What Would You Do With a $100 Bill Covered by Invisible Transistors?

Banknotes could soon get a layer of printed electronics, and wireless readability, to make faking essentially impossible.

What Would You Do With a $100 Bill Covered by Invisible Transistors?
dollar circuits


Cash counterfeiters have had a hell of a good run. Now the fakers may get a serious sprint for their money.

The battle to make paper currency un-counterfeitable has already seen some cutting-edge science in action, but the latest efforts may be the highest-tech yet: Banknotes could soon get a layer of printed electronics, and wireless readability, to make faking essentially impossible.

The new tech is coming out of research in Germany and Japan, and it involves our old future-tech friends–transparent, flexible microelectronics.

Anti-counterfeiting measures in modern paper currency include tricks like holograms, never-drying ink, textured printing, un-copyable colors, watermarks, woven-in fibers, and many more special features–each incrementally added to the mix as counterfeiters get cleverer at copying the previous generation of defenses. Despite all these advances, counterfeit cash still thrives–in 2000 alone the Secret Service seized over $126 million in fake bills produced in foreign countries before it hit the streets in the U.S., and in 2006 the estimate was that for every $12,500 in circulation, $1 was fake (a figure that rapidly adds up when you realize around a trillion dollars are in wallets and banks).

Hence the pressure to add technology that makes money difficult to copy. The new research has seen a breakthrough in printing thin-film transistors out of a mix of gold, aluminum oxide, and organic molecules through a patterned mask (similar to how silicon chips are “printed” in layers) onto paper currency. The real trick has been to achieve the printing process without “aggressive chemicals or high temperatures,” both of which could compromise or preclude other anti-counterfeit measures, or damage the actual paper of the notes themselves.

The result is an array of around 100 organic transistors on each note’s surface, each less than 250 nanometers thick and capable of turning on an off with just 3 volts of juice–the kind of power that can easily be transmitted over short ranges by wireless tech. In other words, the notes could be detected as real by passing them over similar detectors as the ones used in metro stations (and soon, many smartphones).


As yet this research is in its infancy, but it’s so very promising that it could easily find its way onto your cash sooner rather than later. Since you can build quite complicated electronic structures on the notes, the circuits are potentially capable of performing basic computations–meaning you could even encrypt an extra layer of protection into the design, which may tempt mints around the world to quickly embrace the idea. And this has prompted us to wonder if you could turn your pocket full of cash into a mini computer that could do useful stuff like–we jest, but you never know. Imagine if your cash counted itself as you spent it, or you could work out how much was in a folded pile of cash simply by holding it against your future NFC iPhone, or you could track what you spent your money on via an online portal?

We’ve just gotta hope that the Federal Reserve, when it gets its hands on this tech, doesn’t mess it up and cause another $100 billion printing error recall. Because that kind of mistake is expensive.

To read more news on this, and similar stuff, keep up with my updates by following me, Kit Eaton, on Twitter.

About the author

I'm covering the science/tech/generally-exciting-and-innovative beat for Fast Company. Follow me on Twitter, or Google+ and you'll hear tons of interesting stuff, I promise.