Liquid‐crystal photoaligning by azo dyes (Invited Paper)

Abstract— Liquid‐crystal (LC) photoalignment using azo dyes is described. It will be shown that this photoaligning method can provide a highly uniform alignment with a controllable pretilt angle and strong anchoring energy of the LC cell, as well as a high thermal and UV stability. The application of LC photoalignment to the fabrication of various types of liquid‐crystal displays, such as VAN‐LCDs, FLCDs, TN‐LCDs, and microdisplays, on glass and plastic substrates is also discussed. Azo‐dye photoaligned super‐thin polarizers and phase retarders are considered as new optical elements in LCD production, in particular for transflective displays.     

Current status and future prospect of in‐cell‐polarizer technology

Abstract— A thin‐crystalline‐film (TCF) polarizer has been developed which can be used internally in liquid‐crystal‐display cells. Based on this material, a manufacturing process has been developed for the fabrication of monochrome LCDs with internal polarizers. A new TCF polarizer material and coating equipment, developed to realize a high‐performance color TFT‐LCD, are discussed.     

Evaluation and optimization by colorimetry of polarizers for liquid crystal display

This paper describes the development of useful polarizers for LCD application, their optimization and evaluation based on colorimetry. Figures of merit are suggested for the characterization of LCDs and polarizers using this technique. More than 50 polarizers were used in the experiment, which also evaluated their use for both twisted nematic black-and-white LCDs and guest-host colour LCDs. Their optical properties and the associated display legibility were shown to be best exprssed colorimetrically.     

Single‐cell‐gap transflective liquid‐crystal display using double‐ and single‐mode approaches

Abstract— In this paper, many popular methods to study transflective liquid‐crystal‐displays (LCDs) have been discussed, and several new transflective LCD configurations with a single‐cell gap have been proposed. The traditional double‐cell‐gap method gives the best match of the transmittance/reflectance voltage curve (TVC/RVC) and also the widest viewing angle, but also brings the highest fabrication complexity. The single‐cell‐gap transflective LCD is much easier to fabricate and also shows a good match of TVC/RVC. A new methodology has been shown to find optimal configurations for single‐cell‐gap transflective LCDs. New configurations using multimode in a single pixel include twisted nematic (TN) optically compensated bend (OCB), TN electrically controlled birefringence (ECB), and TN low‐twisted nematic (LTN). TN and hybrid‐aligned nematic (HAN) modes have been investigated for single‐mode transflective LCDs. The results exhibit high contrast ratio, a good match of TVC/RVC, as well as wide viewing angle.     

Review of viewing‐angle compensation of TN‐mode LCDs using WV film

Abstract— Wide‐view (WV) films for TN‐mode LCDs, which optimize the optical parameters of the polymerized discotic material (PDM) layer and cellulose triacetate (CTA) have been developed. The development concept of the WV film and realization of its concept in the past and for the future will be reviewed. In particular, the discotic molecular alignment control enabled the improvement of the contrast ratio at oblique viewing angles of TN‐mode LCDs. In addition, color shifts at oblique angles are important for large‐screen TN‐mode LCD monitors and LCD‐TV sets. To improve the color‐shift problem, new technologies have been developed.     

Reflective and transflective color LCDs with double polarizers

Abstract— Reflective color LCDs with double polarizers have been developed by means of optimizing liquid-crystal modes, aperture ratio, color-filter properties, thickness of the glass substrate, polarizers, reflectors, etc. These LCDs are sufficiently bright, display many colors, have good hue, and are light weight with thin outline and low power consumption. Since they have double polarizers, a very high contrast ratio can be obtained. Therefore, they are superior in text character displays. Moreover, transflective color LCDs have been developed without visible deterioration of reflective displays by adoption of a reflective polarizer and backlight system in place of a lower polarizer and reflector.     

Advanced liquid‐crystal materials for TFT monitor and TV applications

Notebook applications have been one of the most important driving forces behind the remarkable growth of liquid‐crystal displays (LCDs). LCDs have recently been well accepted in the monitor market and large growth is forecasted because of the replacement of CRTs. The next challenge for LCDs is the TV market. These new application areas are supported by advanced LC technologies such as film‐compensated twisted nematic (TN), in‐plane switching (IPS), and vertically aligned (VA) modes. Each TFT technology requires a corresponding LC material improvement. We will review the recent liquid‐crystal material development for these advanced LC technologies.     

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.     

Two‐parameter optimization procedure for a TN display

Abstract— In our work, a two‐parameter optimization procedure for a TN display has been performed. The procedure consists of the numerical calculation of the optical parameters of a TN display, such as contrast ratio and luminance as a function of both the LC‐layer dichroic properties and the polarization coefficient of the polarizers used. The calculations have been done for: human eye sensitivity; real spectral characteristics of light sources (both internal and external ones); both the positive and negative modes of operating of the display; real director profile of the LC layer. Additionally, our procedure takes into account the interference phenomena of the display and the quasi‐real properties of the polarizing films. As a result of our work, a close relationship between the TN display optical parameters and the dichroic LC layer and polarizing films used have been obtained. This makes it possible to choose the initial display elements for different display application and user requirements.     

A novel approach to LCD optimization

Abstract— A novel approach to optimization liquid‐crystal displays (LCDs) is presented. The optimization module allows for a prediction with a high accuracy for the best results, which can be obtained for one or the other configuration of the polarizers and phase retarders in various electro‐optical modes, if the LC parameters and the operating voltages are fixed. The module is a part of our program, MOUSE‐LCD, which is efficient software for LCD optimization and modeling.     

