Transversely-excited film bulk acoustic resonator and filter with a uniform-thickness dielectric overlayer

A method of fabricating an acoustic filter device, comprising:

• bonding a back surface of a lithium niobate piezoelectric plate to a surface of a substrate, portions of the lithium niobate piezoelectric plate forming a plurality of diaphragms that span respective cavities in the substrate;
• forming a conductor pattern on a front surface of the lithium niobate piezoelectric plate, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a plurality of acoustic resonators, interleaved fingers of each IDT of the plurality of IDTs disposed on a respective diaphragm of the plurality of diaphragms;
• and
• depositing one or more dielectric layers over all of the plurality of IDTs and the plurality of diaphragms, wherein a total deposited thickness of the one or more dielectric layers is the same for all of the plurality of acoustic resonators, wherein
• the interleaved fingers of all of the plurality of IDTs are aluminum with a common thickness tm, where 0.12 ts<tm<0.32 ts, and
• each IDT of the plurality of IDTs has a respective pitch p within one of following ranges:
• 2.8 ts to 4.0 ts, 5.0 ts to 7.2 ts, and 8.2 ts to 10.6 ts.

An acoustic resonator device comprising:

• a substrate having a surface;
• a lithium niobate piezoelectric plate having front and back surfaces and a thickness ts, the back surface attached to the surface of the substrate except for a portion of the lithium niobate piezoelectric plate forming a diaphragm that spans a cavity in the substrate;
• and
• an interdigital transducer (IDT) formed on the front surface of the lithium niobate piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm, wherein
• the interleaved fingers are aluminum with a thickness tm, where 0.12 ts≤tm≤0.32 ts, and
• a pitch p of the interleaved fingers falls within one of the following ranges:
• 2.8 ts to 4.0 ts, 5.0 ts to 7.2 ts, and 8.2 ts to 10.6 ts.