Microcup® displays: Electronic paper by roll‐to‐roll manufacturing processes

Abstract— Rolls of flexible displays or electronic paper have recently been prepared by a high‐speed roll‐to‐roll manufacturing process based on SiPix's novel Microcup® and top‐sealing technologies. Both Microcup® electrophoretic displays (EPDs) and LCDs have been demonstrated. The display rolls are format flexible and may be cut into desirable size and shape for a variety of applications. High‐performance flexible passive‐matrix Microcup® EPDs having a wide range of threshold voltages have also been demonstrated.     

A rugged display: Recent results of flexible cholesteric liquid‐crystal displays

Abstract— A 3‐m‐long rugged flexible display having a novel single‐plastic‐substrate structure has been demonstrated with a coated cholesteric liquid‐crystal mixture. The display is designed to be fabricated by a roll‐to‐roll process to increase productivity at a competitive cost. It has the advantage of having almost no limitation in display length. The high‐resolution (300‐dpi) monochrome cholesteric liquid‐crystal display (ChLCD) can be achieved by using a photo‐addressing method. A single‐layered 10.4‐in. color ChLCD also has been developed with good color and contrast.     

Technologies toward flexible liquid‐crystal displays

Abstract— Several leading technologies for flexible liquid‐crystal displays have been developed recently at ERSO. The roll‐to‐roll compatible techniques, polymer‐added liquid crystal, have been applied on a film‐like substrate. A flexible black‐and‐white cholesteric liquid‐crystal display was also implemented by photo‐induced phase separation. Color filters placed on a plastic substrate by a low‐temperature manufacturing process was successfully fabricated. A novel design of a wide‐viewing‐angle color plastic LCD was also proposed.     

Flexible hybrid substrates of roll‐to‐roll manufacturing for flexible display application

A flexible hybrid substrate was developed and demonstrated for roll‐to‐roll (R2R) manufacturing. Layer‐by‐layer misalignment can be well controlled within 5 µm. Top‐gate amorphous InGaZnO thin‐film transistor was fabricated on the flexible hybrid substrate by R2R process for the first time. A 4.3‐in. segment‐type reflective Electro‐Phoretic Display (EPD) display was also demonstrated to show the R2R capability of flexible substrates.     

A Flexible electronic‐paper display with an ultra‐thin and flexible LSI driver using quick‐response liquid‐powder technology

Abstract— A thin and flexible LSI driver with a thickness of less than 35 μm for a passive‐matrix‐driven Quick‐Response Liquid‐Powder Display (QR‐LPD?) was successfully mounted onto the flexible printed circuit (FPC) and the back substrates of a flexible QR‐LPD?. Amounted LSI driver on a plastic substrate shows no significant degradation in the driving performances and maintains physical flexibility without any connection failures. This technology can realize a fully flexible electronic paper in combination with a plastic‐substrate QR‐LPD? fabricated by a roll‐to‐roll process.     

Color‐breakup evaluation of spatio‐temporal color displays with two‐ and three‐color fields

Abstract— Spatio‐temporal color displays have higher transmission and resolution than conventional LCDs, but suffer from color breakup. In this paper, a 120‐Hz display with two‐color filters and two‐color fields is described and the amount of color breakup is compared with that of a 180‐Hz full‐color‐sequential display with no color filters and three‐color fields. The results indicate that color breakup in a color‐filterless display is annoying, whereas it is just visible in displays with two‐color filters even though the refresh rate is much lower.     

Development of a high‐resolution RGBW flexible display using a white organic light‐emitting diode with microcavity structure and that of a side‐roll touch panel

In this study, white organic electroluminescent devices with microcavity structures were developed. A flexible high‐resolution active‐matrix organic light‐emitting diode display with low power consumption using red, green, blue, and white sub‐pixels formed by a color‐filter method was fabricated. In addition, a side‐roll touch display was developed in combination with a capacitive flexible touch screen.     

Development of rollable silicon thin‐film‐transistor backplanes utilizing a roll‐to‐roll continuous lamination process

Abstract— Rollable silicon thin‐film‐transistor (TFT) backplanes utilizing a roll‐to‐roll process have been developed. The roll‐to‐roll TFT‐backplane technology is characterized by a glass‐etching TFT transfer process and a roll‐to‐roll continuous lamination process. The transfer process includes high‐rate, uniform glass‐etching to transfer TFT arrays fabricated on a glass substrate to a flexible plastic film. In the roll‐to‐roll process, thinned TFT‐glass sheets (0.1 mm) and a base‐film roll are continuously laminated using a permanent adhesive. Choosing both an appropriate elastic modulus for the adhesive and an appropriate tension strength to be used in the process is the key to suppressing deformation of the TFT‐backplane rolls caused by thermal stress. TFT backplanes that can be wound, without any major physical damage such as cracking, on a roll whose core diameter is approximately 300 mm have been sucessfully obtained. Incorporating the TFT‐backplane rolls into other roll components, such as color‐filter rolls, will make it possible to produce TFT‐LCDs in a fully roll‐to‐roll manufacturing process.     

