JPH05129886A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To extract an output signal with high S/N by tilting the rear side of a substrate of the surface acoustic wave element at a specific angle so as to cancel a bulk wave signal reflected in the rear side and made incident in the different position of an output electrode or a surface acoustic wave guide path formed on the front side of the substrate. CONSTITUTION:This element consists of 1st and 2nd input electrodes 2, 3 stimulating 1st and 2nd surface acoustic waves and an output electrode 4 formed on the 1st face 1-1 of a substrate 1 and extracting a signal caused by the inter- action of the 1st and the 2nd surface acoustic waves. At least part of a 2nd face 1-2 opposite to the 1st face 1-1 is formed to be a face tilted with respect to the 1st face 1-1 in a prescribed direction, and the relation of equation L>=3lambdaB/ sin2theta is satisfied, where L is a length of the output electrode 4 in a prescribed direction, lambdaB is the wavelength of a bulk wave generated by the inter-action of the 1st and the 2nd surface acoustic waves and theta is the tilt angle of the 2nd face 1-2 opposite to the 1st face 1-1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention allows two surface acoustic waves to propagate in opposite directions on a piezoelectric substrate and utilizes the physical non-linear effect of the substrate to cause the surface acoustic waves to interact with each other. The present invention relates to a surface acoustic wave device adapted to extract a signal.

[0002]

2. Description of the Related Art In recent years, surface acoustic wave devices have become increasingly important as key devices for performing spread spectrum communication. In addition, it has many applications as a real-time signal processing device and is being actively researched.

FIG. 2 shows such a surface acoustic wave device.
A surface acoustic wave convolver as shown in 0 is known.
This element is configured by providing comb-shaped input electrodes 12 and 13 and an output electrode 14 on a piezoelectric substrate 11 made of Y-cut (Z-propagation) lithium niobate or the like. When an electric signal is input to the input electrodes 12 and 13, the piezoelectric substrate 1
A surface acoustic wave is excited at 1, and this is taken out as a convolution signal at the output electrode 14.

These electrodes are usually formed by patterning by photolithography using a conductive material such as aluminum.

When taking out the convolution output using such a surface acoustic wave convolver, first, two signals of the carrier angular frequency ω are input to the comb-shaped input electrodes 12 and 13, respectively, and these electrical signals are inputted. Convert the signal to a surface acoustic wave signal. Then, these surface acoustic waves are propagated in mutually opposite directions on the surface of the piezoelectric substrate 11, and the physical non-linear effect of the substrate is utilized to take out the convolution signal of the carrier angular frequency 2ω from the output electrode 14.

That is, two surface acoustic waves are

[0007]

[Outer 1] Then, the product is on the substrate due to the nonlinear effect of this substrate.

[0008]

[Outside 2] Surface waves are generated. This signal is integrated in the electrode area by providing a uniform output electrode, and if the interaction area length is 1,

[0009]

[Outside 3] Is taken out as a signal represented by. Here, the integration range may be substantially ± ∞ when the interaction length is larger than the signal length,

[0010]

[Outside 4] Then, equation (1) becomes

[0011]

[Outside 5] And the signal is a convolution of two surface acoustic waves.

The mechanism of such convolution is described in detail, for example, in "Shibayama," Application of surface acoustic waves "Television, 30 457 (1976)".

On the other hand, when two surface waves propagate in the opposite directions to each other on the substrate surface as described above, a bulk wave having a carrier angular frequency 2ω traveling in a direction perpendicular to the substrate surface is caused by the physical nonlinear effect of the substrate. What happens to the journal
Of Applied Physics (Journal o
f Applied Physics) Vol. 49, No. 1
2, pp. 5924-5927, 1978.

Such a bulk wave is reflected on the back surface of the substrate 11, returns to the front surface of the substrate 11 again, and a part thereof is extracted from the output electrode 14. Further, a part of the light is reflected on the front surface of the substrate 11, propagates toward the back surface of the substrate, and is reflected again on the back surface.

As described above, the bulk wave generated in the direction of the back surface of the substrate is repeatedly reflected on the back surface, and the signal of the reflected wave is taken out from the output electrode 14, which adversely affects the convolution signal. It was

On the other hand, in order to suppress the influence of the reflection of the bulk surface on the back surface of the substrate as described above, the surface acoustic wave element in which the substrate is tapered in the propagation direction of the surface acoustic wave is an applied physics device.・ Letters (Appl
ied Physics Letters) Volume 15,
No. 9, pp. 300-302, 1969.

An example of such a conventional element is shown in FIG. 21, the same members as those in FIG. 20 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the element of FIG. 21, the piezoelectric substrate 15
Has its thickness varied along the propagation direction of the surface acoustic wave.

[0019]

However, at the taper angle of the above-mentioned conventional example, the bulk wave reflected on the back surface of the substrate is taken out as an electric signal at the output electrode, so that the convolution signal is taken out at a high SN ratio. I couldn't.

An object of the present invention is to provide a surface acoustic wave device in which a bulk wave reflected on the back surface of a substrate hardly affects an output signal.

