A method for fabricating a multi-layer resonator assembly includes sequentially fabricating a plurality of vertically-stacked resonator layers including, for each resonator layer of the plurality of resonator layers, depositing a dielectric layer, forming at least one film bulk acoustic resonator (FBAR) cavity in the deposited dielectric layer, filling each FBAR cavity of the at least one FBAR cavity with a sacrificial material block, and depositing a FBAR material stack over the at least one FBAR cavity. The deposited FBAR material stack is in contact with the sacrificial material block and the dielectric layer. The method further includes removing the sacrificial material block from the at least one FBAR cavity for each resonator layer of the plurality of resonator layers subsequent to sequentially fabricating the plurality of resonator layers.

The present disclosure relates to an acoustic wave device for asymmetric frequency bands and a manufacturing process for making the same. The disclosed acoustic wave device includes at least one first electrode (102:152), at least one second electrode (104:152), a first piezoelectric layer (114) with a recess (116), and a second piezoelectric layer (118) fully covering the recess. Herein, the at least one first electrode is formed over the first piezoelectric layer, and the at least one second electrode is formed over the second piezoelectric layer and confined within the recess. The second piezoelectric layer does not cover a portion of the first piezoelectric layer, which is vertically underneath the at least one first electrode. The first piezoelectric layer and the second piezoelectric layer are formed of different piezoelectric materials.