JP2006222512A - Surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device capable of eliminating its warpage, maintaining a desired inter-IDT-electrode distance and a propagation distance of a surface acoustic wave, and obtaining a desired sound velocity of the surface acoustic wave, thereby obtaining a desired frequency. <P>SOLUTION: The surface acoustic wave device 10 is configured such that a piezoelectric layer 30 is formed on a front side of a substrate 20, and IDTs 40 are formed on the surface of the piezoelectric layer 30, when the thermal expansion coefficient of the substrate 20 differs from the thermal expansion coefficient of the piezoelectric layer 30, an intermediate layer 60 is provided between the substrate 20 and the piezoelectric layer 30 so as to hold a condition of the thermal expansion coefficient of the substrate 20<the thermal expansion coefficient of the intermediate layer 60<the thermal expansion coefficient of the piezoelectric layer 30. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to the structure of a surface acoustic wave element.

  Conventionally, a semiconductor substrate, a piezoelectric film provided on the front surface side of the semiconductor substrate, an IDT (transducer) formed in contact with the piezoelectric film, and an elastic film including the piezoelectric film and IDT formed on the back surface side of the semiconductor substrate. A surface acoustic wave element formed from a peripheral circuit element for driving a surface acoustic wave element is known (see, for example, Patent Document 1).

Japanese Utility Model Publication No. 3-24719 (FIG. 3)

  In such Patent Document 1, a piezoelectric film is formed on the surface of a semiconductor substrate, and generally formed of Si (silicon) as a material of the semiconductor substrate, and a material as a piezoelectric film is formed of ZnO (zinc oxide). However, Si and ZnO have different thermal expansion coefficients. When heated to the room temperature and returned to room temperature, the surface acoustic wave element may warp due to the difference in thermal expansion coefficient. If the surface acoustic wave element is warped, the distance between the electrodes of the IDT changes or the propagation distance of the sound wave changes, so that the desired sound velocity of the surface acoustic wave cannot be obtained and the desired frequency cannot be obtained. There is a problem like this.

  The object of the present invention is to eliminate the warpage of the surface acoustic wave element, maintain the desired distance between the IDT electrodes and the propagation distance of the surface acoustic wave, and obtain the desired acoustic velocity of the surface acoustic wave. To provide a surface acoustic wave element capable of obtaining a desired frequency.

  A surface acoustic wave device according to the present invention is a surface acoustic wave device in which a piezoelectric layer is formed on a surface of a substrate and an IDT is formed on the surface of the piezoelectric layer, and the thermal expansion coefficient of the substrate and the piezoelectric layer is Are different from each other, an intermediate layer is provided between the substrate and the piezoelectric layer, and the following condition is satisfied: thermal expansion coefficient of the substrate <thermal expansion coefficient of the intermediate layer <thermal expansion coefficient of the piezoelectric layer It is characterized by being.

  When the thermal expansion coefficients of the substrate and the piezoelectric layer are different, it is conceivable that the surface acoustic wave element is warped when heat treatment is performed in the process of manufacturing the surface acoustic wave element. According to the present invention, by providing an intermediate layer having a thermal expansion coefficient intermediate between the respective thermal expansion coefficients between the substrate and the piezoelectric layer, the warpage is suppressed and the IDT (Interdigital Transducer) generated by the warpage is suppressed. A change in the distance between the electrodes and a change in the propagation distance of the surface acoustic wave can be reduced to obtain a desired frequency.

  In addition, a dummy region having a thermal expansion coefficient smaller than that of the substrate is provided in the piezoelectric layer, and the substrate and the piezoelectric layer are configured to behave in equivalent thermal expansion / contraction. It is preferable.

  In this case, since the dummy region is provided in the piezoelectric layer with a material smaller than the thermal expansion coefficient of the substrate, the piezoelectric layer and the substrate behave as equivalent thermal expansion / contraction. The warpage of the element can be suppressed.

  In the surface acoustic wave device of the present invention, piezoelectric layers are formed on both surfaces of the substrate, IDT is formed on one surface of the piezoelectric layer, and equivalent thermal expansion / It is configured to behave as contraction.

