JPH09205341A - Surface acoustic wave filter - Google Patents

Abstract

(57) [Abstract] (Modified) [PROBLEMS] To increase the amount of attenuation outside the pass band of a surface acoustic wave filter to reduce the number of manufacturing steps and improve the yield. SOLUTION: Two sets 2 and 3 of at least one pair of crossing electrodes are provided on a piezoelectric substrate, one set of the crossing electrodes is a normal type electrode having a uniform crossing length, and the other set 3 is an apodizing type. As an electrode, a shield electrode 4 is arranged between the regular type electrode 2 and the apodized type electrode 3, and a sound absorbing material 5 is applied to the end portion orthogonal to the propagation direction of the surface acoustic wave so that the surface acoustic wave propagates in the propagation direction. The parallel ends include the bus bar portion of the shield electrode 4, and the reflection is prevented by applying the sound absorbing materials 5 and 6 up to the maximum intersection of the apodizing electrode 3 and the inside of the shield electrode 4,
The attenuation characteristics outside the pass band of the surface acoustic wave filter are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving the attenuation characteristic outside the pass band of a surface acoustic wave filter.

[0002]

2. Description of the Related Art In the prior art, two sets of at least one pair of crossing electrodes are provided on a piezoelectric substrate, and one set of crossing electrodes is a normal type electrode having a uniform crossing length, and another set of crossing electrode fingers. In order to prevent surface acoustic wave reflection at the end face of a surface acoustic wave filter with an apodized electrode whose crossing length is changed with respect to the array direction, and a shield electrode is arranged between the regular electrode and the apodized electrode. For the end portion orthogonal to the propagation direction of the surface acoustic wave, the sound absorbing material is applied so as not to contact the metal portion such as the electrode at the end portion. Further, with respect to the end surface parallel to the propagation direction of the surface acoustic wave, the sound absorbing material has been applied to the end portion which does not come into contact with the metal portion such as the electrode and the bus bar existing in parallel with the end portion.

[0003]

However, two sets of at least one pair of crossing electrodes are provided on the piezoelectric substrate, one set of the crossing electrodes is a normal type electrode having a uniform crossing length, and another set of the crossing electrodes is provided. In the surface acoustic wave filter in which the shield electrode is arranged between the regular type electrode and the apodized type electrode, the apodized type electrode whose crossing length is changed with respect to the arrangement direction of the electrode fingers is used to prevent the reflection of the surface acoustic wave at the end face. It is effective to apply a sound absorbing material to the end portion orthogonal to the propagation direction of surface acoustic waves so as not to contact metal parts such as electrodes, but electrodes and bus bars at the end portion parallel to the propagation direction of surface acoustic waves. Although the sound absorbing material was applied to the end that did not contact the metal part such as the metal surface, reflection was not prevented at the end parallel to the propagation direction of the surface acoustic wave, so the surface acoustic wave filter was affected by the reflected wave. Has a good attenuation characteristic outside the pass band of There is a problem to say that can not be obtained in.

[0004]

Means for Solving the Problem Two sets of at least one pair of crossing electrodes are provided on a piezoelectric substrate, one set of the crossing electrodes is a normal type electrode having a uniform crossing length, and another set of the crossing electrode fingers. In the surface acoustic wave filter with an apodized electrode with a change in the crossing length with respect to the array direction, and a shield electrode arranged between the regular electrode and the apodized electrode, the surface acoustic wave filter has an end portion orthogonal to the propagation direction of the surface acoustic wave. As usual, apply a sound absorbing material so that it does not come into contact with metal parts such as electrodes, and at the end parallel to the propagation direction of surface acoustic waves, including the bus bar part of the shield electrode, up to the maximum intersection of the apodizing electrode (however, Parallel to the propagation direction of the surface acoustic wave by applying a sound absorbing material to the end of the shield electrode parallel to the propagation direction of the surface acoustic wave so that it does not enter the intersection, that is, the propagation path of the surface acoustic wave. Sufficient prevention of reflections at sharp edges Out-of-band attenuation characteristic passage of the reflected wave influences the surface acoustic wave filter so are alleviated is favorably obtained problem is resolved.

[0005]

FIG. 1 is a plan view showing an embodiment of the present invention. Two pairs of at least one pair of cross electrodes are provided on the piezoelectric substrate 1,
The one set of cross electrodes is a normal type electrode 2 having a uniform cross length, and the other is a set of apodized electrodes 3 having different cross lengths in the arrangement direction of the cross electrode fingers. This is a surface acoustic wave filter in which a shield electrode 4 is arranged between mold electrodes 3.

