Determination of the elastic modulus of thin film materials using self-deformed micromachined cantilevers

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Abstract
The elastic modulus is a very important mechanical property in micromachined structures. There are several design issues such as resonant frequencies and stiffness in micromachined structures that are related to the elastic modulus. In addition, the accuracy of the results from a finite element model is highly dependent upon the elastic modulus. In this study a simple technique to characterize the elastic moduli of thin films of any thickness was developed. The film to be measured formed a bilayer cantilever with another film through standard micromachining processes. Due to the residual stresses of these two films the bilayer cantilever was deformed without any external load. Through the deformation profile of this self-deformed bilayer cantilever, the elastic modulus of the deposited film was determined. A theoretical model was developed to predict the variations of the elastic modulus of a deposited film and the deformation profile of a bilayer cantilever. Experiments were also conducted to demonstrate the applications of this approach. In the experiments, bilayer cantilevers constructed from thin films of different materials and residual stresses were fabricated and measured.