Transflective twisted‐nematic liquid‐crystal display with double twisted‐nematic cell and twisted liquid‐crystal retarder

Abstract— Two configurations, (i) a double‐cell‐gap twisted nematic (DTN) liquid‐crystal display (LCD) and (ii) a single‐cell‐gap twisted‐nematic (TN) liquid‐crystal display (LCD) using a twisted LC retarder, were optimized for transflective liquid‐crystal displays. For the DTN configuration, both the single‐cell‐gap approach and the double‐cell‐gap approach were considered. The optimized configurations exhibit a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. They are easy to fabricate and also possess a perfect dark state. Both are suitable for high‐quality transflective TFT‐LCDs.     

Application of re‐crystallized metal‐induced unilaterally crystallized polycrystalline‐silicon thin‐film‐transistor technology to reflective liquid‐crystaldisplay

Single‐polarizer reflective twisted‐nematic (RTN) liquid‐crystal modes offer larger viewing angles, higher contrast ratios and lower power dissipation compared to regular double‐polarizer transmissive‐ reflective liquid‐crystal implementations. The application of re‐crystallized metal‐induced unilaterally crystallized polycrystalline‐silicon thin‐film‐transistor (TFT) technology to realize active matrices and peripheral circuit components for hand‐held direct‐view RTN‐mode video displays is reported.     

A submillisecond‐response liquid crystal for color sequential projection displays

We report a new LC with low viscosity and high clearing point (T_c ~102 °C) for color‐sequential projection displays. Using a 1.95‐µm mixed‐mode twisted nematic cell, the averaged gray‐to‐gray response time is less than 1 ms, which is ~3.6× faster than the current state of the art. Such a mixed‐mode twisted nematic liquid‐crystal‐on‐silicon can be used for near‐to‐eye wearable projection displays and head‐up displays in vehicles.     

A single‐cell‐gap transflective liquid‐crystal display using different pretilt angles in transmissive and reflective regions

Abstract— A single‐cel l‐gap transflective liquid‐crystal display with two types of liquid‐crystal alignment based on an in‐plane‐switching structure is proposed. The transmissive region is almost homeotropically aligned with the rubbed surfaces at parallel directions while the reflective region has a homeotropic liquid‐crystal alignment. For every driving voltage for a positive‐dielectric‐anisotropy nematic liquid crystal, the effective cell‐retardation value in the transmissive region becomes larger than that in the reflective region because of optical compensation film which is generated by low‐pretilt‐angle liquid crystal in the transmissive region. Under the optimization of the liquid‐crystal cell and alignment used in the transmissive and reflective areas, the transmissive and reflective parts have similar gamma curves. An identical response time in both the transmissive and reflective regions and a desirable viewing angle for personal portable displays can also be obtained.     

Single‐cell‐gap transflective liquid‐crystal display using double‐ and single‐mode approaches

Abstract— In this paper, many popular methods to study transflective liquid‐crystal‐displays (LCDs) have been discussed, and several new transflective LCD configurations with a single‐cell gap have been proposed. The traditional double‐cell‐gap method gives the best match of the transmittance/reflectance voltage curve (TVC/RVC) and also the widest viewing angle, but also brings the highest fabrication complexity. The single‐cell‐gap transflective LCD is much easier to fabricate and also shows a good match of TVC/RVC. A new methodology has been shown to find optimal configurations for single‐cell‐gap transflective LCDs. New configurations using multimode in a single pixel include twisted nematic (TN) optically compensated bend (OCB), TN electrically controlled birefringence (ECB), and TN low‐twisted nematic (LTN). TN and hybrid‐aligned nematic (HAN) modes have been investigated for single‐mode transflective LCDs. The results exhibit high contrast ratio, a good match of TVC/RVC, as well as wide viewing angle.     

A broadband wide‐incident‐angle reflective polarization converter

Abstract— A high‐performance reflective polarization converter which could be used in a backlight recycling system for liquid‐crystal‐display (LCD) devices is proposed. The device consists of a twisted‐nematic (TN) liquid‐crystal film, a uniaxial A‐plate, and a reflector. The configuration parameters, such as thickness and orientation of the films, are optimized using a genetic algorithm. As a result, the design can convert light from TM to TE polarization (or TE to TM) at a maximum 99.7%, minimum 91.3%, and average 96.7% conversion efficiency for the entire visible spectrum and incident angle from 0 to 60°. Such a broadband reflective polarization converter is particularly useful for enhancing the light efficiency and reducing the power consumption of LCDs.     

