Frequency Characterization of AlN Piezoelectric Resonators

In this paper, we analyze the vibrational spectra of mechanical resonators actuated piezoelectrically with aluminum nitride (AlN) films. The microresonators consist in bimorph cantilevers with different lengths containing a piezoelectric metal/AlN/metal stack supported by a silicon nitride structural layer. The thicknesses of both the AlN and Si₃N₄ layers are varied between 0.3 mum and 1 mum to study their influence on the mechanical response of the cantilevers. The motion of the cantilevers electrically driven is first assessed by optical laser interferometry; resonant frequencies varying between 100 kHz and 8 MHz are obtained. Additionally, many of the vibrational modes are detected by measuring the changes of the electrical impedance at the resonant frequencies. The mass detection factor of the cantilevers is assessed by measuring the frequency shift after mass loading with thin SiO₂ layers. A value of 0.18 fg/Hz is obtained for vibrational modes around MHz.