Interface acoustic wave device made of lithium tantalate
View Patent ↗The invention relates to interfaces acoutics wave components made of lithium tantalate. Two substrate make up the filter have the same cut and the same crystal orientation, the invention gives the best cut angles in particular for optimizing the electromechanical coupling coefficient that determines the final performance characteristics of the component produced. Curves giving the variations of the coupling coefficient an the attenuation as a function of the cut angles and of the direction of propagation are provided. The values of the main acoustic characteristics of the component for these optimum cut angles are also given. The application of this type of device are, on the on hand, uses as a passive component such a resonator or a filter or a delay line, or as an integrated device, either in a measurement chain or in any array of devices operating according to the principle of recognition of the device by a phase code.
1. An interface acoustic wave device, comprising:
a first crystal substrate (S 1 ) made of lithium tantalate (LiTaO 3 );
a second crystal substrate (S 2 ), also made of lithium tantalate;
said first and second crystal substrates being joined together via a plane interface region (I) serving for the propagation of acoustic waves and comprising at least one electroacoustic transducer;
interconnection means for electrically connecting said transducers; the substrates, referenced in an initial orthonormal coordinate system (X,Y,Z), Z being parallel to the optical axis, X being defined by the piezoelectricity of the crystal and Y being perpendicular to (X,Z), having their identical cut plane and a common crystal orientation, said cut plane being identified by two successive angles of rotation φ and θ, φ corresponding to a first rotation about the Z axis, the coordinate system obtained thus being denoted by (X′,Y′,Z′) with Z ′ coincident with Z, and θ representing a second rotation about the X′ axis, the coordinate system obtained thus being denoted by (X″,Y″,Z″), with X″ coincident with X′, the direction of propagation of the acoustic waves being defined by a third angle ψ taken in said coordinate system (X″,Y″,Z″) representing a rotation about the Y″ axis, characterized in that, for any direction of propagation ψ:
the cut angles (φ,θ) lie within one of the following two angular ranges called the (0,0,0,) a cut and the (60,0,0) a :
-
(
0
,
0
,
0
)
a
cut
:
-
5
°
≤
φ
≤
+
5
°
-
20
°
≤
θ
≤
+
30
°
-
(
60
,
0
,
0
)
a
cut
:
+
55
°
≤
φ
≤
+
65
°
-
30
°
≤
θ
≤
+
20
°
.
2. The acoustic wave device as claimed in claim 1 , in that the angles (φ,θ,ψ), taken within the (X″,Y″,Z″) coordinate system lie within one of the following two angular ranges called the (0,0,0,) b cut and the (60,0,0,) b cut:
-
(
0
,
0
,
0
)
b
cut
:
-
5
°
≤
φ
≤
+
5
°
-
10
°
≤
θ
≤
+
10
°
-
5
°
≤
ψ
≤
+
5
°
-
(
60
,
0
,
0
)
b
cut
:
+
55
°
≤
φ
≤
+
65
°
-
10
°
≤
θ
≤
+
10
°
-
5
°
≤
ψ
≤
+
5
°
.
3. The device as claimed in claim 1 , in that the thicknesses of the two substrates are large compared with the operating acoustic wavelength (λ) and the thickness of the interface region is small compared with the operating acoustic wavelength (λ).
4. The device as claimed in claim 1 , in that the interface region is in the form of a laminated structure comprising at least one electroacoustic transducers and one or more layers of dielectric material.
5. The device as claimed in claim 1 in that the interface region comprises only one electroacoustic transducers, which are then etched on one of the two surfaces of the substrates in contact with each other, said interface region then being reduced to an interface plane.
6. The device as claimed in claim 1 in that said device is a passive component such as a resonator or a filter or a delay line or a phase code device.
7. A measurement sensor composed of a chain of devices, wherein said chain comprises at least one device as claimed in claim 1 .
8. A device operating according to the phase code principle and composed of a chain of devices, characterized in that said chain comprises at least one device as claimed in claim 1 .