Repeatedly foldable AMOLED display

In this study, a 5.9‐inch foldable active‐matrix organic light emitting diode (AMOLED) display was developed. A folding test was performed repeatedly. The display survived the folding test (100,000 folds) with a curvature radius of 2 mm. To protect an organic light emitting diode (OLED) against moisture, inorganic passivation layers are provided on the upper and lower sides of the flexible display. Using our transfer technology, high density passivation layers can be obtained. The measured water vapor transmission rate of the layer is 7 × 10^?6 g/m²?day or less, which improves OLED reliability. With these techniques, we have developed a book‐type display, which is repeatedly foldable like a book, and a tri‐fold display including a display area, which is foldable in three.     

PIN OLEDs — Improved structures and materials to enhance device lifetime

Abstract— Currently, three issues are identified that decide upon the commercial success of organic light‐emitting diodes (OLEDs), both in display and lighting applications: power efficiency, lifetime, and price competitiveness. PIN OLEDs are widely seen as the preferred way to maximize power efficiency. Here, it is reported that this concept also delivers the world longest lifetimes. For a highly efficient deep‐red PIN OLED, a half‐lifetime of 25,000 hours for a starting brightness of 10,000 cd/m² and a minimal voltage increase over lifetime is reported. This value corresponds to more than 1 × 10⁶ hours at 1000 cd/m² using an exponent of n = 1.7, which was measured by driving the OLEDs at different starting luminances. Because there is no initial luminance drop, these PIN OLEDs also exhibit a very high 80% lifetime (>300,000 hours at 1000 cd/m²). New record lifetime values for blue and green will be reported as well. Additionally, further topics that have impact on the production yield and cost such as the newly developed air‐stable organic n‐doping material NDN‐26 and top‐emitting structures will be discussed.     

High‐performance white OLEDs with high color‐rendering index for next‐generation solid‐state lighting

Abstract— Several white‐OLED structures with a high color‐rendering index (CRI) were investigated for lighting applications. A two‐unit fluorescent/phosphorescent hybrid white OLED achieved an excellent CRI of 95, high luminous efficacy of 37 lm/W, and long lifetime of over 40,000 hours at 1000 cd/m². White‐OLED lighting panels of 8 × 8 cm for high‐luminance operation were fabricated, and a stable emission at 3000 cd/m² was confirmed. Quite a small variation in chromaticity in a different directions was achieved by using an optimized optical device structure. With a light‐outcoupling substrate, a higher efficacy of 56 lm/W, high CRI of 91, and longer half‐decay lifetime of over 150,000 hours at 1000 cd/m² was achieved. All‐phosphorescent white OLEDs placed on the light‐outcoupling substrate show a high CRI of 85 and higher efficacy of 65 lm/W with a fairly good half‐decay lifetime of over 30,000 hours. With a further voltage reduction and a high‐index spherical extractor, 128 lm/W at 1000 cd/m² has been achieved.     

AlGaN multiple quantum well deep-ultraviolet micro-light-emitting diodes for high color conversion efficiency quantum dots display

Displays based on inorganic micro-light-emitting diodes (micro-LEDs) are highly anticipated for next-generation technologies. AlGaN-based deep-ultraviolet (deep-UV) micro-LED as the excitation source for quantum dots display with high efficiency was reported in this paper. To achieve optimized electro-optical performance, deep-UV micro-LEDs with different electrodes were fabricated and analyzed in sizes from 200 × 200 to 10 × 10 μm². At the same forward bias, the devices with Ti/Al-based electrodes achieved 10 times injection current and three times electroluminescence intensity than those with Cr/Al-based electrodes. The blueshift phenomenon of deep-UV light was observed from 292 nm at 2 A/cm² to 287 nm at 200 A/cm² with the increasing current density. By the excitation of deep-UV micro-LED, quantum dot film achieved high light conversion efficiency and optimized color rendering, as the converted color emission peak was separate from the pumping source. The high energy of deep-UV photons and the narrow emission bandwidth of QDs resulted in prominent color purity. The forward voltage and electroluminescence intensity uniformity of a 250 × 250 micro-LED array with each pixel size of 30 × 30 μm² were further discussed. The optical microscope images of green QD film pumped by a deep-UV micro-LED demonstrated its competitive application in the color-converted display.     

