JPH0422208A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To set the intersection width of an excitation electrode to a value by which impedance matching to an external circuit can be taken easily, and to set the width of the whole waveguide to a value for giving the maximum efficiency by converting the beam width of a surface acoustic wave by a horn type waveguide. CONSTITUTION:When a signal of a center angular frequency omega is inputted to an excitation electrode 2, a surface acoustic wave of width being equal to intersection width d1 of the electrode 2 is excited, proparated in the positive direction of (x) and made incident on a horn type waveguide 6. In the waveguide 6, an incident wave of width d1 is propagated, becomes width d2 and is made incident on waveguides 4-l-4-n. Also, when a signal of a center angular frequency omega is inputted to an excitation electrode 3, a surface wave of width being equal to intersection width d3 of the electrode 3 is excited, propagated in the negative direction of (x) and made incident on a horn type waveguide 7. In the waveguide 7, an incident wave of width d3 is propagated, becomes width d4 and is made incident on the waveguide 4. In the waveguide 4, a surface wave of a center angular frequency 2omega propagated in the (y) axis direction is generated. This wave becomes a convolution electric signal of two input signals by an acousto-electric transducer 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device, and particularly to a surface acoustic wave convolver that extracts a convolution signal of two signals.

[Prior art] Fig. 4 shows the results of "Chuyo et al., Transactions of the Institute of Electronics and Communication Engineers, 86/2,
VOl, J69-C, N [L2 pp 190-19
8J is a schematic plan view showing the configuration of a conventional surface acoustic wave element.

In FIG. 4, 1 is a piezoelectric substrate, and 2 and 3 are a pair of comb-shaped electrodes for surface acoustic wave excitation, which are arranged facing each other at an appropriate distance in the X direction on the surface of the substrate 1. be.

4-1.4-2.4-3゜..., 4-n are elastic electrodes formed on the surface of the substrate 1 extending in the X direction and parallel to each other between these electrodes 2 and 3. It is a surface wave waveguide. Further, 5 is an acoustoelectric transducer formed on the surface of the substrate 1 at an appropriate distance from the waveguide in the X direction. The acoustoelectric transducer consists of comb-shaped electrodes.

In this surface acoustic wave element, when an electrical signal with an angular frequency ω is input to the comb-shaped electrodes 2 and 3 for surface acoustic wave excitation,
Surface acoustic waves of this frequency are excited, and the surface acoustic waves propagate in the waveguides 4-1 to 4-n in mutually opposite directions in the X-axis direction, and due to parametric mixing phenomenon in the surface acoustic wave waveguides, A surface acoustic wave with an angular frequency of 2ω is generated that propagates in the X-axis direction. This surface acoustic wave is transmitted to the acoustoelectric transducer 5.
, where a convolution electrical signal of the above two input signals can be obtained.

[Problems to be Solved by the Invention] However, in the conventional example described above, as shown in FIG. 5, the efficiency depends on the number of waveguides, and the efficiency is maximum when the number of waveguides is 8 to 10. On the other hand, since the beam width of the surface acoustic wave excited by the comb-shaped electrode for surface acoustic wave excitation is equal to the intersection width d of the comb-shaped electrode for surface acoustic wave excitation, the electrode intersection width d
must be the same as the overall width of the surface acoustic wave waveguide,
Furthermore, since the impedance of the comb-shaped electrode for surface acoustic wave excitation changes depending on the width of the electrodes, it is necessary to determine the width d of the electrodes in consideration of impedance matching with an external circuit.

Therefore, in the conventional example described above, if the number of waveguides is set to have the maximum efficiency, the crossing width d of the comb-shaped electrode for surface acoustic wave excitation must be set in accordance with the width of the waveguide due to the number of waveguides. Impedance matching with the circuit becomes difficult, and conversely, if the intersection width d of the comb-shaped electrode for surface acoustic wave excitation is set to a width that facilitates impedance matching, the number of surface acoustic wave waveguides will be limited, resulting in a decrease in efficiency. There was the problem of inviting.

