Tuesday, November 20, 2007

E-Paper Comes Alive

E Ink is making color and video versions of its e-paper, but commercial products are a few years off.

By David Talbot

Color e-paper: Advances in ink brightness have allowed E Ink, of Cambridge, MA, to add filters to its monochrome e-paper displays, transforming them into color displays, as in this prototype. No commercialization plans have been announced for the color version of e-paper. Credit: E Ink

The new Amazon Kindle e-reader, unveiled yesterday, is the latest in a line of ever-improving black-and-white e-paper displays that don't use much power and are bright even in daylight; they more closely reproduce conventional paper and ink than do backlit displays. But bigger technology leaps are imminent. E-paper pioneer E Ink--the company whose technology underpins the Amazon gadget's display--is prototyping versions of the electronic ink that are bright enough to support filters for vivid color displays, and that have a fast-enough refresh rate to render video.

Add it all up, and it represents an emerging trifecta of color, video, and flexibility set to transform a display technology once seen as suited only for rigid black-and-white e-readers like the Kindle and the Sony Reader, and other niche applications like train-station schedule displays that don't need to change quickly. "This latest thing they've done with the video is a key milestone in the history of e-paper technology development," says Gregory Raupp, director of the Flexible Display Center at Arizona State University. "Until this point, you have been limited to static image applications."

E Ink's basic technology uses a layer of microcapsules filled with flecks of submicrometer black and white pigment chips in a clear liquid. The white chips can be positively charged, the black chips negatively charged. Above this layer is a transparent electrode; at the base is another electrode. A positive charge on the bottom electrode pushes the white chips to the surface, making the screen white. A negative charge pushes the black chips up, rendering words and images.

But the basic technology only produces a black-and-white image. So, E Ink has been refining the ingredients, the electronics, and the mechanics of that process. For example, in recent months the company has developed ultrabright inks that reflect 47 percent of ambient light--a significant improvement over the 35 to 40 percent in existing E Ink black-and-white displays. Higher reflectivity versions should go into commercial products, such as the Sony Reader, in about two years.

This higher brightness makes color displays possible. E Ink uses transparent red, green, or blue filters affixed above the picture elements. In essence, software controls groups of microcapsules sitting below filters of particular hues, and it only turns the microcapsules white when those hues are sought. The E Ink filters are custom-made by a partner, Toppan Printing of Tokyo, to work well with the specific shades, brightness, and reflectivity of the E Ink technology. The first color experimentation began several years ago, but it has been steadily improving in brightness and contrast, says Michael McCreary, E Ink's vice president of research and advanced development. He offered no estimate for a commercialization date.

In another set of advances, tweaks to the E Ink particles and their polymer coatings, and to the chemistry of solution inside the microcapsules, have helped improve the speed at which the particles can move. McCreary says that for years, conventional wisdom held that E Ink technology could never be made video ready, because particles had to be moved through a liquid. But E Ink has done it, thanks to polymer particle coatings and "special stuff in the clear liquid," McCreary says.