Bulk acoustic wave resonator

A bulk acoustic wave resonator, comprising:

• a carrier substrate, having a main surface extending along a first direction;
• a piezoelectric layer, located on a side of the carrier substrate in a second direction perpendicular to the main surface of the carrier substrate;
• a first electrode and a second electrode, disposed on opposite sides of the piezoelectric layer in the second direction;
• a cavity boundary structure, disposed between the carrier substrate and the piezoelectric layer in the second direction, wherein the cavity boundary structure has a body part and a protruding part, the body part extends along the first direction, and the protruding part protrudes from the body part along the second direction away from the carrier substrate and toward the piezoelectric layer;
• a resonant cavity, defined by the cavity boundary structure and the piezoelectric layer;
• and
• a periphery dielectric layer, located on a side of the protruding part of the cavity boundary structure away from the resonant cavity, and between the body part of the cavity boundary structure and the piezoelectric layer, a material of the periphery dielectric layer is different from a material of at least a portion of the protruding part adjacent to the periphery dielectric layer.