19 November 2001 Design of rotating MEMS tunable capacitors for use at rf and microwave frequencies
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With the recent surge in popularity of RF and Microwave MEMS many different device topologies are being explored. Some devices provide large changes in capacitance, but lack the ability to provide a linear range of capacitance values between the minimum and maximum values of the device. We present a device design for a low-loss rotating MEMS tunable capacitor that once programmed to the required value consumes no power. This device design is transformed from gear structures currently designed in the SUMMiT process with modifications made so that the device may be used as a varactor. Modifications include alterations of physical structure, drive mechanism for programming capacitance value, and additional post processing steps needed to provide low-loss at RF and Microwave frequencies. Many different device structures are possible each with performance, potential reliability, and potential yield trade offs that must be considered. Post processing is required to add metal to provide sufficiently low loss for high quality components. Since device planarity is critical for operation, a novel post-process metal deposition technique for providing low stress metal was concieved. Additional modifications to compensate for polysilicon warpage are considered for future investigation. Simulation results based on high frequency full wave analysis software show a highly linear tuning range and a capacitance ratio approaching 6 to 1. A model is extracted from the scattering parameters provided by HFSS and then various device sizes and topologies are compared.
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John M. Wilson, Rizwan Bashirullah, David P. Nackashi, David A. Winick, Bruce E. Duewer, Paul D. Franzon, "Design of rotating MEMS tunable capacitors for use at rf and microwave frequencies", Proc. SPIE 4593, Design, Characterization, and Packaging for MEMS and Microelectronics II, (19 November 2001); doi: 10.1117/12.448850; https://doi.org/10.1117/12.448850

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