Cholesteric Display Research Articles

P‐75: Development of Medium and Large Size Active Bistable State Dual&Four Color Cholesteric LCDs †

Compared with cholesteric display technology, which is mainly a passive driver under 5inch, this paper report one 7.5inch actively driven bistable display device. We use cyan cholesteric liquid crystal reflecting 528nm light and red ink to achieve red & white dual color display. In order to enrich the display information, one red (660nm) cell and one cyan (528nm) cell are fitted with pixel precision, and black ink is printed on the bottom, control the status of the two cells respectively, so as to achieve red, cyan, black, and white four color display. In addition, we optimized drive mode, and update traditional two‐stage drive to three‐stage drive, which improved the stability of the LCD FC state and the image quality of the display device, especially at high and low temperatures. In this paper, red&white dual color and four color display technologies are the first in the LCD industry.

P‐136: Electrical Color and Intensity Tuning in Cholesteric Reflective Display

AbstractWe developed reflective cholesteric displays whose color and reflectance can be electrically tuned. The displays were made from polymer stabilized cholesteric liquid crystals. Monomers and cholesteric liquid crystals were mixed and then polymerized under UV light. When the monomer was achiral, the resulted display exhibited a narrow reflection band, and the reflectance and color can be tuned by applying AC voltages. When the monomer is chiral, the resulted display exhibited a broad reflection band, and the reflectance can be tuned by applying DC voltages.

Continuous Pitch Stabilization of Cholesteric Liquid Crystals and Display Applications

We report a mechanism of the continuous pitch variation of the cholestric liquid crystal (CLC) with reactive mesogen based on the phase separation model and the 4 × 4 matrix analysis. From the density variation of the polymerized RM with chirality, the corresponding pitch variation was directly estimated and the reflectance was calculated using the 4 × 4 matrix analysis. The calculated result quantitatively coincided with the experimental result with broadband reflection spectrum. Also, we demonstrated a simple transflective LC display using the CLC white reflector with broadband reflection spectrum covering entire visible range.

Uni-axial Cracking of ITO to Form Row and Column Electrodes for Roll to Roll Production of Flexible Displays and Electronics

ABSTRACTUniformly uni-axially aligned electrodes are formed by uniaxially cracking an indium tin oxide, ITO, film vacuum deposited on a polyester substrate. The cracks are produced by bending the film around a small radius of curvature, producing narrow, parallel cracks in the ITO separated by 5-10 μm. The cracks are enhanced by etching or uniaxial stretching. Heating and stretching is the most effective, producing a crack width of about 0.05 μm and a differential conductivity (measured parallel and perpendicular to the cracks) several orders of magnitude or greater. A passive matrix bistable cholesteric display is fabricated using top and bottom substrates with perpendicularly aligned electrodes. The addressed lines on each substrate are defined by the contact electrode, which contacts multiple cracked ITO lines. Because of the small dimension of the cracks (much less than the thickness of the active layer) they are not visible in the display. The separation between the contact electrodes must be great than 20 μm in order to include at least one crack and electrically isolate each individual line. The resulting display demonstrates how controlled cracking of ITO can replace photolithographic etching of ITO or printing of conducting polymers to produce the line electrodes required for flexible, passive matrix displays and related electronic applications. Un-axially cracking can be easily integrated into a roll-to-roll manufacturing process.

Characteristics of dual mode reflective cholesteric display

AbstractIn this article, we report our study of a dual mode reflective cholesteric display, which works in the traditional bistable mode as well as in the new and fast monostable mode. Because both modes are compatible, they can be used according to the need for video or static images. The bistable mode operates between the reflecting planar state and non‐reflecting focal conic state, both of which are stable at zero voltage. The bistable mode is suitable for displaying static images. In the monostable mode, it is operated on wrinkled cholesteric layers. It is fast and has low driving voltage, and can exhibit gray levels of reflectance determined by the applied voltage. The monostable mode is suitable to display video rate dynamic images.

40.3: Distinguished Student Paper: Dual Mode Reflective Cholesteric Display

AbstractWe developed a dual mode reflective cholesteric display which works in the traditional bistable mode as well as in a monostable mode. In the bistable mode, it is operated between the reflecting planar state and non‐reflecting focal conic state, both of which are stable at zero voltage. The bistable mode is suitable to display static images. In the monostable mode, it is operated on all the intermediate states between the planar and focal conic states. It is fast and has low driving voltage, and can exhibit gray levels of reflectance determined by the applied voltage. The monostable mode is suitable to display video rate dynamic images.

40.2: Novel Phototunable Chiral Materials for Single Layer Color Cholesteric Display

AbstractNon‐symmetric phototunable chiral compounds (1a, 1b) were designed and synthesized, which exhibited high helical twisting power (about 60um−1). The materials tuned the colors for the entirely visible light region from 450nm to 670nm with high color stability and good NTSC. Single layer full color cholesteric display can be generated by the chiral compounds.

Chiral Flexoelectro-Optic Effect in a Surface-Polymer Assisted Cholesterics with Uniform Lying Helix

Fast-switching flexoelectric cholesteric liquid crystal displays that can be operated in two modes: amplitude (flexoelectric effect, in-plane-switching) and phase (dielectric coupling, out-of-plane switching) have been developed. The device comprises of a small amount of polymer network localized at the substrate surfaces and short-pitch cholesteric liquid crystal whose helical axis laid in the direction parallel to the substrates. The surface-localized polymer network stabilizes the helical axis in the plane parallel to the substrates at zero voltage. The response times for amplitude and phase switching of a polymer-stabilized cholesteric display with 2 microns cell gap are 200 μs at 3.5 V/μm and 3 ms at 12.5 V/μm, respectively. Using a dual-frequency switchable nematic liquid crystal, we are able to improve the contrast of the amplitude switching by obtaining a larger deviation angle of helical axis with a high voltage and in the same time, suppressing the helix unwinding.

