Abstract
The goal of this thesis is the design of a surface acoustic wave (SAW) pressure sensor using Aluminum Nitride (AlN). Theoretical studies, realization, and characterization of the pressure sensor on different SAW structures are presented. The modeling of the sensor was performed using an equivalent circuit based on Mason model and Coupling-Of-Mode. The theoretical study, SAW parameters in different structures of AlN/SiO2/Si, AlN/Si, and AlN/Mo/Si are calculated and analyzed. From these analysis, the wave velocity as well as coupling factor could depend on the wave propagation medium. For each structure using AlN, we establish the range of thickness of AlN layer, in which there is a weak dependence of the wave velocity and coupling factor on the AlN layer thickness. The SAW devices should be designed, in particular for the choice of the thicknesses of the different layers, by taking into account the accuracy of the manufacturing process, to reduce dispersion effects on the sensors characteristics. Besides, we also performed the mechanical analysis of the membrane under pressure and we have deduced the pressure sensitivity. The effect of frequency variation due to temperature change in SAW device using AlN is given. For pressure measurement applications, we propose a method to reduce temperature change effects. Concerning the manufacturing process, we propose to use surface micro-machining. This kind of manufacturing process allows to obtain exactly the dimensions of membranes used in pressure sensors and it also allows to have any kind of geometry due to the silicon etch stop wall. Characterizations of AlN film are done during manufacturing process. We found that to increase the piezoelectric behavior of AlN, there are three possible ways: using a bottom Mo layer, decreasing the roughness of the layer below the AlN layer up to 0.2nm and increasing the thickness of AlN. Acoustic propagation losses, coupling factor, effect of Mo layer and the effect of thin polyimide film on the center frequency are experimentally analyzed. Finally, the measured pressure sensitivity of our device is presented. This last result is promising.