# US 12,119,803 B2 · Bulk acoustic wave resonators having convex surfaces, and methods of forming the same

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- Number: US 12,119,803 B2
- Document ID: US12119803B2
- Status: Granted
- Kind: B2
- Application number: 18/449,098
- Filed: 2023-08-14
- Published: 2023-12-07
- Granted: 2024-10-15
- Earliest claimed: 2017-06-30
- Assignees: Texas Instruments Incorporated
- Applicants: Texas Instruments Incorporated
- Inventors: Ting-Ta Yen
- Web page: https://patentgrep.com/patent/US12119803B2

## CPC

- H03H 9/0211: {of reflections}
- H03H 3/02: for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence)
- H03H 9/02015: {Characteristics of piezoelectric layers, e.g. cutting angles}
- H03H 9/02157: {Dimensional parameters, e.g. ratio between two dimension parameters, length, width or thickness}
- H03H 9/02047: {Treatment of substrates}
- H03H 9/172: {Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume}
- H03H 2003/021: {the resonators or networks being of the air-gap type}
- H03H 2003/025: {the resonators or networks comprising an acoustic mirror}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

In one example, a method of forming a bulk acoustic wave (BAW) resonator comprises: forming an electrode on at least one of a semiconductor substrate, a sacrificial layer, or an acoustic reflector; and forming a piezoelectric layer on the electrode, the piezoelectric layer having a convex surface.

## Claims

### Claim 1

A method, comprising:
forming an electrode of a bulk acoustic wave (BAW) resonator on at least one of a semiconductor substrate, a sacrificial layer, or an acoustic reflector; and
forming a piezoelectric layer of the BAW resonator on the electrode, in which the electrode covers entirely a surface of the piezoelectric layer, and the piezoelectric layer has a convex portion with a non-uniform thickness.

### Claim 2 (depends on 1)

The method of claim 1, wherein the surface of the piezoelectric layer is a planar surface, and the convex portion has a convex surface opposing the planar surface.

### Claim 3 (depends on 1)

The method of claim 1, wherein forming the piezoelectric layer on the electrode includes:
forming a piezoelectric material on the electrode; and
setting a shape of the piezoelectric material to form the piezoelectric layer having the convex portion.

### Claim 4 (depends on 3)

The method of claim 3, wherein the shape is a first shape, and setting the first shape of the piezoelectric material includes:
setting a second shape of a photoresist material on the piezoelectric material; and
etching the photoresist material having the second shape and the piezoelectric material to set the first shape of the piezoelectric material.

### Claim 5 (depends on 4)

The method of claim 4, wherein the second shape is based on a rate of etching of the piezoelectric material and the photoresist material.

### Claim 6 (depends on 4)

The method of claim 4, wherein setting a second shape of a photoresist material includes performing a gray-scale lithography operation on the photoresist material.

### Claim 7 (depends on 4)

The method of claim 4, wherein setting a second shape of a photoresist material includes performing a shaped lithography operation on the photoresist material.

### Claim 8 (depends on 4)

The method of claim 4, wherein setting a second shape of a photoresist material includes performing a sloped lithography operation on the photoresist material.

### Claim 9 (depends on 4)

The method of claim 4, wherein the convex portion is a first convex portion, and setting a second shape of a photoresist material includes forming a second convex portion on the photoresist material.

### Claim 10 (depends on 9)

The method of claim 9, wherein the first and second convex portions have convex surfaces of different curvatures.

### Claim 11 (depends on 1)

The method of claim 1, wherein the piezoelectric layer includes aluminum nitride.

### Claim 12 (depends on 1)

The method of claim 1, wherein the piezoelectric layer includes zinc oxide.

### Claim 13 (depends on 1)

The method of claim 1, wherein the electrode is a first electrode, and the method further comprises forming a second electrode of the BAW on the piezoelectric layer.

### Claim 14 (depends on 1)

The method of claim 1, further comprising:
mounting the semiconductor substrate or the acoustic reflector having the piezoelectric layer and the electrode thereon on an integrated circuit.

### Claim 15 (depends on 14)

The method of claim 14, further comprising: forming an interconnect between the electrode and the integrated circuit.

### Claim 16 (depends on 15)

The method of claim 15, wherein the interconnect includes a bond wire.

### Claim 17 (depends on 13)

The method of claim 13, wherein the surface is a first surface, and the second electrode covers entirely a second surface of the piezoelectric layer opposite the first surface.

### Claim 18 (depends on 1)

The method of claim 1, wherein the convex portion has a first thickness at a center and a second thickness on two sides of the center, the second thickness being smaller than the first thickness.

### Claim 19 (depends on 1)

The method of claim 1, wherein the convex portion has a plano-convex shape.

### Claim 20 (depends on 1)

The method of claim 1, wherein the BAW resonator is part of an integrated circuit.