Advanced technologies for UHD curved OLED TV

Ultra‐high definition (UHD) curved organic light‐emitting diode (OLED) TV requires advanced technologies to realize mass production. White, red, green, and blue (WRGB) OLED TV based on stripe WRGB sub‐pixel structure has distinct advantages in luminance of white, faster response time, wider viewing angle, and potential higher resolution. In this paper, we will introduce technological progress for commercializing large‐sized and UHD curved OLED TV. Those technologies including oxide thin film transistors, white OLEDs, compensation circuit, and solid phase encapsulation enable panel size scalability as well as mass production with lifetime reliability.     

Compact and efficient RGB to RGBW data conversion method and its application in OLED microdisplays

In many electronic information displays, a colour pixel comprises three spatially distinct sub‐pixels containing red, green and blue (RGB) colour filters. The option of adding a fourth white (W) sub‐pixel that allows light to pass through unfiltered can significantly improve the optical efficiency of the pixel that, in turn, increases the power efficiency of the display. Such a display is called an RGBW display, and the required transformation of data format from incoming RGB to pixel RGBW is termed as “RGB to RGBW conversion.” This paper reports a method of RGB to RGBW conversion that is highly compact and efficient in terms of system resources while retaining image quality. It processes incoming data through a new colour space conversion algorithm in order to reduce the average power consumption with no noticeable visual artefacts. We explain the method and demonstrate its cost‐effective and power‐effective implementation for the specific case of an organic light emitting diode microdisplay.     

Curved OLED display to effectively enhance natural3D

We studied the stereoscopic effect obtained from a two‐dimensional image without using binocular parallax, which we call “natural3D” (n3D). Unlike a parallax‐based three‐dimensional (3D) display system, n3D causes less tiredness and is free from a decrease of the resolution by half because of image division and viewing position dependence. To make the display with these effects comfortable to use, we conducted statistical tests with sensory evaluation experiments and a quantitative evaluation based on physiological responses. These examinations revealed that the n3D effect can be effectively obtained by using, for example, the characteristics of an organic light‐emitting diode display, such as high contrast and easy bendability. This study discusses optimal display curvatures for displays of different sizes that enhance n3D and reduce tiredness, which are revealed through statistical tests. In addition, we performed an experiment with a frame called an n3D window (n3Dw) that is placed before the display such that a subject views the display through the opening of the frame. We found that the combination of a curve and the n3Dw causes n3D more effectively.     

基于 OLED 器件的封装材料研究进展

有机电致发光器件(Organic Light-Emitting Diode,OLED)因其轻薄、视角广、响应时间短、发光效率高、成本低等优点成为公认的新一代显示技术。为减少甚至避免有机发光材料受到外界环境的侵蚀、保证OLED的使用寿命,OLED封装材料得到了大力的研究和发展。OLED封装材料必须具有优秀的水氧阻隔能力,此外,还要求有良好的热导率、透光率、机械强度、耐腐蚀性与基底的粘结性等性质。文章对OLED封装材料的发展作了详细的介绍,包括传统后盖式封装所用的金属、玻璃、陶瓷和薄膜封装所用的无机化合物、聚合物、复合材料。根据OLED器件的性能以及封装形式的需求,探讨了封装材料的未来发展方向。     

Flexible OLED display development: Strategy and status

Abstract— In this paper, the current status of flexible OLED (FOLED®) display development will be reviewed, including previous results for passive‐matrix displays on plastic and current progress on active‐matrix displays on steel foil. The displays incorporate high‐efficiency small‐molecule phosphorescence OLED (PHOLE?) technology. The ultimate goal is to develop high‐information‐content high‐performance long‐lived, and large‐area FOLED displays that can be pulled or rolled out from a smaller pen‐like housing. The strategy for achieving this goal will be presented.     

Ultra‐high‐resolution 1058‐ppi OLED displays with 2.78‐in size using CAAC‐IGZO FETs with tandem OLED device and single OLED device

We fabricated new 2.78‐in 1058‐ppi organic light‐emitting diode (OLED) displays. The displays used OLED devices with a tandem structure and a single structure and a field effect transistor (FET) using c‐axis aligned crystalline In–Ga–Zn–O (CAAC‐IGZO) for an active layer and employing the 1.5‐µm rule over a glass substrate. Even in the displays with such high resolution exceeding 1000 ppi, crosstalk that was observed in the lower luminance region was suppressed. The displays achieved high color reproducibility and reduced viewing angle dependence.     

