Electronic memory chips may soon gain the ability to bend and twist as a
result of work by engineers at the National
Institute of Standards and Technology (NIST). As reported in the July 2009
issue of IEEE Electron Device Letters,* the engineers have found a way to build
a flexible memory component out of inexpensive, readily available materials.
Though not yet ready for the marketplace, the new device is promising not only
because of its potential applications in medicine and other fields, but because
it also appears to possess the characteristics of a memristor, a fundamentally
new component for electronic circuits that industry scientists developed in
2008.** NIST has filed for a patent on the flexible memory device (application
Electronic components that can flex without breaking are coveted by portable
device manufacturers for many reasons—and not just because people have
a tendency to drop their mp3 players. Small medical sensors that can be worn
on the skin to monitor vital signs such as heart rate or blood sugar could benefit
patients with conditions that require constant maintenance, for example. Though
some flexible components exist, creating flexible memory has been a technical
barrier, according to NIST researchers.
Hunting for a solution, the researchers took polymer sheets—the sort
that transparencies for overhead projectors are made from—and experimented
with depositing a thin film of titanium dioxide, an ingredient in sunscreen,
on their surfaces. Instead of using expensive equipment to deposit the titanium
dioxide as is traditionally done, the material was deposited by a sol gel process,
which consists of spinning the material in liquid form and letting it set, like
making gelatin. By adding electrical contacts, the team created a flexible memory
switch that operates on less than 10 volts, maintains its memory when power
is lost, and still functions after being flexed more than 4,000 times.
What’s more, the switch’s performance bears a strong resemblance
to that of a memristor, a component theorized in 1971 as a fourth fundamental
circuit element (along with the capacitor, resistor and inductor). A memristor
is, in essence, a resistor that changes its resistance depending on the amount
of current that is sent through it—and retains this resistance even after
the power is turned off. Industrial scientists announced they had created a
memristor last year, and the NIST component demonstrates similar electrical
behavior, but is also flexible. Now that the team has successfully fabricated
a memristor, NIST can begin to explore the metrology that may be necessary to
study the device’s unique electrical behavior.
“We wanted to make a flexible memory component that would advance the
development and metrology of flexible electronics, while being economical enough
for widespread use,” says NIST researcher Nadine Gergel-Hackett. “Because
the active component of our device can be fabricated from a liquid, there is
the potential that in the future we can print the entire memory device as simply
and inexpensively as we now print a slide on an overhead transparency.”
* N. Gergel-Hackett, B. Hamadani, B. Dunlap, J. Suehle, C. Richter, C. Hacker,
D. Gundlach. A flexible solution-processed memristor. IEEE Electron Device Letters,
Vol. 30, No. 7. Posted online the week of June 8, 2009.
** D. B. Strukov, G. S. Snider, D. R. Stewart, and S. R. Williams. The missing
memristor found. Nature, Vol. 453, May 1, 2008.
NIST researchers have used inexpensive, readily available materials to create
an electronic memory chip that can be bent or twisted—some 4,000 times
in tests—and still keep functioning.