Novel characterization method for MEMS devices

A novel characterization method for MEMS devices based on the combination of measurement and simulation results is introduced on the example of an electrostatically actuated micro mirror array. The aim of this method is to determine geometrical parameters and built-in mechanical stress on the base of the measured eigenfrequencies. A Laser Doppler interferometer and a signal analyzer are used to determine the frequency response function (FRF) of the micro mechanical structure and the eigenfrequencies are calculated. For the numerical simulation of the micro mirrors behavior the finite element (FE) model is used and a series of nonlinear coupled-field analysis and pre-stressed nonlinear modal analysis have been performed. Hence the dependence of the eigenfrequencies on geometrical parameters and built-in mechanical stress is obtained. The comparison to the measured frequencies yields in values for the searched parameters that are mean values for the entire micro mechanical structure. The presented method is very efficient because it determines several characteristics of a MEMS device on the base of only one measured frequency response function. The article demonstrates that a sufficient accuracy is achieved and stress values are calculated that are hardly ascertainable using common measurement methods.