Forming XBAR devices with excess piezoelectric material removed

1. A method of forming a filter device comprising:

forming a bonding layer on a substrate having at least a location for a first cavity and a location for a second cavity on a single die, the location for the first cavity having a first perimeter and the location for the second cavity having a second perimeter;

bonding a piezoelectric layer to the bonding layer;

forming the first and second cavities in the substrate before or after the bonding layer is bonded to the piezoelectric layer;

removing excess portions of the piezoelectric layer that extend a certain length past respective perimeters of the location for the first cavity and of the location for the second cavity; and

forming a first interdigital transducer (IDT) on the piezoelectric layer, such that interleaved fingers of the first IDT are over the location for the first cavity,

wherein removing the excess portions of the piezoelectric layer includes removing a length and a width of a perimeter of piezoelectric material of the piezoelectric layer spanning the location for the first cavity and the location for the second cavity that extends past the perimeter by 2 to 25 percent of a length and a width of the respective perimeter of the location for the first and the location for the second cavity, respectively.

2. The method of claim 1 , wherein removing the excess portions of the piezoelectric layer includes:

patterning the bonded piezoelectric layer; and

etching the patterned piezoelectric layer to remove the excess portions of the piezoelectric layer.

3. The method of claim 2 , wherein removing the excess portions of the piezoelectric layer includes:

etching the bonding layer to remove excess portions of the bonding layer that extend past the respective perimeters of the locations for first cavity and of the second cavity.

4. The method of claim 1 , wherein the substrate is Si, the bonding layer is SiO2 and the IDT is metal; and wherein the piezoelectric layer is one of lithium niobate or lithium tantalate.

5. The method of claim 1 , further comprising:

forming a second IDT on the piezoelectric layer that has interleaved fingers over the location for the second cavity; and

forming at least one conductor attaching the first IDT to the second IDT;

wherein forming the piezoelectric layer includes removing portions of the piezoelectric layer that either do not span the location for the first cavity and location for the second cavity, are not under the first or second IDTs, or are not under the at least one conductor.

6. The method of claim 1 , wherein removing the excess portions of the piezoelectric layer includes removing the excess portions of the piezoelectric layer either before forming the first IDT or after forming the first IDT; and

the method further comprises forming the first and second cavities either before bonding the piezoelectric layer to the substrate or after forming the first IDT.

7. The method of claim 6 , further comprising configuring the piezoelectric layer, the first IDT and the second IDT such that respective radio frequency signals applied to the first and second IDTs excite respective primary shear acoustic modes in the piezoelectric layer over the first and second cavities.

8. The method of claim 7 , further comprising selecting a thickness of the piezoelectric layer to tune the primary shear acoustic modes in the piezoelectric layer.

9. The method of claim 6 , further comprising forming connections to the first and second IDTs that form an RF filter input and output.

10. A method of forming a filter device comprising:

bonding a piezoelectric layer to a substrate, the piezoelectric having a portion that spans a location for a cavity, the location for the cavity having a perimeter;

forming the cavity;

removing excess portions of the piezoelectric layer that extend past the perimeter of the location for the cavity by 2 and 25 percent of the perimeter of the location for the cavity; and

forming an interdigital transducer (IDT) on the piezoelectric layer, such that the IDT includes interleaved fingers that extend over the location for the cavity.

11. The method of claim 10 , wherein removing the excess portions of the piezoelectric layer includes:

patterning the piezoelectric layer, and etching the patterned piezoelectric layer to remove the excess portions of the piezoelectric layer.

12. The method of claim 10 , further comprising:

forming a bonding layer on the substrate;

wherein the bonding of the piezoelectric layer to the substrate comprises bonding the piezoelectric layer to the bonding layer.

13. The method of claim 12 , wherein removing the excess portions of the piezoelectric layer includes etching the bonding layer to remove excess portions of the bonding layer that extend past the perimeter of the location of the cavity by 2 and 25 percent of the perimeter of the location of the cavity.

14. The method of claim 12 , wherein the substrate is Si, the bonding layer is SiO2, the IDT is metal, and the piezoelectric layer is one of lithium niobate or lithium tantalate.

15. The method of claim 10 , wherein removing the excess portions of the piezoelectric layer includes removing the excess portions of the piezoelectric layer either before forming the IDT or after forming the IDT; and

wherein the method further comprises forming the cavity either before bonding the piezoelectric layer to the substrate or after forming the IDT.

16. The method of claim 15 , further comprising:

configuring the piezoelectric layer and the IDT such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the piezoelectric layer over the cavity; and

selecting a thickness of the piezoelectric layer to tune the primary shear acoustic mode in the piezoelectric layer.

17. A method of forming a filter device comprising:

bonding a piezoelectric layer to a substrate having a location for a cavity having a perimeter, the piezoelectric layer over the location for the cavity;

forming an interdigital transducer (IDT) on the piezoelectric layer, such that interleaved fingers of the IDT are over the location for the cavity;

removing excess portions of the piezoelectric layer that extend past the perimeter of the location for the cavity by more than 10 percent of a length and a width of the perimeter of the location for the cavity; and

forming the cavity.

18. The method of claim 17 , wherein removing the excess portions of the piezoelectric layer includes:

patterning the piezoelectric layer; and

etching the patterned piezoelectric layer to remove the excess portions of the piezoelectric layer.

19. The method of claim 17 , further comprising forming a bonding layer on the substrate and bonding the piezoelectric layer to the substrate via the bonding layer.

20. The method of claim 19 , wherein removing the excess portions of the piezoelectric layer includes etching the bonding layer to remove excess portions of the bonding layer that extend past the perimeter of the location of the cavity by more than 10 percent of the perimeter length and width of the location of the cavity.

21. The method of claim 17 , wherein the substrate is Si, the bonding layer is SiO2, the IDT is metal, and the piezoelectric layer is one of lithium niobate or lithium tantalate.

22. The method of claim 10 , wherein removing the excess portions of the piezoelectric layer includes removing the excess portions of the piezoelectric layer either before forming the IDT or after forming the IDT; and

wherein the method further comprises forming the cavity either before bonding the piezoelectric layer to the substrate or after forming the IDT.

23. The method of claim 22 , further comprising:

configuring the piezoelectric layer and the IDT such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the piezoelectric layer over the cavity; and

selecting a thickness of the piezoelectric layer to tune the primary shear acoustic mode in the piezoelectric layer.