Organic Light-emitting Diode Display Research Articles

Paper] Laser-Induced Micro-Patterning of Organic Semiconductor Layers for Use in Organic Light-Emitting Diode Displays

We proposed a novel method for micro-patterning organic semiconductor layers by using a laser irradiation system. The method was demonstrated with a precursor that changes solubility after thermal conversion. For micro-scale patterning, brief irradiation was crucial to prevent heat diffusion in the substrate. We found that preheating on a hot-plate is important for shortening the laser irradiation time necessary for the thermal conversion. The patterning resolution also depended on the kind of substrates as well as the laser exposure time. High-resolution line patterns with a width of 12 μm were successfully achieved on ITO substrates. Organic light-emitting diodes utilizing a patterned emitting layer, with line widths of 20 μm and spacing of 85 μm, were demonstrated.

Image-Quality-Based Power Control Technique for Organic Light Emitting Diode Displays

This paper presents a new image-quality-based power control algorithm for an organic light-emitting diode display. The proposed algorithm calculates the optimal tradeoff between image quality and power consumption by employing an objective function that integrates a roll-off curve to eliminate the clipping error, which severely degrades the perceptual image quality. In addition, a sampling technique is adopted to reduce the computational complexity. The simulation results show that the proposed algorithm reduces the average power consumption by up to 0.310 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> (11.75% decrease) while preserving the image quality above the target level. When applying the sampling technique to the proposed method, the average computation time per pixel is reduced by up to 1.025 μs (37.63% decrease) whereas the image quality and power consumption remain virtually unchanged.

Wideband antireflective circular polarizer exhibiting a perfect dark state in organic light-emitting-diode display.

We proposed wideband antireflective circular polarizer for realizing a true black state in all viewing directions in organic light-emitting-diode displays (OLEDs). Present commercialized wideband circular polarizer consisted of a half wave and a quarter wave plates having the refractive index parameter (Nz) of 1.5 in both films exhibits light leakage in the oblique viewing directions, deteriorating image quality of a black state. We evaluated Nzs of both films and proposed a new wideband antireflective circular polarizer with a perfect dark state in all viewing directions with Nz = 0.5 in both plates, which will greatly improve image quality of OLEDs.

A gamma-type current-mode digital-to-analog converter for active-matrix organic light-emitting diode display drivers

This paper describes the design of a gamma-type current-mode digital-to-analog converter (DAC) for active-matrix organic light-emitting diode display (AMOLED) drivers. The proposed nonlinear DAC is composed of division-based bypassing DAC units for gamma correction. This multiple stack of DAC units dramatically reduces the chip size of the display driver while realizing more natural gamma correction. Moreover, it does not require an additional memory, such as a digital look-up table block and a DAC with a higher resolution, which can achieve significant manufacturing cost savings. Consequently, the proposed multi-stacked gamma-type DAC provides high area efficiency, low cost, and more natural gamma correction. The prototype 8-bit DAC is implemented in a TowerJazz 3.3 V CMOS process. The simulated gamma values of the double- and triple-stacked DAC units are varied from 1 to 2 and from 1 to 3, respectively. In addition, the Monte-Carlo simulation demenstrates that the proposed design shows uniform gamma transfer curves regardless of the process variation.

Driving technology for improving motion quality of active-matrix organic light-emitting diode display

This paper reports transient response characteristics of active-matrix organic light emitting diode (AMOLED) displays for mobile applications. This work reports that the rising responses look like saw-tooth waveform and are not always faster than those of liquid crystal displays. Thus, a driving technology is proposed to improve the rising transient responses of AMOLED based on the overdrive (OD) technology. We modified the OD technology by combining it with a dithering method because the conventional OD method cannot successfully enhance all the rising responses. Our method can improve all the transitions of AMOLED without modifying the conventional gamma architecture of drivers. A new artifact is found when OD is applied to certain transitions. We propose an optimum OD selection method to mitigate the artifact. The implementation results show the proposed technology can successfully improve motion quality of scrolling texts as well as moving pictures in AMOLED displays.

