Acoustic resonator comprising vertically extended acoustic cavity

An acoustic resonator device, comprising:

• a substrate;
• a bottom electrode disposed on an acoustic reflector formed in or on the substrate;
• a piezoelectric layer disposed over the bottom electrode;
• and
• a top electrode disposed over the piezoelectric layer, the top electrode comprising:
• a first top comb electrode comprising a first top bus bar and a plurality of first top fingers extending in a first direction from the first top bus bar;
• and
• a second top comb electrode comprising a second top bus bar and a plurality of second top fingers extending in a second direction from the second top bus bar, the second direction being substantially opposite to the first direction such that the first and second top fingers form a top interleaving pattern,
• wherein one of the bottom electrode and the top electrode comprises a composite electrode having a thickness of approximately λ/2, λ being a wavelength corresponding to a thickness extensional resonance frequency of the acoustic resonator, and
• wherein the piezoelectric layer and one of the bottom electrode and the top electrode not comprising the composite electrode have a combined thickness of approximately λ/2.