Reflective Display Research Articles

Electroholographic display unit for three-dimensional display by use of special-purpose computational chip for holography and reflective LCD panel

We developed an electroholography unit, which consists of a special-purpose computational chip for holography and a reflective liquid-crystal display (LCD) panel, for a three-dimensional (3D) display. The special-purpose chip can compute a computer-generated hologram of 800x600 grids in size from a 3D object consisting of approximately 400 points in approximately 0.15 seconds. The pixel pitch and resolution of the LCD panel are 12 mum and 800x600 grids, respectively. We implemented the special purpose chip and LCD panel on a printed circuit board of approximately 28cmx13cm in size. After the calculation, the computer-generated hologram produced by the special-purpose chip is displayed on the LCD panel. When we illuminate a reference light to the LCD panel, we can observe a 3D animation of approximately 3cmx3cmx3cm in size. In the present paper, we report the electroholographic display unit together with a simple 3D display system.

A Simple Method for Determining the Pretilt Angle of a Vertically Aligned Reflective LCD

A field-induced birefringence method is demonstrated for determining the pretilt angle of a vertically aligned reflective liquid crystal display. We derive theoretically that the field-induced optical phase retardation is linearly proportional to the square of the applied voltage in the low-voltage regime. The pretilt angle can be deduced from the slope of this linear relation. The optical phase retardation is measured by a simple optical system and the pretilt angle can be determined easily. The experimental results agree well with that obtained theoretically. We also describe the applicable range of the applied voltage and the advantage of our method.

P-113: Generalized Optimization of Reflective Liquid Crystal Display for Direct-View and Single-Panel Projection Applications

A general method is presented for optimizing the reflective liquid crystal display (RLCD) with one polarizer for direct-view and single-panel projection displays. Using quarter-wave mode as an example, the combination of RLCD parameters (polarizer angle, LC twist angle, and retardation) satisfying zero reflectance at dark state is obtained. Our method presents the optimized parameters in a two-dimensional plot explicitly. The retardation of the maximized contrast RLCD falls between 0.14 mm and 0.25 mm.

31.5L: Late-News Paper: Development of a Combined Liquid Crystal and Fine Pitch Light Source Display (LFD)

We propose a novel display system that we call an LFD (combined liquid crystal and fine pitch light source display). In an LFD, an auxiliary light source patterned with a fine pitch is attached to a reflective liquid crystal display (LCD), and a light shield is formed on the observer's side of the light source. A vertical alignment LCD (VA-LCD) is attached as the reflective LCD, and an organic light-emitting diode (OLED) is attached as the fine pitch light source. An LFD can produce bright, high-contrast images under any ambient light. We built a test sample and confirmed its display characteristics.

High ambient-contrast-ratio display using tandem reflective liquid crystal display and organic light-emitting device

A high ambient-contrast-ratio (A-CR) and large aperture-ratio display is conceptually demonstrated and experimentally validated by stacking a normally black reflective liquid crystal display (NB-RLCD) and an organic light-emitting device (OLED). Such a tandem device can be switched between the NB-RLCD mode and the OLED mode under bright and dark ambient light, respectively. The normally black characteristic of the RLCD also helps to boost the A-CR under OLED-mode operation. To obtain a better image quality in the RLCD mode, a bumpy and transmissive structure is used to eliminate the specular reflection and to increase the viewing angle performance that results in CR>2:1 over 55 degrees viewing cone. Besides, such a structure can also increase the external quantum efficiency of the OLED by 49.4%. In our experiments, regardless of the ambient intensity the A-CR is kept higher than 100:1.

Fabrication of a flexible cholesteric liquid crystal display based on pixel isolation method

A flexible reflective cholesteric liquid crystal display (ChLCD) is fabricated on plastic substrates by using the pixel isolation method. The polymer walls between pixels and the polymer layers in the pixels are formed by two‐step UV irradiation. Electro‐optical response of the ChLCD with polymer wall and layer is studied and compared with conventional bistable ChLCD cells.

Liquid crystal elastomers, networks and gels: advanced smart materials

The principal concepts, preparation methods, important features of liquid crystal elastomers, anisotropic networks and gels, as well as recent exciting progress in this field are reviewed. Discussions are focused on their potential applications as smart materials for converting electrical or optical energy into mechanical energy and vice versa – such applications include artificial muscles, light scattering electro-optical switches and display materials, electro- or photo-controllable micro- or nano-machinery, electrically switchable color-tunable reflectors (mirrors) and full-color reflective display, fine-tunable and low-threshold mirror-less lasing, etc. In addition, some innovative anisotropic networks consisting of ferroelectric liquid crystals, discotic mesogens and mesomorphic ladder-like polysiloxanes are also highlighted.

