Filter using transversely-excited film bulk acoustic resonators with multiple frequency setting layers

A method of fabricating a filter device, comprising:

• attaching a back surface of a single-crystal piezoelectric plate to a surface of a substrate such that portions of the single-crystal piezoelectric plate form one or more diaphragms spanning respective cavities in the substrate;
• forming a conductor pattern on a front surface of the piezoelectric plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a plurality of resonators, interleaved fingers of each of the plurality of IDTs disposed on a respective diaphragm of the one or more diaphragms;
• forming a first frequency setting dielectric layer having a first thickness over the fingers of the IDTs of a first subset of the plurality of resonators;
• and
• forming a second frequency setting dielectric layer having a second thickness greater than the first thickness over the fingers of the IDTs of a second subset of the plurality of resonators, wherein the first subset and the second subset are not identical.