Printed RFID Circuits with Polymer Electronics

Smart labels and displays are expected to be the first two applications of such polymeric circuits because, initially at least, they will act too slowly to be used in, say radar or television, and they will have a large footprint compared to silicon.

 

Philips demonstrated a working polymer smart label in their laboratory three years ago and now over 30 companies have major research programmes in this arena including Motorola, IBM, Dai Nippon Printing, Canon, 3M, Xerox, Epson, PolyIC, Lucent and DuPont.

 

However, the first generation of monolithic memory circuits in plastic produced by Philips worked but the complex organic molecules used to replace silicon usually degraded and stopped functioning after only a few days. More recent plastic circuits have had a practical lifetime of several months, which is sufficient to make them useful for short-lived consumer products and some successfully employ around 1,000 transistors.

 

These new plastic transistor circuits use pentacene and polyaniline to provide the conducting and insulating properties that are necessary to fashion electronic components. This is because organic compounds such as pentacene are what are called "conjugate molecules". They have a long chain-like structure, with some of the electrons in the molecule free to move up and down the chain, so providing its conducting properties.

However, Plastic Logic in the UK hopes to leapfrog all their timescales, by using different polymers and processes (e.g. an inkjet printing rather than a spin coating technique). The company's enthusiasm has led the Financial Times to project $10 billion of sales of polymer electronics, including LEDs and displays in 2004 vs $1,000 billion of sales of silicon chips in that year (FT 27.11.00). We think volume production at low price after 2005 is a more prudent projection.

 

Polymers are poor conductors, so to work at frequencies used by most smart labels, or even frequencies of 125 KHz, will require the size of the plastic chip to be reduced, to increase its conductance. However, this significantly increases the price of producing the circuit, so much so that the price of the silicon chip is comparable. However, Plastic Logic use a completely different method of creating the plastic chips, which allows them to obtain a high resolution at a low price. The FT thinks geometry will be only 25 to 50 microns but price "a few cents" each per plastic chip device.

In parallel with these developments, there will doubtless be other new and radically improved chipless technologies appearing. Major companies backing chipless now include Checkpoint, Raytheon, International Paper, Appleton Papers, Illinois Toolworks and Mitsui. Small companies with intellectual property in digitally-encoded chipless include, in Japan, Navitas and Miyake and, in Europe, Flying Null, Remoso and BTG. In the US there is CW Over and RFCode and several Israeli companies are doing exciting things. That may well mean major breakthroughs at any time. Most of the proponents of chip smart labels are noticeably absent in developing chipless varieties because they are busy and concerned to leverage their chip skills.