Transversely-excited film bulk acoustic resonator with optimized piezoelectric plate thickness
Acoustic resonators and filter devices. An acoustic resonator includes a piezoelectric plate having front and back surfaces, a portion of the piezoelectric plate forming a diaphragm, and a conductor pattern on the front surface, the conductor pattern including a multi-mark interdigital transducer (IDT), fingers of the IDT on the diaphragm. A thickness between the front and back surfaces is greater than or equal to 200 nm and less than or equal to 1000 nm.
1 . An acoustic resonator, comprising:
a piezoelectric plate having front and back surfaces, a portion of the piezoelectric plate including a diaphragm; and
a conductor pattern on the front surface, the conductor pattern comprising a multi-mark interdigital transducer (IDT) having a plurality of fingers disposed on the diaphragm,
wherein a thickness between the front and back surfaces of the piezoelectric plate is greater than or equal to 200 nm and less than or equal to 1000 nm,
wherein the plurality of fingers include a first edge finger, a second edge finger and at least one finger between the first edge finger and the second edge finger, and
wherein a mark of the first edge finger is m(1−δ m ), and a mark of the second edge finger is m(1+δ m ) when a mark of the at least one finger is m, and om is greater than 0 and less than 1,
wherein:
the plurality of fingers include a first set of fingers extended from a first busbar and a second set of fingers extended from a second busbar,
the first and second sets of fingers are interleaved fingers that include the first edge finger, the second edge finger and the at least one finger,
at least a first hole is disposed between an end of a finger of the first set of fingers and the second busbar, the first hole being closer to the end of the finger of the first set of fingers than the second busbar, and
at least a second hole is disposed between an end of a finger of the second set of fingers and the first busbar.
2 . The acoustic resonator of claim 1 , wherein at least one of the first hole and the second hole are substantially rectangular in shape.
3 . The acoustic resonator of claim 1 , wherein the piezoelectric plate is one of Z-cut lithium niobate, rotated Z-cut lithium niobate, and rotated Y-cut lithium niobate.
4 . The acoustic resonator of claim 1 , further comprising a substrate having a surface that is attached to the back surface of the piezoelectric plate, and wherein the diaphragm is over a cavity of the acoustic resonator.
5 . The acoustic resonator of claim 1 , wherein the piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode within the piezoelectric plate, and the primary shear acoustic mode is a bulk shear wave where acoustic energy propagates along a direction substantially orthogonal to a direction of a primarily laterally excited electric field generated by the IDT, and the electric field is primarily laterally excited when atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric plate, while the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.
6 . The acoustic resonator of claim 4 , wherein the cavity is a recess in the substrate.
7 . The acoustic resonator of claim 4 , wherein the cavity extends through a thickness of the substrate.
8 . A filter device, comprising:
a piezoelectric layer having front and back surfaces, portions of the piezoelectric layer comprising one or more diaphragms; and
a conductor pattern on the front surface of the piezoelectric layer, the conductor pattern comprising a plurality of multi-mark interdigital transducers (IDTs),
wherein interleaved fingers of the plurality of IDTs are disposed on the one or more diaphragms, respectively,
wherein a thickness between the front and back surfaces of the piezoelectric layer is greater than or equal to 200 nm and less than or equal to 1000 nm
wherein the interleaved fingers of at least one IDT of the plurality of IDTs include a first edge finger, a second edge finger and at least one finger between the first edge finger and the second edge finger, and
wherein a mark of the first edge finger is m(1−δ m ), and a mark of the second edge finger is m(1+δ m ) when a mark of the at least one finger is m, and om is greater than 0 and less than 1,
wherein, for the at least one IDT:
the interleaved fingers include a first set of fingers extended from a first busbar and a second set of fingers extended from a second busbar,
at least a first hole is disposed between an end of a finger of the first set of fingers and the second busbar, the first hole being closer to the end of the finger of the first set of fingers than the second busbar, and
at least a second hole is disposed between an end of a finger of the second set of fingers and the first busbar.
9 . The filter device of claim 8 , further comprising a substrate having a surface that is attached to the back surface of the piezoelectric layer, and wherein the one or more diaphragms are each over a respective cavity of a plurality of cavities of the filter device.
10 . The filter device of claim 9 , wherein the substrate is one or more of silicon, sapphire, and quartz.
11 . The filter device of claim 9 , wherein the plurality of cavities are respective recesses in the substrate.
12 . The filter device of claim 9 , wherein the plurality of cavities extend through a thickness of the substrate.
13 . The filter device of claim 8 , wherein the piezoelectric layer is one of Z-cut lithium niobate, rotated Z-cut lithium niobate, and rotated Y-cut lithium niobate.
14 . The filter device of claim 8 , wherein at least one of the first hole and the second hole are substantially rectangular in shape.
15 . The filter device of claim 8 , wherein the piezoelectric layer and the plurality of IDTs are configured such that a radio frequency signal applied to each of the plurality of IDTs excites a respective primary acoustic mode within the piezoelectric layer, and the primary acoustic mode is a bulk shear wave where acoustic energy propagates along a direction substantially orthogonal to a direction of a primarily laterally excited electric field generated by the respective IDT, and the electric field is primarily laterally excited when atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, while the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.