  According to the present invention, the piezoelectric layers having substantially the same thermal expansion coefficient are formed on both the front and back surfaces of the substrate, so that equivalent thermal expansion and contraction behave on both the front and back surfaces of the substrate and the warpage of the surface acoustic wave element is suppressed. can do. As a result, a change in the distance between the electrodes of the IDT and a change in the propagation distance of the surface acoustic wave can be reduced, and a desired frequency can be obtained.

  In the surface acoustic wave device of the present invention, an intermediate layer is formed on both front and back surfaces of the substrate, a piezoelectric layer is further formed on the surface of the intermediate layer, and an IDT is formed on the surface of one of the piezoelectric layers. It is configured to satisfy the condition that the thermal expansion coefficient of the substrate <the thermal expansion coefficient of the intermediate layer <the thermal expansion coefficient of the piezoelectric layer, and behave equivalent thermal expansion / contraction on both the front and back surfaces of the substrate. It is characterized by that.

  According to this invention, since the intermediate layer and the piezoelectric layer are formed on both the front and back surfaces of the substrate, equivalent thermal expansion and contraction behave on both surfaces of the substrate, and thermal expansion and contraction can be achieved by providing the intermediate layer. It is mitigated, and the warpage of the surface acoustic wave element is further suppressed, and the change in the interelectrode distance of the IDT and the change in the propagation distance of the surface acoustic wave are reduced, whereby a desired frequency can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 3 show a surface acoustic wave device according to Embodiment 1 of the present invention, FIG. 4 shows Embodiment 2, FIG. 5 shows Embodiment 3, and FIGS. FIG. 8 shows a surface acoustic wave device according to the prior art.
(Prior art issues)

  First, the prior art and problems according to Patent Document 1 described above will be described with reference to the drawings. FIG. 8 is a cross-sectional view schematically showing the structure and the warping direction of a surface acoustic wave element according to the prior art. In FIG. 8, the surface acoustic wave element 100 has a piezoelectric layer 120 formed on the surface of a substrate 110, and IDTs (transducer electrodes) 130 and 140 formed on the surface of the piezoelectric layer 120. Further, a peripheral circuit element 150 for driving the surface acoustic wave element is provided on the back surface of the substrate 110.

Here, as a general material, when the substrate 110 is Si (silicon) and the piezoelectric layer 120 is ZnO (zinc oxide), the thermal expansion coefficient of Si is 3.55 × 10 ⁻⁶ / ° C., and the thermal expansion of ZnO. Since the coefficient is 4.0 × 10 ⁻⁶ / ° C., there is a heating step when forming the ZnO film or forming the electrode of the IDT. Therefore, when heated, ZnO expands more than Si, and the initial state E It is known that since warping in the C direction (before warpage occurs), ZnO contracts more than Si and warps in the D direction when it is returned to room temperature.
Hereinafter, the body expansion coefficient is shown as the thermal expansion coefficient.

  As described above, when the surface acoustic wave element 100 is warped, the distance between the electrodes of the IDTs 130 and 140 is shorter than the target distance, or the propagation distance of the surface acoustic wave is shortened, so There is a problem that the speed of sound cannot be obtained, that is, a desired frequency cannot be obtained.

In addition, a plurality of such surface acoustic wave elements 100 are formed on the wafer at a time. However, as described above, when the surface acoustic wave elements 100 are warped, the wafer itself is also warped, and the wafer surface state is increased. In the characteristic inspection, if the probe is aligned with the outer peripheral portion, there is a problem that the central portion cannot be inspected.
(Embodiment 1)

FIG. 1 is a plan view showing the arrangement of surface acoustic wave elements according to the present invention formed on a wafer. FIGS. 2 and 3 are a plan view and a sectional view of the surface acoustic wave element according to the first embodiment. .
In FIG. 1, a plurality of surface acoustic wave elements 10 are simultaneously formed on a wafer 1 as illustrated in FIG. From this state, a single surface acoustic wave element 10 is obtained by scribing.

