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‘Hybridized’
memory device developed
This discovery
may send CDs the way of LPs
by Steven Schultz
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Photo by Frank Wojciechowski
Professor Stephen Forrest led the research team that
discovered a new hybridized memory device.
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Engineers
at Princeton University and Hewlett-Packard (HP) have invented
a combination of materials that could lead to cheap and super-compact
electronic memory devices for archiving digital images or other
data.
The invention could result in a single-use memory card that
permanently stores data and is faster and easier to use than
a compact disk (CD). The device could be very small because
it would not involve moving parts such as the laser and motor
drive required by CDs.
The researchers, who published a description of the device in
the Nov. 13, 2003, issue of Nature, achieved the result
by discovering a previously unrecognized property of a commonly
used conductive polymer plastic coating.
Hybridized
device
Their memory device combines this polymer, which is inexpensive
and easy to produce, with very thin-film, silicon-based electronics.
“We are hybridizing,” said Princeton Professor of
Electrical Engineering Stephen Forrest, who
led the research group. “We are making a device that is
organic (the plastic polymer) and inorganic (the thin-film silicon)
at the same time.”
As a result, the device would be like a CD, in that writing
data onto it makes permanent physical changes in the plastic
and can be done only once. But it also would be like a conventional
electronic memory chip because it would plug directly into an
electronic circuit and would have no moving parts.
“The device could probably be made cheaply enough that
one-time use would be the best way to go,” Professor Forrest
said.
Basic discovery
The research was done in Professor Forrest’s laboratory
by former postdoctoral researcher Sven Möller,
who is now at HP in Corvallis, Ore. Craig Perlov, Warren Jackson,
and Carl Taussig, scientists at HP Labs in Palo Alto, Calif.,
are also co-authors of the Nature paper.
Dr. Möller made the basic discovery by experimenting with
polymer material called PEDOT, which is clear and conducts electricity.
It has been used for years as an antistatic coating on photographic
film, and more recently as an electrical contact on video displays
that require light to pass through the circuitry.
Dr. Möller found that PEDOT conducts electricity at low
voltages, but permanently loses its conductivity when exposed
to higher voltages (and thus higher currents), making it act
like a fuse or circuit breaker.
This finding led the researchers to use PEDOT as a way of storing
digital information. Digital images and all computerized data
are stored as numbers that are written as long strings of ones
and zeroes.
A PEDOT-based memory device would have a grid of circuits in
which all the connections contain a PEDOT fuse. A high voltage
could be applied to any of the contact points, blowing that
particular fuse and leaving a mix of working and non-working
circuits.
These open or closed connections would represent zeros and ones
and would become permanently encoded in the device. A blown
fuse would block current and be read as a zero, while an unblown
one would let current pass and act as a one.
Ultrasmall
circuits
This grid of memory circuits could be made so small that, based
on the test junctions the researchers made, 1 million bits of
information could fit in a square millimeter of paper-thin material.
If formed as a block, the device could store more than one gigabyte
of information, or about 1,000 high-quality images, in one cubic
centimeter, which is about the size of a fingertip.
Developing the invention into a commercially viable product
would require additional work on creating a large-scale manufacturing
process and ensuring compatibility with existing electronic
hardware, a process that might take as little as five years,
Professor Forrest said.
Funding for Professor Forrest’s research came in part
from HP as well as from the National Science Foundation through
a long-term grant that funds a materials research science and
engineering center at Princeton. Princeton University has filed
for a patent on the invention. HP has an option to license rights
to the technology.
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