JP2000286674A - Surface acoustic wave filter device and resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the adverse influence of reflected waves from the end faces of a surface acoustic wave filter device. SOLUTION: The end faces 10 and 11 of a crystal substrate 1 are mirror finished and the distances between an input-side converter 2 and the end face 10 and between an output-side converter 4 and the end face 11 in the propagating direction of surface acoustic waves are respectively set at an integer multiple the half wavelength of a fundamental surface acoustic wave. Thus, the conversion efficiency of the surface acoustic waves are rather improved further, because the phases of reflected waves from the end phases 10 and 11 become the same as that of a main wave and the main wave does not receive the adverse influence of the reflected waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave filter device and a resonator for reducing an adverse effect of a reflected surface acoustic wave on a main wave.

[0002]

2. Description of the Related Art Conventionally, in a surface acoustic wave filter device and a resonator, a sound absorbing agent is applied to an end portion of a substrate in order to reduce an adverse effect of an end surface reflected wave of a surface acoustic wave on a main wave.

[0003]

However, when such a sound absorbing agent is applied, the size of the element increases in the propagation direction of the surface acoustic wave (actually, about 0.5 to 1 mm), and the size of the product is reduced. Contrary to the request.

[0004] Instead of applying a sound absorbing agent, it is conceivable to reduce the adverse effect of the reflected wave by roughening the edge of the substrate, but it is difficult to roughen such a narrow range.

An object of the present invention is to provide a surface acoustic wave filter device and a resonator which can reduce the adverse effect of the end face reflected wave with a simple configuration.

[0006]

According to a first aspect of the present invention, there is provided a surface acoustic wave filter device comprising: a piezoelectric substrate having an end face mirror-polished; and a piezoelectric substrate formed on the piezoelectric substrate, wherein an electric signal is inputted from the outside. An input converter for converting the electric signal into a surface acoustic wave, and formed on the surface of the quartz substrate,
An output converter for converting the surface acoustic wave excited by the input-side converter into an electric signal, and outputting the electric signal to the outside, wherein λ is the propagation wavelength of the basic surface acoustic wave; The distance in the propagation direction of the surface acoustic wave between the side transducer and the end face of the piezoelectric substrate adjacent to the transducer is (k + ／).
λ (k = 0, 1, 2,...), and the distance in the propagation direction of the surface acoustic wave between the output-side converter and the end face of the piezoelectric substrate adjacent thereto is (l + ／) ( l = 0,1,
2,. . . ) Λ.

The distance in the propagation direction of the surface acoustic wave between the input-side transducer and the end face close to the input-side transducer and the distance in the direction of propagation of the surface acoustic wave between the output-side transducer and the end face close to the input side transducer are respectively set as follows. Since the phase of the end-face reflected wave becomes the same as the phase of the main wave, the adverse effect of the end-face reflected wave is not exerted on the main wave, but the conversion efficiency of the surface acoustic wave is further improved.

In the surface acoustic wave filter device according to a second aspect of the present invention, the end surface has a surface roughness of 0 to 0.2 μm. With such a surface roughness, the end face reflected wave is effectively reflected by the input-side converter and the output-side converter.

The surface acoustic wave filter device according to a third aspect of the present invention is characterized in that the piezoelectric substrate is made of a single crystal material. The end face can be satisfactorily mirror-polished by using such a single crystal material.

According to a fourth aspect of the present invention, there is provided a resonator according to the fourth aspect of the present invention, wherein the piezoelectric substrate has a mirror-polished end face, a positive electrode having a plurality of electrode fingers formed on the piezoelectric substrate, and And a negative electrode having a plurality of electrode fingers formed in the case where λ is the propagation wavelength of the basic surface acoustic wave, between one end face and the electrode finger of the positive electrode or the negative electrode closest to it. The distance in the propagation direction of the surface acoustic wave is (m + 1 /
2) λ (m = 0, 1, 2,...), And the distance in the propagation direction of the surface acoustic wave between the other end face and the electrode finger of the closest positive electrode or negative electrode is (n + 1). / 2) λ
(N = 0, 1, 2,...).

The distance in the propagation direction of the surface acoustic wave between one end face and the electrode finger of the closest positive electrode or negative electrode, and the distance between the other end face and the electrode finger of the closest positive or negative electrode. By setting the distance in the propagation direction of the surface acoustic wave between them, the phase of the end-face reflected wave becomes the same as the phase of the main wave, so that the main wave is not adversely affected by the end-face reflected wave. Wave conversion efficiency is further improved.

