We report on unique flexible ReflexTM displays based on bistable, reflective, cholesteric liquid crystal display
technology. Reflex displays are attractive for numerous applications because of the low power consumption and paper
like reflective color. As the possible applications grow for flexible, reflective displays the new methods to manufacture
these displays, such as web processing, also become important. We will report on several unique display types such as a
pressure induced writing display and a switchable color electronic skin display. In addition, the current status of
traditional Reflex displays will be discussed.
Flexible Cholesteric liquid crystal displays have been rapidly maturing into a strong contender in the flexible display
market. Encapsulation of the Cholesteric liquid crystal permits the use of flexible plastic substrates and roll-to-roll
production. Recent advances include ultra-thin displays, laser-cut segmented displays of variable geometry, and smart
card applications. Exciting technologies such as simultaneous laser-edge sealing and singulation enable high volume
production, excellent quality control and non-traditional display geometries and formats.
Bistable reflective cholesteric displays are a liquid crystal display technology developed to fill a market need for very low power displays. Their unique look, high reflectivity, bistability, and simple structure make them an ideal flat panel display choice for handheld or other portable devices where small lightweight batteries with long lifetimes are important. Applications ranging from low resolution large signs to ultra high resolution electronic books can utilize cholesteric displays to not only benefit from the numerous features, but also create enabling features that other flat panel display technologies cannot. Flexible displays are the focus of attention of numerous research groups and corporations worldwide. Cholesteric displays have been demonstrated to be highly amenable to flexible substrates. This paper will review recent advances in flexible cholesteric displays including both phase separation and emulsification approaches to encapsulation. Both approaches provide unique benefits to various aspects of manufacturability, processes, flexibility, and conformability.
We developed a novel technology for the fabrication of reflective cholesteric liquid crystal displays coatable on a single
substrate using a layer-by-layer approach. Encapsulated cholesteric liquid crystals serving as an electro-optical layer and
transparent conducting polymer films serving as electrodes are coated and printed on a variety of unconventional
substrates, including ultra-thin plastic, paper, and textile materials to create conformable displays. The displays are
capable of offering excellent electro-optical properties of the bulk cholesteric liquid crystals, including full-color, IR
capability, bistability, low power, high brightness and contrast, combined with the ruggedness and pressure insensitivity
of the liquid crystal droplets embedded in a polymer matrix. Durability of encapsulated cholesteric liquid crystals and
single substrate approach allows for display flexing, folding, rolling and draping during image addressing without any
image distortion. Our single substrate approach with natural cell-gap control significantly simplifies the fabrication
process of the LCDs especially for large area displays. This paper will discuss the development, status, and merits of
this novel display technology.
This paper highlights recent advances toward flexible cholesteric displays including new night vision applications for military use and full color. Particular emphasis is paid to recently developed encapsulated cholesteric liquid crystals that are necessary for printing and coating the materials as well as prevent erasure of the image during flexing or handling the display. The paper presents recent results from encapsulation of cholesteric materials using polymerization induced phase separation and their progression towards thin flexible plastic based cholesteric displays. Several other key issues in the transition from smooth rigid glass substrates to flexible plastic substrates including spacing control and preparation of surfaces are discussed. Lastly, the night vision mode and night vision applications of cholesteric displays are also presented.
Bistable reflective cholesteric displays are a liquid crystal display technology developed to fill a market need for very low power displays on a low-cost, high resolution passive matrix. Their unique look, high reflectivity, bistability, and simple structure make them an ideal flat panel display choice for handheld or other portable devices where small lightweight batteries with long lifetimes are important. We discuss recent advances in cholesteric display technology at Kent Displays such as progress towards single layer black and white displays, standard products, lower cost display modules, and various interface options for cholesteric display applications. It will be shown that inclusion of radio frequency (rf) control options and serial peripheral interface (spi) can greatly enhance the cholesteric display module market penetration by enabling quick integration into end devices. Finally, some discussion will be on the progress of the development of flexible reflective cholesteric displays. These flexible displays can dramatically change industrial design methods by enabling curved surfaces with displays integrated in them. Additional discussion in the paper will include applications of various display modes including signs, hand held instrumentation, and the electronic book and reader.
