# US 7,411,333 B2 · Surface acoustic wave device

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- Number: US 7,411,333 B2
- Document ID: US7411333B2
- Status: Granted
- Kind: B2
- Application number: 11/457,960
- Filed: 2006-07-17
- Published: 2007-01-25
- Granted: 2008-08-12
- Earliest claimed: 2005-07-21
- Assignees: TDK Corporation
- Inventors: Yoshikazu Kihara; Katsunori Osanai; Yukio Hirokawa; Masaki Sobu
- Web page: https://patentgrep.com/patent/US7411333B2

## CPC

- H03H 9/02559: {of lithium niobate or lithium-tantalate substrates}
- H03H 9/02921: {Measures for preventing electric discharge due to pyroelectricity}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

A SAW device comprises a single crystal piezo-electric strate (made, for example, of LiTaO3 or LiNbO3), and an interdigital transducer (IDT) formed of a material mainly containing Al and disposed on the piezo-electric substrate. The piezo-electric strate contains an additive (for example, Fe, Mn, Cu, Ti), and an orientation rotated by an angle in a range of 42° to 48° (more preferably 46°±0.3°) from a Y-axis toward a Z-axis about an X-axis. The IDT presents a normalized thickness h/λ (h: thickness of electrode, and λ: spacing between digits of the IDT) of 7% to 11%. A more appropriate substrate cut angle can be shown for the SAW device which employs a piezo-electric substrate containing an additive, to improve the electric characteristics thereof.

## Claims

### Claim 1

A surface acoustic wave device comprising:
a single crystal piezo-electric substrate; and
an interdigital transducer formed of a material mainly containing aluminum and disposed on a surface of said piezo-electric substrate,
wherein said single crystal piezo-electric substrate contains an additive, and has an orientation rotated by an angle in a range of 42° to 48° from a Y-axis to a Z-axis about an X-axis,
said piezo-electric substrate is a lithium tantalate substrate or a lithium niobate substrate, and
said additive comprising iron, added at a weight percentage of 1.24 wt. % or less,
said interdigital transducer presents a normalized thickness h/λ in a range of 7 to 11 %, said normalized thickness being derived by normalizing a thickness h of said interdigital transducer with a spacing λ between digits of said interdigital transducer.

### Claim 2 (depends on 1)

A surface acoustic wave device according to claim 1, wherein:
said single crystal piezo-electric substrate has an orientation rotated by an angle in a range of 46°±0.3° from the Y-axis to the Z-axis about the X-axis.

### Claim 3 (depends on 2)

A surface acoustic wave device according to claim 2, wherein:
said normalized thickness h/λ is approximately 9%.

### Claim 4 (depends on 3)

Surface acoustic wave device according to claim 3, wherein said single crystal piezo-electric substrate exhibits a volume resistivity in a range of 3.6×1010 to 1.5×1014Ω·cm.

### Claim 5 (depends on 2)

A surface acoustic wave device according to claim 2, wherein said single crystal piezo-electric substrate exhibits a volume resistivity in a range of 3.6×1010 to 1.5×1014Ω·cm.

### Claim 6 (depends on 1)

A surface acoustic wave device according to claim 1, wherein:
said normalized thickness h/λ is approximately 9%.

### Claim 7 (depends on 6)

A surface acoustic wave device according to claim 6, wherein said single crystal piezo-electric substrate exhibits a volume resistivity in a range of 3.6×1010 to 1.5×1014Ω·cm.

### Claim 8 (depends on 1)

A surface acoustic wave device according to claim 1, wherein said single crystal piezo-electric substrate exhibits a volume resistivity in a range of 3.6×1010 to 1.5×1014Ω·cm.