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Abstract: This paper presents a simple and robust process for fabrication of functional electrostatic RF-MEMS switching devices with lifetimes easily exceeding 108 cycles by unipolar actuation at 100Hz. The device implements a switchable air gap capacitor and is therefore not limited in lifetime by dielectric charging as opposed to contact-type capacitive switches implementing high-k dielectrics. Even though these switched air gap capacitors have a rather low capacitance ratio of around 5–6, they can still form adequate switching devices and RF-circuits by making use of properly designed transmission lines and when combined with high-Q inductors. Examples described include tunable notch band filters designed for the 2GHz and 20GHz range and a tunable stop band filter. The novelty of the proposed process is that it combines a sacrificial layer consisting of a single layer with a single dry etching step for the dimples which define the height of the air gap in the down-state. This air gap is switched by electrostatic actuation of a thick (7μm) electroplated nickel bridge structure. The device is realized in a 4 lithographic steps process with low complexity and high robustness. [Copyright &y& Elsevier]

A process to fabricate functional polysilicon structures above large (4×4 mm2) thin (200 nm), very flat LPCVD silicon rich nitride membranes was developed. Key features of this fabrication process are the use of low-stress LPCVD silicon nitride, sacrificial layer etching, and minimization of membrane stress and deformation after fabrication, which was done by complete removal of the sacrificial layer, avoidance of sharp corners in the design of the functional polysilicon structures, and annealing of the polysilicon after doping. A polysilicon layer that was directly attached to the silicon nitride membrane was used. The polysilicon was doped locally to separate the rotors from the stators electrically, preventing short-circuiting. The layer was patterned with a hexagonal supporting structure that serves three main functions: membrane strengthening, electrical wiring and microactuation. As a demonstration of the technology a pseudo hexagonal polysilicon framework with embedded comb-drive actuated microshutter suspended above a ∼150-nm thick membrane, was successfully fabricated. [Copyright &y& Elsevier]

Abstract: In this paper, we show that substrate charging is another possible failure mechanism limiting the lifetime of capacitive RF MEMS switches. Switches fabricated on different substrates can exhibit a different lifetime. Also the influence of environmental conditions on the lifetime can depend on the type of substrate. In addition, we show that switches actuated with an actuation voltage below pull-in voltage can pull-in after some time due to charging of the substrate. We show results of experiments dedicated to emphasize this substrate charging by minimizing charging of the interposer dielectric. [Copyright &y& Elsevier]