Effects of pressure on suspended micromechanical membrane arrays

The effects of pressure on micromechanical air-filled cavities made by a pair of suspended, parallel silicon nitride membranes are investigated in the free molecular and quasi-molecular regimes. Variations of the fundamental drummode mechanical resonant frequencies and damping with air pressure are determined by means of optical interferometry. A kinetic damping linear friction force and a positive resonant frequency shift due to the compression of the fluid between the membranes are observed to be proportional with pressure in the range 0.01-10 mbars. For resonators with near-degenerate modes hybridization of the modes due to this squeeze film effect is also observed and well accounted for by a simple spring-coupled oscillator model.