Characterization and displacement control of low surface-stress AlN-based piezoelectric micro-resonators

Micro-cantilevers and micro-bridges actuated by sputter-deposited aluminium nitride (AlN) thin films were measured with a scanning laser Doppler vibrometer up to 6 MHz, covering more than 10 resonance modes of different nature. A finite element model (FEM) was used to simulate the modal response of the micromachined structures. The comparison between experiment and simulation, regarding modal shapes and frequencies, resulted in an excellent agreement. An interferometric microscope was also used to study the static deflection of the structures. These measurements revealed a very low surface stress for the different micro-resonators. Finally, we point out how the amplitude of a given resonant mode can be controlled depending on the piezoelectric charge collected by the top electrode layout.