Transversely-excited film bulk acoustic resonators with two-layer electrodes having a narrower top layer

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 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, the piezoelectric plate and all of the IDTs configured such that respective radio frequency signals applied to each IDT excite respective shear primary acoustic modes in the respective diaphragm,
• wherein the interleaved fingers comprise a first layer adjacent the one or more diaphragms and a second layer over the first layer, the second layer having a narrower width than the first layer.

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, the IDT configured to excite a primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT,
• wherein the interleaved fingers comprise a first layer adjacent the diaphragm and a second layer over the first layer, the second layer having a narrower width than the first layer.