JPH0946163A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain miniaturization by adopting the structure that interdigital electrodes with a specific width and inter-electrode length extended from plural bus bars on a substrate are in crossing mutually and providing a floating electrode to a tip of the interdigital electrode in its extending direction so as to eliminate the need for correction of the propagation speed. SOLUTION: Interdigital electrodes 2 with a width of λ/4 (λ is a wavelength of a surface acoustic wave) and an inter-electrode length of λ/4 extended from two bus bars 3 formed on a piezoelectric substrate 1 are in crossing with each other and a floating electrode 4 is provided to a tip of each interdigital electrode 2 in the extending direction. The width of the floating electrode 4 is selected the same as the width of the interdigital electrode 2 and the interval between the interdigital electrode 2 and the floating electrode 4 is selected smaller than 1/10 of the wavelength λequivalenet to the operating frequency. Thus, the electric field strength around the electrode end in the electric field strength of the interdigital electrode 2 is suppressed and a flat strength characteristic is obtained. Thus, it is not required to provide a correction efficiency for the propagation speed to keep the propagation speed in the crossing uniform, miniaturization and high performance are attained and the productivity and the reliability are improved.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a technique for improving the performance of a surface acoustic wave filter.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 3, comb-shaped electrodes extend from two opposing bus bars at regular intervals and are arranged in a state where they intersect with each other. The intersecting portion of the comb-shaped electrodes intersecting with each other serves as a waveguide of the surface acoustic wave. If the tip of the comb-shaped electrode is square, the distribution of the electric field strength in the crossing portion is not flat, and as shown in the graph, there is an inconvenient characteristic that it becomes stronger near the tip of the comb-shaped electrode. In order to improve these, there are already Japanese Utility Model Publication No. 2-15390 and Japanese Patent Application Laid-Open No. 7-15272.

[0003]

Generally, all of the conventional techniques have taken measures to improve the characteristics by taking measures for the electrodes in the intersections. , Length, shape, etc.) causes non-uniformity in the propagation velocity in the intersection. The cause of non-uniformity of the propagation velocity is that the propagation velocity is different in the place where there is a conductor and the place where there is no conductor. In order to make the same correction in any of the propagation paths, the correction metal must be attached to the part with few conductors in the propagation path so that it becomes the same as the part with many conductors in the propagation path. There was a problem saying that it would not happen.

[0004]

[Means for Solving the Problems] In order to solve the problem, the electrode is not taken at the intersection of the comb-shaped electrodes, but the electrode is taken at a place other than the intersection so that the propagation velocity in the intersection is increased. Therefore, the problem was solved by eliminating the need to correct the propagation velocity by maintaining the uniformity of.

[0005]

EXAMPLE FIG. 1 shows an example of a comb-shaped electrode arrangement according to the present invention. A comb-shaped electrode 2 and a bus bar 3 are formed on the piezoelectric substrate 1. The ← mark represents the traveling direction of the surface wave. The width and the interval length of the electrodes are λ / 4, respectively.
(Λ indicates the wavelength of the surface acoustic wave) The comb-shaped electrode is a normal type in which a large number of pairs are arranged in the propagation direction of the surface wave, but in order to facilitate the description, in FIG. Extract the pairs and explain.

Comb-shaped electrodes 4 extend from the two bus bars 3 at regular intervals and are arranged to intersect with each other. At the tip of the comb-shaped electrode 2, floating electrodes 4 (three described in the embodiment) are arranged in the extension direction of the electrodes. The width of the floating electrode 4 is the same as the width of the electrode, and the distance between the floating electrode 4 and the comb-shaped electrode or the dummy electrode is set to be smaller than 1/10 of the circumferential wavelength λ used.

FIG. 2 shows electric field strength characteristics in the case of the comb-shaped electrode structure shown in FIG. Comparing with the characteristic of the electric field strength of the prior art of FIG. 3, it can be seen that the effect of the electrode tip is suppressed and the characteristic of the electric field strength is flat.

FIG. 4 shows an embodiment in which the technique of the present invention is applied to an apodized type in which electrodes are weighted. The width and the interval length of the electrodes are λ / 4. The floating electrode 4 is provided at the tip of each comb-shaped electrode. The electrode existing up to the opposing bus bar beyond the floating electrode 4 is the dummy electrode 5. In the case of the apodized type, the waveguide is inside the tip of the deepest intersecting electrode as shown in FIG. Therefore, the tips of the electrodes with shallow intersections are in the waveguide.

