Etude et modélisation de capteurs piézoélectriques

Abstract

The work of this thesis focuses on the design, modeling and realization of capacitive pressure sensors using the combination of two techniques PCB-MEMS. We started by describing the various manufacturing processes of pressure sensors and summarizing the state of the art of the various methods of manufacturing the capacitive pressure sensor. The modeling of the mechanical behavior of square, rectangular and circular membranes is carried out to study the influence on the variation of capacitance as a function of the applied pressure (the capacitive response), as well as the sensitivity to the pressure. We determined the influence of the geometric parameters of the membrane on the performance of the capacitive pressure sensor. We performed a comparative study between the simulation results obtained from COMSOL software and the theoretical results. We found that the simulation results are consistent with those of the theory. We proposed two structures made of capacitive pressure sensors using PCB-MEMS technology. The BETTS process is used to fabricate the SU-8 membrane and chemical etching as well as the lift-off process to realize the two electrodes of the capacitive pressure sensor. The gap between the two electrodes is defined by the thickness of the copper layer of the commercial printed circuit. The main advantage of the proposed procedure is the simplicity and low cost of the manufacturing process. Moreover, the ease of integrating auxiliary electronic circuits on the same printed circuit and the possibility of modifying the geometry of the structure for the specific application. Then, two prototypes were manufactured, simulated and characterized to determine their characteristics. We found that the sensitivity of the capacitive pressure sensor (first prototype) is 4.25 pF/ bar and the second prototype has a sensitivity of 20.13 pF/bar. A simple calibration procedure is mentioned to overcome the inherent deviations of the manufacturing process. We studied the effect of temperature on the response of the capacitive pressure sensor. Consequently, the results obtained by the COMSOL simulation are in good agreement with those of the experimental.