GOOD old-fashioned cash is to go down the electronic route, now that it is possible to stamp simple electronic circuits directly onto banknotes.
Modern banknotes contain up to 50 anti-counterfeiting features, but adding electronic circuits programmed to confirm the note's authenticity is perhaps the ultimate deterrent, and would also help to simplify banknote tracking.
Silicon-based electronic circuits are clearly too thick to be incorporated into thin and fragile banknotes, but semiconducting organic molecules might be a viable alternative.
A team of German and Japanese researchers created arrays of thin-film transistors (TFTs) by carefully depositing gold, aluminium oxide and organic molecules directly onto the notes through a patterned mask, building up the TFTs layer by layer.
All this is done "without aggressive chemicals or high temperatures, both of which might have damaged the surface of the banknotes", says team member Ute Zschieschang from the Max Planck Institute for Solid State Research in Stuttgart, Germany.
The result is an undamaged banknote containing around 100 organic TFTs, each of which is less than 250 nanometres thick and can be operated with voltages of just 3V. Such small voltages could be transmitted wirelessly by an external reader, such as the kind that communicates with the RFID tags found on many products (Advanced Materials; DOI: 10.1002/adma.201003374).
The team's technique has been tested on US dollars, Swiss francs, Japanese yen and Euro notes. Although the researchers have yet to work out how the organic electronics could be harnessed as an anti-counterfeit measure, the circuits are able to perform simple computing operations.
