Polymer transistors show their soft side.
What if electronics could shed that hard edge? What if soft polymers and organic materials could offer sufficient electronic control to spawn a new generation of lightweight, flexible machines that could bend to human needs in ways that current products cannot?
Pursuing this vision, Francis Garnier, a materials scientist at the Laboratoire des Materiaux Moleculaires in Thiais, France, and his colleagues tell of their efforts to make flexible plastic electronic circuits.
Reporting in the Sept. 16 Science, they describe a method for making field-effect transistors entirely from organic polymers, using what they call "printing techniques."
"These are very simple, low-energy manufacturing methods compared to what people usually use to make amorphous, silicon-based devices," Garnier says. "Think of printing large circuits continuously on a roller, like a magazine."
Ordinarily, producing a computer chip requires powerful vacuums and high temperatures to deposit metallic materials on a silicon substrate. Such processes are cumbersome, energy-draining, and prone to error. Impurities often cause manufacturers to reject large numbers of chips. The new printing technique bypasses many of these difficulties, Garnier says.
Though researchers have managed to make electrically conductive polymers in the past, both as electroluminescent diodes and as other forms of transistors (SN: 3/30/91, p.207; 10/16/93, p.246), they have been unable until now to rid the devices completely of metal attachments.
"This has been a problem,"' says Garnier, "because the polymers are flexible. So when they bend, the rigid connections tend to break."
The new method does away with metallic electrodes entirely, the group reports. As a result, the transistors not only show reliable electrical characteristics, such as low resistance and high current output, but also "are insensitive to mechanical treatments such as bending and twisting."
In a series of tests, the scientists rolled, twisted, and bent the devices as much as 90[degrees] Yet they kept on working. By contrast, other rigid devices, including various organic transistors with metallic connections, stopped functioning when bent that much.
From such organic polymer electronics, Garnier envisions "pocket-sized |smart' cards with plastic logic circuits." He also sees "car and airplane windshields that can display information," as well as "a large flat panel display, like a television, that you could roll up."
"Even 5 years ago, people in the field said that to make good transistors only from plastics was totally unrealistic," he adds. "Now here it is."