High‐performance organic‐inorganic hybrid plastic substrate for flexible displays and electronics

Abstract— An inorganic‐dominated silica/polyimide (PI) hybrid film has been successfully developed for the fabrication of flexible AMOLEDs. The existence of networks between silica particles in the PI matrix have been confirmed by 3‐D tomography, respectively. The inorganic—organic hybrid film was achieved by roll‐type processing with a variety of attractive properties, such as low coefficient of thermal expansion (CTE, 20 ppm/°C), high transmittance (within the wavelength range of 400–700 nm), excellent flexibility, and high Young's modulus. Additionally, a flexible color‐filter, an AMEPD, and a flexible touch film were fabricated on hybrid film.     

Inorganic light‐emitting diode displays using micro‐transfer printing

Large quantities of microscopic red, green, and blue light‐emitting diodes (LEDs) made of crystalline inorganic semiconductor materials micro‐transfer printed in large quantities onto rigid or flexible substrates form monochrome and color displays having a wide range of sizes and interesting properties. Transfer‐printed micro‐LED displays promise excellent environmental robustness, brightness, spatial resolution, and efficiency. Passive‐matrix and active‐matrix inorganic LED displays were constructed, operated, and their attributes measured. Tests demonstrate that inorganic micro‐LED displays have outstanding color, viewing angle, and transparency. Yield improvement techniques include redundancy, physical repair, and electronic correction. Micro‐transfer printing enables revolutionary manufacturing strategies in which microscale LEDs are first assembled into miniaturized micro‐system “light engines,” and then micro‐transfer printed and interconnected directly to metallized large‐format panels. This paper reviews micro‐transfer printing technology for micro‐LED displays.     

A4‐sized flexible ferroelectric liquid‐crystal displays with micro color filters

Abstract— We demonstrated an A4‐paper‐sized flexible ferroelectric liquid‐crystal (FLC) color displays fabricated by using a new plastic‐substrate‐based process which was developed for large‐sized devices. Finely patterned color filters and ITO electrodes were formed on a plastic substrate by a transfer method to avoid surface roughness and thermal distortion of the substrate, which induce disordering of the FLC molecular alignment. The thickness of an FLC/monomer solution sandwiched by two plastic‐film substrates was well controlled over a large area by using flexographic printing and lamination techniques. Molecular‐aligned polymer walls and fibers were formed in the FLC by a two‐step photopolymerization‐induced phase‐separation method using UV‐light irradiation. A fabricated A4‐sized flexible‐sheet display for color‐segment driving was able to exhibit color images even when it was bent.     

Review Paper: Multi‐primary‐color displays: The latest technologies and their benefits

Abstract— Multi‐primary‐color (MPC) display technology is one of the fastest emerging research areas in recent years. Wide‐color‐gamut display devices have been required for visually sufficient and/or accurate color reproduction. It is well known that MPC displays can reproduce accurate colors with high efficiency. In addition, not only the image‐quality improvement but some other performance of display devices is also required for display devices. This paper reviews achievements in MPC display technologies and focuses on the benefits of MPC displays: power‐savings and high resolution.     

Flexible electronic‐paper active‐matrix displays

Abstract— A QVGA active‐matrix backplane was produced on a 25‐μm thin plastic substrate. A four‐mask photolithographic process was used. The insulator layer and the semiconductor layer were organic material processed from solution. This backplane was a combination of the electrophoretic display effects supplied by SiPix and E‐Ink Corp., resulting in electronic‐paper displays with a thickness of 150 and 100 μm, respectively; this is the world's thinnest active‐matrix display ever made.     

Active‐matrix and flexible liquid‐crystal displays with carbon‐nanotube pixel electrodes

Abstract— The necessary processes to use random carbon‐nanotube networks as transparent conductors in twisted‐nematic liquid‐crystal displays have been developed, replacing indium tin oxide. Because the nanotubes are deposited vacuum‐free from suspension, the potential advantages are lower costs for material, equipment, and production. Nanotube networks are also much better suited for flexible displays than the commonly used metal oxides. With the developed processes, the world's first full‐color active‐matrix LCDs as well as directly addressed flexible displays on plastic substrates with carbon‐nanotube pixel electrodes, have been realized.     

