Elastic wave device

Abstract

The present invention provides an elastic wave device capable of sufficiently suppressing a ripple caused by a Rayleigh wave. The elastic wave device has a piezoelectric layer (5) directly or indirectly laminated on a support substrate (3), has a first IDT electrode (6) provided on a first main surface (5a) of the piezoelectric layer (5), sets a thickness of a metal film constituting the first IDT electrode (6) normalized by a wavelength λ as te, sets a thickness of the piezoelectric layer (5) normalized by the wavelength λ as tp, sets te / tp = x, sets an average density of the metal film normalized by a total mass of the metal film as y [g / cm 3 ], and at this time, F(x) shown in the following formula (1) is 10 or less, F(x) = Ax 2 +Bx+C... Formula (1) In addition, in the formula (1), A and B are represented by the following formula (2) and formula (3), C = 19, A = 1.0392y 2 +8.4182y - 45.223... Formula (2) B = 0.0334y 2 - 11.363y + 28.984... Formula (3).

Description

Technical Field

[0001] The present invention relates to an elastic wave device having a piezoelectric layer comprising lithium tantalate directly or indirectly stacked on a support substrate. Background Technology

[0002] In the elastic wave device described in Patent Document 1 below, a piezoelectric layer containing LiTaO3 is disposed directly or indirectly on a support substrate. An IDT electrode is disposed on the piezoelectric layer. In this elastic wave device, an optimal cut angle θ of the piezoelectric layer is selected to minimize stray noise caused by Rayleigh waves.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2018-092511 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] Similar to the elastic wave device described in Patent Document 1, in a piezoelectric composite substrate with a thin piezoelectric layer containing LiTaO3 disposed on a support substrate, ripples caused by Rayleigh waves are generated at a lower frequency than the main resonance. In Patent Document 1, to suppress these ripples, the cutting angle of LiTaO3 was optimized based on the thickness of the piezoelectric layer and the IDT electrodes, which was normalized according to the wavelength λ. Furthermore, λ is the wavelength determined by the electrode finger spacing of the IDT electrodes.

[0008] However, when multiple resonators are constructed on the same piezoelectric composite substrate, the electrode finger spacing sometimes varies between the resonators. In such cases, the normalized thickness of the piezoelectric layer and the normalized thickness of the IDT electrodes differ for each electrode finger spacing. Therefore, depending on the resonator, it is sometimes difficult to suppress spurious emissions caused by Rayleigh waves in all resonators, even with an angle that differs from the optimal one.

[0009] The purpose of this invention is to provide an elastic wave device that can effectively suppress ripples caused by Rayleigh waves.

[0010] Technical solutions for solving the problem

[0011] The first invention relates to an elastic wave device comprising: a piezoelectric composite substrate having a piezoelectric layer and a support substrate, the piezoelectric layer having a first main surface and a second main surface facing each other and comprising lithium tantalate, the piezoelectric layer being directly or indirectly stacked on the support substrate from the first main surface side; and a first IDT electrode disposed on the first main surface of the piezoelectric layer, the first IDT electrode comprising a metal film, wherein the wavelength determined by the electrode finger spacing of the first IDT electrode is denoted as λ, the thickness of the metal film of the first IDT electrode normalized to wavelength λ is denoted as te, the thickness of the piezoelectric layer normalized to wavelength λ is denoted as tp, te / tp = x, and the average density of the metal film normalized to the total mass of the metal film using the thickness te of the metal film is denoted as y [g / cm³]. 3 At this time, F(x) given by the following equation (1) is 10 or less.

[0012] F(x) = Ax 2 +Bx+C… equation (1)

[0013] In addition, in equation (1), A and B are represented by equations (2) and (3) below, and C = 19.

[0014] A = 1.0392y 2 +8.4182y-45.223… Equation (2)

[0015] B = 0.0334y 2 -11.363y+28.984… Equation (3)

[0016] The second invention relates to an elastic wave device comprising: a piezoelectric composite substrate having a piezoelectric layer and a support substrate, the piezoelectric layer having a first main surface and a second main surface facing each other and comprising lithium tantalate, the piezoelectric layer being directly or indirectly stacked on the support substrate from the first main surface side; a first IDT electrode disposed on the first main surface of the piezoelectric layer; and a second IDT electrode disposed on the second main surface of the piezoelectric layer, facing the first IDT electrode across the piezoelectric layer, the second IDT electrode comprising a metal film, the wavelength determined by the electrode finger spacing of the second IDT electrode being denoted as λ, the thickness of the metal film of the second IDT electrode normalized to wavelength λ being denoted as te, the thickness of the piezoelectric layer normalized to wavelength λ being denoted as tp, te / tp = x, and the average density of the metal film normalized to the total mass of the metal film using the thickness te of the metal film being denoted as y [g / cm³]. 3 At this point, G(x) given by the following equation (4) is less than 10.

