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 phr.