Technology Papers
A brief abstract of the paper is provided under the title. Should you wish more, simply clicking on the title will open the full paper in a new window.
A brief abstract of the paper is provided under the title. Should you wish more, simply clicking on the title will open the full paper in a new window.
Amorphous Silicon Thin-Film Transistor Active-Matrix Reflective Cholesteric Liquid Crystal Display
Active-matrix array using hydrogenated amorphous silicon thin-film resistors, operated at the high data (50 V) and high gate (60 V) line voltages, was developed for the reflective cholesteric liquid crystal display, which was fabricated and operated at the frame rate.
Gray Scale of Bistable Reflective Cholesteric Displays
We report the first gray scale reflective bistable cholesteric display with dynamic drive. We successfully achieve 8 to 16 levels of gray on a VGA format display at 133 dpi. The image shows good contrast and rich gray depth.
Long Time Scale Relaxation of the Hometropic to Planar Transition of Short Pitch Cholesteric Materials
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Modeling of Polymer Stabilized Liquid Crystals
In this work we present an extension to the continuum theory for nematic liquid crystals to include the effects of polymer networks. We model polymer stabilized homogeneous liquid crystal cells and show that excellent agreement between the model and experimental data can be obtained if we assume that the polymer network is non-uniformly distributed throughout the sample.
Effects of cell structure on the reflection of cholesteric liquid crystal displays
Cholesteric liquid crystal displays employ cells consisting of parallel glass plates which have indium-tin-oxide coating as the electrode and polyimide as the alignment layer. We have performed a systematic study of the reflections from the interfaces and the liquid crystal. We measured the reflection spectra using various incident light, various polarizations, and detection polarizations. Using the Berreman 4 x 4 method, we simulated the reflection spectra without fitting parameters; the results agreed well with the experimental results.
Recent Developments in Bistable Cholesteric Displays
Bistable reflective cholesteric displays offer a solution for low power consumption displays. Image retention in zero field combined with inherent reflectivity (no need for backlighting) makes them ideal for applications such as portable document viewers. Here, we present an overview of the current research activities and achievements in this technology with focus on recent developments in white-on-black and stacked color displays, low cost drive electronics, video rate potential, and newly developed field induced polymer walls.
Tunable chiral materials for multicolour reflective cholesteric displays
A polymerizable tunable chiral material (TCM) has been prepared for the fabrication of multicolour reflective cholesteric displays. This photosensitive chiral material, whose chirality is adjustable upon UV irradiation, enables us to adjust the pitch of a cholesteric material and thus to produce the three reflected colours (red, green, and blue) for a mutlicolour reflective cholesteric display. Furthermore, the possibility of linking this compound to a polymer network helped to solve the problem of colour diffusion. Reflection spectra of the corresponding cells show broad reflection peaks, because of scattering from the large amount if polymerizable compound. We also report the difference of response under UV irradiation between this polymerizable tunable chiral material and a non- polymerizable material.
Paper-Like Displays for Electronic Books
There would be an electronic book in the hands if the general public today if there were a suitable commercially available flat panel display to support it. Other parts of the e-book such as memory storage, smart electronics with adequate power management, and even batteries with sufficient energy density are available today for construction of the book. It is the display technology that has slowed its development. Flat panel displays that we see today on the laptop computers and other hand held devices require too much power and do not provide the readability we expect from ink on paper used in a book. Inks and paper have been highly developed over many years to provide a reading surface that is easy on the eye, and can be read under a broad range of lighting conditions from low level room light to bright sunlight at the beach.
Polymer-stabilized cholesteric-texture reverse-mode light shutter:cell design
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Full Color (4096 Colors) Reflective Cholesteric Liquid Crystal Display
We report a full color, high resolution reflective cholesteric liquid crystal display with 4096 colors. A brightness approaching 40% reflected luminance is achieved over a wide view angle with an RGB triple-stack configuration. Gray scale drive schemes are capable of providing 2.5 ms/line address rate with standard STN driver. The image is retained without any power.
Recent Developments in Bistable Cholesteric Displays
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A novel bistable reflective liquid crystal display device for use with night vision goggles
Bistable reflective cholesteric displays (Ch-LCD) can be modified for compatibility with various classes of NVGs (Night Vision Goggles). Stacking near-infrared reflecting displays and visible reflecting displays can produce a novel dual use display module. Due to the optical clarity of the visible display in NVIS mode, the two displays are stacked on top of each other without any visual compromise. This module has high reflectivity and contrast in both the visible, and NVIS cases. The display is also bistable, enabling a low power device. This paper describes variations in this configuration including a single cholesteric layer for both viewing conditions. Various methods of contrast optimization and multiple color capability are also discussed. Military applications of this unique display device for cockpits and handheld devices with night vision requirements are discussed.