[0017] G(x)=Ax 2 +Bx+C… equation (4)

[0018] In addition, in equation (4), A and B are represented by equations (5) and (6) below, and C = 19.

[0019] A = 0.0564y 2 +39.909y-29.023… Equation (5)

[0020] B = 0.1407y 2 -11.875y+5.4093… Equation (6)

[0021] Invention Effects

[0022] The elastic wave device according to the present invention can effectively suppress ripples caused by Rayleigh waves. Attached Figure Description

[0023] Figure 1 This is a front sectional view showing the main parts of the elastic wave device according to the first embodiment of the present invention.

[0024] Figure 2 This is a schematic top view showing the electrode structure in the elastic wave device according to the first embodiment of the present invention.

[0025] Figure 3 This is a graph showing the relationship between the Euler angle θ of LiTaO3 and the coupling coefficient of Rayleigh waves.

[0026] Figure 4 This is a graph showing the relationship between the wavelength-normalized thickness tp and the optimal angle (degrees) of LiTao3 in the case where the IDT electrode contains Al in a conventional elastic wave device.

[0027] Figure 5 This is a graph showing the relationship between the wavelength-normalized thickness tp and the optimal angle (degrees) of LiTao3 in the case where the IDT electrode contains Cu in a conventional elastic wave device.

[0028] Figure 6 This is a graph showing the relationship between the wavelength-normalized thickness tp of LiTaO3 and the optimal angle (degrees) of the Euler angle θ in the case where the IDT electrode contains Cu in the elastic wave device according to the first embodiment of the present invention.

[0029] Figure 7 This is a graph showing the relationship between the wavelength-normalized thickness tp of LiTaO3 and the optimal angle (degrees) of the Euler angle θ when the IDT electrode contains Pt in a conventional elastic wave device.

[0030] Figure 8This is a graph showing the relationship between the wavelength-normalized thickness tp of LiTaO3 and the optimal angle (degrees) of the Euler angle θ when the IDT electrode in the elastic wave device according to the first embodiment of the present invention contains Pt.

[0031] Figure 9 This shows the difference θ between the te / tp ratio and the optimal cut angle when the piezoelectric layer wavelength ratio is 15%λ and 45%λ, in the case that the IDT electrode in the conventional elastic wave device and the elastic wave device according to the first embodiment of the present invention contains Cu. H -θ L A graph showing the relationship between (degrees).

[0032] Figure 10 This shows the difference θ between the te / tp ratio and the optimal cut angle when the piezoelectric layer wavelength ratio is 15%λ and 45%λ, in the case that the IDT electrode contains Pt in the conventional elastic wave device and the elastic wave device according to the first embodiment of the present invention. H -θ L A graph showing the relationship between (degrees).

[0033] Figure 11 It is a graph showing the relationship between the density of the metal film constituting the first IDT electrode and A and B in equation (1).

[0034] Figure 12 This is a front sectional view showing the main parts of the elastic wave device according to the second embodiment of the present invention.

[0035] Figure 13 This is a graph showing the relationship between the density of the metal constituting the second IDT electrode in the elastic wave device according to the second embodiment of the present invention and A and B in formula (4).

[0036] Figure 14 This is a front sectional view used to illustrate the main parts of the elastic wave device according to the third embodiment of the present invention.

[0037] Figure 15 This is a front sectional view used to illustrate the main parts of the elastic wave device according to the fourth embodiment of the present invention. Detailed Implementation

[0038] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0039] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.

[0040] Figure 1This is a front sectional view showing the main parts of the elastic wave device according to the first embodiment of the present invention. Figure 2 This is a schematic top view showing the electrode structure of the elastic wave device.

[0041] In the elastic wave device 1, the piezoelectric composite substrate 2 has a support substrate 3, a dielectric layer 4 stacked on the support substrate 3, and a piezoelectric layer 5. Alternatively, the dielectric layer 4 may not be provided.