What monitor can replace the cathode-ray tube for visual stimulation to elicit multifocal electroretinograms?

To compare a conventional cathode-ray tube (CRT) screen to organic light-emitting diode (OLED) and liquid crystal display (LCD) screens as visual stimulators to elicit multifocal electroretinograms (mfERGs), mfERGs were recorded from seven eyes of seven healthy volunteers (21 ± 2 years). The mfERGs elicited by a conventional CRT screen (S710, Compaq Computer Co.) were compared to those elicited by a studio-grade master OLED monitor (PVM-1741, Sony, Japan) and a conventional LCD (S1721, Flexscan, Eizo Nanao Corp., Japan). The luminance changes of each monitor were measured with a photodiode. CRT, OLED, and LCD screens with a frame frequency of 60 Hz were studied. A hexagonal stimulus array with 61 stimulus elements was created on each monitor. The serial white stimuli of the OLED screen at 60 Hz did not fuse, and that of the LCD screens fused. The amplitudes of P1 and P2 of the first-order kernels of the mfERGs were not significantly different from those elicited by the CRT and OLED screens, and the P1 amplitude of the first-order kernel elicited by the LCD stimuli was significantly smaller than that elicited by the CRT in all the groups of the averaged hexagonal elements. The implicit times were approximately 10 ms longer in almost all components elicited by the LCD screen compared to those elicited by the CRT screen. The mfERGs elicited by monitors other than the CRT should be carefully interpreted, especially those elicited by LCD screens. The OLED had good performance, and we conclude that it can replace the CRT as a stimulator for mfERGs; however, a collection of normative data is recommended.

Effects of Grain Size in Sequential Lateral Solidification Processed on Active Matrix Organic Light Emitting Diode Displays

In this work, we investigated the correlation between the spacing of primary grain boundaries in sequential lateral solidification (SLS) polycrystalline silicon and the brightness non-uniformity of active matrix organic light emitting diode panels. The oblique line is attributed both to the SLS method and the thin film transistor fabrication process. We found that the oblique line type of brightness non-uniformity disappeared when the spacing of primary grain boundaries is exactly the same in the individual transistor channel or when the non-uniform size is between 2.7 and 3.3 μ m( � Lg < ±10%) in active patterns. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0071408ssl] All rights reserved.

30.2: Invited Paper: Advancements in Inkjet Printing for OLED Mass Production

AbstractContinuous improvements in inkjet printing of organic light emitting diode (OLED) displays have resulted in a number of recent demonstrations of uniform, mura‐free TV‐sized panels. These improvements combined with steady progress in solution OLED material performance, have allowed inkjet to become a realistic near term enabler of cost‐effective mass production of large size OLED TVs. However, for inkjet to make the transition from R&amp;D to mass production, a number of equipment challenges must be overcome, including achieving low particle contamination, maintaining the optimal process environment while preserving serviceability, and providing consistent, uniform, mura‐free results with a wide process window. In this paper, the methodology (with respect to algorithms and process control) used in Kateeva's YIELDjet platform are described that lead to the uniform deposition of ink across an OLED display using inkjet printing, resulting in a highly uniform OLED emission with a wide process window.

Power-constrained contrast enhancement algorithm using multiscale retinex for OLED display.

This paper presents a power-constrained contrast enhancement algorithm for organic light-emitting diode display based on multiscale retinex (MSR). In general, MSR, which is the key component of the proposed algorithm, consists of power controllable log operation and subbandwise gain control. First, we decompose an input image to MSRs of different sub-bands, and compute a proper gain for each MSR. Second, we apply a coarse-to-fine power control mechanism, which recomputes the MSRs and gains. This step iterates until the target power saving is accurately accomplished. With video sequences, the contrast levels of adjacent images are determined consistently using temporal coherence in order to avoid flickering artifacts. Finally, we present several optimization skills for real-time processing. Experimental results show that the proposed algorithm provides better visual quality than previous methods, and a consistent power-saving ratio without flickering artifacts, even for video sequences.

