Scientists at Phillips have presented a new technology for reflective, paper-like displays. The technology is fast enough to display video content and can be used to build a reflective full-color display that is at least two times brighter than other technology. The display is based on electrowetting--a technology that allows rapid control and manipulation of fluid motion on a micrometer scale. The technology was presented in the September 25 issue of Nature.
The technology is based on controlling the shape of a confined water/oil interface by an applied voltage. With no voltage applied, the (colored) oil forms a flat film between the water and a hydrophobic (water-repellent), insulating coating of an electrode, resulting in a colored pixel. When a voltage is applied between the electrode and the water, the interfacial tension between the water and the coating changes. As a result the stacked state is no longer stable, causing the water to move the oil aside. This results in a partly transparent pixel, or, in case a reflective white surface is used under the switchable element, a white pixel. Because of the small size of the pixel, the user only experiences the average reflection, which means that a high-brightness, high-contrast switchable element is obtained, which forms the basis of the reflective display. The switching between white and colored reflection is fast enough to display video content. Furthermore, it is a low-power and low-voltage technology, and displays based on the effect can be made flat and thin.
In addition, the technology offers a path towards high-brightness full-color displays, leading to displays that are brighter than reflective LCDs and other emerging technologies. Instead of using red, green, and blue (RGB) filters or alternating segments of the three primary colors, which effectively result in only one third of the display reflecting light in the desired color, electrowetting allows for a system in which one sub-pixel is able to switch two different colors independently. This results in the availability of two thirds of the display area to reflect light in any desired color. This is achieved by building up a pixel with a stack of two independently controllable colored oil films plus a color filter. The colors used are cyan, magenta, and yellow, which is a so-called subtractive system, comparable to the principle used in inkjet printing for example. The technology has particular potential for electronic-paper like applications, for which high-brightness and contrast-rich reflective displays are needed, as well as application areas that make use of the full color and video speed capability.