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.     

Recent progress in flexible color reflective cholesteric displays

Abstract— Highly flexible layered full‐color cholesteric displays fabricated using ultra‐thin substrates with encapsulation through the phase‐separation approach is reported. Recent progress of the state of the art of cholesteric display technology will be discussed as well.     

Comparison of reflective PNLCDs and reflective single‐polarizer Heilmeier guest‐host displays

In this paper, the applicability of a zero‐polarizer reflective display (PNLC) and a single‐polarizer reflective display (Heilmeier guest host) for direct‐view applications is analyzed. A measurement set‐up is designed to analyze the applicability of all types of reflective displays. Simulation of the different types of illumination caused by the environmental light is essential for this set‐up. The measurements indicate that the contrast ratio and reflectance greatly depend on the type of illumination. It is demonstrated that the worst‐case illumination for one display technology may be the best‐case illumination for another one and vice versa.     

Comparative studies of single-polarizer reflective liquid-crystal displays

Abstract— The electro-optic effects and viewing-angle characteristics of some recently developed single-polarizer reflective liquid-crystal displays are compared under the same material parameters. The mixed-mode twisted-nematic cells and biaxial film-compensated thin homogeneous cells are promising for both direct-view and projection displays employing crossed polarizers. How to improve contrast ratio for the parallel-polarizer displays remains a technical challenge.     

Electrofluidic displays: Fundamental platforms and unique performance attributes

Abstract— Electrofluidic displays transpose brilliant pigment dispersions between a fluid reservoir of small viewable area and a channel of large viewable area. Recent progress in the technology, a new multi‐stable device architecture, and a novel approach for segmented displays that can display pigment without the optical losses of pixel borders is reported. The fundamental aspects of electrofluidics that make it compelling for the next generation of e‐paper products is reviewed.     

Optimization of polymer-stabilized bistable black-white cholesteric reflective display

Abstract— Cholesteric liquid crystals at zero field exhibit two optically contrasting stable states: planar texture and focal-conic texture. When a cholesteric liquid crystal is in the planar texture, the helical axis is perpendicular to the cell surface; the material Bragg-reflects colored light. When the liquid crystal is in the focal-conic texture, the helical axis is more or less parallel to the cell surface; the material is forward-scattering and has a black appearance if the back plate of the cell is painted black. We develop a cholesteric liquid-crystal/polymer composite in which a small amount of polymer is dispersed in the liquid crystal. The dispersed polymer changes the planar texture to a poly-domain structure, which has a white appearance but has little effect on the optical properties of the focal-conic texture. The result is a bistable black-white reflective display which is a good candidate for electronic-paper applications.     

Progress in flexible and drapable reflective cholesteric displays

Abstract— Recent results from encapsulation work on the development of flexible and drapable cholesteric liquid‐crystal displays (LCDs) on substrates such as thin plastics, fabrics, and even paper will be presented. The approaches used to create flexible displays using single‐ and dual‐substrate methods based on printable emulsions and polymerization‐induced phase‐separation (PIPS) techniques will be discussed.     

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.     

Effects of 3D displays: A comparison between shuttered and polarized displays

The current study investigates the effects of 3D displays (shuttered display vs. polarized display). People experienced superior fidelity and brightness when they watched 2D still images on a shuttered display, rather than on a polarized display. Conversely, people experienced greater brightness when they watched 3D still images on a polarized display, rather than on a shuttered display. Second, people were able to read a smaller font or characters on a shuttered display than on a polarized display. Third, people noticed flickering on a shuttered display when they watched 3D images. Fourth, people experienced greater brightness when they watched 3D moving images on a shuttered display, rather than on a shuttered display. The perceived brightness of the screen positively correlated with enjoyment, content satisfaction, and 3DTV satisfaction when the viewers watched a 3D movie. The flickering, on the other hand, has a negative correlation with enjoyment and 3DTV satisfaction.     

An optical design for reflective color STN‐LCDs

In reflective color STN‐LCDs, it is necessary to achieve achromatic representation in single‐polarizer STN‐LCD modes. We propose an optimization method for the optical components of single‐polarizer STN‐LCD modes in order to achieve achromatic representation. By applying this method, it is shown that a contrast ratio of more than 20 can be achieved in the normally black (NB) mode. Furthermore, we prove that the normally white (NW) mode can be realized as well as an NB mode which is usually used in current reflective color STN‐LCDs. Comparing the viewing‐angle characteristics of the NW and NB modes, it was found that those of the NW mode are better than those of the NB mode. Particularly, high reflectance can be realized even at larger viewing angles in the NW mode.     

An electrophoretic deposition process for screening phosphor powders for color displays

Abstract— A new process incorporating electrophoretic deposition and a photolithographic technique was developed for coating repeating triads of 75‐μm‐wide stripes composed of green ZnSiO₄:Mn (P1), red Y₂O₃:Eu (P56), and blue ZnS:Ag, Cl (P11) phosphor particles. The resolution of the screens produced is 100 triads of phosphor stripes per inch of substrate. SEM micrographs show a high degree of phosphor stripe edge precision with relatively little cross‐contamination. Cathodoluminescence measurements revealed that the chromaticity of the phosphors were not altered by the coating process.     

