Transversely-excited film bulk acoustic resonators with gap dielectric stripes in busbar-electrode gaps
An acoustic resonator device includes a substrate having a surface; an 82Y-cut lithium niobate piezoelectric plate attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in an intermediate dielectric layer of the substrate; an interdigital transducer (IDT) at the piezoelectric plate such that interleaved fingers of the IDT are at the diaphragm; and a plurality of stripes of a dielectric material extending over ends of the interleaved fingers and portions of gaps between the ends of the interleaved fingers and opposing busbars of the IDT.
1. An acoustic resonator device comprising:
a substrate having a surface;
an 82Y-cut lithium niobate piezoelectric plate attached to the surface of the substrate, the piezoelectric plate including a portion that forms a diaphragm that is over a cavity;
an interdigital transducer (IDT) at the piezoelectric plate such that interleaved fingers of the IDT are on the diaphragm; and
a plurality of stripes of a dielectric material that each have at least a portion that extends in a gap between the ends of the interleaved fingers and opposing busbars of the IDT,
wherein the 82Y-cut lithium niobate piezoelectric plate has Euler angles in a range (0° , x, 90° ) with−15° <x<0° .
2. The acoustic resonator device of claim 1 , wherein the IDT includes a first plurality of fingers attached to a first busbar of the opposing busbars and a second plurality of fingers attached to a second busbar of the opposing busbars, such that the interleaved fingers include the first plurality of fingers and the second plurality of fingers.
3. The acoustic resonator device of claim 1 , wherein the plurality of stripes of the dielectric material have a width of between 2 um and 5 um, and wherein the width is measured in a direction perpendicular to a lengthwise direction of the interleaved fingers.
4. The acoustic resonator device of claim 3 , wherein the plurality of stripes of the dielectric material have a thickness of between 10 nm and 50 nm, and wherein the thickness is measured in a direction normal to the surface of the substrate.
5. The acoustic resonator device of claim 1 , wherein the plurality of stripes of the dielectric material have a thickness of 30 nm, and wherein the thickness is measured being in a direction normal to the surface of the substrate.
6. The acoustic resonator device of claim 1 , wherein each of the plurality of stripes of the dielectric material comprises a thickness that is 0.02 to 0.07 of a respective thickness of the piezoelectric plate, and whereinthe respective thicknesses is measured in a direction normal to the surface of the substrate.
7. The acoustic resonator device of claim 1 , wherein the plurality of stripes are configured to lower an amplitude of and a frequency range of output gap mode spurs appearing immediately below the resonant frequency of the resonator.
8. The acoustic resonator device of claim 1 , wherein the cavity extends into an intermediate dielectric layer of the substrate.
9. The acoustic resonator device of claim 1 , wherein the IDT is configured to excite shear acoustic waves in the piezoelectric plate in response to respective radio frequency signals applied to the IDT.
10. The acoustic resonator device of claim 1 , wherein at least a portion of each of the plurality of stripes of the dielectric material overlaps at least an end of one or more fingers of the interleaved fingers.
11. The acoustic resonator device of claim 1 , wherein at least one stripe of the plurality of stripes of the dielectric material extends in a direction substantially parallel to the first busbar and in a gap that extends contiguously without any intervening items between the first busbar and ends of the second plurality of fingers attached to the second busbar.
12. An acoustic resonator device comprising:
a substrate having a surface;
an 82Y-cut lithium niobate piezoelectric plate attached to the surface of the substrate, the piezoelectric plate including a portion that forms a diaphragm that is over a cavity;
an interdigital transducer (IDT) at the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm; and
at least one stripe of a dielectric material that has at least a portion that extends in a gap between the ends of the interleaved fingers and an opposing busbar facing the ends of the interleaved fingers,
wherein the 82Y-cut lithium niobate piezoelectric plate has Euler angles in a range (0° , x, 90° ) with−15° <x<0° .
13. The acoustic resonator device of claim 12 ,
wherein the at least one stripe has a width of between 2 um and 5 um, and wherein the width is measured in a direction perpendicular to a lengthwise direction of the interleaved fingers, and
wherein the at least one stripe has a thickness of between 10 nm and 50 nm, and wherein the thickness is measured being in a direction normal to the surface of the substrate.
14. The acoustic resonator device of claim 12 , wherein the at least one stripe has a thickness of 30 nm, and wherein the thickness is measured in a direction normal to the surface of the substrate.
15. The acoustic resonator device of claim 12 , wherein the at least one stripe of the dielectric material comprises a thickness that is 0.02 to 0.07 of a respective thickness of the piezoelectric plate, and wherein the respective thicknesses are measured in a direction normal to the surface of the substrate.
16. The acoustic resonator device of claim 12 , wherein the cavity extends into an intermediate dielectric layer of the substrate.
17. The acoustic resonator device of claim 12 , wherein the IDT is configured to excite shear acoustic waves in the piezoelectric plate in response to respective radio frequency signals applied to the IDT.
18. A method of fabricating an acoustic resonator device comprising:
attaching a substrate to an 82Y-cut lithium niobate piezoelectric plate that has Euler angles in a range (0° , x, 90° ) with−15° <x<0° ;
forming an interdigital transducer (IDT) on a side of the piezoelectric plate, the IDT comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device; and
forming a plurality of stripes of a dielectric material in gaps between the ends of the interleaved fingers and opposing busbars of the IDT.
19. The acoustic resonator device of claim 12 , wherein at least a portion of the at least one stripe of the dielectric material overlaps at least an end of one or more fingers of the interleaved fingers.
20. The acoustic resonator device of claim 12 , wherein:
wherein the IDT includes a first plurality of fingers attached to a first busbar of the opposing busbars and a second plurality of fingers attached to a second busbar of the opposing busbars, the interleaved fingers including the first plurality of fingers and the second plurality of fingers, and
the at least one stripe of the dielectric material extends in a direction substantially parallel to the first busbar and in a gap that extends contiguously without any intervening items between the first busbar and ends of the second plurality of fingers attached to a second busbar.