A high-luminance and high-resolution CRT for projection HDTV display

Abstract— We have developed a 3-in. YAG (yttrium aluminum garnet) projection CRT for an HDTV display. The densely packed phosphor screen with a multi-layer interference filter is prepared by depositing phosphor on a YAG faceplate using a centrifugal sedimentation method. The tube's envelope is made from a glass whose expansion coefficient is well-matched with that of YAG. The focusing characteristics of an optimally designed pre-focusing electron gun and focusing magnet are improved for a HDTV display application. As a result, the green, red, and blue tubes reached luminances of 1.4 × 10⁵, 6.2 × 10⁴, and 8 × 10³ cd/m² at a cathode current of 1.0 mA and an anode voltage of 29 kV, respectively, with a half-intensity linewidth of 85 μm. An experimental 48-in. rear-projection TV set using the YAG projection tubes achieves more than 1000-TV-lines horizontal resolution and 300-cd/m² mean white luminance.     

Experiment to select a suitable visual display and evaluate its washout characteristics

Two separate experiments were carried out on a display for a portable microprocessor. Of three phosphorescent displays available for installation, readability times, error rates and subjective preferences were recorded and compared using fifteen subjects. On these measures recorded, the small dot-matrix display (3.5 mm × 5.0 mm) performed better than the large dot-matrix display (5 mm × 8 mm) and considerably better than the segmented display (5 mm × 8 mm). The second experiment set out to quantify the effects of a range of three ambient illuminance levels on the readability of the small dot-matrix display, using the same criteria. Results suggested that for ambient illuminance levels between 0 lux and 15000 lux, a single display intensity was feasible, this being about 40 cdm^?2.     

Active‐matrix organic light‐emitting displays employing two thin‐film‐transistor a‐Si:H pixels on flexible stainless‐steel foil

Abstract— An active‐matrix organic light‐emitting diode (AMOLED) display driven by hydrogenated amorphous‐silicon thin‐film transistors (a‐Si:H TFTs) on flexible, stainless‐steel foil was demonstrated. The 2‐TFT voltage‐programmed pixel circuits were fabricated using a standard a‐Si:H process at maximum temperature of 280°C in a bottom‐gate staggered source‐drain geometry. The 70‐ppi monochrome display consists of (48 × 4) × 48 subpixels of 92 ×369 μm each, with an aperture ratio of 48%. The a‐Si:H TFT pixel circuits drive top‐emitting green electrophosphorescent OLEDs to a peak luminance of 2000 cd/m².     

An integrated poly‐Si TFT current data driver with a data‐line pre‐charge function

Abstract— We have developed an integrated poly‐Si TFT current data driver with a data‐line pre‐charge function for active‐matrix organic light‐emitting diode (AMOLED) displays. The current data driver is capable of outputting highly accurate (±0.8%) current determined by 6‐bit digital input data. A novel current‐programming approach employing a data‐line pre‐charge function helps achieve accurate current programming at low brightness. A 1.9‐in. 120 × 136‐pixel AMOLED display using these circuits was demonstrated.     

Bezel free design of organic light emitting diode display via a‐InGaZnO gate driver circuit integration within active array

In this article, we described an innovative design technology of active matrix organic light emitting diode (AMOLED) display, to provide a bezel free design. We designed gate driver circuit of amorphous indium‐gallium‐zinc oxide thin‐film transistors (TFTs) not on the bezel area but within the active array. Although we applied challengeable design, no degradation of electrical/optical properties of panel was observed. Because we effectively prevented capacitive coupling and interference between the emission circuit and integrated gate driver circuit in active array, finally, we successfully demonstrated a bezel free designed AMOLED display of 18.3″ HD (1366 × 768) driven by a‐InGaZnO TFTs.     

