RF Mems Capacitive Switches for Tunable Microsystems

Abstract

This thesis deals with the design, simulation, fabrication and characterization of low voltage Radio Frequency Micro-electro-mechanical Systems (RF MEMS) capacitive shunt switches. Switch membrane geometry is modified to achieve low actuation voltage in the range of 10 − 18:5 V and good RF performance in different bands. Commercial CAD tool CoventorWare is used for design and DC analysis while RF analysis is carried out using ANSYS HFSS and Agilent ADS. Inductive tuning of switch membranes is employed to tune the RF characteristics to optimize X, Ku, K and Ka band performance. Inductance is added to the shunt membranes by modifying beam geometry. The fabrication of the switches is carried out as a five mask surface micromachining process on silicon substrate. DC and RF parameters are measured and are found to be very good. Further, the design, electromechanical and electromagnetic modeling of Single Pole Four Throw switch is carried-out as part of the thesis. The DC and RF simulation results show low actuation voltage of 13.75 V, insertion loss and isolation better than 0.7 dB and 52 dB respectively in X-band. Additionally, wide-band and narrow-band tunable bandpass filters in X and Ku bands are designed on co-planar waveguides using cantilever series and capacitive shunt switches and realized as cascaded sections of highpass and lowpass filters. Tunability in center frequency from 11.76 GHz to 15.86 GHz is achieved by the controlled actuation of shunt switches and bandwidth tunability from 2.34 GHz to 5.4 GHz by series switches. Further, distributed true time delay phase shifter is designed on slow wave co-planar waveguide employing five sets of metallic membranes as floating shield. The controlled actuation of the floating membranes result in variable capacitive loading and thereby achieving good phase tunability. The design provided a phase shift tunability in the range 18◦ to 28◦ at 10 GHz, 124◦ to 180◦ at 70 GHz and a liniar variation in the above range for the intermediate frequencies.