Thin-film RFID chips are made on plastic foil, with organic or oxide thin-film semiconductors. Until now, RFID tags with such thin-film chips on plastic were based on a tag-talks-first principle: as soon as the RFID tag gets powered from the RF field of the RFID reader, it transmits its code to the reader. But in retail applications, many tags will try to contact the reader at the same time, requiring an effective anti-collision mechanism. Such a scheme has never before been implemented; tag-talks-first RFID anti-collision measures have been limited to about maximum 4 tags and come at the cost of a slow reading time.
"With this technology," says Paul Heremans, imec director large-area electronics and coordinator of ORICLA, "we are for the first time able to realize a reader-talks-first low-temperature thin-film transistor (TFT) RFID circuit. When the RFID reader first powers and contacts the tag, it transmits a clock and identification data. The tag then uses this data and clock to determine when to send its code. This mechanism for the first time allows implementing a practical anti-collision scheme for thin-film RFID tags."
For this new RFID tag, a complementary hybrid organic-oxide technology was used, combining a 250°C solution-processed n-type metal-oxide TFT with typical charge carrier mobility of 2cm2/Vs with a pentacene p-type TFT with mobility of up to 1cm2/Vs. A high-k Al2O3 dielectric was used, which increases the transistors current drive.
Thin-film electronics are circuits that are made up of organic and metal-oxide molecules. They have the potential to be produced very cheaply, with print-like processes on thin plastic sheets. One of the driving forces of this industry is the ambition to create intelligent RFID tags that are at the same time intelligent enough and cheap enough to be printed and used on mass-produced retail products.
The realization of this technology is supported by the EU FP7 project ORICLA. The project partners are the project coordinator imec (Belgium), Holst Centre – TNO (The Netherlands), Evonik Industries AG (Germany), and PolyIC (Germany).