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Smaller, Taller Micro-Machines Show Commercial Promise

Electrical and Computer Engineering Professor Henry Guckel has been pursuing the "taller is better" premise for years in his applied micro-electronics laboratory, and his techniques are beginning to make their way into commercial products. By using deep X-ray lithography techniques on metal rather than the standard silicon, Guckel builds machines as dust-speck tiny as their counterparts, but with greatly increased height.

Micro gears

These gears were fabricated using deep x-ray lithography and electroplating. They are free components which can be assembled into other components to form systems. Tight tolerances and complex structures can be created by assembly. (large image)

Guckel said the added dimension of his micro-machines dramatically increase their power storage capability and make them more functional for devices such as actuators and sensors.

"The more three-dimensional we can make something, the more applications we will have," Guckel said. "We're building devices now that take up a very small area, but are vertically very tall and consequently offer greatly increased energy storage," he said.

Most of Guckel's parts are smaller in size than the width of a human hair, which is 75 microns. But he has produced parts as tall as 1,000 microns.

Guckel gave a presentation recently during "Engineering the Future with Microsystem Technologies," a session at the American Association for the Advancement of Science (AAAS) annual meeting. Guckel focused on the benefits of using X-ray lithography in building devices with commercial potential.

The deep X-ray lithography process offers two advantages over making parts with silicon, Guckel said. By using metals such as nickel, copper and iron alloys in micro-motors, the machines are driven by magnetic rather than electrical fields. And metal can be layered faster than silicon, so parts can be made taller within industry's normal time demands.

Magnetic linear actuator

Linear actuator with externally wound and assembled micro coils. The coil has 300 turns and tip forces near 1 milliNewton is expected for applied currents of 40 mA. These estimates are from inductance measurements as a function of plunger position. Resonant frequencies are near 350 kHz with input powers in the tens of milliWatts. (large image)

One strong market for metal micro-motors is actuators, the mechanical devices in systems that transmit energy to control precise functions such as computer memory. Guckel said micro-motors could control the movement of magnetic recording heads more precisely, expanding the amount of information stored on computer disks. Current technology can read information on computer disks within two microns. But a micro-mechanical actuator could read the disk within one-tenth of a micron, a factor of ten improvement, Guckel said.

Commercial ventures into micro-machines are just beginning to develop in the United States, Guckel said. A new company called MEMSTek, based in Vancouver, Wash., started last year and has licensed a number of Guckel's patents. The company is crafting microscopic nozzles for use in ink-jet printers that make finely detailed copies, and making tiny pumps for use in medical equipment.

Deep X-ray lithography uses X-ray light to shine through a stencil-like mask and etch precise patterns into a metal plate. The light source is generated at UW-Madison's Synchrotron Radiation Center. Guckel's lab has improved on the process by combining it with surface micro-machining, which holds the dimensions of parts more precisely.

One of the drawbacks of the process has been its high cost, Guckel said, but they are pursuing ways to bring costs down by creating more parts per each X-ray exposure. The development of shared "print houses," such as the one at Brookhaven National Laboratory, has also produced cost-effective results for companies just getting into micro-mechanics.

More information is available on the laboratory's website at http://www.bnl.gov/world/.

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