JPH04239214A - Acoustic wave device - Google Patents

Abstract

PURPOSE:To simplify a package structure without changing the resonance characteristic of the surface acoustic wave resonator by providing a resin layer so as to cover an interdigital transducer. CONSTITUTION:An acoustic wave resonator element 1 is provided with a piezo-electric substrate 2 polarized in the direction shown by an arrow P, and a pair of comb-shaped electrodes 3 and 4 are formed on the upper surface of the piezo-electric substrate 2, and the comb-shaped electrodes 3 and 4 are provided with plural electrode fingers to be thinned out each other. A BGS wave is excited in the direction shown by an arrow X by applying AC electric field between the comb-shaped electrodes 3 and 4, and this BGS wave is constructed so as to be reflected by face ends 2a and 2b. Since the interdigital transducer composed of the comb-shaped electrodes 3 and 4 are covered by a gelatinous or a less-than-80-Shore-hardness resin layer 5, voids complicating the structure in producing the surface acoustic wave can be omitted.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to SH
This invention relates to a surface wave device that utilizes a type of surface wave.

0002

2. Description of the Related Art Conventionally, in surface acoustic wave devices, it has been considered taboo to attach an elastic body to the surface acoustic wave propagation path and onto the interdigital transducer. this is,
This is because the surface acoustic waves are absorbed by the elastic body, and the output is attenuated. Therefore, when configuring the surface wave element as a component, a cavity is provided on the surface wave propagation path and on the interdigital transducer so as not to interfere with the propagation of the surface acoustic wave. As a result, the package structure of the surface acoustic wave device has become complicated and expensive.

[0003] On the other hand, Japanese Patent Application Laid-open No. 108551/1983,
In a surface wave filter using BGS waves, a structure in which the cavity is omitted has been disclosed. That is, in this prior art, an insulating rubber that is sticky and hardens by heating or moisture absorption in the atmosphere at room temperature and pressure is placed on the interdigital transducer and on the surface wave propagation path.
Thereby, a structure is disclosed in which the cavity is omitted. Here, it is shown that even if the above-mentioned insulating rubber is placed on the interdigital transducer and on the surface wave propagation path, the output of the BGS wave is not attenuated. The above-mentioned insulating rubber, which is in the form of mucus and hardens by heating or moisture absorption in the atmosphere at room temperature and pressure, is as follows:
Specifically, only moisture curable silicone rubber is shown.

0004

[Problem to be solved by the invention] However, BGS
In a surface acoustic wave resonator that uses waves, if the interdigital transducer and the surface wave propagation path are coated with silicone rubber, the resonance resistance and propagation loss will become considerably high, which will change the resonance characteristics and filter characteristics. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surface acoustic wave device using SH type surface waves, which not only simplifies the package structure by coating an interdigital transducer with an elastic body, but also improves resonance characteristics. The purpose is to provide something with a structure that does not easily fluctuate.

[0006]

[Means for Solving the Problems] In view of the fact that simply providing insulating silicone rubber on the interdigital transducer and on the surface wave propagation path in a resonator using BGS waves causes deterioration in resonance resistance, the present inventors investigated the resonance characteristics of various surface acoustic wave devices using BGS waves by coating the interdigital transducer and/or the surface wave propagation path with various resins. As a result, in surface acoustic wave devices that utilize not only BGS waves but also other SH type surface waves whose displacement is mainly perpendicular to the surface wave propagation direction, such as Love waves,
We have found that when an interdigital transducer is coated with a specific resin layer, the output does not attenuate. Furthermore, after examining various resins, we found that not only silicone resin, but also urethane resin, epoxy resin, etc., did not cause attenuation of the surface wave output, and that any resin could be used. However, in order to suppress fluctuations in resonance characteristics, the inventors have discovered that it is necessary to use a gel-like resin or a resin with a Shore hardness of 30 or less, and have accomplished the present invention.

That is, the present invention is a surface acoustic wave device that utilizes an SH type surface wave, in which the displacement is mainly in a direction perpendicular to the surface wave propagation direction, among surface waves propagating in a piezoelectric substrate. a piezoelectric substrate and at least one interdigital transducer formed on the piezoelectric substrate;
It is characterized by comprising a gel-like resin layer or a resin layer having a Shore hardness of 30 or less provided to at least cover the interdigital transducer.

[0008] Resins that can be used in the present invention include silicone resins, urethane resins, and epoxy resins. In addition, "gel-like" refers to a state with flexibility that cannot be measured by the Shore hardness measurement method, and specifically, it is measured based on the JIS K2220 penetration measurement method. Refers to those whose penetration is in the range of about 100 to 40. On the other hand, Shore hardness is defined as ASTM
Hardness measured by D676 is shown.

