Transversely-excited film bulk acoustic resonators with improved coupling and reduced energy leakage
Acoustic resonators, acoustic filter devices and methods of making the same. An acoustic resonator device includes a piezoelectric plate having front and back surfaces, an interdigital transducer (IDT) on the front surface including interleaved fingers extending alternately from opposed first and second busbars, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device, and a dielectric layer formed over and between the interleaved fingers, wherein the dielectric layer extends from between an edge of the aperture and the first busbar to between the an opposite edge of the aperture and the second busbar.
1 . An acoustic resonator device comprising:
a piezoelectric layer;
an interdigital transducer (IDT) on a surface of the piezoelectric layer and comprising a plurality of first fingers extending from a first busbar and a plurality of second fingers extending from a second busbar, such that the first and second plurality of fingers are interleaved fingers that have an overlapping distance that defines an aperture of the IDT; and
at least one dielectric layer over and between the interleaved fingers of the IDT,
wherein the aperture has a first edge that is defined by a line passing along ends of the first plurality of fingers and that opposes the second busbar,
wherein the aperture has a second edge that is defined by a line passing along ends of the second plurality of fingers and that opposes the first busbar,
wherein the at least one dielectric layer continuously extends beyond the first edge of the aperture but not to the second busbar and also continuously extends beyond the second edge of the aperture but not to the first busbar, and
wherein the least one dielectric layer is thinner in at least a region between the first edge of the aperture and the second busbar than a region over the aperture of the IDT.
2 . The device of claim 1 , wherein a shape of the at least one dielectric layer is configured to improve performance as compared to an acoustic resonator device with a dielectric layer that extends over an entirety of the IDT.
3 . The device of claim 1 , wherein a portion of the piezoelectric layer comprises a diaphragm that is over a cavity in a substrate.
4 . The device of claim 3 , wherein the interleaved fingers are on the diaphragm.
5 . The device of claim 1 , wherein the region of the at least one dielectric layer extends a distance past the first edge of the aperture by a distance less than or equal to 20 tp, wherein tp is a thickness of the piezoelectric layer.
6 . The device of claim 1 , wherein the region of the at least one dielectric layer extends approximately 2 μm past the first edge of the aperture.
7 . A filter device comprising:
a piezoelectric layer;
a conductor pattern on a surface of the piezoelectric layer and comprising a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, each of the plurality of IDTs comprising
a plurality of first fingers extending from a first busbar and a plurality of second fingers extending from a second busbar, such that the first and second plurality of fingers are interleaved fingers that have an overlapping distance that defines an aperture of each of the plurality of IDTs; and
wherein at least one resonator of the plurality of resonators comprises at least one dielectric layer over and between the interleaved fingers,
wherein the aperture of the at least one resonator has a first edge that is defined by a line passing along ends of the first plurality of fingers and that opposes the second busbar,
wherein the aperture of the at least one resonator has a second edge that is defined by a line passing along ends of the second plurality of fingers and that opposes the first busbar,
wherein the at least one dielectric layer continuously extends beyond the first edge of the aperture but not to the second busbar and also continuously extends beyond the second edge of the aperture but not to the first busbar, and
wherein the least one dielectric layer on the at least one resonator is thinner in at least a region between the first edge of the aperture and the second busbar than a region over the aperture of the IDT.
8 . The filter device of claim 7 , wherein a shape of the at least one dielectric layer on the at least one resonator is configured to improve performance as compared to an acoustic resonator device with a dielectric layer that extends over an entirety of the IDT.
9 . The filter device of claim 7 , wherein a portion of the piezoelectric layer forms a plurality of diaphragms that are over respective cavities.
10 . The filter device of claim 9 , wherein the interleaved fingers of the at least one resonator are on a respective diaphragm of the plurality of diaphragms.
11 . The filter device of claim 7 , wherein the region of the at least one dielectric layer on the at least one resonator extends a distance past the first edge of the aperture by a distance less than or equal to 20 tp, wherein tp is a thickness of the piezoelectric layer.
12 . The filter device of claim 7 , wherein the region of the at least one dielectric layer extends approximately 2 μm past the first edge of the aperture.
13 . A method of fabricating an acoustic resonator device comprising:
forming an interdigital transducer (IDT) on a surface of a piezoelectric layer, the IDT comprising a plurality of first fingers extending from a first busbar and a plurality of second fingers extending from a second busbar, such that the first and second plurality of fingers are interleaved fingers that have an overlapping distance that defines an aperture of the IDT; and
forming at least one dielectric layer over and between the interleaved fingers of the IDT,
wherein the aperture has a first edge that is defined by a line passing along ends of the first plurality of fingers and that opposes the second busbar,
wherein the aperture has a second edge that is defined by a line passing along ends of the second plurality of fingers and that opposes the first busbar,
wherein the at least one dielectric layer continuously extends beyond the first edge of the aperture but not to the second busbar and also continuously extends beyond the second edge of the aperture but not to the first busbar, and
wherein the least one dielectric layer is thinner in at least a region between the first edge of the aperture and the second busbar than a region over the aperture of the IDT.
14 . The method of claim 13 , wherein a portion of the piezoelectric plate forms a diaphragm spanning a cavity in a substrate, and the interleaved fingers are on the diaphragm.
15 . The method of claim 13 , wherein the region of the at least one dielectric layer extends a distance past the first edge of the aperture by a distance less than or equal to 20 tp, wherein tp is a thickness of the piezoelectric layer.
16 . The method of claim 13 , wherein the region of the at least one dielectric layer extends approximately 2 μm past the first edge of the aperture.
17 . The device of claim 1 , wherein the at least one dielectric layer includes a passivation dielectric layer that is over the piezoelectric layer and the IDT.
18 . The device of claim 1 , wherein the interleaved fingers of the IDT have a mark to pitch ratio that is greater than 0.05 and less than 0.5, wherein the mark is a width of at least one finger of the interleaved fingers and the pitch is a center-to-center spacing between two adjacent fingers of the interleaved fingers.
19 . The filter device of claim 7 , wherein the at least one dielectric layer of the at least one resonator includes a passivation dielectric layer that is over the piezoelectric layer and the IDT.
20 . The filter device of claim 7 , wherein the interleaved fingers of the IDT of the at least one resonator have a mark to pitch ratio that is greater than 0.05 and less than 0.5, wherein the mark is a width of at least one finger of the interleaved fingers and the pitch is a center-to-center spacing between two adjacent fingers of the interleaved fingers.