Dynamic behavior of ZnO on Si3N4 biomorphs

The deflection of ZnO on Si₃N₄ biomorphs has a quadratic dependence on the applied voltages. The fundamental resonant frequencies of the 2980-μm-long bimorphs range from 140 Hz to 180 Hz. Because of the quadratic dependence, resonances are also observed at the subharmonics of the fundamental resonant frequencies. The resonant frequencies vary with the DC biasing voltages. The shifting of the resonant frequency can be explained by the change of the effective length of the curved bimorph, the stiffening of piezoelectric ZnO film by the biasing voltages, and the increase in the elastic compliance of the bimorph as a result of Joule heating. Air damping is observed with a cut-off frequency around 22 Hz