In this paper effects of the material property assumed as isotropy on the design of microstructures are discussed and examples of silicon-based micropressure sensors are illustrated. Finite Element Method (FEM) is utilized to analyze stress and displacement distributions of microstructures under loading and results of FE analysis where monolithic silicon is modeled as isotropic or anisotropic materials are compared. Moreover, in the simulations, von Mises criterion and Huber Mises criterion are adopted as yielding criterions for isotropic and anisotropic materials, respectively. The results reveal that for micropiezoresistive pressure sensors, modeling the silicon as an isotropic material will yield a design with an overestimated sensitivity when compared with the anisotropic model, which may result in the pressure sensors with lower sensitivities and performances. For microcapacitive pressure sensor, besides erroneous expectation of their sensitivities, the diaphragm of a microsensor modeled as isotropic material may touch the bottom electrode to cause the device out of work. From two examples, it is evident that the design of microstructures will be unacceptable if single-crystal silicon is postulated as the isotropic material. One can expand the research in this paper to other materials and various microsensors of MEMS.
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