Medical displays in the healthcare system

Abstract— As the healthcare system changes and progresses, the need for different types of high‐performing displays is also evolving. There are three categories of displays: (a) embedded (as part of life saving devices), (b) informative (for patient data and history, and managing workflow), and (c) imaging (high performing for diagnosis). The challenges of AMLCDs, which are the display of choice at the moment mainly in digital imaging, will be discussed. These challenges include very high resolution, high brightness, and wide viewing angle. The current performance of AMLCDs and the areas which they need to improve will be reviewed. A brief summary of the standards used to specify medical (diagnostic) displays will follow. A look into the future will predict the role of displays in hospitals.     

A new modeling interface for the pen-input displays

Sketch interactions based on interpreting multiple pen markings into a 3D shape is easy to design but not to use. First of all, it is difficult for the user to memorize a complete set of pen markings for a certain 3D shape. Secondly, the system will be waiting for the user to complete the sequence of the pen markings, often causing a certain mode error. To address these problems, we present a novel, interaction framework, suitable for interpretations based on single-stroke marking on pen-input display; within this framework 3D shape modeling operations are designed to create appropriate communication protocols.     

New approach to developing LC materials for IDS driving on reflective displays

As usage time for portable electronic terminals increases, associated problems regarding such extended use (e.g., battery holding times and eyestrain) are highlighted. Within the domain of power saving, we previously developed an idling stop (IDS) driving that avoids unnecessary refresh. Moreover, for reducing eyestrain to the highest extent possible, we calculated a luminance change in IDS driving that is not perceived as flickering by humans, via the use of a temporal modulation transfer function. According to the results of such calculations, a liquid crystal mixture that suppresses luminance changes perceived by humans was hence constructed. With the combined use of the liquid crystal mixture and a c‐axis‐aligned crystal oxide semiconductor with low off‐state leakage current, a display could be developed wherein leakage current in IDS driving could be significantly reduced, along with enjoyed benefits of prolonged refresh intervals and power savings. The subject display is very eye‐friendly, with less flickering than comparable technologies.     

A reflective color STN-LCD with a single polarizer and double retardation films

Abstract— A reflective color STN-LCD with a single polarizer and double retardation films has been investigated. The double retardation films arranged in front of the LC layer enabled the LCD to contain reflective electrodes inside the panel. This configuration achieves a bright image with no parallax. A new construction of a reflective STN-LCD with a single polarizer has been developed by means of our own method in which the color difference ΔE* as the optimizing parameter has been used. Further, RGB color filters have been newly designed for our reflective LCD, and an aluminum (Al) layer has been introduced as a reflective electrode. As a result, we have realized a 7.8-in.-diagonal reflective color STN-LCD (640 × 480) which has 15% reflectance, 14:1 contrast ratio, 4096-color capability, and sufficient color gamut. It has been confirmed that the single-polarizer reflective color STN-LCD has sufficient performance for mobile business tools. We believe that it will be a key device for this application.     

Improved gray‐scale monochrome and color AMEL displays using analog pixel

Abstract— Active‐matrix electroluminescent (AMEL) microdisplays have been known for their numerous beneficial characteristics such as low weight, compactness, high brightness, and high contrast ratio. Beside these desirable characteristics, some of their drawbacks include difficulty in obtaining a high number of gray‐scale levels or a large number of colors, and interface‐electronics complexity. To address these drawbacks, AMEL displays using an analog addressing architecture have been developed. Utilizing this new driving scheme, 256 monochrome levels or 16 million colors are obtainable. Gray shade is proportional to an analog voltage stored on the hold node of each pixel. For color displays, each pixel is comprised of red, green, and blue subpixels arranged in vertical stripes, and can be sized independently to achieve the appropriate white balance. With the integration of control‐signal circuit blocks on the same substrate as the microdisplay, the number of input control signals is minimized and the display can be driven with very simple interface electronics. This results in low overall system cost, compact electronic packaging, and low power consumption. To accommodate most optical orientations, the display has built‐in modes to flip the image both vertically and horizontally. Additionally, the display supports multiple interlace addressing modes.     

Measuring color breakup of stationary images in field‐sequential‐color displays

Abstract— Color breakup is an artifact perceivable on field‐sequential‐color (FSC) displays, both in stationary and in moving images. In this work, a unique device and a method for measuring color breakup on stationary images is proposed. Rotating the field of view of a high‐speed measurement camera in milliseconds simulates saccadic behavior. The target can be a virtual display, a direct‐view display or a projector image. Captured images can be used for quantifying the color breakup of a target display. The results along with an exploration of their application to breakup characterization will be presented.     

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.     

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.     

Flexible and bistable FLC and cholesteric displays on plastic substrates for mobile applications and smart cards

Abstract— New smart-card applications like purse cards, etc. require an integrated display which allows the card-holder to read information which is stored on the IC of the card. On the other hand, the integration of a display into a plastic card requires some very specific features like flexibility and pressure stability, low-voltage CMOS-addressing, memory capability, and, of course, a reflective mode since no backlight is available. In this paper, two bistable reflective LCD solutions using ferroelectric and cholesteric LCs are discussed and very promising prototype results are presented. Pressure and bending tests as well as contrast measurements are compared in order to show the potential of meeting the requirements for use in smart cards.