A Fast Frame-Rate Bistable Cholesteric Reflective Display
In this paper we discuss the design of fast frame rate Bistable Cholesteric Texture (BCT) reflective displays. A theoretical study of the effect of relaxation time from homeotropic to planar on brightness is shown. We experimentally determine of the effect of frame rate, level of interlacing, and size of the display on brightness and contrast ratio. A summary of drive waveforms is also presented.
A Novel Method for the Formation of Polymer Walls in Liquid Crystal/Polymer Displays
We have investigated the formation of polymer walls using a patterned electric field for rugged liquid crystal (LC) displays. The patterned electric field induces patterned phase separation. The LC molecules segregate in the high electric field regions, i.e. pixels, whereas the monomers segregate in the low field regions, i.e. inter-pixels. Subsequent photo-polymerization forms polymer walls between the pixels. We discuss the features of polymer walls formed by using this novel method.
A Study of the Dynamics of Reflection Color, Helical Axis Orientation, and Domain Size in Cholesteric Liquid Crystal Displays
The relaxation from the field-induced homeotropic state to the equilibrium planar state of cholesteric liquid crystals is investigated. By using an optical retro-reflection technique, we have isolated the dynamics of the orientation and pitch of cholesteric helices, and through scattering and microscopy techniques, we have determined domain size as a function of time for various surface treatments. These three factors determine the viewing angle, color, and brightness of a display. An analysis of the significance of surface selection in cholesteric displays is presented.
Cell Designs for Fast Reflective Cholesteric LCDS
We numerically study the dynamic process of transitions among textures in bistable cholesteric reflective displays, and analyze the effects of the parameters: surface anchoring, applied field, cell thickness, pitch and elastic constants. Our result shows that fast homeotropic-planar transition, essential in order to use cholesteric liquid crystals in video rate operations, can be achieved using cells with homeotropic anchoring.
Cumulative Drive Schemes for Bistabie Reflective Cholesteric LCDs
We have designed drive schemes which can update gradually the content of a bistable reflective cholesteric display. These scheme make use of the “kicking” effect as in addressing STN displays. The cholesteric material is kicked from the planar texture to the focal conic texture step-by-step or vice versa. We have also developed a new cholesteric display cell structure which has a 2 ms homeotropic-planar transition time. Using the new cell structure and the new drive scheme, we have achieved an addressing speed of 0.5 msfline; the cholesteric display can be operated at a quasi-video rate.
Eight-Color High-Resolution Reflective Choiesteric LCDs
We report a unique eight color and black on white surface stabilized reflective cholesteric liquid crystal display. The display prototype is a triple stack, 100 dpi, 1/8 VGA, which shows eight vivid colors without parallax. The display is bistable so no power is used to show the image between user updates.
Plastic VGA Reflective Cholesteric LCDS with Dynamic Drive
We report the first fully addressable VGA size reflective cholesteric liquid crystal displays fabricated using thin plastic substrates. These displays have resolution of 133 dpi and are addressed with our dynamic drive scheme at a rate of two frames per second. These displays are bistable and require no backlight, resulting in very low power consumption that is ideal for portable battery-powered applications. The displays have electro-optical and optical properties similar to those made with glass but are thin and light weight. The displays are integrated into demonstration devices that store up to 16 images on interchangeable flash cards..
Temperature Compensation of the Dynamic Bistable Cholesteric Displays
The parameters of the 3-phase dynamic drive scheme depend on the transitions among cholesteric textures, which themselves are strongly temperature dependent. Temperature compensation must be made in order for the drive scheme to work in a wide temperature region. We have developed a compensation method in which the frequency of the driver clock is the only parameter that is required to be adjusted with temperature. Using this simple method, we have achieved consistently high contrast ratio of the display in a wide temperature region.
White Reflective Displays from Polymer-Stabilized Cholesteric Textures
We report the optical and electro-optical properties of a white reflective display from a chiral polymer stabilized cholesteric texture (C-PSCT). The new PSCT system is prepared by photopolymerizing a small quantity of a chiral monomer in a cholesteric host. The chiral polymer network phase separates into micron-size regions, which provide the additional chirality and influence the pitch and orientation of helical axes of a cholesteric liquid crystal. Therefore, a distribution of cholesteric helical axes Bragg reflects a white image.