JP3301168B2 - Surface acoustic wave filter and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonator type surface acoustic wave filter having a one-terminal pair surface acoustic wave resonator (hereinafter referred to as a "surface acoustic wave resonator"), and more particularly, to a surface acoustic wave filter caused by a pyroelectric effect in a manufacturing process. The present invention relates to a surface acoustic wave filter having means for preventing the electrode from being destroyed.

2. Description of the Related Art Surface acoustic wave filters have hitherto been used for video filters typified by IF filters for televisions and videos, but recently, taking advantage of their small size and inexpensive characteristics, mobile telephones and mobile phones are widely used. Demand for communication filters is rapidly increasing.

In a surface acoustic wave filter, a comb-shaped electrode formed on a piezoelectric substrate for exciting a surface acoustic wave and a comb-shaped electrode for reception are paired. Conventionally, a plurality of comb-shaped electrodes are connected in multiple stages. Many transversal surface acoustic wave filters have been used.

On the other hand, recently, by using a surface acoustic wave resonator having reflectors on both sides of an excitation comb-shaped electrode to resonate a surface acoustic wave, insertion loss is greatly improved and an external matching circuit is added. Promising resonator-type surface acoustic wave filters have become unnecessary.

However, the next generation of mobile phones and mobile phones
1.5GH _Z and 1.9GH has been considered for use in quasi-microwave band of _Z, further miniaturized excitation comb-shaped electrodes as the frequency increases are easily destroyed by specific pyroelectric effect in the piezoelectric crystal Become.

Therefore, there is a need for the development of a surface acoustic wave filter having means for preventing the electrodes from being destroyed due to the pyroelectric effect.

[0007]

2. Description of the Related Art FIG. 6 is a plan view showing an example of a conventional resonator type surface acoustic wave filter, and FIG. 7 is a view showing a mechanism of electrode breakdown caused by a pyroelectric effect.

In FIG. 6, the resonator type surface acoustic wave filter has a surface acoustic wave resonator 2 formed on a substrate 1 made of a piezoelectric crystal, and a surface acoustic wave resonator 2 formed of a metal film.
Is composed of a pair of excitation comb electrodes 21, reception comb electrodes 22, and reflectors 23 which form a pair.

Excitation comb electrode 21 and reception comb electrode 22
The electrode fingers 24 are combined so that one electrode finger 24 enters between the other electrode fingers 24, and a reflector composed of open or short-circuited comb electrodes, strip array electrodes, etc. on both sides of the comb electrodes 21 and 22 23 are located.

Assuming that the wavelength of the surface acoustic wave is λ, all the electrode fingers 24 in the conventional resonator type surface acoustic wave filter are λ / 4.
Insulation band 25 having a conductor width of
And an insulating band interposed between the comb-shaped electrodes 21 and 22 and the reflector 23
26 also has a width of λ / 4.

A phenomenon peculiar to a device using a substrate made of such a piezoelectric crystal is the destruction of a conductor pattern due to a pyroelectric effect. Hereinafter, the mechanism of electrode breakdown in a surface acoustic wave filter using a piezoelectric crystal for a substrate will be described in detail with reference to FIG.

The piezoelectric crystal has the property that the magnitude of spontaneous polarization changes in response to the crystal temperature, and charges are generated on the substrate surface. However, when the temperature change is relatively slow, it is generated on the substrate surface. The charge is gradually neutralized by the charge in the atmosphere and does not cause any trouble.

However, when the temperature changes rapidly, neutralization by charges in the atmosphere cannot follow the generation of charges, and excessive charges accumulate on the substrate surface. When a conductor pattern is formed on the substrate, Has a potential corresponding to the amount of charge in that region.

When the temperature changes rapidly, a temperature difference is generally likely to occur between the central portion and the peripheral portion of the substrate, causing a difference in the amount of electric charge accumulated on the substrate surface, and as shown in FIG. comb electrodes 21 and 22, and reflectors 23 are potential [Phi ₁ respectively different, [Phi _2, having [Phi _3.

The potential Φ _{1 of one} comb-shaped electrode 21 and the reflector
If the potential Φ ₂ of the other comb-shaped electrode 22 is significantly different from the potential Φ ₃ of the other comb-shaped electrode 22, as shown by a broken line in FIG.
In addition, a large number of equipotential lines 27 exist in the insulating band 25 sandwiched between the electrode fingers 24 of the comb-shaped electrode 22.

In particular, in the insulating band 25 between the electrode finger 24 of the comb-shaped electrode 21 and the electrode finger 24 of the comb-shaped electrode 22 adjacent to the reflector 23, all the equipotential lines 27 are affected by the reflector 23, as shown in FIG. As described above, the interval between the equipotential lines 27 is closer to the electrode fingers 24 of the comb-shaped electrode 22 than the other insulating bands 25.

If the potential gradient ΔΦ / ΔL between the electrode finger 24 of the comb-shaped electrode 21 and the electrode finger 24 of the comb-shaped electrode 22 is within an allowable value, no dielectric breakdown occurs, but the interval between the equipotential lines 27 becomes tight. When the potential gradient ΔΦ / ΔL exceeds the allowable value, insulation breaks and the comb-shaped electrode
The 22 electrode fingers 24 are destroyed.

