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Conducting Domain Walls in Insulating Oxides





Scientists at Berkeley Lab have built on their discovery that the 2-nm wide domain walls in insulating multiferroic oxides conduct electricity at room temperature. The researchers are able to reversibly manipulate the number, position, and conductivity of these walls. This technology will make it possible to read, write, and erase memory and logic in electronic devices on an unprecedented nanometer scale.

The scientists discovered these properties in thin films (100-nm) of bismuth ferrite (BiFeO3), which is antiferromagnetic and ferroelectric and contains as-grown domains. The angular difference in the direction of the ferroelectric polarization in adjacent domains can be set to 71°, 109°, or 180°, depending on an applied electrical field, provided, for example, by an atomic force microscope. This controllable angular difference between domains in turn determines the conductivity of the intervening domain wall, such that 109°- and 180°-walls are conductive, and 71°-walls are not. Different patterns of highly, partially, or non-conductive walls could therefore be written and read to encode information in a binary or higher-order system. The writing and reading of these patterns does not require high current pulses, as do existing systems, and the pattern density can be as low as 10-50 nm, as the distance between domain walls (domain width) can be controlled. In addition, thin films of the material can be fabricated with a single ferroelectric domain, i.e., with no domain walls. Into this “blank slate,” new domain walls of selected angular differences can be inserted with freely definable geometries.

Subsequent experiments also demonstrated that the photovoltaic effect occurs in the domain walls and produces extraordinarily high open-circuit voltages above the bandgap. This photovoltaic effect can be switched on and off or reversed in polarity. Thus, the unique and controllable features of the domain walls will allow for both greater photovoltaic efficiency in the field of solar energy and a significant reduction in the size of electronic memory and logic in computing.

DEVELOPMENT STAGE: Bench scale demonstration performed.

STATUS: Patent pending. Available for licensing or collaborative research.

Seidel J., L.W. Martin, Q. He, Q. Zhan, Y.-H. Chu, A. Rother, M.E. Hawkridge, P. Maksymovych, P. Yu, M. Gajek, N. Balke, S.V. Kalinin, S. Gemming, F. Wang, G. Catalan, J.F. Scott, N. A. Spaldin, J. Orenstein, R. Ramesh. “Conduction at domain walls in oxide multiferroics,” Nature Materials 8:229-234 (2009).

Yang S.Y., J. Seidel, S.J. Byrnes, P. Shafer, C.-H. Yang, M.D. Rossell, P. Yu, Y.-H. Chu, J.F. Scott, J.W. Ager, III, L.W. Martin, R. Ramesh. “Above-bandgap voltages from ferroelectric photovoltaic devices,” Nature Nanotechnology 5:143-147 (2010).


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Last updated: 08/04/2010