JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 16, NO. 5, OCTOBER 2007
Direct Contact-Area Computation for MEMS
Using Real Topographic Surface Data
Daniel J. Dickrell, III,
, Michael T. Dugger,
Matthew A. Hamilton, and W. Gregory Sawyer,
—Direct computation of interfacial contact area for
microelectromechanical-system applications was performed nu-
merically using the measured device surface topography and the
material hardness to deFne the ±ow stress of an individual ele-
ment. The simulation results compared well with the established
contact-area determination methods and also introduced new ca-
pabilities that enabled the visualization of the spatial distribution
of contact spots to be computationally mapped and rendered
directly onto device surfaces.
—Contact mechanical factors, contacts, friction.
NTERFACIAL contact-area determination is very important
for microelectromechanical-system (MEMS) device design.
The phenomena that affect the MEMS device performance
and lifetime are primarily dependent on the interaction area
between device surfaces (examples include surface adhesion,
friction, wear, and electrical contact resistance). The gross
contact geometry of most MEMS electrical switches is planar,
which stems from the layered fabrication processes that are
used to create the device. The actuation forces in the operation
of MEMS contacts are typically on the order of 10–100
The local surface roughness mainly determines the real area of
contact as very few asperity contacts are required to support
these loads , ; the real area of contact is likely orders-
of-magnitude smaller than the apparent area of contact, as
de±ned by the device design. The combination of low con-
tact forces and nominally ²at contact geometry accentuates
this subtle in²uence of the surface-roughness variation on
device contact-area spot size and distribution. An accurate
determination of interfacial contact area in MEMS requires
proper surface-roughness characterization and appropriate uses
of these measurements to predict contact-area size and distri-
bution under these extremely low force operating conditions.
Fig. 1(a) and (b) shows the characteristic roughness exhib-
ited by a MEMS device contact surface. Fig. 1(a), which is
obtained by scanning electron microscopy, shows the over-
Manuscript received December 13, 2006; revised April 9, 2007. Sandia
is a multiprogram laboratory operated by Sandia Corporation, a Lockheed
Martin Company, for the United States Department of Energy’s Na-
tional Nuclear Security Administration under Contract DE-AC04-94AL85000.
Subject Editor L. Lin.