Capacitance Based Tunable Resonators

We present four electrostatic actuators that tune the stiffness and hence the resonant frequency of a micromechanical oscillator. Using these actuators, resonant frequencies have been reduced to 7.7% and raised to 146% of the original values. These shifts correspond to approximately two orders of magnitude reduction in stiffness and a doubling in stiffness, respectively. Comparisons are drawn between these actuators based on functionality, area utilization efficiency, linearity and stability. Other issues discussed are asymmetries, nonlinearities and failure modes. With regard to the nonlinearities, near the limit of resonant frequency reduction, we show the ability to tune the system into a bistable state.