This colorized electron microscope image reveals the boxy shape of the pits the NIST team etched into the diamond surface, exhibiting their smooth vertical sidewalls and flat bottom. The pits were between 1 and 72 um in size. Image: NIST
Diamonds may be best known as a symbol of long-lasting love.
But semiconductor makers are also hoping they’ll pan out as key components of
long-lasting micromachines if a new method developed at NIST for carving these
tough, capable crystals proves its worth. The method offers a precise way to
engineer microscopic cuts in a diamond surface, yielding potential benefits in
both measurement and technological fields.
By combining their own observations with background gleaned
from materials science, NIST semiconductor researchers have found a way to
create unique features in diamond—potentially leading to improvements in
nanometrology in short order, as it has allowed the team to make holes of
precise shape in one of the hardest known substances. But beyond the creation
of virtually indestructible nanorulers, the method could one day lead to the
improvement of a class of electronic devices useful in cell phones, gyroscopes,
and medical implants.
Well known for making the hugely complex electronic
microchips that run our laptops, the semiconductor industry has expanded its
portfolio by fabricating tiny devices with moving parts. Constructed with
substantially the same techniques as the electronic chips, these microelectromechanical
systems, or MEMS, are just a few micrometers in size. They can detect
environmental changes such as heat, pressure, and acceleration, potentially
enabling them to form the basis of tiny sensors and actuators for a host of new
devices. But designers must take care that tiny moving parts do not grind to a
disastrous halt. One way to make the sliding parts last longer without breaking
down is to make them from a tougher material than silicon.
“Diamond may be the ideal substance for MEMS devices,” says
NIST’s Craig McGray. “It can withstand extreme conditions, plus it’s able to
vibrate at the very high frequencies that new consumer electronics demand. But
it’s very hard, of course, and there hasn’t been a way to engineer it very
precisely at small scales. We think our method can accomplish that.”
The method uses a chemical etching process to create
cavities in the diamond surface. The cubic shape of a diamond crystal can be
sliced in several ways—a fact jewelers take advantage of when creating facets
on gemstones. The speed of the etching process depends on the orientation of
the slice, occurring at a far slower rate in the direction of the cube’s “faces”—think of chopping the cube into smaller cubes—and these face planes can
be used as a sort of boundary where etching can be made to stop when desired.
In their initial experiments, the team created cavities ranging in width from 1
to 72 um, each with smooth vertical sidewalls and a flat bottom.
“We’d like to figure out how to optimize control of this
process next,” McGray says, “but some of the ways diamond behaved under the
conditions we used were unexpected. We plan to explore some of these mysteries
while we develop a prototype diamond MEMS device.”