Lamb waves pressure sensor using an AlN/Si structure

Among sensors using a thin membrane covered with a piezoelectric layer, we focused on the study of a pressure sensor using an AlN film over a silicon membrane. The membrane was micromachined using both anisotropic and isotropic chemical etchings. The AlN thin film was deposited by a sputtering method with very good stochiometric results. Elastic waves were generated and detected through IDT transducers calculated at a frequency of 88 MHz for the SO Lamb wave mode. We studied the velocity and the electromechanical coupling factor of the first symmetric and antisymmetric Lamb modes according to the thickness of the piezoelectric layer. The pressure and the temperature behavior of such a sensor using the SO Lamb mode are presented. We have analysed the pressure sensitivity and we propose some solutions to obtain a well temperature compensated structure. Especially, we were thinking to achieve a self-compensated structure by using the opposite temperature behavior of silicon and AlN