Static crack growth and fatigue modeling for silicon MEMS

Fatigue in silicon microstructures has been widely observed but is currently not well understood. In this paper, it is shown that typical silicon MEMS fatigue can be described by a 'classic' stress corrosion cracking (SCC) model for glass fracture. The model can be used to describe the slow crack propagation and ultimate failure of MEMS structures due to mechanical stress under different conditions. With this SCC model it is possible to do full lifetime predictions, and these correspond very well with measured fatigue data from literature, as a function of applied stress and temperature. This suggests that at least part of the literature data available can be explained by static fatigue, which is better described by a time to failure than cycles to failure. However, not all failures can be explained by SCC alone, a notable exception being those of MEMS devices with very thin surface oxides.