JP2012015767A - Elastic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic wave device suppressing deterioration of frequency characteristics caused by bulk waves without making the backside of a piezoelectric substrate coarse.SOLUTION: An elastic wave device 10 comprises: (a) a piezoelectric substrate 12 on whose one main surface 12a IDTs 14 and 16 are formed, and through which an elastic wave excited by the IDT 14 propagates; and (b) an additional member 20 joined with the other main surface 12b of the piezoelectric substrate 12. The additional member 20 is configured so that an incidence component, which propagates toward the other main surface 12b of the piezoelectric substrate 12 in the piezoelectric substrate 12 and is incident on the additional member 20 from the other main surface 12b, in the bulk wave excited by the IDT 14 is irregularly reflected within the additional member 20.

Description

  The present invention relates to an acoustic wave device, and more particularly, to an acoustic wave device using a surface acoustic wave or a boundary acoustic wave propagating through a piezoelectric substrate.

  The acoustic wave device excites a surface acoustic wave or a boundary acoustic wave by an interdigital transducer (IDT) formed on the surface of a piezoelectric substrate having piezoelectricity. At this time, the frequency characteristics may be deteriorated by a bulk wave of unnecessary vibration generated in the IDT.

  For example, as schematically shown in the cross-sectional view of FIG. 7, an unnecessary bulk wave excited by the input side IDT 14 of the acoustic wave device 10x propagates toward the back surface 12b of the piezoelectric substrate 12 as indicated by an arrow 30, After being reflected by the back surface 12b, it propagates as indicated by the arrow 32 and is received by the output-side IDT 16, thereby generating ripples in the frequency characteristics, which may cause deterioration of the frequency characteristics.

  As a countermeasure against this, it is known that the back surface of the piezoelectric substrate is roughened.

  For example, as shown in the cross-sectional view of FIG. 8, in the surface wave filter in which the input side electrodes 120 a and 120 b and the output side electrodes 122 a and 122 b are formed on the surface of the piezoelectric substrate 110, A region 114 formed as a rough surface is provided inside the margin frame 110a. Thereby, the bulk wave is diffusely reflected in the region 114 on the back surface, the bulk wave reaching the output side electrodes 122a and 122b side is weakened, and the deterioration of the frequency characteristics due to the bulk wave can be suppressed. (For example, see Patent Document 1)

JP 2003-8396 A

  If no measures are taken to roughen the back surface of the piezoelectric substrate, ripples may occur in the frequency characteristics, which may be unacceptable. However, if the back surface of the piezoelectric substrate is roughened by lapping or the like in order to diffusely reflect bulk waves, minute cracks are formed, and the piezoelectric substrate is easily cracked during subsequent processing steps. The back surface of the piezoelectric substrate is preferably in a mirror state in order to reduce the occurrence of cracks.

  On the other hand, in recent years, there is a high demand for low-profile electronic components. In order to reduce the height, it is conceivable to reduce the thickness of the piezoelectric substrate. However, since the strength of the piezoelectric substrate is insufficient when it is thinned, cracks are easily generated or broken during the process.

  Moreover, the piezoelectric substrate is easily warped due to the thinning and roughening of the piezoelectric substrate, and the handling of the piezoelectric substrate during the manufacturing process becomes troublesome.

  Furthermore, since the influence of the bulk wave increases as the piezoelectric substrate becomes thinner, it is necessary to make the back surface of the piezoelectric substrate rougher in order to suppress the deterioration of the frequency characteristics due to the bulk wave. However, when the back surface of the piezoelectric substrate is roughened, the piezoelectric substrate is more easily broken.

  If the back surface of the piezoelectric substrate is not roughened, problems such as cracking will not occur, but frequency characteristics will be degraded by bulk waves.

  In view of such circumstances, the present invention intends to provide an elastic wave device that can suppress deterioration of frequency characteristics due to bulk waves without roughening the back surface of a piezoelectric substrate.

  In order to solve the above problems, the present invention provides an elastic wave device configured as follows.

  The elastic wave device includes: (a) a piezoelectric substrate on which an IDT is formed on one main surface and propagating an elastic wave excited by the IDT; and (b) an additional member bonded to the other main surface of the piezoelectric substrate. With. The additional member propagates in the piezoelectric substrate from the bulk wave excited by the IDT toward the other main surface of the piezoelectric substrate, and is incident on the additional member from the other main surface. However, it is configured so as to diffusely reflect in the additional member.