Contrast‐ratio analysis of sunlight‐readable color LCDs for outdoor applications

Abstract— This paper presents contrast‐ratio data measured from high‐brightness TFT color LCDs under various ambient illumination levels encountered in outdoor environments. In these measurements, several LCD front polarizers with anti‐glare (AG) and anti‐reflective (AR) coatings have been used. The measured contrast‐ratio data are compared and the impact due to the AG and AR coatings is briefly discussed. The test equipment that simulates different cases of outdoor illumination is also presented.     

Effects of carbon‐nanotube doping on the performance of a TN‐LCD

Abstract— The electro‐optical characteristics of a 90° twisted‐nematic liquid‐crystal display (TN‐LCD) were analyzed. The test cell was composed of a minute amount of dopant, multiwalled carbon nanotubes, and a standard nematic mixture, E7, used in TN‐LCDs with direct addressing. Under the experimental conditions, no hystereses in optical transmittance were observed in either the doped cell or a neat counterpart under an applied ac voltage. Experimental results show that doping with nanotubes rectifies the electro‐optical properties of the cells by reducing the driving voltage as well as the rise time. Similar results were found in a TN cell of a TFT‐grade liquid crystal instead of the mixture consisting completely of polar compounds.     

An addressing technique for displaying restricted patterns in rms‐responding LCDs by selecting a few rows at a time

Abstract— An addressing technique that will allow rms‐responding matrix LCDs to display restricted patterns is proposed. This technique is based on the selection of a few rows at a time while scanning the display. In applications such as logic analyzers and oscilloscopes, mostly single‐valued functions of time are displayed. This restriction in the image is useful in enhancing the selection ratio so that good contrast is achievable even with TN‐LCDs. It is shown that a large reduction in the hardware complexity of the column drivers and the supply voltage is possible when the waveforms being displayed do not overlap each other and are equally spaced.     

Optimization of bi‐layered nano‐wire grids as high‐efficiency polarizers for power recycling in liquid‐crystal displays

Abstract— Bi‐layered Al nano‐wire grids (N WGs) are proposed as high‐efficiency polarizers for power recycling in liquid‐crystal displays (LCDs). In comparison with single‐layered NWGs, the bi‐layered scheme is more cost‐effective with both less and more controllable fabrication steps. Two types of 150‐nm‐period NWGs with different cross sections were characterized and theoretically analyzed. A TM transmittance of over 66% and a contrast ratio as high as 8000 in the visible range were calculated. Furthermore, 5–8% increase in TM transmittance and an almost 20% enhancement in contrast ratio are achievable. The NWG sheet with a large contrast ratio as well as a high optical throughput acts as a reflective polarizer in the power‐recycling system of LCD backlight units. A total transmittance of above 70% in the visible region is predicted for the power‐recycling process, which is at least 9% higher in total light efficiency than the claimed result of commercial dual brightness‐enhancement film (DBEF).     

Novel WV film for wide‐viewing‐angle TN‐mode LCDs

Abstract— A new optical compensation film refered to as WV‐EA film for TN‐mode TFT‐LCDs has been developed, resulting in higher contrast ratio, wider‐viewing‐angle characteristics, and improved color shift than their predecessors, especially in the horizontal direction. These features of the new WV film were achieved as a result of haze reduction and optimizing the optical characteristics of the polymerized discotic material layer and TAC film. These features are suitable for large‐sized and wide‐aspect‐ratio LCD monitors and TVs.     

Liquid‐crystal mixtures having tolane substances for field‐sequential‐color TN‐LCDs

Novel liquid‐crystal (LC) mixtures featuring high optical anisotropy Δn) and small rotational viscosity (γ¹) were developed for field‐sequential‐color TN‐LCD applications. The dynamic behavior of the TN cells in a narrow‐gap range was studied and new tolane LC substances were introduced. The newly developed LC mixtures, having a narrow‐gap cell, enable a TN‐LCD to switch fast enough to be applied to field‐sequential‐color displays not only at a room temperature but also at low temperatures. It was also confirmed that the voltage‐holding ratio (VHR) is sufficiently high in field‐sequential addressing conditions and, therefore, the LC mixtures can be used in active‐matrix LCDs. For practical use, a storage test of the TN cells under light irradiation was performed to evaluate their voltage‐holding property. It was also confirmed that their high VHR can be maintained for over 10,000 hours under practical conditions.     

LCD applications of thin‐crystal‐film polarizers

Abstract— We have developed a new technique for the production of thin crystal film (TCF) by deposition, molecular alignment, and the drying of water‐based lyotropic‐liquid‐crystal (LLC) materials. TCF exhibits high optical anisotropy and birefringence. This paper presents liquid‐crystal‐display (LCD) applications and opportunities for TCF plastic sheet polarizers, retarders, and color‐correction films as well as LCD designs with TCF internal polarizers.     

An overview of product issues in wide‐viewing TFT‐LCDs

Abstract— Several TFT‐LCD devices exhibiting high image quality have been developed and commercialized, overcoming the narrow viewing‐angle characteristics of conventional twisted‐nematic (TN) devices. Nevertheless, no single device dominates large‐sized TFT‐LCDs. In this paper, the product issues of existing LC devices related to manufacturing process and performance are discussed.     

Consideration of LCD legibility for automobiles

Some improvement is required in legibility of liquid crystal displays for them to be used in cars. Many factors - for example LCD material characteristics, cell gap, polarizers, operating conditions and instrument panels arrangements - influence the legibility. The dependence of contrast, viewing angle and response on such factors was investigated and a method of using LCDs for automobiles established.     

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.