Multiple mode micromechanical resonators

Abstract

Two resonant micromechanical structures that have been designed, fabricated, and tested and which exhibited multiple modes of vibration are described. The first had a cantilevered inertial mass that was actuated by a curved-comb electrostatic drive attached near the root of the cantilever. The second structure had a straight-comb electrostatic-drive with a folded flexure suspension that was used to actuate the cantilevered inertial mass. The first structure exhibited two distinct vibration modes, and the second structure exhibited three distinct vibration modes. An analytic dynamic model has been developed and it predicted the vibrational mode shapes of the structures. Tests of the fabricated structures have demonstrated that peak-to-peak lateral displacements greater than 10 microns were feasible. Further, peak-to-peak angular displacements greater than 10 degrees have been measured during second mode vibration. The resonant frequencies of the structure varied from 1.7 to 33 kHz, depending on structure geometry. Cantilever structures with overhang lengths as great as 864 microns have been fabricated and operated with no perceptible contact between the inertial mass and the substrate. >