Beyond Bar Codes: Tuning up plastic radio labels

Electronic labels made from plastic semiconductors can now pick up and respond to radio signals at a frequency suitable for use on products. At an electronics conference in San Francisco this week, two European industrial-research teams described plastic radiofrequency-identification (RFID) prototypes with those advanced capabilities.

Although silicon-based RFID tags are already in wide use—for instance, in so-called smart cards used to pay mass-transit fares—the new developments bring closer the prospect of RFID tags becoming as common as bar codes, or perhaps even more so, the researchers say. Besides labeling consumer products, plastic tags might make novel electronic tracking and transactions possible, from computer monitoring of what’s in the refrigerator to mail routing by means of smart address labels.

To make that leap, tags must become much less expensive than is possible if they’re made of silicon. Hence, the move to plastic.

Until recently, developers of all-plastic tags have turned out only low-frequency devices. Mainly because of bulky antennas, they’re unsuited for consumer applications. However, some engineers have created components that operate at high frequencies, such as the plastic diode reported last year by researchers in Belgium (SN: 8/13/05, p. 100: Available to subscribers at Electronic Leap: Plastic component may lead to ubiquitous radio tags).

At the 2006 IEEE International Solid-State Circuits Conference, researchers from the Netherlands unveiled an all-plastic device that operates at the sought-after, industry-standard frequency of 13.56 megahertz (MHz). When queried via radio waves by a nearby gadget known as a reader, the device responds with an eight-bit code, says Eugenio Cantatore of Philips Research Laboratories in Eindhoven.

“It’s not just one or two elements that we’ve proven in the lab. We’ve proven the entire thing,” says Philips’ engineer Leo Warmerdam.

In another talk at the conference, Markus Böhm of the company PolyIC in Erlangen, Germany, described an experimental 13.56-MHz tag that PolyIC produced last fall. This device sends back just one bit of information. “It’s just a very simple signal saying ‘I’m here,'” says PolyIC physicist Wolfgang Clemens.

The Philips researchers made their device from the plastic pentacene and exploited its property of increasing the speed of electricity’s flow—and therefore the device’s frequency—when the voltage is raised.

The PolyIC team used a different plastic and formed it into a diode similar to the one invented in Belgium. Because the diode contains thin layers, electric charges have short distances to travel and the circuit operates quickly, Clemens explains.

Despite such progress, many hurdles remain before plastic RFID tags will show up in supermarkets or mailboxes. For instance, neither team used printing technology to make its device—a must for inexpensive production. Also, neither tag broadcasts its signal more than a few centimeters.

Still, each of the new devices “constitutes an advance toward making a manufacturable RFID tag,” comments Klaus J. Dimmler of Organic ID in Colorado Springs, Colo.

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