2‐D/3‐D displays based on switchable lenticulars

Abstract— An attractive concept for 3‐D displays is the one based on LCDs equipped with lenticular lenses. This enables autostereoscopic multiview 3‐D displays without a loss in brightness. A general issue in multiview 3‐D displays is their relatively low spatial resolution because the pixels are divided among the different views. To overcome this problem, we have developed switchable displays, using liquid‐crystal (LC) filled switchable lenticulars. In this way, it is possible to have a high‐brightness 3‐D display capable of fully exploiting the native 2‐D resolution of the underlying LCD. The feasibility of LC‐filled switchable lenticulars was shown in several applications. For applications in which it is advantageous to be able to display 3‐D and 2‐D content simultaneously, a 42‐in. locally switchable prototype having a matrix electrode structure was developed. These displays were realized using cylindrically shaped lenticular lenses in contact with LC. An alternative for these are lenticulars based on gradient‐index (GRIN) LC lenses. Preliminary results for such switchable GRIN lenses are presented as well.     

Optical performance characterization of flexible mobile displays

The high interest in the display industry to produce curved or flexible displays for mobile, wearable, and television markets has raised concerns on the performance of displays in their bent state. Flexible display technologies have been developed for this purpose, but their optical characteristics have not been previously reported at various degrees of curvature. The measurement of flexible displays is possible only with special measurement arrangements using common display characterization devices. A conoscope with a working distance of 15 mm was used to demonstrate the curvature dependence of luminance, viewing angle, and color coordinates of the white point of a flexible active‐matrix organic light‐emitting display. The results show that the effect of curvature on the optical characteristics of the display is most evident at the smallest measured bending radii of +/?50 mm and that the effects are most visible when viewing the bent ends of the display, from the central normal vantage point, with uniform curvature along the display.     

Roll‐to‐roll manufacturing considerations for flexible,cholesteric liquid‐crystal display (Ch‐LCD) media

Abstract— Roll‐to‐roll methods and equipment to manufacture a bistable, passively driven display media on a flexible substrate have been developed. Using continuous coating techniques and equipment, cholesteric liquid‐crystal droplets in a gelatin binder and a dark layer are simultaneously coated onto laser‐etched‐patterned transparent ITO conductors on a polymeric web. Second conductors are printed with a UV‐curable polymer thick‐film ink over the active display layers, followed by slitting and chopping to complete the manufacture of display media in a full roll‐to‐roll mode. Segmented‐ and matrix‐display media can be generated using these techniques. This paper will focus on the manufacturing considerations for producing matrix‐display media.     

Flexible active‐matrix OLED displays: Challenges and progress

Abstract— Organic light‐emitting‐device (OLED) devices are very promising candidates for flexible‐display applications because of their organic thin‐film configuration and excellent optical and video performance. Recent progress of flexible‐OLED technologies for high‐performance full‐color active‐matrix OLED (AMOLED) displays will be presented and future challenges will be discussed. Specific focus is placed on technology components, including high‐efficiency phosphorescent OLED technology, substrates and backplanes for flexible displays, transparent compound cathode technology, conformal packaging, and the flexibility testing of these devices. Finally, the latest prototype in collaboration with LG. Phillips LCD, a flexible 4‐in. QVGA full‐color AMOLED built on amorphous‐silicon backplane, will be described.     

Flexible AMOLED displays on stainless‐steel foil

Abstract— The world's thinnest flexible full‐color 5.6‐in. active‐matrix organic‐light‐emitting‐diode (AMOLED) display with a top‐emission mode on stainless‐steel foil was demonstrated. The stress in the stainless‐steel foil during the thermal process was investigated to minimize substrate bending. The p‐channel poly‐Si TFTs on stainless‐steel foil exhibited a field‐effectmobility of 71.2 cm²/N‐sec, threshold voltage of ?2.7 V, off current of 6.7 × 10¹³ A/μm, and a subthreshold slope of 0.63 V/dec. These TFT performances made it possible to integrate a scan driver circuit on the panel. A top‐emission EL structure was used as the display element, and thin‐film encapsulation was performed to realize a thin and flexible display. The full‐color flexible AMOLED display on stainless‐steel foil is promising for mobile applications because of its thin, light, rugged, and flexible properties.     

Wrap‐around electrodes for microLED tiled displays

The authors have developed a process to create wrap‐around electrodes (WAEs) on glass for use in tiled microLED display applications. The electrodes have small size and spacing, low resistance, and good reliability. In addition, an opaque overcoat protects the edges of the tiles and reduces seam visibility. These electrodes allow bezel‐free tiled operation for high‐resolution displays.