[Means for Solving the Problems] In the present invention, as a means for solving the above-mentioned problems, a first and a second surface acoustic wave are excited on a piezoelectric substrate (two excitation electrodes, a surface acoustic wave waveguide for propagating the first and second surface acoustic waves excited from the excitation electrode in opposite directions; and a surface acoustic wave waveguide for generating the first and second surface acoustic waves in the surface acoustic wave waveguide. a surface acoustic wave element having at least one acoustoelectric transducer that converts a third surface acoustic wave propagating in a transverse direction into an electrical signal, a horn-shaped waveguide between the excitation electrode and the surface acoustic wave waveguide; will be established.

Further, in the surface acoustic wave device of the present invention, the surface acoustic wave waveguide is composed of a plurality of elements divided along the propagation direction of the first and second surface acoustic waves, and the arrangement pitch of the elements (adjacent elements (distance between the center lines of
is preferably equal to the wavelength of the surface acoustic wave.

[Function] According to this configuration, by converting the beam width of the surface acoustic wave using the horn-shaped waveguide, the intersection width of the excitation electrodes and the width of the entire surface acoustic wave waveguide (number of waveguide elements) can be changed. can be chosen independently.

Therefore, the intersection width of the excitation electrodes can be set to a value that facilitates impedance matching with the external circuit, and the width of the entire surface acoustic wave waveguide can be set to a value that provides maximum efficiency.

In addition, the arrangement pitch β of the surface acoustic wave waveguides 4-1 to 4-n
is the same as the wavelength of the surface acoustic wave generated in the surface acoustic wave waveguide.
By arranging and forming 4-n, the surface acoustic waves generated in each surface acoustic wave waveguide element overlap in phase,
It can be excited efficiently.

In addition, the incident angle θ when the surface acoustic wave reflects the shape of the horn-shaped waveguide at the boundary of the horn-shaped waveguide is cos θ>V,
/VQ (where Vl is the surface acoustic wave velocity on the surface of the horn-shaped waveguide, and vo is the surface acoustic wave velocity on the free surface). It is totally reflected without any reflection, and is highly efficient (
Beam width of surface acoustic waves can be converted (FIG. 2) 6 [Example] Examples of the present invention will be described below.

(Example 1) FIG. 1 is a schematic plan view showing a first example of a surface acoustic wave element according to the present invention.

In FIG. 1, reference numeral 1 denotes a piezoelectric substrate, and a piezoelectric substrate such as lithium niobate can be used as the piezoelectric substrate.

2.3 are surface acoustic wave excitation electrodes formed on the surface of the substrate 1 and facing each other at an appropriate distance in the X direction. The electrodes 2 and 3 are comb-shaped electrodes made of a conductor such as aluminum, silver, or gold, and are provided so that surface acoustic waves propagate in the X direction.

4-1.1-2. ..., 4-n are surface acoustic wave waveguides extending in the X direction in the electrodes 2 and 3 and arranged parallel to each other at a thermally constant pitch on the surface of the substrate 1.

Surface acoustic wave waveguides are described in detail in "Surface Acoustic Wave Engineering" supervised by Kenio Shibayama, Institute of Electronics and Communication Engineers, pp. 82-102, and there are thin film waveguides and topographic waveguides. A Δv/v waveguide coated with a conductor such as aluminum, silver, or gold is preferable.

5, the surface acoustic wave waveguides 4-1 to 4-1 are formed on the surface of the substrate 1;
This is an acoustoelectric transducer arranged and formed at an appropriate distance from 4-n in the X direction. The acoustoelectric transducer is a comb-shaped electrode made of a conductor such as aluminum, silver, or gold, and is provided so that surface acoustic waves propagating in the X direction can be efficiently converted into electrical signals.

6.7 is on the surface of the substrate 1 between the electrode 2 and the surface acoustic wave waveguides 4-1 to 4-n, and between the electrode 3 and the surface acoustic wave waveguides 4-1 to 4-n. These are horn-shaped waveguides arranged and formed respectively.