[0021]

The above object of the present invention is to provide a piezoelectric substrate and first and second piezoelectric substrates formed on a first surface of the substrate to excite first and second surface acoustic waves, respectively. Of the first electrode and the second electrode formed on the first surface of the substrate.
And an output electrode for taking out a signal generated by the interaction of the surface acoustic waves, and at least a part of the second surface of the substrate facing the first surface is along a predetermined direction with respect to the first surface. In the surface acoustic wave device having a slanted surface, the length of the output electrode in the predetermined direction is L, and the wavelength of the bulk wave generated by the interaction of the first and second surface acoustic waves is λ.
_B , where θ is an inclination angle of the second surface with respect to the first surface, the conditional expression L ≧ 3λ _B / sin2θ is satisfied.

In the present invention, the first and second surface acoustic waves are propagated in a plurality of waveguides, and the third surface acoustic waves corresponding to the convolution output are generated from the waveguides, so-called split guidance. It can also be applied to a waveguide type surface acoustic wave element. Such a surface acoustic wave element has a piezoelectric substrate and
First and second input electrodes formed on a first surface of the substrate and exciting first and second surface acoustic waves, respectively, and the first and second input electrodes formed on the first surface of the substrate. And a plurality of waveguides for propagating the second surface acoustic waves in opposite directions to excite the third surface acoustic waves generated by the interaction of these surface acoustic waves, and are opposed to the first surface. At least a part of the second surface of the substrate is a surface inclined along a predetermined direction with respect to the first surface, and the length of the region in which the waveguide is formed in the predetermined direction is L, the first and the second surfaces. The wavelength of the bulk wave generated by the interaction of the two surface acoustic waves is λ _B , the first
When the inclination angle of the second surface with respect to the surface is θ, the conditional expression L ≧ 3λ _B / sin2θ is satisfied.

In the surface acoustic wave device of the present invention, the second surface of the substrate may be inclined along a direction parallel to the propagation directions of the first and second surface acoustic waves. You may incline along the direction orthogonal to the propagation direction of the 1st and 2nd surface acoustic waves. Further, in the present invention, the second surface of the substrate may be composed of two surfaces having inclinations opposite to each other.

According to the surface acoustic wave device of the present invention, among bulk waves generated at the output electrode or the waveguide and reflected on the back surface (second surface) of the substrate, waves at distant positions cancel each other. Since it reaches the substrate surface (first surface) with such a phase difference, the signal due to the bulk wave is greatly attenuated, and the convolution output signal is hardly affected.

[0025]

1 is a schematic perspective view showing a first embodiment of a surface acoustic wave device of the present invention. 2 is a schematic cross-sectional view taken along the line segment AA ′ of the device of FIG.

1 and 2, reference numeral 1 indicates a piezoelectric substrate made of Y-cut (Z-propagation) lithium niobate or the like. Further, reference numerals 2 and 3 respectively indicate the first of the substrate 1.
2 shows the first and second comb-shaped input electrodes formed on the surface 1-1 of FIG. Reference numeral 4 indicates an output electrode provided between the input electrodes 2 and 3 on the first surface 1-1. The input electrodes 2 and 3 and the output electrode 4 are usually formed by patterning by photolithography using a conductive material such as aluminum.

In the element of this embodiment, the back surface of the substrate, that is, the second surface 1-2 facing the first surface 1-1 of the substrate 1 on which the input electrodes and the like are formed is the first surface 1-1. With respect to the input electrode, the surface acoustic wave is inclined along the propagation direction of the surface acoustic wave (the direction parallel to the x axis in the figure). This tilt angle is θ
And the length of the output electrode in the x-axis direction is L and the wavelength of the bulk wave generated by the interaction of the first and second surface acoustic waves is λ _B , the condition of the following equation (3) is satisfied. ing.

L ≧ 3λ _B / sin2θ (3) As a more specific structural example, for example, the length L of the output electrode is 60 mm, the wavelength of the bulk wave is λ _B = 20 μm, and the second surface of the substrate 1- The inclination angle θ of 2 may be 0.028 °.

In such a surface acoustic wave element, the first
When a first signal of the carrier angular frequency ω is input to the input electrode 2 of, a first surface acoustic wave corresponding to the first input signal is generated from this electrode 2 and propagates in the positive direction of the x axis. On the other hand, when the second signal of the carrier angular frequency ω is input to the second input electrode 3, a second surface acoustic wave corresponding to the second input signal is generated from this electrode 3 and the negative direction of the x axis is generated. Propagate. The first and second surface acoustic waves propagating in the opposite directions interact with each other in the region where the output electrode 4 is provided. Then, due to the physical non-linear effect of the substrate 1, an electric signal having a carrier angular frequency 2ω corresponding to the convolution signals of the first and second input signals is extracted from the output electrode.

When the signal is taken out from the electrode 4 as described above, at the same time, in the interaction area of the surface acoustic wave,
A bulk wave 7 having a carrier angular frequency 2ω is generated, and the first surface 1-1
And propagate vertically. The broken line in FIG. 2 indicates the in-phase wavefront of the bulk wave, and its wavelength is λ _B. The bulk wave 7 is reflected by the second surface 1-2 of the substrate 1 and enters the output electrode. At this time, since the second surface 1-2 has an angle of θ with respect to the first surface 1-1, the bulk wave 7
Are reflected at an angle of 2θ with respect to the normal to the first surface.