Flexible ISFET Biosensor Using IGZO Metal Oxide TFTs and an ITO Sensing Layer

This letter presents the fabrication details and measured performance of a prototype flexible extended-gate ion-sensitive field effect transistor (ISFET) biosensor, manufactured using a metal oxide indium-gallium-zinc oxide thin film transistor and an indium-tin oxide sensing layer on a 125- μm thick flexible plastic substrate. ISFET drain current was shown to respond correctly to the pH buffer concentration with repeatable pH sensitivity observed over multiple cycles. These results demonstrate the initial viability of directly extending flexible plastic substrate organic light emitting diode display technology to the production of low-cost, plastic ISFET biosensors.

Improvement in Brightness Uniformity by Compensating for the Threshold Voltages of Both the Driving Thin-Film Transistor and the Organic Light-Emitting Diode for Active-Matrix Organic Light-Emitting Diode Displays

This paper proposes a novel pixel circuit design and driving method for active-matrix organic light-emitting diode (AM-OLED) displays that use low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) as driving element. The automatic integrated circuit modeling simulation program with integrated circuit emphasis (AIM-SPICE) simulator was used to verify that the proposed pixel circuit, which comprises five transistors and one capacitor, can supply uniform output current. The voltage programming method of the proposed pixel circuit comprises three periods: reset, compensation with data input, and emission periods. The simulated results reflected excellent performance. For instance, whenΔVTH=±0.33 V, the average error rate of the OLED current variation was low (&lt;0.8%), and whenΔVTH_OLED=+0.33 V, the error rate of the OLED current variation was 4.7%. Moreover, when theI×R(current × resistance) drop voltage of a power line was 0.3 V, the error rate of the OLED current variation was 5.8%. The simulated results indicated that the proposed pixel circuit exhibits high immunity to the threshold voltage deviation of both the driving poly-Si TFTs and OLEDs, and simultaneously compensates for theI×Rdrop voltage of a power line.

Mapping Temperature in OLED Displays Using CCD Thermoreflectance

Effective thermal management is essential to engineering organic devices, since heating accelerates their degradation. However, as pixels in organic light-emitting diode (OLED) displays continue to shrink, an important tool for thermal management, infrared thermography, approaches the limits of its spatial resolution. To address this problem, we adapt high-resolution thermoreflectance imaging, which measures minute changes in reflectivity of visible light, to map temperature in a commercial OLED display. We identify a slowly varying thermal signal and find strong evidence of thermal crosstalk, in which a biased pixel heats up its nearest neighbors, even when the neighbors are unbiased. Such crosstalk is indicative of insufficient heat dissipation, which can lead to reduced display lifetime.

Flexible high‐resolution full‐color top‐emitting active‐matrix organic light‐emitting diode display

AbstractWe developed a high‐performance 3.4‐in. flexible active‐matrix organic light‐emitting diode (AMOLED) display with remarkably high resolution using an oxide semiconductor in a backplane, by applying our transfer technology that utilizes metal separation layers. Using this panel, we also fabricated a prototype of a side‐roll display for mobile uses. In these AMOLED displays, a white OLED combined with a color filter was used in order to achieve remarkably high resolution. For the white OLED, a tandem structure in which a phosphorescent emission unit and a fluorescent emission unit are serially connected with an intermediate layer sandwiched between the emission units was employed. Furthermore, revolutionary technologies that enable a reduction in power consumption in both the phosphorescent and fluorescent emission units were introduced to the white tandem OLED.

Design of OLED Controlling Circuit Based on FPGA

Organic light-emitting diode (OLED) has many advantages such as ultra light, ultra thin, high brightness, high definition, self-luminous, wide angle, quick response.It quickly attracts peoples attention to make one of today's hottest panel display subject. Based on the characteristics and working principle of OLED, the OLED display controlling circuit using the decoding module of DSP and controlling module of FPGA is designed.According to it,the use of each module in the circuit and the working process of the whole circuit are analysed.The simulations and tests are done.Verilog HDL is used to design the controlling circuit in the whole system and a top-down design method is used which is penetrated into each layer from top to bottom and devided carefully.The simulation results show that the gray scale display of OLED can be achieved and better display performance is obtained.