Regarding horn waveguides, MANAS K, ROY
Author rA Raylei, gh Wave Beam
Compressor Using Δv/v-T
ype GuidanceJ IEEE Trans,
on 5onics and Ultrasonics,
Vol, 5U-23, July 1976.276-2
It is explained in detail on page 79.

Horn waveguides include thin film waveguides and topographic waveguides, but in the present invention, Δv/v waveguides in which the substrate surface is coated with a conductor such as aluminum, silver, or gold are preferred.

In the surface acoustic wave element of this example, when an electric signal with a center angular frequency ω is input to one excitation electrode 2, a surface acoustic wave with a beam width equal to the intersection width d of the excitation electrode 2 is excited. , propagates in the positive direction of X and enters the horn waveguide 6. In the bone waveguide 6, a surface acoustic wave that is incident with a beam width d1 propagates while being reflected at the boundary of the horn waveguide 6, and is emitted as a beam width d2, and is emitted from the surface acoustic wave waveguides 4-1 to 4-. incident on n. Similarly, when an electric signal with a center angular frequency ω is input to the other excitation electrode 3, a surface acoustic wave with a beam width equal to the intersection width d3 of the excitation electrode 3 is excited and propagates in the negative direction of X. The light is incident on the horn-shaped waveguide 7. In the horn waveguide 7, the beam width d
The surface acoustic wave incident on the waveguide 3 propagates while being reflected at the boundary of the horn-shaped waveguide 7, is emitted with a beam width d4, and enters the surface acoustic wave waveguides 4-1 to 4-n.

Here, the shape of the horn waveguide is as shown in Figure 2.
The angle of incidence θ when the surface acoustic wave is reflected at the boundary of the horn-shaped waveguide is cos θ〉■, /vo (■I is the surface acoustic wave velocity on the surface of the horn-shaped waveguide, vo is the surface acoustic wave velocity on the free surface ), the surface acoustic waves are totally reflected without leaking out of the horn-shaped waveguide, and the beam width of the surface acoustic waves can be converted with good efficiency.

Now, two surface acoustic waves propagate in opposite directions from both ends of the surface acoustic wave waveguides 4-1 to 4-n, and due to a parametric mixing phenomenon in the surface acoustic wave waveguides,
A surface acoustic wave with a central angular frequency of 2ω is generated that propagates in the y-axis direction. This surface acoustic wave reaches the acoustoelectric transducer 5,
Here, a convolution electrical signal of the above two input signals can be obtained.

In addition, each element 4-1 of the surface acoustic wave waveguides 4-1 to 4'-n
The surface acoustic wave waveguides 4-1 to 4-n are arranged and formed so that the array pitch ρ of ~4-n is the same as the wavelength of the surface acoustic wave generated and sewn in the surface acoustic wave waveguide. By doing so, the surface acoustic waves generated in each surface acoustic wave waveguide element overlap in phase, and can be efficiently excited.

(Other Embodiments) FIG. 3 is a schematic plan view showing a second embodiment of the surface acoustic wave device according to the present invention. In this figure, members similar to those in FIG. 1 are given the same reference numerals.

In this embodiment, an acoustoelectric transducer 8 similar to the acoustoelectric transducer 5 is provided on the surface of the substrate l as a surface acoustic wave waveguide 4-
1 to 4-n, the only points that are formed on the opposite side from the acoustoelectric transducer 5 in the y direction are the same distance apart from the acoustoelectric transducer 5.
This is different from the example.

This embodiment also provides the same effects as the first embodiment, but furthermore, in this embodiment, the surface acoustic waves generated in the surface acoustic wave waveguide propagate in both directions of the ±yy axes. Therefore, by outputting these from the two acoustoelectric transducers 5.8 and combining them, the second embodiment of the first embodiment can be achieved.
You can get twice the output. In addition, by making the distances from the surface acoustic wave waveguides 4-1 to 4-n different between the two acousto-electric transducers 5 and 8, the output from one acousto-electric transducer is converted to the other acousto-electric transducer. The output from the device can be delayed as appropriate.