Here, the signal output by such a reflected bulk wave 7 has a relationship with the length L of the output electrode as shown in FIG. In FIG. 3, the horizontal axis is Lsin2θ,
The vertical axis is mixed with the convolution signal of the output electrode,
The signal output of a bulk wave is shown. As can be seen from FIG. 3, in the signal of the bulk wave, Lsin2θ is the wavelength λ _{B of the} bulk wave.
When it is equal to an integer multiple of 0, the output becomes 0, and the output gradually decreases as the length of the output electrode becomes longer. When Lsin2θ ≧ 3λ _B , that is, when the length L of the output electrode satisfies the condition of the expression (3), the bulk wave signal is hardly output. As described above, since the surface acoustic wave device of the present invention is formed so that the angle of the back surface of the substrate and the length of the output electrode satisfy a predetermined relationship, the influence of the bulk wave is removed and the convolution signal is extracted with a high SN ratio. Is something that can be done.

The relationship between the length of the output electrode and the signal due to the bulk wave is explained as follows. That is, as shown in FIG. 4, in the element of the present invention, the bulk wave 9 reflected on the back surface of the substrate 1 is incident on the output electrode 4 such that the wave front and the substrate surface form an angle of 2θ. At this time, the difference in propagation path length between the bulk wave incident on point b and the bulk wave incident on point c in the center of the electrode 4 is (L / 2) sin2θ. When Lsin2θ is equal to the wavelength λ _{B of the} bulk wave, that is, Lsin2θ = λ _B , the difference in the lengths of the propagation paths is λ _B / 2. Therefore, the signal output from the electrode 4 by the bulk wave incident on the point b and the signal by the bulk wave incident on the point c have a phase difference of ½ wavelength and cancel each other. Similarly, the signal due to the bulk wave incident between points b and c is canceled by the signal due to the bulk wave incident between points a and b, and the signal output due to the bulk wave is 0 in the entire electrode 4. Become. Similarly, when Lsin2θ is an integral multiple of λ _B , the bulk wave output is zero. As described above, the present invention is configured so that the bulk waves incident on the output electrode or the waveguide described later almost cancel each other and do not affect the convolution signal.

FIG. 5 is a schematic perspective view showing a second embodiment of the surface acoustic wave device of the present invention. 6 is a schematic cross-sectional view of the device of FIG. 5 taken along the line BB '. 5 and 6
2, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the piezoelectric substrate 5 has a direction (y) orthogonal to the propagation direction of the surface acoustic wave excited from the input electrode.
It differs from the first embodiment only in that it is inclined along a direction (parallel to the axis).

In the element of this embodiment, the back surface of the substrate, that is, the second surface 5-2 facing the first surface 5-1 of the substrate 5 on which the input electrodes and the like are formed is the first surface 5-1. Is inclined along the y-axis direction at an angle θ. If the length of the output electrode 4 along the y-axis direction (corresponding to the width of the output electrode in the present embodiment) in the region where the output electrode 4 is formed is W, in the element of the present embodiment, The condition of expression (4) is satisfied.

W ≧ 3λ _B / sin2θ (4) In such a surface acoustic wave element, if the first and second signals of the carrier angular frequency ω are input to the first and second input electrodes 2 and 3, respectively. The first and second surface acoustic waves are excited from these electrodes. These surface acoustic waves interact with each other in the region where the output electrode 4 is provided, and the convolution output signal is extracted from the electrode 4 as in the first embodiment.

When the signal is taken out from the electrode 4 as described above, at the same time, in the surface acoustic wave interaction region,
A bulk wave 8 having a carrier angular frequency 2ω is generated, and the first surface 5-1
And propagate vertically. The bulk wave 8 is reflected by the second surface 5-2 of the substrate 5 at an angle of 2θ and returns to the output electrode 4. Here, from the relationship of the equation (4), as in the first embodiment,
Most of the bulk waves incident on the output electrode 4 cancel each other out, and hardly affect the convolution signal. Further, in the surface acoustic wave element, the width W of the output electrode is usually shorter than the length L. Therefore, in the present embodiment, the angle θ satisfying the above condition is taken as compared with the first embodiment. However, there is an advantage that the thickness of the substrate does not become so large.

FIG. 7 is a schematic perspective view showing a third embodiment of the surface acoustic wave device of the present invention. 8 is a schematic cross-sectional view of the device of FIG. 7 taken along the line CC ′. 7 and 8
2, the same members as those in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the present embodiment, the thickness of the piezoelectric substrate 6 increases as it moves away from the central point f along the propagation direction of the surface acoustic wave excited from the input electrode (the direction parallel to the x axis). Only the point that is formed in the reverse taper shape that becomes thicker,
Different from the first embodiment.