The resonator according to claim 5 of the present invention is characterized in that the end face has a surface roughness of 0 to 0.2 μm. With such a surface roughness, the end face reflected wave is effectively reflected by the input-side converter and the output-side converter.

According to a sixth aspect of the present invention, in the resonator, the piezoelectric substrate is made of a single crystal material. The end face can be satisfactorily mirror-polished by using such a single crystal material.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave filter device and a resonator according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a surface acoustic wave filter device according to the present invention. An input-side converter 2, a shield electrode 3, and an output-side converter 4 are sequentially formed on the surface of a quartz substrate 1 that is a single crystal material along the propagation direction of surface acoustic waves.

The input-side converter 2 includes a positive electrode 5 and a negative electrode 6.
And a short-circuit type floating electrode 7 disposed between the electrode fingers of the positive electrode 5 and the negative electrode 6. The width of the electrode finger in the propagation direction of the surface acoustic wave of the positive electrode 5, the negative electrode 6, and the short-circuit type floating electrode 7 is set to λ / 12, respectively.
Set to. Here, λ is the wavelength of the basic surface acoustic wave. The electrode fingers of the positive electrode 5 and the negative electrode 6 are formed at a pitch of λ, and the center distance between the electrode finger of the positive electrode 5 and the electrode finger of the negative electrode 6 adjacent thereto is set to λ / 2. Further, the electrode finger of the short-circuit type floating electrode 7 is shifted by λ / 12 from the intermediate position between the electrode finger of the positive electrode 5 and the electrode finger of the negative electrode 6 adjacent thereto to the upstream side in the propagation direction of the surface acoustic wave. To enhance the unidirectionality based on the asymmetric structure. In the present embodiment, the number of electrodes of the input-side converter 2 is set to, for example, 4
Although the number of pairs is set to 0, the logarithm can be set to an optimum condition as appropriate according to the required filter characteristics.

The output converter 4 also includes a positive electrode 8 and a negative electrode 9.
And a short-circuit type floating electrode 10 disposed between the electrode fingers of the positive electrode 8 and the negative electrode 9.
The width of the electrode finger in the propagation direction of the surface acoustic wave of each of the positive electrode 8, the negative electrode 9, and the short-circuit type floating electrode 10 is λ /
Set to 12. Here, λ is the wavelength of the basic surface acoustic wave. Each electrode finger of the positive electrode 8 and the negative electrode 9 is formed at a pitch of λ, and the center distance between the electrode finger of the positive electrode 8 and the electrode finger of the adjacent negative electrode 9 is set to λ / 2. Further, the electrode finger of the short-circuit type floating electrode 10 is shifted from the intermediate position between the electrode finger of the positive electrode 5 and the electrode finger of the negative electrode 6 adjacent thereto by λ / 12 toward the downstream side in the propagation direction of the surface acoustic wave. To enhance the unidirectionality based on the asymmetric structure. In the present embodiment, the number of pairs of electrodes of the input-side converter 2 is set to, for example, 40 pairs.

In the present embodiment, the end face 1 of the quartz substrate 1
1 and 12 are mirror-polished, and the distance in the propagation direction of the surface acoustic wave between the input-side transducer 2 and the end face 11 of the quartz substrate 1 adjacent thereto is set to (k + ／) λ (k = 0, 1,
2,. . . ), And the distance in the propagation direction of the surface acoustic wave between the output-side converter 4 and the end face 12 of the quartz substrate 1 adjacent thereto is (l + ／) (l = 0, 1, 2,...) Λ. And The surface roughness of the end faces 11 and 12 is 0 to 0.2 μm.
And

The operation of the embodiment will be described. End face 1
The reflected waves reflected by the input-side converter 2
The distance in the direction of propagation of the surface acoustic wave between the end surface 11 and the distance in the direction of propagation of the surface acoustic wave between the output-side converter 4 and the end surface 12 is set to an integral multiple of the wavelength of the basic surface acoustic wave. Is added, the phase becomes the same as the phase of the main wave, and the main wave is not adversely affected by the end-face reflected wave, but the conversion efficiency of the surface acoustic wave is further improved.

