Processes,characterizations, and system applications of color‐filter liquid‐crystal‐on‐silicon microdisplays

Abstract— A color‐filter liquid‐crystal‐on‐silicon (CF‐LCOS) microdisplay that integrates color filters on silicon for color will be presented. The color‐filter process on silicon was optimized to achieve fine resolution and precise alignment of the color filters on the pixel array, good adhesion to the silicon suface, and a flat surface for the liquid‐crystal cell assembly. Important optical and electrical parameters of the color filters were extracted to establish an electro‐optical model of the CF‐LCOS microdisplays for device simulation. Thermal, chemical, and light‐stability characterizations were performed to ensure the stabilty of the color filters and CF‐LCOS microdisplays. With color CF‐LCOS microdisplays already available, the projection or viewing optics is greatly simplified. This CF‐LCOS microdisplay is ideal for near‐to‐eye displays because of its low‐power consumption and compactness. The CF‐LCOS microdisplay could also withstand medium light illumination for medium‐sized projectors. A single‐panel projector based on one CF‐LCOS microdisplay of 1280 × 768 × RGB resolution was demonstrated.     

Birefringent properties of cyclic block copolymers and low‐retardation‐film development

Abstract— Cyclic block copolymers (CBCs) are a new class of optical polymers made by fully hydrogenating block copolymers of styrene and conjugated diene. This class of materials has excellent optical transparency, photostability, and good thermal resistance. By changing the copolymer composition and the resulting block‐copolymer morphology, a unique set of birefringence properties can be achieved. The focus of this work was to study various sources of birefringence in block copolymers using a series of model CBC materials. One particularly interesting finding relates to the development of an ultra‐low‐phase‐retardation CBC film. Unlike the conventional approach of using an additive or blend, a CBC film prepared by melt extrusion can readily achieve near‐zero retardation in both the film plane and thickness direction. This nearly isotropic CBC film is useful as a polarizer protection film in flat‐panel displays. When used as the inner protective layer of a polarizer, CBC film helps to reduce the color shift of IPS‐LCDs at oblique angles and offer a wider viewing angle.     

A novel quarter‐wave retardation film for improving viewing angle properties in time‐sequential stereoscopic 3D‐LCDs

We have successfully developed a quarter‐wave retardation film (QWF) for wide viewing angle 3D liquid crystal displays (3D‐LCDs) that provides high luminance, low crosstalk, low color change, and low head‐tilt‐angle dependency. It was found that the out‐of‐plane retardation (Rth) of the QWF in the LCD needs to be close to 0 nm in order to improve the 3D display properties at an off‐axis position and that the in‐plane retardation (Re) needs to be adjusted from 120 to 130 nm to achieve low color change with head tilting. We adopted a coating process for making our QWF because of its potential for retardation control. 3D‐LCDs with this QWF whose Rth was nearly zero had high performance and allowed off‐axis other than on‐axis.     

Single‐layered retardation films with negative wavelength dispersion birefringence made from liquid‐crystalline monomers

Organic light‐emitting diode displays have a cathode composed of a layer of highly reflective metal. Reflection of external light from this layer can be suppressed with a broadband quarter‐wave plate. Although various types of quarter‐wave plate retardation films have been prepared by copolymerizing, mixing, or laminating multiple polymers, ideal wavelength dispersion has not been achieved with thin retardation films because of their relatively low birefringence and the complexity of the procedure required manufacturing them. In this study, we developed (i) new liquid‐crystalline monomers with negative wavelength dispersion birefringence that we used to obtain thin, single‐layered retardation films suitable for coating and (ii) retardation films with different molecular alignments. We found that the monomers showed high solubility and high regularity of molecular alignment, with less damage to the substrate and alignment films. We also investigated the wavelength dispersion and thermal stability of the films. We succeeded in developing retardation films that had a homeotropic alignment or a hybrid alignment with negative wavelength dispersion. These alignments can be used to obtain antireflection films with an improved viewing angle for organic light‐emitting diode displays or next‐generation thin displays.     

