# US 7,612,488 B1 · Method to control BAW resonator top electrode edge during patterning

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- Number: US 7,612,488 B1
- Document ID: US7612488B1
- Status: Granted
- Kind: B1
- Application number: 11/654,244
- Filed: 2007-01-16
- Granted: 2009-11-03
- Earliest claimed: 2007-01-16
- Assignees: Maxim Integrated Products, Inc.
- Inventors: Guillaume Bouche; Ralph N. Wall
- Web page: https://patentgrep.com/patent/US7612488B1

## CPC

- H03H 9/589: {Acoustic mirrors}
- H03H 9/131: {consisting of a multilayered structure}
- Y10T 29/42: Piezoelectric device making
- Y10T 29/49156: with selective destruction of conductive paths
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A piezoelectric resonator include a multi-layer top electrode. The multi-layer top electrode includes at least a top metal layer and a bottom metal layer. A top metal layer edge is recessed compared to a bottom metal layer edge allowing conformal deposition of a passivation layer. The passivation layer covers and protects the underlying layers from subsequent etching, thereby preventing etch undercut of the top electrode. In some embodiments, the multi-layer top electrode is configured as a bi-layer. In other embodiments, an extra layer is configured between the top metal layer and the bottom metal layer, for example a shunt load layer.

## Claims

### Claim 1

A piezoelectric resonator comprising:
a. a bottom electrode;
b. a piezoelectric layer coupled to the bottom electrode;
c. a top electrode coupled to the piezoelectric layer, wherein the top electrode comprises a bottom metal layer and a top metal layer configured such that an entire perimeter side surface of the top metal layer is recessed relative to a perimeter edge of the bottom metal layer; and
d. a passivation layer coupled to the top electrode such that the top metal layer and the bottom metal layer are isolated from a subsequent metal etch step.

### Claim 2 (depends on 1)

The piezoelectric resonator of claim 1 wherein the bottom metal layer comprises a refractory metal.

### Claim 3 (depends on 2)

The piezoelectric resonator of claim 2 wherein the bottom metal layer comprises a tungsten alloy.

### Claim 4 (depends on 2)

The piezoelectric resonator of claim 2 wherein the bottom metal layer comprises molybdenum, ruthenium, tungsten, platinum, osmium, rhenium or iridium.

### Claim 5 (depends on 1)

The piezoelectric resonator of claim 1 wherein the top metal layer comprises aluminum, gold, platinum, or an aluminum alloy composition.

### Claim 6 (depends on 1)

The piezoelectric resonator of claim 1 wherein the top metal layer comprises a metal alloy composition.

### Claim 7 (depends on 1)

The piezoelectric resonator of claim 1 wherein the passivation layer includes an etched contact area and the piezoelectric resonator further comprises an interconnect metal layer coupled to the top electrode at the etched contact area.

### Claim 8 (depends on 7)

The piezoelectric resonator of claim 7 wherein the interconnect metal layer comprises a first interconnect metal layer and a second interconnect metal layer.

### Claim 9 (depends on 8)

The piezoelectric resonator of claim 8 wherein the first interconnect metal layer comprises titanium tungsten.

### Claim 10 (depends on 8)

The piezoelectric resonator of claim 8 wherein the second interconnect metal layer comprises aluminum copper or copper.

### Claim 11 (depends on 7)

The piezoelectric resonator of claim 7 wherein the interconnect metal layer comprises titanium tungsten, tungsten, or molybdenum.

### Claim 12 (depends on 7)

The piezoelectric resonator of claim 7 wherein the interconnect metal layer comprises a metal material that is selectively etched relative to the passivation layer.

### Claim 13 (depends on 1)

The piezoelectric resonator of claim 1 wherein the piezoelectric resonator comprises a bulk acoustic wave resonator.

### Claim 14 (depends on 1)

The piezoelectric resonator of claim 1 wherein the passivation layer is initially configured such that all exposed portions of the top metal layer and the bottom metal layer are covered.

### Claim 15

A piezoelectric resonator comprising:
a. a bottom electrode;
b. a piezoelectric layer coupled to the bottom electrode;
c. a top electrode coupled to the piezoelectric layer, wherein the top electrode comprises a bottom metal layer and a top metal layer configured such that a perimeter edge of the top metal layer is recessed relative to a perimeter edge of the bottom metal layer;
d. a passivation layer coupled to the top electrode, wherein the passivation layer includes an etched portion configured to provide a contact point with the top electrode, further wherein the passivation layer is further configured to isolate a remaining portion of the top electrode; and
e. an interconnect metal layer coupled to the top electrode at the contact point through the etched portion of the passivation layer.

### Claim 16 (depends on 15)

The piezoelectric resonator of claim 15 wherein the bottom metal layer comprises a refractory metal.

### Claim 17 (depends on 16)

The piezoelectric resonator of claim 16 wherein the bottom metal layer comprises a tungsten alloy.

### Claim 18 (depends on 16)

The piezoelectric resonator of claim 16 wherein the bottom metal layer comprises molybdenum, ruthenium, tungsten, platinum, osmium, rhenium or iridium.

### Claim 19 (depends on 15)

The piezoelectric resonator of claim 15 wherein the top metal layer comprises aluminum, gold, platinum, or an aluminum alloy composition.

### Claim 20 (depends on 15)

The piezoelectric resonator of claim 15 wherein the top metal layer comprises a metal alloy composition.

### Claim 21 (depends on 15)

The piezoelectric resonator of claim 15 wherein the interconnect metal layer is configured to be in physical contact with the top metal layer and the bottom metal layer at the contact point.

### Claim 22 (depends on 15)

The piezoelectric resonator of claim 15 wherein the interconnect metal layer comprises a first interconnect metal layer and a second interconnect metal layer.

### Claim 23 (depends on 22)

The piezoelectric resonator of claim 22 wherein the first interconnect metal layer comprises titanium tungsten.

### Claim 24 (depends on 22)

The piezoelectric resonator of claim 22 wherein the second interconnect metal layer comprises aluminum copper or copper.

### Claim 25 (depends on 15)

The piezoelectric resonator of claim 15 wherein the interconnect metal layer comprises titanium tungsten, tungsten, or molybdenum.

### Claim 26 (depends on 15)

The piezoelectric resonator of claim 15 wherein the interconnect metal layer comprises a metal material that is selectively etched relative to the passivation layer.

### Claim 27 (depends on 15)

The piezoelectric resonator of claim 15 wherein the piezoelectric resonator comprises a bulk acoustic wave resonator.

### Claim 28

A piezoelectric resonator comprising:
a. a bottom electrode;
b. a piezoelectric layer coupled to the bottom electrode;
c. a top electrode coupled to the piezoelectric layer, wherein the top electrode comprises a bottom metal layer and a top metal layer configured such that a perimeter portion of a top surface of the bottom metal layer is uncovered by the top metal layer; and
d. a passivation layer coupled to the top electrode such that the top metal layer and the bottom metal layer are isolated from a subsequent metal etch step.