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.     

A rugged display: Recent results of flexible cholesteric liquid‐crystal displays

Abstract— A 3‐m‐long rugged flexible display having a novel single‐plastic‐substrate structure has been demonstrated with a coated cholesteric liquid‐crystal mixture. The display is designed to be fabricated by a roll‐to‐roll process to increase productivity at a competitive cost. It has the advantage of having almost no limitation in display length. The high‐resolution (300‐dpi) monochrome cholesteric liquid‐crystal display (ChLCD) can be achieved by using a photo‐addressing method. A single‐layered 10.4‐in. color ChLCD also has been developed with good color and contrast.     

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.     

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.     

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.     

A novel bistable reflective display using quick‐response liquid powder

Abstract— We have developed new powder materials that exhibit liquid behavior, which can lead to the realization of novel bistable and reflective displays having paper‐white appearance, high contrast, and quick response. Two types of display were demonstrated, one had 160 × 160 array of pixels and the other had 320 × 320 in a 3.1‐in.‐diagonal viewable image size corresponding to 66 and 132 dpi, respectively. These displays were driven by passive‐matrix addressing. The displays showed a reflectivity of more than 41%, a contrast more than 1:10, and a pixel response time of less than 0.2 msec. The seven‐segment display for use in clocks was also demonstrated.     

Fast full‐color reflective display via photoluminescent enhancement

Reflective displays are advantageous in applications requiring low power or daylight readability. However, there are no low‐cost reflective technologies capable of displaying bright colors. By employing photoluminescence to more efficiently use ambient light, we created a prototype display that provides bright, full color in a simple, low‐cost architecture. This prototype includes a novel electrokinetic shutter, a layer that incorporates patterned luminescent red, green, and blue sub‐pixel elements, and a novel optical out‐coupling scheme. The luminescent elements convert otherwise‐wasted portions of the incident spectrum to light in the desired color band, resulting in improved color saturation and lightness. This prototype provides a color gamut that is superior to competing reflective display technologies that utilize color filters in single‐layer side‐by‐side sub‐pixel architectures. The current prototype is capable of switching in <0.5 s; future displays based on an alternative electro‐optic shutter technology should achieve video rate operation. A transflective version of this technology has also been prototyped. The transflective version utilizes its backlight with a power efficiency that is at least three times that of a conventional liquid crystal display. These photoluminescence‐based technologies enable a host of applications ranging from low‐power mobile products and retail pricing signage to daylight readable signage for outdoor advertising segments.     

Bistable cholesteric reflective displays: Two‐level dynamic drive schemes

Abstract— Among the many known dynamic drive schemes for bistable cholesteric liquid‐crystal displays, the simplest driving voltage waveforms are realized only in two‐level dynamic drive schemes. Voltage waveforms that are applied to rows and columns of a display in two‐level drive schemes consist of only two voltage levels: U and 0. The addressing speed for these drive schemes is defined by the fast transition time of a cholesteric liquid crystal from the homeotropic state to the transient planar state per row. Two‐level dynamic drive schemes were analyzed. The possibility of increasing the addressing speed will be discussed.     

Review of operating principle and performance of polarizer‐free reflective liquid‐crystal displays

Abstract— In this paper the operational principle and performance of guest‐host, liquid‐crystal/polymer‐composite scattering, and cholesteric liquid‐crystal reflective displays are reviewed. These displays do not use polarizers and have the advantage of providing high reflectance and compatibility with flexible plastic substrates.     

Flexible area‐color reflective displays based on electric‐field‐induced blueshift in a cholesteric liquid‐crystal film

Abstract— An electrically controllable blueshift of the reflection band is observed in a cholesteric liquid crystal with either positive or negative dielectric anisotropy. The change in optical properties is a result of a two‐dimensional periodic undulation of the cholesteric texture, known as Helfrich deformation. This blueshift mechanism was used to demonstrate area‐color reflective displays in a cholesteric cell and a rollable polymeric film.     