[0018]

In the conventional resonator type surface acoustic wave filter, the width of the electrode finger and the width of the insulating band are fixed to λ / 4 in order to stabilize the characteristics. However, as the band used becomes shorter, the width of the insulating band becomes smaller and more likely to cause dielectric breakdown due to the pyroelectric effect.

In addition, as the operating band becomes shorter, the conductor width of the electrode finger becomes smaller, and the adhesion of the metal film to the substrate is further reduced. As a result, even if the potential difference between the conductors due to the pyroelectric effect is small, there is a problem that the electrode fingers are broken and the yield is reduced.

It is an object of the present invention to provide a surface acoustic wave filter having means for preventing the electrodes from being destroyed due to the pyroelectric effect.

[0021]

FIG. 1 is a plan view showing a surface acoustic wave filter according to the present invention. The same object is denoted by the same symbol throughout the drawings.

The above object is achieved by combining a comb electrode for excitation having electrode fingers and a comb electrode for reception so that one electrode finger enters between the other electrode fingers, and a surface acoustic wave resonator having reflectors on both sides of the comb electrode. In the surface acoustic wave filter formed on the piezoelectric substrate, the comb-shaped electrode 31 for excitation and the comb-shaped electrode 3
This is achieved by the surface acoustic wave filter of the present invention in which the dummy electrode 38 connected to the reflector 33 and the conductor 33 via the conductor is formed on the piezoelectric substrate 1.

[0023]

In FIG. 1, for example, by forming a dummy electrode connected to a comb electrode for excitation and a comb electrode for reception through a conductor, the position of the center of gravity of the comb electrode is shifted in the peripheral direction, resulting from the pyroelectric effect. The potential difference between the conductor patterns can be made substantially zero.

As a result, the problem that the electrode fingers are destroyed by the potential difference between the conductors due to the pyroelectric effect and the yield is reduced is solved. That is, it is possible to realize a surface acoustic wave filter including means for preventing the electrodes from being destroyed due to the pyroelectric effect.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a plan view showing another embodiment of the present invention,
FIG. 3 is a plan view showing a modification of the embodiment, FIG. 4 is a plan view showing another embodiment of the present invention, and FIG. 5 is a perspective view showing a manufacturing method according to the present invention.

In the surface acoustic wave filter according to the present invention, a surface acoustic wave resonator 3 is formed on a substrate 1 made of a piezoelectric crystal as shown in FIG. And a comb electrode 32 for reception, a comb electrode 32 for reception, and a reflector 33.

Exciting comb electrode 31 and receiving comb electrode 32
The electrode fingers 34 are combined so that one electrode finger 34 enters between the other electrode fingers 34, and a reflector composed of open or short-circuited comb electrodes, strip array electrodes, etc. on both sides of the comb electrodes 31, 32. 33 are arranged.

As means for preventing electrode breakdown due to the pyroelectric effect, at least one dummy electrode is provided along the periphery of the substrate 1.
The dummy electrode 38 is connected to, for example, the excitation comb electrode 31 and the reception comb electrode 32, which are likely to generate a potential difference with the reflector 33.

As described above, for example, by forming the dummy electrode connected to the excitation comb electrode and the reception comb electrode via a conductor, the position of the center of gravity of the comb electrode is shifted in the peripheral direction, resulting in the pyroelectric effect. The resulting potential difference between the conductor patterns can be made substantially zero.

As a result, the problem that the electrode fingers are destroyed by the potential difference between the conductors due to the pyroelectric effect and the yield is reduced is solved. That is, it is possible to realize a surface acoustic wave filter including means for preventing the electrodes from being destroyed due to the pyroelectric effect.

In another embodiment of the surface acoustic wave filter according to the present invention, as shown in FIG. 2, instead of the dummy electrode 38 formed in the above embodiment, an equipotential line 37 is provided as means for preventing electrode breakdown due to the pyroelectric effect. Electrode finger adjacent to the dense insulation band 35
34 conductor width is widened.

That is, as shown in FIG. 7B, in the insulating band 25 between the electrode finger 24 of the comb-shaped electrode 21 and the electrode finger 24 of the comb-shaped electrode 22 adjacent to the reflector 23, the equipotential is influenced by the reflector 23. The line 27 is biased toward the electrode finger 24 of the comb-shaped electrode 22, and the interval between the equipotential lines 27 is narrower than in the other insulating bands 25.

However, by increasing the width of the electrode finger 24 of the comb-shaped electrode 22 and increasing the influence of the comb-shaped electrode 22 on the equipotential line 27, the bias is corrected, and the interval between the equipotential lines 27 is changed to other insulating bands.
This is equivalent to the interval at 25, and it is possible to prevent electrode destruction due to the pyroelectric effect.

Therefore, as shown in FIG. 2, the conductor width of the electrode finger 34 facing the electrode finger 34 of the comb-shaped electrode 31 adjacent to the reflector 33 via the insulating band 35 is wider than the conductor width of the other electrode fingers 34. By doing so, the equipotential lines 37 in the insulating band 35 biased by the influence of the reflector 33 are corrected.