A new method for measuring ultra‐low water‐vapor permeation for OLED displays

Abstract— It is well known that proper encapsulation is crucial for the lifetime of organic light‐emit‐ting‐diode (OLED) displays. With the development of increasingly better barrier coatings and perimeter seals, it has now become very desirable to be able to precisely measure the rate of water‐vapor and oxygen permeation through barrier coatings and perimeter sealing. This paper demonstrates a new permeation‐measurement method that uses tritium‐containing water (HTO) as a tracer material. The theoretical detection limit of this direct method is 2.4 × 10^?8 g/(m²‐day).     

Phosphorescent OLEDs: Enabling energy‐efficient lighting with improved uniformity and longer lifetime

Abstract— In this paper, the design criteria for scaling up from small‐area organic light‐emitting‐diode (OLED) pixels to large‐area OLED light panels is described. Particular focus is placed on using phosphorescent OLEDs (PHOLEDs) to maximize panel efficacy and uniformity and minimize operating temperature. Data for a pair of all‐phosphorescent 15 × 15 cm OLED light panels are also presented: Panel 1 has 62‐lm/W efficacy, CRI = 81, CCT = 3180K, and lifetime to LT70 = 18,000 hours at 1000 cd/m² and Panel 2 has 58‐lm/W efficacy, CRI = 82, CCT = 2640K, and lifetime to LT70 = 30,000 hours at 1000 cd/m². Operating at a 3000 cd/m² (7740 lm/m²), Panel 2 has 49‐lm/W efficacy with lifetime to LT70 = 4000 hours. Excellent panel lifetime is enabled by a stable light‐blue phosphorescent materials system and by the use of efficient phosphorescent emitters that ensure very low panel temperature without any additional thermal management.     

Sharpness and noise characteristics of a half‐mirror stereoscopic display

Stereoscopic displays are becoming popular in entertainment and industrial applications. We characterize the spatial resolution and noise properties of a stereoscopic display with a half‐mirror and passive polarizing glasses. The upper display images reflected off the mirror have slightly degraded sharpness and reduced high spatial‐frequency noise resulting in modulation transfer functions (MTFs) of 0.59 and 0.50 at the Nyquist frequency with corresponding noise power spectra (NPS) values of 4.79 × 10^?6 and 5.17 × 10^?6 mm² at 10 mm^?1 in the horizontal and vertical directions. These results are compared to the characteristics of the individual displays with MTF values of 0.64 and 0.53 and NPS values of 6.24 × 10^?6 and 5.87 × 10^?6 mm². The polarizing glasses cause minimal reduction in sharpness and high‐frequency noise. The MTFs in the upper images observed with glasses are decreased to 0.54 and 0.47, while the NPS are decreased to 2.86 × 10^?6 and 2.01 × 10^?6 mm². When both displays are turned on and using the mirror and glasses, the observed luminance for each eye is increased from the luminance of the individual displays owing to crosstalk. We find that sharpness and noise are not affected by the interaction between the displays at the particular geometry tested in this study.     

Transfer technology using inorganic separation layer and apparatus for fabricating flexible OLED displays

We established a fabrication process of flexible displays, adopting a transfer technology using an inorganic tungsten‐separation‐layer. Our separation process requires physical force and water. Tungsten oxide over tungsten in the separation layer plays a key role in separation: water injection into the tungsten oxide reduces the force necessary for separation. In this study, we describe the apparatus we built for the fabrication process of flexible displays. This apparatus fabricated an 8k (7680 × 4320 effective pixels) flexible organic light‐emitting diode display.     

