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.     

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.     

Transflective ferroelectric liquid‐crystal display with a single‐cell gap

Abstract— A ferroelectric liquid‐crystal (FLC) display was optimized as a transflective liquid‐crystal display (LCD). In this configuration, the single‐cell‐gap approach was considered. The optimized configuration exhibits a high contrast ratio, wide viewing angles, and achromatic (black/white) switching in both the transmissive and reflective modes. Because no double‐cell‐gap structure, no subpixel separation, and no patterning polarizers and retarders are included in the configuration, the configuration is easy to fabricate and also possess a perfect dark state. This configuration is also suitable for bistable applications.     

Domain walls in photoaligned double‐domain twisted‐nematic LCDs

Abstract— Advanced two‐ and three‐dimensional modelling was used to explain microscopic measurements on two different double‐domain twisted‐nematic liquid‐crystal‐display (TN‐LCD) configurations that were made using photoalignment. The shape of domain walls and their effect on the transmitted intensity were described correctly. For some double‐domain configurations, the brightness and contrast of the display will be affected by the domain walls.     

Viewing‐angle compensation of TN‐ and ECB‐LCD modes by using a rod‐like liquid‐crystalline polymer film

Abstract— A liquid‐crystal line retardation‐film technology by using a rod‐like liquid‐crystalline polymer (LCP) for various LCD modes have been developed. In particular, considerable improvements in viewing‐angle performance have been achieved for the twisted‐nematic (TN) and the transmissive/transflective electrically controlled birefringence (ECB) modes by using hybrid aligned nematic film (NH Film).     

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.     

Novel application of ink‐jet‐printing technology in multi‐domain alignment liquid‐crystal displays

Abstract— Based on the drop‐on‐demand characteristics of ink‐jet printing, the multi‐domain alignment liquid‐crystal display (LCD) could be achieved by using patterned polyimide materials. These polyimide ink locations with different alignment procedures could be defined in a single pixel, depending on the designer 's setting. In this paper, we combined the electro‐optical design, polyimide ink formulation, and ink‐jetting technology to demonstrate the application of multi‐domain alignment liquid‐crystal display manufactory. The first one was a multi‐domain vertical‐alignment LCD. After the horizontal alignment material pattern on the vertical alignment film, the viewing angle would reach 150° without compensation film. The second one was a single‐cell‐gap transflective LCD within integrating the horizontal alignment in the transmissive region and hybrid alignment in the reflective one in the same pixel. In addition, this transflective LCD was also demonstrated in the form of a 2.4‐in. 170‐ppi prototype.     

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.     

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.     

A silicon‐chip‐based light valve with reflective twisted‐nematic mode for high‐definition projectors

Crystalline‐silicon‐chip‐based reflective light valves are suitable for realizing high definition and bright liquid‐crystal projectors. We have developed an XGA (1025 × 769 pixels) silicon‐chip‐based light valve with a diagonal display area of 2.54 cm (1 in.). The reflective twisted‐nematic mode was examined by using the Jones matrix method as a display mode, and the normally white reflective twisted‐nematic mode was selected. This mode is suitable for a narrow cell gap, and a fast response time can be expected. In addition, the driving voltage of this mode is low and has good chromaticity with small retardation. The cell gap of the light valve is 2 μm. The cell gap support is made using spacer posts formed on the silicon chip with a photodefinable resin. The response time is 12 msec, including both rise and fall times. The contrast ratio is more than 1000 at 5 Vrms.     

Transflective blue‐phase liquid‐crystal display with corrugated electrode structure

Abstract— A transflective polymer‐stabilized blue‐phase liquid‐crystal display (BP‐LCD) with a corrugated electrode structure is proposed. To balance the optical phase retardation between the transmissive (T) and reflective (R) regions, two device structures are proposed. The first device structure has the same inclination angles but different cell gaps in the T and R regions. And the second device structure has the same cell gap but different inclination angles in the T and R regions. Both of the device structures can obtain well‐matched VT and VR curves. This display exhibits low operating voltage, high optical efficiency, and a wide viewing angle.     

