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
memory technology."
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.
