Polymer-based RFID tags are here to stay. But, as Brian Holliday explains, one company is aiming to manufacture the electronic components they require using high-volume printing techniques.

A specialist company in the field of polymer electronics has introduced the world’s first fully functioning polymer-based eight-bit RFID tag that operates at the industry standard radio frequency of 13.56MHz.

While this particular transponder chip has been produced using conventional clean room processes, the goal for its manufacturer – PolyIC – is to manufacture low cost electronic components for RFID tags using high volume printing techniques, with the first fruits of this labour due to be unveiled later this year.

The market capacity for a step-change in technology of this magnitude is substantial. For RFID alone, the potential to replace optical barcodes is now tangible. Using printed polymer technology, the application of RFID will be broadened to price sensitive mass markets such as the packaging of consumer goods, brand protection, anti-theft devices, simple identification, aviation baggage tracking and electronic ticketing.

In fact, many of these applications are currently being assessed as part of the three-year printed smart labels (PRISMA) project being promoted by the German Federal Ministry of Education and Research. PolyIC is co-ordinating the project.

RFID tags based on printed polymer electronics will also bring with them a higher level of ‘intelligence’, making it possible to differentiate between separate product items. The vision of individual yoghurt pots with RFID on supermarkets shelves could soon become a reality.

Affixed to products, these radio chips can open up new possibilities in terms of delivery, inventory management and labelling of goods, particularly when combined with software such as Simatic RF-Manager – a new product from Siemens Automation & Drives. This manages read/write devices, collects and compresses RFID data and makes it available to the merchandise information system, potentially recording entire goods flows.

One of the great advantages of printed electronics is its ease of integration into products or packages. For example, they can be applied easily to flexible packaging materials by laminating or labelling, or by direct application. Thus, as a first step it becomes possible to apply labels with printed electronics, for example as an RFID tag, on to a product. Secondly, printed electronics can be integrated directly into the package and thus become ‘intelligent’ or ‘smart’ products. This means that packages/products can communicate through their RFID tag with a respective reader – hereby the vision of ubiquitous computing or the so-called ‘internet of things’ will be made possible.

Conceivable applications for this technology include intelligent fridges, washing machines or better automation in production processes. The automatic supermarket checkout is another potential reality, where customers will simply move their shopping trolleys past a radio scanner that automatically registers everything the customer has collected in an instant.

Since its formation in 2003, PolyIC – a joint venture between Siemens and Leonhard Kurz – has been striving towards the production of flexible, low cost, pervasive, disposable polymer electronic components for use in RFID tags. Just three years later, the company’s goal is set to become a reality, a development that will change the face of RFID forever.

So how does it all work? The astonishing electronic properties of polymers are derived from their chemical structure, which contain so-called conjugated polymer main chains that consist of a strictly alternating sequence of single and double bonds. As a consequence, these polymers possess a delocalised electron system that provides semi-conducting properties. Following chemical doping processes, polymers that are fully conductive can then be created.

Conclusions from extensive research have established that soluble polymers that become fluid in a special dissolvent can be used in a printing process as electronic ink, releasing the potential to revolutionise the production of electronics. With this process, it is possible to fabricate low cost electronics in a continuous printing process on flexible polyester (PET) foil substrate, more or less similar to the way a newspaper is printed on paper.

To print a functioning transistor, an organic semiconductor such as polythiophene and an insulator are required. These consist of polymers and are printed as liquids. Printing is the most direct way of achieving structured layer deposition and is much more attractive to manufacturers in terms of volume and costs than conventional electronics production processes.

Polymer electronics are thin and flexible and can be printed on to polyester film in several layers. For this process, different polymers and printing techniques are used. PolyIC is using continuous printing methods that, in the long-term, could realise production costs of less than one cent per chip. These methods are essentially based on established printing techniques such as:

* Flexoprinting: a high-pressure method that is especially suited to printing on plastic substrates.
* Offset printing: a flat printing technique that makes high resolution possible.
* Gravure printing: a low pressure printing method that permits high volumes and the use of organic dissolvent.
* Rotary screen printing: a method that allows printing in thick layers.
* Coating methods: diverse techniques to apply homogeneous and thin layers.

Of course, these methods have to be adapted to the special requirements of polymer electronics, such as exceptionally high resolution, high cleanliness and precision of register. PolyIC has developed suitable production techniques for polymer electronics based on high volume roll-to-roll processes using flexible substrate films.

To design printed electronics, a number of different materials are required that have completely different features, but which need adjusting to suit one another (Fig. 1). The most important materials are: the substrate – a flexible polyester film on which the electronics are printed; the conductor – electrical conducting polymers for electrode structures; the semiconductor – electrical semi-conducting polymers for transistors and diodes; and the dielectric – electrical insulating polymers to divide between semi-conducting and conducting polymer layers.

Typically, the distance between the two conductors is less than 0.05mm. Considering the nature of the material, some could be forgiven for raising an eyebrow concerning suitability. However, these chips will even function after being stored for two days at a temperature of 60°C and 100 per cent humidity, and will continue to work until temperatures exceed 120°C.
Printed electronic applications have enormous market potential. In a 2005 study, the British market research company, IdTechEx, estimated the market for organic electronics at 30 billion in 2015. Printed RFID tags will undoubtedly constitute a considerable part of this market. PolyIC intends to gradually produce more complex circuits with several thousand transistors and up to 128-bits of memory. Today's barcodes can typically store 44 bits.

Brian Holliday is General Manager Industrial Automation Systems at Siemens Automation and Drives. For more information, visit www.siemens.co.uk/automation