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Working Science

Diamonds are a MEMS Best Friend

by David Baurac and Jane Andrew,
Argonne National Laboratory

diamond film magnified millions of timesThis silicon plate holds 40,000 diamond-film dots. The computer screen in the background shows the dots magnified millions of times, looking more like banana slices than diamonds. Using a photolithographic etching process, dots like these can be made into diamond parts and components for micro-electro-mechanical systems (MEMS).
(Photo courtesy of George Joch, Argonne National Laboratory)


A revolutionary new method for growing the world's smoothest and purest diamond films has been developed at Argonne. This technology—"ultra-nanocrystalline diamond films"—could provide the materials breakthrough needed to push the fledgling field of micro-machines called "MEMS" into the commercial mainstream.

Already researchers worldwide are developing MEMS—short for micro-electro-mechanical systems—for medical, transportation, industrial and aerospace uses. Among the devices now on the market are sensors that trigger car airbags, nozzles for ink-jet printers, and blood-pressure monitors so small they can be implanted in the human body.

Visionaries talk about the day when implanted MEMS will help kidneys function, remove plaque from arteries and dispense cancer-fighting drugs directly to tumors. Satellites no bigger than a deck of playing cards may one day be launched into orbit packed with hundreds of micro-instruments and -sensors based on MEMS technology.

But the applications for current MEMS devices are limited because they are made almost exclusively from silicon. Silicon's poor friction and wear properties make it unsuitable for micro-motors, -pumps and other micro-machines with fast-moving parts.

"Gears assembled into a microscopic motor would spin at something like 400,000 revolutions per minute," explains Dieter Gruen, who invented Argonne's diamond-film technology and later extended it in collaboration with Argonne colleague Alan Krauss and many other Argonne researchers. "The gears are so tiny they have to spin that fast to create enough torque to perform mechanical work, such as pumping. If you do that with a silicon gear, it will wear out after only a few minutes."

Free-standing Micro-objects

free-standing diamond tubeTo overcome this problem, Gruen and his group are working to make gears and other objects out of diamond, the hardest, most wear-resistant substance known. They have already made a freestanding tube and a strain gauge (caliper) of pure diamond film. Their preliminary experiments suggest that diamond films may be 1,000 times more wear-resistant than silicon.

free-standing diamond caliperTheir basic approach is to grow a diamond film on a silicon-dioxide base, or substrate, then chemically remove the silicon dioxide, leaving a freestanding diamond structure. Diamond films grown with conventional methods won't readily attach to silicon dioxide, but those grown with Argonne's new method attach naturally.

Conventional Method

The conventional method for making diamond films uses methane as its carbon source and a great deal of hydrogen to produce films that adhere to silicon. This method produces crystals that measure 1 to 10 micrometers in size. (A micrometer is one-millionth of a meter, about 40 millionths of an inch.) The film feels like fine-grit sandpaper to the human touch.

Argonne's New Process

Argonne's process, on the other hand, uses Buckeyballs (Buckminster Fullerenes) as the carbon source in an atmosphere of argon gas that contains little hydrogen. The resulting diamond films have crystals one million times smaller than those in conventionally grown films. As a result, their surfaces are so smooth they don't need polishing.

"Comparing the crystal size in conventional films to ours is like comparing a boulder to a pebble," says Gruen.

Ultra-nanocrystalline diamond films open doors for many applications
Diamond has many outstanding physical and chemical properties such as extreme hardness, low coefficient of friction, resistance to corrosion by many substances, the ready ability to emit electrons and the ability to transmit sound faster than any other material. These properties can be influenced and fine-tuned by using Argonne's new ultra-nanocrystalline diamond-film process to control the size of the crystals that make up diamond films. In addition to MEMS devices, there are other potential applications for this technology.

Flat panel displays—Diamond flat panel displays would be cheaper to manufacture than the current display based on liquid crystal technology, would consume less battery power and have a larger viewing angle.

Surface acoustic wave (SAW) devices—Diamond SAW devices for high-frequency telecommunications currently operate at peak frequencies around one gigahertz. Ultra-nanocrystalline diamond films could raise practical frequencies to the five-to-seven-gigahertz range, greatly expanding the speed of information transmission.

Rotary shaft seals— Diamond coatings on rotary shaft seals have shown reduced torque and virtually no wear, potentially leading to longer seal life and lower energy consumption in liquid pump operations.

Electrochemical electrodes—Ultra-nanocrystalline diamond films are electrically conducting and form continuous layers as thin as 500 carbon atoms. This gives them high promise for use in electrochemical electrodes, particularly for the oxidation of many organic substances that are environmental hazards.

This research was supported by the Department of Energy's Office of Basic Energy Sciences.

Contact: Dieter Gruen, Argonne National Laboratory, dmgruen@anl.gov, (630) 252-3513

Related Information:

"Diamond Films for Microelectromechanical Systems (MEMS)," Technology Transfer at Argonne National Laboratory
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