Researchers
at the University of Illinois at Urbana-Champaign
have developed a fully stretchable form of single-crystal
silicon with micron-sized, wave-like geometries that
can be used to build high-performance electronic
devices on rubber substrates.
"Stretchable silicon offers different capabilities
than can be achieved with standard silicon chips," said
John Rogers, a professor of materials science and
engineering and co-author of a paper to appear in
the journal Science, as part of the Science Express
Web site, on Dec 15.
Functional, stretchable and bendable electronics
could be used in applications such as sensors and
drive electronics for integration into artificial
muscles or biological tissues, structural monitors
wrapped around aircraft wings, and conformable skins
for integrated robotic sensors, said Rogers, who
is also a Founder Professor of Engineering, a researcher
at the Beckman Institute for Advanced Science and
Technology and a member of the Frederick Seitz Materials
Research Laboratory.
To create their stretchable silicon, the researchers
begin by fabricating devices in the geometry of ultrathin
ribbons on a silicon wafer using procedures similar
to those used in conventional electronics. Then they
use specialized etching techniques to undercut the
devices. The resulting ribbons of silicon are about
100 nanometers thick - 1,000 times smaller than the
diameter of a human hair.
In the next step, a flat rubber substrate is stretched
and placed on top of the ribbons. Peeling the rubber
away lifts the ribbons off the wafer and leaves them
adhered to the rubber surface. Releasing the stress
in the rubber causes the silicon ribbons and the
rubber to buckle into a series of well-defined waves
that resemble an accordion.
"The resulting system of wavy integrated device
elements on rubber represents a new form of stretchable,
high-performance electronics,"
said Young Huang, the Shao Lee Soo Professor of Mechanical
and Industrial Engineering. "The amplitude and
frequency of the waves change, in a physical mechanism
similar to an accordion bellows, as the system is
stretched or compressed."
As a proof of concept, the researchers fabricated
wavy diodes and transistors and compared their performance
with traditional devices.
Not only did the wavy devices perform as well as
the rigid devices, they could be repeatedly stretched
and compressed without damage, and without significantly
altering their electrical properties.
"These stretchable silicon diodes and transistors
represent only two of the many classes of wavy electronic
devices that can be formed,"
Rogers said. "In addition to individual devices,
complete circuit sheets can also be structured into
wavy geometries to enable stretchability."
Besides the unique mechanical characteristics of
wavy devices, the coupling of strain to electronic
and optical properties might provide opportunities
to design device structures that exploit mechanically
tunable, periodic variations in strain to achieve
unusual responses.
In addition to Rogers and Huang, co-authors of the
paper were postdoctoral researcher Dahl-Young Khang
and research scientist Hanqing Jiang. The Defense
Advanced Research Projects Agency and the U.S. Department
of Energy funded the work.
CONTACT: James E. Kloeppel, Physical
Sciences Editor 217-244-1073; kloeppel@uiuc.edu
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