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Researchers at the University of Illinois at Urbana-Champaign have
developed a fully stretchable form of single-crystal silicon with
micron-sized, wavelike 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 that
appeared in the journal Science, as part of the Science Express
website, 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.
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 "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.
[University
of Illinois news release]
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