68.3: An Advanced Transflective TFT LCD using Dual Thickness Color Filter

A new advanced color filter has developed for applying a series of transflective LCDs. It doesn't only make the same color gamut in both transmissive and reflective display modes, but also increase more than 30 % of reflectance ratio from the ambient light. This special color filter structure has thinner color resister layer on reflective area than on transmissive area was called dual thickness color filter (DTCF). An irregular diffraction photolithographic (IDP) exposure technology and new color resister material were developed in order to produce this advanced color filter.

低屈折率異方性のツイスト配向ゲストホスト液晶を用いた反射型表示素子

We fabricated reflective display devices using twisted-alignment guest-host liquid crystal with low refractive index anisotropy and evaluated their electro-optic properties. The dark state reflectance of the devices was reduced to 1/3 by using the liquid crystal (containing dichroic dye) with low refractive index anisotropy. The bright state reflectance could keep more than 50% by using liquid crystal with a high alignment order parameter. These results indicated that high-contrast reflective display devices can be made using a liquid crystal material with low refractive index anisotropy and a high order parameter.

A physical model describing the electro-optic behavior of switchable optical elements based on electrowetting

Recently, we have demonstrated reflective display pixels based on the voltage-controlled two-dimensional movement of an oil/water interface across a hydrophobic fluoropolymer insulator [R. A. Hayes and B. J. Feenstra, Nature (London) 425, 383 (2003)]. Here a physical model is reported that describes the basic electro-optic behavior of these electrowetting-based optical elements. The model extends the classical electrowetting theory developed for a free water droplet on an insulator surface to the controlled two-dimensional movement of a confined oil/water interface. The model takes into account the spatial extent of the oil layer (<5mm), where the oil film is well approximated by a spherical cap. The calculated results are in very good agreement with experimental data without employing fitting parameters. The model can be used to predict and optimize the electro-optic behavior of devices as a function of a range of well-defined parameters including the oil film thickness, the thickness of the insulating layer, the size of the optical element, and the oil/water interfacial tension.

A novel reflective image display using total internal reflection

We are developing a new reflective display technology, based on total internal reflection, which achieves a large difference between the maximum and minimum reflectance values. This yields a surface with greatly improved legibility under a wide range of illumination conditions. Such devices can display an image with a maximum reflectance ranging from 55% under uniform background illumination to over 85% under common non-uniform illumination conditions, even at viewing angles greater than 80° from the surface normal. This approach, which we call ‘CLEAR’ (Charged Liquid Electro-Active Response), uses polymeric microstructures to efficiently redirect incoming ambient light back toward the viewer. One advantage of this technique is the ability to achieve bright, full-color images over a wide range of viewing angles, much like ink printed on paper. The displayed image can be updated rapidly since switching from the reflective state to the absorptive state requires only about a half-micron of motion of absorbing material into the evanescent field associated with TIR. This new approach offers significant advantages in a number of reflective display applications.

Holographically formed polymer dispersed liquid crystal displays

Bragg gratings are holographically recorded in polymer dispersed liquid crystal materials to create a stratified composite material known as holographically formed polymer dispersed liquid crystals (H-PDLCs). Through a photo-induced diffusion-counter diffusion process, a refractive index modulation is permanently created. By choosing proper pitches of gratings and geometry, the gratings can be utilized for reflective displays with high color-purity. By applying a sufficient voltage, the reflective displays can be turned on and off in sub-milliseconds. In this contribution, we review H-PDLC technology in the context of reflective display applications.

