Stress-tolerant and temperature-stable RF MEMS capacitive switches and tunable filters

This dissertation presents RF MEMS capacitive switches which are based on a thin-film aluminum circular beam geometry that exhibit reduced sensitivity to both initial residual stress and stress-changes versus ambient temperature. The device symmetry also facilitates low-series-inductance compact device arrays for high-value capacitances. These switches are built in the Raytheon RF MEMS process and show an 8-10x improvement in temperature stability over the standard fixed-fixed beam designs. Also, cascadable RF MEMS switched capacitors are demonstrated that are suitable for VHF and UHF tunable filters and reconfigurable matching networks. These devices are fabricated in the UCSD and Raytheon RF MEMS processes and result in a near ideal capacitor impedance over a 30:1 frequency range. The circular geometry is then used to demonstrate an RF MEMS switched capacitor with > 10 W power handling at 10 GH under hot-switching conditions that maintains a relatively-low (< 30 V) pull-in voltage. The device consists of separate RF and DC electrodes, which are defined underneath a temperature-stable circular beam, to result in both increased restoring force above the RF electrode and higher RF self-actuation voltage.;This thesis also presents a compact low-loss tunable X-Band bandstop filter that is implemented on a quartz substrate using both miniature RF-MEMS capacitive switches and GaAs varactors. The 2-pole filter is based on capacitively loaded folded-lambda/2 resonators that are coupled to a microstrip line, and the filter analysis includes the effects of non-adjacent inter-resonator coupling. The RF MEMS loaded filter results in a measured 25 dB improvement in power handling and linearity compared to the GaAs varactor design.;Finally, a 1.6-2.4 GHz suspended 3-pole RF MEMS tunable filter is presented. The filter results in an insertion loss of 1.34-3.03 dB over the tuning range and a 3-dB bandwidth of 201-279 MHz. This design results in a tunable Qu of 50-150 over the frequency range, and to our knowledge, is the first suspended RF MEMS filter with the best Qu. The Appendix presents in full detail the UCSD RF MEMS capacitive switch process on a high-resistivity silicon substrate.