Fabrication of BAW resonators based on piezoelectric AlN and reflector-on-membrane structure

In this work we present a new approach to fabricate Bulk Acoustic Wave resonators based on reflector-on-membrane structure, on which piezoelectric film and electrodes are deposited as active part. The reflector provides enhancement of the fundamental thickness mode resonance of the piezoelectric layer, and strong attenuation of additional resonances of the membrane structure. The membrane in turn avoids the presence of multiple resonances close to the fundamental one, as it happens in the case of a simple two-layers reflector SMR. Moreover a novel combination of layers is proposed for the acoustic reflector