Next, the configuration of the surface acoustic wave element 10 will be described with reference to the drawings.
FIG. 2 is a plan view showing an example of the configuration of the surface acoustic wave element 10 according to the present embodiment, and FIG. 3 is a cross-sectional view showing the AA cross section of FIG. First, a cross-sectional configuration will be described with reference to FIG. In the surface acoustic wave element 10, an intermediate layer 60 made of ZnO is formed on the surface of a substrate 20 made of Si. A piezoelectric layer 30 made of LiNbO ₃ (lithium niobate) is laminated on the surface of the intermediate layer 60.
Furthermore, an IDT 40 and reflectors 50 and 51 made of aluminum (Al) are formed on the surface of the piezoelectric layer.

Here, the thermal expansion coefficient of each component is 3.55 × 10 ⁻⁶ / ° C. for Si of the substrate 20, 4.0 × 10 ⁻⁶ / ° C. for ZnO of the intermediate layer 60, and LiNbO _{3 for the} piezoelectric layer 30. Is 15.4 × 10 ⁻⁶ / ° C. The thermal expansion coefficient of the piezoelectric layer 30 is about four times as large as the thermal expansion coefficient of the substrate 20. According to the conventional technique in which the piezoelectric layer 30 is directly laminated on the surface of the substrate 20, the piezoelectric layer 30 is formed by a CVD method (Chemical). When a film is formed by vapor deposition) or the like, heat of about 300 ° C. is applied, so that the surface acoustic wave element 10 warps due to a difference in thermal expansion coefficient.

Therefore, in the present embodiment, the intermediate layer 60 is provided between the substrate 20 and the piezoelectric layer 30. The thermal expansion coefficient of ZnO in the intermediate layer 60 is 4.0 × 10 ⁻⁶ / ° C., and the relationship between the three thermal expansion coefficients is that of the substrate 20 <intermediate layer 60 <piezoelectric layer 30. .

The material of the intermediate layer 60 satisfying the relationship of the substrate 20 <intermediate layer 60 <piezoelectric layer 30 is not only ZnO but also Ba ₂ NaNb ₅ O ₁₅ , Ba ₂ Ge ₂ TiO ₈ , Ba ₂ Si ₂ TiO. ₈ , Pb ₅ GeO ₁₁ , CdS, CdSe, ZnS, AlN, GaAS, InSb, InAs, TiO ₂ , PbMoO 4, Gd ₃ Ga ₅ O ₁₂ , Y ₃ A ₁₅ O ₁₂ , Cr, or the like can be used.

  Although the IDT 40 and the reflectors 50 and 51 are formed on the surface of the piezoelectric layer 30, these electrodes are formed in a comb-teeth shape and thus have little influence on the warp. In consideration of the difference in thermal expansion coefficient between the layer 30 and the substrate 20 and the influence of the IDT 40 and the reflectors 50 and 51, the material and thickness are preferably selected so as to minimize the amount of warpage.

  Next, the planar configuration of the surface acoustic wave element 10 will be described with reference to FIG. In FIG. 2, IDT 40 is formed on the surface of the piezoelectric layer 30, and both sides of the IDT 40, that is, directions in which surface acoustic waves (hereinafter simply referred to as sound waves) propagate (X ′ direction in the figure). Reflectors 50 and 51 are formed.

  The IDT 40 is composed of two blocks on the left and right, one being the input side IDT and the other being the output side IDT. The IDT 40 includes a comb-shaped electrode 41 and a bus bar 42 that connects the comb-shaped electrode 41. The bus bar 42 is connected to a connection pad (not shown).

  The reflectors 50 and 51 are not always necessary and can be omitted. In this case, side surfaces at both ends of the piezoelectric layer 30 in the propagation direction of the sound wave serve as reflection walls.

  Therefore, according to the first embodiment described above, when the thermal expansion coefficients of the substrate 20 and the piezoelectric layer 30 are different, the substrate 20 is subjected to heat treatment in the manufacturing process of the surface acoustic wave element 10 and returned to room temperature again. By providing an intermediate layer 60 having a thermal expansion coefficient intermediate between the respective thermal expansion coefficients between the piezoelectric layer 30 and the piezoelectric layer 30, the amount of warpage of the surface acoustic wave element 10 is suppressed, and the comb teeth of the IDT 40 generated by the warp A desired frequency can be obtained by suppressing the interelectrode distance of the electrode 41, the interelectrode distance between the IDT 40 and the reflectors 50 and 51, and the change of the propagation distance of the sound wave.

