News FocusMATERIALS RESEARCH SOCIETY MEETING

Printable Electronics That Stick Around

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Science  30 Apr 2004:
Vol. 304, Issue 5671, pp. 675
DOI: 10.1126/science.304.5671.675

SAN FRANCISCO—Technology and basic science mingled at MRS's spring meeting, held here 12 to 16 April with the International Union of Materials Research Societies' 9th International Conference on Electronic Materials

Plastic electronics are big business these days. They are still sparse on the sales floor, but electronics giants in Japan, Europe, and North America are all pushing hard on the technology to make ultracheap printable electronics for everything from smart cards and product ID tags to the electronic drive circuitry for large-screen displays. Researchers have shown that they can make many of these devices with materials that already exist. But among the deviling details, most of today's plastic electronic materials that can be printed from liquids—the cheapest manufacturing method—are unstable in air and quickly degrade. At the meeting, researchers at the Xerox Research Centre of Canada in Mississauga, Ontario, revealed hints and a few details of far-more-stable materials to come.

Xerox materials scientist Beng Ong reported that his team has come up with air-stable versions of printable semiconductors, conductors, and insulators, all three of the electronic elements needed to make circuitry. And even though Ong said he was unable to reveal the full details of the conductor and insulator, others in the field are hailing the achievement. “It will make it easier to make long-lasting devices,” says Zhenan Bao, a chemist and organic electronics expert at Stanford University in Palo Alto, California. “That is critical for devices to be used as commercial products.”

Xerox's new semiconductor builds on an advance that Bao and colleagues reported in 1996, when she was at Lucent Technologies' Bell Laboratories in Murray Hill, New Jersey. They devised a polymer called regioregular polythiophene, which was liquid-processible and capable of switching from a good to a poor carrier of electrical current, an essential requirement for semiconductors. Unfortunately, the material had to be processed in an inert environment and carefully sealed, because oxygen molecules reacted with the plastic, causing it to turn into a metal-like conductor with a current-carrying prowess that could not be turned off.

Let us spray.

Plastic transistors created with an ink-jet printer may herald a new wave of low-cost electronics.

CREDIT: PALO ALTO RESEARCH CENTER

Lucent's regioregular polythiophene contained numerous rigid tails designed to help orient the polymer to form continuous sheets, an arrangement that improves its current-carrying ability. At the meeting, Ong reported that removing all but one of the tails reduces the polymer's ability to react with oxygen, yet the polymer still maintains its ability to arrange itself on a surface. The change makes the material drastically more stable in air without sacrificing its semiconducting behavior.

Ong said that because Xerox is still trying to patent its new conductor and insulator, he could not give complete descriptions of these materials. But he did say that the conductor is an organic-inorganic hybrid material with an electrical conductivity as much as 100,000 times higher than the conventional plastic material used today. And the insulator—an organic polymer—performs up to three times as well as conventional materials while being more stable in air.

Xerox has already used an ink-jet printer to pattern its semiconductor to make working transistors (above). And company researchers are now working to print their new conductor and insulator as well. If they can put all the pieces together, they may soon be able to turn out electronics as easily and cheaply as printers today generate paper copies.

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