Advanced micromechanisms in a multi-level polysilicon technology Page: 1 of 12
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Advanced micromechanisms in a multi-level
M. S. Rodgers, J. J. Sniegowski, S. L. Miller, C. C. Barron, and P. J. McWhorter
Sandia National Laboratories
Mail Stop 1080
P. O. Box 5800
Albuquerque, NM 87185-1080
Quad-level polysilicon surface micromachining tech-
nology, comprising three mechanical levels plus an
electrical interconnect layer, is giving rise to a new
generation of micro-electromechanical devices and as-
semblies. Enhanced components can now be produced
through greater flexibility in fabrication and design.
New levels of design complexity that include multi-
level gears, single-attempt locks, and optical elements
have recently been realized. Extensive utilization of
the fourth layer of polysilicon differentiates these latter
generation devices from their predecessors.1 This level
of poly enables the fabrication of pin joints, linkage
arms, hinges on moveable plates, and multi-level gear
assemblies. The mechanical design aspects of these
latest micromachines will be discussed with particular
emphasis on a number of design modifications that
improve the power, reliability, and smoothness of op-
eration of the microengine? The microengine is the
primary actuation mechanism that is being used to
drive mirrors out of plane and rotate 1600-pm diameter
gears.? Also discussed is our most advanced microme-
chanical system to date, a complex proof-of-concept
batch-fabricated assembly that, upon transmitting the
proper electrical code to a mechanical lock, permits the
operation of a micro-optical shutter.
Keywords: microengine, mirror, gear train, transmis-
sion, microactuator, polysilicon
The complexity of devices that can be created using
JUL 3 0 97
surface micromachining methods is significantly influ-
enced by the number of mechanical layers fabricated in
the process. Most components are currently limited to
designs that can be defined in only two or three levels
of polysilicon. The unique quad-level technology
available at Sandia National Laboratories offers much
greater flexibility. Consisting of three mechanical
layers plus an underlying electrical interconnect, this
technology permits the fabrication of actuators, gears,
hubs, and the mechanical linkage arms required to
interconnect these components. The microengine is a
prime example of this technology, and its fabrication
would not be possible with fewer layers. However, the
full potential of the final polysilicon level was not
initially realized due to process artifacts generated
from the multi-level topography.
The implementation of chemical mechanical polishing
(CMP) for planarization effectively eliminates these
artifacts,4 which show up as process stringers and
mechanical interferences. Now known as the Sandia
Ultra-planar Multi-level MEMS Technology
(SUMMiT)5, this process allows new levels of design
complexity. Previously, the designer was constrained
to defining upper level structures that were essentially
isolated islands of polysilicon. Although these islands
could encompass large surface areas, each had to be at
least several microns from its neighbor. This made it
impractical to define close-packed electrostatic ele-
ments and intermeshing gears with reasonable geome-
try. A significant increase in device reliability was
another benefit realized through the improvements to
the multi-level process technology.
Finally, the mechanical design aspects of the latest
generation of multi-level micro-electromechanical sys-
Further author information -
M.S.R.:Emr a a v; Telephone: 505-844-1784; Fax: 505-844-2991
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Rodgers, M.S.; Sniegowski, J.J.; Miller, S.L.; Barron, C.C. & McWhorter, P.J. Advanced micromechanisms in a multi-level polysilicon technology, article, August 1, 1997; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc691586/m1/1/: accessed July 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.