Text 9. Electronic Paper: A Revolution About to Unfold?

In spite of its name, electronic paper is the technological cousin of the flat-panel computer screen. A computer’s liquid crystal display (LCD) consists of two sheets of glass sandwiched around a layer of tiny transistors and a layer of liquid crystal material – a soup of rodlike molecules that snuggle together a bit like sardines in a can. The screen is illuminated from behind, and ordinarily the molecules let light pass through them. But when a transistor applies a voltage to a point on the screen, or pixel, the molecules rearrange themselves to block the light and darken the pixel. Filters tint the light from neighboring pixel red, blue, or green to create a color image.

In electronic paper, too, each pixel changes color when a voltage is applied. But instead of emitting light, electronic paper merely reflects it, dramatically reducing power consumption. A pixel in electronic paper also holds its color without voltage. Thanks to such “bistabillity”, electronic paper uses power only when the image on it changes. Electronic paper may use less than 1/10,000 as much power as a computer’s LCD.

Researchers are developing several different technologies for the color-changing electronic ink. E Ink’s “electrophoretic” material consists of microcapsules embedded in a plastic sheet, each filled with a clear liquid and submicrometer-sized particles, some colored black and others colored white. The black and white particles carry opposite electric charges; a pulse of voltage from the underlying transistor can make the white ones rise toward the surface of the display and the black ones sink away from it, or vice versa.

Creating a truly paperlike, flexible display poses equally challenging technical problems. The problem lies behind the electronic ink, in the “backplane” of transistors that activate it. That’s because the crystalline silicon from which transistors are usually made is brittle and must be deposited on a stiff substrate such as glass.

To make a flexible backplane, researchers are developing materials such as non crystalline amorphous silicon. Perhaps most promising are plastics that have electrical properties similar to those of silicon. Such “organic semiconductors” bend easily and can be deposited on flimsy plastic substrates. And in theory a simple inkjet printer could lay down organic circuits much more cheaply than the complicated multistep process now used to etch circuits into silicon.

Philips and E Ink have teamed up to make a flexible electronic paper display driven by organic semiconductors. The low-resolution screen, roughly as thick as a sheet of printer paper, measures 12.7 centimeters along the diagonal and rolls up into a tube 1.5 centimeters wide. Philips envisions using the screens for retractable displays on hand-held devices and plans to begin design for production this year. Philips guarantee the screen will roll and unroll at least 2000 times before it conks out – which may not be enough for people who make 10 calls per day from their cell phones.

Electronic paper may someday rewrite the concept of the book, but to bring the technology to market, developers are using it first to spruce up the humble store sign. Gyricon sells a wirelessly programmable sign for $1295 and has introduced a system to control multiple signs from a central location.

Developers also hope to produce larger, lower-power, and easier-to-read displays for cell phones and other hand-held devices. E Ink has positioned itself to sell its electronic ink by the sheet as a commodity to electronics manufacturers. The company already supplies the displays for Sony’s LIBRIé electronic book reader. Introduced last year and sold only in Japan, the LIBRIé weighs 300 grams, holds 10 megabytes of text, and can flip more than 10,000 virtual pages before draining its four AAA batteries. Still, the book reader looks less like a new type of paper than a black-and white subspecies of personal digital assistance.

Ultimately, developers envision a kind of smart scroll that downloads newspapers, magazines, and books wirelessly. To turn their prototypes into commercial products developers will have to learn to make electronic paper cheaply and in large quantities and build a manufacturing infrastructure capable of challenging existing display technologies. Electronic paper is coming. The question is when will it arrive – and what will it do when it gets here?

(the source: adapted from (the source: adapted from http://www.sciencemag.org/search?site_area=sci&y=5&fulltext=electronic%20paper%3A%20a%20revolution%20about%20to%20unfold%3F&x=22&submit=yes )

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