P‐54: A Single‐Inductor Bipolar‐Output Converter with Power Conservation Mechanism (PCM) for Driving Cholesteric LCD

AbstractCholesteric liquid‐crystal display (Ch‐LCD) has the bi‐stable characteristic to achieve the energy‐saving for the green technology. Backlight is even unnecessary in the Ch‐LCD system. The single‐inductor bipolar‐output (SIBO) converter is one of best candidate to supply the power management function for the Ch‐LCD with dual positive and negative output voltages by using a single inductor for a compact solution. The energy control methodology with the current‐mode control and the power conservation mechanism (PCM) can strengthen the voltage quality to get high display quality. The test chip fabricated by 0.25 μm CMOS technology demonstrates the non‐noticeable cross‐regulation at dual outputs with 90 % peak power conversion efficiency.

53.4: Novel Pulsed Drive Scheme for Improved Gray‐Level Uniformity of Large‐Area Cholesteric Displays

AbstractA new drive scheme is presented for producing uniform grays over large‐area, low‐resolution cholesteric liquid crystal displays. Gray‐level sensitivity to display non‐uniformities is minimized, which simplifies display manufacturing. While applicable to both rigid and flexible displays, the impact on flexible displays will be particularly important with roll to roll manufacturing capability coming online.

60.2: Novel Optically Addressable Photochiral Displays Erica Montbach

AbstractWe show for the first time, a novel optically written bistable cholesteric display using a simple electrode structure and reversible photo addressable azo binaphthyl chiral materials. These displays are inherently high resolution, require no drive electronics and can be made flexible.

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.

A polymer-stabilized single-layer color cholesteric liquid crystal display with anisotropic reflection

The authors report a method of fabricating single-layer color cholesteric liquid crystal displays from a polymer-stabilized cholesteric liquid crystal. The reflective wavelength can be electrically switched to reflect blue or green from a cell initially reflecting a red color. The color change is a result of the compression to the helical pitches in planar layers in response to the applied voltage. The unique feature of the polymer stabilization is in the fact that the electrically switched colors preserve good reflectivity and the colors are reversible with voltage ramping. Conspicuously, the polymer-stabilized cholesteric display exhibits anisotropic reflection and has a temperature independent of reflected color.

P‐105: Improvement of 2+2 Dynamic Drive Schemes for Cholesteric Displays

AbstractWe have demonstrated the waveform composition method for 2+2 dynamic drive schemes for bistable cholesteric displays with increased addressing speed. The special method of addition of segments into each selection stage makes it possible to increase the addressing speed on 30−35 percent in comparison with the standard 2+2 dynamic drive schemes. Influence of the number of additional segments on the ratio of the peak voltage to effective voltages during different addressing stages and on the frequency of driving pulses has been analyzed. Possibilities of gray scale implementation with proposed improvement have also been discussed.

6.1: Invited Paper: Recent Progress in Color Flexible Reflective Cholesteric Displays

AbstractWe report on highly flexible layered full color cholesteric displays built using ultra thin substrates with encapsulation through the phase separation approach. Recent progress of the state of the art of the cholesteric display technology will be presented as well.

56.4: Cholesteric PDLC Displays with Low Driving Voltage

We present a new single-substrate approach for cholesteric polymer-dispersed liquid crystal (PDLC) displays that provides a uniform monolayer of liquid crystal domains over large areas. The monolayer structure, in combination with the most recent commercially available liquid crystal mixtures, enables the creation of flexible display devices with very low driving voltage.

P-234L: Late-News Poster: Polymer Stabilized Black and White Reflective Cholesteric Displays

Polymer stabilized black and white reflective cholesteric displays have been developed. This type of displays employ a small amount of helical polymer network to stabilize the bistability and enable a distribution of helical pitches that reflect different wavelengths of white light, which are suitable for electronic signs and papers. The features affecting performance of the displays such as type and concentration of polymer network and alignment are investigated against brightness, color and electro-optical properties. A prototype display displaying both black and white images at zero voltage is presented.

56.3: Flexible Ink Jet Printed Conductive Polymer Electrode Cholesteric Display

We report on the first flexible cholesteric display made with ink jet printed conducting polymers as top and bottom electrodes on thin plastic substrates. Ink jet printed conductive polymer electrodes provide ease of patterning as well as enable highly flexible displays. This paper focuses on deposition techniques and trade-offs and benefits of printed flexible electrodes.

Full‐color transflective cholesteric LCD with image‐enhanced reflector

Abstract— A full‐color bistable transflective cholesteric liquid‐crystal display (Ch‐LCD) was demonstrated by using an imbedded image‐enhanced reflector (IER) on top of each transmissive subpixel. The RGB colors were achieved by patterning conventional color filters on a black‐and‐white Ch‐LCD. In addition, the IER on top of each transmissive subpixel provides similar paths for the transmissive backlight and the reflected ambient light. A simple transflective Ch‐LCD was demonstrated.

22.4: Novel Drive Techniques and Temperature Compensation Mechanisms in Reflective Cholesteric Displays

AbstractThe driving techniques used for bistable reflective cholesteric displays are typically a function of application, temperature, and other material constraints. As such, new and unique driving techniques are employed continuously in order to optimize the updating methods of cholesteric displays. This paper focuses on several such techniques and related issues with these methods.