JPH04150217A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To eliminate, generation of an electromagnetic wave from a surface acoustic wave guide path, to improve the characteristic by connecting the surface acoustic wave guide path to ground through an electric circuit. CONSTITUTION:Surface acoustic wave guide path 4-1-4-n are connected electrically to a hermetic seal 7 by bonding wires 6-1-6-n and the hermetic seal 7 connects to ground through a case or the like electrically. That is, the surface acoustic wave guide path 4-1-4-n are connected to ground. Thus, the production of an electromagnetic wave from the surface acoustic wave guide path 4-1-4-n is suppressed. Thus, the interference of a convolution signal generated by the electromagnetic wave is suppressed and the characteristic of the surface acoustic wave element is improved.

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. 3 shows "Chuyo et al., Transactions of the Institute of Electronics and Communication Engineers 86/2.V
FIG. 2 is a schematic plan view showing the configuration of a conventional surface acoustic wave element described in "J69-C, No. 2, pp. 190-198".

In FIG. 3, numeral 1 is a piezoelectric substrate, and numerals 2 and 3 are two comb-shaped electrodes for surface acoustic wave excitation, which are formed on the surface of the substrate 1 so as to be opposed to each other at an appropriate distance in the X direction.

4-1.4-2. ..., 4-n are these electrodes 2.3
These are surface acoustic wave waveguides formed on the surface of the substrate 1 in parallel to each other and extending in the X direction between them. Reference numeral 5 designates an acoustoelectric transducer formed on the surface of the substrate 1 at an appropriate distance from the surface acoustic wave waveguide in the X direction.

Further, the coordinate axes shown in FIG. 3 are added for convenience and do not mean the crystal axes of the substrate or the like.

In this surface acoustic wave element, when an electrical signal with an angular frequency ω is input to the comb-shaped electrode 2.3 for surface acoustic wave excitation,
A surface acoustic wave of the frequency is excited, and the surface acoustic wave is transmitted through the surface acoustic wave waveguides 4-1, 4-2. ..., 4-n propagate in opposite directions to each other in the X-axis direction, and a surface acoustic wave with an angular frequency of 2ω that propagates in the y-axis direction is generated by a parametric mixing phenomenon in the surface acoustic wave waveguide. This surface acoustic wave reaches the acoustoelectric transducer 5, where a convolution electric signal of the two input signals can be obtained.

[Problems to be Solved by the Invention] However, in the conventional example described above, a convolution electric signal is also generated in the surface acoustic wave waveguide due to a parametric mixing phenomenon different from that described above. This convolution electric signal reaches the acousto-electrical transducer as an electromagnetic wave, and interferes with the convolution electric signal converted from the surface acoustic wave into an electric signal by the acousto-electric transducer, resulting in deterioration of the characteristics of the element. was there.

[Object of the Invention] An object of the present invention is to provide a surface acoustic wave element that generates electromagnetic waves from a surface acoustic wave waveguide and has improved characteristics.

[Means and Actions for Solving the Problems] The present invention provides at least two excitation electrodes for exciting first and second surface acoustic waves on a piezoelectric substrate; a surface acoustic wave waveguide that propagates the first and second surface acoustic waves excited from the electrodes in opposite directions; and a surface acoustic wave generated in the surface acoustic wave waveguide that crosses the first and second surface acoustic waves. A surface acoustic wave element having at least one acoustoelectric transducer that converts a third surface acoustic wave propagating in the direction into an electric signal, and an electric circuit including the surface acoustic wave element, The present invention provides a surface acoustic wave element characterized in that the surface acoustic wave waveguide is grounded in the electric circuit.

According to the above means of the present invention, in an electric circuit including a surface acoustic wave element, the surface acoustic wave waveguide of the surface acoustic wave element is grounded (thereby, electromagnetic waves from the surface acoustic wave waveguide are The occurrence of can be suppressed.

[Example] (First Example) 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, 1 is a piezoelectric substrate. As the piezoelectric substrate, for example, a piezoelectric substrate such as lithium niobate can be used.

Reference numerals 2 and 3 denote surface acoustic wave excitation electrodes which are formed on the surface of the substrate 1 so as to be opposed to 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.

4-1.4-2. ..., 4-n are surface acoustic wave waveguides extending in the X direction between the excitation electrodes 2.degree. 3 and arranged parallel to each other at a 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 made of a conductor such as aluminum, silver, or gold, and is provided to efficiently convert surface acoustic waves propagating in the X direction into electrical signals.

