JP2712842B2 - Surface acoustic wave device 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 surface acoustic wave device utilizing an SH type surface wave and a method of manufacturing the same.
The present invention relates to a surface acoustic wave device provided with a structure for suppressing spurious due to a bulk wave.

[0002]

2. Description of the Related Art Surface waves propagating through a piezoelectric substrate include SH type surface waves whose displacement is mainly a displacement in a direction perpendicular to the propagation direction, such as a BGS wave and a Love wave. FIG. 2 shows a conventional surface acoustic wave resonator using a BGS wave. In FIG. 2, the surface acoustic wave resonator 1 has a structure in which an interdigital transducer composed of comb electrodes 3 and 4 is formed on the upper surface of a piezoelectric substrate 2 made of a piezoelectric material such as piezoelectric ceramics. The comb electrodes 3 and 4 have a plurality of electrode fingers 3a and 4a interposed between each other. Note that the arrow P indicates the polarization axis.

In the surface acoustic wave resonator 1, if an AC electric field is applied from the comb electrodes 3 and 4, only a displacement in a direction perpendicular to the surface wave propagation direction X, that is, a BGS wave having only a transverse wave component is excited. .

[0004]

However, the above-described surface acoustic wave resonator 1 has a problem that not only SH waves but also bulk waves are generated, and unnecessary spurious due to the bulk waves appears in a considerable size. Was. In commercializing the surface acoustic wave device, it is usual to provide a cavity on the interdigital transducer and on the surface acoustic wave propagation path so as not to hinder the excitation and propagation of the surface acoustic wave. As a result, when assembling as a product, it is necessary to provide the above-mentioned cavity, so that there is a problem that the production process and the package structure are complicated, and the cost is high.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a surface acoustic wave device capable of effectively suppressing spurious due to a bulk wave and simplifying a package structure, and a method of manufacturing the same.

[0006]

Means for Solving the Problems The first invention of the present application is an SH
A surface wave device using a surface wave type, a piezoelectric substrate, wherein a least one interdigital transducer formed on the surface of the piezoelectric substrate, substantially of the piezoelectric substrate end face on the surface wave propagation direction A step extending outward is formed at the intermediate height position, and an end portion below the step is rougher than an upper end portion,
A gel layer or a resin layer having a Shore hardness of 30 or less is provided so as to cover an upper surface of the piezoelectric substrate and an end surface portion above the step.

Further, a second invention of the present application is a method of manufacturing a surface acoustic wave device using an SH type surface wave, comprising the steps of preparing a piezoelectric mother substrate, and providing a plurality of interdigital transducers on an upper surface of the piezoelectric mother substrate. And applying a gel or resin having a Shore hardness of 30 or less from the upper surface of the piezoelectric mother substrate, applying the resin to the upper surface of the piezoelectric substrate and in the grooves, and curing the resin. Dividing the piezoelectric mother substrate into individual surface acoustic wave devices along the groove.

[0008]

The energy of the SH type surface wave is concentrated on a layer near the surface of the piezoelectric substrate. On the other hand, the energy of the bulk wave is dispersed throughout the thickness of the piezoelectric substrate.
According to the present invention, the step is formed at an almost intermediate height position of the end face of the piezoelectric substrate existing in the direction of propagation of the surface wave, and the end face portion below the step is roughened. , The bulk wave is scattered, and the spurious due to the reflection at the end face of the bulk wave can be reduced. Moreover, since the resin layer is provided on the end face of the piezoelectric substrate so as to cover the end face portion above the step, the reflection of the bulk wave on the end face portion above the step is also suppressed, thereby further spurious. Is reduced.

It has been confirmed by the present inventor that in a surface acoustic wave device using an SH type surface acoustic wave, the output of the surface acoustic wave does not attenuate much even if a resin layer is provided on the interdigital transducer. Therefore, in the present invention, the resin layer is provided so as to cover the upper surface of the piezoelectric substrate, and it is not necessary to provide a cavity on the upper surface of the piezoelectric substrate, so that the package structure of the surface acoustic wave device can be simplified. .

Further, according to the manufacturing method of the present invention, it is possible to obtain a surface acoustic wave device capable of reducing spurious due to a bulk wave and simplifying a package structure as described above. Moreover, a groove extending from the upper surface side of the piezoelectric mother substrate to the intermediate depth position is formed, and the piezoelectric mother substrate is simply divided along the groove, and the end surface portion below the step of the end surface of the piezoelectric substrate is roughened. can do. Further, since the resin layer is provided only by applying and curing the resin in a state where the groove is formed in the piezoelectric mother substrate, spurious due to a bulk wave is reduced as described above, and the package structure is simplified. The surface acoustic wave device can be mass-produced by a relatively simple process.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing non-limiting embodiments of the present invention with reference to the drawings. In this embodiment, first, a disk-shaped piezoelectric mother substrate for obtaining a plurality of surface acoustic wave devices is prepared. Next, a plurality of interdigital transducers for forming a plurality of surface acoustic wave devices are formed on the upper surface of the piezoelectric mother substrate. The interdigital transducer is formed by depositing and etching an electrode material on the entire upper surface of the piezoelectric mother substrate. The formation of the interdigital transducer may be performed by other thin film forming techniques such as printing or sputtering.

