Characterization of Polysilicon Strength through On-Chip Testing at MEMS Stoppers

Constraints limiting the motion of movable structures of Micro-Electro-Mechanical Systems (MEMS) are important to avoid internal electrical contact, that could lead to pull-in events, and to avoid failure of compliant components, in case of events like accidental drops. A study of the failure of ad-hoc designed stoppers is therefore crucial to increase MEMS reliability. A MEMS device has been fabricated for on-chip testing to investigate the mechanical behavior of stoppers, till failure. Electro-statically induced loading conditions have been used to provide tensile stresses along the out-of-plane direction, so that the experimental data can be interpreted to get insights into the tensile strength of columnar polysilicon. Different stopper sizes have been tested and data have been interpreted according to Weibull statistics for brittle materials, to define a characteristic value of the tensile strength of polysilicon and a confidence interval around it.