Plastic computer memory advances

By Kimberly Patch, 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 said.

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
Funding:   Government
TRN Categories:  Materials Science and Engineering; Data Storage Technology
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.


June 26/July 3, 2002

Page One

PCs augment reality

Stamps bang out tiny silicon lines

Bent wires make cheap circuits

Mixes make tiniest transistors

Plastic computer memory advances


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