JPH1188109A - Surface acoustic wave filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove spurious waves except the surface acoustic wave, to eliminate a nonuniformity between chips in production and to attain improvement in reliability and yielding by coating a thin metal film on the whole rear side surface and the side surfaces of a piezoelectric substrate and perfectly permitting bulk wave to be grounded on a chip base surface or an end surface. SOLUTION: The piezoelectric substrate 1 of a surface acoustic wave filter is the one formed by a piezoelectric element provided with a piezoelectric effect and an input interdigital (counter interdigital shape) electrode 2 and an output interdigital electrode 3 are laminated. A ground electrode 4 is arranged between the electrodes 2 and 3 for the purpose that electromagnetic connection is directly prevented and a damper agent 5 for preventing the reflection of acoustic wave is coated on the outside of the electrodes 2 and 3. Surface roughening 7 to obtain a frosted glass state is executed on the rear side surface of the piezoelectric substrate 1 and the metallic thin film 6 is adhered by a conductive adhesive resin 9 so as to be coated. The metallic thin film 6 is adhered on a package 8 by the conductive adhesive resin 9.

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 utilizing surface acoustic waves, and more particularly, to preventing reflection of unnecessary waves by coating a metal thin film on the entire back surface and side surfaces of the device as a ground for the back surface of the device. A surface acoustic wave filter having improved characteristics outside the pass band.

[0002]

2. Description of the Related Art A surface acoustic wave filter that obtains a predetermined frequency characteristic by using a surface acoustic wave of a piezoelectric element is known.
FIG. 2 shows an example of such a conventional surface acoustic wave filter. A piezoelectric substrate 1 shown in the figure is a substrate made of a so-called piezoelectric element having a piezoelectric effect, on which an input interdigital (opposite comb-teeth) electrode 2 and an output interdigital electrode 3 are laminated.

The input interdigital electrode 2 has a pair of comb-tooth-shaped portions opposed to each other, and the cross width of the comb-tooth-shaped portions is appropriately weighted to form a so-called apodized interdigital electrode. Input interdigital electrode 2
And the output interdigital electrode 3 disposed through the surface acoustic wave pass band, a pair of comb-shaped portions are opposed to each other, and the intersecting width of the comb-shaped portions is constant, and the interdigital electrode 3 is a regular interdigital electrode. I have.

A ground electrode 4 is disposed between the input interdigital electrode 2 and the output interdigital electrode 3 in order to prevent direct electromagnetic coupling. Each of these electrodes is formed of an aluminum thin film. Damper agents 5, 5 for preventing reflection of elastic waves are applied to the outside of the input interdigital electrode 2 and the output interdigital electrode 3. On the back surface of the piezoelectric substrate 1, a surface frosted glass
And the back surface is packaged with a conductive adhesive 9.
Is pasted on.

[0005]

In the above-mentioned conventional surface acoustic wave filter, the adhesion of the conductive adhesive 9 tends to be uneven. In particular, the tendency increases as the size of the chip of the piezoelectric substrate 1 increases. If the bonding is uneven, bulk waves (longitudinal waves and transverse waves) propagated from the inside of the piezoelectric substrate 1 cannot be completely dropped to the ground, and as a result, out-of-band characteristics deteriorate. For example, a place where suppression outside the band is desired to be 40 dB is 35 dB. Such a phenomenon causes a variation between chips during mass production, which causes a problem of deteriorating the yield.

The present invention has been made in view of the above points, and an object of the present invention is to completely drop a bulk wave to the ground on the chip bottom face and end face,
It is an object of the present invention to provide a surface acoustic wave filter that does not deteriorate characteristics.

[0007]

A surface acoustic wave filter according to the present invention is provided with a pair of input interdigital electrodes and a pair of output interdigital electrodes opposite to each other on a surface of a piezoelectric substrate that propagates surface acoustic waves. In a surface acoustic wave filter in which a ground electrode is arranged between these electrodes, the entire back surface and side surfaces of the piezoelectric substrate are coated with a metal thin film.

Further, a surface acoustic wave filter according to the present invention comprises:
In a surface acoustic wave filter in which a pair of input interdigital electrodes and a pair of output interdigital electrodes are provided on the surface of a piezoelectric substrate that propagates a surface acoustic wave, a metal thin film is coated on the entire back surface of the piezoelectric substrate. The piezoelectric substrate is bonded to a package base via the metal thin film using a conductive adhesive.

