Three years ago, theoretical work of a University of Nebraska-Lincoln research group predicted a new effect that could revolutionize the field of microelectronics by allowing faster, smaller and more energy-efficient memory devices. Now that theory has been proven.
Recent measurements of the electrical properties of ferroelectric materials performed at the Alexei Gruverman lab at UNL led to experimental verification of the behavior predicted by a research group of physics and astronomy professor Evgeny Tsymbal at the UNL Materials Research Science and Engineering Center. In their paper published online Aug. 21 in the scientific journal Nano Letters, Gruverman, an associate professor of physics and astronomy, and Tsymbal, with co-authors demonstrated a several-orders-of-magnitude change in electrical resistance upon flipping of polarization in ultra-thin ferroelectric films.
Because of their ability to retain permanent electric polarization in the absence of the electric field, for decades ferroelectrics have been the subject of intense development for use in nonvolatile memory, where tiny bits of information are stored as polarization dipoles oriented up and down. The effect discovered at the UNL center could help overcome one of the most serious problems related to miniaturization of charge-based memory technologies — reduced charge and increasing leakage current — that leads to larger power consumption and progressive loss of stored information. In fact, it can turn this problem into an advantage because it will allow nondestructive read-out of the polarization state of the film simply by measuring its electrical resistance, which can be performed at a significantly lower voltage.
Application of the advanced measurements techniques showed that a single bit of information can be as small as 20 nanometers in diameter, approximately 1/1000th the diameter of a human hair.
The ferroelectric films for this study were grown by collaborators at the University of Wisconsin, Madison. Funding from the U.S. National Science Foundation helps support this research.
The two papers referenced are available online. "Tunneling Across a Ferroelectric" by
Evgeny Y. Tsymbal and Hermann Kohlstedt is at http://www.sciencemag.org/cgi/content/summary/313/5784/181 and "Tunneling Electroresistance Effect in Ferroelectric Tunnel Junctions at the Nanoscale" by A. Gruverman, et al, is at
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