Next‐generation mobile LCDs with in‐cell retarders

Abstract— In‐cell retarders can be a major breakthrough for mobile LCDs. When a patterned in‐cell retarder replaces the external retarders on transflective LCDs, brighter and thinner transflective LCDs with lower power consumption and wider viewing angle can be obtained. Additionally, when in‐cell retarders are applied in reflective LCDs, the thickness of the LCD is considerably reduced without affecting the optical performance of the reflective LCD. This paper presents the technology needed to make in‐cell retarders and the performance of reflective and transflective LCDs with in‐cell retarders.     

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.     

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 TFT‐LCDs with high optical performance

Abstract— In order to reduce panel cost, reduce power consumption, and minimize thickness, a single panel with dual functions for high‐transmissive main displays and high reflective sub‐displays is becoming the trend. Two novel RGB‐W transflective 1.9‐in. a‐Si TFT LCDs have been developed to meet the requirements. By using the traditional seven‐mask dual‐cell‐gap structure, novel transflective tRGB‐t/rW TFT LCD and tRGB‐rW TFT‐LCD panels were fabricated with high transmittance and high reflectance, respectively. The optical clarity is excellent in both dark and bright conditions. Their superior optical performance is attributed to the high‐efficiency “transflective white” subpixel or “reflective white” subpixel.     

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 single‐cell‐gap transflective LCD using active‐level‐shift technology

Abstract— A single‐cell‐gap transflective LCD using active‐level‐shift (ALS) technology has been developed and is presented. An efficient pixel architecture has recently been designed to apply different voltages on transmissive and reflective subpixels through two separated storage capacitors, formed by a boosting electrode and pixel electrodes. A 2.2‐in. vertical‐alignment‐mode (VA) transflective LCD prototype with a similar gamma for both the transmissive and reflective areas was obtained. Compared to a conventional dual‐cell‐gap design, the new single‐cell‐gap design achieves a 17% higher aperture ratio and the contrast increased from 200:1 to 500:1.     

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).     

Advanced IPS technology for mobile applications

Abstract— In‐plane‐switching LCD (IPS‐LCD) technologies originally developed for LCD monitors and TV applications are applied to mobile applications. Advantages of the IPS mode over other optical modes for mobile applications are quantitatively clarified. The panel achieves stable color reproduction and chromaticity in the viewing‐angle range for mobile displays. Superiority of the IPS mode over other optical modes is discussed also from the viewpoints of stability in chromaticity during the brightness change and the driving power consumption. A transflective IPS mode with good performance is accomplished by the use of a proper optical design. A new structure, IPS‐Pro, which enables sunlight readability by increasing the transmittance, i.e., the brightness of the panel, without additional cost and power consumption in contrast to additional fabrication processes required to fabricate the transflective mode is realized. Furthermore, to improve the users' convenience, an automatic luminance control system and a controllable viewing‐angle device are developed. The panels developed fulfill the market requirements of increasing the function and performance variations and will be the most appropriate ones to be applied to mobile appliances, such as cellular phones, digital still cameras, music players, GPS, mobile TV sets, etc.     

Transflective IPS‐LCD with improved reflective contrast ratio

Abstract— In order to improve the reflective contrast ratio of transflective IPS‐LCDs, a novel pixel design for a normally white reflective IPS has been proposed. In this design, the large‐inter‐electrode‐spacing layout using a novel driving method and a double‐layered electrode have effectively reduced the light leakage. By applying these two technologies, a transflective IPS‐LCD has been successfully demonstrated with a high contrast ratio (15:1) in the reflective mode and a wide‐viewing‐angle characteristic in the transmissive mode.     

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.     

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.     

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.     

Improved image quality of a high‐transflective tRGB‐t/rW TFT‐LCD

Abstract— This work combines a very simple resolution rescaling method, a well‐known RGB‐to‐YUV converting technique and a detection strategy into an optimized switchable mechanism in order to eliminate the problems of obvious zigzag profiles caused by the special layouts of transflective tRGB‐t/rW TFT‐LCDs and the poor reflective gray‐level contrast ratio effected by the minimum white data in the transmissive RGB‐W + subpixel rendering algorithms. Finally, a transflective tRGB‐t/rW TFT‐LCD is revealed not only to have no visible zigzag profiles and high visibility of reflective gray‐level contrast ratio, but also to have extreme reflectance and transmittance. The excellent optical performance of the proposed system makes it particularly suitable for single‐panel applications that need both high‐transmissive main displays and high‐reflective subdisplays.     

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.     

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.     

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.     

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.     

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.     

Optical rewritable liquid‐crystal‐alignment technology

Abstract— A new optical rewritable (ORW) liquid‐crystal‐alignment technology has been developed to create a display and to demonstrate its maturity and potential. ORW displays have no electrodes and use polarizers as substrates. The display requires no photolithography on plastic. Its simple construction secures durability and low cost for mass production. The on‐screen information is optically changed in a writing unit that consists of an LCD mask and an exposure source that is based on LEDs, low power, and low cost in comparison with Hg lamps or lasers. A high contrast image can be easily written, viewed, and rewritten through a polarizer, while the multi‐stable gray‐level image requires zero power to maintain the image. Reconfigurable LC alignment using ORW technology best suits plastic‐card displays as well as for LC photonics and various one‐mask processes of patterned LC‐alignment applications.     

Liquid‐crystal photoaligning by azo dyes (Invited Paper)

Abstract— Liquid‐crystal (LC) photoalignment using azo dyes is described. It will be shown that this photoaligning method can provide a highly uniform alignment with a controllable pretilt angle and strong anchoring energy of the LC cell, as well as a high thermal and UV stability. The application of LC photoalignment to the fabrication of various types of liquid‐crystal displays, such as VAN‐LCDs, FLCDs, TN‐LCDs, and microdisplays, on glass and plastic substrates is also discussed. Azo‐dye photoaligned super‐thin polarizers and phase retarders are considered as new optical elements in LCD production, in particular for transflective displays.