SAW and BAW Components

The technological and scientific objective is to realize the components answering the future requests of the systems treated within the CoSyMA team.

SAW / BAW

Historically, the high performance elastic wave components are made of mono crystalline material and metal electrodes. The metal electrodes are structured on the surface to provide surface elastic wave (SAW) devices, or they are placed on either side of the material to generate bulk elastic waves (BAW). Current needs require a rise in frequency. The SAW will be limited in this respect by the resolution of the electrodes and the losses in the material. As for BAW, they are limited by the thickness of the material.

The innovative SAW and BAW features of the CoSyMA team utilize structures with a thin piezoelectric film on a substrate. For SAW, the waves will be guided by the substrate. The apparent phase velocity can thus be increased. The choice of substrate improves frequency variations due to temperature. The intrinsic losses of the device are controlled. For BAW, several architectures exist, such as SMR (Solidly Mounted Resonator), HBAR (High-overtone Bulk Acoustic Resonator). These devices belong to the FBAR family (Film Bulk Acoustic resonator) and have the advantage of having the piezoelectric film supported by the substrate. HBAR also takes advantage of the qualities of the substrate to improve the intrinsic performance of the component.

The realization of these devices is done, within CoSyMA, by the hybrid technology for the realization of the proofs of concept.

Ferroelectric, Electrostrictive, Electrostatic ...

Other structures, using surface or volume waves, will use other principles of transduction. These principles are:
-   Periodic ferroelectric domains for generating periodic spatial excitation.
-   An electrostrictive material, where a DC voltage will unbalance the barycentre of the charges of the material, thus making it piezoelectric.
-   Capacitive transduction, to generate elastic waves on any type of material.