New approaches to process simplification for large‐area high‐resolution TFT‐LCDs

Abstract— Novel process architectures are proposed for fabricating large‐area high‐resolution TFT‐LCDs with a minimal number of process steps. A low contact resistance between Al bus lines and the transparent conductive oxide layer, necessary for large‐area panels, is obtained by inducing a self‐formed inter‐metallic compound layer at the interface without using any additional buffer or capping layers. For enhanced brightness and resolution, a new TFT array structure integrated on a color‐filter substrate, referred to as an Array on Color Filter (AOC) structure, has been developed. Good‐quality TFTs were successfully constructed on the newly developed color filter for AOC within a sufficiently wide process margin. By adopting these novel technologies, a 15.0‐in. XGA prototype panel was fabricated and shows good display performance. Thus, these novel technologies have improved cost efficiency and productivity for TFT‐LCD manufacturing, and can be applied to the development of TFT‐LCDs of extended display area and enhanced resolution, benefiting from the low resistance bus lines, the high aperture ratio, and reduction in total process steps.     

Capacity improvement for color‐filter fabs through computer modeling and iterative simulation

Abstract— This study proposes the iterative Simulation‐Based Release (ISR) policy for color‐filter (CF) fabs based on iterative simulation. In the studied CF fabs, multi‐domain vertical‐alignment (MVA) equipment has the capability and flexibility to provide additional production capacity of black‐matrix (BM) and red, green, and blue (RGB) layers. Fab throughput can be increased by setting up MVA equipment to process BM and RGB layers when its available production capacity is larger than the scheduled manufacturing target. An AutoMod simulation model was developed and validated based on a real CF fab in Taiwan. A heuristic lot release plan was developed and used as the input of simulation. A better release plan can be developed by taking advantage of the MVA's line idle periods over the planning horizon generated from simulation and releasing new lots to the MVA line to increase its throughput. Release plans can be modified iteratively when the simulation results of the previous release plans show sufficient idle periods for the MVA line operation. The case study demonstrated that the proposed ISR is effective in idle‐time reduction (more than 60%) and throughput improvement (more than 2% in following months).     

An IPS‐LCD with a high contrast ratio of over 80:1 at all viewing angles

Abstract— A 32‐in. IPS‐LCD with a significantly wide‐viewing‐angle performance has been developed using a new optical compensation method. It provides a contrast ratio of over 80:1 at all viewing angles, which enhances its color saturation at oblique angles. According to our study, it is important to shorten the path of the optical compensation in the Poincaré sphere. We have found an effective method using two retardation films, one with an Nz value larger than 0.5 and one with a value smaller than 0.5.     

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.     

Electron‐beam curing of color filters for flexible‐display applications

Abstract— Color filters spin‐coated on plastic and glass substrates have been cured by electron‐beam radiation instead of by the conventional thermal‐heating method. The electron‐beam curing of the color filters has many advantages over the thermal curing method. Electron‐beam curing is, in principle, a non‐thermal method where low‐temperature (<100°C) curing of color filters on plastic substrates can be realized for the manufacturing process of flexible display panels. A color‐filter resist having a 1.5‐μm thickness was spin‐coated on plastic (polycarbonate) and glass (corning 1737) substrates. The effect of the electron‐beam radiation conditions, such as electron‐beam energy (0.3–1.0 keV), radiation dosage (10–200 kGy), and ambient oxygen has been characterized. The degree of curing was analyzed by using the characteristic absorption peaks at 808 and 1405 cm^?1 in the FT‐IR spectrum. These two peaks originate from the carbon double bonds (>C=C<) of the multi‐functional acrylate monomer which exist in the color‐filter resist. By electron‐beam radiation, the spin‐coated color filter can be effectively polymerized at g (glass transition temperature) of the plastic substrates. The electron beam can solve the problems of the conventional thermal curing method, such as thermal deformation of a plastic substrate and difficulty in achieving dimensional control of a color‐filter pattern due to a large coefficient of thermal expansion (20–70 ppm/°C) compared to that of a glass substrate.     