A plurality of surface acoustic wave elements 10 are simultaneously formed on the wafer 1, but since the warpage of the surface acoustic wave element 10 is suppressed as described above, when performing characteristic inspection or the like in the wafer state, An inspection probe can be reliably connected to the outer peripheral portion and the central portion of the wafer 1, and there is an effect that the inspection can be reliably performed.
(Embodiment 2)

Subsequently, Embodiment 2 according to the present invention will be described with reference to the drawings.
FIG. 4 is a cross-sectional view showing the surface acoustic wave element 10 according to the second embodiment. Since the planar configurations of the IDT 40 and the reflectors 50 and 51 are the same as those of the first embodiment, the description thereof is omitted. In FIG. 4, the surface acoustic wave element 10 includes a piezoelectric layer 30 formed on the front side of a substrate 20 made of Si, and a piezoelectric layer 31 formed on the back side. The IDT 40 and the reflectors 50 and 51 having the planar shape shown in FIG. 2 are formed.

In the present embodiment, the piezoelectric layers 30 and 31 are made of LiNbO ₃ and are formed with substantially the same thickness. The piezoelectric layers 30 and 31 are formed by a film forming technique such as a CVD method. At this time, a heat treatment of about 300 ° C. is performed.

  Although the piezoelectric layers 30 and 31 may have substantially the same thickness, the thickness of the piezoelectric layer 31 that does not affect the propagation of sound waves in consideration of the effects of thermal expansion and contraction of the IDT 40 and the reflectors 50 and 51. Adjust.

  The piezoelectric layer 31 is preferably made of the same material as that of the piezoelectric layer 30, but has substantially the same thermal expansion coefficient as that of the piezoelectric layer 30 and behaves equivalently to thermal expansion / contraction on the front and back of the substrate 20. If the conditions are satisfied, there is no particular limitation.

Therefore, according to the second embodiment described above, the piezoelectric layers 30 and 31 having substantially the same thermal expansion coefficient are formed on both the front and back surfaces of the substrate 20, so that equivalent thermal expansion and contraction behave on both surfaces of the substrate 20. Further, warpage of the surface acoustic wave element 10 can be suppressed. As a result, a change in the distance between the electrodes of the IDT 40, a change in the distance between the electrodes of the IDT 40 and the reflectors 50 and 51, and a change in the propagation distance of the surface acoustic wave can be reduced to obtain a desired frequency.
(Embodiment 3)

  Next, the structure of the surface acoustic wave element according to the third embodiment of the present invention will be described with reference to the drawings. The third embodiment is characterized in that the structure in which the intermediate layer 60 and the piezoelectric layer 30 are laminated on the surface of the substrate 20 in the first embodiment (see FIG. 3) is also formed on the back side of the substrate 20. Have.

FIG. 5 is a cross-sectional view illustrating a configuration of the surface acoustic wave element 10 according to the third embodiment. In FIG. 5, intermediate layers 60 and 61 are respectively formed on the front and back surfaces of the substrate 20 made of Si, and piezoelectric layers 30 and 31 are formed on the surfaces of the intermediate layers 60 and 61, respectively. In the present embodiment, the intermediate layers 60 and 61 are made of ZnO, and the piezoelectric layers 30 and 31 are made of LiNbO ₃ .

  An IDT 40 and reflectors 50 and 51 are formed on the surface of one piezoelectric layer 30. Since the IDT 40 and the reflectors 50 and 51 have the same configuration as that of the first embodiment (see FIG. 2), description thereof is omitted.

As described in the first embodiment, the thermal expansion coefficient of Si of the substrate 20 is 3.55 × 10 ⁻⁶ / ° C., the ZnO of the intermediate layers 60 and 61 is 4.0 × 10 ⁻⁶ / ° C., the piezoelectric layer 30, The LiNbO _{3 of} 31 is 15.4 × 10 ⁻⁶ / ° C., and the material of the intermediate layers 60 and 61 is the thermal expansion coefficient of the substrate 20 <the thermal expansion coefficient of the intermediate layers 60 and 61 <the piezoelectric layers 30 and 31. It is still more preferable that the thermal expansion coefficient is selected in a range satisfying the condition.