FIG. 2 is a diagram showing an embodiment of the resonator according to the present invention. This resonator is periodically formed on the quartz substrate 21 at a pitch of λ, where λ is the propagation wavelength of the basic surface acoustic wave, and the width in the propagation direction of the surface acoustic wave is λ / Positive electrode 22 having twelve electrode fingers
Similarly, a plurality of electrode fingers are formed periodically on the quartz substrate at a pitch of λ, and the width of the surface acoustic wave in the propagation direction is λ / 12, and each electrode finger is in contact with the electrode finger of the positive electrode 22. and negative electrodes 23 respectively located with a center distance of λ / 2.

In this embodiment, the end face 2 of the quartz substrate 21
4 and 25 are mirror-polished, and the distance in the direction of propagation of the surface acoustic wave between the end face 24 and the electrode finger 26 of the positive electrode 22 closest to the end face 24 is (m +）) λ (m = 0, 1,
2,. . . ), And the distance in the propagation direction of the surface acoustic wave between the end face 25 and the electrode finger 27 of the positive electrode 22 closest to the end face 25 is (l + ／) (l = 0, 1, 2,...) Λ. I do. In addition, the surface roughness of the end faces 24 and 25 is 0 to 0.2 μm.
And

The operation of the embodiment will be described. End face 2
The reflected waves reflected by the end faces 2 and 25 are the distance in the propagation direction of the surface acoustic wave between the end face 24 and the electrode finger 26 and the end face 2
Since the distance in the propagation direction of the surface acoustic wave between 5 and the electrode finger 27 is set to a distance obtained by adding half the wavelength to an integral multiple of the wavelength of the basic surface acoustic wave, the phase is the same as the phase of the main wave. The main wave is not adversely affected by the end face reflected wave, but the conversion efficiency of the surface acoustic wave is further improved.

The present invention is not limited to the above-described embodiment, and many modifications and variations are possible. For example,
The input side converter and the output side converter of the surface acoustic wave filter device can be any conventionally known converters. The present invention can be applied to a resonator having another structure.

Furthermore, although a quartz substrate is used as the piezoelectric substrate, it may be made of another single crystal material such as lithium borate (Li ₂ B ₄ O ₇ ).

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a surface acoustic wave filter device according to the present invention.

FIG. 2 is a diagram showing an embodiment of a resonator according to the present invention.

[Explanation of symbols]

1,21 crystal substrate, 2 input side converter, 3 shield electrode, 4 output side converter, 5,8,22 positive electrode, 6,6
9,23 Negative electrode, 7,10 Short-circuit type floating electrode, 11,
12, 24, 25 end face, 26, 27 electrode finger

Claims (6)

[Claims] 1. A piezoelectric substrate having an end surface mirror-polished, and an electric signal formed on the piezoelectric substrate and externally inputted,
An input-side converter for converting the electric signal into a surface acoustic wave,
An output-side converter formed on the surface of the quartz substrate and converting a surface acoustic wave excited by the input-side converter into an electric signal, and outputting the electric signal to the outside; Assuming that the propagation wavelength of the wave is a wave, the distance in the propagation direction of the surface acoustic wave between the input-side converter and the end face of the piezoelectric substrate adjacent thereto is (k + ／) λ (k =
0, 1, 2,. . . ), And the distance in the propagation direction of the surface acoustic wave between the output-side converter and the end face of the piezoelectric substrate adjacent thereto is (l + ／) (l = 0, 1,
2,. . . A) a surface acoustic wave filter device characterized by λ. 2. The surface acoustic wave filter device according to claim 1, wherein the surface roughness of said end face is 0 to 0.2 μm. 3. The surface acoustic wave filter device according to claim 1, wherein the piezoelectric substrate is made of a single crystal material. 4. A piezoelectric substrate having an end surface mirror-polished, a positive electrode having a plurality of electrode fingers formed on the piezoelectric substrate, and a negative electrode having a plurality of electrode fingers formed on the piezoelectric substrate. When λ is the propagation wavelength of the basic surface acoustic wave, the distance in the propagation direction of the surface acoustic wave between one end surface and the electrode finger of the closest positive electrode or negative electrode is (m + 1). / 2) λ
(M = 0, 1, 2,...), And the distance in the propagation direction of the surface acoustic wave between the other end face and the electrode finger of the closest positive electrode or negative electrode is (n +＋ １). λ (n =
0, 1, 2,. . . ). 5. The resonator according to claim 4, wherein said end face has a surface roughness of 0 to 0.2 μm. 6. The resonator according to claim 4, wherein said piezoelectric substrate is made of a single crystal material.