Thermally cross‐linkable copolymer and its evaluation as a hole transport layer in organic light‐emitting diode devices

This study reports on the synthesis of new thermally cross‐linkable copolymers containing a reactive cross‐linking comonomer. Synthesized polymers showed narrow molecular weight distribution (polydispersity) between 1.18 to 1.22 and 54 to 67% monomer conversion and incorporation of 2 to 7 mol% vinylbenzylcyclobutene comonomer. The polymer was soluble in nonpolar organic solvents such as chloroform, dichloromethane, toluene, and chlorobenzenes, and when cross‐linked, showed resistance to solubility in the previously listed solvents. The cross‐linked films exhibited uniform surface roughness below 1 nm. A polymer containing ~3.6 mol% vinylbenzylcyclobutene was thermally cross‐linked and evaluated as a hole‐transporting layer in green organic light‐emitting diode devices. The devices showed a maximum current efficiency of 39.5 cd/A at a current density of 2.7 mA/cm² and a brightness of 1000 cd/m² with an International Commission on Illumination coordinate (0.33, 0.62). The device performances are found comparable with the ones with the conventional hole‐transporting layer material, NPD.     

Optimization of photo‐aligned ferroelectric liquid‐crystal display under passively addressed driving

Abstract— A ferroelectric liquid‐crystal (FLC) passively addressed 64 × 64 display based on the photo‐alignment technique has been developed. The display matrix has dimensions of 33 × 33 mm², and the FLC layer thickness is about 5 μm. Asymmetric boundary conditions, when only one of ITO surfaces of the display matrix is covered with the photo‐aligning layer while another one is not, have been used for providing both high contrast ratio and steady multiplex operation. The electro‐optical performance of the 5‐μm FLC display is presented, including bistable switching in static operation, optimization in multiplexing operation, and gray‐scale generation.     

Three-axis pneumatic tactile display with integrated capacitive sensors for feedback control

In this paper, we propose a three-axis pneumatic tactile display that is precisely controlled by using integrated capacitive displacement sensors. The proposed tactile display consists of a core body with a 3 × 3 balloon array on its top surface, four lateral balloons made of latex rubber, and inner and outer frames that include capacitive displacement sensors based on a flexible printed circuit board. The 3 × 3 balloon array on the core body is designed to apply normal haptic stimulation to a human fingertip. In addition, the lateral motions of the core body and each frame produce haptic stimulation in a tangential direction. Precise control of lateral motion was achieved by feedback control using the capacitive displacement sensors. The size of the fabricated tactile display was 26 × 26 × 18 mm³. We experimentally performed manipulation of the proposed device with a custom control system, thereby demonstrating accurate control of displacement.     

Metal (IV) tetras (8‐hydroxyquinoline) (M = Zr,Hf) used as electroluminescent material and electron‐transport layer in OLEDs

