Higher-Mode Free-Free Beam Micromechanical Resonators

Polysilicon free-free beam micromechanical resonators based on MEMS technology operating in second and third-mode flexural vibrations have been demonstrated at frequencies as high as 102 MHz with Q’s on the order of 11,500. Via strategic placement of electrodes, and careful determination of the exact support beam attachment locations that minimize anchor loss, these new resonators actually exhibit higher Q in the second mode than in the fundamental at the same frequency. Experiments to gauge the effect of variations in support beam dimensions and attachment locations on free-free beam microresonator performance show that an offset of only 0.6 μm in the support beam attachment location results in a 7X degradation in the Q. In addition, measured temperature coefficients for second-mode free-free beam μresonators are on the order of −13.1 ppm/oC, which is on par with that for fundamental mode resonance.