[0042] The support substrate 3 includes a suitable insulator and a semiconductor. In this embodiment, the support substrate 3 includes Si.

[0043] The dielectric layer 4 contains a suitable dielectric material, which in this embodiment contains silicon oxide.

[0044] The piezoelectric layer 5 has a first main surface 5a and a second main surface 5b that are opposite to each other. The piezoelectric layer 5 is stacked on the dielectric layer 4 from the side of the first main surface 5a. A first IDT electrode 6 is disposed on the first main surface 5a of the piezoelectric layer 5.

[0045] The piezoelectric layer 5 contains lithium tantalate. Preferably, it is lithium tantalate that is rotated Y-cut and X-propagated, and more preferably, the cutting angle is 40° or more and 60° or less.

[0046] Furthermore, the first IDT electrode 6 comprises a metal film containing a suitable metal or alloy. The first IDT electrode 6 may also comprise a stack of multiple metal films.

[0047] like Figure 2 As shown, reflectors 7 and 8 are arranged on both sides of the elastic wave propagation direction of the first IDT electrode 6. Thus, a single-port type elastic wave resonator is formed.

[0048] Return to Figure 1 The first IDT electrode 6 is disposed on the first main surface 5a of the piezoelectric layer 5, and is embedded in the dielectric layer 4 except for the portion in contact with the first main surface 5a. The wavelength determined by the distance between the electrode fingers in the first IDT electrode 6 is denoted as λ. The wavelength-normalized thickness of the metal film constituting the first IDT electrode 6 is denoted as te, and the wavelength-normalized thickness of the piezoelectric layer 5 is denoted as tp. Here, te / tp = x. Furthermore, te is the thickness of the electrode fingers, and tp is the thickness of the piezoelectric layer 5 in the intersection region. Moreover, the density of the metal film constituting the first IDT electrode 6, normalized to the total mass of the metal film with respect to the thickness te, is denoted as the average density y [g / cm³]. 3 At this point, F(x) given by the following equation (1) is set to 10 or less.

[0049] F(x) = Ax 2 +Bx+C… equation (1)

[0050] In addition, in equation (1), A and B are represented by equations (2) and (3) below, and C = 19.

[0051] A = 1.0392y 2 +8.4182y-45.223… Equation (2)

[0052] B = 0.0334y 2 -11.363y+28.984… Equation (3)

[0053] In the elastic wave device 1, the aforementioned F(x) is 10 or less, thus effectively suppressing ripples caused by Rayleigh waves. (Refer to...) Figures 3 to 11 This will be explained in more detail.

[0054] Figure 3 This is a graph showing the relationship between the Euler angle θ and the Rayleigh wave coupling coefficient of LiTaO3 in a conventional elastic wave device. Additionally, results are shown for the case where the IDT electrode is Al. Figure 3 In the diagram, the solid line shows the results when tp = 0.2, and the dashed line shows the results when tp = 0.3. Regardless of whether tp = 0.2 or tp = 0.3, the Euler angle θ at which the coupling coefficient of the Rayleigh wave becomes minimal remains almost unchanged.

[0055] also, Figure 4 This is a graph showing the relationship between tp and the optimal Euler angle θ when te / tp = 0.15, 0.2, or 0.25. According to... Figure 4 It is clear that even assuming te / tp varies to 0.15, 0.2, or 0.25, the change in the optimal angle is small. Therefore, it can be seen that when the IDT electrode contains Al, even if resonators with different spacings are constructed on the same piezoelectric composite substrate, the Euler angle θ can be easily set to the optimal angle, and Rayleigh waves can be suppressed in resonators with different electrode finger spacings in any case.

[0056] However, in conventional elastic wave devices, when the IDT electrode is Cu, such as Figure 5 As shown, if te / tp varies to 0.12, 0.16, or 0.2, the optimal Euler angle θ changes significantly. Therefore, when multiple resonators are constructed on the same piezoelectric composite substrate, if the electrode finger spacing of the multiple resonators is different, the Euler angle will deviate from the optimal Euler angle θ depending on the resonator. Consequently, there may be resonators that cannot suppress the ripple caused by Rayleigh waves.

