Transversely-excited film bulk acoustic resonators with electrodes having a second layer of variable width

A 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, portions of the single-crystal piezoelectric plate forming one or more diaphragms spanning respective cavities in the substrate;
• and
• a conductor pattern formed on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, interleaved fingers of each of the plurality of IDTs disposed on one of the one or more diaphragms,
• wherein each of the interleaved fingers comprises a first layer adjacent the one or more diaphragms and a second layer over the first layer opposite the one or more diaphragms, and wherein a width of the second layer varies along a length of each finger.

A method of fabricating an acoustic resonator device, comprising:

• bonding a piezoelectric plate to a substrate;
• forming a cavity in the substrate, before or after bonding the piezoelectric plate to the substrate, such that a portion of the piezoelectric plate forms a diaphragm spanning the cavity;
• and
• forming an interdigital transducer (IDT) on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm,
• wherein the interleaved fingers comprise a first layer having a rectangular shape adjacent the diaphragm and a second layer over the first layer opposite the diaphragm, and wherein a width of the second layer varies along a length of each finger.