JPH07240658A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To suppress the ripple within a pass band by groove mode spurious wave to minimum and to improve insertion loss by making the surface opposed to the bus bar opposed to a reflector have a specified angle. CONSTITUTION:Bus bars 1a and 1b opposed to the reflector formed on the surface of a piezoelectric substrate are disposed in a wedge shape so as to avoid mutural parallel of the both bus bars with an angle of alpha for the line in the longitudinal direction and in the vertical direction of the electrode of each reflector, and a wedge electrode is disposed between these opposed bus bars at prescribed space. When these disposals are performed, the horizontal mode surface acoustic wave reflected on the bus bar is reflected in the direction shifted by 2.alpha from an advancing route and does not attain the opposed bus bar even if the surface acoustic wave of the horizontal mode is generated. As a result, a standing wave is not generated. Therefore, the generation of the spurious wave of the horizontal mode can be prevented.

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 device having improved characteristics by changing an electrode structure.

[0002]

2. Description of the Related Art Conventionally, an interval between facing bus bars of a transducer and a reflector is generally an integral multiple of a wavelength λ of a used frequency.

[0003]

However, in the method of the prior art, since the distance between the opposing bus bars of the reflector is generally an integral multiple of the wavelength λ of the used frequency, the surface acoustic wave of the transverse mode is not generated. Since standing waves are generated and spurious due to the surface acoustic wave in the transverse mode is generated, ripples are generated in the pass band of the filter and the insertion loss of the filter is increased.

[0005]

In order to solve the above-mentioned problems, the angle .alpha.
The surface acoustic wave of the transverse mode reflected by the surface of the opposing bus bar of the reflector is prevented from reaching the bus bar of the opposing reflector by setting the constant distance between the bus bars of the opposing reflector. The above problems have been solved by preventing the occurrence of standing waves.

[0006]

【Example】

(Embodiment 1) FIG. 1 shows an electrode pattern of a first embodiment of the present invention. In the embodiment shown in FIG. 1, the opposing bus bars 1a and 1b of the reflector formed on the surface of the piezoelectric substrate are arranged such that the two bus bars are at an angle of α with respect to a line in a direction perpendicular to the longitudinal direction of the reflector electrode. Avoid being parallel,
The electrodes are arranged in a wedge shape, and the comb-shaped electrodes are arranged at predetermined intervals between the opposing bus bars. By doing so, even if a transverse mode surface acoustic wave is generated, the transverse mode surface acoustic wave reflected by the bus bar is 2
It is reflected in a direction shifted by α and does not reach the opposing bus bar. Therefore, no standing wave is generated, and therefore spurious in the transverse mode can be prevented.

(Embodiment 2) FIG. 2 shows an electrode pattern according to a second embodiment of the present invention. In the embodiment shown in FIG. 2A, the opposing bus bars 2a, 2a of the reflector formed on the surface of the piezoelectric substrate are shown.
b are arranged in parallel with each other, and comb-shaped electrodes are arranged at predetermined intervals between the opposing bus bars. FIG. 2B shows an enlarged view of the slit shown in FIG. If the left and right dimensions of the slit are L ₁ and L ₂ , respectively, the relationship of L ₁ <L ₂ is selected so that the intersection angle between the parallel line of the opposing bus bar and the line in contact with the bus bar of the slit matches α degrees. To do. In this way, even if a transverse mode surface acoustic wave is generated as in the first embodiment, the transverse mode surface acoustic wave reflected by the bus bar is 2..alpha.
It is reflected in a direction shifted by just the distance and does not reach the opposite bus bar. For this reason, no standing wave is generated, so that the occurrence of transverse mode spurious can be prevented.

Note that α is represented by the following equation. α = tilt angle ± 5 ° For example, in the case of a substrate material of ST cut made of quartz, the power flow angle is about 10 degrees. Therefore, α = 10 ± 5 ° = 5
It becomes ~ 15 °. It was found that in the case of other piezoelectric substrates, although the tilt angle is different, if α is in the range of ± 5 degrees, sufficiently good characteristics can be obtained. FIG. 3 is a graph showing the relationship between the ripple characteristic in the pass band of the surface acoustic wave device and the α angle. FIG. 4 is a graph showing the relationship between the insertion loss characteristic of the surface acoustic wave device and the α angle. When the α angle is changed, the minimum value of the ripple in the pass band and the minimum value of the insertion loss are almost the same, and the power flow angle of the board is ± 5 ° in both cases.
Is consistent with.

[0009]

EFFECTS OF THE INVENTION According to the present invention, by providing the facing surfaces of the opposing busbars of the reflector with an angle α, the transverse mode surface acoustic waves reflected on the facing surfaces of the busbars of the reflector are reflected by the opposing surfaces. By preventing the standing waves from reaching the busbars of the reflectors by preventing them from reaching the busbars of the opposing reflectors, the surface acoustic wave in the transverse mode is generated between the pair of opposing busbars. Since standing waves can be prevented from waving, there is an effect that ripples in the pass band due to transverse mode spurious can be minimized and insertion loss can be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing an example in which a pair of opposing bus bars of a reflector of the present invention are inclined by α degrees.

FIG. 2 (a) is a plan view showing an example in which the surfaces of the slits of a pair of opposing bus bars of the reflector of the present invention are inclined by α degrees. FIG. 2B is an enlarged view of FIG.

FIG. 3 is a graph showing a relationship between α angle and ripple.

FIG. 4 is a graph showing the relationship between α angle and insertion loss.

[Explanation of symbols]

 1a, 1b Busbar 2a, 2b Busbar 3 Sudden electrode

Claims (3)

[Claims] 1. A surface acoustic wave device in which a plurality of reflector electrodes are arranged in parallel on the surface of a piezoelectric substrate, and a pair of bus bars connecting the reflector electrodes to each other are arranged at both ends of the reflector electrodes. At, the bus bar is α with respect to a line (the traveling direction of the surface acoustic wave) perpendicular to the longitudinal direction of the reflector electrode.
A surface acoustic wave device characterized by being inclined at an angle. 2. A surface acoustic wave in which a plurality of reflector electrodes are arranged in parallel on a surface of a piezoelectric substrate, and bus bars connecting the reflector electrodes to each other are arranged in parallel to both ends of the reflector electrode. In the device, a surface acoustic wave device, wherein a slit surface of the bus bar is inclined by α degrees with respect to a line (a traveling direction of a surface acoustic wave) perpendicular to a longitudinal direction of the reflector electrode. 3. The surface acoustic wave device according to claim 1, wherein the piezoelectric substrate is an ST cut quartz substrate, and an α angle is 5 to 15 degrees.