JPH0238495Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a surface acoustic wave device used as a surface acoustic wave filter, a surface acoustic wave resonator, or the like.

[Technical background of the invention]

Conventionally, this type of surface acoustic wave device has a piezoelectric substrate 1 with a
The opposing comb-shaped electrodes 2 and 3 are crossed so that the respective electrode fingers 2 ₁ , 2 ₂ , 2 ₃ , ... and 3 ₁ , 3 ₂ , 3 ₃ , ... are inserted into each other at a predetermined interval, In addition, the electrode fingers 2 ₁ , 2 ₂ ,
2 ₃ , . . . and 3 ₁ , 3 ₂ , 3 ₃ , . . . so-called weighted structures are often used.

In the same figure, the symbols 4 ₁ , 4 ₂ , 4 ₃ , ... and 5 ₁ , 5 ₂ , 5 ₃ , ... are dummy electrodes for compensating for disturbances in the planar phase of the propagating surface waves, and A
is a curve showing the change in the geometric cross width of the electrode plate due to weighting.

In this way, the intersecting electrode fingers 2 ₁ , 2 ₂ , 2 ₃ ,
...and 3 ₁ , 3 ₂ , _{3 3 , ...} as shown in FIG _{. +1} and electrode finger 3 _o have different crossover widths l _o+1 , and respond to input pulses with different positions and sizes on the time axis, and input at the respective crossover widths l _o and l _o+1. Strains of different positions and magnitudes are propagated on the piezoelectric substrate 1 through the electric field caused by the signal.

Therefore, when designing such a surface acoustic wave device, consider an equivalent δ oscillation source array B corresponding to the intersection width of these electrode fingers, as shown in FIG. By designing B to have the desired frequency characteristics and then setting the crossing width of the electrode fingers so that it is proportional to the size of the equivalent δ oscillation source array B, a surface acoustic wave device with the desired frequency characteristics can be created. It has gained.

[Problems with background technology]

However, in the above surface acoustic wave device, as shown in FIG. 4, a leakage electric field C is formed at the tips of the electrode fingers, so the effective crossover width L _o is smaller than the geometrical crossover width L _o . The problem was that the . Note that the symbol D indicates lines of electric force.

Therefore, in order to determine the geometric crossover width using the equivalent δ vibration source sequence obtained by calculation, the effective crossover width is
Frequently, an error occurred between the frequency _{characteristics} and the frequency characteristics as designed. Particularly, when the crossing width is not sufficiently large compared to the interval between the gap portions, there is a problem in that the error due to the leakage electric field C becomes large and the influence on the error in the frequency characteristics becomes large.

[Purpose of invention]

The present invention was made to solve these conventional drawbacks, and is a surface acoustic wave device that can reduce weighting errors caused by leakage electric fields between electrode fingers and achieve desired stable characteristics. For the purpose of providing.

[Summary of the idea]

That is, the present invention provides a surface acoustic wave device formed by intersecting the electrode fingers of a pair of comb-shaped electrodes on a substrate, in which the side edges of the electrode fingers of each comb-shaped electrode are connected to the other. The electrode fingers of the side comb-shaped electrodes are each curved inwardly near the tips thereof.

[Example of idea]

The details of the present invention will be explained below with reference to the drawings.

FIG. 5 is a partially enlarged plan view showing an embodiment of the surface acoustic wave device of the present invention.

In FIG. 5, parts common to those in FIG. 1 are given the same reference numerals.

The general structure of the surface acoustic wave device of the present invention is almost the same as that shown in FIG. The electrode fingers 2 ₁ , 2 ₂ , 2 ₃ , ... and 3 ₁ , 3 ₂ , 3 ₃ , ... are crossed so as to be inserted into each other at a predetermined interval, and the electrode fingers 2 ₁ are arranged so as to meet the desired characteristics. , 2 ₂ , 2 ₃ , . . . and 3 ₁ , 3 ₂ , 3 ₃ , .

