Transversely excited film bulk acoustic resonator using rotated z-cut lithium niobate

A filter device, comprising:

• a substrate;
• a rotated z-cut lithium niobate plate having front and back surfaces, the back surface attached to the surface of the substrate, portions of the lithium niobate 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 the one or more diaphragms, wherein
• the lithium niobate plate and all of the IDTs are configured such that respective radio frequency signals applied to the IDTs excite respective shear primary acoustic modes within the respective diaphragms, and
• the Euler angles of the rotated z-cut lithium niobate plate are 0°,β, 90°, where β is greater than or equal to −15° and less than 0°.

A method of fabricating an acoustic resonator device, comprising:

• bonding a rotated z-cut lithium niobate plate to a substrate;
• forming a cavity in the substrate, before or after bonding the lithium niobate plate to the substrate, such that a portion of the lithium niobate plate forms a diaphragm spanning the cavity;
• and
• forming an interdigital transducer (IDT) on a front surface of the lithium niobate plate such that interleaved fingers of the IDT are disposed on the diaphragm, the IDT and the lithium niobate plate configured such that a radio frequency signal applied to the IDT excite˜ a shear primary acoustic mode within the diaphragm, wherein
• the Euler angles of the rotated z-cut lithium niobate plate are 0°,β, 90°, where β is greater than or equal to −15° and less than 0°.