By widening the conductor width of the electrode finger 34 in this manner, the bias of the equipotential lines 37 is formed, thereby preventing electrode breakdown due to the pyroelectric effect, and increasing the adhesion force of the electrode finger 34 to the substrate 1 to prevent electrode breakdown. Separation of the electrode fingers 34 from the substrate 1 can be eliminated.

FIG. 3 shows a modification of the above-described embodiment, in which an insulating band 35 is provided.
The electrode finger 34 facing the electrode finger 34 of the comb-shaped electrode 31 adjacent to the reflector 33 is divided into two, so that the insulating band 35 biased by the influence of the reflector 33 as in the previous embodiment is formed. Potential line
37 can be corrected.

In another embodiment of the surface acoustic wave filter according to the present invention, as shown in FIG. 4, an equipotential line is provided near the reflector 33 as a means for preventing electrode breakdown due to the pyroelectric effect.
The width of the insulating band 35 where the density is 37 is made wider than other insulating bands 35 where the equipotential lines 37 are coarse.

As described above, when the width is increased as a means for preventing electrode destruction, an electrode finger 34 and an insulating band 35 which are out of the standard of λ / 4 are formed. However, the comb-shaped electrodes 31 and 32 have many electrode fingers 34, and the characteristics are not affected even if the outer electrode fingers 34 and the insulating band 35 deviate from the standard.

When the electrode fingers 34 are enlarged as shown in FIG. 2 or when the electrode fingers 34 are divided as shown in FIG. 3, the characteristics required for the surface acoustic wave filter are affected by conforming to the standard of λ / 4. Thus, it is possible to prevent electrode destruction due to the pyroelectric effect without giving any effect.

Electrode destruction due to the pyroelectric effect is caused when excessive charge is accumulated on the surface when the temperature of the piezoelectric substrate rapidly changes during manufacturing. Therefore, it is possible to prevent the change in the substrate temperature during the manufacturing process of the surface acoustic wave filter by making it slow.

As shown in FIG. 5, the method of manufacturing a surface acoustic wave filter according to the present invention comprises attaching a wafer 4 made of a piezoelectric crystal to a metal plate 5 and forming at least comb-shaped electrodes 31 and 32 and a reflector.
The operation from the formation of 33 to the mounting of the cut individual pieces 6 on the carrier 7 is performed.

Since the cut individual piece 6 has a small heat capacity, when heated during drying or the like, the temperature rapidly changes and the electrode is destroyed by the pyroelectric effect. By sticking the individual pieces 6 to the metal plate 5 having a large heat capacity, a rapid change in the temperature is eliminated, and the destruction of the electrodes can be prevented.

[0043]

As described above, according to the present invention, it is possible to provide a surface acoustic wave filter having means for preventing the electrodes from being destroyed due to the pyroelectric effect.

[Brief description of the drawings]

FIG. 1 is a plan view showing a surface acoustic wave filter according to the present invention.

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

FIG. 3 is a plan view showing a modification of the embodiment.

FIG. 4 is a plan view showing another embodiment of the present invention.

FIG. 5 is a perspective view showing a manufacturing method according to the present invention.

FIG. 6 is a plan view showing an example of a conventional resonator-type surface acoustic wave filter.

FIG. 7 is a diagram showing a mechanism of electrode destruction caused by a pyroelectric effect.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric substrate 3 Surface acoustic wave resonator 4 Wafer 5 Metal plate 6 Piece 7 Carrier 21, 22 Comb electrode 23 Reflector 24 Electrode finger 25 Insulation band 27 Equipotential line 31, 32 Comb electrode 33 Reflector 34 Electrode finger 35 Insulation Obi 37 Equipotential line 38 Dummy electrode

Continuation of the front page (56) References JP-A-61-181215 (JP, A) JP-A-59-200513 (JP, A) JP-A-58-13009 (JP, A) JP-A-5-90861 (JP, A) JP-A-5-37276 (JP, A) JP-A-4-24311 (JP, A) JP-A-2-70114 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) H03H 9/145 H03H 3/08

Claims (2)

(57) [Claims] 1. A surface acoustic wave resonator having a comb-like electrode having electrode fingers and a comb-like electrode for reception such that one electrode finger is located between the other electrode fingers, and a reflector is provided on both sides of the comb electrode. In a surface acoustic wave filter formed on a piezoelectric substrate, as a means for preventing electrode breakdown due to the pyroelectric effect, the conductor width of the electrode finger adjacent to the insulating band where the equipotential lines are dense A surface acoustic wave filter characterized by being wider than an electrode finger adjacent to another rough insulating band. 2. A comb-shaped excitation electrode having electrode fingers and a comb electrode for reception are combined so that one electrode finger enters between the other electrode fingers, and a surface acoustic wave resonator having reflectors on both sides of the comb electrode is provided. In the surface acoustic wave filter formed on the piezoelectric substrate, the equipotential lines sandwiched by the electrode fingers are sandwiched by the electrode fingers as a means for preventing electrode breakdown due to the pyroelectric effect. A surface acoustic wave filter characterized in that equipotential lines are made wider than a coarse insulation band.