High Performance RF MEMS Series Contact Switch - Design and Simulations

In this paper, we present a detailed discussion of the design and simulation of a RF MEMS contact switch. Process-induced stress effects are discussed and included in the simulations. The advantage of the design is described by comparing its static characteristics with that of a simple cantilever switch device. When comparing to a typical cantilever switch, this MEMS switch design is unique in the following aspects: 1) the dielectric cantilever, together with the top electrostatic electrode, extends beyond the metal shorting bar; and 2) the metal shorting bar, instead of being an insulated metal line attached to the bottom of the dielectric cantilever, is at one end permanently fixed (and electrically connected) to either the RF signal input or output trace. The connection is made through etching a via (side-contact) in the sacrificial layer on top of the RF signal line trace and overlapping the shorting-bar metal line with the via (side-contact) opening. The shorting-bar side contact decreases the stress-induced cantilever bending and therefore improves stability with regard to stress and temperature. It also reduces the number of necessary switch contacts from two to one, resulting in lower contact resistance and better device reliability. The use of an extended actuation cantilever design leads to a large and stable contact area at high actuation voltages. This, combined with the single contact feature enabled by the side contact design, results in a high performance MEMS series contact switch. The measured switch DC resistance is <1Omega with insertion loss <0.3 dB and isolation >25 dB up to 40 GHz.