In the element of the present embodiment, the back surface of the substrate, that is, the second surface facing the first surface 6-1 of the substrate 6 on which the input electrodes and the like are formed, has two inclinations having opposite inclinations. It is composed of faces 6-2 and 6-3. These inclined surfaces 6-2 and 6-3 have angles of θ ₁ and θ ₂ with respect to the _first surface 6-1 respectively. Assuming that the length of the output electrode along the positive direction of the x-axis from the point f is L ₁ and the length of the output electrode along the negative direction of the x-axis from the point f is L ₂ , the element of the present embodiment is as follows. The conditions of the expressions (5) and (6) are satisfied.

L ₁ ≧ 3λ _B / sin2θ ₁ (5) L ₂ ≧ 3λ _B / sin2θ ₂ (6) In such a surface acoustic wave device, a carrier angle is formed between the first and second input electrodes 2 and 3. When the first and second signals of the frequency ω are input, the first and second surface acoustic waves are excited from these electrodes. These surface acoustic waves interact with each other in the region where the output electrode 4 is provided, and the convolution output signal is extracted from the electrode 4 as in the first embodiment.

When the signal is taken out from the electrode 4 as described above, at the same time in the interaction area of the surface acoustic wave,
A bulk wave 8 having a carrier angular frequency 2ω is generated, and the first surface 6-1
And propagate vertically. Of this bulk wave, x from point f
The bulk wave generated on the positive side of the axis is reflected by the inclined surface 6-2 at an angle of 2θ ₁ and returns to the output electrode 4. here,
From the relation of the expression (5), most of the bulk waves incident on the output electrode 4 cancel each other. Similarly, the bulk wave generated on the negative side of the x axis from the point f is 2 at the inclined surface 6-3.
It is reflected at an angle of θ ₂ and returns to the output electrode 4. From the relationship of the equation (6), most of the bulk waves cancel each other. Therefore, also in this embodiment, the convolution output signal can be extracted with a high SN ratio as in the first embodiment. Further, in the present embodiment, even if the output electrodes have the same length, the inclination angle that satisfies the conditions of equations (5) and (6) can be halved as compared with the first embodiment, so that the thickness of the substrate is reduced. It has the effect of making it thin.

In the third embodiment, the bent portion is provided substantially at the center (point f) of the output electrode. However, if the equations (5) and (6) are satisfied, the bent portion is displaced from the center. May be provided. In addition, the angle θ ₁ of the two inclined surfaces with respect to the first surface
And θ ₂ may be the same or different from each other.

Although the output electrodes are provided between the input electrodes in the first to third embodiments described above, the output efficiency of the convolution signal is increased by providing a plurality of waveguides between the electrodes. The surface acoustic wave element that further improves
"Nakagawa et al., IEICE Transactions '86 / 2, Vol.j69-C, No.2, p
p190-198 "and the like. The present invention can also be applied to such a so-called split waveguide type element. Examples of the split waveguide type of the present invention will be shown below.

FIG. 9 is a schematic perspective view showing a fourth embodiment of the surface acoustic wave device of the present invention. Further, FIG. 10 is a schematic cross-sectional view of the element of FIG. 9 taken along the line segment EE ′.

In FIGS. 9 and 10, reference numeral 21 is 1
A piezoelectric substrate made of 28 ° rotated Y-cut (X-propagation) lithium niobate or the like is shown. Further, reference numerals 22 and 23 are
The first and second comb-shaped input electrodes are formed on the first surface 21-1 of the substrate 21, respectively. Reference numerals 24-1 and 24
Reference numerals -2, 24-3, ..., 24-n denote a plurality of surface acoustic wave waveguides arranged in parallel with each other between the input electrodes 22 and 23 on the first surface 21-1. The longitudinal direction of each of these waveguides coincides with the propagation direction of the surface acoustic wave excited from the input electrode (direction parallel to the x axis). Also,
The array pitch of these waveguides (the distance between the centers in the width direction of the waveguides) is formed to be equal to the wavelength of the surface acoustic waves generated from these waveguides. Comb-shaped output electrodes 25 are formed at positions appropriately separated from these waveguides in the y-axis direction.

The input electrodes 22 and 23 and the output electrode 25 are usually made of a conductive material such as aluminum, silver or gold.
It is formed by patterning by photolithography. Waveguides 24-1, 24-2, 24-3, ..., 2
The details of 4-n are described in “Surface Acoustic Wave Engineering” edited by Inui Shibayama, Institute of Electronics and Communication Engineers, pages 82 to 102,
There are types such as thin film waveguides and topographic waveguides. In the present invention, the substrate surface is made of aluminum, silver,
A Δv / v waveguide coated with a conductor such as gold is preferably used.

In the element of this embodiment, the back surface of the substrate, that is, the first surface 21-1 of the substrate 21 on which the input electrodes and the like are formed
The second surface 21-2 opposite to the first surface 21-1 is inclined with respect to the first surface 21-1 along the propagation direction of the surface acoustic wave excited from the input electrode (the direction parallel to the x axis in the figure). There is. Letting this inclination angle be θ, the length along the x-axis direction of the region 28 in which the waveguides 24-1 to 24-n are formed (in this embodiment, it corresponds to the length in the longitudinal direction of the waveguide) is L. Then, the element of this example satisfies the condition of the following expression (7).

