We have developed an experimental protocol for studying slow crack growth in MEMS materials, and we have used this protocol to show that polycrystalline silicon (polysilicon) MEMS are susceptible to stress corrosion cracking. Using a model of the nonlinear dynamics of the specimen, we were able to estimate crack length and crack closure from the frequency response of the specimen. The procedure can resolve 1 nm crack extensions and crack growth rates below 10−13m/s. Crack closure, which has a pronounced effect on the dynamics of this nonlinear system, is possibly associated with the native oxide which grows on the faces of the crack. The data show that subcritical crack growth in polysilicon MEMS is driven by the synergistic effects of water and stress. In contrast to macroscale stress corrosion cracking behavior, we have not found a clear relationship between crack growth rate, stress intensity, and humidity.

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