Film bulk acoustic wave resonator and preparation method thereof

A preparation method of a film bulk acoustic wave resonator, comprising:

• providing a substrate, and forming a recessed third cavity in an upper surface of the substrate;
• forming a first sacrificial layer on the upper surface of the substrate, comprising a first part filling into the third cavity, and a second part located above the first part and higher than the upper surface of the substrate;
• forming a bottom electrode on the upper surface of the substrate, which has a first arched part covering the second part;
• forming a second sacrificial layer at a slope of the first arched part;
• sequentially forming a piezoelectric layer and a top electrode on the bottom electrode;
• and
• releasing the first sacrificial layer and the second sacrificial layer so as to respectively form an air gap between the bottom electrode and the substrate and a first reflection cavity, located at the slope of the first arched part, between the bottom electrode and the piezoelectric layer,
• wherein the air gap comprises the third cavity and a first cavity which is located on the upper surface of the substrate, the third cavity communicates with the first cavity, a thickness of the first cavity is less than a thickness of the third cavity.