JPS63266912A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To contrive the reduction of a periodical spurious radiation by providing a tilt ridge tilted at an angle in the propagation direction of a surface acoustic wave to the end of a comb-line electrode opposed to a common electrode with at least a signal applied thereto. CONSTITUTION:The surface acoustic wave device is constituted by providing an apotized type comb-line electrode 21 of tilt electrode structure to a substrate 20 made of a prescribed piezoelectric substance. The electrode 21 has plural electrode fingers 21a crossed with a tilt and common electrodes 21b, 22 connected in common to the electrode fingers. The common electrode 21b is connected to ground and a dummy electrode 15 not crossed with the electrode finger 21a is connected to the other common electrode 22. The normal comb-line electrode 23 is opposed to the electrode 21 at the interval of nearly 1mm. The electrode 23 consists of the electrode finger 23a crossed uniformly and common electrodes 23b, 23c connected in common to the electrode finger 23a, the eleotrode 23b is connected to ground and the other electrode 23c is connected to ground via a load 5. Thus, the electrode 23 has a larger opening length than that of the electrode 21.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a surface acoustic wave device including a comb-shaped electrode with intersecting electrode fingers.

(Technical Background of the Invention) This type of surface acoustic wave device is used as a filter, an AM ray, etc., but especially when used as a filter in a repeater of an image transmission device, it is used in multiple stages, so each The transmission distortion generated in each stage is added up sequentially, causing image deterioration. Therefore, as a surface acoustic wave device for an image transmission device, the spurious amplitude and group delay within the band are Oold B (peak to peak). )below,
Characteristics satisfying ±2 to 31 LSec are required.

FIG. 6 shows a conventional surface acoustic wave device.
II, Cono surface acoustic wave device 1112B'Y-X A 7-potized comb-shaped electrode 2 with an inclined electrode structure is provided on a substrate l made of a piezoelectric material such as niobium lithium, and this comb-shaped electrode 2 has an inclined electrode structure. A plurality of electrode fingers 2a that intersect
and common electrodes 2b and 2c that are commonly connected to these electrode fingers 2a. A signal source 4 is connected to one common electrode 2C, and a conductive film 6 made of an aluminum film with a thickness of about 200 OA is integrally formed. This conductive film 6 is an electrode finger 2a located on the right side of the acoustic center A in the figure.
Covers non-intersecting parts of groups. A regular comb-shaped electrode 3 is opposed to the comb-shaped electrode 2. This comb-shaped electrode 3 has electrode fingers 3a that are uniformly crossed, and these electrode fingers 3a.
It has common electrodes 3b, 3b that are commonly connected to a, and one common electrode 3b is grounded via a load 5. The comb-shaped electrode 3 has an aperture length larger than the aperture length a of the comb-shaped electrode 2, which allows for impedance matching with an external circuit, suppression of deterioration of filter characteristics due to diffraction phenomenon, etc. We are trying to In addition, in the figure, 7
indicates sound absorbing material.

Now, the comb-shaped electrode 2 of the conventional surface acoustic wave device mentioned above.
, unnecessary surface waves are generated from the electrode fingers 8 and 8' located at both ends along the propagation direction of the main response surface wave (see arrow), and this causes periodic spurious waves in the band. known to occur. That is, the length dimension of the common electrode 2c (2b) of the comb-like electrode 2 is expressed as 2, and the surface wave of the main response generated from the acoustic center A of the same electrode 2 is expressed as Wo.
, the propagation speed of the surface wave on the substrate 1 is 71, and the comb-shaped electrode 2
．． If the interval between 3 and 3 is d, then the surface wave W.

The time required for propagation to the regular comb-shaped electrode 3 is (
d, +1)/V. On the other hand, the phase of the surface wave W generated from the electrode finger 8 is advanced by Q/V seconds with respect to the main response surface wave Wo, and the surface wave W2 generated from the electrode finger 8' is in phase with respect to the surface wave WO of the main response. The phase is delayed by M/V seconds. Therefore,
These both surface waves W9. Since W2 is received by the regular comb-shaped electrode 3, spurious waves occur at a period such that u/V=fl. This also agrees with the actually measured results.

(Problems in the Background Art) By the way, in the common electrode 2C on the signal applying side of the abotized comb-shaped electrode 2 having the above-mentioned inclined electrode structure, the same problem occurs from the edge 2d facing the regular comb-shaped electrode 3. It was found that a spurious signal with an f1 period was generated. Therefore, by preventing the surface waves generated from the common electrode 2C on the signal application side from being received by the regular comb-shaped electrode 3, the above f+ period spurious can be reduced and image transmission distortion etc. It can be prevented.

