Transversely-excited film bulk acoustic resonator with half-lambda dielectric layer
Acoustic resonator devices and filters 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 attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The piezoelectric plate and the IDT configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode in the diaphragm. A half-lambda dielectric layer is formed on one of the front surface and back surface of the piezoelectric plate.
1. An acoustic resonator device comprising:
a substrate having a surface;
a single-crystal piezoelectric layer having front and back surfaces, the back surface attached to the surface of the substrate either directly or via at least one intermedia layer, with a portion of the single-crystal piezoelectric layer forming a diaphragm over a cavity;
an interdigital transducer (IDT) at the single-crystal piezoelectric layer such that interleaved fingers of the IDT are at the diaphragm; and
a dielectric layer on one of the front surface and the back surface of the single-crystal piezoelectric layer, with the dielectric layer having a thickness of a half lambda.
2. The acoustic resonator device of claim 1 , wherein
a thickness ts of the single-crystal piezoelectric layer and a thickness td of the dielectric layer are defined as follows:
2ts=λ 0,s , and
0.85λ 0,d ≤2td≤1.15λ 0,d ,
where λ 0,s is a wavelength of a fundamental shear bulk acoustic wave resonance in the single-crystal piezoelectric layer, and
λ 0,d is a wavelength of a fundamental shear bulk acoustic wave resonance in the dielectric layer.
3. The acoustic resonator device of claim 1 , wherein the dielectric layer is one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 , and AlN.
4. The acoustic resonator device of claim 1 , wherein:
the single-crystal piezoelectric layer is lithium niobate,
the dielectric layer is SiO 2 , and
a thickness ts of the single-crystal piezoelectric layer and a thickness td of the dielectric layer are defined by the relationship: 0.875ts≤td≤1.25ts.
5. The acoustic resonator device of claim 4 , wherein a temperature coefficient of frequency of the acoustic resonator device is between −32 ppm/C° and −42 ppm/C° at a resonance frequency and between −20 ppm/C° and −36 ppm/C° at an anti-resonance frequency.
6. The acoustic resonator device of claim 1 , wherein the single-crystal piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode in the diaphragm.
7. A filter device, comprising:
a substrate;
a piezoelectric layer having parallel front and back surfaces and a thickness ts, the back surface attached to the substrate either directly or via at least one intermedia layer;
a conductor pattern at the piezoelectric layer and including a plurality of interdigital transducers (IDTs) of a respective plurality of resonators including a shunt resonator and a series resonator, interleaved fingers of each of the plurality of IDTs at respective portions of the piezoelectric layer over one or more cavities;
a first dielectric layer having a thickness tds deposited over and between the fingers of the series resonator; and
a second dielectric layer having a thickness tdp deposited over and between the fingers of the shunt resonator, wherein
ts, tds, and tdp are related by the equations:
2ts=λ 0,s , and
2tds<2tdp
where λ 0,s is a wavelength of a fundamental shear bulk acoustic wave resonance in the piezoelectric layer.
8. The filter device of claim 7 , wherein
0.85λ 0,d ≤2tds≤2tdp≤1.15λ 0,d ,
where λ 0,d is a wavelength of the fundamental shear bulk acoustic wave resonance in at least one of the first dielectric layer and the second dielectric layer.
9. The filter device of claim 7 , wherein the first dielectric layer and the second dielectric layer are one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 , and AlN.
10. The filter device of claim 7 , wherein the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode in at least part of the piezoelectric layer.
11. A filter device, comprising:
a substrate;
a piezoelectric layer having parallel front and back surfaces and a thickness ts, the back surface attached to the substrate either directly or via at least one intermedia layer;
a conductor pattern at the piezoelectric layer and including a plurality of interdigital transducers (IDTs) of a respective plurality of resonators including a shunt resonator and a series resonator, interleaved fingers of each of the plurality of IDTs at respective portions of the piezoelectric layer over one or more cavities;
a first SiO 2 layer having a thickness tds deposited over and between the fingers of the series resonator; and
a second SiO 2 layer having a thickness tdp deposited over and between the fingers of the shunt resonator,
wherein tds, and tdp are related by the equation:
tds<tdp.
12. The filter device of claim 11 , wherein tds, and tdp are related by the equation:
0.85ts≤tds≤tdp≤1.25ts.
13. The filter device of claim 11 , wherein a temperature coefficient of frequency of each of the plurality of resonators is between −20 ppm/C° and −42 ppm/C° at the resonance frequencies and the anti-resonance frequencies of all of the plurality of resonators.
14. The filter device of claim 11 , wherein the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode in at least part of the piezoelectric layer.
15. A method of fabricating an acoustic resonator device on a single-crystal piezoelectric layer having parallel front and back surfaces, the back surface attached to a substrate either directly or via at least one intermedia layer, the method comprising:
forming a cavity in the substrate such that a portion of the single-crystal piezoelectric layer forms a diaphragm over the cavity;
forming an interdigital transducer (IDT) at the single-crystal piezoelectric layer such that interleaved fingers of the IDT are at the diaphragm; and
forming a dielectric layer on one of the front surface and the back surface of the single-crystal piezoelectric layer, with the dielectric layer having a thickness of a half lambda.
16. The method of claim 15 , wherein
a thickness ts of the single-crystal piezoelectric layer and a thickness td of the dielectric layer are defined as follows:
2ts=λ 0,s , and
0.85λ 0,d ≤2td≤1.15λ 0,d ,
where λ 0,s is a wavelength of a fundamental shear bulk acoustic wave resonance in the single-crystal piezoelectric layer, and
λ 0,d is a wavelength of the fundamental shear bulk acoustic wave resonance in the dielectric layer.
17. The method of claim 15 , wherein forming the dielectric layer further comprises depositing one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 , and AlN.
18. The method of claim 15 , wherein
the single-crystal piezoelectric layer is lithium niobate, and
forming the dielectric layer comprises depositing SiO 2 to a thickness td, where td is greater or equal to 0.875ts and less than or equal to 1.25ts, where ts is a thickness of the single-crystal piezoelectric layer.
19. The method of claim 15 , wherein the single-crystal piezoelectric layer and the IDT configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the diaphragm.