Qualcomm enters e-paper video race

A novel electronic-paper display developed by Qualcomm can deliver high-quality video images, making it more versatile than other e-paper technologies. The display employs microscopic mechanical switches that turn pixels on and off at rates more than fast enough to display video.

The first versions of the display will be monochrome; one is featured in an Audiovox Bluetooth headset, released this week. A two-color display will be used next year in a phone made by the Chinese phone company Hisense. Full-color versions will follow.

Like ordinary paper, e-paper displays are designed to be reflective, making them much easier to view in a range of different lighting conditions, such as bright sunlight, than are traditional displays, such as backlit LCDs. The other main advantage is that they are bi-stable, meaning that once they have been switched to a state, they will hold that state without requiring an electrical current. The benefit of this is that they use considerably less power. These features make them ideal for applications such as signs and electronic books, including Sony's eBook reader.

In most e-paper displays, however, pixels switch on and off too slowly to display video, says James Cathey, vice president of business development for Qualcomm MEMS Technologies, based in San Diego. Indeed, other e-paper technologies can take longer than half a second to respond. Such slow switching can lead to "ghosting," in which moving subjects blur. In contrast, pixels in the new Qualcomm display can switch in just tens of microseconds--fast enough to produce sharp video images. Cathey says that this ability to use the displays for video could make e-paper less of a niche technology and suitable for more mainstream multimedia displays for mobile devices like cell phones.

The new display technology uses a novel method for producing color. The method employs mechanisms that are similar to the ones that give films of oil on water a colorful sheen, says André Arsenault, a chemist at the University of Toronto, and cofounder and chief technology officer of Opalux, a Toronto-based e-paper startup.

When light hits a film of oil, it splits, with some reflecting and the rest passing through the oil before being reflected off the surface of the water. The light reflecting off the oil is slightly out of phase with the light reflecting from the water. As a result, light waves interfere with each other, with some wavelengths being reinforced and others canceled out. The distance between these surfaces determines which colors are amplified and which are canceled. Films of oil of a certain thickness, for example, would amplify green light while canceling out red and blue light, making the oil appear green.

In the display, each pixel consists of several color-specific cells that mimic the film of oil on water. Each cell is made up of two reflective layers, one on top of the other. The top layer is only partially reflective, allowing some light to pass through it and bounce off the second surface. In each cell, the gap between these surfaces is spaced so that constructive interference occurs for only one specific range of wavelengths, causing them to amplify a single primary color while canceling out other colors. To create a full-color display, each pixel is made up of three different types of cells, each having a different-size gap between the layers that reflects red, green, or blue.

Each cell can be turned off by bringing together the two layers using an electromechanical switch. (When there is little space between the layers, no visible light is amplified, making the cell appear black.) The switch moves after a pulse of voltage and stays in place until another pulse moves it back. As a result, the display is bi-stable, using little energy except to change the image.

By combining different sets of colored cells as subpixels, researchers can get any color of the spectrum, says Cathey. These MEMS devices are very robust, he says, and have been demonstrated to be reliable for more than 12 billion cycles.

"I personally think this technology is very cool," says Arsenault. But because of the fabrication processes used to create MEMS devices, there is a constraint on how big such displays can be made, he says, which is the reason that Qualcomm is targeting small mobile displays.

What's more, the energy savings will only apply when the display is used to view static, not video, images,

says Johan Feenstra, one of the founders of Liquavista, a spinout from Philips Research, based in Eindhoven, the Netherlands, which is also developing e-paper capable of video rates. "Bi-stability is only useful when you have an application where you don't change the image often," Feenstra says.

For video, this isn't the case because the pixels have to be switched on and off almost continuously, says Guido Aelbers, chief operating officer at Polymer Vision, also in Eindhoven. "The moment you go to high speeds, you lose the low-power advantage," he says.

Even so, both Aelbers and Feenstra believe that having video capabilities as well as color opens up a much bigger marketplace for e-paper displays. But with LCD technology constantly improving and costing less, it could well give the new display a run for its money, says Aelbers.

Via MIT

Color E-ink and video expected soon

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 the next year or so.

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 milestone 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.

via MIT