JPS62161209A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To eliminate the need for sound absorbing substance by arranging many splits with a tilt angle and an interval to the edge of a piezoelectric base in a way that the primary surface acoustic wave caused from a surface acoustic electrode touches the adjacent split after the wave passes through the edge of one split. CONSTITUTION:A piezoelectric base 1 is a rectangular thin plate, an exciting electrode 2 and a reception electrode 3 are formed on the surface and the electrodes are formed interdigitally by vapor deposition by means of a light metal such as aluminum. Absorbing devices 4, 4 are provided to both ends of the base 1 and the splits 5, 5 having a tilt angle theta, length L are provided in parallel in the progressing direction of the primary surface acoustic wave at a prescribed interval (d). The relation among the tilt angle theta, the length L and the interval (d) is decided so that the primary surface acoustic wave A touches without fail to the adjacent split after the wave passes through the edge of one split. Thus, the primary surface acoustic wave generated from the surface acoustic wave electrode is attenuated rapidly and lost while repeating the reflection drawing a stepwise locus between two adjacent splits. Thus, the coating of sound absorbing substance is not required.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to surface acoustic wave devices such as filters and delay elements, and particularly to a device for removing unnecessary reflected waves from a piezoelectric substrate.

<Prior Art> When a comb-shaped electrode is provided on a piezoelectric substrate and the electrode is excited, surface acoustic waves propagate in a predetermined direction. When this surface acoustic wave is reflected by the end face of the element and the reflected wave is re-entered into the electrode, it has a negative effect on the characteristics of the element.

Conventionally, therefore, a method has been used in which the reflected waves are absorbed by applying a sound absorbing material such as an adhesive to the upper surface of the piezoelectric substrate near the end surface of the substrate.

<Problems to be Solved by the Invention> However, this method requires a step of applying a sound absorbing material, and this step is difficult to automate.

Further, if the sound absorbing material adheres to the electrodes, there is a problem that the device becomes a defective product, and furthermore, there is a problem that gas generated from the sound absorbing material causes deterioration of aging characteristics.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a device that removes reflected waves without using sound-absorbing materials.

Means for Solving the Problems> The surface acoustic wave device of the present invention has a piezoelectric base (on the opposite end, a primary surface acoustic wave generated by a surface acoustic wave electrode passes through the end of one splint). It is characterized in that a large number of splints are arranged with inclination angles, lengths, and intervals such that when the splints hit adjacent splints, they hit adjacent splints.

<Operation> The primary surface acoustic wave generated by the surface acoustic wave electrode reaches the edge of the substrate and is reflected by the first split, for example, 90 degrees, and this secondary surface acoustic wave is re-reflected by the adjacent split, In this way, the light is rapidly attenuated by repeating reflection between adjacent splits. Further, the secondary reflected wave due to the splint is not reflected toward the surface acoustic wave electrode.

<Example> FIG. 1 shows a perspective view of a surface acoustic wave delay element embodying the present invention, and FIG. 2 shows an enlarged plan view of its main parts.

The piezoelectric substrate 1 is a rectangular thin piece made of LiNbO3, for example, and has an excitation electrode 2 and a reception electrode 3 on its surface.
is formed. These surface acoustic wave electrodes 2.3 are formed by attaching a light metal such as Aβ into a comb shape.

Absorption devices 4 of the present invention are provided at both ends of the piezoelectric substrate 1, respectively.
．． 4 are provided. As shown in the enlarged view in Fig. 2, this has an inclination angle θ with respect to the traveling direction of the primary surface acoustic wave, and long splits 5-5 are arranged parallel to each other at a predetermined interval d. has been done. The relationship between the inclination angle θ and the length 1 interval d of this split 5-5 is the first surface acoustic wave A
When passes through the edge of one splino 1~, this surface wave A
The relationship is such that always hits an adjacent split. This split 5 can be formed using the same material and the same process as the electrodes 2 and 3, and in that case, the manufacturing process can be streamlined.

In addition, a material heavier than the material forming the electrodes 2 and 3, such as Pb, may be used.
, Sn, Cu, etc., improve the absorption effect compared to light metals such as A1. Similarly, if the split 5 is formed using the same material and in the same process as the electrodes 2 and 3, it will naturally have the same thickness, but if it is formed in a separate process, the absorption effect will improve as the thickness increases.

In the case of the linear split shown in Figure 2, the inclination angle θ
is preferably 45° or slightly smaller. When the length is large, the distance d can be made large; on the other hand, when the length L is small, the distance d is also small. To give an example, when a 128° Y-cut substrate of LiNbO3 is used as the substrate and the frequency is 100 MHz, the wavelength is about 40 μm, and the size of the split is θ=45°.
L#565μm, d=14μm.

In such an absorption device, the surface acoustic wave electrode 2 or 3
When the first-order surface acoustic waves generated by the waves arrive, as shown in FIG. 2, they rapidly attenuate and practically disappear while repeating reflections in a step-like trajectory between two adjacent splits.

The shape of the sublime 1- of the present invention can be implemented through various modifications. The item 5A shown in Fig. 3 is the inclination/one angle θ
It is an intermediate refraction shape in which the angle changes in the middle. The tilt angle θ is θ-45° at the front stage near the center of the board, but it is 45° at the rear stage.
° has increased. Therefore, the interval d1 is reduced in the latter stage,
The number of reflections increases accordingly. The device 5B shown in FIG. 4 has an intermediate refraction type similar to that shown in FIG. 3, and the inclination angle at the rear stage is θ.
It is 45 degrees. The one 50 shown in FIG. 5 has a curved shape, and the angle of inclination at the front end is θ≦45°, but θ increases as it approaches the rear end. The one shown in FIG. 6 is one in which the linear type shown in FIG. 2 is connected at its rear and rear ends with one splice (5D).

<Effects of the Invention> According to the present invention, there is no need to apply a sound-absorbing material as in the past, and various problems associated with this are resolved. Also,
When formed using the same material as the surface acoustic wave electrode, they can be formed simultaneously in the same process, which streamlines the process and reduces manufacturing costs.

[Brief Description of the Drawings] Fig. 1 is a perspective view showing one embodiment of the present invention, and Fig. 2 is a perspective view showing an embodiment of the present invention.
Front view showing the main parts of the figure, Figures 3, 4, 5 and 6
The figure is a front view showing a modified embodiment of the present invention. 1-Piezoelectric substrate 2.3--Surface acoustic wave electrode 4-Absorption device 5-Split

Claims (2)

[Claims] (1) At the end of the piezoelectric substrate, there are a number of electrodes with an inclination angle, length, and spacing such that when the primary surface acoustic wave generated by the surface acoustic wave electrode passes through the end of one split, it hits the adjacent split. A surface acoustic wave device characterized in that a number of splits are arranged. (2) The surface acoustic wave device according to claim 1, wherein the split is formed of the same material as the surface acoustic wave electrode.