Organic transistors - the future for food freshness?

An electronic device that tells the supermarket when food has gone bad could be gracing the shelves in the near future, according to new research in the US.

In response to the statement "What we really want is communication between the food and the supermarket,"​ Dr. Subramanian, a scientist at the University of California, has set out to develop sensors and other electronic devices that could be incorporated into food packages to provide and transmit information about inventory and freshness. Such devices would use organic rather than silicon-based transistors, the New York Times reports this week.

According to the report the devices will aim to be far from prohibitive in cost. "We have to make them so cheap that you're willing to throw them away,"​ said Dr. Subramanian.

The cheapest electronic devices that can be used today to track a package, known as radio frequency ID tags, cost a dollar or more because they use conventional silicon circuits, which require expensive lithography and processing in a clean environment.

An organic or plastic circuit, however, could theoretically be printed directly onto a package's surface in one step by an ink-jet printer at a much lower cost, perhaps less than a penny, the report continues. Made of carbon and hydrogen as opposed to inorganic silicon, such circuits are soluble and can be attached to organic substrates like plastic, paper or even cloth - materials that would never survive the high temperatures required to make circuits out of silicon.

"They're inherently printable,"​ said Dr. Subramanian, who expects his team's prototype inkjet printer to be printing full circuits by this summer. A supermarket radio frequency tag requires about 5,000 transistors for its processor, compared with about 40 million for Intel 's Pentium 4. It also requires power circuitry and wireless communication circuitry, consisting of inductors and capacitors.

"There are still things we have to solve,"​ Dr. Subramanian said."We're literally where the semiconductor industry was in the late 60's or early 70's - we don't quite understand them, but we can kind of make them work."​

The processing speed of organic transistors is vastly inferior to that of silicon devices. Organic circuits can also become useless within days or weeks if exposed to air or water.

Depending on the application, however, performance may not matter so much. A sensor designed to detect the presence of E. coli bacteria in a package of meat, for example, may work fine at the slow speeds of organic transistors. "It's O.K. if it takes a few minutes to derive that information,"​ said Thomas Jackson, a professor of electrical engineering at Pennsylvania State University. "You're not asking it to control the launching of nuclear missiles or anything like that."​

But before organic transistor products can be marketed, researchers must break through barriers to performance, stability and manufacturing cost. In addition to small academic teams like Dr. Subramanian's, big companies like I.B.M, Lucent , Mitsubishi , Chemicals, Philips and Xerox are working on such devices.

To compensate for the deficiencies of organic transistors, according to the New York Times report, Dr. Subramanian's team is focusing on improving circuit design and manufacturing. By simplifying the circuit design for the radio frequency tags, he hopes to lower their performance requirements.

His team is experimenting with spray coatings to extend the stability and longevity of the circuits once they have been printed on a package. And he is starting to think about the infrastructure that will be needed to support the supermarket sensors.

"I still have to convince every supermarket in the world to use this thing, even if we do it at under a penny,"​ he said.