[0009] The above hardness and penetration were measured after the resin used was cured at a temperature of 70 to 150°C for 1 to 2 hours. In the present invention, it is necessary to use the above-mentioned gel-like resin layer or a resin layer with a Shore hardness of 30 or less.If the interdigital transducer is covered with a resin layer with a Shore hardness of more than 30, the resonance resistance will be significantly higher. This is because changes in resonance characteristics cannot be ignored.

[0010] The resin layer may be provided to at least cover the interdigital transducer, and may be formed over the entire surface of the piezoelectric substrate on which the interdigital transducer is formed. However, if the surface wave propagation path is also coated with the resin layer, the output will be slightly attenuated, which is not preferable. More preferably, the resin layer covers not only the surface of the piezoelectric substrate on which the interdigital transducer is formed;
It is applied so as to reach the side surface of the piezoelectric substrate. In this way, by coating the side surfaces of the piezoelectric substrate with a resin layer, reflection of bulk waves and the like on the side surfaces of the piezoelectric substrate can be suppressed, thereby reducing spurious waves.

[0011]

[Operation] In the present invention, at least the top of the interdigital transducer is coated with a gel-like resin layer or a resin layer with a Shore hardness of 30 or less. Therefore, when commercializing a surface acoustic wave device, a cavity which becomes a factor of complicating the structure can be avoided. Can be omitted. Furthermore, since the interdigital transducer is coated with the above-mentioned specific resin layer, not only is output attenuation less likely to occur, but also resonance characteristics are less likely to change.

0012

Embodiment FIG. 2 shows a surface acoustic wave resonator used in an embodiment of the present invention. The surface acoustic wave resonator 1 is constructed using a piezoelectric substrate 2 polarized in the direction of arrow P. On the top surface of the piezoelectric substrate 2, a set of comb-shaped electrodes 3, 4 are provided.
is formed. The comb-teeth electrodes 3 and 4 have a plurality of electrode fingers interposed with each other. By applying an alternating electric field between the comb-teeth electrodes 3 and 4, a BGS wave is excited in the direction of the arrow X, and the BGS wave is reflected by the end faces 2a and 2b.

In this embodiment, a resin layer 5 is formed on the upper surface of the surface acoustic wave resonator 1, as shown in a cross-sectional view in FIG. 1, to constitute a surface acoustic wave resonator 6. That is, the resin layer 5 is provided so as to cover the interdigital transducer composed of the comb-shaped electrodes 3 and 4. As the resin layer 5, gel-like silicone rubber (Toray) with various penetration degrees was used.
Manufactured by Dow Corning Silicone Co., Ltd., product name SE4
440, SH1851, JCR6110) and silicone rubbers of various hardnesses (manufactured by Toshiba Silicone Corporation, trade names TSE3431H, TSE3251) to construct a surface acoustic wave resonator 6, and its resonance resistance was measured. Penetration and hardness were measured in the following manner. (1) Measuring method of penetration…JIS K2220
or the measurement method based on JIS K2207 (in the case of this measurement method, the value is converted to the same value as that obtained with the measurement method based on JIS K2220). (2) Shore hardness measurement method…ASTM D6
76, or a measurement method based on JIS K6301 (measured values by this measurement method approximately correspond to Shore hardness).

[0014] In addition, each of the above-mentioned gel-like silicone rubbers and the silicone rubbers whose hardness was measured had a hardness of 70 to 150.
After curing at a temperature of 1 to 2 hours, the penetration or hardness was measured. The results are shown in FIGS. 3 and 4. Note that the resonance resistance of the surface acoustic wave resonator 1 without the resin layer 5 is 5Ω.

As is clear from FIGS. 3 and 4, gel-like silicone rubber with a penetration degree in the range of 100 to 40 and silicone rubber with a Shore hardness of 30 or less have a resonance resistance of 11Ω or less, and the resin layer It can be seen that there is not much difference from the resonance resistance of the surface acoustic wave resonator, which is 5Ω, when the surface acoustic wave resonator is not provided. On the other hand, it can be seen that when silicone rubber with a hardness exceeding 30 is used, the resonance resistance becomes significantly higher.

Further, in the above embodiment, the resin layer 5 was made of silicone rubber such as gel silicone rubber or two-component silicone foam, but it may be made of other resins such as urethane resin or epoxy resin. Good too. FIG. 5 shows a surface acoustic wave resonator according to another embodiment of the invention. Surface wave device 1
1, two sets of interdigital transducers 13 and 14 are formed on a piezoelectric substrate 12, and a shield electrode 10 is formed between the interdigital transducers 13 and 14. That is, the surface acoustic wave device 11 of this embodiment includes two sets of interdigital transducers 1.
3 and 14. The SH type surface wave excited by the interdigital transducer 13 or 14 is propagated in the direction of arrow B in FIG.

