The Mechatronics of MEMS
“If I had to do it over again, I would’ve pursued a physics degree,” says Jonathan Hammond, staff design engineer for MEMS Technology Development at RF Micro Devices Inc. (RFMD) in Greensboro, N.C.
Hammond
is one of a team of MEMS design
and process experts who are developing
an improved RF MEMS switch
for cell-phone RF (radio-frequency) front-ends.
The MEMS effort at RFMD includes electrical
engineers, physicists, and chemical engineers.
“MEMS can be an interesting place to work because
it is multidisciplinary,” says Hammond. “You are
actuating a machine with currents and voltages, so
you have to understand how electronic components
or circuits deliver those stimuli. And you have to
understand how the stimuli translate into forces and
displacements on your machine.”
Hammond says he has found people with physics
degrees have the best grasp of fundamentals, a big
advantage when it comes to working with MEMS.
“When you first build something it often behaves in
an unexpected way, and you have to
go back into the physics to figure out
what’s going on,” he says.
Because MEMS is a multidisciplinary
field, engineers use multiphysics
tools optimized for MEMS. At
RFMD, designers use a package from Coventor Inc., Cary,
N.C., known as Architect
that includes 3D visualization
features. To
address the complicated
multidomain nature of a
MEMS device, Architect
employs a lumped-element approach where the behavior
of each portion of a machine is simulated
using underlying physics-based
equations. It is parametric and less
computationally intensive than FEA
and thus can be faster. RFMD uses
the FEA portion of Coventor tools to
establish the merit of a given design
and also to confirm and verify the
lumped-element result.
The 3D visualization feature is
a recent addition to the Coventor
lumped-element simulation tool. It’s
useful for “seeing how the mechanical
elements of our switches relate
to each other, how they contact,
bounce, and vibrate in the conditions
we apply,” says Hammond. “We can
then adjust the mechanical design
or electrical input from control circuitry
to improve performance. Before
the 3D visualization package, we
had to surgically extract data from
Coventor Architect output files — a
bit like looking at every square inch
of a painting through a magnifying
glass — and then try to put all of
the pieces together to see the whole
painting,” he says.
Make Contact
Coventor Inc.,
coventor.com
RF Micro Devices,
RFMD.com