[0057] In contrast, Figure 6 This is a graph showing the relationship between tp and the optimal angle θ when the first IDT electrode 6 in the first embodiment of the present invention contains Cu. According to... Figure 6It is clear that even assuming te / tp varies to 0.12, 0.16, or 0.2, the optimal Euler angle θ remains almost unchanged. Therefore, according to the elastic wave device 1 of this embodiment, even assuming that multiple elastic wave resonators with different electrode finger spacings are formed on the same piezoelectric composite substrate 2, ripple caused by Rayleigh waves can be effectively suppressed. This is because, in this embodiment, as will be described later, F(x) is set to 10 or less.

[0058] Figure 7 This is a graph showing the relationship between tp and the optimal Euler angle θ when the IDT electrode contains Pt in a conventional elastic wave device. According to... Figure 7 It is clear that when the IDT electrode contains Pt, the optimal Euler angle θ will vary significantly depending on whether te / tp changes to 0.06, 0.08, or 0.1. Therefore, similar to the case with Cu, when multiple elastic wave resonators are constructed on the same piezoelectric composite substrate, elastic wave resonators that cannot adequately suppress ripples caused by Rayleigh waves will be produced.

[0059] Figure 8 This is a graph showing the relationship between tp and the optimal Euler angle θ when the IDT electrode is Pt in the elastic wave device of the first embodiment of the present invention. Figure 8 It is clearly known that the difference in the optimal angle of the Euler angle θ is small regardless of whether te / tp is 0.06, 0.08, or 0.1. Therefore, in the case of Pt as the IDT electrode, the ripple caused by Rayleigh waves can be effectively suppressed according to this embodiment, just as in the case of Cu.

[0060] Figure 9 This shows the difference θ between te / tp and the optimal cut angle for the piezoelectric layer when the IDT electrode is Cu and the wavelength ratio of the piezoelectric layer is at its minimum of 15%λ and its maximum of 45%λ. H -θ I The graph shows the relationship between the two embodiments. The solid line shows the results of the first embodiment, and the dashed line shows the results of the elastic wave device of the conventional embodiment.

[0061] also, Figure 10 This shows te / tp and θ when the IDT electrode is Pt. H -θ L The graph shows the relationship between the results of the first embodiment (solid line) and the results of the conventional elastic wave device (dashed line).

[0062] according to Figure 9 as well as Figure 10 It is clear that, in cases where the metal film constituting the IDT electrode is relatively heavy, such as Cu or Pt, as te / tp increases, θ increases, unlike in conventional elastic wave devices. H -θL It continuously decreases. In contrast, in conventional elastic wave devices, the larger te / tp becomes, the smaller the optimal cutting angle difference θ becomes. H -θ L It gets bigger and bigger.

[0063] Therefore, when using high-density metal films such as Cu and Pt, the elastic wave speed can be reduced, and the response is less likely to change due to Rayleigh waves relative to the change in tp.

[0064] Therefore, in order to obtain an elastic wave device that is not prone to ripples caused by Rayleigh waves due to variations in tp, the optimal cutting angle difference θ at the upper and lower limits of tp is determined. H -θ L Smaller is better. Moreover, according to... Figure 9 as well as Figure 10 It is clear that, given a fixed electrode density, this value becomes a function of te / tp. The inventors of this application have discovered that, when te / tp = x, this function can be expressed by equation (1).

[0065] Therefore, preferably, the metal film constituting the first IDT electrode 6 comprises a metal layer containing a metal with a higher density than Al. More preferably, the metal layer with a higher density than Al is the main metal layer of the metal film.

[0066] In addition, the coefficients A and B in equation (1) are represented by the aforementioned equations (2) and (3), and C is 19.

[0067] Furthermore, when the first IDT electrode 6 comprises n (n is a natural number) stacked films, if the density of the i-th layer is ρi and the volume is ti, then y is represented by the average density of the electrode layers, i.e., by y = ∑(ti × ρi) / ∑(ti). Here, ∑(ti × pi) is the total mass. Additionally, ti is the volume, but when the electrode finger cross-section is approximately rectangular, it can be replaced by the thickness.

[0068] Figure 11 This diagram illustrates the coefficients A and B in the elastic wave device according to the above embodiment. It can be seen that regardless of whether the metal film constituting the IDT electrode is Al, Cu, or Pt, A and B can be represented by the above equations (2) and (3). Furthermore, Figure 11 y is Figure 11The density value of the metal film. Therefore, in this invention, by setting te / tp and the density of the metal constituting the IDT electrode such that F(x), as expressed by formula (1), is below a certain range, ripple caused by Rayleigh waves can be effectively suppressed. In this invention, F(x) is 10 or less, more preferably 5 or less. Thus, ripple caused by Rayleigh waves can be effectively suppressed regardless of the type and density of the metal film constituting the IDT electrode.

