JPH03132208A - Surface elastic wave element - Google Patents

Abstract

PURPOSE:To increase a sound reflecting volume without increasing film thickness and to attain quality stabilization and the improvement of performance by providing a part where two electrode fingers with width of 1/8lambda and one electrode finger with width of 1/4lambda are arranged within the length lambda of one cycle of an electrode finger string at a part of the electrode finger string of a comb-line converter. CONSTITUTION:The electrode finger 11 with width of 1/8 lambda whose electrode width is set at 1/8lambda assuming the length of one cycle of the electrode finger string as lambda, and the electrode finger 12 with width of 1/4lambda in which at least a part of the electrode finger width is set at 1/4lambda are provided at least at one of the comb-line converters provided on a piezoelectric substrate. And the part in which the two electrode fingers 11 with width of 1/8lambda and the one electrode finger 12 with width of 1/4lambda are arranged is provided at least at a part of the electrode finger string of the comb-line converter within the length lambda of one cycle. Therefore, no offset between the component of a reflected wave due to an energy storage effect and that of the reflected wave due to the addition of mass and an electric field short-circuit effect occurs. Thereby, it is possible to increase the sound reflecting volume without increasing the film thickness, and to attain the quality stabilization and the improvement of performance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a surface acoustic wave element such as a surface acoustic wave delay line or a surface acoustic wave filter.

(Prior art) Conventionally, in a comb-shaped transducer of a surface acoustic wave element, when giving directionality to wave propagation or reflection, the length of one period of a periodic row of electrode fingers is set as shown in Fig. 8. If λ is
The structure was such that two electrode fingers 1 with a width of 1/8λ and one electrode finger 2 with a width of 3/8λ were arranged within one period λ.

FIG. 9 shows that when a wave is incident from the direction of the arrow in the figure in the comb-shaped transducer configured in this way,
1% JSks 1% This is a phase diagram of an acoustic reflected wave (component due to mass addition and electric field short circuit effect) from a portion indicated by m, with the A-A position as a reference. As shown in this figure, in the case of this comb-shaped converter, 3/8λ
Directionality is produced by the reflection of the width of the electrode finger 2 (portion indicated by the symbol m).

This type of comb-shaped transducer is usually called a unidirectional transducer, but the ratio of this directionality is
corresponds to the total amount of reflection in the pair.

Therefore, the greater the amount of reflection, the stronger the directionality.
Low loss or triple transit echo (
It is possible to construct a surface acoustic wave element with less ripple due to TTIE).

(Problems to be Solved by the Invention) However, the conventional surface acoustic wave element having the above-mentioned comb-shaped transducer has the following problems.

In other words, in such a comb-shaped transducer, the electrode fingers have unequal pitches, so that not only the mass addition and electric field short-circuit effects but also the energy storage effect contributes to acoustic reflection components. . The phase diagram shown in FIG. 9 shows components due to mass addition and electric field short-circuit effects, and FIG. 10 shows the phase diagram of reflected components due to energy storage effects at the same position. As shown in this figure, the reflected component due to the mass addition and electric field short-circuit effect and the reflected component due to the energy storage effect are out of phase by 180''.

For this reason, in substrates such as LiTaO2 and 8102, the respective reflection components cancel each other out, resulting in a decrease in the total amount of reflection.

Further, in the electrode finger portion having a width of 378λ, since the vectors of the reflected components are not in the same direction, the orthogonal components cancel each other out, resulting in a decrease in the total amount of reflection.

For this reason, the amount of acoustic reflection has conventionally been increased by increasing the thickness of the film, but increasing the thickness increases the variation in film thickness, making it difficult to supply products with stable quality. There is a problem.

The present invention was made in response to such conventional circumstances, and is capable of increasing the amount of acoustic reflection without increasing the thickness of the film, thereby stabilizing quality and improving performance compared to the past. The aim is to provide a surface acoustic wave device that can

[Structure of the Invention] (Means for Solving the Problems) That is, the present invention provides a surface acoustic wave element including a piezoelectric substrate and a plurality of comb-shaped transducers provided on the piezoelectric substrate. At least one of the tooth profile transducers is
The length of one period of the electrode finger row of the comb-shaped transducer is λ,
The comb-shaped transducer has an electrode finger of 1/8λ width with an electrode width of 1/8λ and an electrode finger of 1/4λ width with at least a part of the electrode width of 1/4λ. Two electrode fingers of the l/8λ width and one electrode finger of the l/4λ width are arranged within one period length λ of the electrode finger row in at least a part of the electrode finger row. It is characterized by having a part.

(Function) In the surface acoustic wave element of the present invention having the above configuration, for example, the first
As shown in the figure, at least one of the comb-shaped transducers provided on the piezoelectric substrate has an electrode of 1/8λ width, where the length of one period of the electrode finger row is λ, and the electrode width is 1/8λ. finger 1
1, and an electrode finger 12 having a width of l/4λ, in which at least a part of the electrode width (the entire width in the example shown in FIG. 1) is l/4λ.

Then, in at least a part of the electrode finger row of this comb-shaped transducer, two electrode fingers 11 having a width of 1/8λ are provided within a length λ of L periods.
It has a portion in which one electrode finger 12 having a width of 1/4λ is arranged.

Figures 2 and 3 show that when a wave is incident from the direction of the arrow in the comb-shaped transducer shown in Figure 1, the acoustic reflections from the parts indicated by the symbols A, I, Tsu, Work, O, and Force in the figures are shown. It shows the phase diagram of the wave with the A-A position as a reference,
FIG. 2 shows components due to mass addition and electric field short circuit effects, and FIG. 3 shows components due to energy storage effects.

