Surface micromachined platinum structures with a high thermal stability

Nowadays, the armatures in RF-MEMS devices such as switches and variable capacitors mostly consist of highly conductive metals which often show a low thermal stability. This can result in undesired changes in the characteristics of these devices after exposure to high temperatures during (post-)processing steps such as packaging and dry release steps. Therefore we investigated for the first time the application of Platinum as material for the armatures of (RF-)MEMS devices. In this paper we report the realization of a thermally stable capacitive RF-MEMS switch with platinum armature and the findings from a comparison with aluminum with 0.5% copper alloy (AlCuo.s%) armatures. Besides thermal stability, also the mechanical and RF-performance have been investigated. In order to realize selectively released, 1 mum thick, freestanding platinum structures, a new process flow has been developed that allows patterning of the platinum film by lift-off on a polyimide sacrificial layer.