Flexible Displays Gain Momentum

Researchers at Cambridge, MA-based E Ink have completed the first working prototype of an electronic ink display attached to a flexible, silicon-based thin-film transistor backplane, the sheet of electronics that controls display pixels. The prototype is a functional display that you can twist, bend or throw against the wall without disturbing a single electron.

This proof-of-concept prototype confirms that it will soon be possible to mass-produce reams of self-erasing electronic paper that combine sheets of electronic ink with flexible silicon circuitry. Last year, Lucent Technologies demonstrated an electronic-ink display driven by flexible plastic transistors, but E Ink researchers believe that silicon-based transistors have several big advantages over plastic.

The company’s ultimate goal is to produce RadioPaper, sheets of reusable e-paper containing radio frequency ID tags that download a new edition of, for example, the Wall Street Journal each morning into the same physical display.

On Display

Electronic ink is composed of tiny, translucent microcapsules no wider than a human hair. Each capsule contains millions of particles, each of which has either a positive or negative charge. The positive particles are black and the negative ones white, and the type of electrical charge applied to the microcapsule determines which particles will rise to its surface and therefore which color will appear. The “ink”-a sheet of these microcapsules-is integrated into a display, where the final product presents an image that mimics the printed page: it’s easy on the eye and can even be read outside on the beach-and at an angle.

Until now, electronic ink has been used with standard, rigid backplanes designed for liquid crystal displays. But after several years of research, E Ink is now able to fabricate pliable, non-crystalline silicon transistors on both stainless steel foil and plastic substrates, creating flexible backplanes. Laying a sheet of electronic ink over these backplanes creates the all-flexible prototype display.

“We have demonstrated the feasibility of a fully flexible electronic paper-like display. We’ve proven that it works,” says Michael McCreary, E Ink’s vice president of research and development. The company has also developed a prototype similar to Lucent’s, using plastic transistors on a flexible backplane. However, according to McCreary, plastic transistors have a shelf life of just a few months-a technical obstacle which, in addition to plastic’s slow switching speed, currently stalls further development.

Stretching into the Future

The completion of E Ink’s prototype is “a significant milestone” for the company, says Pat Dunn, director of technology at DisplaySearch, an Austin, TX-based research and consulting firm. “This will bring their technology closer to that paper-like feel. It evens the playing field for them in terms of screen resolution, which is a very important criteria.”

To reach its next milestone, E Ink will have to keep up with a number of other players in the flexible display field. Palo Alto, CA-based Gyricon Media is their only direct e-paper competitor, but other companies such as Menlo Park, CA-based Rolltronics, Morgan Hill, CA-based Alien Technologies and Cambridge, England-based Plastic Logic are all developing novel production techniques for fabricating transistors on flexible substrates.

Researchers at E Ink don’t know exactly when their prototype will go into full production, but they estimate that by sometime in 2005 they’ll be building fully-flexible displays for commercial use. For now, the company is working with Philips Electronics to produce displays using electronic ink against rigid, glass backplanes, to be built into mobile, handheld devices starting next year.