Further, a surface acoustic wave filter according to the present invention has a pair of input interdigital electrodes and a pair of output interdigital electrodes provided on the surface of a piezoelectric substrate that propagates a surface acoustic wave. , A metal thin film is coated on the entire back surface and side surfaces of the piezoelectric substrate, and the piezoelectric substrate is bonded to a non-magnetic package base via the metal thin film using a conductive adhesive.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave filter according to an embodiment of the present invention will be described with reference to FIG. A piezoelectric substrate 1 shown in the figure is a substrate made of a so-called piezoelectric element having a piezoelectric effect, on which an input interdigital (opposite comb-teeth) electrode 2 and an output interdigital electrode 3 are laminated.

The input interdigital electrode 2 has a pair of comb-shaped portions opposed to each other, and the cross width of the comb-shaped portions is appropriately weighted to form a so-called apodized interdigital electrode. Input interdigital electrode 2
And the output interdigital electrode 3 disposed through the surface acoustic wave pass band, a pair of comb-shaped portions are opposed to each other, and the intersecting width of the comb-shaped portions is constant, and the interdigital electrode 3 is a regular interdigital electrode. I have.

A ground electrode 4 is disposed between the input interdigital electrode 2 and the output interdigital electrode 3 for the purpose of preventing direct electromagnetic coupling. Each of these electrodes is formed of an aluminum thin film. Damper agents 5, 5 for preventing reflection of elastic waves are applied to the outside of the input interdigital electrode 2 and the output interdigital electrode 3. On the back surface of the piezoelectric substrate 1, a surface frosted glass
, And the metal thin film 6 is adhered and coated with the conductive adhesive 9. The metal thin film 6 is attached to the package 8 with a conductive adhesive 9.

A bulk wave generated near the input interdigital electrode 2 on the front surface of the piezoelectric substrate 1 passes through the inside of the substrate, repeatedly reflects on the front and back surfaces, reaches the output interdigital electrode 3, and adversely affects the inside and outside of the band. , Piezoelectric substrate 1
Can be prevented by the surface storm 7, the metal thin film 6, and the conductive adhesive 9 on the back surface. In particular, it is effective for the adverse effect of the degree of suppression appearing in the out-of-band characteristics. In addition, the characteristic deterioration due to the external influence is improved by the metal thin film 6. That is, the grounding effect is improved. As described above, since there is no influence from the outside, a non-magnetic material can be used for the package 8.

The reflection of the surface acoustic wave on the end face of the piezoelectric substrate 1 is prevented by dampers 5 and 5 made of silicon rubber as in the prior art.

Although the embodiment is constituted as described above, the invention is not limited to this. For example, by coating a metal thin film on the side surface of the piezoelectric substrate, the reflection of the bulk wave on the side surface is prevented and the characteristics are improved. Can be better.

[0016]

According to the surface acoustic wave filter of the present invention, unnecessary waves (particularly, bulk waves) other than surface acoustic waves are effectively removed, and variations between chips in manufacturing are eliminated.
The reliability and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a side view showing a schematic configuration of a surface acoustic wave filter according to an embodiment of the present invention.

FIG. 2 is a side view showing an example of a conventional surface acoustic wave filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 2 Input interdigital electrode 3 Output interdigital electrode 4 Ground electrode 5 Damper agent 6 Metal thin film 7 Surface storm 8 Package 9 Conductive adhesive

Claims (3)

[Claims] 1. A surface acoustic wave in which a pair of input interdigital electrodes and a pair of output interdigital electrodes are provided facing each other on the surface of a piezoelectric substrate that propagates surface acoustic waves, and an earth electrode is arranged between the electrodes. A surface acoustic wave filter, wherein a metal thin film is coated on the entire back surface and side surfaces of the piezoelectric substrate. 2. A surface acoustic wave filter in which a pair of input interdigital electrodes and a pair of output interdigital electrodes are provided on the surface of a piezoelectric substrate that propagates a surface acoustic wave in opposition to each other. A surface acoustic wave filter comprising a thin film coated thereon and a piezoelectric substrate bonded to a package base via the metal thin film using a conductive adhesive. 3. A surface acoustic wave filter having a pair of input interdigital electrodes and a pair of output interdigital electrodes opposed to each other on a surface of a piezoelectric substrate that propagates a surface acoustic wave. A surface acoustic wave filter, wherein a metal thin film is coated on the substrate, and the piezoelectric substrate is bonded to the non-magnetic package base through the metal thin film using a conductive adhesive.