L ≧ 3λ _B / sin2θ (7) As a more specific configuration example, for example, the length L of the output electrode is 60 mm, the wavelength of the bulk wave is λ _B = 20 μm, and the second surface of the substrate 1- The inclination angle θ of 2 may be 0.028 °.

In such a surface acoustic wave element, the first
When a first signal of the carrier angular frequency ω is input to the input electrode 22 of the above, a first surface acoustic wave corresponding to the input signal is generated from this electrode 22, and x is generated in each of the waveguides 24-1 to 24-n. Propagate in the positive direction of the axis. On the other hand, when a second signal having the carrier angular frequency ω is input to the second input electrode 23, a second surface acoustic wave corresponding to the second input signal is generated from this electrode 23, and each waveguide 24-1 Propagate in the negative direction of the x-axis through ˜24-n. These first and second propagating in opposite directions
Of the surface acoustic wave of the carrier wave propagating in the y direction due to the parametric mixing phenomenon due to the physical nonlinear effect of the substrate 21 in the waveguides 24-1 to 24-n.
The third surface acoustic wave of is excited. The third surface acoustic wave is converted into an electric signal by the output electrode 25, and is output from the output electrode as a convolution signal of the first and second input signals.

When a signal is taken out from the output electrode 25 as described above, a bulk wave 8 having a carrier angular frequency 2ω is simultaneously generated in the region where the waveguide is provided, and the first surface 2
Propagate in the direction perpendicular to 1-1. The bulk wave 8 is reflected by the second surface 21-2 of the substrate 1 and returns to the region 28 where the waveguide is formed again. At this time, since the second surface 21-2 has an angle of θ with respect to the first surface 21-1, the bulk wave 8 is reflected at an angle of 2θ with respect to the normal line of the first surface. To be done. Here, from the relationship of equation (7), most of the bulk waves incident on the region 28 in which the waveguide is formed cancel each other out, and have almost no effect on the convolution signal. Therefore, also in the present embodiment, as in the first embodiment, the convolution output signal can be taken out with a high SN ratio.

FIG. 11 shows a fifth surface acoustic wave device of the present invention.
It is a schematic perspective view which shows an Example. In addition, FIG.
FIG. 6 is a schematic cross-sectional view of the element of FIG. 11
12, the same members as those in FIGS. 9 and 10 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this embodiment, the piezoelectric substrate 25 is inclined only along the direction orthogonal to the propagation direction of the surface acoustic wave excited from the input electrode (the direction parallel to the y-axis). Different from the embodiment.

In the element of this embodiment, the back surface of the substrate, that is, the first surface 26-1 of the substrate 26 on which the input electrodes and the like are formed.
The second surface 26-2 opposite to the first surface 26-2 is inclined along the y-axis direction at an angle of θ with respect to the first surface 26-1. Assuming that the length of the region 27 in which the waveguide is formed along the y-axis direction is W, the element of this embodiment satisfies the condition of the following expression (10).

W ≧ 3λ _B / sin2θ (10) In such a surface acoustic wave device, when the first and second signals of the carrier angular frequency ω are input to the first and second input electrodes 22 and 23, respectively. The first and second surface acoustic waves are excited from these electrodes. These surface acoustic waves are
Interactions are generated in the waveguides 24-1 to 24-n to generate a third surface acoustic wave. Then, by receiving the third surface acoustic wave at the output electrode 25, the convolution output signal is extracted as in the fourth embodiment.

When the signal is taken out from the output electrode 25 as described above, at the same time, the bulk wave 8 having the carrier angular frequency of 2ω is generated in the surface acoustic wave interaction region, and the bulk wave 8 is perpendicular to the first surface 21-1. Propagate. The bulk wave 8 is reflected by the second surface 21-2 of the substrate 5 at an angle of 2θ and returns to the region 27 where the waveguide is formed. Here, from the relationship of the equation (10), as in the fourth embodiment, most of the bulk waves incident on the region 27 cancel each other out, and hardly affect the convolution signal. Therefore, also in the present embodiment, the convolution output signal can be taken out with a high SN ratio as in the fourth embodiment. Further, in the surface acoustic wave element, the width W of the region where the waveguide is formed is usually
Is shorter than the length L of the waveguide, the advantage of this embodiment is that the thickness of the substrate does not become so thick even when the angle θ that satisfies the above conditions is taken, as compared with the fourth embodiment. have.

FIG. 13 shows a sixth surface acoustic wave device of the present invention.
It is a schematic perspective view which shows an Example. In addition, FIG.
FIG. 3 is a schematic cross-sectional view of the element of FIG. FIG.
14, the same members as those in FIGS. 9 and 10 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the present embodiment, the thickness of the piezoelectric substrate 29 increases with increasing distance from the center r point along the propagation direction of the surface acoustic wave excited from the input electrode (direction parallel to the x axis). Only the point that is formed in the reverse taper shape that becomes thicker,
Different from the fifth embodiment.