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.     

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.     

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.     

New measuring method for determining alignment parameters in twisted‐nematic and super‐twisted‐nematic cells

Abstract— A new method for determining the thickness, twist angle, and azimuth of the director for a substrate with twisted‐nematic (TN) and super‐twisted‐nematic (STN) liquid‐crystal (LC) cells has been proposed. The measurement was carried out by using an optical system which consisted of a monochromatic light source, polarizer, rotating analyzer, and software programs. The polarization transfer matrix, or Jones matrix, of a TN or an STN LC cell is formulated by the Fourier coefficient of the signal that is modulated by the rotating analyzer. These three alignment parameters are derived directly from components of the Jones matrix. We made a special effort to design the system to ensure accurate, stable, and quick measurement. Thus, the three parameters were determined simultaneously within a few seconds with good reproducibility; e.g., the standard deviation of the twist angle in the TN cell is 0.02° or less.     

A single‐cell‐gap transflective blue‐phase liquid crystal display based on fringe in‐plane switching electrodes

A transflective blue‐phase liquid crystal display (TRBP‐LCD) based on fringe in‐plane switching (FIS) electrodes is proposed. The proposed structure generates combined fringe and in‐plane electric fields that cause more liquid crystal (LC) molecules to reorient almost in plane above and between the pixel electrodes. The fringe field is mainly generated in the transmissive (T) region, and the horizontal electric field is mainly generated in the reflective (R) region. By optimizing the width of the pixel electrodes and the gap between two adjacent pixel electrodes, the different electric field intensity in the T and R regions contribute to balance the optical phase retardation between the T and R regions. As a result, the proposed TRBP‐LCD exhibits a low operating voltage and high optical efficiency, while it preserves a relatively simple fabrication process.     

A continuous‐viewing‐angle‐controllable liquid‐crystal display using a blue‐phase liquid crystal

Abstract— A continuous‐viewing‐angle‐controllable liquid‐crystal display (LCD) using a blue‐phase liquid crystal is proposed. To realize both wide‐viewing‐angle (WVA) mode and narrow‐viewing‐angle (NVA) mode with a single liquid‐crystal panel, each pixel is divided into a main pixel and a subpixel. The main pixel is for displaying images in both modes. The subpixel is for displaying images in WVA mode and controlling the viewing angle in NVA mode. The device exhibits a good viewing‐angle‐controlling characteristic and high transmittance.     

Accurate determination of pretilt angle in twisted‐nematic liquid‐crystal cells by using a rotating analyzer

Abstract— A new optical method for determining the pretilt angle ψ⁰, particularly on twisted‐nematic (TN) liquid‐crystal (LC) cells, is proposed. ψ⁰ was rapidly determined with good reproducibility on a TN‐LC cell by using a rotating analyzer optical system, a twist angle Φ, the azimuth of the director at a substrate, ϕ⁰, and the retardation Δnd as known values. The thickness d was also determined simultaneously with ψ⁰. ψ⁰ and d were determined within minutes. ψ⁰ was previously determined to be in the range of 0.1° with a standard deviation of 0.01°; this was obtained by repeating the measurement 50 times. The principle behind the determination and the experimental set up are described in detail.     

Comb‐on‐plane switching electrodes for liquid‐crystal displays

Abstract— Although the common twisted‐nematic liquid‐crystal displays (TN‐LCD) has excellent contrast and low color dispersion, it suffers from small viewing angle when driven into the homeotropic state. Among the many techniques proposed, in‐plane switching (IPS) has been quite effective in improving viewing angle. However, there may be difficulty in adopting conventional IPS to higher‐definition displays because it suffers from limited storage capacitance and reduced transmittance. A new comb‐on‐plane switching (COPS) electrode design is proposed. Compared to conventional IPS, COPS allows for lower switching voltage and offers advantages including naturally scalable storage capacitance, wide viewing angle with TN‐like high transmittance, and low color dispersion.     

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.