Organic ferroelectric molecule shows promise for memory chips, sensors
Jiangyu Li, University of Washington |
At the heart of computing are tiny crystals that transmit and
store digital information's ones and zeroes. Today these are hard and brittle
materials. But cheap, flexible, nontoxic organic molecules may play a role in
the future of hardware. A team led by the University of Washington in Seattle
and the Southeast University in China discovered a molecule that shows promise
as an organic alternative to today's silicon-based semiconductors. The
findings, published this week in the journalScience, display properties that make
it well suited to a wide range of applications in memory, sensing and low-cost
energy storage.
"This
molecule is quite remarkable, with some of the key properties that are
comparable with the most popular inorganic crystals," said co-corresponding
author Jiangyu Li, a UW associate professor of mechanical engineering.
The
carbon-based material could offer even cheaper ways to store digital
information; provide a flexible, nontoxic material for medical sensors that
would be implanted in the body; and create a less costly, lighter material to
harvest energy from natural vibrations.
The new
molecule is a ferroelectric, meaning it is positively charged on one side and
negatively charged on the other, where the direction can be flipped by applying
an electrical field. Synthetic ferroelectrics are now used in some displays,
sensors and memory chips.
In the
study the authors pitted their molecule against barium titanate, a long-known
ferroelectric material that is a standard for performance. Barium titanate is a
ceramic crystal and contains titanium; it has largely been replaced in
industrial applications by better-performing but lead-containing alternatives.
The new
molecule holds its own against the standard-bearer. It has a natural
polarization, a measure of how strongly the molecules align to store
information, of 23, compared to 26 for barium titanate. To Li's knowledge this
is the best organic ferroelectric discovered to date.
A recent study in Nature announced
an organic ferroelectric that works at room temperature. By contrast, this
molecule retains its properties up to 153 degrees Celsius (307 degrees F), even
higher than for barium titanate.
The new
molecule also offers a full bag of electric tricks. Its dielectric constant --
a measure of how well it can store energy -- is more than 10 times higher than
for other organic ferroelectrics. And it's also a good piezoelectric, meaning
it's efficient at converting movement into electricity, which is useful in
sensors.
The new
molecule is made from bromine, a natural element isolated from sea salt, mixed
with carbon, hydrogen and nitrogen (its full name is diisopropylammonium
bromide). Researchers dissolved the elements in water and evaporated the liquid
to grow the crystal. Because the molecule contains carbon, it is organic, and
pivoting chemical bonds allow it to flex.
The
molecule would not replace current inorganic materials, Li said, but it could
be used in applications where cost, ease of manufacturing, weight, flexibility
and toxicity are important.
Li is
working on a number of projects relating to ferroelectricity. Last year he and
his graduate student found the first evidence for ferroelectricity in soft
animal tissue. He was co-author on a 2011 paper in Science that documents
nanometer-scale switching in ferroelectric films, showing how such molecules
could be used to store digital information.
"Ferroelectrics
are pretty remarkable materials," Li said. "It allows you to
manipulate mechanical energy, electrical energy, optics and electromagnetics,
all in a single package."
He is
working to further characterize this new molecule and explore its combined
electric and mechanical properties. He also plans to continue the search for
more organic ferroelectrics.
The
joint first authors of the new paper are Yuanming Liu, a UW postdoctoral
researcher in mechanical engineering, and Da-Wei Fu, a doctoral student working
with co-corresponding author Ren-Gen Xiong at Southeast University. Other
co-authors are Hong-Ling Cai, Qiong Ye, Wen Zhang and Yi Zhang at Southeast
University; Xue-Yuan Chen at the Chinese Academy of Sciences; and Gianluca
Giovannetti and Massimo Capone at the Italian National Simulation Centre.
The
research was funded by the U.S. National Science Foundation, China's National
Natural Science Foundation and the European Research Council.
Source: University
of Washington
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