Furthermore, by using the surface acoustic wave excitation electrodes 2 and 3 in the first and second embodiments as double electrodes (split electrodes), reflection of surface acoustic waves at the surface acoustic wave excitation electrodes 2.3 is suppressed. can.

Similarly, by making the acoustoelectric transducers 5 and 8 double electrodes (split electrodes), reflection of surface acoustic waves in the acoustoelectric transducers 5 and 8 is suppressed, and the characteristics of the element are further improved. be able to.

Further, the coordinate axes shown in FIGS. 1 and 3 are added for convenience and do not mean the crystal axes of the substrate or the like. Furthermore, in the first and second embodiments, the substrate 1 is not limited to a piezoelectric single crystal such as lithium niobate (for example, a structure in which a piezoelectric film is added to a semiconductor or glass substrate, etc.) Any material and structure that is effective may be used.

[Effects of the Invention] As described above, according to the present invention, by providing the horn-shaped waveguide between the excitation electrode and the surface acoustic wave waveguide,
The intersection width d1 of the excitation electrode and the width d2 of the surface acoustic wave waveguide can be selected independently, the intersection width d1 of the excitation electrode is set to a value that facilitates impedance matching with the external circuit, and the width d2 of the surface acoustic wave waveguide is set to a value that facilitates impedance matching with the external circuit. can be set to a value that gives

Moreover, the arrangement pitch C of the surface acoustic wave waveguides 4-1 to 4-n
The surface acoustic wave waveguides 4-1 to 4-1 are arranged so that
By arranging and forming 4-n, the surface acoustic waves generated in each surface acoustic wave waveguide element overlap in phase,
It can be excited efficiently.

In addition, the angle of incidence θ when the surface acoustic wave reflects the shape of the horn-shaped waveguide at the boundary of the horn-shaped waveguide is CO3θ>V
l/V. (V is the surface acoustic wave velocity on the surface of the horn-shaped waveguide, ■ is the surface acoustic wave velocity on the free surface) By arranging and forming the surface acoustic wave so as to satisfy (total reflection, and can efficiently convert the beam width of surface acoustic waves.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing a first embodiment of a surface acoustic wave device according to the present invention, FIG. 2 is an explanatory diagram of a horn-shaped waveguide, and FIG. 3 is a schematic plan view showing a first embodiment of a surface acoustic wave device according to the present invention. FIG. 4 is a schematic plan view showing a conventional example; FIG. 5 is a diagram showing the relationship between the number of waveguides and efficiency. 1 is a substrate, 2 and 3 are surface acoustic wave excitation electrodes, 4-1 to 4
-n is a surface acoustic wave waveguide element, 5 and 8 are acoustoelectric transducers, and 6 and 7 are horn waveguides.

Claims (3)

[Claims] (1) At least two excitation electrodes that excite first and second surface acoustic waves on a piezoelectric substrate, and the first and second surface acoustic waves excited from the excitation electrodes are arranged in opposite directions to each other. a surface acoustic wave waveguide for propagation; and at least one for converting a third surface acoustic wave generated in the surface acoustic wave waveguide and propagating in a direction crossing the first and second surface acoustic waves into an electrical signal. A surface acoustic wave device comprising an acoustoelectric transducer, characterized in that a horn-shaped waveguide is provided between the excitation electrode and the surface acoustic wave waveguide. (2) The surface acoustic wave waveguide is composed of a plurality of elements divided along the propagation direction of the first and second surface acoustic waves, and the arrangement pitch of the elements (distance between center lines of adjacent elements) The surface acoustic wave element according to claim 1, wherein the wavelength of the third surface acoustic wave is substantially equal to the wavelength of the third surface acoustic wave. (3) The shape and position of the horn-shaped waveguide are such that θ is the incident angle of the surface acoustic wave and V_1 is the surface of the horn-shaped waveguide at the boundary where the surface acoustic wave is reflected inside the horn-shaped waveguide. When V_0 is the surface acoustic wave velocity at the free surface, cosθ>V_1/V
The surface acoustic wave element according to claim 1, wherein the surface acoustic wave element is set to a shape and position that satisfy _0.