Surface micromachined metal armatures are commonly used for MEMS applications of which RF-MEMS is the most well known. In most cases metals with a high conductivity, such as aluminum or gold, are used. These metals often have a low melting point and therefore have a low thermal stability and show plastic deformation of the structures at relatively low temperatures (<200 • C). High melting point metals, such as platinum, are expected to show plastic deformation only at higher temperatures which makes them interesting for use as a structural layer in RF-MEMS devices. In this paper, we present a technology to realize suspended platinum structures by means of surface micromachining. An improved lift-off process allows patterning 1 μm Pt films on a polyimide sacrificial layer. A comparison of the characteristics and armature resonance frequencies between RF-MEMS switches with Pt armatures and AlCu 0.5% alloy armatures reveals an increased thermal stability for the former up to at least 250 • C. This enables zero-level packaging of switches at relative high temperatures without affecting their performances. The lower conductivity of Pt compared to AlCu 0.5% does not lead to a significant increase in RF losses. Implementing AlN as a dielectric material, the Pt-based capacitive shunt switches reported in this paper showed lifetimes in excess of 5×10 7 cycles under standard testing conditions.

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We show for the first time that the substrate can influence the lifetime of capacitive RF MEMS switches. We demonstrate that the influence of the substrate should not be ignored. The influence of the environment on the lifetime of a switch is different when it is fabricated on two different substrates. We also present that a switch actuated with a DC voltage lower than the pull-in voltage can pull-in after some time. The goal of the performed experiment was to emphasize the charging of the substrate. The presented results help to understand the substrate charging problem.