N.M. — Just as astronomers want to understand the
atmospheres of planets and moons, so engineers want
atmospheric knowledge of worlds they create that are
the size of pinheads, their “skies” capped by tiny
their silicon inhabitants — microcircuits, microgears,
and micropower drivers — exist in a vacuum? An atmosphere
of nitrogen? Air as we know it? More importantly,
whatever atmosphere was intended, how long will it
stay that way? Is the protective barrier hermetic
or will its atmosphere change over time, potentially
leading to the early death of the device? Will water
vapor seep in, its sticky molecules causing unpredictable
behavior? What, in short, can we say about how long
this little world and its inhabitants will survive
most advanced sampling procedure known — requiring
only picoliters of gas to evaluate the contents of
these small atmospheres — is now in place at Sandia
National Laboratories, a National Nuclear Security
Administration facility. The method was recently revealed
at the SPIE Photonics Meeting in San Jose, Calif.
know of no one, anywhere else, who can do this kind
of testing,” says Sandia innovator Steve Thornberg.
Maciel agrees. Chief Operating Officer of Radant MEMS,
a three-year-old start-up company in Stow, Mass.,
he is under contract with DARPA to develop high-reliability
MEMS (microelectromechanical) switches for microwave
devices and phased array antennas. He also sees markets
for his MEMS switches in cell phones.
long-term reliability, small-atmosphere stability
is a must. “We can’t go to a commercial house to get
this work done,” he says. “We can’t find the capability
anywhere else but Sandia.”
Sandia method — funded by its Laboratory-Directed
Research and Development program, and presented for
consideration to Sandia’s patent office — involves
a small commercial valve that comes down like a trash
compactor and crushes a tiny device until it releases
its gases — currently, about 30 nanoliters — into
a custom-built intake manifold.
Thornberg’s test mechanism requires only picoliters,
his sensitive device can recheck its own measurements
— using bursts of gas delivered in a series of puffs
— dozens of times from the same crushed device in
a 20-minute time span.
method thus provides statistically significant atmospheric
measurements at any given moment in a component’s
industry tests can achieve at best only a single reading
from the release of nanoliters of gas. A single, statistically
unverified result may contain significant error.)
waiting a longer period of time — weeks, or even months
— other microdevices from the same batch can be crushed
and then analyzed to see what changes have occurred
in their atmosphere over time.
the system is able to measure gasses emerging in pressures
ranging from one atmosphere to .0001 torr. (One atmosphere
is 760 torr.) The group hopes soon to decrease its
lower sensitivity limit to .000001 torr — in effect,
to be able to measure the quality of vacuums.
Sandia researcher Danelle Tanner, who describes herself
as “a reliability-and-aging mechanism physicist” working
on a silicon re-entry switch, “We want 100 percent
nitrogen [atmosphere] in our device. Steve’s group
gave us a really good idea of what species other than
nitrogen were present in the package.”
the integrity of the internal atmosphere of a hermetic
device is essential for long-term component reliability,”
says Thornberg. “It is within this environment that
all internal materials age.”
of his group’s new investigatory technique lies in
the details of the test mechanism.
precisely machined sample holder holds the MEMS package
to be crushed within the sampler valve. If the sample
holder is too low, the part would not crush the MEMS
device; too high, and the device would crush prematurely,
letting gases escape unmeasured.
tested devices come in many sizes, height adjustments
to the crushing mechanisms are needed for each sample.
problem of debris from the smashed part interfering
with gases that must pass through tiny tubes was solved
by sintering a filter into a central gasket.
most important, manifold volumes were minimized to
maximize pressures when MEMS-released gases expand,
reducing the amount of gas needed for an analyzable
ahead is success in measuring very small amounts of
moisture, which stick to manifold walls without making
it to the detector.
overcome this problem, the Sandia group is working
with Savannah River National Laboratory to incorporate
that lab’s optical moisture measurement techniques
based on surface plasmon resonance (SPR). In that
technique, an optical fiber is used to transmit light
from a specially coated lens. Moisture levels are
measured from wavelength shifts.
Sandia is a multiprogram laboratory operated by
Sandia Corporation, a Lockheed Martin company, for
the U.S. Department of Energy’s National Nuclear Security
Administration. Sandia has major R&D responsibilities
in national security, energy and environmental technologies,
and economic competitiveness.
media contact: Neal Singer, email@example.com, (505)