In the element of this embodiment, the back surface of the substrate, that is, the first surface 29-1 of the substrate 29 on which the input electrodes and the like are formed.
The second surface facing to is composed of two inclined surfaces 29-2 and 29-3 having inclinations opposite to each other. These inclined surfaces 29-2 and 29-3 are the first surfaces 29-
It has an angle of theta ₁ and theta ₂ respectively 1.
The length of the region 28 (the length of the waveguide) along the positive direction of the x axis from the point r is L ₁ , and the region 2 along the negative direction of the x axis from the point r.
Assuming that the length of 8 is L ₂ , the element of this example satisfies the conditions of the following equations (11) and (12).

L ₁ ≧ 3λ _B / sin2θ ₁ (11) L ₂ ≧ 3λ _B / sin2θ ₂ (12) In such a surface acoustic wave device, a carrier angle is formed between the first and second input electrodes 22 and 23. When the first and second signals of the frequency ω are input, the first and second surface acoustic waves are excited from these electrodes. These surface acoustic waves are
Propagating in the waveguides 24-1 to 24-n in mutually opposite directions,
Generate a third surface acoustic wave. Then, by receiving the third surface acoustic wave at the output electrode 25, the convolution output signal is extracted as in the fourth embodiment.

When the convolution output signal is taken out as described above, the bulk wave 8 having the carrier angular frequency 2ω is simultaneously generated in the region 28 where the waveguide is formed,
It propagates in the direction perpendicular to the first surface 29-1. Of this bulk wave, the bulk wave generated on the positive x-axis side from the point r is reflected by the inclined surface 29-2 at an angle of 2θ ₁ and returns to the region 28 again. Here, from the relationship of the equation (11), most of the bulk waves incident on the region 28 where the waveguide is formed cancel each other out. Similarly, the bulk wave generated on the negative side of the x axis from the point r is reflected by the inclined surface 6-3 at an angle of 2θ ₂ and returns to the region 28. From the relationship of equation (12),
Most of this bulk waves also cancel each other out. Therefore, also in the present embodiment, the convolution output signal can be taken out with a high SN ratio as in the fourth embodiment. Further, in this embodiment, even if the output electrodes have the same length, the inclination angle satisfying the conditions of the expressions (11) and (12) is set to the fourth value.
Since it can be reduced to half that in the case of the embodiment, it has an effect of reducing the thickness of the substrate.

In the sixth embodiment, the bent portion is provided substantially at the center (point r) in the longitudinal direction of the output electrode.
If the expressions (1) and (12) are satisfied, the bent portion may be provided at a position deviated from the center. Further, the angles θ ₁ and θ ₂ of the two inclined surfaces with respect to the first surface may be the same or different from each other.

In the first to sixth embodiments described above,
The entire second surface of the substrate is inclined with respect to the first surface, but only a part of the second surface facing the region where the output electrode or the waveguide is formed on the first surface is used. It may be an inclined surface, and the other part of the second surface may be formed parallel to the first surface.
With such a configuration, the thickness of the substrate can be made thinner than in the first to sixth embodiments, and since the substrate can be easily held, the substrate can be formed in the process of forming electrodes and the like on the substrate. It is easy to handle and it is easy to install the device in the device of the communication system.

The coordinate axes shown in FIGS. 1 to 14 are added for the sake of convenience and do not mean the crystal axes of the substrate.

FIG. 15 is a block diagram showing an example of a communication system using the surface acoustic wave device as described above as a convolver. In FIG. 15, reference numeral 125 indicates a transmitter. This transmitter spreads the signal to be transmitted and transmits it from the antenna 126. The transmitted signal is received by the antenna 120 of the receiver 124,
The received signal 101 is input to the frequency conversion circuit 102.
The IF signal 103 converted into a frequency matching the input frequency of the surface acoustic wave convolver by the frequency conversion circuit 102 is shown in FIG.
~ Input to the convolver 104 composed of the surface acoustic wave device of the present invention as shown in FIG. Where IF signal 1
Reference numeral 03 designates one input excitation electrode of the convolver, for example, FIG.
Is input to the electrode 2.

On the other hand, the reference signal 106 output from the reference signal generation circuit 105 is input to the other input excitation electrode of the surface acoustic wave convolver 104, for example, the electrode 3 in FIG. Then, in the convolver 104, the convolution calculation (correlation calculation) of the IF signal 103 and the reference signal 106 is performed as described above, and the output signal (convolution signal) is output from the output transducer, for example, the output electrode 4 in FIG. ) 109 is output.

This output signal 109 is input to the synchronizing circuit 108. In the synchronizing circuit 108, the synchronizing signals 111 and 1 are output from the output signal 109 of the surface acoustic wave convolver 104.
12 are created and input to the reference signal generation circuit 105 and the despreading circuit 107, respectively. Reference signal generation circuit 10
In 5, the reference signal 106 is output by adjusting the timing using the synchronization signal 111. The despreading circuit 107 uses the synchronization signal 112 to restore the IF signal 103 to a signal before being spread spectrum. This signal is a demodulation circuit 110
Is converted into an information signal and output. FIG. 16 shows a configuration example of the despreading circuit 107. In FIG. 16, 121 is a code generator and 123 is a multiplier. Code generator 121
A sync signal 112 output from the sync circuit 108 is input to the input terminal, and a code 122 whose timing is adjusted by the sync signal 112 is output. The multiplier 123 has I
The F signal 103 and the code 122 are input, and the IF signal 103
And the result of multiplication of the reference numeral 122 is output. At this time, IF
If the timings of the signal 103 and the code 122 match, the IF signal 103 is converted into a signal before spectrum spread and is output.

