Electrostatically actuated thin-film amorphous silicon microbridge resonators

Doped hydrogenated amorphous silicon microbridge resonators are fabricated at temperatures below 110°C on glass substrates using thin-film technology and surface micromachining. The microelectromechanical structures are electrostatically actuated by using a superposition of dc and ac voltage components. The resulting deflection is optically detected. The effects of the measurement pressure, actuation voltage, and geometrical dimensions of the structures on the resonance frequency and quality factor are studied and the results are interpreted using electromechanical models. Resonance frequencies between 600kHz and 31MHz are observed for the micron-sized structures, corresponding to effective elastic spring constants in the range from 10 to 4000N∕m, for both the fundamental flexural mode and the symmetry-allowed harmonics. Young’s moduli of 146 and 80GPa are extracted for hydrogenated amorphous silicon and aluminum, respectively. At a measurement pressure of 10−6Torr, these resonators present quality factors as high as 5000 in the small-deflection limit. The value of the quality factor is very sensitive to both the measurement pressure and excitation voltage amplitude.