Transversely-excited film bulk acoustic resonators using multiple dielectric layer thicknesses to suppress spurious modes
Acoustic filters and methods of fabricating acoustic filters are disclosed. A filter includes a single-crystal piezoelectric plate having a front surface and a back surface attached to a substrate, and a plurality of acoustic resonators including a first shunt resonator, a second shunt resonator, and one or more series resonators. Each of the plurality of acoustic resonators includes an interdigital transducer (IDT) formed on the front surface of the piezoelectric plate, interleaved fingers of the IDT disposed on a respective diaphragm formed by a portion of the piezoelectric plate that spans a cavity in the substrate. A frequency setting dielectric layer is formed over the first and second shunt resonators but not over the one or more series resonators. The frequency setting dielectric layer has a thickness t1 on the first shunt resonator and a thickness t2 on the second shunt resonator, where t1 is not equal to t2.
1. A filter device, comprising:
a substrate;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of the substrate; and
a plurality of acoustic resonators including a first shunt resonator, a second shunt resonator, and one or more series resonators, each of the plurality of acoustic resonators including an interdigital transducer (IDT) at the piezoelectric plate, interleaved fingers of the IDT at a respective diaphragm formed by a respective portion of the piezoelectric plate that spans a respective cavity in the substrate; and
a frequency setting dielectric layer over the first and second shunt resonators but not over the one or more series resonators,
wherein the frequency setting dielectric layer has a thickness t1 on the first shunt resonator and a thickness t2 on the second shunt resonator, where t1 is not equal to t2.
2. The filter device of claim 1 , wherein a magnitude of a difference between t1 and t2 is greater than or equal to 0.5% of a thickness of the piezoelectric plate and less than or equal to 2% of the thickness of the piezoelectric plate.
3. The filter device of claim 1 , wherein t1 and t2 are both greater than or equal to 25% of a thickness of the piezoelectric plate.
4. The filter device of claim 1 , wherein the frequency setting dielectric layer comprises one or more 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 the piezoelectric plate and the IDTs of the plurality of acoustic resonators are configured such that a respective radio frequency signal applied to each IDT excites a respective shear primary acoustic mode in the respective diaphragm.
6. The filter device of claim 1 , wherein:
the plurality of acoustic resonators comprises n shunt resonators including the first and second shunt resonators, where n is an integer greater than or equal to two, and
a respective thickness of the frequency setting dielectric layer over each of the n shunt resonators is different from thicknesses of the frequency setting dielectric layer over all other shunt resonators.
7. A filter device, comprising:
a substrate;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of the substrate; and
a plurality of acoustic resonators including n shunt resonators, where n is an integer greater than one, and one or more series resonator connected in a ladder filter circuit, each of the plurality of acoustic resonators including an interdigital transducer (IDT) at the piezoelectric plate, interleaved fingers of the IDT at a respective diaphragm formed by a respective portion of the piezoelectric plate that spans a respective cavity in the substrate; and
a frequency setting dielectric layer over all of the n shunt resonators but not over the one or more series resonators,
wherein a thickness of the frequency setting dielectric layer over any one of the n shunt resonators is different from thicknesses of the frequency setting dielectric layer over all others of the n shunt resonators.
8. The filter device of claim 7 , wherein a magnitude of a difference between a thickness of the frequency setting dielectric layer over any one of the n shunt resonators and a thickness of the frequency setting dielectric layer over any other of the n shunt resonators is greater than or equal to 0.5% of a thickness of the piezoelectric plate.
9. The filter device of claim 7 , wherein a difference between a thickest frequency setting dielectric layer and a thinnest frequency setting dielectric layer over any of then shunt resonators is less than or equal to 2(n−1)% of a thickness of the piezoelectric plate.
10. The filter device of claim 7 , wherein respective thicknesses of the frequency setting dielectric layer over all of the n shunt resonators are greater than or equal to 25% of a thickness of the piezoelectric plate.
11. The filter device of claim 7 , wherein the frequency setting dielectric layer comprises one or more material selected from silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, beryllium oxide, tantalum oxide, and tungsten oxide.