  In the above configuration, a part of the bulk wave excited by the IDT is incident on the additional member and diffusely reflected in the additional member, so that the bulk wave reaching the IDT becomes weak. As a result, it is possible to reduce an adverse effect on device characteristics due to the bulk wave.

  According to the above configuration, it is not necessary to make the other main surface of the piezoelectric substrate rough. An additional member is bonded to the piezoelectric substrate. Therefore, it is possible to prevent the occurrence of problems such as cracking of the piezoelectric substrate during the manufacturing process.

  In a preferred first aspect, the additional member is formed of a first base material having substantially the same acoustic impedance as that of the piezoelectric substrate. The additional member has a rough surface facing the bonding surface bonded to the other main surface of the piezoelectric substrate.

  In this case, the bulk wave incident on the additional member from the piezoelectric substrate is irregularly reflected on the facing surface of the additional member which is a rough surface.

  In a preferred second aspect, the additional member has an acoustic impedance substantially different from the acoustic impedance of the piezoelectric substrate in a second base material having an acoustic impedance substantially the same as the acoustic impedance of the piezoelectric substrate. The first part is distributed.

  In this case, since the first portion dispersed in the second base material of the additional member has an acoustic impedance substantially different from that of the second base material, the bulk wave incident on the additional member from the piezoelectric substrate is , Diffusely reflected in the first part.

  In a preferred third aspect, the additional member has an acoustic impedance substantially the same as the acoustic impedance of the piezoelectric substrate in a third base material having an acoustic impedance substantially different from the acoustic impedance of the piezoelectric substrate. The second portion is dispersed, and the third base material and the second portion are joined to the other main surface of the piezoelectric substrate.

  In this case, since the acoustic impedance of the piezoelectric substrate and the second portion of the additional member is substantially the same, the bulk wave is transmitted from the piezoelectric substrate to the second main surface of the additional member bonded to the other main surface of the piezoelectric substrate. It is incident on the part. The bulk wave incident on the second portion of the additional member has a substantially different acoustic impedance between the third base material and the second portion of the additional member. Diffusely reflects at the interface with the material.

  Preferably, the first base material, the second base material, or the second portion of the additional member is made of the same material as the piezoelectric substrate.

  In this case, it is easy to make the acoustic impedance of the first base material, the second base material, or the second portion of the additional member substantially the same as the acoustic impedance of the piezoelectric substrate.

  Preferably, the other main surface of the piezoelectric substrate is mirror-polished.

  In this case, the piezoelectric substrate is not easily broken even if it is thin. Further, it is easy to join the additional member to the piezoelectric substrate.

  The present invention also provides a method for manufacturing the acoustic wave device having the above-described configuration.

  In the method of manufacturing an acoustic wave device, after forming the IDT on the one main surface of the piezoelectric substrate, the additional member is bonded to the other main surface of the piezoelectric substrate.

  When the IDT is formed on the piezoelectric substrate in a state where the additional member is not bonded to the piezoelectric substrate, the warpage of the piezoelectric substrate can be reduced as compared to the case where the IDT is formed on the piezoelectric substrate in a state where the additional member is bonded to the piezoelectric substrate.

  According to the present invention, it is possible to suppress deterioration of frequency characteristics due to bulk waves without roughening the back surface of the piezoelectric substrate.

It is sectional drawing of an elastic wave device. Example 1 It is sectional drawing of an elastic wave device. (Modification of Example 1) It is principal part sectional drawing of an elastic wave device. (Example 2) It is principal part sectional drawing of an elastic wave device. (Example 3) It is sectional drawing of an additional member. (Example 3) It is sectional drawing of an additional member. (Modification of Example 3) It is sectional drawing of an elastic wave device. (Example) It is sectional drawing of a surface acoustic wave filter. (Conventional example)

  Embodiments of the present invention will be described below with reference to FIGS.

  Example 1 An acoustic wave device 10 of Example 1 will be described with reference to FIGS. 1 and 2.

