Finite element methods; microelectromechanical devices; microsensors; modeling; piezoresistance; piezoresistive devices
This paper proposes a model for predicting the piezoresistive effect in microflexures experiencing bending stresses. Linear models have long existed for describing piezoresistivity for members in pure tension and compression. However, extensions of linear models to more complex loading conditions do not match with experimental results. A second-order model to predict piezoresistive effects in tension, compression, and more complex loading conditions is proposed. A reduced form of the general second-order model is presented for thin flexures in bending. A three-step approach is used to determine the piezoresistive coefficients for this reduced-form model. The approach is demonstrated for two sets of -type polysilicon. The predictive ability of the model is investigated by comparing the results to the experimental results using the new piezoresistive model and coefficients. One of the ways to implement the model is with multiphysics finite element analysis (FEA). The piezoresistive FEA for flexures algorithm is a FEA implementation of the unidirectional form of the model for flexures. The results presented in this paper are for the simplified cases of long thin flexures experiencing bending and axial loads. This new model could contribute to optimized sensors and feedback control of microdevices, nanopositioning, and self-sensing microdevices.
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