# US 7,411,473 B2 · Elastic boundary wave device

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- Number: US 7,411,473 B2
- Document ID: US7411473B2
- Status: Granted
- Kind: B2
- Application number: 11/624,720
- Filed: 2007-01-19
- Published: 2007-08-02
- Granted: 2008-08-12
- Earliest claimed: 2005-05-20
- Assignees: Murata Manufacturing Co., Ltd.
- Inventors: Hajime Kando
- Web page: https://patentgrep.com/patent/US7411473B2

## CPC

- H03H 9/02834: {of temperature influence (cut angles H03H9/02543)}
- H03H 9/0222: {of interface-acoustic, boundary, pseudo-acoustic or Stonely wave devices}
- H03H 9/02944: {of ohmic loss}
- H03H 9/14532: {Series weighting; Transverse weighting}
- H03H 9/14541: {Multilayer finger or busbar electrode}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

An elastic boundary wave device includes an IDT including laminated conductor layers disposed between a first medium and a second medium, wherein a plane that divides the IDT in half in the thickness direction defines an interface, the energy of an elastic boundary wave present on the side of the first medium of the interface is denoted as E1, and the energy of an elastic boundary wave present on the side of the second medium of the interface is denoted as E2, and wherein if the IDT included only a conductor having the highest density among the laminated conductor layers of the IDT, when the energy of an elastic boundary wave present on the side of the first medium of the interface is denoted as E1′ and the energy of an elastic boundary wave present on the side of the second medium of the interface is denoted as E2′, the energies of an elastic boundary wave would satisfy the relationship of E1/E2<E1′/E2′ so that the sonic velocity of an elastic boundary wave in the IDT including the laminated conductor layers is equal to the sonic velocity of an elastic boundary wave if the IDT included only the conductor layer having the highest density.

## Claims

### Claim 1

An elastic boundary wave device comprising:
a first medium having a positive temperature coefficient of delay in a propagation direction of an elastic boundary wave;
a second medium having a negative temperature coefficient of delay in a propagation direction of an elastic boundary wave; and
an IDT including laminated conductor layers disposed between the first medium and the second medium; wherein
a lamination direction of the first medium and the second medium is the thickness direction of the IDT, a plane that divides the IDT in half in the thickness direction defines an interface, energy of an elastic boundary wave present on the first medium side of the interface is denoted as E1, and energy of an elastic boundary wave present on the second medium side of the interface is denoted as E2; and
if the IDT included only of a conductor layer of a single metal having the highest density among the laminated conductor layers of the IDT, when the energy of an elastic boundary wave present on the first medium side of the interface is denoted as E1′ and the energy of an elastic boundary wave present on the second medium side of the interface is denoted as E2′, the energies of an elastic boundary wave would satisfy the relationship of E1/E2<E1′/E2′ so that the sonic velocity of an elastic boundary wave in the IDT including the laminated conductor layers is equal to the sonic velocity of an elastic boundary wave if the IDT included only of the conductor layer having the highest density.

### Claim 2 (depends on 1)

The elastic boundary wave device according to claim 1, wherein the IDT has a layered structure including a first conductor layer made of a metal having a density in the range of about 7,000 kg/m3 to about 22,000 kg/m3 and a second conductor layer made of a metal having a density in the range of about 1,740 kg/m3 to about 11,000 kg/m3;
the density ρ1 of the first conductor layer and the density ρ2 of the second conductor layer satisfy the relationship of ρ1/ρ2 >1.8 ; and
a conductor layer disposed on the second medium side of the IDT is the first conductor layer.

### Claim 3 (depends on 2)

The elastic boundary wave device according to claim 2, wherein the thickness H of the second conductor layer and the electrode finger period λ of the IDT satisfy the relationship of 0.034λ<H<0.5λ.

### Claim 4 (depends on 2)

The elastic boundary wave device according to claim 2, further comprising an adherent layer disposed at a portion at which the IDT is in contact with at least one of the first medium and the second medium.

### Claim 5 (depends on 2)

The elastic boundary wave device according to claim 2, wherein the first conductor layer is made of a metal selected from the group consisting of Pt, Au, Cu, Ag, Ni, Fe, W, Ta, Cr, and an alloy based thereon; and
the second conductor layer is made of a metal selected from the group consisting of Mg, Al, Ti, Cr, Ni, Cu, Ag, and an alloy based thereon.

