Picosecond Ultrasonics: a Technique Destined for BAW Technology

Since the 80’s, Bulk Acoustic Wave (BAW) resonators technology has been seeing a rapid expansion, due to its potentials in terms of performances and integration for Radio-Frequency (RF) filtering. The control of the frequency is a challenging question for the mass production of such devices, and passes through an accurate control of mechanical properties of the whole stack. The picosecond ultrasonics technique is well-suited for the characterization of such a component. Using a colored setup (i.e. various probe wavelengths), it allows the measurement of several acoustic parameters (longitudinal acoustic phonon velocity, density, acoustic attenuation, thermal expansion and temperature dependence of sound velocity) of complex thin films stacks. Moreover, picosecond ultrasonics is prepared for on product process control measurements, and fits the requirements of a metrological support for BAW production.