Transversely-excited film bulk acoustic resonator with etch-stop layer
Acoustic resonator devices and methods are disclosed. An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. An aluminum oxide etch-stop layer is sandwiched between the surface of the substrate and the back surface of the piezoelectric plate, a portion of the piezoelectric plate and the etch-stop layer forming a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. The aluminum oxide etch-stop layer is impervious to an etch process used to form the cavity.
1. An acoustic resonator device comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces;
an aluminum oxide etch-stop layer sandwiched between the surface of the substrate and the back surface of the single-crystal piezoelectric plate, a portion of the single-crystal piezoelectric plate and the aluminum oxide etch-stop layer forming a diaphragm spanning a cavity in the substrate; and
an interdigital transducer (IDT) formed on the front surface of the single-crystal piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm, wherein
the aluminum oxide etch-stop layer is impervious to an etch process used to form the cavity.
2. The device of claim 1 , wherein the single-crystal piezoelectric plate is one of lithium niobate and lithium tantalate.
3. The device of claim 1 , further comprising:
a back-side dielectric layer between the single-crystal piezoelectric plate and the aluminum oxide etch stop layer, wherein the diaphragm includes the single-crystal piezoelectric plate, the back-side dielectric layer, and the aluminum oxide etch-stop layer.
4. The device of claim 3 , wherein the back-side dielectric layer is silicon dioxide.
5. The device of claim 1 , further comprising:
a bonding layer between the aluminum oxide etch-stop layer and the substrate, wherein the diaphragm includes the single-crystal piezoelectric plate and the aluminum oxide etch-stop layer, but not the bonding layer.
6. The device of claim 5 , wherein the substrate is silicon and the bonding layer is silicon dioxide.
7. The device of claim 1 , wherein a thickness of the aluminum oxide etch-stop layer is less than or equal to 20% of a thickness of the single-crystal piezoelectric plate.
8. The device of claim 7 , wherein the thickness of the aluminum oxide etch-stop layer is 4% to 6% of the thickness of the single-crystal piezoelectric plate.
9. A filter device, comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces;
an etch-stop layer sandwiched between the surface of the substrate and the back surface of the single-crystal piezoelectric plate, portions of the single-crystal piezoelectric plate and the etch-stop layer forming two or more diaphragms spanning respective cavities in the substrate;
a conductor pattern formed on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators including a shunt resonator and a series resonator, interleaved fingers of each of the plurality of IDTs disposed on a respective diaphragm of the two or more diaphragms; and
a frequency setting dielectric layer disposed on the front surface between the fingers of the IDT of the shunt resonator, wherein
the etch-stop layer is impervious to an etch process used to form the cavities.
10. The filter device of claim 9 , wherein
a sum of a thickness of the etch-stop layer and a thickness of the frequency setting dielectric layer is less than or equal to 35% of a thickness of the single-crystal piezoelectric plate.
11. The filter device of claim 9 , wherein the single-crystal piezoelectric plate is one of lithium niobate and lithium tantalate.
12. The filter device of claim 9 , wherein the etch-stop layer is one of an oxide, sapphire, a nitride, silicon carbide, and diamond.
13. The filter device of claim 9 , further comprising:
a back-side dielectric layer between the single-crystal piezoelectric plate and the etch stop layer, wherein each diaphragm of the two or more diaphragms includes the single-crystal piezoelectric plate, the back-side dielectric layer, and the etch-stop layer.
14. The filter device of claim 13 , wherein the back-side dielectric layer is silicon dioxide.
15. The filter device of claim 9 , further comprising:
a bonding layer between the etch-stop layer and the substrate, wherein each diaphragm of the two or more diaphragms includes the single-crystal piezoelectric plate and the etch-stop layer, but not the bonding layer.
16. The filter device of claim 15 , wherein the substrate is silicon and the bonding layer is silicon dioxide.
17. A method of fabricating an acoustic resonator device comprising:
forming an aluminum oxide etch-stop layer sandwiched between a surface of a device substrate and a first surface of a single-crystal piezoelectric plate having a second surface attached to a sacrificial substrate;
removing the sacrificial substrate to expose the second surface of the single-crystal piezoelectric plate;
using an etch process to form a cavity in the device substrate, a portion of the single-crystal piezoelectric plate and the aluminum oxide etch-stop layer forming a diaphragm spanning the cavity; and
forming an interdigital transducer (IDT) on the second surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm, wherein
the aluminum oxide etch-stop layer is impervious to the etch process used to form the cavity.
18. The method of claim 17 , wherein the single-crystal piezoelectric plate is one of lithium niobate and lithium tantalate.
19. The method of claim 17 , further comprising:
forming a back-side dielectric layer between the single-crystal piezoelectric plate and the aluminum oxide etch stop layer, wherein the diaphragm includes the single-crystal piezoelectric plate, the back-side dielectric layer, and the aluminum oxide etch-stop layer.
20. The method of claim 19 , wherein the back-side dielectric layer is silicon dioxide.
21. The method of claim 17 , further comprising:
forming a bonding layer between the etch-stop layer and the device substrate, wherein the diaphragm includes the single-crystal piezoelectric plate and the aluminum oxide etch-stop layer, but not the bonding layer.
22. The method of claim 21 , wherein the device substrate is silicon and the bonding layer is silicon dioxide.
23. The method of claim 17 , wherein a thickness of the aluminum oxide etch-stop layer is less than or equal to 20% of a thickness of the single-crystal piezoelectric plate.
24. The method of claim 23 , wherein the thickness of the aluminum oxide etch-stop layer is 4% to 6% of the thickness of the single-crystal piezoelectric plate.