Piezoelectric microresonators based on aluminum Nitride for mass sensing applications

In this work we analyze the vibrational behavior of microresonators (cantilevers and bridges) actuated with piezoelectric aluminum nitride (AlN) films, to investigate the suitability of these devices as mass sensors. The resonators of different geometries consisted of a freestanding unimorph structure made up of a metal/AlN/metal piezoelectric stack supported by a Si₃N₄ structural layer. The out-of-plane motion of the resonators was assessed by laser interferometry. The electrical impedance of the devices exhibited significant variations at some resonant frequencies ranging from 0.5 MHz to 13 MHz. The mass sensitivity of the microresonators was evaluated through the frequency shift of the resonant modes when loading the resonators with SiO₂ films. High order resonant modes provided higher mass sensitivities, with values as low as 6 ag/Hz, which improved significantly our previous results.