12. The filter device of claim 7 , wherein the piezoelectric plate and the IDTs of the plurality of acoustic resonators are configured such that a respective radio frequency signal applied to each IDT excites a respective shear primary acoustic mode in the respective diaphragm.
13. A filter device, comprising:
a substrate;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of the substrate; and
a plurality of acoustic resonators including a first shunt resonator, a second shunt resonator, and one or more series resonators, each of the plurality of acoustic resonators including an interdigital transducer (IDT) at the piezoelectric plate, interleaved fingers of each IDT at a respective diaphragm formed by a respective portion of the piezoelectric plate that spans a respective cavity in the substrate; and
a frequency setting dielectric layer between the interleaved fingers of the first and second shunt resonators but not the interleave fingers of the one or more series resonators,
wherein the frequency setting dielectric layer has a thickness t1 between the interleaved fingers of the first shunt resonator and a thickness t2 between the interleaved fingers of the second shunt resonator, where t1 is not equal to t2.
14. The filter device of claim 13 , wherein a magnitude of a difference between t1 and t2 is greater than or equal to 0.5% of a thickness of the piezoelectric plate and less than or equal to 2% of the thickness of the piezoelectric plate.
15. The filter device of claim 13 , wherein t1 and t2 are both greater than or equal to 25% of a thickness of the piezoelectric plate.
16. The filter device of claim 13 , wherein the frequency setting dielectric layer comprises one or more materials selected from silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, beryllium oxide, tantalum oxide, and tungsten oxide.
17. The filter device of claim 13 , wherein the piezoelectric plate and the IDTs of the plurality of acoustic resonators are configured such that a respective radio frequency signal applied to each IDT excites a respective shear primary acoustic mode in the respective diaphragm.
18. The filter device of claim 13 , wherein:
the plurality of acoustic resonators comprises n shunt resonators including the first and second shunt resonators, where n is an integer greater than or equal to two, and
a respective thickness of the frequency setting dielectric layer over each of the n shunt resonators is different from thicknesses of the frequency setting dielectric layer over all other shunt resonators.
19. A filter device, comprising:
a substrate;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of the substrate; and
a plurality of acoustic resonators including n shunt resonators, where n is an integer greater than one, and one or more series resonator connected in a ladder filter circuit, each of the plurality of acoustic resonators including an interdigital transducer (IDT) at the piezoelectric plate, interleaved fingers of the IDT at a respective diaphragm formed by a respective portion of the piezoelectric plate that spans a respective cavity in the substrate; and
a frequency setting dielectric layer between the interleaved fingers of all of the n shunt resonators but not between the interleaved fingers of the one or more series resonators,
wherein a thickness of the frequency setting dielectric layer between the interleaved fingers of any one of then shunt resonators is different from thicknesses of the frequency setting dielectric layer between the interleaved fingers of all others of the n shunt resonators.
20. The filter device of claim 19 , wherein a magnitude of a difference between a thickness of the frequency setting dielectric layer over any one of the n shunt resonators and a thickness of the frequency setting dielectric layer over any other of the n shunt resonators is greater than or equal to 0.5% of a thickness of the piezoelectric plate.
21. The filter device of claim 19 , wherein a difference between a thickest frequency setting dielectric layer and a thinnest frequency setting dielectric layer over any of then shunt resonators is less than or equal to 2(n−1)% of a thickness of the piezoelectric plate.
22. The filter device of claim 19 , wherein respective thicknesses of the frequency setting dielectric layer over all of the n shunt resonators are greater than or equal to 25% of a thickness of the piezoelectric plate.
23. The filter device of claim 19 , wherein the frequency setting dielectric layer comprises one or more material selected from silicon dioxide, silicon nitride, aluminum oxide, aluminum nitride, beryllium oxide, tantalum oxide, and tungsten oxide.
24. The filter device of claim 19 , wherein the piezoelectric plate and the IDTs of the plurality of acoustic resonators are configured such that a respective radio frequency signal applied to each IDT excites a respective shear primary acoustic mode in the respective diaphragm.