  In this embodiment, the piezoelectric layers 30 and 31 are formed with substantially the same thickness, and the intermediate layers 60 and 61 are also formed with substantially the same thickness, both of which are formed by a film forming technique such as a CVD method. At this time, a heat treatment of about 300 ° C. is performed.

  Although the piezoelectric layers 30 and 31 may have substantially the same thickness, the thickness of the piezoelectric layer 31 that does not affect the propagation of sound waves in consideration of the effects of thermal expansion and contraction of the IDT 40 and the reflectors 50 and 51. Adjust.

  The piezoelectric layer 31 is preferably made of the same material as that of the piezoelectric layer 30, but the thermal expansion coefficient of the piezoelectric layer 30 is substantially the same, and equivalent thermal expansion / contraction occurs on the front and back of the substrate 20. If the conditions are satisfied, there is no particular limitation.

  Further, the intermediate layers 60 and 61 are selected so as to minimize the amount of warpage and the material and thickness in consideration of the difference in thermal expansion coefficient between the piezoelectric layer 30 and the substrate 20 and the influence of the IDT 40 and the reflectors 50 and 51. It is preferable.

Therefore, according to the above-described third embodiment, the intermediate layers 60 and 61 and the piezoelectric layers 30 and 31 are formed on both the front and back surfaces of the substrate 20, so that equivalent thermal expansion and contraction are performed on both the front and back surfaces of the substrate 20. By providing the intermediate layers 60 and 61, the thermal expansion and contraction are alleviated, the warpage of the surface acoustic wave element 10 is further suppressed, the change in the interelectrode distance of the IDT 40, and the IDT 40 and the reflectors 50 and 51 are reduced. The change in the distance between the electrodes and the change in the propagation distance of the sound wave can be reduced, whereby a desired frequency can be obtained.
(Embodiment 4)

Next, Embodiment 4 according to the present invention will be described with reference to the drawings. The fourth embodiment is characterized in that a dummy region made of a material smaller than the thermal expansion coefficient of the substrate 20 is formed in the piezoelectric layer 30 based on the technical idea of the first embodiment described above.
6 and 7 show the surface acoustic wave element 10 according to the present embodiment, FIG. 6 is a plan view, and FIG. 7 is a cross-sectional view showing the AA cross section of FIG.

First, a cross-sectional configuration will be described with reference to FIG. In the surface acoustic wave element 10, an intermediate layer 60 made of ZnO is formed on the surface of a substrate 20 made of Si, and a piezoelectric layer 30 made of LiNbO ₃ is formed on the surface of the intermediate layer 60. An IDT 40 made of Al having comb-like electrodes and reflectors 50 and 51 are formed on the surface of the piezoelectric layer 30.

A plurality of dummy regions 70 are formed in the piezoelectric layer 30 so as to penetrate the piezoelectric layer 30. In the present embodiment, the dummy region 70 is formed of SiO ₂ (silicon oxide).

Here, the thermal expansion coefficients of the surface acoustic wave device 10 are 3.55 × 10 ⁻⁶ / ° C. for Si of the substrate 20, 4.0 × 10 ⁻⁶ / ° C. for ZnO of the intermediate layer 60, and piezoelectric. LiNbO _{3 of the} body layer 30 is 15.4 × 10 ⁻⁶ / ° C., and SiO _{2 of the} dummy region 70 is 0.55 × 10 ⁻⁶ / ° C. The thermal expansion coefficient of the dummy region 70 is as small as about 1/8 of the thermal expansion coefficient of the substrate 20.

  Next, a planar configuration of the surface acoustic wave element 10 will be described with reference to FIG. In FIG. 6, IDT 40 is formed on the surface of piezoelectric layer 30, and reflectors 50 and 51 are formed on both sides of IDT 40, that is, in the direction in which sound waves propagate (X ′ direction in the figure).

