Method for making transversely-excited film bulk acoustic resonators with piezoelectric diaphragm supported by piezoelectric substrate
Methods of making acoustic resonators and filter devices. A method includes attaching a piezoelectric plate to a substrate, and forming a conductor pattern including an interdigital transducer (IDT) on a portion of the piezoelectric plate that forms a diaphragm spanning a cavity such that interleaved fingers of the IDT are on the diaphragm. The substrate and the piezoelectric plate are the same material.
1. A method of fabricating an acoustic resonator device comprising:
forming a buried oxide layer above a substrate;
forming a lateral etch stop in the buried oxide layer;
attaching a piezoelectric plate to the buried oxide layer, such that the buried oxide layer is between the substrate and the piezoelectric plate, and attaches the substrate to the piezoelectric plate; and
forming a conductor pattern comprising an interdigital transducer (IDT) at a portion of the piezoelectric plate that forms a diaphragm spanning a cavity, such that interleaved fingers of the IDT are at the diaphragm, wherein the substrate and the piezoelectric plate are the same material.
2. The method of claim 1 , further comprising forming the cavity to extend entirely through the substrate.
3. The method of claim 1 , further comprising forming the cavity to extend through a portion of the substrate, such that the cavity does not extend entirely through the substrate.
4. The method of claim 1 , further comprising:
forming the lateral etch stop to define a boundary of the cavity; and
forming the cavity via an etchant etching the buried oxide layer within the boundary of the cavity.
5. The method of claim 4 , further comprising introducing the etchant to the cavity via a through hole in the diaphragm.
6. The method of claim 1 , further comprising forming the cavity to extend through the substrate and the buried oxide layer.
7. The method of claim 1 , further comprising forming the cavity such that the cavity does not extend into the substrate.
8. The method of claim 1 , wherein the buried oxide layer is one of SiO 2 and Al 2 O 3 .
9. The method of claim 1 , further comprising forming the buried oxide layer to not extend across the cavity.
10. The method of claim 9 , wherein the substrate and piezoelectric plate are one of Z-cut, rotated Z-cut, and rotated YX-cut.
11. The method of claim 1 , wherein a thickness of the buried oxide layer is in a range between 10 nm and 50 microns.
12. The method of claim 1 , further comprising configuring the piezoelectric plate and interleaved fingers, such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm.
13. The method of claim 1 , wherein the substrate and piezoelectric plate are one of lithium niobate and lithium tantalate.
14. A method of fabricating an acoustic resonator device, the method comprising:
forming a buried oxide layer above a substrate;
attaching a piezoelectric plate to the buried oxide layer, such that the buried oxide layer is between the substrate and the piezoelectric plate, and attaches the substrate to the piezoelectric plate;
forming a conductor pattern comprising an interdigital transducer (IDT) at a portion of the piezoelectric plate that forms a diaphragm spanning a cavity, such that interleaved fingers of the IDT are at the diaphragm, wherein the substrate and the piezoelectric plate are the same material; and
forming a sacrificial layer in a portion of the buried oxide layer corresponding to the cavity.
15. The method of claim 14 , further comprising removing the sacrificial layer to form the cavity.
16. The method of claim 15 , further comprising:
forming a through hole in the diaphragm; and
removing the sacrificial layer by an etchant introduced to the cavity via the through hole.
17. The method of claim 14 , further comprising forming the sacrificial layer of phosphosilicate glass or polysilicon.
18. A method of fabricating an acoustic resonator device, the method comprising:
forming a buried oxide layer above a substrate;
attaching a piezoelectric plate to the buried oxide layer, such that the buried oxide layer is between the substrate and the piezoelectric plate, and attaches the substrate to the piezoelectric plate;
forming a conductor pattern comprising an interdigital transducer (IDT) at a portion of the piezoelectric plate that forms a diaphragm spanning a cavity, such that interleaved fingers of the IDT are at the diaphragm;
wherein the substrate and the piezoelectric plate are the same material, and
wherein the buried oxide layer extends across the cavity.