### Claim 6 (depends on 2)

The elastic boundary wave device according to claim 2, wherein the first conductor layer is made of Au, and the second conductor layer is made of a metal selected from the group consisting of Al, Mg, Ti, Cr, Ni, Cu, Ag, and an alloy based thereon.

### Claim 7 (depends on 6)

The elastic boundary wave device according to claim 6, wherein the film thickness of the IDT is about 0.3λ or less.

### Claim 8 (depends on 2)

The elastic boundary wave device according to claim 2, wherein the first conductor layer is made of Cu, and the second conductor layer is made of a metal selected from the group consisting of Al, Mg, Ti, and an alloy based thereon.

### Claim 9 (depends on 8)

The elastic boundary wave device according to claim 8, wherein the film thickness of the IDT is about 0.3λ or less.

### Claim 10 (depends on 1)

The elastic boundary wave device according to claim 1, wherein the first medium is composed of one material selected from the group consisting of LiTaO3, LiNbO3, quartz crystal, PZT, LBO, langasite, langanite, and glass.

### Claim 11 (depends on 1)

The elastic boundary wave device according to claim 1, wherein the second medium is composed of at least one material selected from the group consisting of SiO2, quartz crystal, LBO, langasite, langanite, and glass, the material being different from a material used for the first medium.

### Claim 12 (depends on 1)

The elastic boundary wave device according to claim 1, further comprising a reflector disposed between the first medium and the second medium, the reflector being made of the same electrode material as the IDT.

### Claim 13

An elastic boundary wave device comprising:
a first medium having a positive temperature coefficient of delay in a propagation direction of an elastic boundary wave;
a second medium having a negative temperature coefficient of delay in a propagation direction of an elastic boundary wave; and
an IDT disposed between the first medium and the second medium; wherein
the IDT has a layered structure including a first conductor layer made of a metal having a density in the range of about 7,000 kg/m3 to about 22,000 kg/m3 and a second conductor layer made of a metal having a density in the range of about 1,740 kg/m3 to about 11,000 kg/m3;
the density ρ1 of the first conductor layer and the density ρ2 of the second conductor layer satisfy the relationship of ρ1/ρ2<1.8;
a conductor layer disposed on the second medium side of the IDT is the first conductor layer, and
the thickness H of the second conductor layer and the electrode finger period λ of the IDT satisfy the relationship of 0.034λ<H<0.5λ.

### Claim 14 (depends on 13)

The elastic boundary wave device according to claim 13, further comprising an adherent layer disposed at a portion at which the IDT is in contact with at least one of the first medium and the second medium.

### Claim 15 (depends on 13)

The elastic boundary wave device according to claim 13, wherein the first medium is composed of one material selected from the group consisting of LiTaO3, LiNbO3, quartz crystal, PZT, LBO, langasite, langanite, and glass.

### Claim 16 (depends on 13)

The elastic boundary wave device according to claim 13, wherein the second medium is composed of at least one material selected from the group consisting of SiO2, quartz crystal, LBO, langasite, langanite, and glass, the material being different from the material used for the first medium.

### Claim 17 (depends on 13)

The elastic boundary wave device according to claim 13, wherein the first conductor layer is made of a metal selected from the group consisting of Pt, Au, Cu, Ag, Ni, Fe, W, Ta, Cr, and an alloy based thereon, and
the second conductor layer is made of a metal selected from the group consisting of Mg, Al, Ti, Cr, Ni, Cu, Ag, and an alloy based thereon.

### Claim 18 (depends on 13)

The elastic boundary wave device according to claim 13, wherein the first conductor layer is made of Au, and the second conductor layer is made of a metal selected from the group consisting of Al, Mg, Ti, Cr, Ni, Cu, Ag, and an alloy based thereon.

### Claim 19 (depends on 18)

The elastic boundary wave device according to claim 18, wherein the film thickness of the IDT is about 0.3λ or less.

### Claim 20 (depends on 13)

The elastic boundary wave device according to claim 13, wherein the first conductor layer is made of Cu, and the second conductor layer is made of a metal selected from the group consisting of Al, Mg, Ti, and an alloy based thereon.

### Claim 21 (depends on 20)

The elastic boundary wave device according to claim 20, wherein the film thickness of the IDT is about 0.3λ or less.

### Claim 22 (depends on 13)

The elastic boundary wave device according to claim 13, further comprising a reflector disposed between the first medium and the second medium, the reflector being made of the same electrode material as the IDT.