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Friday, January 21, 2011
Physics Building, Room 204
Note special time.
[Host: Stu Wolf]
"Memristance and Negative Differential Resistance in Transition Metal Oxides"
Memristive devices are nonlinear dynamical systems that exhibit continuous, reversible and
nonvolatile resistance changes that depend on the polarity, magnitude and duration of an applied
electric field. The memristive properties of metal/metal oxide/metal (MOM) materials
systems were discovered in the 1960s and studied without reaching a consensus on the physical
mechanism, while the theoretical foundation of memristance was derived by Chua in 1971
without realizing there were physical examples of this circuit property. Recent studies on the
mechanism revealed that memristive switching is caused by electric field-driven motion of
charged dopants that define the interface position between conducting and semiconducting regions
of the film. There have also been multiple reports of current-controlled negative differential
resistance (CC-NDR) in electroformed MOM devices since the early 1960s (e.g. oxides
of V, Nb, Ta, Ti and Fe), and there have been a variety of proposals for the physical mechanism.
Current work presents persuasive evidence that CC-NDR in these materials is due to a
Joule-heating induced metal-insulator transition (MIT). We have found that both memristance
and CC-NDR coexist in many transition metal oxides, and the fact that both effects have been
called "switching" has caused a great deal of confusion in the literature and prevented
comprehensive understanding of these systems. I will explain the origin of both effects in
titanium oxides and show some potential applications of combining the two effects in a
single nanoscale device.
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