Frequency Modulated Electrostatically Coupled Resonators for Sensing Applications

This work presents a proof-of-concept for a frequency modulated output MEMS sensor based on electrostatic coupling of two resonators. Change in the gap between a single resonator and a movable capacitive electrode can modulate the electrostatic force acting on the resonator, and therefore, alter its resonance frequency. A second resonator is used as the movable electrode to facilitate displacement amplification in response to the external force at resonance. In this work, clamped-clamped beams are used for both resonators. Three devices are fabricated with different dimensions, and a DC magnetic field is used to actuate the second beam at resonance frequency, while the frequency of the first beam is monitored. It is shown that by actuating the movable electrode at its resonance, sensitivity is enhanced by more than 3 orders of magnitude compared to DC actuation, and sensitivity of 8Hz/mAmT is achieved for a device with 10001.1mx5 pm and 200p.mx3 tim beams and a capacitive gap of I.5ttm. While Lorentz force is used to actuate the beam in this work, the concept is not limited to magnetic field sensing.