Surface acoustic wave device

• US 7,327,071 B2
• Filed: 09/01/2006
• Issued: 02/05/2008
• Est. Priority Date: 03/02/2004
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Takata, Eiichi, Kadota, Michio, Nakao, Takeshi, Nishiyama, Kenji
• Primary Examiner(s): BUDD, MARK OSBORNE
• Application Number:
  US11/469,505
• Publication Number:
  US 20060290233A1
• Time in Patent Office: 522 Days
• Field of Search: 310/313.A, 310/313.R, 310/363, 310/364
• US Class Current: 310/313.00A
• CPC Class Codes: H03H 3/08 for the manufacture of resonators or networks using surface acoustic waves
• CPC Class Codes: H03H 9/02984 Protection measures against damaging
• CPC Class Codes: H03H 9/14538 Formation
• CPC Class Codes: H03H 9/25 Constructional features of resonators using surface acoustic waves devices for manipulating acoustic surface waves in general G10K11/36

Abstract

A surface acoustic wave device includes a piezoelectric substrate made of LiTaO₃ or LiNbO₃ having an electromechanical coefficient of about 15% or more, at least one electrode which is disposed on the piezoelectric substrate and which is a laminate film having a metal layer defining a primary metal layer primarily composed of a metal having a density higher than that of Al or an alloy of the metal and a metal layer which is laminated on the primary metal layer and which is composed of another metal, and a first SiO₂ layer which is disposed in a remaining area other than that at which the at least one electrode is located and which has a thickness approximately equivalent to that of the electrode. In the surface acoustic wave device described above, the density of the electrode is at least about 1.5 times that of the first SiO₂ layer. In addition, a second SiO₂ layer disposed so as to cover the electrode and the first SiO₂ layer and a silicon nitride compound layer disposed on the second SiO₂ layer are further provided.

Claims

1. A surface acoustic wave device comprising:

a piezoelectric substrate made of one of LiTaO₃ or LiNbO₃ and having an electromechanical coefficient of at least about 15%;

at least one electrode disposed on the piezoelectric substrate and defined by a laminate having a metal layer defining a primary metal layer made of a metal having a density greater than that of Al or an alloy primarily composed of the metal and a metal layer which is laminated on the primary metal layer and which is made of another metal;

a first SiO₂ layer disposed in a remaining area other than that at which said at least one electrode is located and having a thickness approximately equal to that of the at least one electrode;

a second SiO₂ layer disposed to cover the at least one electrode and the first SiO₂ layer; and

a silicon nitride compound layer disposed on the second SiO₂ layer;

wherein

the density of the at least one electrode is at least about 1.5 times that of the first SiO₂ layer.

2. The surface acoustic wave device according to claim 1, wherein when the thickness of the second SiO₂ film is represented by h, and the wavelength of a surface acoustic wave is represented by λ

, 0.08≦

h/λ

≦

0.5 is satisfied.

3. The surface acoustic wave device, according to claim 1, wherein the silicon nitride compound layer is composed of an SiN layer, and when the thickness of the SiN layer is represented by h and the wavelength of a surface acoustic wave is represented by λ

, 0<

h/λ

≦

0.1 is satisfied.

4. The surface acoustic wave device according to claim 1, further comprising:

a diffusion inhibition film made of SiN and disposed between the second SiO₂ layer and the at least one electrode;

wherein

when the thickness of the diffusion inhibition film is represented by h, and the wavelength of a surface acoustic wave is represented by λ

, 0.005≦

h/λ

≦

0.05 is satisfied.

5. The surface acoustic wave device according to claim 1, wherein the at least one electrode is made of one of Cu, a Cu alloy, or a laminate film comprising a metal layer primarily composed of Cu or a Cu alloy.

6. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate is made of one of rotated Y-plate X-propagation LiTaO₃ or LiNbO₃, and when the thickness of the second SiO₂ layer is represented by h₁, the thickness of the silicon nitride compound layer formed on the second SiO₂ layer is represented by h₂, the wavelength of a surface acoustic wave is represented by λ

, and the following equations are satisfied;

coefficient A₁=−

190.48;

coefficient A₂=76.19;

coefficient A₃=−

120.00;

coefficient A₄=−

47.30;

coefficient A₅=55.25;

H₁=h₁/λ

, H₂=h₂/λ

, and θ

=(A₁H₁²+A₂H₁+A₃)H₂+A₄H₁+A₅,

a Y-X cut angle of the rotated Y-plate X-propagation piezoelectric substrate is in the range of θ

±

5°

.

7. The surface acoustic wave device according to claim 1, wherein the density of the at least one electrode is at least about 2.5 times that of the first SiO₂ layer.