High‐efficiency phosphorescent OLED technology

Abstract— Universal Display Corp. (UDC), together with its academic partners at Princeton University and the University of Southern California, are developing high‐efficiency electrophosphorescent small‐molecule OLED devices, based on triplet emission. These device systems show good lifetimes, and are well suited for the commercialization of low‐power‐consumption full‐color active‐matrix OLED displays. In this paper we also show how these phosphorescent devices may be driven by low‐cost amorphous‐silicon backplanes, and discuss benefits that could be gained by employing bistable OLED pixels.     

4032 ppi High‐resolution OLED microdisplay

A 0.5‐inch Ultra Extended Graphics Array (UXGA) organic light‐emitting diodes microdisplay has been developed with 6.3 μm pixel pitch. Not only 4032 ppi high resolution but high frame rate, low power consumption, wide viewing angle, and high luminance have been achieved. This newly developed organic light‐emitting diodes microdisplay is suitable for Near‐to‐Eye display applications, especially electronic viewfinders.     

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.     

A foldable OLED display with an in‐cell touch sensor having embedded metal‐mesh electrodes

A foldable organic light‐emitting diode display integrating a touch sensor is fabricated. The touch sensor has an in‐cell structure where metal‐mesh sensor electrodes are formed in a counter substrate. It is demonstrated that touch on the entire panel surface, including a bent portion, is detected and that the touch panel operates correctly after 100,000 folding operations with a radius of curvature of 5 mm.     

Thin‐film encapsulated white organic light top‐emitting diodes using a WO3/Ag/WO3 cathode to enhance light out‐coupling

An alternative design of a semitransparent cathode for top‐emission white‐fluorescent organic light‐emitting diodes (OLEDs) has been investigated. The scope of this study was to improve the luminance of OLEDs used for displays while keeping the current density versus voltage characteristic unchanged for addressing purposes. The use of an optical simulation tool allowed the optimization of the tri‐layer cathode WO₃/Ag/WO₃ to increase the light out‐coupling coefficient of the device leading to an increased white emission compared with a reference device with a Ca/Ag cathode. An increase of ~40% in luminance has been calculated by simulation and experimentally confirmed. The p‐i‐n OLED structure underneath the tri‐layer cathode allowed an efficient injection of electrons independently from the work function of WO₃. The WO₃/Ag/WO₃ cathode has been also confirmed to be compatible with the atomic layer deposition technique for thin film encapsulation. Finally, lifetime measurements up to 600 h have been carried out to quantify the enhancements induced by the new cathode compared with the control device. It has been found that lifetimes of both cathode architectures are similar on this time scale, while the WO₃/Ag/WO₃ cathode shows a lower voltage drift versus aging.     

Flat‐plate encapsulation solution for OLED displays using a printed getter

Abstract— The encapsulation of organic light‐emitting layers is a key development item on the road‐map to OLED commercialization and needs to be resolved in order to compete with the incumbent LCD technology. DuPont? Drylox? cover glass is a product developed by DuPont Displays to improve the features of the OLED encapsulation solution. Thin displays, low design cycle time, and substantial reduction in encapsulation cost are the driving forces for the product improvement. This paper discusses permeation theory, describes a manufacturing method, and documents the performance characteristics achieved to date.     

A digitally driven pixel circuit with current compensation for AMOLED microdisplays

A novel digitally driven pixel circuit for active‐matrix organic light‐emitting diode (OLED) microdisplays is proposed and evaluated. This circuit supports both pulse width modulation and pulse density modulation digital drive approaches. Only three transistors and one capacitor are required per pixel for the proposed circuit. A current mirror is used to compensate for the pixel current changes that occur because of the degradation of the OLEDs over time. The compensation current depends on the potential of the common cathode, the properties of the current mirror, and the Width/Length (W/L) ratio of the drive transistor. The proposed digital pixel circuit also has advantages in circuit layout compared with analog pixel circuits.     

RGB‐to‐RGBW conversion with current limiting for OLED displays

Abstract— Organic‐light‐emitting‐diode (OLED) displays employing white‐light‐emitting OLEDs in combination with RGBW color filters can demand high peak currents to present images with bright, highly saturated colors. Image‐processing methods that take advantage of a very highly efficient white subpixel in addition to filtered RGB subpixels to reduce the peak current and power of these displays are described. The image‐quality impact of these algorithms are explored to develop a final image‐processing algorithm.     