A new vertical‐alignment LC mode with high‐transmittance and fast‐response‐time features

Abstract— A novel pixel design for vertical‐alignment LCDs with superior transmittance has been developed. The new liquid‐crystal mode, refered to as the hole‐induced vertical‐alignment mode (Hi‐VA), uses a via hole of an organic layer on a TFT substrate to achieve multi‐domain alignment. Compared to the conventional design, the Hi‐VA mode has a transmittance of up to 135% with a contrast ratio of 2000:1. Moreover, the new structure is free from ITO patterning or protrusion on the color‐filter side, which makes the fabrication process simple and low cost.     

A reflective color STN-LCD with a single polarizer and double retardation films

Abstract— A reflective color STN-LCD with a single polarizer and double retardation films has been investigated. The double retardation films arranged in front of the LC layer enabled the LCD to contain reflective electrodes inside the panel. This configuration achieves a bright image with no parallax. A new construction of a reflective STN-LCD with a single polarizer has been developed by means of our own method in which the color difference ΔE* as the optimizing parameter has been used. Further, RGB color filters have been newly designed for our reflective LCD, and an aluminum (Al) layer has been introduced as a reflective electrode. As a result, we have realized a 7.8-in.-diagonal reflective color STN-LCD (640 × 480) which has 15% reflectance, 14:1 contrast ratio, 4096-color capability, and sufficient color gamut. It has been confirmed that the single-polarizer reflective color STN-LCD has sufficient performance for mobile business tools. We believe that it will be a key device for this application.     

A field‐sequential‐color display with a local‐primary‐desaturation backlight scheme

Abstract— Field‐sequential‐color technology eliminates the need for color filters in liquid‐crystal displays (LCDs) and results in significant power savings and higher resolution. But the LCD suffers from color breakup, which degrades image quality and limits practical applications. By controlling the backlight temporally and spatially, a so‐called local‐primary‐desaturation (LPD) backlight scheme was developed and implemented in a 180‐Hz optically compensated bend (OCB) mode LCD equipped with a backlight consisting of a matrix of light‐emitting diodes (LEDs). It restores image quality by suppressing color breakup and saves power because it has no color filter and uses local dimming. A perceptual experiment was implemented for verification, and the results showed that a field‐sequential‐color display with a local‐primary‐desaturation backlight reduced the color breakup from very annoying to not annoying and even invisible.     

Novel transmissive color filter using cholesteric liquid crystal with wide viewing angle

Abstract— A new design for a cholesteric liquid‐crystal (CLC) color filter has been devised. Since this system absorbs no light, it uses backlight energy very efficiently. When CLCs of this type with an expanded selective reflection band are combined with light sources with sharp RGB emission peaks, such as LEDs, it is possible to reduce the dependence of color shift on viewing angle and make more efficient use of light.     

Practical CNT‐FED structure for high‐luminance character displays

Abstract— A high‐luminance CNT‐FED character display using a simple line rib structure was constructed. The display panel had 48 × 480 dots and the subpixel pitch was 1 mm. The greatest benefit of a display using CNT technology is high luminance performance with low‐power consumption. The luminance of the green‐color dot wasca. 10,000 cd/m² under 1/1 6 duty‐cycle driving at a 6‐kV anode voltage. The high luminance of the display panel can provide good visibility when installed even in outdoor locations, and the power consumption was ca. 4 W at the character displaying module. This, a CNT‐FED for character displays also has potential multifunctionality, which could be battery driven. It should be useful for public displays even under emergency no‐power conditions. In this work, a practical structure and process technologies for making ribs with reasonable cost were developed. The newly introduced 2‐mm‐tall line ribs as spacers were formed by using innovative production processes; i.e., the rib paste was pushed out of a multi‐slit nozzle, and the rib shape was formed by UV‐light irradiation. The developed panel structure and manufacturing processes also had the advantages of size flexibility and high production yield.     

Multi‐band reconfigurable microwave filter using dual concentric resonators

This article presents the design and testing of a novel frequency reconfigurable microwave filter. The filter structure is composed of an all stop resonator coupled with C‐ and E‐shaped parasitic resonators. PIN diodes are located at suitable positions to achieve multi‐band reconfiguration from 1.2 to 3.2 GHz making the filter suitable for multiple wireless communication systems. The frequency and bandwidth of the filter are governed by the length of the resonators and coupling between the resonators and the transmission line, respectively. A sharp rejection of ?30 dB is observed between the passbands. The proposed filter offers 56% size reduction with flat group delay performance. The prototype filter is fabricated and the simulation results are validated using experimental measurements. The measurement results show good agreement with the simulation results.     

