Design project for a micromirror for GE4230 Design/Simulation of MEMS at UW-Platteville

1. MICROMIRROR DESIGN USING SANDIA SUMMIT TOOLS
GE 4230: Design and Fabrication of MEMS
Dr. Osama Jadaan
University of Wisconsin – Platteville
Jon Zickermann
November 28, 2011
Abstract: A fabrication layout for a micromirror was designed and developed using the SUMMiT V
design and visualization tools provided by Sandia National Laboratories for the first project of the year.
In addition to the tools, the dimensions for the spring of the micromirror were provided along with a
basic layout and PowerPoint slides from Sandia to give an example to model after. After a 2d layout was
drawn in AutoCAD 2010, a 3d model was created and imported into ANSYS Workbench for FEA
simulation. Using Workbench the behavior of the mirror was observed when put under static loading
and modal analysis.

2. 1
TABLE OF CONTENTS
Objective ....................................................................... 2
Development ...................................................................... 2
Fabrication Layout ........................................................... 2
Layers .................................................................... 4
Simulations .................................................................... 8
Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. 2
OBJECTIVE
Previously in EP3930 (Introduction to MEMS/Nanotech) students were introduced to the
concepts of the microscale, including the physics, applications and the fabrication of devices at
this scale. One method included surface microfabrication, which is used to create MEMS
devices like micromotors and micromirrors. Currently in GE4230 a more in -depth look has been
taken with the focus on the Sandia SUMMiT V tools, which allow a user to create a MEMS
device that can be fabricated using the SUMMiT batch surface microfabricat ion method. In
addition, the tools allow for the user to preview the design while in AutoCAD to verify if the
design will work even without any loads present. Given the dimensions for the spring of the
micromirror along with a basic layout and PowerPoint slides from Sandia, students in GE4230 were
challenged to design a micromirror with the SUMMiT tools and simulate in ANSYS workbench to verify
the design.
DEVELOPMENT
Fabrication Layout:
The basis behind the design was to fabricate a mirror template that would be strong with
a minimal usage of material. With the basic shape of the Poly2 layer given and the dimensions
for the structure of Poly3 (the spring) given, the first focus was to secure the respective layers
down to the substrate. At the ends of the spring, a SacOx3 layer was offset from the Poly3 end
to secure to the Poly2 structure, while another square was offset and assigned to the SaxOx1

4. 3
Layer to secure the Poly2 structure to the base. The Poly2 structure was further supported by
additional SaxOx1 layers equally spaced along the base.
Fig i: Cross section at the spring end
Fig ii: Cross section through the center of the Poly2 “arm”
The next task was to create etch holes in the spring and supporting structure. Originally
the holes were circles, however due to excessive node counts in the meshes for the FEA
simulations, the circles were changed to squares. Following this, the focus shifted to the spring.
The first task was to secure the plate to the Poly2 structure to further su pport the spring.
After, a base for the Poly4 layer was need. As with the etch holes, the original ideas contained
circles protruding from the Poly3 layer, however, the design was changed to a more typical
structure due to a bad FEA outcome with very high stress concentrations at the supports.
Fig iii: Cross section through the center of the Poly3 support
Fig iv: Cross section through the center spring with Poly4 layer added
The last task in fabrication was to add the Poly4 layer. The dimensions were a square
based from the maximum width of the Poly2 structure. Etch holes were added in the similar
style as the previous designs and two slots were added to further match the Sa ndia design.

5. 4
Layers:
Fig1: Fabrication layout dimensions:

6. 5
Fig 2: Poly 2 Layer
Fig 3: SaxOx1 Layer on Poly2, all dimensions same for other side

7. 6
Fig 4: Poly3 Layer
Fig 5: SacOx3 Layer

8. 7
Fig 6: Poly4 Layer
Simulations
Fig 7: Deformation Analysis
*Using a load of 0.0054µNm – see discussion

9. 8
Fig 8: Stress Analysis
Fig 9: Modal Analysis Diagrams:

10. 9

11. 10

12. 11
DISCUSSION
For the FEA simulation, the substrate was chosen as the fixed support and a 0.0054µNm
moment load was applied. The moment load was estimated from a paper on a torsional
micromirror estimating the attraction force of the mirror to the electrode would be 5 µN (Zhang,
Chau, Quan, Lam, & Liu, 2001) and the width calculated from half of the length of the Poly4
layer structure. To prepare for the FEA simulation, several steps were taken including many
face and body sizing operations to cut down on the number of nodes from over 350,000 to
about 60,000. Without the reduction of nodes, no solution would be provided. Overall, the
mirror deflected as expected that should prove durable according to the FEA simulation.
REFERENCES
Zhang, X., Chau, F., Quan, C., Lam, Y., & Liu, A. (2001). A study of the static characteristics of
a torsional micromirror. Elsevier Science B.V.