FILTER USING TRANSVERSELY-EXCITED FILM BULK ACOUSTIC RESONATORS WITH DIVIDED FREQUENCY-SETTING DIELECTRIC LAYERS
An acoustic filter is provide that includes a substrate; a piezoelectric plate attached to the substrate; and a plurality of bulk acoustic resonators including one or more shunt resonators and one or more series resonators. One or more of the shunt resonators includes an interdigital transducer having interdigital fingers on the piezoelectric plate; a front-side frequency setting layer at least partially on a front side of the at least one shunt resonator; and a back-side frequency setting layer on a back side of the at least one shunt resonator. Moreover, a thickness of the back-side frequency setting layer is at least 30% of a total thickness of the front-side frequency setting layer and the back-side frequency setting layer.
1 . A filter device, comprising:
a substrate;
a piezoelectric plate attached to the substrate; and
a plurality of bulk acoustic resonators including one or more shunt resonators and one or more series resonators, at least one shunt resonator of the one or more shunt resonators comprising:
an interdigital transducer having interdigital fingers on the piezoelectric plate;
a front-side frequency setting layer at least partially on a front side of the at least one shunt resonator; and
a back-side frequency setting layer on a back side of the at least one shunt resonator,
wherein a thickness of the back-side frequency setting layer is at least 30% of a total thickness of the front-side frequency setting layer and the back-side frequency setting layer.
2 . The filter device of claim 1 , wherein the front-side frequency setting layer is also over the interdigital fingers of the at least one shunt resonator.
3 . The filter device of claim 1 , wherein the thickness of the back-side frequency setting layer is greater than or equal to 35% and less than or equal to 50% of the total thickness of the front-side frequency setting layer and the back-side frequency setting layer.
4 . The filter device of claim 1 , wherein the front-side frequency setting layer and the back-side frequency setting layer are a material selected from silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, beryllium oxide, tantalum oxide, and tungsten oxide.
5 . The filter device of claim 1 , wherein a thickness of the front-side frequency setting layer and the thickness of the back-side frequency setting layer are configured such that a peak admittance of an A2 spurious mode is substantially reduced compared to a peak admittance of an A2 spurious mode of a resonator with only a front-side frequency setting layer.
6 . The filter device of claim 1 , where a total thickness of the front-side frequency setting layer and the back-side frequency setting layer is greater than 25% of a thickness of the piezoelectric plate.
7 . The filter device of claim 1 , wherein the one or more shunt resonators comprise a first shunt resonator and a second shunt resonator, and wherein a first thickness of the front-side frequency setting layer of the first shunt resonator and a second thickness of the front-side frequency setting layer of the second shunt resonator are different.
8 . The filter device of claim 1 , wherein the one or more shunt resonators comprise a first shunt resonator and a second shunt resonator, and wherein a first thickness of the back-side frequency setting layer of the first shunt resonator and a second thickness of the back-side frequency setting layer at the second shunt resonator are different.
9 . The filter device of claim 1 , wherein at least one series resonator of the one or more series resonators comprise a front-side frequency setting layer at least partially on a front side of the at least one series resonator, and a back-side frequency setting layer on a back side of the at least one series resonator.
10 . The filter device of claim 9 , wherein the one or more series resonators comprise a first series resonator and a second series resonator, and wherein a first thickness of the front-side frequency setting layer of the first series resonator and a second thickness of the front-side frequency setting layer of the second series resonator are different.
11 . The filter device of claim 9 , wherein the one or more series resonators comprise a first series resonator and a second series resonator, and wherein a first thickness of the back-side frequency setting layer of the first series resonator and a second thickness of the back-side frequency setting layer of the second series resonator are different.
12 . The filter device of claim 1 , further comprising:
a passivation and tuning layer over all of the plurality of bulk acoustic resonators.
13 . A filter device, comprising:
a substrate;
a piezoelectric plate having front and back surfaces, the back surface attached to a surface of the substrate;
a plurality of acoustic resonators connected in a ladder filter circuit, the plurality of acoustic resonators including one or more shunt resonators and one or more series resonators, at least one shunt resonators of the one or more shunt resonators comprising:
an interdigital transducer having interleaved fingers on the front surface of the piezoelectric plate;
a first front-side frequency setting layer over the interleaved fingers and at least partially on the front surface of the piezoelectric plate;
a back-side frequency setting layer at least partially on the back surface of the piezoelectric plate, and
wherein a thickness of the back-side frequency setting layer is at least 30% of a total thickness of the front-side frequency setting layer and the back-side frequency setting layer.
14 . The filter device of claim 13 , wherein the thickness of the back-side frequency setting layer is greater than or equal to 35% and less than or equal to 50% of the total thickness of the first front-side frequency setting layer and the back-side frequency setting layer.
15 . The filter device of claim 13 , wherein a thickness of the first front-side frequency setting layer and the thickness of the back-side frequency setting layer are configured such that a peak admittance of an A2 spurious mode is substantially reduced compared to a peak admittance of an A2 spurious mode of a resonator without a back-side frequency setting layer.
16 . The filter device of claim 13 , where a total thickness of the first front-side frequency setting layer and the back-side frequency setting layer is greater than 25% of a thickness of the piezoelectric plate.
17 . A filter device, comprising:
a substrate;
a piezoelectric layer attached to the substrate either directly or via one or more intermediate layers; and
a plurality of bulk acoustic resonators including at least one shunt resonator and at least one series resonator, at least one shunt resonator comprising an interdigital transducer (IDT) on the piezoelectric layer;
a front-side frequency setting layer at least partially on a front side of the at least one shunt resonator; and
a back-side frequency setting layer on a back side of the at least one shunt resonator, the back side being opposite the front side,
wherein a thickness of the back-side frequency setting layer is at least 30% of a total combined thickness of the front-side frequency setting layer and the back-side frequency setting layer.
18 . The filter device of claim 17 , wherein the thickness of the back-side frequency setting layer is greater than or equal to 35% and less than or equal to 50% of the total thickness of the front-side frequency setting layer and the back-side frequency setting layer.
19 . The filter device of claim 17 , wherein the front-side frequency setting layer and the back-side frequency setting layer are a material selected from silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, beryllium oxide, tantalum oxide, and tungsten oxide.
20 . The filter device of claim 17 , wherein a thickness of the front-side frequency setting layer and the thickness of the back-side frequency setting layer are configured such that a peak admittance of an A2 spurious mode is substantially reduced compared to a peak admittance of an A2 spurious mode of a resonator with only a front-side frequency setting layer.