MICROMIRROR DESIGN USING SANDIA SUMMIT TOOLS GE 4230: Design and Fabrication of MEMS Dr. Osama Jadaan University of Wisconsin – Platteville Jon Zickermann November 28, 2011Abstract: A fabrication layout for a micromirror was designed and developed using the SUMMiT Vdesign 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 abasic layout and PowerPoint slides from Sandia to give an example to model after. After a 2d layout wasdrawn in AutoCAD 2010, a 3d model was created and imported into ANSYS Workbench for FEAsimulation. Using Workbench the behavior of the mirror was observed when put under static loadingand modal analysis.
2OBJECTIVE Previously in EP3930 (Introduction to MEMS/Nanotech) students were introduced to theconcepts of the microscale, including the physics, applications and the fabrication of devices atthis scale. One method included surface microfabrication, which is used to create MEMSdevices like micromotors and micromirrors. Currently in GE4230 a more in -depth look has beentaken with the focus on the Sandia SUMMiT V tools, which allow a user to create a MEMSdevice that can be fabricated using the SUMMiT batch surface microfabricat ion method. Inaddition, the tools allow for the user to preview the design while in AutoCAD to verify if thedesign will work even without any loads present. Given the dimensions for the spring of themicromirror along with a basic layout and PowerPoint slides from Sandia, students in GE4230 werechallenged to design a micromirror with the SUMMiT tools and simulate in ANSYS workbench to verifythe design.DEVELOPMENTFabrication Layout: The basis behind the design was to fabricate a mirror template that would be strong witha minimal usage of material. With the basic shape of the Poly2 layer given and the dimensionsfor the structure of Poly3 (the spring) given, the first focus was to secure the respective layersdown to the substrate. At the ends of the spring, a SacOx3 layer was offset from the Poly3 endto secure to the Poly2 structure, while another square was offset and assigned to the SaxOx1
3Layer to secure the Poly2 structure to the base. The Poly2 structure was further supported byadditional SaxOx1 layers equally spaced along the base.Fig i: Cross section at the spring endFig ii: Cross section through the center of the Poly2 “arm” The next task was to create etch holes in the spring and supporting structure. Originallythe holes were circles, however due to excessive node counts in the meshes for the FEAsimulations, 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 containedcircles protruding from the Poly3 layer, however, the design was changed to a more typicalstructure due to a bad FEA outcome with very high stress concentrations at the supports.Fig iii: Cross section through the center of the Poly3 supportFig 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 squarebased from the maximum width of the Poly2 structure. Etch holes were added in the similarstyle as the previous designs and two slots were added to further match the Sa ndia design.
11DISCUSSION For the FEA simulation, the substrate was chosen as the fixed support and a 0.0054µNmmoment load was applied. The moment load was estimated from a paper on a torsionalmicromirror 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 Poly4layer structure. To prepare for the FEA simulation, several steps were taken including manyface and body sizing operations to cut down on the number of nodes from over 350,000 toabout 60,000. Without the reduction of nodes, no solution would be provided. Overall, themirror deflected as expected that should prove durable according to the FEA simulation.REFERENCESZhang, X., Chau, F., Quan, C., Lam, Y., & Liu, A. (2001). A study of the static characteristics ofa torsional micromirror. Elsevier Science B.V.