Thin flexible photosensitive cholesteric displays

Abstract— A novel optically addressable, flexible bistable cholesteric liquid‐crystal display (ChLCD) is presented. These displays utilizeazo‐binaphthalene photosensitive chiral dopants that undergo photo‐isomerization upon exposure to light. The isomerization results in a change in the pitch of the cholesteric liquid crystal (ChLC), which enables the creation of inherently high‐resolution light‐weight displays that are optically written. The displays can be photo‐addressed without patterned electrodes or complex addressing schemes. Capitalizing on the dynamic pitch and the bistability of photosensitive ChLCDs, the display is switched with a single pulse at a specific single voltage to drive the region of the display with a shorter pitch to the focal‐conic texture and the region of the display with a longer pitch to the planar texture. Once in the different textures, the display can hold an image indefinitely regardless of ambient lighting. As such, these displays are a natural fit for badges, shelf‐labels, and point‐of‐sale cards. In this paper, the photosensitive properties of an encapsulated display system in comparison to an unencapsulated display system is discussed. Properties such a photosensitivity, thermal relaxation, and electro‐optical response are studied and reported. In addition, a flexible optically addressable ChLCD is developed and demonstrated.     

Reflective cholesteric displays: From rigid to flexible

Abstract— Bistable reflective cholesteric liquid‐crystal displays are low‐power displays that are suitable for a variety of applications ranging from signage to high‐resolution electronic books. Recent advancements have included higher brightness, full color, black and white from a single layer, and lighting solutions. Cholesteric displays also lend themselves to simple integration into flexible materials since they may be coated and printed. We have developed reflective cholesteric displays on thin flexible plastic substrates, as well as other unconventional substrates such as paper and drapable fabrics. This paper serves as a review for recent advances in the cholesteric‐display technology at Kent Displays.     

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 reflective‐display QR‐LPD®

Abstract— A novel reflective display [Quick‐Response Liquid Powder Display (QR‐LPD®)], has been developed. This paper‐like display has the advantages of outstanding image stability, easy viewing, low‐power consumption, and a high‐response time. QR‐LPD® will be promoted, initially, for use as electronic price‐tag displays for merchandise. In addition, QR‐LPD® is suitable for flexible display applications because it does not require TFT arrays or a high‐temperature process while maintaining an excellent paper‐like image as well as glass‐type display compatibility.     

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.     

Transmission and reflection dual operational mode MEMS display device

A novel MEMS display device comprising a light separator and MEMS light shutters is introduced. This device is operable both in transmissive mode using internal light source and in reflective mode using external sun light. In transmissive mode, the light separator directs internal backlight illuminated on its incident surface into a plural of small openings (grooves) on the viewing surface. The MEMS light shutters are used to control the color and intensity of light at individual pixels. Internal light utilization efficiency of this display is the greatest compared to any other transmissive displays. The device is capable of having true black background, hence a very high contrast ratio. In reflective mode, MEMS shutters direct part of the sun light for image display. MEMS shutters have fast response time, making the new device suitable for vivid motion picture display, and operable at very low voltages, suitable for mobile device applications.     

A quick‐response liquid‐powder display (QR‐LPD®) with plastic substrate

Abstract— Paper‐like displays as thin as 290 μm have been developed using QR‐LPD technology. We fabricated two types of displays. One is a dot‐matrix type with a 160 × 160 array of pixels and a 3.1‐in.‐diagonal viewable image size. The other is a segmented type for clock use. Each display has a paper‐like appearance and exhibits high contrast. Plastic substrates with a thickness of 120 μm were used, resulting in flexible displays that can be bent up to a radius of curvature of 20 mm.     

Electrochemically-switchable emission and absorption by using luminescent Lanthanide(III) complex and electrochromic molecule toward novel display device with dual emissive and reflective mode

Electroswitching of emission and coloration was achieved by a combination of a luminescent Eu(III) complex and an electrochromic molecule of diheptyl viologen (HV²⁺), indicating that the complex-molecule combination could be used as a display material with dual emissive and reflective modes. The coloration of the material was associated with the electrochromism of HV²⁺. Emission control was found to be possible due to the electrochromism of HV²⁺ via intermolecular energy transfer from the excited state of the Eu(III) ion to the reduced state of HV⁺. By using this mechanism, dual emissive and reflective representation of numerical characters were demonstrated.     

Brilliant cosmetic film for ambient displays,with cholesteric liquid crystal

We have successfully developed a cosmetic film with polymerized cholesteric material. The film features a variety of colors by helical pitch gradients, diffusive texture, and arbitrary color patterns. It hides the display when turned off, and transmits display images when turned on. We believe it could change the display in the OFF‐state from the conventional black wall to specially designed decorations. In addition, they can be applied to hidden sensors.