Over the past four decades, integrated circuits have worked their way into our computers, televisions, phones, automobiles, appliances, and toys. They're in our air conditioners and airplanes, our cameras and copiers.
Now imagine where else they could go if they weren't small and rigid.
If integrated electronics could be big, flexible, and lightweight, they would be suitable for a dazzling array of items that technologists have long dreamed of. Flexible displays, many meters across, would be sharp, bright, and vivid, and yet they would roll up like
window shades when not in use. Radio frequency identification tags could follow the contours of the products they identified. Light, portable, and powerful antennas would unfurl in space, on the battlefield, or at the beach. Similar lightweight sheets of sensors and circuits, large and pliable, could cover airplane fuselages or nuclear-reactor pipes--and someday, space-station or moon-base exteriors--continually monitoring their physical integrity and triggering an alarm the instant a tiny crack forms.
Indeed, lightweight flexible electronics, in the form of small display screens for wristwatches and the like, are at last taking their first tentative steps into a few niche markets. But as with many novel technologies, greater commercial success awaits cheaper manufacturing methods. And now, engineers are close to delivering one: by adapting the ubiquitous, low-cost technologies of inkjet printing, they have already managed to produce simple flexible circuits of up to 50 square centimeters. In fact, the research division of Royal Philips Electronics NV is now working with Dimatix Inc., which makes inkjet printheads, to produce light-emitting-diode displays for cellphones using an inkjet process.
If this and similar work live up to their promise, it could herald a radical advance in the electronics industry: the cheap and fast fabrication of high-quality, even custom, plastic-based ICs with equipment not much bigger than a microwave oven.
Today, the few flexible plastic-based circuits trickling out commercially are produced in ordinary chip fabrication facilities, using a modification of the standard technique that produces conventional ICs in silicon. Kimberly Allen, director of display technology and strategy for market analyst iSuppli, El Segundo, Calif., says that most of these units are being used in electronic signs [see photo, " Sign of the Future"]. E Ink Corp., in Cambridge, Mass., produces a low- to medium-resolution monochrome plastic display for signs and portable electronics that changes from dark to light when voltage is applied [see "A Bright New Page in Portable Displays," IEEE Spectrum, October 2000]. And Nike sells the Triax sports watch, which has a liquid-crystal display (LCD) on plastic; the Japanese wristwatch companies Citizen and Seiko Epson are reportedly readying models for introduction [see photo, " Watch It Bend"].
In Japan and Korea, two countries with large concentrations of display manufacturers, work on big flexible displays is intense. Earlier this year, researchers at Samsung Electronics Co.'s production facility in Tanjeong, South Korea, claimed to have built the world's largest transparent plastic display--an active-matrix LCD with a diagonal measuring 5 inches [see photo, " On Display"].
Other companies, including Acellent Technologies, Nanosolar, and the Palo Alto Research Center, all in California, are developing flexible-circuit technologies for structural monitoring, solar energy conversion, and X-ray imagers, respectively [see photo, " Pixel Perfect"]. And Philips Research, in Eindhoven, the Netherlands, along with E Ink, continues its promising work on flexible, paperlike displays. These displays could soon be used in electronic books and newspapers, as shown in the opening illustration.
Encouraging as these advances are, researchers still have obstacles to overcome in their quest to make large-scale flexible electronics the next big thing. Besides getting the cost for producing plastic circuits down to pennies, rather than dollars, per square centimeter, they also need to find a plastic-compatible transistor technology that can switch millions of times a second, rather than thousands of times a second. Faster transistors would allow a broader range of applications for flexible electronics.