Transversely-excited film bulk acoustic resonator with spiral interdigitated transducer fingers
Acoustic resonator devices, filers, and methods. An acoustic resonator includes a substrate and a piezoelectric plate, a portion of the piezoelectric plate being a diaphragm spanning a cavity in the substrate. A conductor pattern on a front surface of the piezoelectric plate includes interleaved interdigital transducer (IDT) fingers connected alternately to first and second busbars. The interleaved IDT fingers are on the diaphragm, and the interleaved IDT fingers include at least a first pair of interleaved spiral IDT fingers.
1. An acoustic resonator, comprising:
a substrate;
a piezoelectric plate include a portion that forms a diaphragm that is over a cavity in the substrate; and
a conductor pattern on a front surface of the piezoelectric plate, the conductor pattern comprising interleaved interdigital transducer (IDT) fingers connected alternately to first and second busbars,
wherein the interleaved IDT fingers are on the diaphragm and comprise at least a first pair of interleaved spiral IDT fingers that each comprise one or more semicircular curved portions, and
wherein each of the first and second busbars includes recesses such that gaps between each of the first and second busbars and the one or more semicircular curved portions of the first pair of interleaved spiral IDT fingers are effectively equal to a gap between adjacent interleaved fingers of the first pair of interleaved spiral IDT fingers.
2. The acoustic resonator of claim 1 , wherein each finger of the first pair of interleaved spiral IDT fingers bends at least 180 degrees.
3. The acoustic resonator of claim 1 , wherein a center-to-center spacing of the first pair of interleaved spiral IDT fingers is effectively constant.
4. The acoustic resonator of claim 1 , wherein a center-to-center spacing of the first pair of interleaved spiral IDT fingers is constant within a predetermined tolerance.
5. The acoustic resonator of claim 4 , wherein the predetermined tolerance is ±5%.
6. The acoustic resonator of claim 1 , wherein each finger of the first pair of interleaved spiral IDT fingers comprises two or more 90-degree bends.
7. The acoustic resonator of claim 6 , wherein gaps between each of the first and second busbars and adjacent IDT fingers are effectively equal to a gap between adjacent interleaved IDT fingers.
8. The acoustic resonator of claim 1 , wherein the piezoelectric plate is one of Z-cut lithium niobate and Z-cut lithium tantalate.
9. The acoustic resonator of claim 1 , wherein all of the interleaved IDT fingers are interleaved spiral IDT fingers.
10. A filter device, comprising:
a piezoelectric plate including portions that form diaphragms that are over respective cavities in a substrate; and
a conductor pattern on a front surface of the piezoelectric plate, the conductor pattern comprising a plurality of interdigital transducers (IDTs), each IDT comprising interleaved IDT fingers connected alternately to first and second busbars,
wherein the interleaved IDT fingers of each IDT are on a respective diaphragm, and the interleaved IDT fingers of a least one IDT comprise a pair of interleaved spiral IDT fingers,
wherein the pair of interleaved spiral IDT fingers that each comprise one or more semicircular curved portions, and
wherein each of the first and second busbars includes recesses such that gaps between each of the first and second busbars and the one or more semicircular curved portions of the pair of interleaved spiral IDT fingers are effectively equal to a gap between adjacent interleaved fingers of the pair of interleaved spiral IDT fingers.
11. The filter device of claim 10 , wherein each finger of the pair of interleaved spiral IDT fingers bends at least 180 degrees.
12. The filter device of claim 10 , wherein a center-to-center spacing of the pair of interleaved spiral IDT fingers is effectively constant.
13. The filter device of claim 10 , wherein the piezoelectric plate is one of Z-cut lithium niobate and Z-cut lithium tantalate.
14. A method of fabricating an acoustic resonator, comprising:
attaching a back surface of a piezoelectric plate to a substrate;
forming a conductor pattern on a front surface of the piezoelectric plate, the conductor pattern comprising interleaved interdigital transducer (IDT) fingers connected alternately to first and second busbars; and
forming a cavity in the substrate such that the interleaved IDT fingers are on a portion of the piezoelectric plate spanning the cavity,
wherein the interleaved IDT fingers include at least a first pair of interleaved spiral IDT fingers that each comprise one or more semicircular curved portions, and
wherein each of the first and second busbars includes recesses such that gaps between each of the first and second busbars and the one or more semicircular curved portions of the first pair of interleaved spiral IDT fingers are effectively equal to a gap between adjacent interleaved fingers of the first pair of interleaved spiral IDT fingers.
15. The method of claim 14 , wherein each finger of the pair of interleaved spiral IDT fingers bends at least 180 degrees.
16. The method of claim 14 , wherein a center-to-center spacing of the pair of interleaved spiral IDT fingers is effectively constant.
17. The method of claim 14 , wherein the piezoelectric plate is one of Z-cut lithium niobate and Z-cut lithium tantalate.