(Object of the Invention) An object of the present invention is to provide a p-type surface wave device with extremely small periodic spurious.

(Summary of the Invention) The present invention provides an inclination that is inclined at an angle with respect to the propagation direction of a surface wave, at least at the end of the comb-shaped electrode on the side of the comb-shaped electrode opposite to the common electrode to which a signal is applied. It is characterized by having an edge.

(Embodiments of the Invention) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 2, the surface acoustic wave device according to the present invention has the following features:
A substrate 20 is provided. This board 20 is 128°x-Y
A seven-bottom r-shaped comb-shaped electrode 21 made of a piezoelectric material such as lithium niobate and having an inclined electrode structure is provided. This comb-like electrode 21 has a plurality of electrode fingers 21a that intersect at an angle, and common electrodes 21b and 22 that are commonly connected to these electrode fingers. One common electrode 21b is grounded, and the other common electrode 22 is connected to a signal source 4.
A dummy electrode 15 that does not intersect with the electrode finger 21a is also connected to these common electrodes 21b and 22.

A regular comb-shaped electrode 23 faces the comb-shaped electrode 21 with an interval of approximately 1 mm. This comb-shaped electrode 23 consists of electrode fingers 23a that are uniformly crossed, and common electrodes 23b and 23c that are commonly connected to these electrode fingers.One common electrode 23b is grounded, and the other common electrode 23c is grounded via the load 5. The regular comb-shaped electrode 23 has a larger opening length than the comb-shaped electrode 21.

In the 7-botified comb-shaped electrode 21 with the inclined electrode structure, the length of the non-intersecting portion of the electrode fingers 21a is gradually increased from the acoustic center A position in the portion of the common electrode 22 that is spaced apart from the regular comb-shaped electrode 23. The bending part 2
2A is formed. The refracting portion 22A has an inclined edge 22a on the outer end side, which is inclined at a predetermined angle with respect to the propagation direction (see arrow) of the main response surface wave. A sound absorbing material 25 made of epoxy adhesive is provided on the bent portion 22A, including the inclined edge 22a. This sound absorbing material 25 is formed in a substantially U-shape, and the common electrode 22
It has sound absorbing parts 26 and 27 including a non-bending part and each edge of the conducting electrode 21b.A sound absorbing material 28 made of the same material is also provided near the comb-shaped electrode 23. ing.

Now, as shown in FIGS. 1 and 2, an inclined edge 22b is formed at the end of the common electrode 22 on the signal application side facing the regular comb-shaped electrode 23. As shown in FIG. 1, this inclined edge 22b has an inclination angle of θ with respect to an imaginary line M extending downward from the electrode finger 15' where the end is located. This inclination angle θ is set to be larger than the angle θ' formed by the above-mentioned imaginary line M and a line segment L' perpendicular to the imaginary line connecting the open ends of the comb-like electrodes 21, 23. That is, if the inclination angle is 0>θ', the inclination edge 2
The surface waves generated from 2b are generated by the opposing regular comb-shaped electrodes 2.
3 will not be received.

In the surface acoustic wave device of the present invention having the above configuration,
As shown in FIG. 3, the surface wave W3 generated from the acoustic center A and propagating toward the bending portion 22A of the common electrode 22 is absorbed at the center of the sound absorbing material 25, and a part of it is absorbed by the inclined edge. 2
2a and is sequentially absorbed by the sound absorbing parts 27 and 26.

In addition, the surface waves w2 generated at the inclined edge 22a and not absorbed at the center of the sound absorbing material 25 are as shown in FIG.
The sound propagates in a direction perpendicular to the edge 22a, and most of the sound is absorbed by the sound absorbing portion 27.

Furthermore, in the apotized comb-like electrode, at each outer edge of the non-bending portion of the common electrode 22 and the other common electrode 21b, a portion of the surface waves W2, W3, etc. Since it is reflected, reflected waves W4 and Ws are generated. However, the non-bending portion of the common electrode 22 and the other common electrode 21b
Since each end edge of W4. Ws is these sound absorbing parts 26°27
Sound is absorbed by

By the way, an inclined edge 22b having an angle of 0 is formed at the end of the common electrode 22 on the signal application side. Therefore,
The unnecessary surface waves generated on this inclined edge 22b are
2b, and is absorbed by the sound absorbing material, so it is not received by the regular comb-shaped electrode 23. Therefore, not only periodic spurious waves caused by surface waves W2 to W5 are generated. , periodic spurious waves caused by surface waves generated at the ends of the common electrode 22 can also be reduced, so that periodic spurious waves can be significantly reduced.

