Air gap-based MEMS switch technology using nickel surface micromachining

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 100 Hz. 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 2 GHz and 20 GHz 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 (7 μm) electroplated nickel bridge structure. The device is realized in a 4 lithographic steps process with low complexity and high robustness.