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December 1, 2003
Volume 81, Number 48
CENEAR 81 48 p. 11
ISSN 0009-2347


Porphyrins designed for computer data storage weather heat, repetitive cycling


DATA STORAGE Porphyrins like these hold up under harsh conditions
Porphyrin molecules created for data storage are remarkably hardy, holding up under the high temperatures and trillions of read-write cycles required of current silicon-based technology, says David F. Bocian, chemistry professor at the University of California, Riverside [Science, 302, 1543 (2003)].

Molecular computing, Bocian says, may supplement or replace semiconductor technology that, limited by the physics of silicon, is rapidly reaching its limit in terms of compactness and efficiency.

Bocian collaborated with Jonathan S. Lindsey, a chemist at North Carolina State University, Raleigh, and others to create silicon-tethered porphyrins, both individual and stacked molecules. Porphyrins are proven players in data storage, Bocian says. In nature, cytochrome porphyrins, for example, form -cation radicals at relatively low potentials, allowing multiple stabilized redox states. This ability expedites information flow in and out of the molecule. Porphyrins' potential for multibit information storage and their low power consumption make them attractive candidates for computer memory chips.

But "the first question that anyone in the computer chip fabrication plant will ask you is about stability under high temperatures," Bocian says. So he and Lindsey baked the porphyrins for up to an hour at 400 °C. Most organic molecules fall apart in such heat, but the porphyrins worked just as well as before heating. In addition, the scientists ran the porphyrins through a battery of endurance tests. They cycled the molecules through oxidation states (what would be required for storing and erasing data) up to 1 trillion times with no degradation.

This robustness suggests that porphyrin-based memory chips could be assembled in the same fabrication plants as silicon devices. This is a good "transition technology," Bocian says--one that perhaps could be used in hybrid semiconductor-molecular computer memories.


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