Film bulk acoustic resonator fabrication method

A method of fabricating a plurality of acoustic resonators on a piezoelectric plate having opposed front and back surfaces, the method comprising:

• bonding the back surface of the piezoelectric plate to a surface of a substrate;
• performing thickness measurements of a thickness of the piezoelectric plate at a plurality of positions on the piezoelectric plate;
• removing excess material from the front surface of the piezoelectric plate in accordance with the thickness measurements to improve a thickness uniformity of the piezoelectric plate;
• after removing the excess material, selectively thinning portions of the piezoelectric plate from the first thickness to a second thickness less than the first thickness,
• after selectively thinning portions of the piezoelectric plate, forming a conductor pattern on the front surface of the piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of the plurality of acoustic resonators;
• and
• forming cavities in the substrate such that portions of the piezoelectric plate form a plurality of diaphragms spanning respective cavities,
• wherein, after the cavities and the conductor pattern are formed:
• interleaved fingers of one or more IDTs of the plurality of IDTs are disposed on respective diaphragms having the first thickness, and
• interleaved fingers of one or more IDTs of the plurality of IDTs are disposed on respective diaphragms having the second thickness.