MATERIALS SCIENCE: Bistable Atomic Memories

Science  21 Apr 2006:
Vol. 312, Issue 5772, pp. 338b
DOI: 10.1126/science.312.5772.338b

The conductivity of ferroelectric perovskites, such as strontium titanate, is related to lattice dislocations and local oxygen concentration. SrTiO3 has a simple cubic structure and a high dislocation density at the crystal surfaces, and bistable switching between insulating and metallic states has been observed after doping with chromium.

Szot et al. show that bistable switching is possible in undoped SrTiO3 crystals if the oxygen concentration is varied at the surface. For bulk crystals, cycling was achieved by heat treatment under vacuum to lower resistance, followed by reoxidation to a more insulating state at room temperature, and then restoration of the metallic state by exposure to an electric field under vacuum. Individual dislocations could also be switched using an atomic force microscope with a conducting tip; application of the local electric field transported oxygen along the dislocation, thereby varying the conductance. The material therefore holds strong promise for fabrication into memory devices with a bit size of only a few atoms and with state stabilities that would eliminate the current need for refreshing in fast-responding static and dynamic memory chips. — MSL

Nat. Mater. 5, 312 (2006).

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