JPS59139714A - Surface wave element - Google Patents

Abstract

PURPOSE:To decrease the opposing width of the comb-shaped electrodes and to increase the impedance by providing a diffusing means of surface waves at an outer edge part rolling approximately along the propagating direction of the surface wave of an electrode formed on a piezoelectric substrate. CONSTITUTION:The grooves 6 are cut above an input electrode 2, an output electrode 3 and an earth electrode 4 with a sawtooth-shaped pattern so that these grooves cross outer edges 2a, 2b, 3a, 3b, 4a and 4b of electrodes 2-4 respectively. Thus a means 5 which diffuses undesired surface waves, and therefore the effects of undesired waves can be avoided. This reduces satisfactorily the opposing width (w) of comb-shaped electrodes and increases the impedance. Thus it is not needed that the distance (d) between the opposing part and the outer edge of an electrode is set there times as much as the wavelength. As a result, the overall size of a surface element can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface wave element such as a surface wave filter that utilizes surface waves.

For example, as shown in FIG. 1, this type of surface wave element includes input electrodes (2) in which pairs of comb-shaped electrodes are alternately arranged facing each other on a surface wave propagation medium, that is, a piezoelectric substrate (11). An output electrode (3) is deposited thereon, and a ground electrode (4) is arranged between the two electrodes (2) and (3).

In this type of surface wave element, the electrodes (2) and (3)
), the opposing width W of each pair of comb-shaped electrodes is made as large as possible to increase the energy of the effective surface waves directly directed toward the output electrode (3) among the surface waves excited and generated by the input electrode (2), and the other The influence of unnecessary waves due to reflection of unnecessary surface waves that spread in the direction due to diffraction is minimized by /J% as much as possible.

However, if the facing width W of the comb-teeth electrodes is increased in this way,
In particular, for example, piezoelectric ceramics made of PZT (solid solution of lead titanate and lead zirconate) threads whose dielectric constant 6 is 10
In a surface wave element using a surface wave propagation medium having a dielectric constant of about 0.00, the impedance is low and the load on the external circuit becomes heavy.

Therefore, in order to increase the impedance of a surface wave element using such a piezoelectric ceramic, it is desired that the facing width W of the comb-teeth electrodes be made as small as possible. now,
Describing a 10.7 MHz surface wave filter using specific gravity ceramics, in this case, if the facing width W of the comb-shaped electrodes is 1.5 mm or more, the energy of the surface waves traveling through the original propagation path is large. The influence of unnecessary surface waves is hardly a problem, but if this width W is set to 1.01 or less, the influence of unnecessary surface waves becomes significant. This is due to the fact that the surface waves spread due to diffraction reach the acoustic impedance mismatched areas, that is, the edges of each electrode (21 (31) and (41), in particular, approximately in the direction of surface wave propagation. Indicate the direction in which the original surface wave should propagate, and connect both electrodes (
2) and (3)) extending along the inner and outer edges (2a) (2b), (3a) (3b)
The reflections in (4a) and (4b) have a particularly large influence.

In Figures 2 to 8, the surface wave velocity is 2300 m /
Figure 2 shows the characteristics (each frequency - attenuation gain) of a 10.7 MH2 surface wave filter using a piezoelectric ceramic base +11 of sec, and the opposing width W is 2.5 mm.
, when the distance d is 550μ-, Fig. 3 shows that the opposing width W is 1.7 mm, and when the distance d is 550 μm, Fig. 4 shows that the opposing width W is 1.5 mm+, the distance is 1111 d, and the distance is 550 μm.
(In case D, in Fig. 5, the opposing width W is 1.0 mm and the distance d
is 550μ-, the opposing width W is 0.7II1 in Fig. 6.
ml, the respective characteristics when the distance d is 550 μm, and FIG. 7 shows the opposing width W when the width W is 1.0 μm and the distance d is 600 μm, and FIG.
In each characteristic when fill d is 150 p m, as is clear from these characteristics, when the opposing width W is 11 m or less,
When the distance d is 550 μm, the influence of diffraction and reflection occurs as shown by the broken line in Figures 5 and 6, and the theoretical characteristics cannot be obtained. As shown in Figure 8, even if the facing width W is 1llllll or less, the influence of unnecessary waves can be removed for chopsticks whose distance d is set to be three times or more than one wavelength of the surface wave. Recognize.

