Floating Electrode Microelectromechanical System Capacitive Switches: A Different Actuation Mechanism E. PAPANDREOU 1 , S. COLPO 2 , M. KOUTSOURELI 1 , F. GIACOMOZZI 2 , G. PAPAIOANNOU 1 , B. MARGESIN 2 1 National Kapodistrian University of Athens, Solid State Physics Section of Physics Dpt., Panepistimiopolis Zografos, Athens 15784, Greece 2 FBK- IRST, Via Sommarive 18, 38050 Povo Trento, Italy Abstract. The paper investigates the actuation mechanism in floating electrode MEMS capacitive switches. It demonstrated that in the pull-in state the device operation turns from voltage to current controlled actuation. The current arises from Poole-Frenkel mechanism in the dielectric film and Fowler- Nordheim in the bridge-floating electrode air gap. The pull-out voltage seems to arise from the abrupt decrease of Fowler-Nordheim electric field intensity. This mechanism seems to be responsible for the very small difference with respect to the pull-in voltage. The radio frequency (RF) microelectromechanical systems (MEMS) switches and varactors have been developed more than fifteen years ago for low loss switching/routing circuits and X-band to millimeter-wave (mm-wave) phase shifters, which have seen increasing applications in tunable filters, antennas and reconfigurable matching networks [1, 2]. Among the different designs, the capacitive switches proved to exhibit excellent RF performance and power handling [3, 4]. The performance of the capacitive switches depends on the down-state capacitance that can be limited by the finite roughness as well as the low planarity of both the dielectric layer and the beam [5, 6]. In order to diminish this effect and ensure a constant capacitance in the pull-in state, the deposition of an additional (electrically floating) metal layer on the dielectric layer was proposed [7, 8, 9]. Such devices are actuated through side actuation pads or by applying the bias directly to the transmission line. Among the two actuation methods, the former is similar to the one used in conventional capacitive switches and the pull-in condition has been analyzed in details in many papers including or not the charging effect, e.g. [1, 2, 10, 11. In these switches the actuation through the floating electrode has received no attention in spite of the dramatic change of bridge to floating electrode capacitance, hence