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Optical chips could pack more bits, run cooler

Posted: 24 Nov 2008     Print Version  Bookmark and Share

Keywords:electronic chips  ultra low power  crystalline insulators  nanoscale structures 

Conventional wisdom says that as long as data is stored as a charge, CMOS will likely remain king-of-the-hill for electronic chips. Johns Hopkins University theorists are now proposing an ultra low power alternative to charge that uses lasers to encode data as excitons inside insulators.

If experimental data confirms the theory, then ultra low power computers based on this new optical phenomenon could someday use lasers to store data within crystalline insulators.

"It is only theory, so our results will have to be verified by experiment," said professor Alexander Kaplan of Department of Electrical and Computer Engineering at Johns Hopkins. "But, if we are correct, one of the outcomes of our discovery could be solving the heat build-up problems associated with scaling semiconductors to smaller and smaller sizes."

According to Kaplan, the careful formation of specific, finite lattices or arrays of atoms, molecules or quantum dots, illuminated by a laser, can produce nanoscale strata that break the restrictions imposed by a conventional Lorentz-Lorenz theory. That theory, from the perspective of information, prohibits local encoding of states on the atoms inside insulators. Kaplan said his team has found a way to customise nanoscale structures inside insulators, enabling them to store data and "sense" their environment.

In Kaplan's scheme, lasers with relatively low power, stimulate the encoding of data in the form of different excitation states of localised, bound electrons held stationary inside a crystalline-like lattice. It is then driven into non-linear mode of excitation by a laser.

The researchers are essentially proposing optical bistability at the atomic level. Called locsitons, or local excitons, the excitations don't require current flow during laser-controlled reading and writing. Thus, they could enable the ultimate low-power nanoscale memory cell or logic element.

The downside for locsitons is that they can only provide dynamic memory functions. As with volatile electronic memories that lose their data when disconnected from a power source, once the laser switches off, locsitons vanish and the atoms in the lattice return to their ground state.

"This limitation, however, is no worse than that for regular electronics, like random-access memories and logic elements today, where you have to keep the power on for them to retain their states," said Kaplan.

The Johns Hopkins technique could also be used to create atomic sensitivity in sensors using a designer structure in its linear mode of operation. Designer lattices would use specific types of atoms with resonances that are tuned to various aspects of the environment, thereby enabling atomic-scale sensitivity in sensors that consume no power except when being read with a laser.

- R. Colin Johnson
EE Times

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