Philips demonstrates video-speed electronic-paper technology based on electrowetting

The technology is fast enough to display video content and can beused to build a reflective full-colour display that is at least twotimes brighter than what is possible with any other technology. Thedisplay is based on electrowetting - a technology that allows rapidcontrol and manipulation of fluid motion on a micrometer scale.

The technology is based on controlling the shape of a confinedwater/oil interface by an applied voltage. With no voltage applied, the(coloured) oil forms a flat film between the water and a hydrophobic(water-repellent), insulating coating of an electrode, resulting in acoloured pixel. When a voltage is applied between the electrode and thewater, the interfacial tension between the water and the coatingchanges.

As a result the stacked state is no longer stable, causing the waterto move the oil aside. This results in a partly transparent pixel, or,in case a reflective white surface is used under the switchableelement, a white pixel. Because of the small size of the pixel, theuser only experiences the average reflection, which means that ahigh-brightness, high-contrast switchable element is obtained, whichforms the basis of the reflective display.

Displays based on electrowetting have several attractive features.The switching between white and coloured reflection is fast enough todisplay video content. Furthermore, it is a low-power and low-voltagetechnology, and displays based on the effect can be made flat and thin.The reflectivity and contrast are better or equal to those of otherreflective display types and are approaching those of paper.

In addition, the technology offers a unique path towardshigh-brightness full-colour displays, leading to displays that are fourtimes brighter than reflective LCDs and twice as bright as otheremerging technologies. Instead of using red, green and blue (RGB)filters or alternating segments of the three primary colours, whicheffectively result in only one third of the display reflecting light inthe desired colour, electrowetting allows for a system in which onesub-pixel is able to switch two different colours independently.

This results in the availability of two thirds of the display areato reflect light in any desired colour. This is achieved by building upa pixel with a stack of two independently controllable coloured oilfilms plus a colour filter. The colours used are cyan, magenta andyellow, which is a so-called subtractive system, comparable to theprinciple used in inkjet printing for example. Compared to LCD anotherfactor two in brightness is gained because no polarizers arerequired.

The technology is particularly appealing for electronic-paper likeapplications, for which high-brightness and contrast-rich reflectivedisplays are needed, and opens up new application areas that make useof the full colour and video speed capability. For more information,visit the Philips Research Web site at www.research.philips.com