Single‐layered multi‐color electrowetting display by using ink‐jet‐printing technology and fluid‐motion prediction with simulation

Abstract— This paper describes a single‐layered multi‐color electrowetting display (EWD) by using ink‐jet‐printing (IJP) technology and comparing different pattern electrodes with the use of the numerical investigations of ANSYS FLUENT®. This work consists of two parts: the first describes the design of implementing a single‐layered multi‐color EWD and the second demonstrates the application of ANSYS FLUENT® simulation in different pattern electrodes settings on the proposed EWD. The single‐layered multi‐color EW device was evaluated by using various colored oils without adopting a color filter. The single‐layered multi‐color EWD at a driving voltage of 25 V can achieve a maximum aperture ratio and reflectivity of 80% and 38.5%, respectively. The colored saturation of R, G, B oils can increase to 50% (NTSC: 13.3–27.8%). In addition, a radiate electrode at the required viewable area condition of 85% and force 5 * F^k, which results in ink stable contraction and a shorter response time of 50% (radiate vs. square), was proposed. The experimental results and simulation demonstrate that ink‐jet‐printing (IJP) technology along with the use of radiate electrodes can result in a single‐layered multi‐color EWD with a shorter response time.     

Full‐color AMOLED with RGBW pixel pattern

Abstract— A full‐color AMOLED display with an RGBW color filter pattern has been fabricated. Displays with this format require about one‐half the power of analogous RGB displays. RGBW and RGB 2.16‐in.‐diagonal displays with average power consumptions of 180 and 340 mW, respectively, were characterized for a set of standard digital still camera images at a luminance of 100 cd/m². In both cases, a white‐emitting AMOLED was used as the light source, and standard LCD filters were used to provide the R, G, and B emission. The color gamuts of these displays were identical and the higher overall efficiency of the RGBW format results from two factors. First, a large fraction of a typical image is near neutral in color and can be reproduced using the white sub‐pixel. Second, the white sub‐pixel in an RGBW AMOLED display is highly efficient because of the absence of any color filter. The efficiency of these displays can be further enhanced by choosing a white emitter optimized to the target display white point (in this case D65). A two‐emission layer configuration based upon separate yellow and blue‐emitting regions is shown to be well suited for both the RGBW and RGB formats.     

Color error from an RGB‐stripe pixel structure

Abstract— Most direct‐view color displays have a sub‐pixel structure similar to the RGB‐stripe structure. The video data for R and B are produced on the condition that they are reproduced at the same position as G but they are displayed on the screen with 1/3 of a pixel separation from the corresponding G pixel. This pixel structure thus entails a convergence error of 1/3 of a pixel. The modified s‐CIELAB method was applied to investigate color errors produced by the RGB‐stripe pixel structure. The results show that the pixel structure can degrade the image quality even for a viewing distance where the pixel structure is not visible because the color difference caused by the structure has a low‐frequency component and the human vision can detect it. The same method was applied to the convergence error and it was shown that the necessary convergence accuracy is around 1/4 of a pixel.     

Two‐Colored Pixels

In this paper we show how to use two‐colored pixels as a generic tool for image processing. We apply two‐colored pixels as a basic operator as well as a supporting data structure for several image processing applications. Traditionally, images are represented by a regular grid of square pixels with one constant color each. In the two‐colored pixel representation, we reduce the image resolution and replace blocks of N × N pixels by one square that is split by a (feature) line into two regions with constant colors. We show how the conversion of standard mono‐colored pixel images into two‐colored pixel images can be computed efficiently by applying a hierarchical algorithm along with a CUDA‐based implementation. Two‐colored pixels overcome some of the limitations that classical pixel representations have, and their feature lines provide minimal geometric information about the underlying image region that can be effectively exploited for a number of applications. We show how to use two‐colored pixels as an interactive brush tool, achieving realtime performance for image abstraction and non‐photorealistic filtering. Additionally, we propose a realtime solution for image retargeting, defined as a linear minimization problem on a regular or even adaptive two‐colored pixel image. The concept of two‐colored pixels can be easily extended to a video volume, and we demonstrate this for the example of video retargeting.     

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.     

