LIKE THE SCARECROW IN The Wizard of Oz, micromachines want a brain. Current microelectromechanical (MEM) systems require two chips--one that functions as an ultra-teensy motor, gear, or sensor and another for the circuits to control it. That's true even though the same techniques are used to make both the machine and the brain.

Engineers at the Energy Dept.'s Sandia National Laboratories in New Mexico have found a way to put brawn and brain on one chip. According to experts at Analog Devices Inc. and the University of California at Berkeley, the breakthrough heralds all manner of smart MEM chips in medicine, communications, computers, and military hardware.

Heat is the hang-up in combining microcircuits and mechanical parts on a single silicon wafer. The machines must be tempered by heating them to around 900C--which melts any existing circuits. But if the machines are made first, the surface of the silicon wafer ends up too hilly to "print" control-circuit lines--it's like writing on sandpaper. So a Sandia team headed by Paul J. McWhorter developed a way to etch micromachines at the bottom of trenches, then fill in the trenches with silicon dioxide to make the wafer's surface smooth again. After the circuitry is formed around the trenches, the silicon dioxide is removed so the tiny gears can turn.

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