Giovanni Nisato

Single-substrate liquid-crystal displays by photo-enforced stratification

Data visualization plays a crucial role in our society, as illustrated by the many displays that surround us. In the future, displays may become even more pervasive, ranging from individually addressable image-rendering wall hangings to data displays integrated in clothes. Liquid-crystal displays (LCDs) provide most of the flat-panel displays currently used. To keep pace with the ever-increasing possibilities afforded by developments in information technology, we need to develop manufacturing processes that will make LCDs cheaper and larger, with more freedom in design. Existing batch processes for making and filling LCD cells are relatively expensive, with size and shape limitations. Here we report a cost-effective, single-substrate technique in which a coated film is transformed into a polymer-covered liquid-crystal layer. This approach is based on photo-enforced stratification: a two-step photopolymerization-induced phase separation of a liquid-crystal blend and a polymer precursor. The process leads to the formation of micrometre-sized containers filled with a switchable liquid-crystal phase. In this way, displays can be produced on a variety of substrates using current coating technology. The developed process may be an important step towards new technologies such as ‘display-on-anything’ and ‘paintable displays’.

P-88: Thin Film Encapsulation for OLEDs: Evaluation of Multi-layer Barriers using the Ca Test

We report on a method to evaluate thin film barriers for direct encapsulation of OLEDs. Based on the corrosion of reactive metal films and modeling thereof, this method is used to quantify the water permeation rate of high-performance diffusion barriers. This method was first used to measure the barrier properties of flexible plastic substrates for display applications [1]. In the present work the system has been automated for improved repeatability and optical calibration has been performed to assess the sensitivity. Effective water vapor transmission rates down to 10−6 g/m2/day can be detected. Permeation data on a multi-layer thin film encapsulant was obtained at three temperatures. To demonstrate compatibility in the application, the same thin film encapsulant was used to package actual passive matrix devices. This is the first report of a quantitative measure of an OLED compatible thin film encapsulant.

5.2: A Fully Flexible, Cholesteric LC Matrix Display

Flexible cholesteric texture liquid crystal displays are demonstrated. The 4.2″ diagonal display can be bent over a 20-mm radius of curvature, even during operation. The driving parameters and the cell-gap homogeneity are comparable to those of glass based cells. Images with 16 gray levels are shown on the display.

16.2: A Fully Flexible Colour Display

A flexible version is shown of a state of the art passive matrix LCD; a full colour STN display. By using polymer substrates, “ultra-thin” optical layers (like retarders, colour filters and polarisers) and a flexible backlight a fully flexible CSTN demonstrator is obtained, that can be bend to a radius of 40 mm during operation.

L‐5: Late‐News Paper: Single‐substrate LCDs Produced by Photo‐enforced Stratification

A new technique to produce polymer covered liquid crystal layers on a single substrate, called photo-enforced stratification, allows cost-effective production of ultra-thin LCDs. The two-step photopolymerisation-induced phase separation of a liquid crystal and a polymer precursor can be performed on a variety of substrates and provides freedom in display design.

Advanced poly-LED displays

Philips have been actively developing polymer OLED (poly-LED) displays as a future display technology. Their emissive nature leads to a very attractive visual appearance, with wide viewing angle, high brightness and fast response speed. Whilst the first generation of poly-LED displays are likely to be passive-matrix driven, power reduction and resolution increase will lead to the use of active-matrix poly-LED displays. Philips Research have designed, fabricated and characterized five different designs of active-matrix polymer-LED display. Each of the five displays makes use of a distinct pixel programming- or pixel drive-technique, including current programming, threshold voltage measurement and photodiode feedback. It will be shown that hte simplest voltage-programmed current-source pixel suffers from potentially unacceptable brightness non-uniformity, and that advanced pixel circuits can provide a solution to this. Optical-feedback pixel circuits will be discussed, showing that they can be used to improve uniformity and compensate for image burn-in due to polymer-LED material degradation, improving display lifetime. Philips research has also been active in developing technologies required to implement poly-LED displays on flexible substrates, including materials, processing and testing methods. The fabrication of flexible passive-matrix poly-LED displays will be presented, as well as the ongoing work to assess the suitability of processing flexible next-generation poly-LED displays.