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E-Paper Comes Alive

E Ink is making color and video versions of its e-paper, but commercial products are a few years off.
November 20, 2007

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.

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.

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.

In the company’s Cambridge, MA, headquarters, two prototypes show the payoff. One is an e-reader display in bright, vivid color. Touch a button, and an image of a bunch of flowers appears; bring the display outside, and it shines brighter because it is reflecting ambient light. (As with black-and-white e-paper, until a user changes that image, the unit consumes virtually no power.) The other prototype, a six-inch display hooked up to a computer, showed a video clip from the animated movie Cars. It was a bit grainy but was switching frames 30 times per second. Two years ago, the switching time in products with E Ink technology was just one frame per second.

While the video version is still several years from market, “this was a landmark research advance in the history of e-paper,” says Russ Wilcox, E Ink’s CEO. Invoking the long-held dream for e-paper–that it can be an electronic replacement for real newsprint–he added, “You can imagine a USA Today weather chart where clouds are actually moving.”

E Ink is working with several leading display makers to develop flexible transistors that will create E Ink and other color displays that are bendable and even rollable. LG Philips recently announced the world’s first 14.1-inch flexible color e-paper display using E Ink technology. The color version uses a substrate that arranges thin-film transistors on metal foil rather than on glass. And last month, Samsung used E Ink technology to set a new world record in terms of the resolution of a large flexible color display. (Samsung’s 14.3-inch screen has a 1,500-by-2,120-pixel resolution.) No commercialization date has been announced for these technologies.

Other companies are also making advances in e-paper. One of them, San Diego’s Qualcomm MEMS Technologies, has developed a MEMS-based version that can produce video-ready refresh rates and will appear in monochrome and bicolor displays in the next year or so. (See “E-Paper Displays Video.”) But E Ink is generally acknowledged to have the best technology in terms of simulating the look of paper, says Raupp, whose research lab has partnerships with 16 display makers, including both E Ink and Qualcomm. “Put the two side by side–which one looks like paper? There would be no contest,” Raupp says of E Ink and Qualcomm. The move into video and color “expands the application space” and makes E Ink a leading candidate to become a fixture in flexible displays, he adds.

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