Electrostatic control of mechanical quality factors for surface-micromachined lateral resonators

We investigate a laterally driven, surface-micromachined microstructure, whose mechanical quality factor can be adjusted electrostatically after fabrication. An electrical method for the mechanical quality factor control is presented and applied for laterally driven micromechanical resonators. The present method is based on the damping-gap change caused by an electrostatic force between parallel planar microstructures. Micromechanical resonators for quality factor control tests have been designed and fabricated by a 4-mask surface-micromachining process, including the dry etching of a 6 mu m-thick LPCVD polycrystalline silicon layer. In the experimental test performed at atmospheric pressure, the quality factors of the microfabricated resonators have been reduced rapidly at the rate of 120 V-1 in the control voltage range of 1.75-2.25 V; thereby demonstrating that 50% reduction of the mechanical quality factor of a microfabricated resonator can be achieved in the control voltage range of 1.75-2.25 V with the maximum 0.8% modification of resonant frequency.