Development of 3+2 dynamic drive scheme for cholesteric liquid crystal displays

In order to achieve fast driving for reflective cholesteric liquid crystal display (Ch-LCD) we have developed a novel 3+2 dynamic driving scheme (3+2 DDS), which uses 3 and 2 level driver ICs for row and columns, respectively. From the transient dielectric study, the selection period of around 1.0 ms/line showed the best contrast ratio at 30 °C in our system. The time of the homeotropic to transient planar state is strongly dependent on temperatures. The row driver IC has 3 level outputs of R H, R M ( R H/2), and R L; 32, 16, and 0 V, respectively. And the outputs of the column driver IC are composed of 2 levels. We found that a preparation period of more than 40 times and an evolution period of around 40 times of the selection period are suitable. Also, we have accomplished a stable gray scale by using, as we call it, the pulse position modulation (PPM) in which the root mean square (RMS) value of the applied field during the evolution period does not change, even under cross-talk pulses. The driving condition made by PPM is more stable than that made by the usual PHM and PWM techniques. By adopting the 3+2 DDS, we have made 8.4 in. foldable VGA Ch-LCD (640×480×2) that shows an addressing speed of around 1.0 ms/line.

A video‐speed reflective display based on electrowetting: principle and properties

Abstract— Electrowetting is presented as a novel principle for a reflective display. By contracting a colored oil film electrically, an optical switch is obtained with many attractive properties that make it very suitable for use as a reflective display, for instance, as electronic paper. Firstly, it has the high reflectivity (>40%) and contrast ratio (15) required for a paper‐like optical appearance. In addition, the principle shows a video‐rate response time (<10 msec) and has a clear route toward a high‐brightness color display. Finally, the electro‐optical response is independent of cell‐gap thickness, which will be very beneficial when moving toward a flexible display.

A Bright Reflective Full-Color Liquid Crystal Display Using Optically Compensated Bend Cell with High Contrast Ratio and Wide Viewing Angle Range

We have proposed a novel full-color reflective liquid crystal display (LCD) using a hybrid aligned LC cell, color filters of red, green and blue, a mirror electrode inside the cell and a light-diffusing film. In this paper, we describe a design concept for improving the contrast ratio of this reflective LCD. In addition, we propose an advanced reflective full-color LCD using a light-control film instead of a Gaussian-type light-diffusing film. This reflective LCD has a wide viewing angle, a high contrast ratio and a high resolution and is promising as a high-quality reflective full-color LCD for next-generation portable information systems.

A flexible, organic QVGA display with gray‐scale capability

Abstract— A flexible 4.7‐in. QVGA active‐matrix display was demonstrated, containing 76,800 solution‐processed organic transistors. The combination of our plastic active‐matrix backplane with electrophoretic‐ink display material developed by E‐Ink resulted in a reflective low‐power display with paper‐like appearance. By using high‐performance organic transistors, it was possible to generate 2‐bit images on the display. The display can be bent to a radius below 2 cm.

Analyses and Improvements of Whiteness of Reflective Liquid Crystal Displays

A reflective liquid crystal display (R-LCD) has become an important component of a portable information device; however, its inadequate whiteness appearance is a major issue in achieving the potential of “electronic paper”. The factors causing inadequate whiteness were examined using a conventional R-LCD. Furthermore, a novel reflectance-profile-controlled component “random grating light control film” and a non dispersed LC mode with a high-cell-gap tolerance were presented to achieve the paper-white image of reflective LCDs.

High contrast polymer-dispersed liquid crystal in a 90° twisted cell

A polymer-dispersed liquid crystal confined in a 90° twisted cell (T-PDLC) is demonstrated. In comparison to a conventional PDLC, the T-PDLC is also polarization independent while exhibiting a higher contrast ratio. Potential applications of the T-PDLC are in polarizer-free reflective display and light switch. A black and white segmented-alphabet reflective display using a dye-doped T-PDLC is demonstrated.

46.2: Ag‐based Coatings with Improved Weatherability and High Reflectivity for Reflective and Transflective Displays

AbstractReflective displays require corrosion resistant layers with a reflectivity of more than 90% in the visible spectral range. Several approaches have been taken to improve weatherability and corrosion resistance of reflective layers. In this study the influence of doping silver with In and Sn was investigated. Both alloys were found to perform better both in weatherability testing and in minimizing loss of reflectivity than currently applied materials. Since no precious metal is used, costs are also minimized.

P‐94: Twisted PDLC for High Contrast Reflective Displays

AbstractA high brightness and high contrast reflective display using twisted‐boundary polymer‐dispersed liquid crystal (TPDLC) is developed. The TPDLC is polarization independent while exhibiting a higher contrast ratio and lower operating voltage as compared to the conventional PDLC film. A black and white segmented‐alphabet reflective display using a dye‐doped TPDLC is also demonstrated.