In addition, the symbols 4 ₁ , 4 ₂ , 4 ₃ , ... and 5 ₁ , 5 ₂ , 5 ₃ ,
... are dummy electrodes for compensating for disturbances in the planar phase of the propagating surface waves.

In the surface acoustic wave device of the present invention, in such a configuration, the electrode fingers 2 ₁ , 2 ₂ ,
The side edges of 2 ₃ , . . _. and 3 1 , 3 ₂ , 3 ₃ , . R indicates a curved portion.

In this way, electrode fingers 2 ₁ , 2 ₂ , 2 ₃ , ... and 3 ₁ , 3 ₂ ,
By forming the side edges of 3 ₃ , ... inwardly in the vicinity of the tips of the electrode fingers of the mating comb-shaped electrode, the electrode The concentration of electric lines of force D at the tips of fingers _2o , 2o ₊₁ , _3o, etc. is reduced, and lines of electric force from areas beyond the intersection width of these electrode fingers are greatly suppressed. The stray electric field is reduced, and the error between the geometric crossover widths _lo , lo ₊₁ and the effective crossover widths _lo , lo ₊₁ is reduced.

As a result, a surface acoustic wave device having predetermined band characteristics as designed is obtained, and its characteristics are also stable.

Furthermore, in the surface acoustic wave device of the present invention, the electrode fingers 2 ₁ ,
By rounding the tip corners of 2 ₂ , 2 ₃ , ... and 3 ₁ , 3 ₂ , 3 ₃ , ..., the electrode fingers 2 ₁ , 2 ₂ , 2 ₃ , ...
The distance between the electrode fingers 3 ₁ , 3 ₂ , 3 ₃ , ... and the area beyond the intersection width l ₁ , l ₂ , is made longer, and the electric force line D from that area is suppressed from reaching. For example, the difference between the geometrical crossover width and the effective crossover width can be further reduced.

Although the above embodiments are surface acoustic wave devices having weighted electrode fingers, the present invention is not limited to such embodiments, and can also be applied to surface acoustic wave devices having non-weighted electrode fingers. It is also applicable to

[Effect of idea]

As explained above, in the surface acoustic wave device of the present invention, the side edges of the electrode fingers of each comb-shaped electrode are placed on the substrate near the side edge of the other comb-shaped electrode.
Since they are each curved inward, the electric lines of force from the area beyond the crossing width due to the crossing of the electrode fingers at the tips of the electrode fingers are reduced, suppressing the leakage electric field, and eliminating the extraneous electric field caused by the leakage field effect. Since the excitation of surface acoustic waves is prevented, the characteristics as originally designed can be obtained extremely easily, and the characteristics are also stabilized.

[Brief explanation of the drawing]

FIG. 1 is an enlarged plan view showing a conventional surface acoustic wave device, FIG. 2 is an enlarged plan view of its main parts, and FIG. 3 is a diagram showing an equivalent δ oscillation source array of the interdigitated electrodes shown in FIG. 1. Fig. 4 is a diagram showing the leakage electric field due to the interdigitated electrodes shown in Fig. 2, Fig. 5 is a partially enlarged plan view showing an embodiment of the surface acoustic wave device of the present invention, and Fig. 6 is the leakage electric field. FIG. 1... Substrate (piezoelectric substrate), 2, 3... Comb-shaped electrode, 2 ₁ , 2 ₂ , 2 ₃ ,..., 3 ₁ , 3 ₂ , 3 ₃ ,... Electrode finger, _lo , lo ₊₁ ... Geometric crossover width, L _o , L _o+1 ...
...Effective crossover width.

Claims (1)

[Claims for Utility Model Registration] (1) In a surface acoustic wave device formed by intersecting the electrode fingers of a pair of comb-shaped electrodes on a substrate, the electrode fingers of each of the comb-shaped electrodes are The side edges are each formed by curving inwardly near the tip of the electrode finger of the comb-shaped electrode on the other side, and the tip corner of the electrode finger of each comb-shaped electrode is rounded. A surface acoustic wave device characterized by: (2) The surface acoustic wave device according to claim 1, wherein the crossed electrode fingers are each weighted.