USAF spends on flexible microcircuits

The Air Force Office of Scientific Research at Wright-Patterson Air Force Base, Ohio, has announced it is funding research on thin, flexible transistors that could be developed into high-performance optoelectronics for high-speed photography, high-performance antennae that could be applied to the skin of aircraft and other innovative uses.

The researchers, led by Zhenquing Ma and Max Lagally of the University of Wisconsin-Madison developed a technique to create highly flexible semiconductors that are able to withstand impact and severe vibration and run at 7 GHz, rather than the current standard, 0.5 GHz.

Part of the performance improvement comes from the tendency of silicon-based semiconductors to run faster after being stretched — a technique semiconductor manufacturers already use.

Rather than etching semiconductors into rigid substrates of insulated silicon — on which normal microchips are based — the flexible versions are built from a three-layer nanofabric of silicon and silicon-germanium, laid on a base of silicon dioxide.

The chip is then dipped in an acid bath to dissolve the oxide and leave a molecules-thick nanomembrane that is stretchable, bendable and runs at much higher frequencies than it would have in a rigid structure. The team needs to find a more economical way to produce and separate the flexible membranes and produce chips larger than about a centimeter square.

Previous methods required researchers to manually create breaks in the crystalline structure of the silicon that could act as spacers or hinges to allow the chip to bend. That method is painstakingly slow, however. The researchers envision low-power flexible electronics wrapped around irregular-shaped objects to act as 360-degree antennae or sensors for light and motion. A laser can read bent circuits more quickly than flat versions, for example, by reaching all points on the circuit’s curve from a single position,rather than having to scan the whole circuit as is now common.

Because germanium reacts much more efficiently to light than regular silicon, silicon-germanium chips have the potential to be two to three times more sensitive in light-sensor and photography applications than current chips.

Researchers at Stanford University, UCLA, the Energy Department’s Argonne National Laboratory and the University of Illinois at Urbana- Champaign are working on similar approaches.