Simulation‐based look‐ahead release planning for color filter fabs

This study presents a look‐ahead release planning approach on the basis of AutoMod simulation model for a sixth‐generation thin film transistor liquid crystal display color filter (CF) fab in north Taiwan. The studied CF fab has two identical lines with the processes of black matrix (BM), color layer [red, green, and blue (RGB)], indium tin oxide, and photo spacer (PS). These two lines share two supporting processes, multi‐domain vertical alignment (MVA) and laboratory (LAB). MVA has the capability and flexibility to provide the functions of RGB and PS, whereas LAB can provide the functions of BM and RGB. The production release planning becomes complex because of the equipment flexibility in supporting each other. An AutoMod simulation model is therefore developed and validated using real data from the fab. The AutoMod simulation model is well representative of the real system with less than 10% difference in throughput in all production stations. Using simulation to look ahead, a production controller can predict potential equipment idleness and make adjustment to better utilize equipment capacity. On the basis of simulation with design of experiments, the proposed simulation‐based look‐ahead release plan is demonstrated to be effective in improving system throughput.     

Electro‐optical characteristics and optimization of vertically aligned STN‐LCDs

A new LCD for high‐duty passive‐matrix driving, referred to as a vertically aligned (VA) STN‐LCD, characterized by high transmittance and a high contrast ratio, has been developed. This LCD can display black‐and‐white images by using crossed polarizers without the use of a color compensator because the LCD has almost zero retardation at the initial alignment state. A fabricated black‐and‐white VA‐STN‐LCD without a black matrix shows high transmittance (>15%) and contrast (CR > 100) under 1/240‐duty direct‐multiplex driving.     

Simulation and design of MIM nanoresonators for color filter applications

We simulated metal–insulator–metal (MIM) nanoresonator structures that can be realized by sandwiching an insulator layer between two metal grating layers with subwavelength periods and heights. Simulation results indicate that it is possible to use relatively low refractive index polymeric materials as the insulator layer and such MIM structures can function as color filters with reasonably narrow bandwidths in transmission mode. Such color filters being superior in performance might find application in liquid crystal display devices replacing the conventional color filters. Simulations suggest that development of plasmonic modes at the metal–insulator interfaces might be responsible for the filter‐like transmission behavior of such structures. The transmission peaks can be tuned by changing the heights of the two grating layers and the refractive index of the insulator layer. Transmission peak is red‐shifted as insulator layer refractive index increases. Simulations were carried out using a home‐grown, monochromatic version of recursive convolution finite‐difference time‐domain method.     

A transparent sheet display by plastic MEMS

Abstract— A new type of color‐image display pixel based on MEMS (microelectromechanical systems) technology of plastic materials is presented. The mechanism for making color is optical interference using a Fabry‐Perot interferometer. A thin sheet of PEN (polyethylene naphthalate) with a metal half‐mirror was laminated over a glass or PEN substrate with an optical cavity inside. The electrostatically controlled deformation of the PEN film changes the color of the transmitting light by interference within the optical cavity. Color pixels of three primary colors (red, green, and blue) were successfully developed and demonstrated, with a driving voltage ranging from 80 to 120 Vdc. Thanks to the mechanical flexibility of the PEN films, the display could operate even when placed on a curved surface.     

High‐luminance 1.8‐mm‐pixel‐pitch CNT‐FED for ubiquitous color character displays

Abstract— A high‐luminance 1.8‐mm‐pixel‐pitch CNT‐FED for color character displays has been developed. The display panel has 32 × 256 color pixels, and the subpixel size is 0.6 × 1.8 mm. The display panel can provide good visibility when installed even in outdoor locations. The power consumption is low enough for the display to be battery driven. The practical application is the display of important messages regarding the evacuation from disaster areas, even under emergent no‐power conditions similar to the messages on vending machines.