Plastic Transistor—First Step to "Electronic Paper"?

December 6, 2001

The days of paper books and newspapers are numbered. What they'll be replaced with, according to some entrepreneurs, is "e-paper"—basically a computer monitor that is so thin you could roll it up and stick it in your pocket.

The goal is to create an electronic display on a material that has the look and flexibility of paper, but, unlike paper, could be erased, updated, and used over and over again.

Researchers speculate that eventually we will download our daily newspaper or the latest bestseller onto a single sheet of electronic paper. It may be possible to incorporate early versions of e-paper into handheld devices within the next five years.

Until now, one major hurdle to creating electronic paper has been that the circuit boards that direct the "electronic ink" to form text and images are not flexible.

Silicon transistors are basically tiny switches that control the color of each pixel—the tiny square units that make up the image on a laptop screen, for example. The transistors are sandwiches of metals and insulators that must be laid down on a flat surface, which produces a rigid display.

Scientists at Philips Research in the Netherlands have replaced the silicon with plastic transistors, which are flexible and cheap to make. Plastic conducts electricity more slowly than silicon but still fast enough for most electronic appliances. Using plastic rather than silicon is also more compatible with manufacturing processes that use other plastics.

Normally transistors are fairly simple components—they are either on or off, which means a single pixel is either, say, black or white. But Philips has created an innovative plastic transistor with 256 levels that can control 256 corresponding shades of gray.

"Rather than just black or white, a pixel can have various shades of gray, producing images that resemble black-and-white photographs," said Russ Wilcox of E Ink in Cambridge, Massachusetts, which is a corporate partner of Philips Research. The research is published in the December 6 issue of the journal Nature.

Using the new type of transistor, researchers created a two-inch liquid-crystal display. It measures 64 pixels by 64 pixels and can form an image using 256 shades of gray. It can also be refreshed at the same speed as a video display.

The current prototype used to test the plastic transistors was mounted on glass. The next step for Philips, according to Wilcox, will be to use plastic rather than glass to create a flexible display that would be robust and lightweight.

Philips is not the only company experimenting with plastic transistors, said Wilcox. The field also includes heavyweights such as Lucent and IBM. Gyricon Media, a spin-off company of Xerox, is also developing Smart Paper, an electronic paper.

Flexible and lightweight but robust electronic displays would have a broad array of potential applications. Items such as cell phones and personal organizers often have poor electronic displays.

Continued on Next Page >>




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