RF MEMS Switches for high power applications

This thesis introduces a new concept in 3D RF MEMS switches intended for power applications. The novel switch architecture employs electrothermal hydraulic microactuators to provide mechanical actuation and 3D out-of-plane silicon cantilevers that have both spring action and latching mechanisms. This facilitates an OFF-state gap separation distance of -200 μLim between ohmic contacts, without the need for any hold power. Having simple assembly, many of the inherent problems associated with the more traditional suspension bridge and cantilever type beam architectures can be overcome. SPST switches have been developed. With the first revised switch, a novel trench structure was introduced, but the device failed mechanically due to excessive lever stiffness. High RF insertion losses were also found, due to an unwanted oxide layer directly underneath the CPW feed lines. With the second revision in which two types of lever structure were devised, mechanically working devices were achieved. The high losses found previously were significantly reduced due to a revised fabrication process to remove an unwanted oxide layer. Although a superior OFF-state isolation characteristic was achieved, unpredicted ripples were present in the ON-state, causing high insertion loss. It was found that the higher conductivity (than the manufacture's specifications) of the silicon wafer used for the cantilevers caused the ripple by carrying out circuit and electromagnetic modelling. Both the design and fabrication process have been improved through the investigation on failure mechanisms. From the final experiment, the measured ON-state insertion loss and retur loss are less than 0.4 dB and greater than 15 dB up to 12 GHz, respectively, while OFF-state isolation is better than 30 dB up to 12 GHz. The switch works well in both hot and cold-switching modes with 4.6 W of RF power at 10 GHz, without any signs of degradation to the ohmic contacts.EThOS - Electronic Theses Online ServiceGBUnited Kingdo