Bulk acoustic wave filter and a method of frequency tuning for bulk acoustic wave resonator of bulk acoustic wave filter

A bulk acoustic wave filter comprising:

• a substrate;
• an insulating layer formed on the substrate, wherein a first cavity and a second cavity are formed in the insulating layer, and the first cavity and the second cavity are defined by sidewalls of the insulating layer and a top surface of the substrate;
• a first bulk acoustic wave resonance structure formed on the first cavity, wherein the first bulk acoustic wave resonance structure comprises a first frequency tuning structure formed on the first cavity, a first bottom electrode formed on the first frequency tuning structure, a first piezoelectric layer portion formed on the first bottom electrode, and a first top electrode formed on the first piezoelectric layer portion, wherein the first frequency tuning structure and the first bottom electrode are made of a same material, and a spacing between a sidewall of the first bottom electrode to an opposite sidewall of the first bottom electrode is greater than a spacing between a sidewall of the first frequency tuning structure to an opposite sidewall of the first frequency tuning structure;
• and
• a second bulk acoustic wave resonance structure formed on the second cavity, wherein the second bulk acoustic wave resonance structure comprises a second bottom electrode formed on the second cavity, a second piezoelectric layer portion formed on the second bottom electrode, and a second top electrode formed on the second piezoelectric layer portion.