Reduction of impedance and feedthrough parasitics of RF micromechanical resonators

Having been demonstrated at frequencies up to 6.2 GHz with measured Q´s >; 4,000, micromechanical resonators hold great promise for enabling on-chip high-Q passives needed in wireless communication systems. However, the acceptance of such devices in present-day transceivers has been hindered by their excessive motional impedances and feedthrough parasitics that prevent direct integration with other RF subsystems and IC´s. This paper reviews strategies for alleviating these issues with focus on the employment of transducers with improved conversion efficiency enabled by atomic layer deposition (ALD) process. Additionally, arrays of mechanically-coupled resonators have been developed to enhance the overall output signal strength of the composite resonators thus lowering the effective motional impedance. Moreover, on-chip Faraday cages were employed to mitigate the effect of the feedthrough noise of the substrate parastics from the motional current of the micromechanical resonator.