Design and characterization of MEMS resonant structures for sensing applications

The work presented in this thesis concerns the design and characterization of MEMS resonant sensors for biomedical applications, interfaced with the conditioning electronics by means of a capacitive technique. Resonant biosensors are micromechanical structures whose resonance frequency changes upon immobilization of the biochemical species of interest on their surface. Such structures are earning a growing interest in the last years, as the development of diagnostic devices is moving towards affordable, portable and easy to use systems. The innovative characteristic of the resonance sensors that will be presented in this work is the use of a pattern of holes in order to obtain an high sensitivity. Two different types of resonators will be presented: clamped-clamped beams and square Lamé mode resonators. For both of them, an analytical model for the estimation of the effect of holes over the resonance frequencies will be developed, validation of these models through comparison with finite element simulations will be performed too. These models will be then employed in the estimation of the resonance sensors performances, therefore showing the beneficial effect of the holes pattern. A comparison between the two proposed types will show the clear superiority of the Lamé resonators. For the beam resonant sensors, preliminary measures of the resonance frequencies, which are in good accordance with both models and finite element simulations, will be also shown. Finally, a new resonant structure based on phononic crystals, whose characteristics are promising for a future application as a biosensor, will be presented as well. As a first step toward the development of such a device, an acoustic transmission line model, capable of describing its behavior, will be developed.