Single-Device and On-Chip Feedthrough Cancellation for Hybrid MEMS Resonators

Microelectromechanical systems (MEMS) resonators typically exhibit large parasitic feedthrough where the input drive signal is directly coupled to the output ports, presenting a challenge to full electrical characterization of resonators where the output is heavily embedded in feedthrough. We here present an on-chip solution that significantly mitigates the undesirable effects of parasitic feedthrough but using only a single device. We have demonstrated its use in a symmetrical mode of vibration (the extensional mode of a square-plate MEMS resonator) to show its applicability to most generic resonator mode shapes. In our measurements, we show that the proposed method for feedthrough cancellation provides a 40-dB common-mode rejection compared to when no feedthrough cancellation is implemented. The necessary matching of drive circuit capacitances is achieved by properly sizing and placing a dummy pad in the vicinity of each drive pad. The studies reported herein demonstrate that the integrity of the output signal from a MEMS resonator is not only determined by device dimensions but also strongly influenced by the interaction between fringing fields radiating from electrodes in proximity. These results could open up a new avenue in the design of hybrid MEMS resonant devices where the issue of feedthrough can be both effectively and cheaply addressed.