Micromechanical Resonators for Oscillators and Filters

Fully monolithic, high-Q, micromechanical signal processors are described. A completely monolithic high-Q oscillator, fabricated via a combined CMOS plus surface micromachining technology, is detailed, for which the oscillation frequency is controlled by a polysilicon micromechanical resonator to achieve high stability. The operation and performance of μmechanical resonators are modelled, with emphasis on circuit and noise modelling. Micromechanical filter design is described, and a prototype two-resonator bandpass filter is demonstrated. An integrated micro-oven that stabilizes the resonance frequency against temperature variations using only 2 mW of power is reviewed. Brownian motion and mass loading phenomena are shown to have a greater influence on short-term stability and dynamic range in this micro-scale. Scaling strategies are proposed to alleviate potential limitations due to Brownian noise.