Andrea Giraldo

Light degradation and voltage drift in polymer light-emitting diodes

It is shown that the voltage drift and light degradation in polymer light-emitting diodes are related and can be explained by the formation of traps and the modification of the space charge in the bulk of the polymer. The energy released by nonradiative carrier recombination is believed to be the driving force for the generation of traps in poly(p-phenylene vinylene) conjugated polymers. A first-approximation model is derived for the voltage drift and the light decrease during operation, which is in good agreement with experimental observations for time and current density dependencies.

Passive and active matrix addressed polymer light-emitting diode displays

Polymer LEDs provide a new alternative to LCDs for many display applications, and are particularly attractive because of their high brightness, near-perfect viewing angle, and very fast response time. In this paper, the basic technology used to form the LED structures, and the performance of these devices is presented. Then, the fabrication and driving of passive addressed matrix displays formed using this technology is discussed. Finally, the necessity for active matrix addressing for larger size and higher resolution displays is demonstrated, and it is shown that this is best achieved using low temperature poly-Si technology. The state-of-the-art poly-Si technology used for active matrix addressed LED displays is described, with particular reference to transistor variation, and the resulting non-uniformities in images on displays. A variety of different addressing techniques, and pixel circuits can be used to drive the LEDs in the active matrix, and the performances of these schemes are compared. These include the basic current source circuit; the modified current source circuit; transistor current mirror circuits; and circuits with optical feedback and correction for uniformity variation. Consideration is given both to analogue and to digital drive methods.

38.1: Optical Feedback for AMOLED Display Compensation using LTPS and a-Si:H Technologies

New optical feedback pixel circuits for a-Si:H and LTPS technologies will be presented. The circuits will enable correction of threshold voltage drift of the drive TFT and degradation of the OLED. In the a-Si:H case this will be achieved with a standard a-Si:H process and for LTPS an a-Si NIP photodiode is integrated. Operation, technology and measurements will be presented.

32.1: Invited Paper: A Comparison of Pixel Circuits for Active Matrix Polymer/Organic LED Displays

In this paper measurements on several types of active matrix polymer LED (AMPLED) displays will be presented. The issues ofimage uniformity and polymer aging will be addressed by pixel circuit designs.

Towards large‐area full‐color active‐matrix printed polymer OLED television

Abstract— We have developed a new multi-head polymer OLED ink-jet-printing technology to make large-screen OLED television displays. This printer is used to make a 13-in.-diagonal 16:9-format polymer-OLED prototype driven by an LTPS active matrix with a pixel circuit which compensates for TFT threshold-voltage variations. A novel scrolling-bar addressing scheme is used to reduce motion artifacts and to make sparkling images with a high local peak brightness. The scalability of the polymer-OLED technology to larger sizes for television applications is discussed.

44.4: Distinguished Paper: Towards Large‐Area Full‐Color Active‐Matrix Printed Polymer OLED Television

We have developed a new multi-head Polymer OLED inkjet print technology to make large screen OLED television. This printer is used to make a 13″ diagonal 16:9 format Polymer OLED prototype driven by an LTPS active matrix with a pixel circuit which compensates for TFT threshold voltage variations. A novel scrolling-bar addressing scheme is used to make sparkling images with a high local peak brightness. Color processing is used to improve the overall perception of the image.

Electrowetting-Based Displays: Bringing Microfluidics Alive On-Screen

We present the use of electrowetting as a technology for very bright and energy-efficient displays. The intrinsic nature of the system as an optical switch provides an excellent starting point upon which a wide variety of display configurations can be based. Here we focus our discussion on reflective displays, in which the main advantages of the technology are best utilized. The properties of the reflective display will be discussed, illustrating the combination of a paper-like optical performance and video-speed switching.

Improved optical feedback for OLED differential ageing correction

— To compete with LCDs and to meet standard display product specifications, OLED displays must have a high degree of tolerance to differential ageing or “burn-in.” A new optical feedback pixel circuit is presented that enables accurate differential ageing correction, can have low power consumption, and enables a high degree of non-uniformity correction. The circuit can be implemented in LTPS, and a-Si:H TFT technologies and circuits for both cases are shown. The a-Si:H approach is low cost and enables correction of both TFT threshold voltage drift and OLED degradation at the same time. The circuit analysis, operation, and technology will be described and results presented.

Optical feedback in active matrix polymer OLED displays

Among the recent emerging flat display technologies organic LED (OLED) is one of the most interesting. Combining the OLED with an active matrix substrate, typically made with low temperature polysilicon, it is possible to greatly reduce the power consumption. In an active matrix substrate the ability of integrating active components can be used to mitigate the OLED differential degradation.

55.3: Diffractive Backlight Light Guide Plates in Mobile Electrowetting Display Applications

Power efficiency demands on mobile displays are increasing rapidly, as new multimedia services and applications are being adopted by users. Diffractive backlights and electrowetting displays have been proposed as some of the solutions to solve the poor efficiency of current mobile display systems. In this study, an electrowetting display was coupled with a pixelated, diffractive becklight light guide plate. This is to our knowledge the first time when a pixelated, diffractive backlight has been demonstrated in conjunction with an actual display. The results of the study show that the backlight and display panel need to be optimized as a system in order to obtain an applicable module for mobile use.