The future of
the ubiquitous UPC bar code looks grim. In development at UC Berkeley
are circuit-laden smart tags printed directly on product packaging
that could revolutionize the supply chain, including your weekly
trip to the supermarket.
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. Of course, the
store itself would always be fully stocked because the electronically-enabled
shelves would take their own inventory and automatically reorder
as necessary. Your refrigerator might even generate its own shopping
list, perhaps sensing when your milk is sour or you're down to
the last egg in the carton.
"We're focused on disposable electronics," says Vivek Subramanian,
Department of Electrical Engineering and Computer Sciences professor.
"The question is, can we print a circuit on a package 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 (RFID) 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. To meet that price point, Subramanian and his research group
have embarked on a multi-disciplinary project spanning chemical,
electrical, and mechanical engineering. The result is an extraordinary
inkjet printer and a family of electronic inks that enable circuits
to be patterned onto paper, plastic, or cloth without damaging
An RFID tag consists of passive components - the inductors,
capacitors, and wires that handle the communication, interconnection,
and power; and active components - the transistors and diodes
that modulate and switch the signal to give the device its brains.
"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 expiry date." To introduce this capability, the
group is also working on adding memory to the tags.
At the April meeting of the Materials Research Society,
Subramanian's group will present their progress in developing a
printed conductor system that could be used to fabricate the RFID
tags' power-scavenging and communication circuitry. The key is "liquid
gold." Synthesized in Subramanian's laboratory, liquid gold consists
of gold nanocrystals that are only 20 atoms across and melt at 100
degrees Celsius, ten times lower than normal.
works on the custom ink jet printer used to print the "disposable
electronics." (Click for larger
The gold nanocrystals are encapsulated in an organic shell of
an alkanethiol (an organic molecule containing carbon, hydrogen,
and sulphur) and dissolved in ink. Then, an inkjet printer - either
the group's cannibalized commercial model or one they have built
from scratch ‚ deposits the material on the plastic, paper, or
fabric in the desired circuit pattern. The liquid gold is also
suitable for screenprinting, commonly employed to print product
packaging. As the circuit is printed, the organic encapsulant
is burned off, leaving the gold as a high-quality conductor.
"Gold is already used in semiconductors and given the amount
you need in our system, the raw material cost is not very high,"
says Subramanian, who is also developing organic electronics for
inexpensive plastic screens that could be rolled up and stuffed
in a pocket.
The next stage of the research is to develop high-quality printable
transistors, probably a year or two away, Subramanian says. One
challenge, he explains, is protecting the printed transistors
from corrosive oxygen and moisture. In collaboration with the
College of Chemistry, the researchers are exploring the use of
the same polysiobutylene rubber-type material used in automobile
tires as a screenprintable packaging for the printed transistors.
In the meantime, Subramanian and his group are studying their
current generation of organic transistors and models of what they
expect their transistors to look like in the near future.
"We want to know just how good the transistors need to be for
the system to work" and stop there, he says. "After all, this
project is truly at the intersection of economics and engineering."
at UC Berkeley
College of Chemistry