Printed RFID tags have been one of the most important drivers of the new electronics.
PolyIC in Germany is one of the companies working in this area for more than 5 years now. An update on the current status and recent progress was given by Dr Wolfgang Clemens, head of the applications department within PolyIC, at the IDTechEx Printed Electronics Conference & Exhibition in Dresden, April 2009.
The main product the company is working on is a 13.56MHz tag, for use in identification, logistics and automation applications - pretty much the same where standard RFID tags are used, which are based on a sophisticated piece of silicon. Since the PolyIC tag can be manufactured using highly efficient roll-to-roll processes, it is potentially cheaper than the silicon versions, thus opening applications where the other versions are seen as too expensive.
The price targets of a few cents per tag and when this can happen, was left open. The long term goal is to get EPC tags - this will require a lot of further effort, but for the time being PolyIC has a 64bit version in the lab. Recent field tests within the project PRISMA were carried out with a tag containing just an organic diode, with no possibilities to store any information on the tag. A 4bit version is in early production state.
For the communication, specialized and proprietary readers are needed, which are developed by PolyIC in close cooperation with Siemens AG, Munich.
One of the major breakthroughs on the way to improved performance of printed RFID is the use of CMOS-like structures, i.e. an electronic design using p- and n-type semiconductors. This will lead to less power required, and this means longer reading distances than with the tags seen so far. Those need to be in intimate contact with the reader, while the new versions allow 4.5 cm distance. The material used for the p-type transistors is P3HT, a commercially available and "established" thiophene derivate. Several companies work on n-type conductors, which are more difficult. PolyIC uses ActivInkTMN1200 by Polyera, a symmetric perylene-dicarboximide derivate with cyano-groups (PDI8-CN2), that is soluble, e.g. in chloroform, and can be spin-coated and inkjet printed.
All other parts of the CMOS RFID tag, which is in lab status now, are made of inorganic materials: The antenna is copper, to achieve highest possible performance in the electromagnetic field, and source and drain of the transistors are made of gold. The chips are made in a separate process, and are applied to the antenna after separation and testing. The aim is to have all processes compatible, so that a continuous manufacturing becomes possible.
At the exhibition booth, PolyIC demonstrated another product line, called PolyLogo. By using a simple, printable display, more functionality is possible, like the direct visual feedback after authentication or validation of origin checks. The display is made of electrochromic ink, and it can be driven by the energy of the electromagnetic reader field. This enables a quite simple and potentially low-cost label for many new applications.
Top image: Printed tags in security documents (Source: Bundesdruckerei).