7 is a hermetic seal as a conductive fixing member for fixing the piezoelectric substrate 1, and 6-1 to 6-n are electrically connecting the surface acoustic wave waveguides 4-1 to 4-n and the hermetic seal 7. It is a bonding wire.

In the surface acoustic wave element of this embodiment, when an electric signal with a central angular frequency ω is input to one of the excitation electrodes 2, a first surface acoustic wave is excited, propagates in the positive direction of The waves enter the waveguides 4-1 to 4-n. Similarly, when an electric signal with a center angular frequency ω is input to the other excitation electrode 3, a second surface acoustic wave is excited and
The wave propagates in the negative direction and enters the surface acoustic wave waveguides 4-1 to 4-n. The first and second surface acoustic waves propagate in opposite directions from both ends of the surface acoustic wave waveguides 4-1 to 4-n, and due to the parametric mixing phenomenon in the surface acoustic wave waveguides, the y-axis A third surface acoustic wave with a center angular frequency of 2ω is generated that propagates in the direction, and this third surface acoustic wave is converted into an electrical signal by the acoustoelectric transducer 5, and a convolution electrical signal of the above two input signals is generated. is obtained.

On the other hand, when the first and second surface acoustic waves propagate in the surface acoustic wave waveguides 4-1 to 4-n in opposite directions, a parametric mixing phenomenon different from that described above causes the surface acoustic wave waveguide 4 to A convolution electric signal of the above two input signals with a center angular frequency of 2ω is generated on -1 to 4-n. Conventionally, this convolution electric signal reaches the acoustoelectric transducer 5 as an electromagnetic wave and causes an interference effect. was causing it.

However, the surface acoustic wave waveguides 4-1 to 4 of this embodiment
-n is electrically connected to the eight-metic seal 7 by bonding wires 6-1 to 6-n, and the hermetic seal 7 is electrically grounded to a national body (not shown), etc., so that the above-mentioned elastic itMi from surface wave waveguide
The generation of waves can be suppressed.

As a result, interference caused by electromagnetic waves in the acoustoelectric transducer 5 is suppressed, and the characteristics of the element are improved.

(Second Example) FIG. 2 is a schematic plan view showing a second example of the surface acoustic wave element according to the present invention. In this figure, members similar to those in FIG. 1 are given the same reference numerals.

In FIG. 2, 8 is a conductor band connecting the elastic surface waveguides 4-1 to 4-n, 9 is connected to the conductor band 8, and the piezoelectric substrate 1
It is a conductor pattern that extends to the end of the .

The conductor band 8 and the conductor pattern 9 are made of, for example, aluminum, silver, gold, etc., and are formed on the piezoelectric substrate 1.

Further, the end of the conductor pattern 9 is electrically connected to a hermetic seal 7 as a conductive fixing member at the end of the piezoelectric substrate 1 by conductive rubber or the like. The seal 7 is grounded to a casing (not shown) or the like.

In the device of the present embodiment, the surface acoustic wave waveguides 4-1 to 4-n are grounded as in the device of the first embodiment, so that the electromagnetic waves from the waveguides 4-1 to 4-n are Occurrence can be suppressed.

Further, the conductor band 8 and the conductor pattern 9 of this embodiment can be formed simultaneously with the excitation electrodes 2 and 3 and the surface acoustic wave waveguides 4-1 to 4-n, so that the conductor band 8 and the conductor pattern 9 can be formed simultaneously with the excitation electrodes 2 and 3 and the surface acoustic wave waveguides 4-1 to 4-n. Since bonding 6-1 to 6-n is also unnecessary, the manufacturing process can be shortened and the yield can be improved.

In this embodiment, the hermetic seal 7 is connected to the hermetic seal 7 by the conductor pattern 9 extending to the end of the piezoelectric substrate 1, but the hermetic seal 7 is connected directly by the conductor band 8.
Alternatively, the conductor pattern 9 that does not extend to the end of the piezoelectric substrate 1 may be connected to the hermetic seal 7 using a bonding wire or the like. Even in this case, since it can be formed by one wire bonding, the process can be shortened and the yield can be improved.

Further, in this embodiment, the conductor bands 8 are formed so as to be connected at the ends of the surface acoustic wave waveguide, but the same effect can be obtained even if the conductor bands 8 are connected at other parts.