In addition, the inner edges (2c) (2d) and (3c) (3d) of each comb-shaped electrode of each electrode (2) and (3) are shown here.
Since this has a zigzag pattern with comb teeth, unnecessary waves are scattered at this edge, so there is almost no influence due to this.

As mentioned above, in a surface wave element, the distance d from the effective part of the electrode, that is, the opposing part of the comb-shaped electrode to the outer edge, is
When the wavelength is more than three times the wavelength of the surface wave to be propagated,
Although the influence of unnecessary waves can be avoided, the present invention does not require such a configuration, or it uses a surface wave element having this configuration and further capable of reliably eliminating the influence of unnecessary waves. This is what we intend to provide.

That is, in the present invention, the surface wave scattering means is provided at the outer edge of the surface line propagation medium, that is, the electrode coated on the piezoelectric substrate, extending substantially along the surface wave propagation direction.

The present invention will be described in detail with reference to FIG. 9. Parts corresponding to those in FIG. 1 will be denoted by the same reference numerals, and redundant explanation will be omitted.

In the present invention, each outer edge (2a) (2b), (3a) (3b), (4) of each electrode (2), (3), (4)
a) Cut grooves (6) across each electrode (2), (3), and (4) using a diamond pen or the like in a serrated zigzag or wavy pattern, for example. It is formed like a notch to form a means (5) for scattering unnecessary surface waves. The frequency characteristic in this case is the first
As shown in Figure 0, the influence of unnecessary waves has been removed. 11th
The figure shows the frequency characteristics when this means (5) is not provided.

As shown in FIG. 12, the present invention is applied to a surface wave filter in which comb-shaped electrodes with a short facing width W are stacked in a series of multiple stages to increase impedance and reduce insertion loss. In this case as well, the influence of diffraction and reflection can be removed. In this case, it is desirable to provide the means (5) in a portion where a plurality of comb teeth face each other at the inner edge of each electrode and the straight line/portion along the propagation direction is relatively long.

As described above, according to the present invention, each electrode (2), (3), (
4) at least each outer edge (2a) (2b), (3a
) (3b), (4a) By providing the unnecessary wave scattering means (5) in (4b), the influence of unnecessary waves can be effectively avoided, so the opposing width W of the comb-shaped electrodes can be made sufficiently small. , it is possible to increase impedance. Therefore, it is not necessary to select the distance d from the facing portion of the comb teeth of the electrode to the outer edge to be three times the wavelength, and the overall size can be reduced.

Incidentally, if necessary, an unnecessary wave absorbing material is applied to both ends of the substrate 11) in the direction of surface wave propagation on the opposite side to the side where the output electrodes and the output electrodes face each other, although not shown in the drawings. You can also do something like this.

[Brief explanation of the drawing]

FIG. 1 is a schematic top view of a conventional surface wave element, FIGS. 2 to 8 are frequency-attenuation gain characteristic curve diagrams for explaining the same, and FIG. 9 is a schematic diagram of an example of a surface wave element according to the present invention. 10 and 11 are frequency-attenuation gain characteristic curve diagrams for explaining the same, and FIG. 12 is a schematic top view of another example of the element of the present invention. (1) is a piezoelectric substrate as a surface wave propagation medium, (2) is an input electrode, (2a) and (2b) are its outer edges, (2c)
and (2d) its inner edge, (3) the output electrode, (3a
) and (3b) are the outer edges thereof, (3c) and (3d) are the inner edges thereof, Shushu Ai

Claims (1)

[Claims] A surface acoustic wave element comprising an unnecessary wave scattering means formed by a groove extending in the surface acoustic wave propagation direction and non-parallel to the propagation direction on the end face of the electrode that is adhered on a surface acoustic wave propagation medium and extending in the surface acoustic wave propagation direction.