Monocrystalline-Silicon Based RF MEMS Devices

Sammanfattning: This thesis presents novel radio-frequency microelectromechanical (RF MEMS) devices, for microwave and millimeter wave applications, designed for process robustness and operational reliability using monocrystalline silicon as structural material. Two families of RF MEMS devices are proposed. The first comprises reconfigurable microwave components integrated with coplanar-waveguide transmission lines in the device layer of silicon-on-insulator wafers. The second consists of analog tuneable millimeter wave high-impedance surface arrays.The first group of reconfigurable microwave components presented in this thesis is based on a novel concept of integrating MEMS functionality into the sidewalls of three-dimensional micromachined transmission lines. A laterally actuated metal-contact switch was implemented, with the switching mechanism completely embedded inside the signal line of a coplanar-waveguide transmission line. The switch features zero power-consumption in both the on and the off state since it is mechanically bistable, enabled by interlocking hooks. Both two-port and three-port configurations are presented. Furthermore, tuneable capacitors based on laterally moving the ground planes in a micromachined coplanar-waveguide transmission line are demonstrated.The second group of reconfigurable microwave components comprises millimeter-wave high-impedance surfaces. Devices are shown for reflective beam steering, reflective stub-line phase shifters and proximity based dielectric rod waveguide phase shifters, as well as a steerable leaky-wave antenna device based on the same geometry. Full wafer transfer bonding of symmetrically metallized monocrystalline silicon membranes, for near-ideal stress compensation, is used to create large arrays of distributed MEMS tuning elements. Furthermore, this thesis investigates the integration of reflective MEMS millimeter wave devices in rectangular waveguides using a conductive adhesive tape, and the integration of substrates with mismatched coefficients of thermal expansion.