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In the field of microwave applications, microelectromechanical systems (MEMS) are attractive devices in order to force miniaturization by on chip integration. Here, we describe the design, fabrication and testing of a silicon based micromachined switch using piezo-electrically actuated elements. The microwave circuit consists of a coplanar waveguide (CPW) design with two piezoelectric activated beams integrated between the middle line and the ground planes. During operation the beams short the CPW by two overhanging bridge contacts and therefore the transmission characteristics of the microwave circuit change. The CPW is realized by 3 µm thick electroplated copper to yield good transmission characteristics, whereas the clamped-clamped beams benefit from a 250 nm thin PZT film between 100 nm thin Pt electrodes on top of a SiO 2 layer. By the use of double side clamped beams awkward stress compensation of the piezoelectric stack is omitted. Instead the system relies on some initial mechanical stress. Measurements prove deflections of more than 13 µm for a 1400 µm long beam with operation voltages below 10 V. This is in good agreement with finite element simulations. The novel RF-MEMS is predicted to reach an isolation (in "on" state) of more than 20 dB up to 15 GHz.

The paper reviews the developments made for designing and fabricating a piezoelectric driven actuator and its integration into coplanar wave guide (CPW) microwave structures. In the first part of this work the electromechanical properties of different lead–zirconate–titanate (PZT) thin films are investigated. A modified precursor route for chemical solution deposition (CSD) is introduced to minimize the thermal budget of the PZT by maintaining its superior piezoelectric properties. The second part deals with the fabrication of a piezoelectric driven actuator for use in RF switching applications. Advantages of bulk and surface micromachined devices are compared and a suitable actuator design is proposed. Based on these results, a piezoelectrically actuated shunt switch for use in CPW devices is developed and optimized, and the concept is confirmed by measurements. Finally, novel reconfigurable CPW band‐pass filters are presented, which demonstrate the usefulness of the developed shunt switches in microwave applications. Microwave switch Distribution of surface current density (background), image of copper contact (top) and micro switch schematic (bottom).

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