Characterization Of Micro-Opto-Electro-Mechanical Devices

This paper describes two examples, which include thermal and comb-drive actuators for optical sensor applications. In both examples, numerical simulation was used to provide an optimum design. A two-dimensional finite element modeling (FEM) was used to predict the state of stress and deformation in the MEM cantilever beam and also to analyze the materials and designs so as to minimize the stress state in the structure. The initial processed device showed a small warpage of more than 300 mu m, which was not acceptable for Rockwell system applications. Using FEM, these devices were optimized to drastically reduce the residual stresses, and resulted in actual fabricated warpage-free structures. Once practical structures were found, parametric two- and three-dimensional models were developed to verify mechanical reliability and the final architecture of the MEM device. The second device example was a MEM comb-drive structure. The frequency response of these dynamic structures provide the designer with the minimum detectable signal which can be resolved as well as the deflection of the mass per given acceleration. Therefore, the knowledge of an accurate frequency response is critical for successful design. Accurate FEM modeling provides the coefficients of the second order differential equation which describes mechanical behavior of the accelerometer. These coefficients can be used to create an equivalent circuit model. The model can be simulated in SPICE together with its interface electronics to evaluate the complete sensor performance.