  FIG. 1 is a cross-sectional view schematically showing the configuration of the acoustic wave device 10 of the first embodiment. As shown in FIG. 1, in the acoustic wave device 10 according to the first embodiment, an input-side IDT 14 and an output-side IDT 16 are formed on a surface 12 a that is one main surface of a piezoelectric substrate 12. The additional member 20 is joined to the back surface 12b which is the other main surface of the piezoelectric substrate 12.

  The additional member 20 has a rough surface facing the bonding surface 20 a bonded to the back surface 12 b of the piezoelectric substrate 12. That is, the opposing surface 20b of the additional member 20 has irregularities.

  The additional member 20 is formed of a first base material having substantially the same acoustic impedance as that of the piezoelectric substrate 12. When formed from the same material as the piezoelectric substrate 12, it is easy for the first base material of the additional member 20 to have substantially the same acoustic impedance as that of the piezoelectric substrate 12.

  Since the additional member 20 having substantially the same acoustic impedance as that of the piezoelectric substrate 12 is bonded to the back surface 12b of the piezoelectric substrate 12, the back surface of the piezoelectric substrate 12 among the bulk waves excited by the input side IDT 14 is used. Most of the component propagating through the piezoelectric substrate 12 toward the 12b is incident on the additional member 22. The incident component incident on the additional member 20 is diffusely reflected on the facing surface 20b of the additional member 20 which is roughened as indicated by an arrow 34.

  Therefore, the bulk wave that reaches the output-side IDT 16 becomes weak, and deterioration of frequency characteristics due to the bulk wave can be suppressed.

  Since the bulk wave may be incident on the additional member 20 from the back surface 12b of the piezoelectric substrate 12, the back surface 12b of the piezoelectric substrate 12 may not be a mirror surface.

  The opposing surface 20b of the additional member 20 only needs to be uneven so that bulk waves reaching the output IDT 16 are weakened. Therefore, for example, the opposing surface 22b of the additional member 22 may have a large undulation like the elastic wave device 10a of a modified example schematically showing the configuration in the cross-sectional view of FIG.

  Next, an example of a procedure for manufacturing the acoustic wave device 10 will be described.

First, a wafer of a piezoelectric substrate such as lithium tantalate (LiTaO ₃ ) is prepared. A wafer whose back surface is mirror-polished in order to ensure physical strength is used.

  Next, a material layer (thin film) having substantially the same acoustic impedance as the wafer is formed on the back surface of the wafer as an additional member. For example, a thin film such as lithium tantalate, which is the same material as the wafer, is formed by CVD (Chemical Vapor Deposition) or sputtering. A material layer may be formed of a metal, a ceramic material, or the like as long as the effect of suppressing the deterioration of the frequency characteristics can be obtained.

  Next, the surface of the material layer exposed to the outside is roughened. The surface of the material layer may be roughened by physical processing such as polishing or sandblasting. Alternatively, the surface of the material layer may be roughened by combining photolithography and etching to roughen the surface.

  A metal layer may be formed at the surface by using a metal mask when forming the material layer. In this case, the direction of the material layer is roughened simultaneously with the formation of the material layer.

  Next, an IDT, a wiring pattern, or the like is formed on the surface of the wafer opposite to the material layer. The formation method of IDT etc. may be a general method and is not particularly limited.

  Thereafter, the elastic wave device 10 is completed through the same post-process as that of a normal SAW (surface acoustic wave) device.

  After forming the IDT on the front surface of the wafer, a material layer may be formed on the back surface of the wafer. In this case, the IDT can be formed with less warpage of the wafer as compared with the case where the IDT is formed on the front surface of the wafer after the material layer is formed on the back surface of the wafer.

  Since the back surface of the wafer is a mirror surface, it is possible to suppress the deterioration of the frequency characteristics due to the bulk wave without causing a crack as a starting point of the crack of the wafer.

  Since the back surface of the wafer is in a mirror state, and the additional member is bonded to the back surface of the wafer, the wafer is reinforced by the additional member even if the wafer is thinned. As a result, the wafer is difficult to break during the processing process.

  Therefore, it is possible to achieve both physical strength securing and characteristic realization (suppression of deterioration of frequency characteristics due to bulk waves) in device height reduction.