When the frequency of the received signal 101 matches the input frequency of the surface acoustic wave convolver 104,
The frequency conversion circuit 102 is unnecessary, and the received signal 101 may be directly input to the surface acoustic convolver 104 through an amplifier and a filter. Although the amplifiers and filters are omitted in FIG. 19 for the sake of clarity, the amplifiers and filters may be inserted before or after each block as needed. Further, although the reception signal is received by the antenna 120 in the present embodiment, the transmitter and the receiver may be directly connected by a wired system such as a cable without using the antenna 120.

FIG. 17 is a block diagram showing a first modification of the receiver 124 in the communication system of FIG.
17, the same members as those in FIG. 15 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, a synchronization tracking circuit 113 is provided,
The IF signal 103 is also input to the synchronization tracking circuit 113. In addition, the synchronization signal 11 output from the synchronization circuit 108
2 is input to the synchronization tracking circuit 113, and the synchronization tracking circuit 11
The sync signal 114 output from the No. 3 is input to the despreading circuit 107. These points differ from the example of FIG. Examples of the synchronization follow-up circuit include a tau dither loop circuit and a delay lock loop circuit, but any of them may be used.

In the present embodiment, the same operational effect as that of the example of FIG. 15 can be obtained, but in the present embodiment, the synchronization circuit 108 is further added.
After the rough synchronization is obtained in step 1, the synchronization follow-up circuit 113 obtains the synchronization more accurately and performs the follow-up of the synchronization, so that out-of-sync is less likely to occur and the error rate can be reduced.

FIG. 18 is a block diagram showing a second modification of the receiver 124 in the communication system of FIG.
18, the same members as those in FIG. 15 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, the output from the surface acoustic wave convolver 104 is input to the detection circuit 115, and demodulation is performed by the output of the detection circuit 115. As the detection circuit 115, there are a synchronous detection circuit, a delay detection circuit, and an envelope detection circuit, which can be selectively used depending on the signal modulation method and the like.

Now, assuming that the received signal 101 is a signal that has undergone certain modulation such as phase modulation, frequency modulation, amplitude modulation, etc.
The modulation information is reflected in the output 109 from the surface acoustic wave convolver 104. In particular, if the length d of the waveguide of the surface acoustic wave convolver 104 is d = vT, where T is the time per data bit of the received signal 101, and v is the surface acoustic wave velocity, modulation information is output 109. Appears as it is. For example, the phase-modulated signal f
It is assumed that (t) exp (jθ) is transmitted and this signal is received as the reception signal 101.

At this time, when the reference signal g (t) 106 is input to the surface acoustic wave element 104, its output 109 is f (t) exp (jθ) g (τ-t) dt = exp (jθ) f (t ) G (τ-t) dt ... (13), and the phase modulation information appears. Therefore, the output 109 of the surface acoustic wave element 104 is detected by the appropriate detection circuit 115.
It can be demodulated by passing through.

FIG. 19 is a block diagram showing a third modification of the receiver 124 in the communication system of FIG.
19, the same members as those in FIG. 18 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, the synchronizing circuit 108 is provided, and the output 109 of the surface acoustic wave convolver 104 is synchronized with the synchronizing circuit 10.
It is also entered in 8. Further, the synchronization signal 111 is output from the synchronization circuit 108 and input to the reference signal generation circuit 105. These points differ from the example of FIG.

In this embodiment as well, the same operation and effect as in the example of FIG. 18 can be obtained. However, in this embodiment, the synchronizing circuit 108 is provided and the reference signal generating circuit 105 is driven by the synchronizing signal 111 output from the synchronizing circuit 108. Since it is controlled, stable synchronization can be achieved.

The present invention can be applied in various ways other than the embodiments described above.

For example, by forming the comb-shaped input electrodes 2 and 3 in the first to sixth embodiments as double electrodes (split electrodes), reflection of surface acoustic waves at these input electrodes 2 and 3 can be suppressed, and the element The characteristics of can be further improved.

Further, in the present invention, the substrate is not limited to the piezoelectric single crystal such as lithium niobate,
For example, any material and structure having a parametric mixing effect such as a structure in which a piezoelectric film is added on a semiconductor or glass substrate may be used.

In the first and second embodiments, the surface acoustic wave excited by the input electrode is directly guided to the output electrode. However, a horn type waveguide is provided between the input electrode and the output electrode. A beam width compressor such as a multi strip coupler or the like may be provided.

In the third to sixth embodiments, the output electrodes are formed only on one side of the surface acoustic wave waveguide. However, the output electrodes are formed on both sides of the surface acoustic wave waveguide, and outputs from the two output electrodes are formed. A double convolution output can be obtained by combining them.

