Bulk acoustic wave resonator and fabrication method thereof

A fabrication method of a bulk acoustic wave (BAW) resonator, comprising:

• obtaining a temporary substrate;
• forming a buffer layer on the temporary substrate;
• forming a piezoelectric layer on the buffer layer;
• forming a first electrode on the piezoelectric layer;
• forming a first dielectric layer on the piezoelectric layer and covering the first electrode;
• forming a trench in the first dielectric layer, the trench surrounding a sacrificial portion of the first dielectric layer;
• forming a second dielectric layer on the first dielectric layer and in the trench in the first dielectric layer;
• forming a third dielectric layer on the second dielectric layer, the third dielectric layer filling in the trench in the first dielectric layer;
• forming a bonding layer on the third dielectric layer;
• bonding a resonator substrate to the third dielectric layer via the bonding layer;
• removing the temporary substrate and the buffer layer to expose a surface layer of the piezoelectric layer;
• removing the surface layer of the piezoelectric layer to obtain a thinned piezoelectric layer;
• forming a second electrode on the thinned piezoelectric layer;
• and
• removing the sacrificial portion of the first dielectric layer surrounded by the trench to form a cavity.