Acoustic resonators and filters with reduced temperature coefficient of frequency

A filter device, comprising:

• a substrate;
• a lithium niobate plate having front and back surfaces, the back surface facing the substrate, portions of the lithium niobate plate forming one or more diaphragms spanning respective cavities in the substrate;
• and
• a conductor pattern on the front surface, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, interleaved fingers of each of the plurality of IDTs on the one or more diaphragms, wherein
• the lithium niobate plate and all of the plurality of IDTs are configured-such that respective radio frequency signals applied to each of the plurality IDTs excite respective shear primary acoustic modes within the respective diaphragms, and
• Euler angles of the lithium niobate plate are 0°, β, 0°, where β is greater than or equal to 40° and less than or equal to 70°.

An acoustic resonator device comprising:

• a substrate;
• a lithium tantalate plate having front and back surfaces, the back surface facing the substrate, a portion of the lithium tantalate plate forming a diaphragm that spans a cavity in the substrate;
• and
• an interdigital transducer (IDT) on the front surface of the lithium tantalate plate such that interleaved fingers of the IDT are on the diaphragm, the IDT and the lithium tantalate plate configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the diaphragm, wherein
• Euler angles of the lithium tantalate plate are [0°, β, 0° ], where β is greater than or equal to 18° and less than or equal to 54°.