Next, as shown in FIGS. 3A and 3B, the upper surface 11a of the piezoelectric mother substrate 11 is
A plurality of grooves 12 extending from the side to the intermediate depth position are formed. Note that, in FIGS. 3A and 3B, a plurality of sets of interdigital transducers formed on the upper surface of the piezoelectric mother substrate 11 are omitted for ease of illustration.

As shown in an enlarged sectional view of FIG. 3B, the groove 12 is configured such that the bottom has a certain width. This is inevitably formed because the cutting edge of the dicing saw has a certain thickness. The grooves 12 in FIG. 3A are provided for dividing the piezoelectric mother substrate 11 in a later step for each surface acoustic wave device. Therefore, the groove 12 is formed at the boundary between the individual surface acoustic wave devices.

As shown in FIG. 4, after forming the groove 12, a resin 13 is applied on the upper surface of the piezoelectric mother substrate 11 and cured. As shown in the enlarged plan view of FIG.
Except for 14d, the process is performed over the entire upper surface 11a of the piezoelectric mother substrate 11. Therefore, as shown in the enlarged cross-sectional view in FIG. 4, the resin layer 13 is applied so as to reach the inside of the groove 12 and is cured.

The resin may be a gel resin having a penetration of 10 to 200 as measured by a penetration measuring method according to JIS K2220, or Shore hardness or JIS K6301.
A resin having a Shore hardness of 30 or less as measured by a hardness measurement method is used. Specifically, a silicon resin, an epoxy resin, or the like can be given. In order to prevent the resin layer 13 from being applied to the portions 14a to 14d of the electrodes, a mask is used for the portions 1a to 1d of the electrodes.
In this state, the resin may be temporarily fixed on the upper surfaces 4a to 14d, and a resin may be applied to the entire upper surface 11a of the piezoelectric substrate 11, or may be printed on a screen masked on portions 14a to 14d of the electrodes.

Next, the piezoelectric mother substrate 11 provided with the resin layer 13 is divided along the grooves 12. This division is performed by applying an external force to the portion of the piezoelectric substrate 11 where the groove 12 is provided, by utilizing the small thickness of the portion where the groove 12 is provided, and dividing the portion. As a result, the surface acoustic wave device 15 of the embodiment shown in the sectional view of FIG. 1 is obtained. Referring to FIG. 1, in a surface acoustic wave device 15, an interdigital transducer having interdigital electrodes 3a and 4a interposed between each other is formed on an upper surface 16a of a piezoelectric substrate 16, and the upper surface of the interdigital transducer is A resin layer 13 is provided to cover. Therefore, the surface acoustic wave device 15
In the case where is packaged as a product, there is no need to separately provide a cavity above the interdigital transducer, and the package structure can be simplified, for example, by simply performing an exterior resin dip.

Further, steps 17a and 17b extending outward are provided substantially at an intermediate height of the end face of the piezoelectric substrate 16 located in the surface wave propagation direction. This step 17
Reference numerals a and 17b denote the bottoms of the grooves 12 described above. That is, along the groove 12, the piezoelectric mother substrate 11
Are obtained, the steps 17a, 17b are formed in the individual surface acoustic wave devices 15, and the steps 17a, 17b are formed.
End portions 18a and 18b below 17b are formed as rough surfaces. On the other hand, the end surface portions 19a and 19b above the steps 17a and 17b are surfaces that appear when the groove 12 is formed by the dicing saw, and thus the end surface portions 18a and 19b are formed.
a and 18b are formed so as to have a smoother surface.

In the surface acoustic wave device 15 of this embodiment, steps 17a and 17b are provided on the end face located in the direction in which the surface wave propagates, and the lower end face portions 18a and 18b are roughened. Therefore, the lower end face portions 18a, 18
At b, the bulk wave can be scattered. Moreover, since the resin layer 13 is provided so as to cover the upper end portions 19a and 19b, the upper end portion can absorb bulk waves. Therefore, spurious due to the bulk wave can be effectively reduced.

Next, specific experimental results will be described. First, as the conventional surface acoustic wave resonator shown in FIG.
A plurality of electrode fingers each having a width of 20 μm are formed on the upper surface of a rectangular piezoelectric substrate 2 made of ZT and having a size of 1.0 × 1.6 × 1.2 mm.
And a surface acoustic wave resonator 1 formed with a pitch between electrode fingers of 80 μm. The impedance-frequency characteristic of this conventional surface acoustic wave resonator 1 is shown by a solid line A in FIG.

