computer memory advances
Technology Research News
Making a digital memory device means finding
a way to represent the ones and zeros of computer logic, devising a relatively
convenient way to retrieve these binary patterns from storage, and making
sure the information remains stable.
Digital memory is an essential component of many electronic devices, and
memory that takes up little space and electricity is in high demand as
electronic devices continue to shrink.
Researchers from the Indian Association for the Cultivation of Science
and the Italian National Research Council have approach the problem by
taking the one-word advice given to Dustin Hoffman's character The
Graduate: plastics. They used positive and negative electric charges,
or space charges, contained within plastic to store binary numbers.
A polymer retains space charges near a metal interface when there is a
bias, or electrical current, running across the surface. These charges
come either from electrons, which are negatively charged, or the positively-charged
holes vacated by electrons. "We can store space charges in a polymer layer,
and conveniently check the presence of the space charges to... know the
state of the polymer layer," said Amlan Pal, a reader at the Indian Association
for the Cultivation of Science.
Space charges are essentially differences in electrical charge in a given
region. They can be read using an electrical pulse because they change
the way the device conducts electricity.
The researchers made the storage device by spreading a 50-nanometer layer
of the polymer regioregularpoly on glass, then topping it with an aluminum
electrode. To write a space charge to the device, they applied a positive
20-second, 3-volt pulse. To read the state, they used a 0.2-volt, one
minute pulse. Any kind of negative electrical pulse erased this high state,
or charge, replacing it with the default low state.
The space charges remain stable for about an hour, according to Pal. They
can also be refreshed by another 3-volt positive pulse. The researchers
intend to increase the memory retention ability of their device beyond
an hour. "We're looking forward to increasing it into days or more," he
Once this is achieved, "polymer devices can be used in data storage devices
[and] also as a switch whose state can be changed externally by a voltage
pulse," said Pal.
The researchers are also working on showing that organic semiconducting
dye molecules can be used as space-charge memory devices. "We aim to [be
able to] read the state of... devices based on both conjugated polymers
and organic dyes," said Pal. They're working toward being able to read
the dye molecule state by measuring changes in photoluminescence, which
would make it easier to read the data, according to Pal.
Pal's research colleagues were Himadri S. Majumdar and Anirban Bandyopadhyay
of the Indian Association for the Cultivation of Science, and Alberto
Bolognesi of the Italian National Research Counsel (CNR). They published
the research in the February 15, 2002 issue of the Journal of Applied
Physics. The research was funded by the Indian Association for the Cultivation
of Science, an autonomous institute financed by the Indian Department
of Science and Technology.
Timeline: 5 years
TRN Categories: Materials Science and Engineering; Data
Story Type: News
Related Elements: Technical paper, "Memory Device Applications
of a Conjugated Polymer: Role of Space Charges," Journal of Applied Physics,
February 15, 2002.
26/July 3, 2002
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