Multimodal characterisation of high-Q piezoelectric micro-tuning forks

This work presents an electrically actuated, aluminium nitride based, piezoelectric tuning fork designed at the micro-scale for selective modal actuation. This well known resonator, whose advantages have been widely studied and exploited in the milli-scale, has been implemented and studied in the micro-scale, showing promising results. A complete optical and electrical characterisation of the device has been carried out, in which various out-of-plane and in-plane vibration modes have been analysed. Its performance has been studied in vacuum, air and water. High-quality factors (Qs) up to 72 in water and up to 5166 in air have been measured for the in-plane anti-phase mode. This Q-factor is higher than any other value published with the in-plane piezoelectric micro-cantilevers in air. Sensitivity as mass sensor and minimum detectable mass has also been estimated in air. Sensitivity values almost three orders of magnitude higher than millimetric commercial tuning forks have been achieved. Easy integration, simple and selective actuation and a Q make this kind of resonator an attractive alternative in a wide range of applications.