In this thesis modelling, design, fabrication and characterization of MEM (MicroElectroMechanical) resonators for RF applications and chemical sensing are discussed. MEM resonators allow to obtain integrated highly selective filters and low phase noise oscillators for RF applications, as well as sensors of chemical and biological species, which can be used to obtain a sensor array on a chip, leading to the possibility of very complex analysis in a very small space. Specifically, a novel RF device, namely a free-free resonator on the third mode, is presented and its basic working is demonstrated. Effect of temperature and axial stress on this device and on other flexural resonators is discussed and an equivalent circuit for free-free resonator is proposed. Furthermore, the optimized design of a bulk-mode disk resonator is presented. The goal of this optimization is the achievement of the maximum quality factor (i.e. maximizing selectivity in filter architecture or minimizing the phase noise in resonator-based oscillators) at a target resonance frequency. The maximization is based on an original strategy of estimation of the quality factor of the device through FEM simulations. Finally, the design of an innovative microbalance is presented. The main features of this device are the actuation and the sensing, which are both magnetic. The device has been fabricated with a CMOS-compatible process. The frequency response of the device was measured, showing the basic working of the device
