BENDY, stretchable computer chips have been made that could one day allow gadgets to be integrated with clothing, or even take electronics to the surface of the human brain.
鈥淲e鈥檇 like to have an electric circuit that could wrap around part of the brain and detect signal patterns to predict the onset of a seizure before it happens,鈥� says of the University of Illinois, Urbana-Champaign, who led the team that developed the bendy chips.
鈥淔or a chip that can wrap around someone鈥檚 brain, you need stretchability鈥�
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Rogers and colleagues use a stamping technique to transfer ultrathin silicon ribbons, grown at high temperature on glass, to a plastic film. They then add trace amounts of silicon dioxide, silver and chromium to form a network of transistors and interconnecting wires. The entire assembly ends up just 1.5 micrometres thick.
鈥淢aking it thin makes it bendable, just as a piece of paper is bendable whereas a piece of wood is not,鈥� Rogers says. Relative to what his team produces, conventional silicon chips are about as flexible as the piece of wood.
To make the chips stretchable, the team binds the silicon-plastic layer to a sheet of rubber that has been stretched by 15 per cent in two dimensions. Once the materials are stuck together, the researchers allow the rubber to snap back to its pre-stretched state. Though this compresses the electronics, it does not damage them and the chips can be stretched out again by the same amount without fracturing, Rogers says (Science, ).
Flexible chips made from semiconducting plastics are also in development, but these aren鈥檛 stretchable. For a chip that can be wrapped around someone鈥檚 brain you really need stretchability, says Rogers. Silicon has another advantage over plastic: as the standard material in conventional microchips, its properties are well understood.
The stretchy circuits will 鈥渇ill an important gap, where regular semiconductors cannot go鈥�, says of the University of Wisconsin-Madison, who is also working on stretchable chips.