A reflective polarizer‐free display using dye‐doped polymer‐stabilized blue‐phase liquid crystals

Abstract— A reflective polarizer‐free display using dye‐doped polymer‐stabilized blue‐phase liquid crystal (DDPSBP‐LC) has been demonstrated. The mechanism is a combination of electrically tunable light absorption and Bragg reflection. In this paper, the influence of light absorption in DDPSBP‐LC by changing the dye concentration and absorption paths has been studied. Increased dye concentration can improve the contrast ratio of DDPSBP‐LC; however, the response time is the tradeoff. Increasing the cell gap can improve the contrast ratio of DDPSBP‐LC; however, the response time remains the same. The study of DDPSBP‐LC can help in shutter‐glass applications of 3‐D displays and electronic paper.     

Local dimming light‐guiding plate type backlight system using alignment‐controlled polymer‐dispersed liquid crystals

A new technology which enables a local brightness control according to the displayed images has been expected in the thin and lightweight backlight systems to improve a contrast ratio and power consumption of the liquid crystal displays (LCDs). In this paper, we have proposed a novel local‐dimming backlight system using alignment‐controlled polymer‐dispersed liquid crystals as a light‐guiding plate and investigated the forming conditions of polymer‐dispersed liquid crystals to achieve both a high‐luminance ratio and a fast response speed. As a result, we found that a luminance ratio and response speed of the backlight system can be improved by using bifunctional LC monomer materials and forming fine and rigid polymer network in the LCs, and achieved high luminance ratio of 16:1 and fast response time less than 0.5 ms. In addition, we fabricated the twisted nematic‐mode LCD using the local dimming light‐guiding plate‐type backlight based on this design, and successfully realized eight times higher contrast ratio than that of the traditional twisted nematic‐mode LCD.     

A dual‐cell‐gap transflective liquid‐crystal display with identical response time in transmissive and reflective regions

Abstract— A dual‐cell‐gap transflective liquid‐crystal display (TR‐LCD) with identical response time in both the transmissive and reflective regions is demonstrated. In the transmissive region, strong anchoring energy is used to decrease the response time, while in the reflective region, weak anchoring energy is used to increase the response time. And overdrive voltage technology is adopted to make the response time identical in both the transmissive and reflective regions. The device structure and operating principle of the TR‐LCD was analyzed, the anchoring energy in the transmissive and reflective regions was designed, and the response time and electro‐optic characteristics of the TR‐LCD was calculated. The simulated dual‐cell‐gap TR‐LCD demonstrated good performances.     

High‐transmittance in‐plane‐switching liquid‐crystal displays using a positive‐dielectric‐anisotropy liquid crystal

Abstract— The in‐plane‐switching (IPS) mode exhibits an inherently wide viewing angle and has been widely used for liquid‐crystal‐display (LCD) TVs. However, its transmittance is limited to ～76% compared to that of a twisted‐nematic (TN) cell if a positive‐dielectric‐anisotropy LC is employed. A special electrode configuration that fuses the switching mechanism of the conventional IPS and the fringe‐field switching (FFS) to boost the transmittance to ～90% using a positive LC has been developed. The new mode exhibits an equally wide viewing angle as the IPS and FFS modes.     

Achromatic quarter‐wave film using two chromatic wave plates and a twisted‐nematic liquid‐crystal cell

Abstract— An achromatic quarter‐wave film using one twisted‐nematic liquid‐crystal (TNLC) cell, a chromatic half‐wave plate, and a chromatic quarter‐wave plate is presented. The Jones matrix is used to calculate the optical properties of the system. An optimal algorithm is used for optimizing the configuration parameters. Simulation results indicate that the designed configuration is capable of turning a linearly polarized light into perfectly circularly polarized light in the wavelength range 400–700 nm. The manufacturing tolerance of the cell gap and twisted angle of the TNLC are good.     

Portable multi‐gray scale video playing scheme for high‐performance electrowetting displays

Electrowetting display technology is realized by tuning the surface energy of a hydrophobic surface by applying a voltage based on electrowetting mechanism. Electrowetting displays have favorable optical properties combined with reflective paper‐like performance. It has been successfully demonstrated in reflective mode with high switching speed. In this paper, we propose a portable driving scheme that can display 4‐bit gray scale dynamic video using an active matrix electrowetting display. The proposed driving scheme includes an electronic system and a dynamic driving waveform design. High‐performance multi‐gray video playing and quick response were obtained for a Quarter Video Graphics Array electrowetting display cell fabricated by our team.     

