A
team of university researchers, aided by scientists at the National
Institute of Standards and Technology (NIST), have succeeded in
integrating a new, highly efficient piezoelectric material into a
silicon microelectromechanical system (MEMS). This development could
lead to significant advances in sensing, imaging and energy harvesting.
A
piezoelectric material, such as quartz, expands slightly when fed
electricity and, conversely, generates an electric charge when squeezed.
Quartz watches take advantage of this property to keep time:
electricity from the watch’s battery causes a piece of quartz to expand
and contract inside a small chamber at a specific frequency that
circuitry in the watch translates into time.
Piezoelectric
materials are also in sensors in sonar and ultrasound systems, which
use the same principle in reverse to translate sound waves into images
of, among other things, fetuses in utero and fish under the water.
Although
conventional piezoelectric materials work fairly well for many
applications, researchers have long sought to find or invent new ones
that expand more and more forcefully and produce stronger electrical
signals. More reactive materials would make for better sensors and could
enable new technologies such as “energy harvesting,” which would
transform the energy of walking and other mechanical motions into
electrical power.
Enter a material named PMN-PT, a crystalline alloy of lead, magnesium niobate and lead titanate.
A
large team led by scientists from the University of Wisconsin-Madison
developed a way to incorporate PMN-PT into tiny, diving-board like
cantilevers on a silicon base, a typical material for MEMS construction,
and demonstrated that PMN-PT could deliver two to four times more
movement with stronger force—while using only 3 V—than most rival
materials studied to date. It also generates a similarly strong electric
charge when compressed, which is good news for those in the sensing and
energy harvesting businesses.
To
confirm that the experimental observations were due to the
piezoelectric’s performance, NIST researcher Vladimir Aksyuk developed
engineering models of the cantilevers to estimate how much they would
bend and at what voltage. Aksyuk also made other performance measures in
comparison to silicon systems that achieve similar effects using
electrostatic attraction.
“Silicon
is good for these systems, but it is passive and can only move if
heated or using electrostatics, which requires high voltage or large
dissipated power,” says Aksyuk. “Our work shows definitively that the
addition of PMN-PT to MEMS designed for sensing or as energy harvesters
will provide a tremendous boost to their sensitivity and efficiency. A
much bigger ‘bend for your buck,’ I guess you could say.”
Other
participants included researchers from Penn State University; the
University of California, Berkeley; the University of Michigan; Cornell
University; and Argonne National Laboratory.