Active matrix field sequential color electrically suppressed helix ferroelectric liquid crystal for high resolution displays

In this article, we disclose a 3‐inch 250ppi active matrix field sequential color (FSC) display based on electrically suppressed ferroelectric liquid crystal (ESHFLC). ESHFLC's ultra‐fast response time (~10 μs at 6.67 V/μm) enables the display resolution to be tripled via FSC technique. The photo‐alignment technology provides ESHFLC with optimal anchoring energy that contributes to a high contrast ratio over 10 K:1 on single pixel level measurement. A specific 3T1C pixel circuit is designed to generate continuous gray scale from FLC binary switching by utilizing the pulse width modulation concept. The low temperature poly silicon thin‐film transistor array has been used to fabricate the FSC ESHFLC display panel. We achieved an 8‐bit gray level for each color subframe, that is, R, G, and B colors that results in 24‐bit color images. We believe, because of the good optical quality and cost‐effective fabrication, this display may replace in‐plane switching or fringe‐field switching in the near future for the portable device market. Moreover, high resolution FSC ESHFLCs can find applications in the emerging virtual reality displays.     

Amorphous‐oxide TFT backplane for large‐sized AMOLED TVs

Abstract— Amorphous‐oxide thin‐film‐transistor (TFT) arrays have been developed as TFT backplanes for large‐sized active‐matrix organic light‐emitting‐diode (AMOLED) displays. An amorphous‐IGZO (indium gallium zinc oxide) bottom‐gate TFT with an etch‐stop layer (ESL) delivered excel lent electrical performance with a field‐effect mobility of 21 cm²/V‐sec, an on/off ratio of >10⁸, and a subthreshold slope (SS) of 0.29 V/dec. Also, a new pixel circuit for AMOLED displays based on amorphous‐oxide semiconductor TFTs is proposed. The circuit consists of four switching TFTs and one driving TFT. The circuit simulation results showed that the new pixel circuit has better performance than conventional threshold‐voltage (VTH) compensation pixel circuits, especially in the negative state. A full‐color 19‐in. AMOLED display with the new pixel circuit was fabricated, and the pixel circuit operation was verified in a 19‐in. AMOLED display. The AMOLED display with a‐IGZO TFT array is promising for large‐sized TV because a‐IGZO TFTs can provide a large‐sized backplane with excellent uniformity and device reliability.     

A 510‐kb SOG‐DRAM for mobile displays with embedded frame memories

Abstract— A system‐on‐glass (SOG) dynamic random access memory (DRAM), which enables the implementation of frame‐memory‐integrated displays, has been developed. A dynamic one‐transistor‐one‐capacitor memory cell, which has a data retention time of over 16.6 msec, and a compression/decompression (CODEC) circuit were developed to reduce the layout area and power. The CODEC enables an 18‐bit/pixel color display, while reducing the memory capacity from 18 to 12 bits/pixel. A frame‐memory macro was created by combining the SOG‐DRAM with an embedded controller that enables independent access for writing and reading. Its operation was verified by chip measurement and demonstration as a frame‐memory operation of 262k‐color QCIF+ displays. The work reported in this paper was the first step to creating a Zero‐Chip Display with an integrated frame memory, and it proved the concept was feasible.     

Energy‐efficient liquid‐crystal displays (e2‐LCDs) using a photonic‐crystal backlight system

Abstract— Cholesteric liquid crystals automatically form one‐dimensional photonic crystals. For a photonic crystal in which light‐emitting moieties are embedded, unique properties such as microcavity effects and simultaneous light emission and light reflection can be expected. Three primary‐color photonic‐crystal films were prepared based on cholesteric liquid crystal in which fluorescent dye is incorporated. Microcavity effects, i.e., emission enhancement and spectrum narrowing, were observed. Two types of demonstration liquid‐crystal displays (LCDs) were fabricated using the prepared photonic‐crystal films in a backlight system. One is an area‐color LCD in which a single photonic‐crystal layer is used for each color pixel and the other is a full‐color TFT‐LCD in which three stacked photonic‐crystal layers are used as light‐conversion layers. The area‐color LCD was excited by using 365‐nm UV light, and the full‐color TFT‐LCD was excited by using 470‐nm blue LED light. Because of the photonic crystal's unique features that allow it to work as light‐emitting and light‐reflecting layers simultaneously, both LCDs demonstrate clear readable images even under strong ambient light, such as direct‐sunlight conditions, under which conventional displays including LCDs and OLED displays cannot demonstrate clear images. In particular, an area‐color LCD, which eliminated color filters, gives clear images under bright ambient light conditions even without backlight illumination. This fact suggests that a backlight system using novel photonic‐crystal layers will be suitable for energy‐efficient LCDs (e²‐LCDs), especially for displays designed for outdoor usage.     