  Example 2 An acoustic wave device 10b of Example 2 will be described with reference to FIG.

  FIG. 3 is a principal cross-sectional view schematically showing the configuration of the acoustic wave device 10b of the second embodiment. As shown in FIG. 3, the acoustic wave device 10 b according to the second embodiment has substantially the same configuration as the acoustic wave device 10 according to the first embodiment. In the following description, the same reference numerals are used for the same components as those in the first embodiment, and the description will focus on the portions that are different from the first embodiment.

  The elastic wave device 10b of the second embodiment is different from the first embodiment in the configuration of the additional member 24 bonded to the back surface 12b of the piezoelectric substrate 12.

  The first portion of the additional member 24 is dispersed in the second base 24s. The second base material 24 s has an acoustic impedance that is substantially the same as the acoustic impedance of the piezoelectric substrate 12. The first portion 24 t has an acoustic impedance that is substantially different from the acoustic impedance of the piezoelectric substrate 12. The first portion 24t is air bubbles dispersed in the second base material 24s, particles of a material different from the second base material 24s, or the like.

  Since the second base member 24s of the additional member 24 has substantially the same acoustic impedance as that of the piezoelectric substrate 12, the bulk wave excited by the input-side IDT 14 is directed toward the back surface 12b of the piezoelectric substrate 12. Most of the component propagating in the piezoelectric substrate 12 is incident on the additional member 24. Since the acoustic impedance is substantially different between the second base 24s and the first portion 24t dispersed in the second base 24s, the bulk wave incident on the additional member 24 is converted into the first portion 24t. Diffuse reflection.

  Therefore, the bulk wave that reaches the output-side IDT 16 becomes weak, and deterioration of frequency characteristics due to the bulk wave can be suppressed.

  Since the bulk wave only needs to enter the additional member 24 from the back surface 12b of the piezoelectric substrate 12, the back surface 12b of the piezoelectric substrate 12 may not be a mirror surface.

  For example, a porous thin film of lithium tantalate is formed as the additional member 24 on the back surface 12 b of the piezoelectric substrate 12 of lithium tantalate. In this case, when a material layer (thin film) of lithium tantalate having an acoustic impedance equivalent to that of the wafer is formed on the back surface of the wafer of the piezoelectric substrate in the same procedure as in Example 1, air, An additive material having an acoustic impedance substantially different from that of the wafer is mixed, and the first portion is formed by bubbles or additive material dispersed in the second base material of the material layer as the additional member.

  Since it is not necessary to make the back surface of the wafer rough, it is possible to weaken the bulk wave reaching the input side IDT 16 and suppress deterioration of the frequency characteristics due to the bulk wave without causing a crack as a starting point of the wafer crack. .

  <Example 3> The acoustic wave device 10c of Example 3 will be described with reference to FIGS.

  FIG. 4 is a principal cross-sectional view schematically showing the configuration of the acoustic wave device 10c of the third embodiment. As shown in FIG. 4, the elastic wave device 10 c according to the third embodiment is different from the first embodiment in the configuration of the additional member 26 bonded to the back surface 12 b of the piezoelectric substrate 12.

  In the additional member 26, the second portion 26 t having an acoustic impedance substantially the same as the acoustic impedance of the piezoelectric substrate 12 is included in the third base material 26 s having an acoustic impedance substantially different from the acoustic impedance of the piezoelectric substrate 12. Is distributed. A third base material 26s and a second portion 26t are joined to the back surface 12b of the piezoelectric substrate 12.

  Next, an example of a manufacturing procedure of the acoustic wave device 10c will be described.

First, a wafer of a piezoelectric substrate such as lithium tantalate (LiTaO ₃ ) is prepared. In order to ensure physical strength and adhesion, a wafer whose back surface is mirror-polished is used.

  Next, the IDT forms a wiring pattern or the like on the surface of the wafer. The formation method of IDT etc. may be a general method and is not particularly limited.

  Next, an additional member is formed on the back surface of the wafer. The additional member can be formed by various methods as follows.

  For example, as shown in the cross-sectional view of FIG. 5, a micro member 24t obtained by pulverizing the same material as the wafer as the second portion is embedded in the surface 26a of the resin sheet to be the additional member 26, and the surface 26a of the resin sheet is embedded in the wafer. The minute member 24t is adhered to the back surface of the wafer.