Attention is paid to the structure of the floating electrode. The gap G between the floating electrodes is selected to be smaller than 1/10 of the wavelength λ of the surface acoustic wave passing through the waveguide. That is, G <λ / 10
It is represented by Thus, the slits that are sufficiently small with respect to the wavelength have almost no effect on the propagation velocity of the surface acoustic wave through the waveguide. Further, even when the comb-shaped electrodes 2 intersect shallowly and the tip of the floating electrode is in the waveguide, since the dummy electrode 5 is provided ahead of the floating electrode 4, the propagation velocity of the surface acoustic wave also passes through the waveguide. It has no effect.

FIG. 5 shows an embodiment of a λ / 8 regular type comb-shaped electrode. A basic set is extracted and shown in comparison with FIG. It is basically the same as λ / 4, but has a structure in which the pair of comb-shaped electrodes in which the width and inter-electrode length of the comb-shaped electrodes are λ / 8 intersect each other. Although not shown in the figure, the apodized type is also the same as the λ / 4 apodized type, but the comb-shaped electrode has a structure in which the comb-shaped electrodes whose width and inter-electrode length are λ / 8 intersect each other. In the structure, the lengths of the electrodes adjacent to each other at the intersection are different. At the tip of each of these comb-shaped electrodes,
The floating electrodes 4 (three described in the embodiment) are arranged in the extension direction of the electrodes. The width of the floating electrode 4 is the same as the width of the electrode, and the distance between the floating electrode 4 and the comb-shaped electrode or dummy electrode is 1 of the operating wavelength λ.
Make it smaller than / 10.

FIG. 6 shows another embodiment of the floating electrode. The bottom of the triangle is the width of the electrode, the height is 1.5 times or less the bottom, and the bottom is arranged so as to face the tip of the electrode. The dummy electrode is cut into an inverted triangle according to the triangle of the floating electrode. It is also the same as the floating electrode that each slit has a gap of λ / 10 or less. This floating electrode is a λ / 4 regular type, apodized type or λ / 8
It can be applied to both regular type and apodized type.

The material of the substrate can be any material that can be used for surface acoustic waves such as quartz, lithium tantalate, lithium niobate, and the like.

[0013]

According to the present invention, the characteristics of the electric field strength at the intersection of the comb-shaped electrodes are flattened in the λ / 4 normal type, the apodized type, or the λ / 8 normal type, the apodized type surface acoustic wave filter. In order to improve, because the electrode for correcting the propagation velocity could be omitted, not only was the size and performance improved, but the productivity and reliability were also improved, and cost reductions were also realized.

[Brief description of drawings]

FIG. 1 is a pattern diagram showing an embodiment of the present invention.

FIG. 2 is a graph of electric field strength showing an example of the present invention.

FIG. 3 is a graph of electric field strength showing an example of the prior art.

FIG. 4 is a λ / 4 apodizing pattern diagram showing an embodiment of the present invention.

FIG. 5 is a pattern diagram of a λ / 8 regular type showing an embodiment of the present invention.

FIG. 6 is a pattern diagram of a floating electrode showing an example of the present invention.

[Explanation of symbols]

 1 substrate 2 comb-shaped electrode 3 bus bar 4 floating electrode 5 dummy electrode

Claims (4)

[Claims] 1. A surface acoustic wave filter having a structure in which the width and interelectrode length of comb electrodes extending from two busbars on a substrate intersect with each other in a surface acoustic wave filter. A surface acoustic wave filter comprising a floating electrode at the tip of the direction. 2. A structure in which comb-shaped electrodes extending from two bus bars on a substrate have a width of λ / 4 and the comb-shaped electrodes intersect each other, and the lengths of adjacent electrodes at the intersections of the comb-shaped electrodes are all the same. The surface acoustic wave filter having a different structure in the comb-shaped electrode, wherein a floating electrode is provided at the tip in the extending direction of the comb-shaped electrode. 3. A surface acoustic wave filter having a structure in which a pair of comb-shaped electrodes extending from two bus bars and having a width and an inter-electrode length of λ / 8 crosses each other on a substrate.
A surface acoustic wave filter comprising a floating electrode at the tip of the comb-shaped electrode in the extending direction. 4. An electrode adjacent to an intersection of comb-shaped electrodes having a structure in which a pair of comb-shaped electrodes extending from two bus bars and having a width and inter-electrode length of λ / 8 intersect on a substrate. A surface acoustic wave filter having different lengths, wherein a floating electrode is provided at the tip in the extending direction of the comb-shaped electrode.