficiency and CCT.     

A single‐cell‐gap transflective liquid‐crystal display with special electrodes

Abstract— A single‐cell‐gap transflective liquid‐crystal display with special electrodes was demonstrated. In the transmissive region, a strong longitudinal electric field was generated by decreasing the distance between the top and bottom transparent indium‐tin‐oxide electrodes; while in the reflective region, a weak longitudinal electric field is generated by increasing the distance between the top and bottom transparent indium‐tin‐oxide electrodes. And slit‐patterned electrodes were used to optimize the fringe field at the junction of the transmissive and reflective regions. As a result, both the transmissive and reflective display modes show well‐matched gray scales. The simulated single‐cell‐gap TR‐LCD has good performances.     

Optimized electro-optical properties of polymer-stabilized vertical-aligned liquid crystal displays driven by an in-plane field

Polymer networks are employed in vertical-aligned liquid crystal (LC) cells to stabilize the LC molecular configuration under the in-plane field driving. Two different polymer morphologies, respectively produced by the monofunctional and bifunctional acrylate monomers, are assembled on the glass-substrate surface. The enhanced electro-optical performance is observed on the LC cell with bifunctional acrylate polymer networks, and the appropriate display cell is developed at an optimum concentration of 2 wt%. This type of polymer-LC cell shows the fast turn-off and turn-on responses at the low driving voltage, which are attributed to the strong anchoring and the stable LC reorientations, respectively. Furthermore, around 30% improvement in the gray-level response on the 2-wt%-TA-9164-polymer-LC cell is successfully achieved, as compared to the pure LC cells.     

Transflective twisted‐nematic liquid‐crystal display with double twisted‐nematic cell and twisted liquid‐crystal retarder

Abstract— Two configurations, (i) a double‐cell‐gap twisted nematic (DTN) liquid‐crystal display (LCD) and (ii) a single‐cell‐gap twisted‐nematic (TN) liquid‐crystal display (LCD) using a twisted LC retarder, were optimized for transflective liquid‐crystal displays. For the DTN configuration, both the single‐cell‐gap approach and the double‐cell‐gap approach were considered. The optimized configurations exhibit a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. They are easy to fabricate and also possess a perfect dark state. Both are suitable for high‐quality transflective TFT‐LCDs.     

Homeotropic alignment of liquid crystals on ITO surface using LBL assembly

In this work, the very thin layer‐by‐layer (LBL) film that was constructed by dip coating method on indium tin oxide surface can be used in liquid crystal (LC) displays devices. The obtained results indicate that the ultrathin LBL film shows the homeotropic alignment layer, and a uniform vertical alignment of LC molecules was gained very easily. The progress of vertical‐aligned LC cells with a LBL layer was evaluated. The obtained threshold voltage and response time of the LC cell were 2.472 V and 12.5 ms, respectively. So, the competitive performance of the LC cell could allow new sign at a low‐cost budget with rubbing process in LC display technology.