Method for making transversely-excited film bulk acoustic resonators with piezoelectric diaphragm supported by piezoelectric substrate

Patent metadata

Field	Value
Publication number	US-11817845-B2
Application number	US-202017131485-A
Country	US
Kind code	B2
Filing date	Dec 22, 2020
Priority date	Jul 9, 2020
Publication date	Nov 14, 2023
Grant date	Nov 14, 2023

Abstract

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.

First claim

It is claimed:

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.

Assignees

• Murata Manufacturing Co

Inventors

• Fenzi Neal
• Hammond Robert
• Turner Patrick
• Garcia Bryant
• Wakabayashi Ryo

Classifications

• H03H9/02228 Primary

  Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer · CPC title

• H03H3/02 Primary

  for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence) · CPC title

• H03H9/02031

  consisting of ceramic · CPC title

• H03H9/174

  Membranes · CPC title

• H03H9/176

  consisting of ceramic material (H03H9/177, H03H9/178 take precedence) · CPC title