Reflective bistable cholesteric liquid crystal display

We studied the design rules of the reflective type liquid crystal display (LCD) and the retardation films in order to prevent the color shift and the change of the reflectance. By analyzing the polarized state of light after passing through the LCD, and excellent reflective LCD, which shows almost constant reflectance in wide viewing angle without color shift by using the twist liquid crystal cell.

The contrast ratios of reflective bistable twisted nematic liquid crystal displays with a rear quarter-wave film are optimized by means of a parameter space approach. By plotting the contrast ratio as a function of the twist angle and thickness-birefringence product (dΔn) of the display, the regions where the displays show the best contrast ratio are clearly shown. Both the absolute reflectance and the wavelength dispersion of two bistable twisted states are investigated. It is confirmed that superhigh contrast ratio (infinite in principle), reflectance about 95% with polarized-light input, a large dΔn value (0.63 μm), and low dispersion are possible for such reflective bistable liquid crystal display.

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.

A reflective and transflective liquid crystal display, a figure of bump structure is defined at a pixel electrode, and a reflective layer is formed around the peripheral at the top or bottom of the figure of bump structure to define the reflective zone and the transmissive zone of each single pixel. The upper electrode can contain the figure of slit or bump structure. By adjusting the relative positions of the figures of slit or bump structure between electrodes, the pre-tilt angles and tilting directions of liquid crystal molecules can be controlled, and a multi-domain division alignment is formed, and thus a multi-domain division, semi-transmissive, and wide view angle liquid crystal panel can be formed.

A high‐resolution 5.7″ VGA mono cholesteric reflective liquid crystal display was demonstrated using a STN driver. We have reduced the driving voltage of Ch‐LCD by optimizing panel conditions and adding low molecular materials. The optimized driving voltage was enough to drive the display, necessary for using a commercial STN driver.

Reflective liquid crystal displays (LCDs) are attracting a great deal of interest for use in portable information systems because of their extremely low power consumption, very thin profile and light weight; also, their color does not wash out in outdoor use. We proposed a new type of reflective LCD composed of a light-diffusing film over the display and mirror electrode inside of the LC cell. This reflective LCD has the advantages of high resolution, a wide viewing angle, fast response and full color capability, and is promising as a future high-quality reflective full-color AM-LCD.

The utilization of large‐sized active matrix reflective cholesteric liquid crystal (ChLC) technology in outdoor public information displays (PID) has gained significant attention. This technology leverages the unique optical properties of ChLC to enhance visibility and reduce power consumption. ChLC technology operates without the necessity of backlight, relying instead on ambient light for image presentation. Its bistable characteristics ensure that energy is only consumed during image updates, thus providing significant energy efficiency. In applications for outdoor PID, the incorporation of wide‐temperature materials, combined with active matrix, has successfully led to the development of the world's largest 32‐inch full‐color ChLC reflective display. Active matrix ChLC displays can achieve large sizes, rapid page transitions, ultra‐low power consumption, and high picture quality, making them one of the most promising technologies currently available.

We focused on the off-state current (Ioff) of oxide semiconductor thin film transistors (TFT) (In–Ga–Zn-oxide TFTs), which is lower than that of amorphous silicon TFTs and successfully made a prototype of a 6.0-in. extended graphics array (XGA) reflective liquid crystal display (RLCD) panel integrally including a data selection demultiplexer and a scan driver and capable of displaying still images at 1/180 fps. When still images are displayed, the frame frequency can be set low. This means that the frequency of rewrites of image data is markedly reduced. This leads to the reduction in the power consumption of an LCD panel. Our panel can solve the problems of electronic paper displays: high drive voltage and difficulty of displaying moving images. Thus, our panel is suitable for electronic paper displays.

We fabricated two types of 6.05‐in. active matrix reflective liquid crystal displays (LCD) using a c‐axis‐aligned crystalline oxide semiconductor (CAAC‐OS) for the driver circuit and field‐effect transistors in pixels: one is of the high‐reflectance type, and the other is of the wide‐gamut type. Because of the small off‐state current of the CAAC‐OS and the improved liquid crystal material, low‐frequency driving at 1/60 fps or lower was achieved without memory in a pixel. Consequently, the still image display does not require data writing, except in turning pages; thus, it is flicker‐free in still image display. We also examined the page‐turning operation for less eye strain.The study shows that a reflective color LCD using a CAAC‐OS results in eye‐friendly still image display without flicker similar to an electrophoretic display (EPD); however, it is capable of moving image display, color display, and eye‐friendly page‐turning operation, which are difficult to achieve with an EPD.