In addition, in this embodiment, since each surface acoustic wave waveguide is connected with a conductor band 8, surface acoustic wave waves generated at the bonding joint when wire bonding is performed directly on the waveguides 4-1 to 4-n are It is suitable for devices operating at high frequencies.

Further, in the first and second embodiments, the acoustoelectric transducer 5 is provided only on one side of the waveguides 4-1 to 4-n, but it may be provided on both sides.

In this case, since the surface acoustic waves generated in the surface acoustic wave waveguide propagate in both directions in the y-axis direction, by outputting these from the two acoustoelectric transducers 5 and combining them, the above-mentioned 1. It is possible to obtain twice the output as in the second embodiment.

Note that the two acoustoelectric transducers 5 form a surface acoustic wave waveguide 4-1.
By making the distances from .about.4-n different, the output from one acoustoelectric transducer can be delayed by an appropriate time with respect to the output from the other acoustoelectric transducer.

Also, the above 1. By using the surface acoustic wave excitation electrode 2.3 in the second embodiment as a double electrode (split electrode), reflection of the surface acoustic wave at the surface acoustic wave excitation electrode 2.3 can be suppressed, and the characteristics of the element can be improved. It can be made even better. Similarly, by making the acoustoelectric transducer 5 a double electrode (split electrode), reflection of surface acoustic waves at the surface acoustic wave excitation electrodes 2 and 3 can be suppressed, and the characteristics of the element can be further improved. be able to.

Further, the coordinate axes shown in FIGS. 1 and 2 are added for convenience and do not mean the crystal axes of the substrate or the like.

Furthermore, the above 1. In the second embodiment, the substrate 1 is not limited to a piezoelectric single crystal such as lithium niobate, but is made of a material and structure that has a parametric mixing effect, such as a structure in which a piezoelectric film is added to a semiconductor or glass substrate. That's fine.

Also, the above 1. In the second embodiment, the surface acoustic wave excited by the surface acoustic wave excitation electrode is guided as it is to the surface acoustic wave waveguide, but there is a horn-shaped waveguide or multi-layer structure between the excitation electrode and the surface acoustic wave waveguide. A beam width compressor such as a strip coupler may also be provided.

[Effects of the Invention] As described above, according to the present invention, generation of electromagnetic waves from the surface acoustic wave waveguide can be suppressed by grounding the surface acoustic wave waveguide. It is possible to suppress the interference of convolution signals that occurs in electrical converters. Therefore, the effect of improving the characteristics of the surface acoustic wave element can be obtained.

[Brief explanation of drawings]

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 a schematic plan view showing a second embodiment of the surface acoustic wave device according to the present invention. FIG. 3 is a schematic plan view showing a conventional example. 1... Piezoelectric substrate, 2, 3... Excitation electrode, 4-1 to 4
-n... Surface acoustic wave waveguide, 5... Acoustoelectric transducer, 6-1 to 6-n... Bonding wire, 7...
・Hermetic seal (conductive fixing member), 8...Conductor band, 9...Conductor pattern agent Patent attorney Seki Yamashita Flat light diagram diagram

Claims (6)

[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 propagated in opposite directions. a surface acoustic wave waveguide; and at least one acoustic electric wave that converts 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 element having a transducer, and an electric circuit including the surface acoustic wave element, wherein the surface acoustic wave waveguide is grounded in the electric circuit. . (2) The surface acoustic wave device according to claim 1, wherein the surface acoustic wave waveguide includes a plurality of waveguides, and the plurality of waveguides are electrically connected. (3) The elasticity according to claim 1, wherein the surface acoustic wave waveguide is composed of a plurality of waveguides, and the plurality of waveguides are connected by a conductive pattern formed on the piezoelectric substrate. surface wave element. (4) The surface acoustic wave element according to claim 1, wherein the surface acoustic wave waveguide is grounded to an electric circuit outside the piezoelectric substrate by a conductive pattern formed on the piezoelectric substrate. . (5) The surface acoustic wave element according to claim 1, wherein the surface acoustic wave waveguide is electrically connected to a conductive fixing member that fixes the piezoelectric substrate. (6) The surface acoustic wave device according to claim 1, wherein the surface acoustic wave waveguide is electrically connected to a conductive fixing member that fixes the piezoelectric substrate by conductive rubber.