Evaluation of an organic light-emitting diode display for precise visual stimulation

A new type of visual display for presentation of a visual stimulus with high quality was assessed. The characteristics of an organic light-emitting diode (OLED) display (Sony PVM-2541, 24.5 in.; Sony Corporation, Tokyo, Japan) were measured in detail from the viewpoint of its applicability to visual psychophysics. We found the new display to be superior to other display types in terms of spatial uniformity, color gamut, and contrast ratio. Changes in the intensity of luminance were sharper on the OLED display than those on a liquid crystal display. Therefore, such OLED displays could replace conventional cathode ray tube displays in vision research for high quality stimulus presentation. Benefits of using OLED displays in vision research were especially apparent in the fields of low-level vision, where precise control and description of the stimulus are needed, e.g., in mesopic or scotopic vision, color vision, and motion perception.

70.2L: Late‐News Paper: 14.7” Active Matrix PHOLED Displays on Temporary Bonded PEN Substrates with Low Temperature IGZO TFTs

AbstractA flexible, 14.7 inch diagonal organic light emitting diode display has been successfully demonstrated. Device fabrication of the thin film transistor backplane occurred below 200 °C on a polyethylene naphthalate substrate using indium gallium zinc oxide with a saturation mobility of 13.5 cm2/V‐s as the active semiconductor.

33.2: Spatial Resolution Characteristics of Organic Light‐emitting Diode Displays: A comparative Analysis of MTF for Handheld and Workstation Formats

AbstractWe characterized the spatial resolution of organic light‐emitting diode displays of various sizes and formats including handheld and workstation devices. We observed in some cases significant signal crosstalk between adjacent pixels resulting in degraded resolution characteristics. Handheld displays showed improved resolution characteristics as evidenced by modulation transfer functions.

Technology Advances in Flexible Displays and Substrates

This paper reports the latest technological advances made by the Industrial Technology Research Institute (ITRI) in flexible displays, especially the flexible substrate, thin-film transistor (TFT) backplane, and active matrix organic light-emitting diode display. Using the leading cholesteric liquid crystal technology of ITRI, we develop a rewritable, environmentally friendly thermal printable e-paper. The epaper, devised to reduce traditional paper consumption, achieves a high resolution of 300 dpi with a memory function. In addition, we report on the ITRI's initial success in demonstrating a complete R2R process for multisensing touch panels on 100-μm thick flexible glass substrates provided by Corning.

Power Modeling and Optimization for OLED Displays

Emerging organic light-emitting diode (OLED)-based displays obviate external lighting, and consume drastically different power when displaying different colors, due to their emissive nature. This creates a pressing need for OLED display power models for system energy management, optimization as well as energy-efficient GUI design, given the display content or even the graphical-user interface (GUI) code. In this work, we study this opportunity using commercial QVGA OLED displays and user studies. We first present a comprehensive treatment of power modeling of OLED displays, providing models that estimate power consumption based on pixel, image, and code, respectively. These models feature various tradeoffs between computation efficiency and accuracy so that they can be employed in different layers of a mobile system. We validate the proposed models using a commercial QVGA OLED module and a mobile device with a QVGA OLED display. Then, based on the models, we propose techniques that adapt GUIs based on existing mechanisms as well as arbitrarily under usability constraints. Our measurement and user studies show that more than 75 percent display power reduction can be achieved with user acceptance.

P‐146L: Late‐News Poster: Development of a Photochromic Circular Polarizer for OLEDs

AbstractA photochromic circular polarizer was studied for use in organic light‐emitting‐diode displays (OLEDs). This polarizer transmits light emitted from an OLED efficiently under ambient light, extending the life and lowering the power consumption of the OLED. Under bright ambient light, the polarizer changes to a high degree of polarization and low transmittance, which maintains the contrast ratio and retains image visibility by reducing light reflection from the OLED electrodes. An outdoor experiment confirmed that the photochromic circular polarizer enhanced the contrast ratio of the OLED.