Investigation of mechanics properties of an awl-shaped serpentine microspring for in-plane displacement with low spring constant-to-layout area

Abstract

The design, fabrication, and experimental test of an awl-shaped serpentine microspring (ASSM) for providing in-plane motion and low spring constant-to-layout area are investigated. The ASSM can provide low stiffness for in-plane motion under a restricted layout area. The spring constants of ASSMs for in-plane motion are theoretically analyzed by using Castigliano’s theorem, and validated through simulation using COMSOL Multiphysics. These ASSMs are successfully fabricated on a silicon-on-insulator wafer. The parameter K/A (spring constant-to-layout area) is used as the performance index. Smaller K/A induces larger deformation under the same layout area. It shows that K/A of ASSM is smaller than the classic one with the same dimensions (total length and number of turns). Geometric sizes having effect on K/A are discussed. The spring constants for in-plane and out-of-plane motion are compared and discussed. The taper angle and beam width-to-thickness ratio (w/h) are two key factors. As w/h being >1, the spring constant of in-plane motion (ky) is always larger than that of out-of-plane motion (kz). If w/h is <1, the spring constant kz would be larger than ky if the taper angle are larger than its critical angle φr.