The generation of a precise and stable reference frequency with low drift and phase noise is a need for electronic products as navigation systems, wireless communication devices or multimedia applications. Recent researches proved that Lamb wave resonators (LWR) made of aluminium nitride (AlN) piezoelectric material is the best technology in term of high resonance frequencies multiplex (from 100MHz to 1GHz), high quality factor (up to 2000) and reduced size and mass. However, even though previous works demonstrated that the thermal dependence of those devices can be reduced by adding a silicon dioxide layer (SiO2), it has not been proven yet that the thermal compensation is stable and reliable over time.
In this master project we built a setup to analyze the influence of temperature ranging from 15°C to 75°C on the resonance frequency and the quality factor of different LWR and their temperature coefficient of frequency (TCF) were calculated from the measured shift of frequency. The results proved that the performances of the resonators were not stable and that the measurements were not repeatable which is not suitable for industrialization and supposes that the fabrication process was not optimal. Moreover, the devices exhibited different resonance frequencies and quality factors at varying pressure and excitation potential which demonstrated that the encapsulation and the power supply of the resonators must be considered carefully. It was also demonstrated through this study that aging was decreasing the quality factor and the resonance frequency of the devices. The structures were simulated on COMSOL multiphysics using both 2D and 3D models and the results showed to be in excellent accordance with the theoretical predictions and the former experimental data which is promising for the understanding and the designing of the LWR.