Electronic devices of the future could be smaller, faster, more powerful
and consume less energy because of a discovery by researchers at the Department
of Energy's Oak Ridge National Laboratory.
The key to the finding, published in Science, involves a method to measure
intrinsic conducting properties of ferroelectric materials, which for decades
have held tremendous promise but have eluded experimental proof. Now, however,
ORNL Wigner Fellow Peter Maksymovych and co-authors Stephen Jesse, Art Baddorf
and Sergei Kalinin at the Center for Nanophase Materials Sciences believe they
may be on a path that will see barriers tumble.
"For years, the challenge has been to develop a nanoscale material that
can act as a switch to store binary information," Maksymovych said. "We
are excited by our discovery and the prospect of finally being able to exploit
the long-conjectured bi-stable electrical conductivity of ferroelectric materials.
"Harnessing this functionality will ultimately enable smart and ultra-dense
In the paper, the authors have demonstrated for the first time a giant intrinsic
electroresistance in conventional ferroelectric films, where flipping of the
spontaneous polarization increased conductance by up to 50,000 percent. Ferroelectric
materials can retain their electrostatic polarization and are used for piezoactuators,
memory devices and RFID (radio-frequency identification) cards.
"It is as if we open a tiny door in the polar surface for electrons to
enter," Maksymovych said. "The size of this door is less than one-millionth
of an inch, and it is very likely taking only one-billionth of a second to open."
As the paper illustrates, the key distinction of ferroelectric memory switches
is that they can be tuned through thermodynamic properties of ferroelectrics.
"Among other benefits, we can use the tunability to minimize the power
needed for recording and reading information and read-write voltages, a key
requirement for any viable memory technology," Kalinin said.
Numerous previous works have demonstrated defect-mediated memory, but defects
cannot easily be predicted, controlled, analyzed or reduced in size, Maksymovych
said. Ferroelectric switching, however, surpasses all of these limitations and
will offer unprecedented functionality. The authors believe that using phase
transitions such as ferroelectric switching to implement memory and computing
is the real fundamental distinction of future information technologies.
Making this research possible is a one-of-a-kind instrument that can simultaneously
measure conducting and polar properties of oxide materials with nanometer-scale
spatial resolution under a controlled vacuum environment. The instrument was
developed and built by Baddorf and colleagues at the Center for Nanophase Materials
Sciences. The materials used for this study were grown and provided by collaborators
at the University of California at Berkeley.
A link to the paper, "Polarization control of electron tunneling into
ferroelectric surfaces," is available here: http://www.sciencemag.org/cgi/content/abstract/324/5933/1421;
Vol. 324, 2009, page 1421. This research was funded by the Office of Basic Energy
Sciences within the Department of Energy's Office of Science. UT-Battelle manages
Oak Ridge National Laboratory for DOE.
The Center for Nanophase Materials Sciences at Oak Ridge National Laboratory
is one of the five DOE Nanoscale Science Research Centers, premier national
user facilities for interdisciplinary research at the nanoscale. Together the
centers comprise a suite of complementary facilities that provide researchers
with state-of-the-art capabilities to fabricate, process, characterize and model
nanoscale materials, and constitute the largest infrastructure investment of
the National Nanotechnology Initiative. The centers are located at DOE's Argonne,
Brookhaven, Lawrence Berkeley, Oak Ridge, Sandia and Los Alamos national laboratories.
For more information about the DOE Nanoscale Science Research Centers, please