Download Assembly Method for Three-Dimensional MEMS Saves Chip Space

Assembly Method for Three-Dimensional MEMS Saves
Chip Space Using Single Magnetic Actuation for Large
Arrays of Devices
Office of Technology Management
U N I V E R S I T Y O F I L L I N O I S AT U R B A N A – C H A M PA I G N
Technology Summary
This technology is an efficient process for assembling large arrays of three-dimensional, hinged micro structures for micro electromechanical systems (MEMS) applications. Using a single electromagnet for actuation, this new method saves chip space
as well as actuates large arrays of devices in parallel. It makes fabrication of MEMS
devices more reliable and simple by eliminating the need for biasing several actuators and not requiring a constant source of energy for actuation. Thousands of
microstructures, each measuring less than 0.1 mm, can be assembled in parallel within
10 sec.
While MEMS fabrication has been the primary area of study, this method also can be a
general process for assembling many types of three-dimensional structures.
Benefits
This new method for assembly of MEMS
devices eliminates the need for individual
biasing of actuators, saves chip space,
and doesn't require a constant energy
source.
• Added reliability and ease of assembly:
A single electromagnet actuates a large
array of devices in parallel.
• Biasing eliminated: The method eliminates any need for individual biasing of
the actuators.
• Lower energy needs: The method does
not require a constant source of energy
(constant actuation) to maintain MEMS
flaps in an off-plane position.
• Less chip space required: Smaller die
sizes and, ultimately, larger area densities can be used on integrated, optical
MEMS.
Applications
• Optical MEMS (e.g., micromirrors,
switches, waveguides)
• Micro sensors (e.g., flow rate sensors)
• Micro probes (e.g., IC testing probes)
Patent Information
The technology holds a U.S. patent.
http:// www.otm.uiuc.edu/technology.htm
Technical Details
This novel technology is a sequential assembly
process that allows fabrication and assembly of
large arrays of three-dimensional, hinged MEMS.
The ability to use a single electromagnet for
actuation saves chip space and actuates large
arrays of devices in parallel—making fabrication
of MEMS devices faster, more reliable, and more
cost-effective.
Another variation of this method involves using a
MEMS assembly with one flap that has a spring
beam (an offset slab). This spring beam increases
the magnetic field strength needed to raise the
flap and also causes the flaps to operate asynchronously in an increasing magnetic field. The
spring beam also provides variable resistance to
the flap when it is positioned at different angles.
Why it Is Better
How it Works
The process is used with a MEMS assembly that
includes at least one hinged flap. The individual
components are cast in place on sacrificial layers,
using planar deposition to electroplate small
amounts of a magnetic material, such as
Permalloy, onto each part. The parts are then
freed from the substrate by a selective etchant,
after which a magnetic field is applied to cause
the pieces to rotate out of the plane on tiny
hinges and lock into place.
Varying the amount of magnetic material applied
to the flaps allows control of the speed at which
the parts fold into position. Because of their
differing amounts of magnetic material, the flaps
are raised asynchronously when placed in an
increasing magnetic field. They also can be
designed to remain interlocked after the magnetic field is removed, thereby enabling use of a
single magnetic field that does not require
actuators on the chip itself.
In order to maintain off-flap displacement, previous methods have required dedicated, on-chip
micro-actuators that are mechanically, electrically,
or magnetically linked to the flap and that supply
a constant energy source to the structure. This
new technology uses only a single electromagnet
to actuate many devices asynchronously.
Previous methods that required individual actuators to deploy large arrays of devices were
compromised because each actuator had to be
individually biased. By eliminating that need, this
new method provides easier, more reliable
assembly.
Most current actuators occupy a large portion of
the chip area (approximately 100 µm2), in
addition to the flap itself, thereby increasing the
die size and limiting the ultimate area density of
integrated optical MEMS. The chip space saved
by this novel process translates to time, materials,
and cost savings. ■
contact:
Roger VanHoy; (217) 244-1275; [email protected]
D&T File Number: T99017 [UI01-044]
2.28.03; T99017 [UI01-044]