VTT Is Developing Printed Sensors

By Rhea Wessel

June 11, 2007—If and when passive RFID tags ever become printable, the tags will not replace their silicon cousins, according to Heikki Seppä, a research professor at the VTT Technical Research Center, a nonprofit independent contract research institute in Finland.

"If they come," Seppä told attendees earlier this month, at IntertechPira's Printed RFID conference in Frankfurt, Germany, "printed RFID tags will only partly replace silicon-based tags. It is more likely that new applications for item-level tagging will be generated by the technology." In the meantime, VTT is developing a printed sensor for companies that could be used to make hybrid RFID tags designed to marry silicon RFID chips with printed sensors and antennas.

Heikki Seppä

Printed passive RFID tags, Seppä postulated, will have limited use because many applications require long-distance reads. Such tags are likely to have short read distances if composed of polymer transistors, which operate at a low speed due to the limited mobility of the transistors' electrons. That, he said, is why printed RFID tags may only partly replace silicon-based high-frequency (13.56 MHz) tags. In the long run, Seppä noted, they could also partially replace UHF tags, though he said that day may never come.

"It will be a very long time before we can print a high-frequency tag," Seppä said, adding, "Of course, something may happen in the research labs. We're trying to make transistors out of nanoparticles." Nanoparticles represent a "promising new opportunity" for replacing polymers in transistors, he stated, because they offer greater possibilities for creating a surface for more highly conductive materials than polymers do; in addition, he added, the material could have better mobility than that of polymers. He cautioned, however, that the concept still must first be tested.

"We start with nanoparticles," Seppä said, "then we sinter them, and then we have more mobility." When nanoparticles are sintered, they are heated until the particles adhere to one another. "By sintering," he explained, "you are making a real connection between particles. They are connecting together physically, and then they're conductive."

Standards are a second hurdle facing the development of printed RFID tags. Now that the EPC Class 1 Gen 2 standard has become widespread for silicon-based tags, researchers in plastic RFID are aiming to meet these standards in producing a tag. "It will be difficult to meet these standards," said Seppä, indicating that separate standards for printed RFID tags would benefit the market.