Dry Clean Only?
by David Pescovitz
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Graduate student Josei Lee holds the first prototype of her loom to weave electronic textiles.
(David Pescovitz photo)
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Someday
soon, dressing smartly may take on a whole new meaning. Electronic
textiles--fabric containing microprocessors, sensors, and actuators--could
lead to shirts with pores that automatically open and close depending
on the temperature, army fatigues with chameleon-like color-changing
properties, or tents that sniff out environmental contaminants. Josei
Lee, a UC Berkeley graduate student in Electrical Engineering and
Computer Sciences, and Professor Vivek Subramanian recently built
the world's first flexible transistors directly on fibers. Their
success is a leap toward the future of computer couture.
The aim of
the project, part of the Center for Information Technology Research
in the Interest of Society (CITRIS), is to weave large bolts
of fabric that incorporate a smart grid-like network of interconnecting
wires. Various devices such as chemical sensors or blood pressure
monitors could then talk to each other through the network of
fibers, much like desktop computers, servers, and printers communicate
on
an office network.
"If one
device is on the fabric's grid, it's connected to everything
else on the grid," Lee says.
While other
researchers have embedded entire circuits into fabric, that kind
of "one-off" approach
is not cost effective or efficient enough for widespread adoption
of the technology.
That's
where Lee and Subramanian's fiber transistors come into play.
"When an
electric textile is first switched on, it most likely won't know
where the arms or legs or peripheral components are
located," Subramanian
adds. "But if you have dynamic switching, you can
identify the signal paths. That way, the fabric can say,
'I'm the
CPU, and in
location X is a sensing unit, and this is the best way
to connect us together.' "
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An array of transistors fabricated using the weave-based masking process. Strips of the semiconducting coating are visible between the gold contacts.
(courtesy the researchers)
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A close-up view of an e-textile sample during the weaving process. The thin wires containing the transistors and the perpendicular interconnect wires are woven between thicker Teflon threads that make up the bulk of the fabric.
(courtesy the researchers)
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Lee's fabric
transistors act as the switches, enabling a grid of fibers to
establish
the path a signal takes from
one device
to the
other. For example, the switches could determine that
the most efficient route for a signal traveling from a temperature
sensor
on the wrist
to a microprocessor in the breast pocket is across the
shoulders.
The dynamic switching even enables the e-textile to be
fault tolerant.
"If I tear
the sleeve of my electronic shirt, does that mean I lose all functionality?" Subramanian
says. "No, because
it adaptively routes around the rip."
The first
step in fabricating the transistors is to coat a
group of parallel hair-thin aluminum wires with
an
organic material
called poly-4-vinylphenol (PVP). The PVP acts as
a flexible insulator so
that the fabric can be bent without breaking the
circuit. Then,
a semiconducting coating is added. After that, another
layer of fibers,
placed perpendicularly over the first group, acts
as a mask so that gold contacts can be patterned onto
specific
portions
of
the wire.
The result is an array of functional transistors.
Interconnecting wires are then woven across the contacts so each
transistor
in the grid can be individually controlled. Traditional
fibers like
cotton
can also be threaded through to fill out the fabric.
"The entire
transistor is made without conventional lithography," Subramanian
says. "The weaving is what sets the location
of the transistor."
Until recently,
Lee individually hand-stitched the wiring for each transistor.
Now though, she's also
experimenting
with
a tiny loom
built in UC Berkeley's machine shop that will
enable her to more quickly produce small samples
of the
e-textile.
"The loom
is similar to what kids use in kindergarten," Lee
says.
Lee is also
working to improve the reliability of the transistors while ensuring
that they're
durable
and
flexible enough
for real-world fabric applications. Meanwhile,
she's developing additional solution-based
processes that will enable the researchers
to coat the wires
with the organic materials by pulling them
through a liquid, just as fibers
are colored in the garment industry.
"Our key goal is to do everything just as it's done in textile manufacturing," Subramanian
says.
Vivek Subramanian's Organic Electronics Group
"Organic
Transistors and the Death of the Bar Code" by David Pescovitz
(Lab Notes, Feb/March 2002)
Center for
Information Technology Research in the Interest of Society
(CITRIS)
Lab Notes is
published online by the Public Affairs Office of the UC Berkeley
College of Engineering. The Lab Notes mission is to illuminate groundbreaking
research underway today at the College of Engineering that will
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Writer, Researcher: David
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© 2004 UC Regents.
Updated 2/19/04.
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