# US 5,081,389 A · Crystal cut angles for lithium tantalate crystal for novel surface acoustic wave devices

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- Number: US 5,081,389 A
- Document ID: US5081389A
- Status: Granted
- Kind: A
- Application number: 07/620,025
- Filed: 1990-11-30
- Granted: 1992-01-14
- Earliest claimed: 1990-11-30
- Assignees: Ascom Zelcom AG
- Inventors: Benjamin P. Abbott; Thor Thorvaldsson
- Web page: https://patentgrep.com/patent/US5081389A

## CPC

- H03H 9/02559: {of lithium niobate or lithium-tantalate substrates}
- Y10T 29/42: Piezoelectric device making
- 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 Lithium Tantalate crystal, defined by the Euler angles lambda (.lambda.) equal to about 0.degree. and mu (.mu.) equal to about 90.degree. with an acoustic wave propagation direction angle theta (.theta.) in the range of plus 130.degree. to plus 150.degree. and preferably equal to about plus 141.25.degree., offers unique properties for surface acoustic wave device applications.

## Claims

### Claim 1

A Lithium Tantalate crystal for acoustic wave propagation having a substantially planar surface defined by the Euler angles lambda (.lambda.) equal about 0.degree. and mu (.mu.) equal about 90.degree. and the acoustic wave propagation direction Euler angle theta (.theta.) equal about plus 130.degree. to about plus 150.degree., or equivalents.

### Claim 2 (depends on 1)

A Lithium Tantalate crystal as set forth in claim 1, in which the acoustic wave propagation direction Euler angle theta (.theta.) preferably equals about plus 141.25.degree..

### Claim 3 (depends on 1)

A unidirectional surface acoustic wave device comprising, interdigitated electrodes on the planar surface of the Lithium Tantalate crystal defined by the Euler angles of claim 1 to obtain unidirectional transmission.

### Claim 4 (depends on 3)

The device of claim 3, in which the crystal is in the form of a wafer.

### Claim 5

A crystal for acoustic wave propagation comprising, a thin Lithium Tantalate plate having a crystal orientation around (1) the Z axis of said plate by an angle lambda (.lambda.) of about 0.degree. and (2) the X axis of said plate by angle mu (.mu.) of about 90.degree. and a wave propagation angle theta (.theta.) of about plus 130.degree. to about plus 150.degree., or equivalents.

### Claim 6 (depends on 5)

A crystal for acoustic wave propagation as set forth in claim 5, in which angle theta (.theta.) is preferably about plus 141.25.degree. and equivalents.

### Claim 7

A method of forming a Lithium Tantalate crystal for acoustic wave propagation comprising the steps of:
a. forming a cut Lithium Tantalate crystal having a substantially planar surface, and
b. defining the planar surface by the Euler angle lambda (.lambda.) equal about 0.degree. and mu (.mu.) equal about 90.degree. and the acoustic wave propagation direction Euler angle theta (.theta.) equal about plus 130.degree. to about 150.degree. and equivalents.

### Claim 8 (depends on 7)

A method of forming a Lithium Tantalate crystal as set forth in claim 7, defining the acoustic wave propagation direction Euler angle theta (.theta.) preferably at about 141.25.degree. and equivalents.

### Claim 9

A method of forming a unidirectional surface acoustic wave device comprising the steps of:
a. forming a cut Lithium Tantalate crystal having a substantially planar surface,
b. defining said crystal by the Euler angles lambda (.lambda.) equal about 0.degree., mu (.mu.) equal about 90.degree. and theta (.theta.) equal about plus 130.degree. to about plus 150.degree., or equivalents, and
c. placing interdigitated electrodes on said planar surface, to propagate acoustic waves in the direction theta (.theta.) equal about plus 130.degree. to about plus 150.degree., or equivalents, to obtain said unidirectional transmission.

### Claim 10 (depends on 9)

The method of claim 9, further comprising the step of constructing said crystal in the form of a wafer.

### Claim 11

The method of forming a crystal cut comprising the steps of:
a. forming said crystal of a thin Lithium Tantalate plate, for acoustic wave propagation,
b. rotating the crystal orientation of said plate around (1) the Z axis of said plate by an angle lambda (.lambda.) equal about 0.degree. and (2) the X axis of said plate by an angle mu (.mu.) equal about 90.degree., and
c. designating the acoustic wave propagation direction in said crystal as an angle theta (.theta.) equal about plus 130.degree. to about plus 150.degree., or equivalents.

### Claim 12 (depends on 11)

The method of forming a crystal cut as set forth in claim 11, in which the angle theta (.theta.) preferably equals about plus 141.25.degree. or equivalents.