By R. Colin Johnson (04/19/2007 11:23
AM EDT)
PORTLAND, Ore. - Angstrom-level accuracy is needed to stabilize
platforms used in applications like microelectromechanical
system testing, nanoscale metrology and semiconductor fabrication
tools. One company is developing products based on a mechanism
called negative stiffness to cancel vibrations.
"The U.S. Air Force couldn't find a place quiet enough
to test their next-generation acceleratometers and gyros,"
said David Platus, CEO of Minus K Technology Inc. (Inglewood,
Calif.). "That got me thinking about a negative stiffness
mechanism to cancel out vibrations."
Since the 1960s, the best way to isolate precise instruments
like atomic-force and scanning-tunneling microscopes along
with fab tools from vibration was passive air tables that
support weight on a cushion of air. A recent alternative is
using active electronic feedback to send canceling forces
that damp out oscillations in springs.
Platus claimed his patented negative stiffness mechanism outperforms
active systems while undercutting the price of passive systems.
"Our negative stiffness mechanism exerts an opposing
force which cancels out the stiffness in a spring," said
Platus. The result is "isolation that is twice as good
as other active systems, but for half the price of air table-style
passive vibration isolation systems."
Minus K has amassed a patent portfolio covering its negative
stiffness mechanism. Its products offer vibration isolation
payload capacities ranging from a 10-pound tabletop unit to
10,000-pound floor panels. When adjusted to a 0.5 Hz natural
frequency, the vibration isolators achieve 93 percent isolation
efficiency at 2 Hz, 99 percent at 5 Hz and 99.7 percent at
10 Hz, the company claims.
Most platforms, even those with active stabilization, have
a certain positive stiffness coefficient that determines their
natural resonant frequency-usually 1 Hz or higher. By subtracting
a spring's negative from positive stiffness, Minus K's negative
stiffness mechanism can block nearly all vibrations higher
than 0.5 Hz, it claimed.
A key application is controlling vibrations in chip manufacturing
equipment. "Transistors have critical dimensions down
around 25 nanometers and the most critical dimension is the
oxide thickness, which is 1 nanometer," said David Ferry,
a nanotechnology researcher and engineering professor at Arizona
State University.
"You have to control 1-nanometer vertical thickness over
300 millimeters of lateral dimension," Ferry added. "That
defines modern manufacturing technoloy's need for effective
vibration isolation, which has never been greater than today,
and will continue to become more demanding as the nano industry
progresses."
Arizona State University isolates its atomic-force and scanning-tunneling
microscopes with Minus K's vibration isolation technology.
