Herbert Lifka

Cathode encapsulation of organic light emitting diodes by atomic layer deposited Al2O3 films and Al2O3/a-SiNx: H stacks

Al2O3 thin films synthesized by plasma-enhanced atomic layer deposition (ALD) at room temperature (25 °C) have been tested as water vapor permeation barriers for organic light emitting diode devices. Silicon nitride films (a-SiNx:H) deposited by plasma-enhanced chemical vapor deposition served as reference and were used to develop Al2O3/a-SiNx:H stacks. On the basis of Ca test measurements, a very low intrinsic water vapor transmission rate of ≤ 2 × 10−6 g m−2 day−1 and 4 × 10−6 g m−2 day−1 (20 oC/50% relative humidity) were found for 20–40 nm Al2O3 and 300 nm a-SiNx:H films, respectively. The cathode particle coverage was a factor of 4 better for the Al2O3 films compared to the a-SiNx:H films and an average of 0.12 defects per cm2 was obtained for a stack consisting of three barrier layers (Al2O3/a-SiNx:H/Al2O3).

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.

58.4: Invited Paper: Flexible Displays and Electronics Made in AM-LCD Facilities by the EPLaR™ Process

Flexible displays have significant advantages for handheld devices by being thin, light, robust and capable of being fitted to curved shapes. We have developed the EPLaR process for making flexible displays in standard AM-LCD factories. In this paper we discuss EPLaR electrophoretic displays driven by a-Si TFTs that were made in a factory and report on progress in developing flexible polycrystalline silicon TFTs and OLEDs.

53.4: Ultra-Thin Flexible OLED Device

A new method of making ultra-thin flexible organic light emitting diodes (OLEDs) using standard OLED fabrication facilities is reported. Through use of the Electronics on Plastic by Laser Release (EPLaR) technology, we have developed and demonstrated 18-μm thick single-pixel OLEDs. In this paper, besides describing the fabrication method, the electrical and optical performance of the flexible OLEDs is reported.

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.

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.

34.1: Ultra-Thin Encapsulation for Large-Area OLED Displays

Organic light emitting displays (OLEDs) can be made as thin as the substrate if thin film packaging is used. We have developed an effective encapsulation method for OLED displays, based on a multi-stack approach of silicon-nitride (N) and silicon-oxide (O) PECVD films as a barrier layer. We present results on the moisture resistance properties of this stack. The water permeability of a NONON stack was measured in the range of 10−6 g/m2⋅day.