We discuss the state of the art of the bistable reflective cholesteric liquid crystal display technology. Numerous applications from low resolutions signs, to medium resolution instrumentation type displays, and high resolution electronic books are discussed. Different modes of the technology are discussed as being viable for the respective display applications. Special emphasis is paid to electronic book applications.
Reflective cholesteric liquid crystal displays (Ch-LCDs) are attracting more interest because power efficient displays are needed for the rapid growing mobile computation applications. Its capability of high-resolution full color with passive matrix drive method provides the market with a very powerful alternative display technology. In this paper, we will review the history of Ch-LCDs as well as the most recent developments.
Cholesteric liquid crystal display (Ch-LCD) are lightweight, low power, sunlight readable displays. In addition, they can serve a dual function as pen-input device switch no additional hardware. Because of the unique properties of this technology, Ch-LCDs can be made with plastic substrates thus making the displayed extremely lightweight, compact and unbreakable. We discuss in this paper cent advances in merging Ch-LCD technology with conducting polymer electrodes. Conducting polymer provides potential benefits over the use of the standard display electrode materials, indium tin oxide, by improving the reliability of the display. Furthermore, the potential to print the conducting polymer electrodes could significantly increase manufacturing volume and decrease display cost. We report on scaling display size and resolution by demonstrating a 1/8 VGA Ch-LCD using polypyrrole as the conducting polymer. We fabricated these displays using either a vacuum fill or polymer wall/lamination approach and we discus subsequent failure analysis to determine the cause for the line-outs observed on these displays. We present initial results in determining the suitability for using Ch-LCD technology as a pen-input device. Finally, we discuss initial work towards printing the conducting polymer electrodes to determine the feasibility of printing electrodes on plastic substrates in a roll-to-roll, high volume, low cost process.
We report a full color 1/4 VGA reflective cholesteric display with 4096 colors. The display can deliver a brightness approaching 40 percent reflected luminance, far exceeding all other reflective technologies. With its zero voltage bistability, images can be stored for days and months without ny power consumption. This property can significantly extend the battery life. The capability of displaying full color complex graphics and images is a must in order to establish a market position in this multimedia age. Color is achieved by stacking RGB cells. The top layer is blue with right chirality, the middle layer is green with left chirality, and the bottom layer is red with right chirality. The choice of opposite chirality prevents the loss in the green and red spectra from the blue layer on the top. We also adjusted the thickness of each layer to achieve color balance. We implement gray scale in each layer with pulse width modulation. This modulation method is the best choice consideration of lower driver cost, simpler structure with fewer cross talk problems. Various drive schemes and modulation methods will be discussed in the conference.
Bistable reflective cholesteric liquid crystal displays (Ch- LCDs) 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.
In a conventional liquid crystal display device (LCD), glass substrates coated with an indium tin oxide layer are typically used for the application of an electric field to the liquid crystal material. For many applications including cockpit and avionic display applications, there is a need for a LCD with plastic substrates. We have demonstrated for the first time the operation of a fully multiplexed plastic LCD using conducting polymers as the substrates and the newly developed reflective cholesteric display technology. The resultant display has several features like light weight, low power consumption, increased ruggedness, bistability, sunlight readability and flicker-free operation. The functioning of the conducting polymer-based LCD is demonstrated and the features that make it attractive for cockpit applications are discussed.
The first monochrome, high resolution reflective 1/8 VGA liquid crystal displays have been built using various plastic substrates for body mounted and hand held applications. These displays have a contrast ratio of over 10:1 with a wide viewing angle. The reflectivity is about 40 percent and the frame update time is less than 2 seconds.
There is a great deal of interest in reflective cholesteric liquid crystal displays (Ch-LCDs) because they are lightweight, low power flat-panel displays. Furthermore, Ch- LCDs can be made bistable which allows for the manufacture of large area, high-resolution displays without the need for expensive, difficult to manufacture active matrix addressing schemes. Also, the bistability enables flicker-free operation. Currently, these displays are made using glass substrates. However, some applications require rugged (i.e., nonbreakable), flexible displays. The use of a plastic substrate would fulfill these requirements. The transparent metal indium tin oxide (ITO) is currently used as the conducting electrode on glass as well as plastic substrates. While ITO works well with glass, it does not adhere as well to plastic, is brittle, and has a tendency to break under constant bend conditions. In this paper, we investigate substituting the more robust conducting polymer for ITO as the display electrode and determine the feasibility of producing a reflective Ch-LCD using plastic substrates with conducting polymer electrodes.
