Fancloth and wearable computers, coming to a Gap Outlet near you
or My new Polo shirt has a P5 4.2 Ghz with 2 gig of memory
by David Pescovitz, Berkley College of Engineering

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.

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"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.'"

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 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, act 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.

posted by awiggins | 12:28 PM