Current and future technology of low‐temperature poly‐Si TFT‐LCDs

Abstract— The state of the art of large‐area low‐temperature TFT‐LCDs will be reported in this paper. High‐performance poly‐Si TFTs are expected to realize various applications such as system display where various signal‐processing functions are added to the display. In the past few years, low‐temperature poly‐Si thin‐film‐transistor (LTPS TFT) technology has made great progress, especially in the areas of excimer laser annealing (ELA) of high‐quality poly‐Si film, ion doping for large‐area doping, and high‐quality gate SiO₂ film formation by using the low‐temperature PE‐CVD method. Also, technology trends and possible applications, such as a system displays, will be discussed.     

Optimization of low‐temperature poly‐Si TFT‐LCDs and a large‐scale production line for large glass substrates

Abstract— An update of the progress of inherently low‐temperature poly‐Si (LTPS) technologies, such as ELA, ion doping, and activation in conjunction with chemical vapor deposition (CVD) and photolithography will be given. We will also discuss whether LTPS LCDs will be applied to a large‐scale production line using a large motherglass substrate. It was found that a more‐powerful excimer laser as well as photolithography with higher‐resolution and a more‐precise overlaid arrangement would enable a large‐scale production line handling motherglass of 4th generation size to be constructed in the very near future with reasonable investment and productivity costs.     

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.     

Color management of reflective‐type LCDs in terms of adaptation of the human visual system to light‐source variation

We have investigated the color management, in terms of the color adoption property of the human visual system, of a reflective‐type TFT‐LCD (R‐LCD). Since the R‐LCD depends on ambient light as the light source, it is expected that the colorimetric color on the R‐LCD must be changed if the source of the ambient light is changed. However, due to the adaptation property of the human visual system, the eye does not perceive colorimetrically corrected colors as the same color even for an R‐LCD. In this research, first, we conducted a subjective experiment to obtain the RGB code value that is required in order to display a corresponding color on the R‐LCD under varying ambient‐light conditions. The result of the experiment shows that the corresponding color of the experimental results was reasonably approximated by the color obtained by using the von Kries model. Secondly, we proposed a color‐compensating mechanism that is described as a cascaded simple 3 × 3 linear matrix. Actual colors displayed are adjusted according to the ambient light. The evaluation of the picture quality of the R‐LCD showed that the proposed model is effective.     

全息反射型LCD

为了降低功耗,延长电池的寿命,反射型ＬＣＤ必须在反射亮度,对比度和可视度方面予以实质性改进,迄今对于各种反射型ＬＣＤ而言,现已制成功的全息反射型ＬＣＤ将是最有生命力的候选者。本文描述了这各新型显示器的工作原理及其性能。     

Multiple color high resolution reflective cholesteric liquid crystal displays

Abstract— A high-resolution multiple-color and black-on-white surface-stabilized reflective cholesteric liquid-crystal display with reflectivities as high as 40% is reported. The double-stacked 1/8-VGA, 100-dpi prototype shows four vivid colors with negligible parallax. The potential for eight colors and ultimately full color is demonstrated in a high-resolution triple-stacked prototype.     

Electro-optical properties of a twisted hybrid aligned nematic mode for reflective liquid crystal displays

Abstract— A twisted hybrid aligned (THA) mode is proposed for reflective liquid-crystal displays. In the reflective configuration, a single polarizer and a reflective electrode are used to achieve electrooptical switching between the black and white states in the THA mode of a chiral nematic liquid crystal. Numerical simulations are performed to optimize the cell parameters such as the cell thickness and the amount of the twist in the hybrid geometry. The reflective THA mode is found to give wider viewing and faster response characteristics than a twisted nematic one. The role of an optical retardation film on device performance of such a reflective THA cell is also discussed.     

Motion‐blur‐free LCD for high‐resolution virtual reality displays

A new liquid crystal display device with fast response time, high transmittance, and low voltage for virtual reality is reported. When driven at 90 Hz with 17% duty ratio, the motion picture response time is 1.5 ms, which is comparable with cathode‐ray tube, leading to indistinguishable motion blur. Moreover, this device enables high‐resolution density because only one thin‐film transistor per pixel is needed and it has a built‐in storage capacitor.     

Driving passive‐matrix LCDs with low hardware complexity and reduced supply voltage

In passive‐matrix liquid‐crystal displays (LCDs), multiplexing is achieved by using the intrinsic non‐linear characteristics of the liquid‐crystal material. If the electro‐optic characteristic is steeper than necessary for the matrix display, the selection ratio need not be maximized. Instead, the selection ratio can be reduced to match the electro‐optic characteristics of the display. This leads to a reduction in the supply voltage of the drive electronics. We have considered the possibility of using addressing techniques with low hardware complexity along with displays having steep electro‐optic characteristics. Supply voltages for these techniques are compared with that of multi‐line addressing (MLA). The supply voltages of the Hybrid Addressing Technique (HAT), Improved Hybrid Addressing Technique‐S3 (IHAT‐S3), and Improved Hybrid Addressing Technique‐S4 (IHAT‐S4) are lower than that of MLA for the lower range of N. These hybrid addressing techniques with lower hardware complexity are a better choice for driving passive‐matrix LCDs, especially in portable equipment.     

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.