Development of Specimen and Test Method for Strength Analysis of MEMS Micromirror

Specimen and fracture test method for the strength analysis of MEMS micromirror have been proposed. Specimen with dimensions that closely resemble that of the actual product in order to mimic the actual working stress environment has been designed. Pure bending and combined loading tests have been performed and torsion strength (fracture criterion) has been estimated based on those results. Two-parameters Weibull distribution was used to evaluate the fractured stresses (nominal maximum principal stress) estimated from FEM model. It is found that there exists the difference in strength between pure bending and combined loading. From the SEM observations, it is found the flaw population depends on the structural geometry and is nonuniformly distributed. Thus, specimen strength will depend on flaw and stress distribution. Consequently, both geometry and stress distribution have to be considered simultaneously to effectively estimate the strength of MEMS. From FEM and load factor analysis, it is found torsional strength of the MEMS micromirror can be estimated on the safe side by using the result of combined loading test. Finally, MEMS design stress based on the confidence interval values for each Weibull parameter was shown