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/°C, which is on par with that for fundamental mode resonance.