In the surface wave device 11 shown in FIG. 5, the resin layer is formed on the surfaces of the interdigital transducers 13 and 14.
That is, it is applied to the areas indicated by broken lines C and D. Note that the resin layer may be formed on the entire upper surface of the piezoelectric substrate 12. However, when a resin layer is formed on the surface wave propagation path shown by arrow E, the output of the surface wave is attenuated. Therefore, preferably, the resin layer is formed in the remaining region avoiding the surface wave propagation path.

More preferably, the resin layer
It is provided so as to reach the side surfaces 12a and 12b of 2. By forming the resin layer so as to extend to the side surfaces 12a and 12b in this way, it is possible to suppress the reflection of bulk waves on the side surfaces 12a and 12b, thereby reducing spurious waves. Next, an example of configuring the surface acoustic wave resonator shown in FIG. 1 as a product will be described with reference to a manufacturing method.

First, as shown in a perspective view in FIG. 6, long metal frames 21 and 22 are prepared. A plurality of terminal portions 23 and 24 are formed from the long metal frame 21 so as to extend toward the metal frame 22 side. Further, terminal parts 25 and 26 are formed so as to extend from the metal frame 22 to the metal frame 21 side, and at the tips of the terminal parts 25 and 26, a rectangular element fixing part 2 having a certain area is provided.
7 is provided. The surface acoustic wave resonator element 1 shown in FIG. 2 is fixed to the upper surface of the element fixing part 27 via a conductive adhesive.

Next, as shown in FIG. 7, a resin layer 5 is applied to the upper surface of the surface acoustic wave resonator 1 and cured. As the resin layer 5, the above-mentioned specific silicone rubber is used. At the stage where the resin layer 5 is cured, the surface acoustic wave resonator 1, the element fixing part 27, etc. are molded with resin, and then, as shown in FIG.
Cut along the dashed-dotted lines F and G. In this way, a surface acoustic wave resonator component 28 shown in a perspective view in FIG. 8 can be obtained. Note that as the reference numbers of the terminals in the obtained surface wave resonator component 28, the reference numbers of the terminal portions provided on the metal frames 21 and 22 described above will be used.

FIG. 9 shows a cross section taken along the dashed line HH in FIG. As is clear from FIG. 9, in this surface acoustic wave resonator component 28, a resin layer 5 is formed on the upper surface of the surface acoustic wave resonator element 1.
is provided, and the outside thereof is covered with a resin mold part 29. Therefore, since there is no need to provide a cavity above the portion of the surface acoustic wave resonator where the interdigital transducer is constructed, it is possible to manufacture the surface acoustic wave resonator through relatively simple steps using the resin molding technique described above.

[0022] In addition to the structure in which the resin mold part 29 is formed as described above, products packaged using other structures such as a hermetic seal case can also be used.
The present invention can be applied.

[0023]

[Effects of the Invention] According to the present invention, since the resin layer made of the above-mentioned specific material is provided so as to cover at least the upper part of the interdigital transducer, the resonance characteristics of the surface acoustic wave resonator are changed. The package structure can be simplified. Therefore, the manufacturing process of the surface acoustic wave device can be simplified and costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a surface acoustic wave resonator according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a surface acoustic wave resonant element used in the example.

FIG. 3 is a diagram showing the resonance resistance of a surface acoustic wave resonator using a gel-like resin layer.

FIG. 4 is a diagram showing the resonance resistance of a surface acoustic wave resonator using silicone rubber.

FIG. 5 is a schematic diagram showing a surface acoustic wave device having another structure to which the present invention is applied.

FIG. 6 is a perspective view showing the surface acoustic wave resonator of FIG. 2 fixed on a metal frame.

FIG. 7 is a perspective view showing a state in which a resin layer is provided on the upper surface of the surface wave resonant element.

FIG. 8 is a perspective view showing a surface acoustic wave resonator component in which a resin molded portion is formed.

9 is a cross-sectional view of the surface acoustic wave resonator component shown in FIG. 8. FIG.

[Explanation of symbols]

1…Surface wave resonant element 2 Piezoelectric substrate 3, 4… Comb tooth electrode 5…Resin layer 6…Surface wave resonator

Claims (1)

[Claims] Claim 1: Of the surface waves propagating in the piezoelectric substrate, S whose displacement is mainly in the direction perpendicular to the surface wave propagation direction.
A surface acoustic wave device using H-type surface waves, comprising a piezoelectric substrate, at least one interdigital transducer formed on the piezoelectric substrate, and a gel-like or A surface wave device comprising: a resin layer having a Shore hardness of 30 or less.