Blue phase liquid crystal display (BPLCD) is emerging as next-generation display, because of its fast response speed and very wide viewing angle. However, it has some weak points to be improved. The light leakage at the dark state affects the contrast ratio, and needs to be analyzed and improved. Considering the double-twist structure of blue phase liquid crystal (BPLC) and the simple twist structure of cholesteric liquid crystal (ChLC), the two twist structures are similar. The transmittances and reflectances of planar and focal conic texture of cholesteric liquid crystal and blue phase II liquid crystal are simulated by finite-difference time domain (FDTD) method. The FDTD method is based on the Maxwell’s equation, and can calculate the optical rotatory power directly. The effective optical rotatory powers of the three liquid crystal states are proposed and compared using the light leakages at the cell with crossed and parallel polarizers. The results show that the transmittance of BPLC with crossed polarizers is lower than that of planar texture and larger than that of focal conic texture of ChLC. The optical rotation of BPLC is not the same at any point in one periodic cross section in the light path because the liquid crystal arrangement is complex, the effective optical rotatory power is defined as the average value of the optical rotatory powers at all points. Comparing with the optical rotatory powers of planar and focal conic textures of ChLC, the optical rotatory power of BPLC is less than that of planar texture and larger than that of focal conic texture. Moreover, the Bragg reflections are also simulated, the results show that blue phase liquid crystal is similar to planar state cholesteric liquid crystal, only the reflection intensity is smaller, and no obvious Bragg reflection appears in focal conic state cholesteric liquid crystal. Considering the optical rotation and Bragg reflection, the light leakage and reflective light of BPLCD cannot be ignored if the helix pitch is not less enough, however, these of focal conic texture of ChLC are very small compared with those of BPLC, as a result, the focal conic texture of ChLC can replace blue phase liquid crystal to obtain the good dark state and high contrast ratio.

This paper provides a photopolymerisation induced phase separation PIPS method for fabricating a bistable cholesteric liquid crystal display. We combine inkjet printing technology and phase separation method producing single substrate sidebyside color cholesteric liquid crystal displays by sequential inkjet printing for each color liquid crystals. The display exhibits an areacolourful image with low switching voltages and can be realized on a large scale and rolltoroll R2R fabrication in the future.

We developed an electroholography unit, which consists of a special-purpose computational chip for holography and a reflective liquid-crystal display (LCD) panel, for a three-dimensional (3D) display. The special-purpose chip can compute a computer-generated hologram of 800x600 grids in size from a 3D object consisting of approximately 400 points in approximately 0.15 seconds. The pixel pitch and resolution of the LCD panel are 12 mum and 800x600 grids, respectively. We implemented the special purpose chip and LCD panel on a printed circuit board of approximately 28cmx13cm in size. After the calculation, the computer-generated hologram produced by the special-purpose chip is displayed on the LCD panel. When we illuminate a reference light to the LCD panel, we can observe a 3D animation of approximately 3cmx3cmx3cm in size. In the present paper, we report the electroholographic display unit together with a simple 3D display system.

A holographic color display is developed with a reflective liquid-crystal display (LCD) panel and with low-power RGB lasers. A holographic system is also developed for simultaneous recording of 3-D color images with a color CCD.

Reflective liquid crystal display has the advantages of energy saving and environmental protection. When the ambient light is low, the front light source is required to provide illumination rays. The front light guide plate has a great influence on display luminance, contrast, etc. Based on Comprehensive considerations on luminance, uniformity, stray light, an analysis and evaluation method for front light guide source is proposed. Taking spherical dots as an example, the influence of dot radius and height on the comprehensive performance of the front light source is analyzed. The simulation results show that when the R:H is 3:1, the comprehensive evaluation parameters of the spherical structure are high, and the signal‐to‐noise ratio is increased by 240%, which can greatly improve the display performance. The analysis and evaluation method proposed in this paper can effectively guide the development of front light guide plates, shorten the development time and reduce the development cost.

The concept of reverse or negative doping of a liquid crystal is introduced, in which the sense of the twist of the helix induced by a chiral dopant in the unconstrained liquid crystal material is opposite to that induced by the alignment layers. Some considerations of the extent to which the liquid crystal may be negatively doped before reverse twist domains appear, and the effect of the threshold voltage, are presented. The concept is applied to a reflective liquid crystal display (LCD) and it is demonstrated how the data voltage and power consumption of twisted nematic reflective LCDs may be reduced.