Simple and Robust Air Gap-Based MEMS Switch Technology for RF-Applications

Abstract

This paper presents a simple and robust process for fabrication of functional electrostatic RF-MEMS switching devices with lifetimes easily exceeding 10 8 cycles with 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. It is shown how these switched capacitors, even though having a capacitance ratio of only 2.8, can still form adequate switching devices and RF-circuits by proper design and combining of these devices with high-Q inductors and transmission lines. 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 air gap in the down-state. This airgap is switched by electrostatic actuation of a thick electroplated Nickel bridge-structure. The device is realized in a 4-lithographic steps process with low complexity and high robustness.

Air gap-based MEMS switch technology using nickel surface micromachining

“…This effectively results in an increased down-state isolation in a narrow frequency band, which offers narrow band switching devices with adequate performance for use in tunable notch band filters and tunable stop band filters. This paper further extends on earlier work [6] by demonstrating devices with an increased capacitance ratio, presentation of process optimization and stress tuning of the electroplated nickel armature layer and by introduction of a new design which allows the implementation of switched air gap devices in the 20 GHz range.…”

Tunable band-stop filter based on single RF MEMS capacitive shunt switch with meander arm inductance

“…However, SAW filters are limited in frequency (<3 GHz). A survey of the recent literature reveals that apart from the traditional active [2] and distributed RC passive [3] notch filters, novel tunable band-stop filter topologies using photonic [4] or electromagnetic band gap (EBG) structures [5], quarter wavelength open stubs, radial stubs or slotted ground structures [6][7][8], complementary split ring resonators (CSRR) utilising metamaterials [9], lumped LC circuits [10,11], multilayer ferromagnetic resonance [12] and bulk acoustic wave (BAW) resonators [13] are chosen as alternatives to address similar problems. In general, all of the above approaches are quite complex systems, requiring large silicon areas (>6 mm in length) and exhibiting moderate performances.…”

“…However, they are not usually integrated with the filter fabrication process and the insertion losses are relatively high. RF MEMS capacitors are still the most promising solution, thanks to their potentially superior RF performance, high Q-factor, monolithic integration and miniaturisation [5,[7][8][9][10][15][16][17][18]. On the other hand, continuous tuning range in analog MEMS filters is usually limited to 10% [5] and digital tunable filter solutions result in just two centre frequency states [8][9][10] or they need multi-bit actuation to achieve 60% tunability in a discrete fashion [7].…”