JPH05343945A - Surface acoustic wave filter - Google Patents

Abstract

PURPOSE:To improve the frequency response characteristic or the like and also to make the chip size small by applying an absorbing material absorbing an undesired surface acoustic wave onto wiring. CONSTITUTION:A sound absorbing member 1 is applied to aluminum wires 4a, 4d, 4e placed in a direction of crossing an undesired propagation wave to the left and right to a surface acoustic wave generated from an interdigital type electrode 2a. The wiring is extended up to the sound absorbing material 1 at a part A especially. The sound absorbing material suppresses a reflected wave reflected from the aluminum wiring 1 in crossing over the propagation wave.

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.

[0002]

2. Description of the Related Art Conventionally, surface acoustic wave filters are VHF, U.
It is used as a bandpass filter for extracting only a specific frequency band of the HF band. FIG. 2 shows (a) a front view and (b) a characteristic view of a conventional surface acoustic wave filter. In FIG. 2A, an interdigital electrode 2a that excites a surface acoustic wave by an electric signal, an interdigital electrode 2b that absorbs the surface acoustic wave and converts it into an electric signal, and an interdigital electrode Shield electrode 3 that suppresses electrostatic coupling and electromagnetic coupling
And a sound absorbing material 1 for absorbing surface acoustic waves propagating in unnecessary directions
And an aluminum wiring 4 for inputting and outputting an electric signal and a bonding pad 6.

Next, the operation of this surface acoustic wave filter will be described. When an electric signal is input from the aluminum wirings 4a and 4b, a surface acoustic wave is excited by the interdigital electrode 2a and propagates left and right. The wave propagating to the left is absorbed by the sound absorbing material 1. A part of the wave propagating to the right is converted into an electric signal by the interdigital electrode 2b and output by the aluminum wirings 6d and 6e. The wave that has not been converted into an electric signal further propagates to the right and is absorbed by the sound absorbing material 1.

However, if an aluminum wiring pattern is present in front of the sound absorbing material, reflection occurs at, for example, the aluminum wiring B shown in the figure. Then, a reflected wave that returns to the left is generated, and this reflected wave interferes with a normally propagating wave to deteriorate the characteristics.

[0005]

As described above, in the surface acoustic wave filter of the conventional example, the aluminum wiring that traverses the propagation path of the surface acoustic wave causes reflection, which is shown in FIG. 2 (b) by the reflected wave. As described above, there is a problem that the frequency response characteristic of the pass band is disturbed, and the out-of-band attenuation amount is usually about 30 dB at a value of 40 dB or more, which is a problem.

[0006]

SUMMARY OF THE INVENTION A surface acoustic wave filter according to the present invention comprises an interdigital electrode formed on a piezoelectric substrate for generating and absorbing a surface acoustic wave, and an electric signal is input / output to / from the interdigital electrode. In a surface acoustic wave filter including a pattern wiring for bonding, a bonding pad, and a sound absorbing material that absorbs the surface acoustic wave propagating in an unnecessary direction, the sound absorbing material is a pattern wiring in a direction crossing a propagation path of the surface acoustic wave. It is provided to cover the part.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1A is a front view and FIG. 1B is a characteristic view of the present embodiment. In FIG. 1A, the aluminum wiring on the propagation path of the surface acoustic wave, particularly the portion indicated by A, extends the aluminum wiring 4d to the location of the sound absorbing material 1, and the extended portion is covered with the sound absorbing material.

Next, the operation of this surface acoustic wave filter will be described. When an electric signal is input from the aluminum wirings 4a and 4b, a surface acoustic wave is excited by the interdigital electrode 2a and propagates in the left-right direction. The wave propagating to the left is absorbed by the sound absorbing material 1. The wave propagating to the right is generated by the interdigital electrode 2
It is converted into an electric signal by b and is output by the aluminum wirings 6d and 6e. The wave that has not been converted to an electric signal further propagates to the right and is almost absorbed by the sound absorbing material 1. The characteristic diagram at that time is shown in FIG. This sound absorbing material 1
Is usually applied to the base of the aluminum wiring portion with silicon resin, but other sound absorbing materials may be used for the silicon resin.

[0009]

As described above, according to the present invention, the reflected wave of the surface acoustic wave on the aluminum wiring is suppressed.
As shown in (b), the frequency response characteristic of the pass band is flat, and the out-of-band attenuation amount is improved to 40 dB or more. In addition, by applying the sound absorbing material on the electric wiring, there is an effect that the chip size can be reduced without requiring a dedicated place for the sound absorbing material.

[Brief description of drawings]

FIG. 1A is a front view and FIG. 1B is a characteristic view of a surface acoustic wave filter according to an embodiment of the present invention.

FIG. 2A is a front view and FIG. 2B is a characteristic diagram of a surface acoustic wave filter of a conventional example.

[Explanation of symbols]

 1 Sound Absorbing Material 2 Interdigitated Electrodes 3 Shield Electrode 4 Aluminum Wiring 6 Bonding Pad

Claims (2)

[Claims] 1. A cross-finger electrode formed on a piezoelectric substrate for generating and absorbing surface acoustic waves, a pattern wiring for inputting and outputting an electric signal to the cross-finger electrode, a bonding pad, and propagating in an unnecessary direction. In a surface acoustic wave filter including a sound absorbing material for absorbing and blocking the surface acoustic wave, the sound absorbing material is provided so as to cover a portion of the pattern wiring in a direction traversing the propagation path of the surface acoustic wave. And a surface acoustic wave filter. 2. The surface acoustic wave filter according to claim 1, wherein the pattern wiring in a direction traversing the propagation path of the surface acoustic wave is extended and the extended portion is covered with the sound absorbing material.