  The IDT 40 is composed of two blocks on the left and right, one being the input side IDT and the other being the output side IDT. The IDT 40 includes a comb-shaped electrode 41 and a bus bar 42 that connects the comb-shaped electrode. The bus bar 42 is connected to a connection pad (not shown).

  In the piezoelectric layer 30, a plurality of dummy regions 70 are formed at predetermined positions as shown in FIG. The dummy region 70 is formed in a cylindrical shape in the piezoelectric layer 30 and is disposed outside the IDT 40 and the reflectors 50 and 51. The dummy region 70 may be formed so as to intersect with the bus bar 42 and a connection pad (not shown), but is not formed in the sound wave propagation range of the IDT 40 and the reflectors 50 and 51.

The dummy region 70 is arranged symmetrically with respect to the straight line connecting AA in the width direction (Y ′ direction) and symmetrical with respect to the center line B in the longitudinal direction (X ′ direction).
(Example of Embodiment 4)

Subsequently, examples of the present embodiment will be illustrated. In order to make the difference in thermal expansion coefficient between the substrate 20 and the piezoelectric layer 30 equivalent, a specific example will be given for each thermal expansion coefficient, thickness, and area. The dummy area 70 is SiO ₂ and the area ratio is calculated.

First, from the relationship of the thermal expansion coefficient, the area ratio in the surface acoustic wave element 10 of SiO ₂ is α, the area ratio in the surface acoustic wave element 10 of ZnO is β, and the respective ratios are determined. .
α × SiO ₂ thermal expansion coefficient + β × ZnO thermal expansion coefficient = Si thermal expansion coefficient (Equation 1).
This is set so that α + β = 1.

Next, a warpage correction coefficient is obtained from a coefficient γ relating to the thickness of each of the substrate (Si) 20 and the piezoelectric layer (LiNbO ₃ ) 30.
γ = LiNbO ₃ thickness / Si thickness (Formula 2).
From these, the product α × γ of α and γ obtained from (Equation 1) and (Equation 2) is the area of the dummy region 70.

The thermal expansion coefficient of each element in Embodiment 1 is as follows: SiO ₂ is 0.55 × 10 ⁻⁶ / ° C., LiNbO ₃ is 15.4 × 10 ⁻⁶ / ° C., and Si is 3.55 × 10 ⁻⁶ / ° C. , (Equation 1) is substituted for this value.
The calculation formula of α × 0.55 × 10 ⁻⁶ + (1−α) × 15.4 × 10 ⁻⁶ = 3.55 × 10 ⁻⁶ is obtained.
From this calculation formula, α = 0.8 is obtained.

Here, if the thickness of the substrate 20 is set to 300 μm and the thickness of the piezoelectric layer 30 is set to 3 μm, γ = 3/300 = 1/100.
Therefore, α × γ = 0.8 / 100 = 0.8%, and by setting the area ratio α in the surface acoustic wave element 10 of SiO ₂ to 0.8%, the substrate 20 and the piezoelectric layer An equivalent relationship of the difference in thermal expansion coefficient from 30 is obtained.

  From this, the area and the number of the individual dummy regions are such that the total area of the dummy regions 70 shown in FIG. 6 is 0.8% of the surface area on which the IDT 40 of the surface acoustic wave element 10 is formed. Is set.

In Embodiment 4 described above, SiO ₂ is used for the dummy region 70, but the material may be selected from materials having a thermal expansion coefficient smaller than that of the substrate 20 without being limited to SiO ₂ .

  In the fourth embodiment, the dummy region 70 is provided in the piezoelectric layer 30. However, the dummy region 70 may be provided in the intermediate layer 60 or both the piezoelectric layer 30 and the intermediate layer 60. Even in such a case, an area where the thermal expansion and contraction is equivalent can be obtained from the above-described calculation formula, and can be provided in a range that does not affect the propagation of sound waves.

  As shown in FIG. 6, the dummy area 70 can be arbitrarily selected such as a triangle or a rectangle in addition to a circular plane shape. In addition, the individual dummy regions 70 can be continuously grooved.

