Bulk acoustic wave resonator with controlled thickness region having controlled electromechanical coupling

A method of forming a BAW resonator, said method comprising:

• forming a piezoelectric layer over a lower electrode of said BAW resonator;
• forming a low density metal segment over said piezoelectric layer in a controlled thickness region of said BAW resonator, said controlled thickness region having a controlled electromechanical coupling;
• forming an upper electrode of said BAW resonator over said low density metal segment, said upper electrode comprising a high density metal.

A bulk acoustic wave (BAW) resonator comprising:

• a piezoelectric layer situated between upper and lower electrodes;
• a controlled thickness region comprising a dielectric segment, said dielectric segment being situated in contact with said piezoelectric layer, said dielectric segment being confined within a perimeter of said piezoelectric layer;
• wherein said controlled thickness region has a controlled electromechanical coupling.