COMSOL
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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
or copied only under the terms of the license agreement. No part of this manual may be photocopied or
reproduced in any form without prior written consent from COMSOL AB.
COMSOL, COMSOL Multiphysics, and COMSOL Script are trademarks of COMSOL AB.
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