  Therefore, according to the fourth embodiment described above, the thermal expansion coefficient of the piezoelectric layer 30 is larger than the thermal expansion coefficient of the substrate 20 so that the piezoelectric layer 30 and the substrate 20 perform equivalent thermal expansion / contraction. Since the dummy region 70 is provided in the piezoelectric layer 30 with a small material, the surface acoustic wave element does not warp when heated during the manufacturing process and returned to room temperature, and the desired distance between the IDT electrodes Since the propagation distance of the surface acoustic wave is maintained, it is possible to obtain the desired sound velocity of the surface acoustic wave, and from this, it is possible to obtain a predetermined frequency.

  Further, since the intermediate layer is provided between the piezoelectric layer 30 and the substrate 20, the amount of warpage due to thermal expansion / contraction can be further reduced.

It should be noted that the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.
For example, in Embodiment 3 described above, the intermediate layers 60 and 61 are provided on both the front and back surfaces of the substrate 20, but only one of the intermediate layers 60 and 61 can be provided.

  Further, the concept of the structure in which the dummy region 70 according to the fourth embodiment is provided can also be applied to the second and third embodiments. In this way, the warpage of the surface acoustic wave element 10 is further suppressed. be able to.

  Therefore, according to the first to fourth embodiments described above, the warp of the surface acoustic wave element 10 is eliminated, the desired distance between the IDT electrodes and the propagation distance of the surface acoustic wave is maintained, and the desired sound velocity of the sound wave is obtained. Thus, it is possible to provide the surface acoustic wave device 10 that can obtain a desired frequency.

The top view which shows arrangement | positioning of the surface acoustic wave element formed on the wafer which concerns on this invention. 1 is a plan view showing a configuration of a surface acoustic wave element according to Embodiment 1 of the present invention. 1 is a cross-sectional view illustrating a configuration of a surface acoustic wave element according to a first embodiment of the invention. Sectional drawing which shows the structure of the surface acoustic wave element which concerns on Embodiment 2 of this invention. Sectional drawing which shows the structure of the surface acoustic wave element which concerns on Embodiment 3 of this invention. FIG. 6 is a plan view showing a configuration of a surface acoustic wave element according to Embodiment 4 of the present invention. Sectional drawing which shows the structure of the surface acoustic wave element which concerns on Embodiment 4 of this invention. Explanatory drawing which shows the cross-sectional shape of the surface acoustic wave element by a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wafer, 10 ... Surface acoustic wave element, 20 ... Board | substrate, 30 ... Piezoelectric layer, 40 ... IDT, 60 ... Intermediate | middle layer.

Claims (4)

A surface acoustic wave element in which a piezoelectric layer is formed on a surface of a substrate, and an IDT is formed on the surface of the piezoelectric layer,
When the thermal expansion coefficients of the substrate and the piezoelectric layer are different,
An intermediate layer is provided between the substrate and the piezoelectric layer,
A surface acoustic wave device characterized by satisfying the following condition: thermal expansion coefficient of the substrate <thermal expansion coefficient of the intermediate layer <thermal expansion coefficient of the piezoelectric layer. The surface acoustic wave device according to claim 1,
The piezoelectric layer is provided with a dummy region having a thermal expansion coefficient smaller than the thermal expansion coefficient of the substrate, and the substrate and the piezoelectric layer are configured to behave in equivalent thermal expansion / contraction. A surface acoustic wave device. Piezoelectric layers are formed on both the front and back surfaces of the substrate, IDT is formed on one surface of the piezoelectric layer,
A surface acoustic wave device characterized in that it is configured to behave equivalently to thermal expansion / contraction on both the front and back surfaces of the substrate. An intermediate layer is formed on both the front and back surfaces of the substrate, a piezoelectric layer is further formed on the surface of the intermediate layer,
IDT is formed on the surface of one piezoelectric layer,
Satisfying the condition of thermal expansion coefficient of the substrate <thermal expansion coefficient of the intermediate layer <thermal expansion coefficient of the piezoelectric layer,
A surface acoustic wave device characterized in that it is configured to behave equivalently to thermal expansion / contraction on both the front and back surfaces of the substrate.

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