| Since the 80’s, RF-filtering has carried the developments of Bulk Acoustic Wave (BAW) resonators. At the same time, picosecond ultrasonics, a non-contact and non-destructive technique for mechanical characterization, sees the light of day in the metrological tools’ arsenal for on product process control measurements. The operating principle of a BAW resonator is the excitation of the thickness mode of a piezoelectric layer sandwiched between two electrodes, and picosecond ultrasonics is well-suited to work in the natural geometry of the component. This technique uses a pulsed laser source to excite and detect longitudinal acoustic waves at very high frequencies (100 GHz to 1 THz). Thus, it enables the measurement of decisive parameters of materials in thin films for the modeling of BAW resonators (sound velocity, thickness, density, acoustic attenuation, temperature coefficients). On this poster we will present experimental results obtained on BAW materials (AlN, Mo, SiO2, W, SiN) for mechanical characterization. Then we will present results obtained on BAW stacks that enables an accurate modeling of resonant frequencies and coupling coefficient. These results will show that more than just a process control tool, picosecond ultrasonics can replace RF-tests for frequential characterization. |