Semiconductor in a can: the future is fluid

The printing of plastic transistors will turn the current semiconductor paradigm on its head, making it possible to manufacture integrated circuits for millions, instead of billions, of dollars, industry experts predict.

Carbon-based semiconductors that can be deposited in liquid form,

combined with the resolution power of inkjet systems, could allow manufacturers to literally spray new-age semiconductor materials onto a flexible sheet and make integrated circuits accordingly, said Steve Kovacic, director of research and development at SiGE Semiconductor in Ottawa.

When this ability hits the market, it will touch off “a major paradigm shift in semiconductor manufacturing that would have some incredible implications,” he said, adding cheaper costs could mean North American and European semiconductor companies will soon be able to afford the manufacture of integrated circuits locally rather than rely on offshore fab facilities.

“When you think about a major semi facility now, you’re talking about a capital investment in the billion-dollar mark,” Kovacic added, referring to the multi-billion-dollar wafer fabrication plants in such locations as China and Taiwan.

But the cost of printing plastic transistors would mean spending millions instead of the billions required for conventional silicon-based counterparts, said Beng Ong, a research fellow who leads a team at the Xerox Research Centre of Canada.

The team recently revealed that it is one step closer to bringing flexible roll-up television screens and computer displays to reality, thanks to a combination of new materials it has developed for printing the conductor and dielectric components of a plastic circuit.

“We’re aiming for a series of applications that could currently be serviced by silicon technologies but cost an arm and a leg for the consumer,” said Ong, who discussed his findings at a recent conference hosted by the Materials Research Society. “The plastic transistor circuit would be able to do it at a cost that is orders of magnitude lower.”

But in order for this to become a reality, plastic transistors must be made via liquid processes such as inkjet printing, screen or stencil printing, and spin coating, said Ong. The other requirement is to be able to do the printing in ambient conditions, as opposed to extracting oxygen from the room, a costly procedure, he explained.

Typically, the electrical properties of most liquid-processable organic semiconductors degrade when exposed to atmospheric oxygen, said Ong.

Xerox claims to have overcome both of the manufacturing and open-air dilemmas.

The first products to be commercialized based on the plastic/inkjet model will likely be some type of flexible electronic paper that is thinner than PDAs, as well as radio frequency identification tags. While the Xerox team has all the necessary materials in its lab, the first product likely won’t reach the market for another couple of years, said Ong.

In the meantime, groups like the Canadian Cattle Identification Agency eagerly await the release of new-generation RFID tags. The agency currently uses a combination of bar code and RFID ear tags on Canadian cows in order to track livestock movements in the national food supply chain. The aim is to completely phase in RFID tags by 2005.

But the biggest stumbling block is the cost of each tag, estimated at $5 each. While costs are expected to decrease to $3 or even $1 per tag if purchased in bulk, this is still a big challenge, experts said.

Consequently, the cattle agency is “continually monitoring any new technology that is out there,” said Julie Stitt, manager of the agency’s national ID program. “As (RFID tags made with plastic transistors) become available, our system will be able to accommodate them. We’re moving toward it, we’re keeping on top of it, but it’s not (available) yet. We wish it was.”

Under a National Institute of Standards and Technology’s Advanced Technology Program grant, Xerox is working with Motorola Inc. and Dow Chemical Co. in developing plastic integrated circuits for electronic applications. Using the Xerox team’s materials, the Palo Alto Research Center is inkjet printing active-matrix addressed arrays as backplane switching circuits for displays, while Motorola is fabricating plastic circuits for applications using printing technologies.

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