Transversely-excited film bulk acoustic resonator with etched conductor patterns

A method of fabricating an acoustic resonator device comprising:

• forming a patterned first photoresist mask on a front surface of a single-crystal piezoelectric plate at locations of a desired IDT pattern;
• blanket depositing an etch-stop layer on the front surface of the single-crystal piezoelectric plate where the patterned first photoresist mask does not exist and on the patterned first photoresist mask;
• removing the patterned first photoresist mask and the etch-stop layer on the patterned first photoresist mask to expose the front surface of the piezoelectric plate at locations of the desired IDT pattern;
• depositing an interdigital transducer (IDT) conductor material on the etch stop layer and on the exposed front surface of the piezoelectric plate;
• forming a patterned second photoresist mask on the conductor material at locations of the desired IDT pattern;
• using an etch process to etch the conductor material over and to the etch-stop layer to form the desired IDT pattern, the desired IDT pattern having interleaved fingers disposed on a diaphragm configured to span a cavity in a substrate, a portion of the piezoelectric plate and the etch-stop layer forming the diaphragm, wherein the etch-stop layer and photoresist mask are impervious to the etch process;
• and
• removing the patterned second photoresist mask from on the conductor material to leave the desired IDT pattern of the conductor material.