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V E R S I O N   3 . 3
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COMSOL Multiphysics MEMS Module Minicourse
© COPYRIGHT 1994–2006 by COMSOL AB. All rights reserved
Patent pending
The software described in this document is furnished under a license agreement. The software may be used 
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Other product or brand names are trademarks or registered trademarks of their respective holders.
Version:
September 2006 
COMSOL 3.3
 
C O N T E N T S
Preface 
Solving Electro-Thermo-Mechanical Problems 
 2
 3
Microresistor Beam 
 4
Introduction    .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .     4
Model Definition .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .     4
Results and Discussion.   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    5
Modeling in COMSOL Multiphysics .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .     6
Modeling Using the Graphical User Interface   .   .   .   .   .   .   .   .   .   .   .   .    7
Solving Piezoelectric Problems 
 22
A Piezoelectric Shear Actuated Beam 
 23
Introduction    .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   23
Model Definition .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   23
Results.   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   25
Modeling in COMSOL Multiphysics .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   26
References  .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   27
Modeling Using the Graphical User Interface   .   .   .   .   .   .   .   .   .   .   .   .   27
Eigenfrequency Analysis   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   32
Frequency-Response Analysis  .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   33
Appendix: Geometry Modeling   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   35
Low-Voltage Electroosmotic Micropump 
 38
Introduction    .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   38
Model Definition .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   41
Results and Discussion.   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   42
Modeling in COMSOL Multiphysics .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   45
References  .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   46
Modeling Using the Graphical User Interface   .   .   .   .   .   .   .   .   .   .   .   .   46
Appendix—Geometry Modeling  .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   54
C O N T E N T S  | i
ii | C O N T E N T S
M E M S   M o d u l e   M i n i c o u r s e
  |   1
Preface
Mathematical modeling has become a very important part of the research and 
development work in engineering and science. Retaining a competitive edge requires 
a fast path between ideas and prototypes, and in this regard mathematical modeling 
and simulation provide a valuable shortcut for understanding both qualitative and 
quantitative aspects of scientific and engineering design.
This minicourse gives you an introduction into the modeling of microscale systems 
using COMSOL Multiphysics and the MEMS Module. It takes you though several 
fields of science commonly encountered when modeling MEMS: electrical and 
structural problems, piezoelectricity, and microfluidics. You do not require any prior 
expertise in mathematical modeling or COMSOL Multiphysics in order to find it 
rewarding.
Enjoy your modeling!
The COMSOL team
2  |   M E M S   M O D U L E   M I N I C O U R S E
Solving Electro-Thermo-Mechanical 
Problems
Electro-mechanical actuators and sensors constitute the backbone of the whole MEMS 
area. The mechanical movement they provide differentiate MEMS devices from 
conventional microelectronics where the mechanics is designed to be fixed and only 
electric (wanted) and heat currents (side effect) are observed.
The MEMS Module contains several example models of MEMS actuators and sensors 
such as cantilever beams, comb drives, micromirrors, resonators, thermomechanical 
microvalves, pressure sensors, and accelerometers. You can make a quick 3D analysis 
of the electrostatic field and calculate capacitance values based on that using 
Electrostatic application mode alone. Or you can model pure continuum mechanics, 
like how residual stresses affect on the resonant frequencies, by using Structural 
Mechanics application modes. Using Moving Mesh application mode you can 
accurately combine movements and geometry changes in your own models. Lastly you 
can create fully electro-thermo-structural couplings, like in the following example of a 
microresistor beam. The application in this example is to move the structure by 
conducting a current through conductive layers and generate a temperature increase 
that leads to a displacement through thermal expansion.
M E M S   M O D U L E   M I N I C O U R S E   |   3
Microresistor Beam
Introduction
This example illustrates the ability to couple thermal, electrical, and structural analysis 
in one model. This particular application moves a beam by passing a current through 
it; the current generates heat, and the temperature increase leads to displacement 
through thermal expansion. The model estimates how much current and increase in 
temperature are necessary to displace the beam. 
Although the model involves rather simple 3D geometry and straightforward physics, 
it provides a good example of multiphysics modeling because it contains several appli-
cation modes added incrementally to the model. Note that this model of a microresis-
tor beam also appears in the companion MEMS Module Model Library in the 
Actuators Models folder under the name micro_beam3d.
Model Definition
Figure 1: Microbeam geometry.
A copper microbeam has a length of 13 µm plus a height and width of 1 µm. Feet at 
both end bond it rigidly to a substrate. An electrical potential of 0.2 V applied between 
the feet induces an electric current. Due to the material’s resistivity, the current heats 
up the structure. Because the beam operates in the open, the generated heat dissipates 
into the air. The thermally induced stress loads the material and deforms the beam.
4  |   M E M S   M O D U L E   M I N I C O U R S E