Comparison of three finite element models for analysis of MEMS micromirrors

We investigate finite element modeling of MEMS micromirrors actuated electrostatically by means of tools available in ANSYS finite element modeling software, and compare numerical results with analytical solutions for the static analysis of MEMS micromirrors. MEMS micromirrors must be accurately modeled in order to achieve precise optical positioning. Analysis of MEMS micromirrors leads to the study of structural and electrostatic fields. Finite Element (FE) method is an effective technique to model structural and electrostatic fields. The FE analysis of these coupled fields is accomplished by several tools in ANSYS. This paper models torsional and flexural-torsional micromirrors by different methods in ANSYS. These methods include: (a) a sequential coupled electrostatic and structural field tool; (b) a directly coupled electrostatic and structural field tool employing one-dimensional (1D) transducer element; and (c) a directly coupled electrostatic and structural field tool utilizing a 2-D or 3-D reduced order model. The torsional micromirror is of 1000 by 250 microns square, and the flexural-torsional micromirror is of 100 by 100 microns square. The numerical results are compared with analytical solutions. Comparisons show advantages and disadvantages of these tools for MEMS micromirror modeling. These comparisons allow a selection to be made of the most suitable tool for a given modeling task and assess the accuracy of analytical solutions.