FILTERS USING TRANSVERSLY-EXCITED FILM BULK ACOUSTIC RESONATORS WITH FREQUENCY-SETTING DIELECTRIC LAYERS
A filter device is provided that includes a substrate; a piezoelectric layer coupled to the substrate either directly or via one or more intermediate layers; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a first cavity the first bulk acoustic resonator device; a second IDT of a second bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a second cavity of the second bulk acoustic resonator device; a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; and a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT. The first thickness is greater than the second thickness.
1 . A filter device, comprising:
a substrate;
a piezoelectric layer coupled to the substrate either directly or via one or more intermediate layers;
a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a first cavity the first bulk acoustic resonator device;
a second IDT of a second bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a second cavity of the second bulk acoustic resonator device;
a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; and
a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT,
wherein the first thickness is greater than the second thickness.
2 . The filter device of claim 1 , wherein a difference between a resonance frequency of the first bulk acoustic resonator device and a resonance frequency of the second bulk acoustic resonator device is based, at least in part, by a difference between the first thickness and the second thickness.
3 . The filter device of claim 1 , wherein the first thickness is less than or equal to 500 nm, and the second thickness is greater than zero.
4 . The filter device of claim 1 , wherein the first bulk acoustic resonator device is configured to excite a bulk shear wave having a propagation direction perpendicular to a direction of a primarily laterally excited electric field generated by the first IDT.
5 . The filter device of claim 4 , wherein 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.
6 . The filter device of claim 4 , wherein the electric field is primarily laterally excited when atomic motion of the bulk shear wave is primarily parallel to a surface of the piezoelectric layer.
7 . The filter device of claim 1 , wherein a thickness between front and back surfaces of the piezoelectric layer is greater than or equal to 200 nm and less than or equal to 1000 nm.
8 . The filter device of claim 1 , wherein one or more of the first IDT and the second IDT have a pitch greater than or equal to 2 times the thickness of the piezoelectric layer and less than or equal to 20 times the thickness of the piezoelectric layer, and wherein the pitch is a center-to-center spacing of two adjacent IDT fingers.
9 . The filter device of claim 1 , wherein the first bulk acoustic resonator and the second bulk acoustic resonators are either both series resonators or both shunt resonators in a ladder filter architecture.
10 . The filter device of claim 1 , wherein the first bulk acoustic resonator is a shunt resonator in a ladder filter architecture and the second bulk acoustic resonator is series resonator in the ladder filter architecture.
11 . The filter device of claim 1 , wherein:
the first dielectric layer is a front-side dielectric layer disposed between the interleaved fingers of the first IDT,
the filter device further comprises a first back-side dielectric layer disposed on a surface of the piezoelectric layer facing the substrate,
the second dielectric layer is a front-side dielectric layer disposed between the interleaved fingers of the first IDT, and
the filter device further comprises a second back-side dielectric layer disposed on a surface of the piezoelectric layer facing the substrate.
12 . The filter device of claim 1 , wherein the first dielectric layer is disposed between the interleaved fingers of the first IDT and also as over the interleaved fingers of the first IDT, and the second dielectric layer is disposed between the interleaved fingers of the second IDT and also over the interleaved fingers of the second IDT.
13 . The filter device of claim 1 , wherein the first cavity is disposed in the one or more intermediate layers between the piezoelectric layer and the substrate, and wherein the one or more intermediate layers is a non-piezoelectric material.
14 . The filter device of claim 1 , wherein the first IDT is on a front surface of the piezoelectric layer facing away from the substrate.
15 . The filter device of claim 1 , wherein the second IDT is on a front surface of the piezoelectric layer facing away from the substrate.
16 . The filter device of claim 1 , further comprising:
a first opening through the piezoelectric layer and to the first cavity; and
a second opening through the piezoelectric layer and to the second cavity.
17 . A filter device, comprising:
a substrate comprising a base and an intermediate layer;
a piezoelectric layer coupled to the substrate;
a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a first cavity the first bulk acoustic resonator device;
a second IDT of a second bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a second cavity of the second bulk acoustic resonator device;
a first dielectric layer having a first thickness disposed between the interleaved fingers of the first IDT; and
a second dielectric layer having a second thickness disposed between the interleaved fingers of the second IDT,
wherein the first thickness is greater than the second thickness.
18 . The filter device of claim 17 , wherein the first bulk acoustic resonator device is configured to excite a bulk shear wave having a propagation direction perpendicular to a direction of a primarily laterally excited electric field generated by the first IDT.
19 . The filter device of claim 17 , wherein a ratio of a mark of at least one of the interleaved fingers of the first IDT to a pitch between at least two adjacent interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.
20 . The filter device of claim 17 , wherein a ratio of a thickness of at least one of the interleaved fingers of one or more of the first IDT and the second IDT to a thickness of the piezoelectric layer is less than 0.5.