Transversely-excited film bulk acoustic resonator with reduced spurious modes

An acoustic filter device comprising:

• a substrate having a surface;
• a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate;
• and
• a conductor pattern formed on the front surface of the piezoelectric plate, the conductor pattern including interdigital transducers (IDTs) of a plurality of acoustic resonators, interleaved fingers of each IDT disposed on a respective diaphragm from the plurality of diaphragms,
• wherein, for each of the IDTs, a pitch of the interleaved fingers and a mark of the interleaved fingers are set in combination such that a resonance frequency of the respective acoustic resonator is equal to a respective predetermined target frequency, and
• for one or more of the IDTs, a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.

A method of fabricating an acoustic resonator device, comprising:

• bonding a back surface of a single-crystal piezoelectric plate to a surface of a substrate, a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate;
• and
• forming a conductor pattern on a front surf ace of the piezoelectric plate, the conductor pattern comprising an interdigital transducers (IDT), interleaved fingers of the IDT disposed on the diaphragm;
• and
• wherein a pitch of the interleaved fingers and a mark of the interleaved fingers are set in combination such that a resonance frequency of the acoustic resonator is equal to a predetermined target frequency, and
• a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.