Abstract— In this paper, we report on the utilization of zirconium (IV) tetras (8‐hydroxyquinoline), Zrq₄, and hafnium (IV) tetras (8‐hydroxyquinoline), Hfq₄, as an electroluminescent material in fluorescent organic light‐emitting diodes (OLED) and as electron transport layer (ETL) for high‐efficiency electrophosphorescent organic light‐emitting diodes (PHOLEDs). Structural studies show that the metal tetraquinolates (Mq₄) have a very low dipole moment (<0.1 D), in contrast to Alq₃ which has an estimated dipole moment of 4.7 D. Mobility measurements show that Mq₄ complexes give mobilities of (3.5 ± 0.5) × 10^?6 cm²/V‐sec, which are close to the values reported for Alq₃, i.e., (2.3–4.3) × 10^?6 cm²/V‐sec. OLEDs were prepared with the structure ITO/NPD (400 Å)/Mq_n (500 Å)/LiF/Al (NPD = 4‐4′‐bis[N‐(1‐naphthyl)‐N‐phenyl‐amino]bi phenyl, Mq_n = Alq₃, Zrq₄, Hfq₄. The Mq₄‐based OLEDs gave external efficiencies of 1.1%, while the Alq₃‐based devices of the same structure gave efficiencies of 0.7%. PHOLEDs have been fabricated with the structure ITO/NPD (500 Å)/CBP‐8% Ir(ppy)³ (250 Å)/BCP (150 Å)/Mq_n (250 Å)/LiF/Al (CBP = N,N′‐dicarbazolyl‐4‐4′‐biphenyl, Ir(ppy)³ = fac‐tris(2‐phenylpyrridine)iridium, BCP = bathocruprione). PHOLEDs with Mq₄ ETLs showed a greatly improved efficiency, when compared to Alq₃‐based PHOLEDs. The Zrq₄‐based PHOLEDs gave a peak external quantum efficiency of 14% at 0.3 mA/cm² (150 cd/m²), while the Hfq₄ based PHOLED gave a peak external quantum efficiency of 15% at 0.6 mA/cm² (300 cd/m²). Comparable PHOLEDs with an Alq₃ ETL give peak external quantum efficiencies of 8.0% at 0.5 mA/cm². The devices gave an electroluminescence (EL) spectrum consisting only of fac‐tris(2‐phenylpyrridine)iridium (Ir(ppy)³) dopant emission (CIE coordinates of 0.26, 0.66), with no Mq₄ emission observed at any bias level.     

Improvement in image quality of a 5.8‐in. OTFT‐driven flexible AMOLED display

Abstract— The image quality of an OTFT‐driven flexible AMOLED display has been improved by enhancing the performance of OTFTs and OLEDs. To reduce the operating voltage of OTFTs on a plastic film, Ta²O⁵ with a high dielectric constant was used as a gate insulator. The organic semiconductor layer of the OTFT was successfully patterned by a polymer separator, which is an isolating wall structure using an organic material. The OTFT performance, such as its current on/off ratio, carrier mobility, and spatial uniformity on the backplane, was enhanced. A highly efficient phosphorescent OLED was used as a light‐emission device. A very thin molybdenum oxide film was introduced as a carrier‐injection layer on a pixel electrode to reduce the operating voltage of the OLED. After an OTFT‐driven flexible AMOLED display was fabricated, the luminance and uniformity on the display was improved. The fabricated display also showed clear moving images, even when it was bent at a low operating voltage.     

Passively addressed FLC display possessing an inherent gray scale and memory

Abstract— A passively addressed 64 × 64 ferroelectric liquid‐crystal display (FLCD) has been developed. The display matrix has a 33 × 33 mm² aperture, and the FLC layer thickness is 5.2 ± 0.2 μm. The display device operates with a frame frequency of 30 Hz (at V_row = ±18 V, V_col = ±9 V, T = 23°C), generating a continuous gray scale which can be memorized for more than 10 days after the driving voltage is switched off. A new approach for multiplex electronic addressing of the FLCD gray scale is proposed. The conditions of the hysteresis‐free gray‐scale generation for multiplex addressing and the gray‐scale memorization after the voltage is switched off, as well as the time steadiness of memorized images, are considered.     

Novel self‐aligned top‐gate oxide TFT for AMOLED displays

Abstract— A novel highly reliable self‐aligned top‐gate oxide‐semiconductor thin‐film transistor (TFT) formed by using the aluminum (Al) reaction method has been developed. This TFT structure has advantages such as small‐sized TFTs, lower mask count, and small parasitic capacitance. The TFT with a 4‐μm channel length exhibited a field‐effect mobility of 21.6 cm²/V‐sec, a threshold voltage of ?1.2 V, and a subthreshold swing of 0.12 V/decade. Highly reliable TFTs were obtained after 300°C annealing without increasing the sheet resistivity of the source/drain region. A 9.9‐in.‐diagonal qHD AMOLED display was demonstrated with self‐aligned top‐gate oxide‐semiconductor TFTs for a low‐cost and ultra‐high‐definition OLED display. Excellent brightness uniformity could be achieved due to small parasitic capacitance.