Stable zipping RF MEMS varactors

Abstract

Novel zipper varactors with the potential for achieving large tuning ranges have been fabricated and characterized. These varactors have a curved cantilever electrode that is actuated by a single pull-down electrode. The shape of the cantilever is designed such that its local stiffness is tailored to enable extended stable zipping. In a series-mounted varactor, the measured capacitance ratio was 16.5 for actuation voltages between 0 and 46 V. However, the presence of an unexpected tuning instability at 32 V bias limited the practical tuning range in this varactor. This behaviour was attributed to fabrication imperfections. The first electrical self-resonant frequency of the same varactor was extrapolated to be 72.6 and 17.2 GHz at 20 and 329 fF, respectively. In a different shunt-mounted varactor, the quality factor (Q) was measured to be 91 (60 fF) and 176 (600 fF) at 2 GHz. Including the anchor, the varactors have a small device footprint and fit within an area of 500 by 100 µm.