Philips Research claims to have developed a color-e-paper technology that allows for personalization of electronic devices and has the potential for use in future large “e-wallpapers,” allowing users to adjust the color of a wall or smart window. According to Philips, its technology allows users to build colors of ink into one layer with separate control of each color. This approach allows a layer to be transparent, the same color as any one of the inks, or a mixture of multiple colors. Users can accurately control the saturation of each color in its e-paper so that they can produce any shade. Philips uses this technique to create “e-skin,” a less complicated and less expensive technology than paper that uses ambient light for energy efficiency and for application in portable devices.

“The first applications using the technology could be e-skins for small devices, such as MP3 players or cell phones,” says Kars-Michiel Lenssen, principal scientist at Philips Research. “However, the technology is highly scalable. In the future, it will be possible to use e-skins to bring new color and a new aura or 'vibe’ to much larger equipment.” A large e-skin could make the concept useful for MRI (magnetic-resonance-imaging) or CT (computer-tomography) scanners, potentially putting patients at ease, he adds. In ambience-creation applications, reflective e-skins complement the emissive ambience-creation technologies that use LEDs (light-emitting diodes) and OLEDs (organic LEDs) to create colorful light. “You could use LEDs or OLEDs when you want a theatrical look and e-skins when you want something more subtle and more natural-looking that uses less energy,” Lenssen says.

Philips based its e-skin technology on its previous work with e-paper. Because the particles in suspension carry a surface charge, you can control their motion using an electric field, or electrophoresis. When you create a pixel with colored particles in a clear suspension, applying an electric field perpendicular to the surface makes the particles migrate to the top of the pixel, turning it dark and serving as the basis of the monochrome e-paper that e-book readers use. The e-skin technology features a gradient of gray levels from a highly transparent optical state to full black to allow future applications, such as smart windows.

To go from monochrome to polychrome, Philips uses in-plane electrophoresis, which applies the field parallel to the surface. This approach causes the colored particles to spread across the pixel, again turning it dark. When you reset the pixel, the colored particles hide behind a mask, so the pixel is completely transparent. Philips builds a gate electrode into each pixel, which provides control over how many colored particles spread across the pixel and the saturation or shade of each color. Philips is open to licensing its technology to other parties in other applications, such as e-paper displays.

Philips Research , www.research.philips.com .