On the failure of silicon thin membranes during free fall tests for MEMS microphones

The effect of the impact against hard surfaces on MEMS thin membranes attached to dummy devices, as observed through guided free fall (GFF) tests, is investigated through three-dimensional, finite element numerical simulations. Accounting for the different scales involved, a multiscale top-down approach is followed, and first both purely fluid-dynamics and purely solid-mechanics macro-scale simulations are carried out, to provide fluid pressure histories and anchor displacements as input for the silicon thin membranes. Then, a micro-scale mechanical analysis is carried out to judge whether possible failures arise in a given GFF test for each membrane. It is shown that in some cases possible failures actually depend from the combination of the fluid-induced and of the solid-induced input transferred to the MEMS membrane, and not from a single domain-induced loading condition.