Film bulk acoustic resonator fabrication method with frequency trimming based on electric measurements prior to cavity etch

A method of fabricating filters on a single-crystal piezoelectric plate having opposing front and back surfaces, comprising:

• bonding the back surface of the piezoelectric plate to a surface of a substrate;
• forming a conductor pattern on the front surface, the conductor pattern including a plurality of ladder filter circuits, each ladder filter circuit including at least one shunt resonator and at least one series resonator, each of the shunt and series resonators including an interdigital transducer (IDT);
• forming a dielectric passivation/tuning layer over the conductor pattern and the front surface of the piezoelectric plate;
• performing electrical measurements of at least some of the resonators;
• selectively removing material from the dielectric passivation/tuning layer in accordance with the electrical measurements;
• and
• after removing material from the dielectric passivation/tuning layer, forming cavities in the substrate such that interleaved fingers of each IDT are disposed on a respective diaphragm spanning a respective cavity.