13.4: A 20.8‐inch WXGA Full Color AMOLED Display by Integrating Scattering Reflector with Micro‐Bumps

Abstract

In order to improve light extraction efficiency from organic light emitting diodes (OLED), we report a novel structure of topemission OLED by integrating a scattering reflector with microbumps into the substrate. The mechanism of light extraction has been investigated by evaluating the dependency of flux on the shape of the micro-bumps. It was confirmed that the scattering effect of the micro-bumps improves the light extraction of OLED. Moreover, the scattering reflector has been applied on a 20.8-inch WXGA full color AMOLED display. This is the world's first report that actually proves a light extraction technology, integrating scattering reflector, applied on AMOLED display. IntroductionOrganic light emitting diode (OLED) displays are one of the most promising next generation flat panel displays on account of their several advantages such as high contrast ratio, extremely fast response, very wide viewing angle, and simple structure. Recently, active-matrix OLED (AMOLED) displays, using thin film transistor (TFT) backplane, have been developed for pursuing higher resolution and lower power consumption [1][2][3][4][5]. However, the problems on power consumption and lifetime, especially for large-scale TV applications, have not been solved. A breakthrough is needed to improve light extraction efficiency. Although several novel structures have been reported in order to effectively extract the light from the OLED emission layer, there are few reports that have been applied to actual display [6][7][8][9][10][11][12], due to the complexity of the structure, procedures, and the limitation of the fabrication area. It is also because of a double-image attributed to the parallax effect in bottom-emission OLED displays.In this paper, we propose a novel light extraction structure of OLED, which can be easily applied to an actual AM-OLED to improve the light extraction. The mechanisms of the scattering reflector are discussed. Moreover, AMOLED display integrating the scattering reflector is demonstrated. PrinciplesThe schematic diagram of AMOLED incorporating a scattering reflector with micro-bumps is presented in Fig. 1. The device structure is based on top-emission type. The scattering reflector consists of micro-bumps layer, reflection layer, and planar layer.Since the refractive index of the planar layer (n=1.51), is smaller than the emission layer (n=1.81), part of the waveguided light in OLED reaches the scattering reflector. Then, the scattered light within the critical angle between the air and the emission layer can be extracted into the air. Figure 1 Cross-section view of AMOLED Figure 2 Cross-section views of experimental devices. Fig. 2 shows the devices with no TFT circuits which were experimentally employed in order to evaluate the effect of the scattering reflector. One is the integrated-type device which is similar to an actual device structure shown in Fig. 1. The other is the attached-type device in which the scattering reflector is optically attached at the bottom, emits light to both sides, with refractiv...

Simulation Study on the Effect of the Emitter Orientation and Photonic Crystals on the Outcoupling Efficiency of Organic Light-Emitting Diodes

“…For example, the glass mode can be extracted from the substrate by forming either a microlens array or a diffusing layer on the glass substrate [5][6][7][8][9][10][11][12]. The internal bulk or interface structures were modified to extract the light trapped in the organic layers by, for example, reflector modification, insertion of low-index grids in the organic layers, interface or structure modification of the organic and ITO layers, and patterning the ITO electrodes along with an insertion of a high-conductivity polymer layer [13][14][15][16][17][18][19][20]. Hybrid structures may be used to extract both the trapped light in the waveguide mode and the glass mode [21,22].…”

13.2: A Floating‐Gate OTFT‐Driven AMOLED Pixel Circuit for Variation and Degradation Compensation in Large‐Sized Flexible Displays

“…AMOLED displays have attracted much attention recently because of their excellent image quality and wide viewing angle [1][2]. Organic TFT (OTFT) is considered as a strong candidate for pixel circuits of large-size flexible displays, because of its mechanical flexibility and compatibility with the low-cost printing process at room temperature [3][4].…”

36.3: An Organic Light‐Emitting Diode with Highly Efficient Light Extraction Using Newly Developed Diffraction Layer

“…We have reported the 20.8-inch WXGA full color AMOLED display by integrating scattering reflector with microbumps to improve the light extraction efficiency [6]. Although novel structures of OLEDs have been reported to extract the light from the emission layer effectively in OLEDs [7][8][9][10][11][12][13][14], there are few reports on application to an actual display [6]. The reasons for that are the difficulties such as the complex structure, the complicated procedures, and the limitation of the fabrication area.…”