Microelectromechanical variable-bandwidth if frequency filters with tunable electrostatical coupling spring

This paper describes the theory, design and test of a novel architecture of highly-selective micromechanical filters employing electrostatically coupled resonators with floating or biased coupling electrodes. This original method avoids the use of mechanical coupling springs thus extending the potential of a given process to higher frequencies. It gives also the possibility to implement more complex filter architectures and to tune the coupling factor of resonators. Filters with 2.8 MHz and 10.6 MHz center frequency having tunable relative bandwidths of 0.025-0.17% have been built from pairs of clamped-clamped beam resonators. Special design techniques have been used to reduce parasitic capacitances on the coupling node.