Development of a Simple Test Method for Torsional Strength of MEMS Micromirror

Abstract

MEMS micromirrors have been used in optical switches and scanning devices. In these kinds of applications, the beams supporting the micromirror are twisted and deformed to a large extent. Consequently, these single crystal silicon beams have failed catastrophically from brittle fractures. In this paper, a simple fracture test method for the torsional strength of MEMS micromirror has been proposed. This method can be realized through the improvement of the previously proposed bending-torsion combined loading test with respect to the specimen dimensions and loading configuration. The developed method was applied to the actual specimens and it was obtained that shape parameter is 4.40 and scale parameter is 1 575 MPa. From the observation of fracture initiation point, it was found that the torsional fracture has taken place competitively at the sidewall subjected to high stress and the notching region involving high etching damage. Therefore, the proposed simple torsional test realizes the evaluation of the torsional strength of MEMS micromirror, which is governed by inhomogeneous defect and stress distributions.