Among the components of these reflected waves, the mass addition shown in Figure 2,
The component due to the electric field short-circuit effect is calculated by canceling out the reflection terms (A, I, T, D) due to the l/8λ width electrode finger 11, and
Only the reflection term (e, force) due to the 4λ-wide electrode finger 12 contributes to the total reflection. Moreover, this reflected component is
Since the directions of the vectors are the same, there is no cancellation due to orthogonal components, and the amount of reflection at the l edge can be utilized to the maximum.

In addition, the component of the reflected wave due to the energy storage effect shown in FIG. 3 is the reflection term (a,
The reflection terms (force) due to the electrode fingers 12 having a width of 1/4λ are also all canceled out.

That is, no reflection by the electrode fingers 11, 12 occurs.

Therefore, the reflected wave component due to the energy storage effect,
The components of the reflected wave due to the addition of mass and the electric field short circuit effect do not cancel each other out, and the total amount of reflection increases.

Therefore, the amount of acoustic reflection can be increased without increasing the film thickness, and quality can be stabilized and performance can be improved compared to the past.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows the main part configuration of a surface acoustic wave device according to an embodiment of the present invention. )
21 and an output-side comb-shaped transducer 22 are arranged along the surface acoustic wave propagation direction (indicated by an arrow in the figure).

These comb-shaped transducers 21 and 22 each have an array N
an electrode finger 11 having an electrode width of l/8λ with respect to the period λ;
Electrode fingers 12 having an electrode width of 1/4λ are provided, and 2 electrode fingers 12 having an electrode width of 1/8λ are provided within the arrangement period λ. ! The arrangement is such that there are two pole fingers 11 and one electrode finger 12 having a width of 1/4λ.

In the surface acoustic wave element of this embodiment having the above configuration, as described above, the amount of acoustic reflection can be increased compared to the conventional one, so that loss and TTE can be reduced. Furthermore, since there is no need to increase the film thickness, surface acoustic wave elements with stable quality can be manufactured.

FIG. 5 shows the main points of a surface acoustic wave device of another embodiment using an electrode finger 11 having a width of 1/8λ and an electrode finger 13 having a width of 1/4λ in a part and a width of 1/8λ in another part. This shows the structure of the parts.

That is, in this embodiment, one of the periodic arrays of electrode fingers is placed in the area marked C among the areas separated by dotted lines in the figure.
Within the period length λ, there are four electrode fingers with a width of l/8λ, and in the region marked with numerals, there are two electrode fingers with a width of l/8λ and two electrode fingers with a width of l/8λ.
There is one electrode finger with a width of /4λ. In the above section C, no acoustic reflection occurs because the effects of mass addition, electric field short circuit, and energy accumulation are canceled out. Therefore, by mixing the 2FIi type parts in this way, the amount of acoustic reflection can be adjusted.

In addition, as shown in Fig. 6, the energy distribution of reflected waves can be improved not only in the direction perpendicular to the propagation direction of surface acoustic waves, but also by mixing the two types of parts described above along the propagation direction of surface acoustic waves. can also be adjusted. As a result, whereas in the above-mentioned embodiment shown in FIG. 4, the directionality was obtained only at the center of the band, in this embodiment, the directionality can be obtained over a wide band.

Furthermore, FIG. 7 shows three comb-shaped transducers 31.32.3.
This figure shows an example consisting of three parts. Comb shape converter 31
consists of a normal split electrode and constitutes the input side.

The comb-shaped transducers 32 and 33 are composed of electrodes similar to those of the embodiment shown in FIG. 6, and constitute the output side.

In the comb-shaped barter 31, no acoustic reflection occurs, but since it is a bidirectional transducer, waves are excited in both directions.

On the other hand, since the comb-shaped transducers 32 and 33 have directionality as described above, they receive waves with less loss. Therefore, in the case of such a configuration, in addition to the essentially low-loss filter characteristic of the three-electrode structure, there is also the advantage of the unidirectional transducer, and the loss can be extremely reduced.

Note that even if the comb-shaped converters 32 and 33 are used as input and the comb-shaped converter 31 is used as output, the effect remains the same.

[Effects of the Invention] As explained above, according to the surface acoustic wave element of the present invention, of the acoustic reflection components, the reflection component due to the mass addition and electric field short-circuit effect and the reflection component due to the energy storage effect cancel each other out. Since the directions of the vectors of the acoustic reflection components match, an extremely large total amount of reflection can be obtained.

Furthermore, since such a large amount of acoustic reflection can be obtained, the film thickness can be made thinner than in the past.

This leads to a significant reduction in the oscillation factor in the process, making it possible to manufacture surface acoustic wave elements with stable quality.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the configuration of the surface acoustic wave device of the present invention, FIGS. 2 and 3 are diagrams showing acoustic reflection phase diagrams in the surface acoustic wave device of FIG. 1, and FIGS. 7
The figure is a diagram for explaining the configuration of a surface acoustic wave element according to an embodiment of the present invention. Figure 8 is a diagram for explaining the configuration of a conventional surface acoustic wave element. Figure 9 and TSLO diagram are Figure 8. FIG. 2 is a diagram showing an acoustic reflection phase diagram in a surface acoustic wave element of FIG.

Claims (1)

[Claims] (1) In a surface acoustic wave element comprising a piezoelectric substrate and a plurality of comb-shaped transducers provided on the piezoelectric substrate, at least one of the comb-shaped transducers includes an electrode finger of the comb-shaped transducer. The length of one period of the row is λ, and the electrode width is 1/8
The electrode finger of the comb-shaped transducer has an electrode finger of 1/8λ width with a width of 1/8λ and an electrode finger of 1/4λ width with at least a part of the electrode width of 1/4λ, and At least in part
An elastic surface having a region in which two electrode fingers of the 1/8λ width and one electrode finger of the 1/4λ width are arranged within the length λ of one period of the electrode finger array. Wave element.