Transversely-excited film bulk acoustic resonators with interdigital transducer configured to reduce diaphragm stress
Acoustic resonators are disclosed. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. The back surface is attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate. The IDT includes: a first busbar and a second busbar disposed on respective portions of the piezoelectric plate other than the diaphragm; a first set of elongate fingers extending from the first bus bar onto the diaphragm; and a second set of elongate fingers extending from the second bus bar onto the diaphragm, the second set of elongate fingers interleaved with the first set of elongate fingers.
1. An acoustic resonator device comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate; and
an interdigital transducer (IDT) formed on the front surface of the piezoelectric plate, the IDT including:
a first busbar and a second busbar disposed completely on respective portions of the piezoelectric plate other than the diaphragm,
a first set of elongate fingers extending from the first bus bar onto the diaphragm,
a second set of elongate fingers extending from the second bus bar onto the diaphragm, the second set of elongate fingers interleaved with the first set of elongate fingers.
2. The acoustic resonator device of claim 1 , further comprising:
a first set of dummy fingers extending from the first busbar onto the diaphragm, each of the first set of dummy fingers aligned with a corresponding one of the second set of elongate fingers; and
a second set of dummy fingers extending from the second busbar onto the diaphragm, each of the second set of dummy fingers aligned with a corresponding one of the first set of elongate fingers.
3. The acoustic resonator device of claim 1 , further comprising:
a second conductor level formed over the front surface of the piezoelectric plate, the second conductor level covering at least portions of the first and second busbars.
4. The acoustic resonator device of claim 3 , wherein the second conductor level covers substantially all of the first and second busbars.
5. The acoustic resonator device of claim 1 , wherein
the piezoelectric plate and the first and second sets of elongate fingers are configured such that a radio frequency signal applied between the first and second busbars excites a primary shear acoustic mode in the diaphragm.
6. The acoustic resonator device of claim 5 , wherein
the piezoelectric plate is one of lithium niobate and lithium tantalate.
7. The acoustic resonator device of claim 6 , wherein
the piezoelectric plate is one of Z-cut, rotated Z-cut, and rotated YX-cut.
8. An acoustic resonator device comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate; and
a first conductor level formed on the front surface of the piezoelectric plate, the first conductor level including:
first and second busbars;
a first set of elongate fingers extending from the first bus bar,
a second set of elongate fingers extending from the second bus bar, the second set of elongate fingers interleaved with the first set of elongate fingers,
wherein an entirety of the first and second busbars are not on the diaphragm, and
the first and second sets of elongate fingers extend from the respective busbars onto the diaphragm.
9. The acoustic resonator device of claim 8 , wherein
a first distance, parallel to the front surface of the piezoelectric plate, from an edge of the first busbar proximate the cavity to an edge of the cavity proximate the first busbar is greater than or equal to zero, and
a second distance, parallel to the front surface of the piezoelectric plate, from an edge of the second busbar proximate the cavity to an edge of the cavity proximate the second busbar is greater than or equal to zero.
10. The acoustic resonator device of claim 9 , wherein
the first distance and the second distance are as small as allowed by expected manufacturing tolerances.
11. The acoustic resonator device of claim 9 , wherein
nominal values of the first distance and the second distance are equal to a worst-case expected misregistration between the cavity and a photomask used to pattern the first conductor level.
12. The acoustic resonator device of claim 8 , further comprising:
a first set of dummy fingers extending from the first busbar onto the diaphragm, each of the first set of dummy fingers aligned with a corresponding one of the second set of elongate fingers; and
a second set of dummy fingers extending from the second busbar onto the diaphragm, each of the second set of dummy fingers aligned with a corresponding one of the first set of elongate fingers.
13. The acoustic resonator device of claim 8 , further comprising:
a second conductor level formed over the front surface of the piezoelectric plate, the second conductor level covering at least portions of the first and second busbars.
14. The acoustic resonator device of claim 13 , wherein the second conductor level covers substantially all of the first and second busbars.
15. The acoustic resonator device of claim 8 , wherein
the piezoelectric plate and the first and second sets of elongate fingers are configured such that a radio frequency signal applied between the first and second busbars excites a primary shear acoustic mode in the diaphragm.
16. The acoustic resonator device of claim 15 , wherein
the piezoelectric plate is one of lithium niobate and lithium tantalate.
17. The acoustic resonator device of claim 16 , wherein
the piezoelectric plate is one of Z-cut, rotated Z-cut, and rotated YX-cut.
18. An acoustic resonator device comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate;
first and second busbars formed on the front surface of the piezoelectric plate;
a first set of elongate fingers extending from the first bus bar onto the diaphragm,
a second set of elongate fingers extending from the second bus bar onto the diaphragm, the second set of elongate fingers interleaved with the first set of elongate fingers;
a first set of dummy fingers extending from the first busbar onto the diaphragm, each of the first set of dummy fingers aligned with a corresponding one of the second set of elongate fingers; and
a second set of dummy fingers extending from the second busbar onto the diaphragm, each of the second set of dummy fingers aligned with a corresponding one of the first set of elongate fingers,
wherein the piezoelectric plate and the first and second sets of elongate fingers are configured such that a radio frequency signal applied between the first and second busbars excites a primary shear acoustic mode in the diaphragm.
19. The acoustic resonator device of claim 18 , wherein the first and second bus bars are not on the diaphragm.
20. The acoustic resonator device of claim 18 , wherein the first and second sets of dummy fingers are shorter than the first and second sets of elongate fingers.
21. The acoustic resonator device of claim 18 , further comprising:
a second conductor level formed over the front surface of the piezoelectric plate, the second conductor level covering at least portions of the first and second busbars.
22. The acoustic resonator device of claim 21 , wherein the second conductor level covers substantially all of the first and second busbars.
23. The acoustic resonator device of claim 18 , wherein
the piezoelectric plate is one of lithium niobate and lithium tantalate.
24. The acoustic resonator device of claim 23 , wherein
the piezoelectric plate is one of Z-cut, rotated Z-cut, and rotated YX-cut.