A corrugated bridge of low residual stress for RF-MEMS switch

Abstract

This paper presents the theory, design, fabrication and characterization of the corrugated membrane for a low-actuation voltage RF-MEMS switch for microwave and millimeter-wave applications. Analytical analyses and experimental results have been carried out to derive algebraic expressions for the mechanical actuation mechanics of corrugated membrane for a low residual stress. It is shown that the residual stress of both types of corrugated and flat membranes can be modeled with the help of a mechanics theory. The residual stress in corrugated membranes is calculated using a geometrical model, confirmed by finite element method analysis and measured by the experimental results. The corrugated electrostatic actuated bridge is suspended over a concave structure of coplanar waveguide, with sputtered nickel as the structural material for the bridge and gold for CPW lines, fabricated on high-resistivity silicon substrate. The corrugated bridge on concave structure requires lower actuation voltage than the flat bridge on planar structure in various thickness Ni RF-MEMS switch. The effective residual stress is measured and calculated about 3–15MPa in the corrugated bridge and 30MPa in the flat bridge. The intrinsic residual stress is about 30MPa regardless of the various thickness of the membrane in the flat bridge. Therefore, the corrugation constants of the bridges with corrugated structure C=σ/σ0 are 0.13–0.5 due to the various thickness membranes 0.3–1.0μm. The residual stress is very low by corrugating both ends of the bridge on concave structure.