Bit‐depth extension: Overcoming LCD‐driver limitations by using models of the equivalent input noise of the visual system

Abstract— Continuous tone, or “contone,” imagery usually has 24 bits/pixel as a minimum, with 8 bits each for the three primaries in typical displays. However, lower‐cost displays constrain this number because of various system limitations. Conversely, higher‐quality displays seek to achieve 9–10 bits/pixel/color, though there may be system bottlenecks limited to 8. The two main artifacts from reduced bit‐depth are contouring and loss of amplitude detail; these can be prevented by dithering the image prior to these bit‐depth losses. Our technique builds on Roberts's noise‐modulation idea and the subsequently influenced work in halftoning for hardcopy and dithering for displays. However, most halftoning/dithering work was primarily directed to displays at the lower end of bits/pixel (e.g., 1 bit as in halftoning) and higher ppi. We approach the problem from the higher end of bits/pixel/color, for example, 6–8, and lower spatial resolution (<100 ppi), which changes the game substantially from halftoning experience. Instead of spatial dither, it is better to use an amplitude dither. In addition, dynamic displays allow for the use of a temporal dithering component. This paper will report on techniques and observations made in achieving contone quality on ～100‐or‐less‐ppi LCDs starting from 4‐ to 8‐bit driver limits, and resulting with no visible dither patterns, noise, contours, or loss of amplitude detail at viewing distances as close as the near focus limit (～120 mm).     

Multi‐view 3‐D display employing a flat‐panel display with slanted pixel arrangement

Abstract— A flat‐panel display with a slanted subpixel arrangement has been developed for a multi‐view three‐dimensional (3‐D) display. A set of 3M × N subpixels (M × N subpixels for each R, G, and B color) corresponds to one of the cylindrical lenses, which constitutes a lenticular lens, to construct each 3‐D pixel of a multi‐view display that offers M × N views. Subpixels of the same color in each 3‐D pixel have different horizontal positions, and the R, G, and B subpixels are repeated in the horizontal direction. In addition, the ray‐emitting areas of the subpixels within a 3‐D pixel are continuous in the horizontal direction for each color. One of the vertical edges of each subpixel has the same horizontal position as the opposite vertical edge of another subpixel of the same color. Cross‐talk among viewing zones is theoretically zero. This structure is suitable for providing a large number of views. A liquid‐crystal panel having this slanted subpixel arrangement was fabricated to construct a mobile 3‐D display with 16 views and a 3‐D resolution of 256 × 192. A 3‐D pixel is comprised of 12 × 4 subpixels (M = 4 and N = 4). The screen size was 2.57 in.     

Development of a color‐tunable polychromatic organic‐light‐emitting‐diode device for roll‐to‐roll manufacturing

A flexible vertically stacked flexible polychromatic color‐tunable OLED has been developed by means of low resistive intermediate electrode technology. The polychromatic OLED has a capability to show 16 million colors with 105% National Television Committee Standard (NTSC) color reproduction. The device can produce arbitrary shape with arbitrary colors, suitable for artistic expressions, just as many as those used in information displays. Independently controlled red, green, and blue light‐emitting layers are stacked vertically. With conventional indium tin oxide technology, because of the temperature restriction, it was quite difficult to achieve low resistance on plastic substrate. The reported numbers were all more than 80 Ω/□. According to the surface mobility control using Fick's law analysis, low sheet resistance 7.34 Ω/□ on plastic film was developed. At first, flexible 7.17 cm² transparent OLED was fabricated for the performance confirmation of transparent electrode. And then polychromatic color‐tunable OLED with the same size were successfully fabricated on plastic. With optical length optimization for each color stack of polychromatic OLED, more than 100% color reproduction in National Television Committee Standard was achieved by stack design. The polychromatic device can be used for colored illumination, as well as for organic‐light‐emitting display pixels for three times emission than conventional pixel design. The device is fabricated on plastic substrate so that the polychromatic organic‐light‐emitting‐diode device is manufacturable with roll‐to‐roll production line.     

Ultra‐fast‐switching flexoelectric liquid‐crystal display with high contrast

Abstract— The flexoelectro‐optic effect provides a fast‐switching mechanism (0.01–0.1 msec), suitable for use in field‐sequential‐color full‐motion‐video displays. An in‐plane electric field is applied to a short‐pitch chiral nematic liquid crystal aligned in the uniform standing helix (or Grandjean) texture. The switching mechanism is experimentally demonstrated in a single‐pixel test cell, and the display performance is investigated as a function of device parameters. A contrast ratio of 2000:1 is predicted.     

