This study concerns the feasibility of piezoelectric components partially released from the substrate on which they are made for the realization of microsystems (MEMS). With PZT, they are microstructured in the shape of bridge or cantilever by means of the thick-film technology associated to the sacrificial layer. Unlike the structures directly screen-printed on the substrate which resonate only on thickness mode (MHz), the free-standing samples also present radial vibrations modes in the plane (tens of kHz). Furthermore, we realized cantilevers of rectangular shape revealing unusual in-plane 31-longitudinal mode (tens of kHz). An analytical modeling associated with the experimental data allowed to determine PZT's Young modulus and that of gold, weaker than those of the massive materials. A numerical modeling (COMSOL multiphysics) verifies the accuracy of the established laws and confirms the validity of our approach consisting of the combination of the various mechanical laws applied to our micro-cantilevers. We showed the low influence of the pressure and the temperature but also the sensitivity to the toluene (qq ppm) of the cantilevers coated PEUT polymer. The first results on the viscosity influence of liquid on the resonant frequency demonstrate the potential use of these micro-cantilevers in the field of the viscoelastic characterization of fluids.
Etude de MEMS piézoélectriques libérés et microstructurés par sérigraphie. Application à la détection en milieu gazeux et en milieu liquide