A method for preventing the reflection of surface acoustic waves on the end surface is as follows.
The sound absorbing material 5 is applied so as not to come into contact with metal parts such as the electrodes at the ends. In addition, at the end portion parallel to the propagation direction of the surface acoustic wave, including the bus bar portion of the shield electrode 4, up to the maximum intersection of the apodizing electrode 3 (however, do not enter the intersection or the surface acoustic wave propagation path). ) By applying the sound absorbing material 6 to the end of the shield electrode 4 parallel to the propagation direction of the surface acoustic wave, the reflection of the end parallel to the propagation direction of the surface acoustic wave is sufficiently prevented. .

FIG. 2 is a plan view of an embodiment showing the application range of the sound absorbing material 6 applied to the end portion parallel to the propagation direction of the surface acoustic wave of the present invention. The application range of the sound absorbing material 6 applied to the end portion parallel to the propagation direction of the surface acoustic wave is such that the maximum application width 7 from the end surface to the inside includes the bus bar portion of the shield electrode 4 and the maximum of the apodizing electrode 3. The sound absorbing material 6 is applied to the inside of the shield electrode 4 in the range up to the intersection (however, so as not to enter the propagation path of the surface acoustic wave), to the end parallel to the propagation direction of the surface acoustic wave. To do. The minimum coating width 8 is
The inside is not applied to the inside of the shield electrode 4 and is the range up to the bus bar, and the outside (end face side) may be applied to the center of the bus bar.

Therefore, as shown in the figure, the maximum coating width 7 of the sound absorbing material 6 is from the maximum intersection of the apodizing electrodes 3 in the shield electrode 4 to the end face of the piezoelectric substrate 1, and the minimum coating width 8 is the shield electrode 4. It is up to half the shield electrode side of the bus bar. The application dimension of the applied sound absorbing material 6 in the traveling direction of the surface acoustic wave is 10λ or more in width when the center of the shield electrode 4 and the center of the applied sound absorbing material 6 are substantially aligned with each other.

FIG. 3 shows the characteristics of the surface acoustic wave filter. The dotted line shows the characteristics when the sound absorbing material 6 is not applied to the end portion parallel to the propagation direction of the surface acoustic wave of the present invention, and the solid line shows the sound absorbing material 6 at the end portion parallel to the propagation direction of the surface acoustic wave of the present invention. The following shows the characteristics in the case of applying.

Compared to the solid line showing the attenuation characteristics of the filter after the sound absorbing material 6 is applied, the dotted line showing the attenuation characteristics of the filter not coated with the sound absorbing material is not much different in the pass band, but in the characteristics outside the pass band. A clear difference is observed, and generally, the amount of attenuation after applying the sound absorbing material (shown by the solid line in FIG. 3) is larger than that after not applying the sound absorbing material (shown by the dotted line in FIG. 3), or Is equivalent. Particularly noteworthy is the difference in the amount of attenuation immediately outside the pass band, that is, in the vicinity of the pass band, and the solid line attenuates significantly. The sound absorbing material used here may be an insulating resin such as an epoxy resin or a silicone resin, as long as it can absorb the unwanted wave. Further, in the case of a resin containing a metal (silver or the like), it is applied on the bus bar so as not to short-circuit the cross electrodes.

[0011]

As described above, according to the present invention, the attenuation characteristic outside the pass band of the surface acoustic wave filter can be improved. Therefore, the production of the surface acoustic wave filter having the strict specifications for the attenuation characteristic outside the pass band of the surface acoustic wave filter. In terms of handling, we were able to significantly reduce the number of processes, stabilize quality and accuracy, and improve yield.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a surface acoustic wave filter of the present invention.

FIG. 2 is a plan view showing details of the embodiment of the present invention.

FIG. 3 is a graph showing a surface acoustic wave filter characteristic of the present invention.

[Explanation of symbols]

 1 Piezoelectric substrate 2 Regular electrode 3 Apotize type electrode 4 Shield electrode 5 and 6 Sound absorbing material

Claims (2)

[Claims] 1. A piezoelectric substrate is provided with two sets of at least one pair of crossing electrodes, one set of the crossing electrodes is a normal type electrode having a uniform crossing length, and another set of crossing electrode fingers is arranged in the arrangement direction. On the other hand, an apodized electrode having a changed crossing length was provided, a shield electrode was arranged between the regular electrode and the apodized electrode, and a sound absorbing material was applied to the end of the piezoelectric substrate in the surface acoustic wave propagation direction. In the surface acoustic wave filter, a sound absorbing material is applied near the bus bar of the shield electrode at an end portion of the shield electrode parallel to the propagation direction of the surface acoustic wave of the piezoelectric substrate. 2. The maximum coating width from the end surface parallel to the propagation direction of the surface acoustic wave toward the inside includes the bus bar portion of the shield electrode and extends to the inside of the shield electrode up to the maximum intersection of the apodize electrode. The minimum coating width is from the bus bar on the shield electrode side to the center of the bus bar on the outer side (end face side), and the coating size in the traveling direction of the surface acoustic wave is in the range of 10λ or more in the center of the shield electrode. The surface elastic filter according to claim 1, wherein a sound absorbing material is applied.