Video processing for active‐matrix polymer OLED TV

Abstract— Active‐matrix OLED panels have inherent features that allow a higher‐quality image reproduction than LCD panels, i.e., high‐contrast, fast response time, and the capability to produce locally high peak luminance levels. We demonstrated a 13‐in.‐ink‐jet‐printed active‐matrix polymer‐OLED prototype for TV applications at SID 2004. This prototype is used as a carrier for studying video‐processing algorithms that take full advantage of the specific characteristics of OLEDs. Addressing schemes, gamut conversion, histogram‐based brightness control, and sparkle processing will be discussed.     

Simple pixel circuits for high resolution and high image quality organic light emitting diode‐on‐silicon microdisplays with wide data voltage range

Two simple pixel circuits are proposed for high resolution and high image quality organic light‐emitting diode‐on‐silicon microdisplays. The proposed pixel circuits achieve high resolution due to simple pixel structure comprising three n‐type MOSFETs and one storage capacitor, which are integrated into a unit subpixel area of 3 × 9 µm² using a 90 nm CMOS process. The proposed pixel circuits improve image quality by compensating for the threshold voltage variation of the driving transistors and extending the data voltage range. To verify the performance of the proposed pixel circuits, the emission currents of 24 pixel circuits are measured. The measured emission current deviation error of the proposed pixel circuits A and B ranges from ?2.59% to +2.78%, and from ?1.86% to +1.84%, respectively, which are improved from the emission current deviation error of the conventional current‐source type pixel circuit when the threshold voltage variation is not compensated for, which ranges from ?14.87% to +14.67%. In addition, the data voltage ranges of the proposed pixel circuits A and B are 1.193 V and 1.792 V, respectively, which are 2.38 and 3.57 times wider than the data voltage range of the conventional current‐source type pixel circuit of 0.501 V.     

Flexible OLED display with 620°C LTPS TFT and touch sensor manufactured by weak bonding method

By weak bonding method, the first organic light‐emitting diode (OLED) display with 620°C low‐temperature poly‐silicon (LTPS) thin film transistor (TFT) and touch sensor, without polyimide (PI) substrate, formed on glass substrates is transferred to non‐PI flexible substrates. After transfer, the display image is free from defect, and touch sensor functions normally. Compared with device made on PI substrate, the advantages of device stability and pitch variation by transferring are shown.     

System considerations for RGBW OLED displays

Abstract— The fabrication of full‐color RGBW OLED displays using a white emitter with RGB color filters has been previously described. This paper discusses the effect of several display‐system factors on the important RGBW OLED display performance attributes of power consumption, lifetime, and perceived image quality. These display‐system factors include the spectrum of the white OLED, the white OLED structure, the color‐filter selection, the subpixel aperture ratios, and the pixel arrangement (including sub‐sampling).     

Recent progress in high‐efficiency phosphorescent OLED technology

Abstract— A key performance attribute for widespread commercialization of OLED technology is achieving maximum power efficiency along with color chromaticity and operational lifetime. Towards this goal, phosphorescent‐OLED (PHOLED) devices have demonstrated potential. Recent PHOLED device results show both excellent device efficiencies and long lifetimes towards the commercialization of low power consumption, full color, passive‐ and active‐matrix (both polysilicon and amorphous‐silicon backplane technologies) OLED displays.     

面向OLED屏像素缺陷检测的新方法

有机发光显示器OLED（Organic LED）的内部像素缺陷常由于尺寸小、对比度不高、且灰度与像素轮廓灰度相近等问题,在使用传统阈值分割方法处理时会将像素轮廓保留下来,因而不能达到缺陷的有效检测目的。提出一种多次迭代差影法的OLED屏像素缺陷检测方法。该检测算法在对图像进行中值滤波和图像增强处理后,对图像实施多次像素模板提取和差影运算,获取到对比度较低的缺陷图,运用K-均值聚类方法对图像进行分割,从而较好地实现缺陷的识别。运用Labview和IMAQ Vision软件包工具,编程实现所提出的算法,并通过实际获取的OLED图片验证了方法的有效性。结果表明,该方法能很好地保持缺陷的细节,并能检测到8 μm×8 μm的微小缺陷。