[0084]

As described above, in the surface acoustic wave device of the present invention, at least a part of the second surface of the substrate, which is opposed to the first surface on which the surface acoustic wave is propagated, has a predetermined angle of θ. When the surface is an inclined surface, the wavelength of the bulk wave is λ _B , and the length of the region where the output electrode or the waveguide is formed along the predetermined direction is L, the conditional expression L ≧ 3λ _B / sin2θ is satisfied. With this configuration, the signals due to the bulk waves incident on different positions of the output electrode or the waveguide cancel each other out, and the effect that the output signal can be taken out with a high SN ratio was obtained.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a first embodiment of a surface acoustic wave device of the present invention.

2 is a schematic cross-sectional view of the device of FIG. 1 along the line segment AA ′.

FIG. 3 is a diagram showing a relationship between a length of an output electrode and a signal output by a bulk wave.

FIG. 4 is a schematic cross-sectional view for explaining a difference in propagation path length of a bulk wave incident on each part of an output electrode.

FIG. 5 is a schematic perspective view showing a second embodiment of the surface acoustic wave device of the present invention.

6 is a schematic cross-sectional view of the device of FIG. 5 taken along the line BB ′.

FIG. 7 is a schematic perspective view showing a third embodiment of the surface acoustic wave device of the present invention.

8 is a schematic cross-sectional view of the device of FIG. 7 taken along the line CC ′.

FIG. 9 is a schematic perspective view showing a fourth embodiment of the surface acoustic wave device of the present invention.

10 is a schematic cross-sectional view of the device of FIG. 9 taken along the line EE ′.

FIG. 11 is a schematic perspective view showing a fifth embodiment of the surface acoustic wave device of the present invention.

12 is a schematic cross-sectional view of the device of FIG. 11 taken along the line FF ′.

FIG. 13 is a schematic perspective view showing a sixth embodiment of the surface acoustic wave device of the present invention.

14 is a schematic cross-sectional view of the device of FIG. 13 taken along the line segment GG ′.

FIG. 15 is a block diagram showing an example of a communication system using the surface acoustic wave device of the present invention.

16 is a block diagram showing a specific configuration example of the despreading circuit in FIG.

17 is a block diagram showing a modified example of the receiver of FIG.

FIG. 18 is a block diagram showing a modified example of the receiver of FIG.

FIG. 19 is a block diagram showing a modification of the receiver of FIG.

FIG. 20 is a schematic perspective view showing a first example of a conventional surface acoustic wave element.

FIG. 21 is a schematic perspective view showing a second example of a conventional surface acoustic wave element.

[Explanation of symbols]

 1 Piezoelectric Substrate 1-1 First Surface of Substrate 1-2 Second Surface of Substrate 2 First Input Electrode 3 Second Input Electrode 4 Output Electrode

Claims (8)

[Claims] 1. A piezoelectric substrate, first and second input electrodes that are formed on a first surface of the substrate and excite first and second surface acoustic waves, respectively, and a first substrate of the substrate. Formed on the surface,
An output electrode for taking out a signal generated by the interaction of the first and second surface acoustic waves, and at least a part of the second surface of the substrate facing the first surface is formed on the first surface. On the other hand, in a surface acoustic wave element having a surface inclined along a predetermined direction, the length of the output electrode in the predetermined direction is L, and the wavelength of the bulk wave generated by the interaction of the first and second surface acoustic waves is A surface acoustic wave device characterized by satisfying a conditional expression L ≧ 3λ _B / sin2θ where λ _B and an inclination angle of the second surface with respect to the first surface are θ. 2. The surface acoustic wave device according to claim 1, wherein the second surface of the substrate is inclined along a direction parallel to the propagation directions of the first and second surface acoustic waves. 3. The surface acoustic wave device according to claim 1, wherein the second surface of the substrate is inclined along a direction orthogonal to the propagation directions of the first and second surface acoustic waves. 4. The surface acoustic wave device according to claim 1, wherein the second surface of the substrate is composed of two surfaces having inclinations opposite to each other. 5. A piezoelectric substrate, first and second input electrodes which are formed on a first surface of the substrate and excite first and second surface acoustic waves, respectively, and a first substrate of the substrate. Formed on the surface,
A surface acoustic wave element comprising a plurality of waveguides for propagating the first and second surface acoustic waves in opposite directions to excite a third surface acoustic wave generated by the interaction of these surface acoustic waves. In at least a part of the second surface of the substrate facing the first surface is a surface inclined along a predetermined direction with respect to the first surface, and a predetermined direction of a region where the waveguide is formed. Is L, the wavelength of the bulk wave generated by the interaction of the first and second surface acoustic waves is λ _B , and
A surface acoustic wave device satisfying conditional expression L ≧ 3λ _B / sin2θ, where θ is an inclination angle of the second surface with respect to the surface. 6. The surface acoustic wave device according to claim 1, wherein the second surface of the substrate is inclined along a direction parallel to the propagation directions of the first and second surface acoustic waves. 7. The surface acoustic wave device according to claim 1, wherein the second surface of the substrate is inclined along a direction orthogonal to the propagation directions of the first and second surface acoustic waves. 8. The surface acoustic wave device according to claim 1, wherein the second surface of the substrate is composed of two surfaces having inclinations opposite to each other.