Next, a surface acoustic wave resonator formed in the same manner as in the above embodiment was manufactured, and the impedance-frequency characteristics were measured. The result indicated by the broken line B in FIG. 6 was obtained. For comparison, the impedance-frequency characteristics of a surface acoustic wave resonator configured exactly the same as in the example except that the resin layer 13 was not provided were measured. The results shown were obtained.

As is clear from the impedance-frequency characteristics shown by the solid line A, the broken line B and the dashed line C in FIG.
According to the present embodiment, spurious can be effectively reduced. Further, as is apparent from FIG. 6, even if the resin layer 13 is provided on the piezoelectric substrate, the peak-to-valley ratio, that is, the resonance resistance / anti-resonance resistance ratio does not decrease.

In the above embodiment, the groove 1 is formed after the interdigital transducer is formed on the piezoelectric mother substrate.
Although the interdigital transducer 2 is formed, the interdigital transducer may be formed on the piezoelectric mother substrate after the groove 12 is formed. Furthermore, in the above embodiment, the lower end face portions 18a, 18b protrude outward due to the steps 17a, 17b. Conversely, the upper end face portions 19a, 19b may be formed so as to protrude outward. Good.

The present invention is applicable not only to the surface reflection type surface acoustic wave resonator shown in FIG. 2 but also to a surface acoustic wave device having another structure such as a surface acoustic wave device having a reflector. Can be applied.

[0024]

According to the present invention, a step is formed at an intermediate height position of the end face of the piezoelectric substrate, and the end face portion below the step is rougher than the upper end face portion. ,
Further, a gel is formed so as to reach the end face portion above the step.
Alternatively, since a resin layer having a Shore hardness of 30 or less is provided, spurious due to reflection at the end face of the bulk wave can be effectively reduced. Further, since the above resin layer is provided on the upper surface of the piezoelectric substrate, it is not necessary to provide a cavity on the upper surface of the piezoelectric substrate, so that the package structure can be simplified, thereby reducing the cost of the surface acoustic wave device. And it becomes possible.

Further, according to the manufacturing method of the present invention, it is possible to efficiently mass-produce a surface acoustic wave device in which the spurious is reduced as described above and which can simplify the package structure, from the piezoelectric mother substrate. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a surface acoustic wave device according to an embodiment.

FIG. 2 is a perspective view showing a conventional surface acoustic wave resonator using a BGS wave.

FIG. 3A is a perspective view of a piezoelectric mother substrate used in an embodiment, and FIG. 3B is a partially cutaway enlarged sectional view of the piezoelectric mother substrate.

FIG. 4 is a partially cutaway enlarged cross-sectional view showing a piezoelectric mother substrate provided with a resin layer.

FIG. 5 is a partially enlarged plan view showing, on an enlarged scale, an upper surface of a piezoelectric mother substrate provided with a resin layer.

FIG. 6 is a diagram illustrating impedance-frequency characteristics of the surface acoustic wave devices of the example, the conventional example, and the comparative example.

[Explanation of symbols]

 Reference Signs List 13 resin layer 15 surface acoustic wave device 16 piezoelectric substrate 16a upper surface 17a, 17b step 18a, 18b lower end surface portion 19a, 19b upper end surface portion

Claims (2)

(57) [Claims] 1. A surface acoustic wave device using an SH type surface wave, comprising: a piezoelectric substrate; and at least one interdigital transducer formed on a surface of the piezoelectric substrate, wherein the interdigital transducer exists in a surface wave propagation direction. A step that protrudes outward is formed at almost the middle height position of the end face of the piezoelectric substrate,
The gel or Shore hardness 30 is set so that an end surface portion below the step is rougher than an upper end surface portion and covers the upper surface of the piezoelectric substrate and the end surface portion above the step. A surface acoustic wave device comprising the following resin layer. 2. A method of manufacturing a surface acoustic wave device using an SH type surface wave, comprising: providing a piezoelectric mother substrate; and forming a plurality of interdigital transducers on an upper surface of the piezoelectric mother substrate. Forming a groove from the upper surface side of the piezoelectric mother substrate to a substantially intermediate depth position and at a boundary separating the individual surface acoustic wave devices; and forming a gel or shore hardness 30 on the upper surface of the piezoelectric mother substrate. Less than
Applying a lower resin, applying a resin to the upper surface of the piezoelectric mother substrate and in the grooves, and curing the resin layer to form a resin layer; dividing the piezoelectric mother substrate into individual surface acoustic wave devices along the grooves And manufacturing the surface acoustic wave device.