UHF IGZO Schottky diode opens the route towards low-cost passive thin-film RFID tags

December 12, 2012 // By Julien Happich
imec presented what the company claims to be the world-first ultra-high frequency Schottky diode based on amorphous IGZO (Indium-Gallium-Zinc Oxide) as semiconductor.

This breakthrough will enable the development of thin-film passive UHF (ultra-high frequency) RFID tags to replace item-level bar codes.

UHF RFID tags have a long reading range (5 to 10 meters) and employ small, printed, low-cost antennas. Compared to Silicon, IGZO based technology has the potential to result in a low-cost solution, since IGZO thin film active devices are fabricated using a cheaper, low-temperature process. This allows the development of chips directly on plastic foils, such as on product packaging.

The diode is the fundamental block in the power supply generator of passive, i.e., battery-less tags. It rectifies the carrier wave captured by the antenna and feeds the power supply on the tag. IGZO is an amorphous semiconductor with gap states that impede the formation of a stable Schottky barrier, irrespective of the metal used. To achieve a stable Schottky barrier, imec developed specific plasma and anneal treatments that alter the chemistry of the Schottky interface. The resulting IGZO Schottky diodes have a rectification ratio of up to nine orders of magnitude (at +1V and -1V), current densities of up to 800A/cm 2 at forward bias of 1V, and a cut-off frequency of 1.8 GHz. When incorporated in a single stage rectifier, the cut-off frequency is 1.1GHz. The rectifiers are demonstrated to operate at ultra-high frequency (868MHz) with low losses.
This research on thin-film UHF RFID technology is supported by the EU FP7-ICT-247798 project ORICLA. Project partners include the project coordinator imec (Belgium), Holst Centre – TNO (The Netherlands), Evonik Industries AG (Germany), and PolyIC (Germany).

Visit imec at www.imec.be