Volume 85 Issue 28 | pp. 20-21
Issue Date: July 9, 2007

Cover Stories: Materials In Motion

Tuning In

Printed RFID tags aren't ready for ubiquity, but niche applications are within reach
Department: Science & Technology
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Shopping Spree
The ultimate goal of printed RFID developers is enabling single-item tagging at retailers.
Credit: PolyIC
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Shopping Spree
The ultimate goal of printed RFID developers is enabling single-item tagging at retailers.
Credit: PolyIC

SOMEDAY, the radio-frequency identification technology that allows motorists to breeze through a toll plaza may offer the same convenience to a consumer buying a can of beans. But even though RFID is becoming commonplace, printed RFID—the technology that would enable RFID to replace supermarket bar codes—is still a work in progress.

In RFID, an electromagnetic pulse sent by a reader induces an electric current in the transponder, or tag. The tag then sends the information stored in it back to the reader in its own electromagnetic pulse.

The vast majority of RFID tags available on the market are based on silicon chips. Such tags are technically powerful, but they are too expensive for large applications such as supermarket product coding.

Silicon-based tags can be made today for about 15 cents apiece. Wolfgang Mildner, managing director of PolyIC, a Fuerth, Germany-based developer of printed electronics technology, says chip makers will lower the cost of silicon circuits in RFID the same way they do for computer chips: by making the chips smaller so more can be made on a single silicon wafer.

As chips shrink, however, integrating them with other components, such as the antenna, gets tougher, Mildner explains. "You can get the chips cheaper and cheaper, but the integration costs get higher," he says. So there is a minimum cost level, about 5 cents per tag, according to Mildner and others.

Yet, for bags of candy and cartons of milk, 5 cents per tag is too expensive, says Peter Eckerle, project manager at BASF Future Business. He says RFID can be rolled out in such applications only if the tags cost about 1 cent apiece. This won't happen unless technologies are developed to print the entire circuit on a flexible substrate in a roll-to-roll process, he says.

Indeed, several companies have made great strides in developing printed RFID technology. PolyIC demonstrated a 13.56-MHz tag in 2005. And last September, PolyIC says it produced "mile-long" rolls of printed electronics. The company aims to launch its first commercial products later this year. Last year, Philips also demonstrated a 13.56-MHz tag; the company, however, canceled its printed RFID program when it spun off its semiconductor business last year as NXP. Colorado Springs, Colo.-based OrganicID, now a part of paper and packaging company Weyerhaeuser, is also working on tags based on 13.56 MHz.

Raghu Das, chief executive officer of the Cambridge, England-based printed electronics and RFID consultancy IDTechEx, says the industry will need many more breakthroughs before printed RFID tags reach grocery stores. "It will take about four or five more years to overcome the technical challenges that these companies are facing to really enable it to be realizable for very large markets," he says.

IN 2006, the global market for RFID, including readers and other equipment, was about $5 billion, Das says. So far, the spending on printed RFID is negligible. By 2015, he expects the total RFID market to grow to $24 billion, with printed RFID representing less than $1 billion of that.

Companies such as BASF concede that progress with printed RFID is slow. In 2005, BASF decided to put more resources into printed RFID after the company, working with the German technology developer Printed Systems, demonstrated printed ring oscillators, an RFID component, according to Eckerle. But he acknowledges that success is still a ways off. "For a number of reasons, I am now reluctant to assume that fully printed RFID tags will become a reality any time soon," Eckerle says. Although rudimentary RFID tags are already available, he says, printed RFID devices comparable to silicon-based tags—with frills such as a 96-bit memory—are seven to 10 years away.

The primary challenge experts cite is the yield of the printing processes, or how many transistors can be printed on a circuit without defects, because if the transistors don't work, the tag fails. "When I ask people what their yields are, they never tell me, which makes me think it is pretty bad," Das says.

Even a 16-bit tag requires close to 1,000 transistors, Eckerle says. Thus, a transistor yield of about 99.999% is required to produce tags with a 99% yield. "So far, the printing processes are not advanced enough to allow production of transistors anywhere near 99%," he says. "That basically means that very few tags will work."

The challenge of reducing defects increases as transistor size shrinks. Mildner says PolyIC's first product will have hundreds of transistors. To go further, the roughly 12,000 transistors on a silicon tag will require further miniaturization, down to circuit lines on the order of micrometers. He says this can be achieved only through better semiconductor materials. The company is looking to evolve today's polythiophene-based materials for subsequent generations of chips, he adds.

BASF is focusing on gaining access to a comprehensive collection of polymer semiconductor materials that can be applied to printed electronic circuits. In February, BASF signed an agreement to manufacture polythiophene-based organic semiconductor materials developed by Lincoln, Neb.-based Rieke Metals. Then in April, it signed a development agreement with Polyera, a Skokie, Ill.-based organic semiconducting materials start-up.

Another technological hurdle to overcome is frequency performance. Although technology developers have demonstrated printed chips operating at high-frequency range, they have yet to succeed at the ultra-high-frequency range-about 900 MHz-that is being adopted by retailers for RFID.

Michael Heckmeier, research director in charge of printed electronics at Merck KGaA, says improving the frequency performance will depend on the mobility of the semiconductors in the tag. Mobility is a measure of how readily electrons move through a semiconductor. "We have nice mobilities that are realized in the lab," he says. "The big challenge is bringing them into the pilot plant and then to mass production."

Improvements in mobility will come from advances in semiconductor materials, Heckmeier suggests. He says future generations of printable semiconductors won't necessarily be polythiophene-based or even organic.

According to Heckmeier, Merck is working with the Technical University of Darmstadt, in Germany, to develop inorganic semiconductor materials for printed electronics. "The potential is there to improve the mobility further," he says. "Maybe hybrid or inorganic printed systems could be better than a wholly organic system in the long run."

EVEN THOUGH more work is needed for the big markets, IDTechEx's Das says potential markets exist for the rudimentary printed tags available today. For instance, they can be used to combat counterfeiting, because their slim profile and physical flexibility are suited to documents and bank notes. "In this application, the limitation of maybe four bits of memory might be okay because all you want to know is if it is there or not," he says.

One natural application is concert tickets, a market where counterfeits can pop up, according to Eckerle. "Given the prices that the tickets are being sold for," it is no problem to pay 50 cents per ticket for the tag if people can make sure they are getting the original ticket, he says. For other markets, he cites a trial program at British retailer Marks & Spencer to tag clothing to ensure that different sizes are kept in stock.

The beginnings of printed RFID may seem humble, but another industry that is now riding high after a similar slow start offers encouragement. In the 1960s, the chip maker Intel "only had a few thousand transistors, and today we talk about millions of transistors per chip," Mildner recalls. "We are just at the very beginning of organic electronics, and we have to go through similar developments."

 
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