Color reproduction with a various number of sub‐pixels

Monochrome reflective‐type displays are widely used for portable reading applications such as electric papers because this type does not need a back light unit and can be used outdoors for a long time. Color reflective‐type displays without back light units are desired to expand the market further. The current color reproduction is based on three sub‐pixel red, green and blue (RGB) methods, and when used in reflective type, its luminance is reduced to a third of that of monochrome type. Adding a white sub‐pixel to the current method can improve the luminance, making the sub‐pixel number four. However, in the case of a high resolution display with a four‐sub‐pixel method, the pixel structure is complex, and the luminance improvement may be limited. Instead of increasing the sub‐pixel number, two sub‐pixel methods are investigated. These methods can improve luminance with limited color gamut. The performances are compared with those of other methods quantitatively.     

Active matrix monolithic micro‐LED full‐color micro‐display

An active matrix monolithic micro‐LED full‐color micro‐display with a pixel density of 317 ppi is demonstrated. Starting from large‐scale and low‐cost GaN‐on‐Si epilayers, monolithic 64 × 36 blue micro‐LED arrays are fabricated and further transformed to full‐color micro‐displays by applying a photo‐patternable color conversion layer. This full‐color fabrication scheme shows feasible manufacturability, suggesting a potential for volume production of micro‐LED full‐color micro‐display.     

Modelling crosstalk through common semiconductor layers in AMOLED displays

High pixel density displays are demanded for active matrix organic light‐emitting diode displays (AMOLED) in applications such as virtual reality headsets, micro‐displays, and high‐end smartphones. Parasitic emission from non‐addressed neighboring pixels (crosstalk) is a common problem in such high pixel density AMOLED, and this crosstalk becomes more severe as the pixel density and fill ratio of the display increases. One of the causes of crosstalk is parasitic currents that travel through common organic semiconductor layers. In this paper, we model and quantify the pixel crosstalk using a 2 + 1D finite element model that is based on the conductivity of the common layer and the luminance–current–voltage curves of the subpixels as measured input parameters. We assess the effect of crosstalk on the pixel current, observed color, and luminance. The 2 + 1D model limits the number of degrees of freedom so that calculations on a standard personal computer are feasible.     

Toward high‐resolution,inkjet‐printed,quantum dot light‐emitting diodes for next‐generation displays

We have investigated the possibility of fabricating quantum dot light‐emitting diodes (QLEDs) using inkjet printing technology, which is the most attractive method for the full‐color patterning of QLED displays. By controlling the quantum dot (QD) ink formulation and inkjet printing condition, we successfully patterned QLED pixels in the 60‐in ultrahigh definition TV format, which has a resolution of 73 pixels per inch. The inkjet‐printed QLEDs exhibited a maximum luminance of 2500 cd/m². Although the performance of inkjet‐printed QLEDs is low compared with that of QLEDs fabricated using the spin‐coating process, our results clearly indicate that the inkjet printing technology is suitable for patterning QD emissive layers to realize high‐resolution, full‐color QLED displays.     

Fabrication and performance characteristics of black‐dielectric electroluminescent 160 × 80‐pixel displays

Abstract— We report on recent technological progress in black‐dielectric electroluminescent (BDEL) displays. Fabrication of the first monochrome BDEL 160 × 80‐pixel 4‐in. displays driven with commercial low‐power (<5 W) drive circuitry is presented. Preliminary results on blue‐dielectric EL full‐color displays are also reported. Improvements in both BDEL display performance and display manufacturability underscore the recent development path.     

An effective way to achieve full color cholesteric liquid crystal displays with single liquid crystal mixture and layer

Two‐step ultraviolet exposure method to achieve flexible color cholesteric LCD with single liquid crystal mixture and layer was proposed. The first step for polymer wall formation via photo‐polymerization induced phase separation and second step for color rendering with the photo‐sensitive chiral dopant were independently carried out without the interference of ultraviolet reaction using proper band‐pass filer. This display has good color performance and mechanical stability, which can be also driven by simplified driving circuit so that it would be a substantive solution for color flexible displays.     

Nano‐emissive display technology for large‐area HDTV

Abstract— Using nano‐emissive display (NED) technology, Motorola labs has successfully developed 5‐in. full‐color display prototypes. Carbon‐nanotube‐based field‐emission displays with a pixel size of 0.726 mm for a 42‐in. HDTV exhibit video image quality comparable to CRT displays and demonstrate a luminance of 350 cd/m². These novel low‐drive‐voltage NEDs take advantage of selective growth of CNTs to obtain the desired electron‐emission performance while maintaining inexpensive manufacturing due to a simple self‐focusing and self‐regulating planar structure. Improved video image quality and color purity are achieved with very low power consumption and without the need for an expensive focusing grid.