In the surface acoustic wave device shown in FIG. 2, the electrode finger 15' located at the end is 0.16 mm, and the electrode finger 21a is
When the frequency characteristics were examined by setting the length dimension ' to 0.2 mm, the results shown in FIG. 4(A) were obtained. That is,
The periodic spurious that occurs in the passband region A is the fourth
As shown in Figure (B), approximately 0.07 dB (peak t
.

peak).

For comparison, in the surface acoustic wave devices shown in FIGS. 1 and 2, the common electrode 22 is not provided with the inclined edge 22b,
As in the conventional case, an edge was provided perpendicular to the propagation direction of the surface wave, and its frequency characteristics were investigated. As a result, as shown in FIG.
(peak to peak). This is because unnecessary surface waves generated from the right-angled edge of the common electrode 22 are received.

In the above embodiment, the inclination angle O of the inclined edge 22b is set within a range where unnecessary surface waves propagating in a direction orthogonal to the edge 22b are not received by the regular comb-shaped electrode 23. Bye.

In addition, in the above embodiment, the common electrode 21b on the ground side
An inclined edge 22c (see dashed line in FIGS. 1 and 2) may also be provided at the end of , which further reduces periodic spurs, albeit slightly.

In the above embodiment, the present invention is applied to a 7-potized comb-shaped electrode with an inclined electrode structure, but the present invention can also be applied to a normal 7-potized comb-shaped electrode and a regular comb-shaped electrode for wave transmission. Of course, it is applicable.

Furthermore, even if the comb-like electrodes on the transmitting side and the receiving side have the same aperture length, there is a risk that unnecessary surface waves generated from the common electrode for signal application may be received due to diffraction phenomenon. Because there is
By applying the present invention, it is possible to reduce periodic spurious.

In the above example, regular comb-shaped electrodes are used on the receiving side, but apotized comb-shaped electrodes are also used on the receiving side, and the apotized comb-shaped electrodes are coupled with a multi-strip coupler. The same effect can be obtained even if the present invention is applied to a surface acoustic wave device having such a structure.

(Effects of the Invention) According to the present invention, at least the end portion of the common electrode on the signal application side of the comb-shaped electrode on the opposing comb-shaped electrode side,
Table 1 By providing an inclined edge that is inclined at an angle with respect to the propagation direction of the plane wave, it is possible to prevent unnecessary surface waves generated from the common pole from being received and eliminate periodic spurious waves. can be significantly reduced. Therefore, it is possible to provide a surface acoustic wave device suitable for use as an image transmission device that needs to sufficiently suppress image transmission distortion, a filter with excellent broadband characteristics, and the like.

[Brief explanation of drawings]

1 and 2 are an enlarged plan view and an overall plan view of the main parts of the surface acoustic wave device according to the present invention, FIG. 3 is a schematic plan view illustrating the operation of the device shown in FIG. 1, and FIG. Figures (A) and (B) are diagrams showing the amplitude frequency characteristics and periodic spurious characteristics of the device in Figure 1, respectively. Figure 5 is a diagram of the periodic spurious characteristics of a surface acoustic wave device as a comparative example. Figure 6 is a diagram showing the periodic spurious characteristics of the device shown in Figure 1. FIG. 2 is a plan view of a surface acoustic wave device. 20-------One substrate, 21.23----<L bar-shaped electrode, 21b, 22---One common electrode, 22A---One bending part, 22a, 22 b --One slanted edge, (1 other person) Figure 1 21.23 --- One comb-shaped electrode 211), 22 --- One common electrode Figure 4 (A) Figure 5 20 --- -----1 Substrate 22A---11 Refraction parts 22a, 22b -----4 Surplus hooks 25---1 Sound absorbing material

Claims (1)

[Claims] In a surface acoustic wave device comprising a comb-shaped electrode including a common electrode that extends along the propagation direction of the surface wave and has intersecting electrode fingers commonly connected, at least the opposite side of the common electrode to which a signal is applied. At the end of the comb-shaped electrode,
1. A surface acoustic wave device comprising an inclined edge that is inclined at an angle with respect to a propagation direction of a surface wave.