In a conventional liquid crystal display device (LCD), glass substrates coated with an indium tin oxide (ITO) layer are typically used for the application of an electric field to the liquid crystal material. For many applications, there is a need for a LCD with a plastic substrate. Polypyrrole is a well known conducting polymer for its high conductivity and chemical stability. Compared with the currently used ITO conducting layer, polypyrrole is more compatible mechanically with plastic. Because it is an organic material, it should be able to bend and flex with the substrate. Therefore, it is a good candidate for the conducting surface needed in a plastic LCD. Here we present the preparation of polypyrrole films on a polyethylene terephthalate (PET) substrate by an in-situ solution deposition process and their patterning by conventional photolithography techniques. We discuss their important physical properties, such as surface resistance and optical transmission, and their suitability as a substitute for ITO as an electrode for a plastic reflective Ch-LCD.
We report on the optical reflective properties of the planar texture of cholesteric liquid crystal displays. The cholesteric liquid crystal is made bistable by either dispersing a low concentration of polymer or by treating the cell substrate surfaces. We determine the role that the polymer network and surface treatment has on the reflective properties as a funciton of viewing angle using both collimated and diffuse illumination. Both the polymer network and surface treatment have the effect of distributing the orientation of the cholesteric helix axes about the cell normal. Theoretically we characterize these cells by this distribution.
Polymer modified materials have been shown to be useful in controlling the operational voltages and speed in TN devices; and the operational voltages and the suppression of the `stripe' deformation in STN cells.
Orientationally ordered polymer networks are prepared in spherical and cylindrical geometries by isothermal photopolymerization of diacrylate molecules dissolved in a nematic liquid crystal. Optical polarizing microscopy textures reveal that the network memorizes the nematic director field. Diacrylate concentrations of 2% by weight suffice to create a stable network embedded in the anisotropic liquid crystal environment for temperatures as high as 150 degree(s)C. Polymer networks that are formed under various surface conditions, applied electric fields, and geometrical constraints are characterized with optical polarizing microscopy.
Optimum concentrations of gel monomer and chiral material are explored to maximize the contrast and reduce the drive voltage of light shutter from cholesteric liquid crystal/polymer gel dispersion. The results indicate that these materials are excellent candidates for use with the active matrix. Their performance is superior in some regards to PDLC materials from isotropic polymers.
Polymer-dispersed liquid crystals (PDLCs) have been developed for modulation of infrared radiation in the 2-5 and 8-14 micrometers wavelength regions. The electro-optic performance of an IR PDLC shutter depends on film thickness, liquid crystal droplet size, and the transparency of the substrates and the PDLC components. The effect of each of these factors on IR electro-optic performance of PDLC films was investigated using double modulation experiments and infrared spectroscopy. The authors have also compared the sensitivity of a pyroelectric vidicon infrared camera using PDLC shutter and a mechanical shutter.
The anchoring strength, anchoring angle and molecular order at the droplet wall are measurable parameters which affect the nematic director configuration and hence the electro- optic response of PDLC display devices. Technologies to measure these quantities and the authors' current understanding of their role in droplet morphology are presented. The cylindrical geometries of Nuclepore filters are shown to be useful in studying the competing effects of anchoring energy and cavity curvature for different surface treatments. Nuclear magnetic resonance methods are used to determine director configurations of submicron cavity sizes while optical microscope textures are preferable in supramicron-size droplets.
The molecular anchoring strength for the liquid crystal E7 (EM Chemicals) confined to
spherical cavities dispersed in the polyurethane TU5OA (CONAP) is measured. The anchoring
strength values result from a study of the radial-to-axial configuration transition when
perpendicular anchoring conditions exist at the polymer/liquid crystal interface. This transition is
also a function of droplet radius, temperature, and the strength of any external fields present. A
study of field-induced configuration transitions provides values for the reduced local electric fields
inside droplets. Computer simulated pictures of nematic droplets are formed to identify director