Single‐cell‐gap transflective liquid‐crystal display and the use of photoalignment technology

Abstract— In this paper, transflective liquid‐crystal‐display (LCD) technology will be reviewed, and several new single‐cell‐gap transflective LCD configurations are proposed. Photoalignment technology is studied especially for transflective‐LCD applications. In order to realize the optimal performance of the display as well as a matched transmittance/reflectance voltage curve (TVC/RVC) for the transflective configurations, two different single‐cell‐gap transflective‐LCD approaches will be discussed. The first one is the dual‐mode single‐cell‐gap approach, in which different liquid‐crystal modes are applied to the transmissive and reflective subpixels of the transflective LCD. The other approach is the single‐mode s ingle‐cell‐gap approach, in which an in‐cell retardation film is applied to adjust the performance and TVC/RVC matching of a transflective LCD. Photoalignment technology is used to fabricate the dual‐mode liquid‐crystal cell in the first approach and also the in‐cell retardation film in the second approach. Prototypes of the proposed configurations have been fabricated, which show good performance and a matched TVC/RVC.     

Electro‐optical characteristics of ion‐beam‐aligned FFS‐LCDs on diamond‐like‐carbon thin film

Abstract— A fringe‐field‐switching (FFS) mode cell having LC alignment has been developed by using a non‐rubbing method, a ion‐beam‐alignment method on a‐C:H thin film, to analyze the electro‐optical characteristics of this cell. The suitable inorganic thin film for FFS‐LCDs and the alignment capabilities of nematic liquid crystal (NLC) have been studied. An excellent voltage‐transmittance (V‐T) and response‐time curve for the ion‐beam‐aligned FFS‐LCDs were observed using oblique ion‐beam exposure on DLC thin films.     

Switchable transmissive and reflective liquid‐crystal display using a multi‐domain vertical alignment

Abstract— A wide‐view transflective liquid‐crystal display (LCD) capable of switching between transmissive and reflective modes in response to different ambient‐light conditions is proposed. This transflective LCD adopts a single‐cell‐gap multi‐domain vertical‐alignment (MVA) cell that exhibits high contrast ratio, wide‐viewing angle, and good light transmittance (T) and reflectance (R). Under proper cell optimization, a good match between the VT and VR curves can also be obtained for single‐gamma‐curve driving.     

Effects of carbon‐nanotube doping on the performance of a TN‐LCD

Abstract— The electro‐optical characteristics of a 90° twisted‐nematic liquid‐crystal display (TN‐LCD) were analyzed. The test cell was composed of a minute amount of dopant, multiwalled carbon nanotubes, and a standard nematic mixture, E7, used in TN‐LCDs with direct addressing. Under the experimental conditions, no hystereses in optical transmittance were observed in either the doped cell or a neat counterpart under an applied ac voltage. Experimental results show that doping with nanotubes rectifies the electro‐optical properties of the cells by reducing the driving voltage as well as the rise time. Similar results were found in a TN cell of a TFT‐grade liquid crystal instead of the mixture consisting completely of polar compounds.     

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 single‐cell‐gap transflective liquid‐crystal display with special electrodes

Abstract— A single‐cell‐gap transflective liquid‐crystal display with special electrodes was demonstrated. In the transmissive region, a strong longitudinal electric field was generated by decreasing the distance between the top and bottom transparent indium‐tin‐oxide electrodes; while in the reflective region, a weak longitudinal electric field is generated by increasing the distance between the top and bottom transparent indium‐tin‐oxide electrodes. And slit‐patterned electrodes were used to optimize the fringe field at the junction of the transmissive and reflective regions. As a result, both the transmissive and reflective display modes show well‐matched gray scales. The simulated single‐cell‐gap TR‐LCD has good performances.     

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.     

Defect‐free deformed‐helix ferroelectric liquid‐crystal mode in a vertically aligned configuration (Invited Paper)

Abstract— A novel deformed‐helix ferroelectric liquid‐crystal (DHFLC) mode in a vertically aligned (VA) configuration is described. In this configuration, several unique features of display performance such as uniform alignment, fast response, and analog gray‐scale capability are obtained. Particularly, this VA‐DHFLC mode allows for the defect‐free uniform alignment of both the FLC molecules and the smectic layers over a large area without employing additional processes such as rubbing or electric‐field treatment that are generally required for planar FLC modes. Based on the VA‐DHFLC mode, a transflective display having a single‐gap geometry with in‐plane electrodes on two substrates in the transmissive regions and on one substrate in the reflective regions is described.