  Alternatively, as shown in the cross-sectional view of FIG. 6, a resin sheet 27 in which a minute member 27t made of the same material as the wafer is mixed in a base material 27t having an acoustic impedance different from that of the wafer is cut along a chain line 27x. Then, the cut surface from which the minute member 27t is exposed is attached to the back surface of the wafer, and the minute member 27t is brought into close contact with the back surface of the wafer.

  Alternatively, a resin mixed with a fine member obtained by pulverizing the same material as the wafer is applied to the back surface of the wafer.

  Or the material which mixed the fine member which atomized the same material as a wafer is sprayed on the back surface of a wafer.

  It is preferable that the minute members are in close contact with the back surface of the wafer at random.

  Thereafter, through the same post-process as that of a normal SAW (surface acoustic wave) device, the acoustic wave device 10c is completed.

  The IDT may be formed on the front surface of the wafer after the additional member is bonded to the back surface of the wafer.

  When an additional member is bonded to the back surface of the wafer after forming IDT or the like on the surface of the wafer, the warp of the wafer is less than when forming an IDT or the like on the surface of the wafer after bonding the additional member to the back surface of the wafer IDT or the like can be formed. In addition, if an additional member is bonded to the back surface of the wafer after IDT or the like is formed on the surface of the wafer, it is not necessary to adsorb the back surface after the additional member is bonded. be able to.

  <Summary> By joining the additional members 20, 22, 24, and 26 to the back surface 12 b of the piezoelectric substrate 12, deterioration of frequency characteristics due to bulk waves can be suppressed without roughening the back surface 12 b of the piezoelectric substrate 12. .

  The present invention is not limited to the above embodiment, and can be implemented with various modifications.

  For example, the present invention can be applied not only to an acoustic wave device that uses surface acoustic waves, but also to an acoustic wave device that uses boundary acoustic waves.

10, 10a to 10c, 10x Elastic wave device 12 Piezoelectric substrate 12a Surface (one main surface)
12b Back surface (the other main surface)
14 Input side IDT
16 Output IDT
20 additional member 20a joint surface 22 additional member 22b opposing surface 24 additional member 24s second base material 24t first part 26 additional member 26s third base material 26t second part

Claims (7)

A piezoelectric substrate on which an IDT is formed on one main surface and an elastic wave excited by the IDT propagates;
An additional member joined to the other main surface of the piezoelectric substrate;
With
The additional member is
Of the bulk wave excited by the IDT, the incident component that propagates in the piezoelectric substrate toward the other main surface of the piezoelectric substrate and enters the additional member from the other main surface is the additional member. An elastic wave device configured to diffusely reflect inside. The additional member is
Formed by a first substrate having an acoustic impedance substantially the same as the acoustic impedance of the piezoelectric substrate;
2. The acoustic wave device according to claim 1, wherein a facing surface facing a bonding surface bonded to the other main surface of the piezoelectric substrate is a rough surface. The additional member is
A first portion having an acoustic impedance substantially different from the acoustic impedance of the piezoelectric substrate is dispersed in a second base material having an acoustic impedance substantially the same as the acoustic impedance of the piezoelectric substrate. The acoustic wave device according to claim 1.   In the additional member, a second portion having an acoustic impedance substantially the same as the acoustic impedance of the piezoelectric substrate is dispersed in a third base material having an acoustic impedance substantially different from the acoustic impedance of the piezoelectric substrate. 2. The acoustic wave device according to claim 1, wherein the third base material and the second portion are bonded to the other main surface of the piezoelectric substrate. 3.   The said 1st base material of the said additional member, the said 2nd base material, or the said 2nd part is the same material as the said piezoelectric substrate, The any one of Claim 2 thru | or 4 characterized by the above-mentioned. The elastic wave device described in 1.   6. The acoustic wave device according to claim 1, wherein the other principal surface of the piezoelectric substrate is mirror-polished. It is a manufacturing method of the elastic wave device according to claim 1,
A method of manufacturing an acoustic wave device, comprising: forming the IDT on the one main surface of the piezoelectric substrate; and bonding the additional member to the other main surface of the piezoelectric substrate.

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