Bulk acoustic wave resonator with patterned mass loading layer and recessed frame

An acoustic wave filter comprising:

• a bulk acoustic wave resonator including a first electrode over an acoustic reflector, a piezoelectric layer over the first electrode, a second electrode over the piezoelectric layer, and a patterned mass loading layer at least contributing to a difference in mass loading between a main acoustically active region of the bulk acoustic wave resonator and a recessed frame region of the bulk acoustic wave resonator, the patterned mass loading layer arranged to affect a resonant frequency of the bulk acoustic wave resonator;
• and
• a plurality of additional acoustic wave resonators, the acoustic wave filter configured to filter a radio frequency signal.

A method of manufacturing a bulk acoustic wave resonator, the method comprising:

• providing a bulk acoustic wave resonator structure including a support substrate;
• and
• during a common processing step, forming a patterned mass loading layer on the bulk acoustic wave resonator structure such that the patterned mass loading layer has a first density in a first area of the bulk acoustic wave resonator structure and a second density in a second area of the bulk acoustic wave resonator structure, the first area corresponding to a main acoustically active region of the bulk acoustic wave resonator, the second area corresponding to a recessed frame region of the bulk acoustic wave resonator, and the first density being higher than the second density.