University of Utah engineers control conductivity with inkjet printer
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University of Utah electrical engineers
Ajay Nahata and Barun Gupta used a $60 inkjet printer with silver and
carbon ink cartridges to create a new, widely applicable way to make
microscopic structures that use light in metals to carry information.
This new technique could be used to rapidly fabricate superfast
components in electronic devices, make wireless technology faster or
print magnetic materials. Photo credit: Dan Hixson,
University of Utah College of Engineering.
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Using an inexpensive inkjet printer,
University of Utah electrical engineers produced microscopic
structures that use light in metals to carry information. This new
technique, which controls electrical conductivity within such
microstructures, could be used to rapidly fabricate superfast
components in electronic devices, make wireless technology faster or
print magnetic materials.
The study appears online March 7 in the
journal Advanced Optical Materials.
High-speed Internet and other
data-transfer techniques rely on light transported through optical
fibers with very high bandwidth, which is a measure of how fast data
can be transferred. Shrinking these fibers allows more data to be
packed into less space, but there's a catch: optical fibers hit a
limit on how much data they can carry as light is squeezed into
smaller and smaller spaces.
In contrast, electronic circuits can be
fashioned at much smaller sizes on silicon wafers. However,
electronic data transfer operates at frequencies with much lower
bandwidth, reducing the amount of data that can be carried.
A recently discovered technology called
plasmonics marries the best aspects of optical and electronic data
transfer. By crowding light into metal structures with dimensions far
smaller than its wavelength, data can be transmitted at much higher
frequencies such as terahertz frequencies, which lie between
microwaves and infrared light on the spectrum of electromagnetic
radiation that also includes everything from X-rays to visible light
to gamma rays. Metals such as silver and gold are particularly
promising plasmonic materials because they enhance this crowding
effect.
"Very little well-developed
technology exists to create terahertz plasmonic devices, which have
the potential to make wireless devices such as Bluetooth—which
operates at 2.4 gigahertz frequency—1,000 times faster than they
are today," says Ajay Nahata, a University of Utah professor of
electrical and computer engineering and senior author of the new
study.
Using a commercially available inkjet
printer and two different color cartridges filled with silver and
carbon ink, Nahata and his colleagues printed 10 different plasmonic
structures with a periodic array of 2,500 holes with different sizes
and spacing on a 2.5-inch-by-2.5 inch plastic sheet.
The four arrays tested had holes 450
microns in diameter—about four times the width of a human hair –
and spaced one-25th of an inch apart. Depending on the relative
amounts of silver and carbon ink used, the researchers could control
the plasmonic array's electrical conductivity, or how efficient it
was in carrying an electrical current.
"Using a $60 inkjet printer, we
have developed a low-cost, widely applicable way to make plasmonic
materials," Nahata says. "Because we can draw and print
these structures exactly as we want them, our technique lets you make
rapid changes to the plasmonic properties of the metal, without the
million-dollar instrumentation typically used to fabricate these
structures."
Plasmonic arrays are currently made
using microfabrication techniques that require expensive equipment
and manufacture only one array at a time. Until now, controlling
conductivity in these arrays has proven extremely difficult for
researchers.
Nahata and his co-workers at the
University of Utah's College of Engineering used terahertz imaging to
measure the effect of printed plasmonic arrays on a beam of light.
When light with terahertz frequency is directed at a periodic array
of holes in a metal layer, it can result in resonance, a fundamental
property best illustrated by a champagne flute shattering when it
encounters a musical tone of the right pitch.
Terahertz imaging is useful for
nondestructive testing, such as detection of anthrax bacterial
weapons in packaging or examination of insulation in spacecraft. By
studying how terahertz light transmits through their printed array,
the Utah team showed that simply changing the amount of carbon and
silver ink used to print the array could be used to vary transmission
through this structure.
With this new printing technique,
Nahata says, "we have an extra level of control over both the
transmission of light and electrical conductivity in these
devices—you can now design structures with as many different
variations as the printer can produce." Nahata says these faster
plasmonic arrays eventually could prove useful for:
• Wireless devices, because the
arrays allow data to be transmitted much more quickly. Many research
groups are actively working on this application now.
• Printing magnetic materials for
greater functionality (lower conductivity, more compact) in different
devices. This technology is more than five years away, Nahata says.
Although the Utah team used two
different kinds of ink, up to four different inks in a four-color
inkjet printer could be used, depending on the application.
Nahata conducted this study with
University of Utah electrical and computer engineering graduate
students Barun Gupta and Shashank Pandey, and Sivaraman Guruswamy,
professor of metallurgical engineering at the university. The study
was funded by the National Science Foundation through the University
of Utah's Materials Research Science and Engineering Center.
University of Utah College of
Engineering
72 S. Central Campus Dr., Room 1650 WEB
Salt Lake City, UT 84112
801-581-6911 fax: 801-581-8692
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