Where economics, engineering meet
Printed circuits may replace barcodes on the soup cans of tomorrow

By David Pescovitz

Professor Vivek Subramanian holds a prototype of a wafer used to fabricate printed circuits. An inkjet printer imprints ‘liquid gold,’ synthesized in his lab, onto the wafer, forming electronic components that may be used in inventory “smart tags” of the future. Peg Skorpinski photo

06 March 2002 | The future of the ubiquitous bar code is looking grim, if a team of Berkeley scientists has anything to say about it. What the team has in mind is a tiny gizmo that could revolutionize commerce, beginning with the supermarket check-out stand: circuit-laden smart tags printed directly on product packaging.

Imagine filling your shopping cart and walking right out of the store, past a sensor that automatically identifies what you’re buying and instantly charges your credit card.

The store, of course, would be fully stocked because electronically-enabled shelves would keep track of inventory and automatically reorder needed items.

Customers’ refrigerators might even generate shopping lists by sensing when the milk has gone sour or the egg carton is empty.

“We’re focused on disposable electronics,” says Professor Vivek Subramanian of the Department of Electrical Engineering and Computer Sciences. “The question is — can we print a circuit on a package so that when you ping it with a radio signal, it’ll reply ‘hey, I’m a can of soup.’ Just as importantly, can we do it very inexpensively?”

For these printable radio-frequency identification tags to catch on, they need to be dirt cheap — adding less than one-half a cent to the price of existing product packages, Subramanian says.

So he and his research group have embarked on a multi-disciplinary project spanning chemical, biological, electrical and mechanical engineering. The result is an inkjet printer and conductive ink that enables a family of electronic inks that make it possible to print circuits onto paper, plastic or cloth without damaging the material.

“In the long term, you’d like to have a bit of programmability,” Subramanian says. “For example, every can of soup could have the same identification number, but each batch could be programmed with a different expiration date.”

To that end, the group is also working on adding memory to the tags and developing something the team calls “liquid gold.” — microscopic gold crystals that are encapsulated in an organic shell and dissolved in ink.

Then, an inkjet printer deposits the material on the plastic, paper, or fabric in the desired circuit pattern. As the circuit is printed, the organic encapsulant is burned off, leaving the gold as a high-quality conductor.

The next research challenge is to develop high-quality printable transistors that are resistant to corrosive oxygen and moisture. The team has hooked up with the College of Chemistry to explore the possibility of using a rubber-type material found in automobile tires as packaging for the printed transistors.

In the meantime, the researchers are working with their current organic transistors and with models of their future transistors.

“We want to know just how good the transistors need to be to for the system to work,” he says. “After all, this project is truly at the intersection of economics and engineering.”