[0069] This can be attributed to the fact that by setting the electrode forming surface in the piezoelectric layer as the first principal surface, i.e., as the support substrate side, the relationship between the Euler angle θ dependence of the Rayleigh wave coupling coefficient and the quality of the metal film constituting the IDT electrode is reversed compared to the case of the elastic wave device in the conventional example.

[0070] Figure 12 This is a front cross-sectional view showing the main parts of the elastic wave device according to the second embodiment of the present invention. In the elastic wave device 21, the piezoelectric composite substrate 2 and Figure 1 Similarly, the device includes a support substrate 3, a dielectric layer 4, and a piezoelectric layer 5. However, in the elastic wave device 21, not only is the first IDT electrode 6 disposed on the first main surface 5a of the piezoelectric layer 5, but the second IDT electrode 22 is also disposed on the second main surface 5b. The second IDT electrode 22 is configured to overlap the first IDT electrode 6 across the piezoelectric layer 5. Furthermore, the metal film constituting the second IDT electrode 22 is the same as that constituting the first IDT electrode 6. However, the metal film constituting the second IDT electrode 22 may also be different from the metal film constituting the first IDT electrode 6.

[0071] In the elastic wave device 21 of the second embodiment, as long as G(x) represented by the following formula (4) is set to 10 or less, preferably 5 or less, ripple caused by Rayleigh waves can be effectively suppressed. Furthermore, the following formulas (4) to (6) are formulas specified in the second IDT electrode 22. Therefore, the following formulas (4) to (6) are defined as follows: the wavelength determined by the electrode finger spacing of the second IDT electrode 22 is set to λ; the wavelength-normalized thickness of the metal film constituting the second IDT electrode 22 is set to te; the wavelength-normalized thickness of the piezoelectric layer 5 is set to tp; te / tp = x; and the average density (g / m³) is set to y, which is the average density of the metal film constituting the second IDT electrode 22 normalized to the total mass of the metal film constituting the second IDT electrode 22 using the thickness te of the metal film. 3 The formula when ].

[0072] G(x)=Ax 2 +Bx+C… equation (4)

[0073] In addition, in equation (4), A and B are represented by equations (5) and (6) below, and C = 19.

[0074] A = 0.0564y 2 +39.909y-29.023… Equation (5)

[0075] B = 0.1407y 2 -11.875y+5.4093… Equation (6)

[0076] In this case, the potential of the second IDT electrode 22 can also have any phase.

[0077] However, when exciting the SH wave, the electrodes of the second IDT electrode 22, which are opposite to the first IDT electrode 6, are preferably in phase with each other. In the second embodiment, it is preferable that the mass addition of the first IDT electrode 6 is greater than the mass addition of the second IDT electrode 22.

[0078] The relationship between the density of the second IDT electrode 22 and the coefficient A or B in equation (4) is shown when the masses of the first IDT electrode 6 and the second IDT electrode 22 are approximately equal. Figure 13 .exist Figure 13 In the diagram, solid lines represent equation (5), and dashed lines represent equation (6). Additionally, Figure 13 y is Figure 13 The value of the density of the metal film.

[0079] A = 0.0564y 2 +39.909y-29.023… Equation (5)

[0080] B = 0.1407y 2 -11.875y+5.4093… Equation (6)

[0081] In the elastic wave device 21 of the second embodiment, G(x) is 10 or less, preferably 5 or less, in which case the ripple caused by Rayleigh waves can be effectively suppressed.

[0082] Figure 14 This is a front cross-sectional view showing the main parts of the elastic wave device according to the third embodiment of the present invention. In the elastic wave device 31, a conductive film 32 is provided on the second main surface 5b of the piezoelectric layer 5. Other structures of the elastic wave device 31 are similar to those of the piezoelectric layer 5. Figure 1 The elastic wave device 1 shown is the same. Similarly, a conductive film 32 can be provided on the second main surface 5b side. In this case, the conductive film 32 can be configured as a floating electrode and positioned opposite at least a portion of the first IDT electrode 6. In this case, a capacitor is formed via the piezoelectric layer 5.

[0083] Alternatively, the conductive film 32 and dielectric layer 4 can be disposed only in the region opposite to the tip of the electrode finger of the first IDT electrode 6. In this case, the sound velocity in the region at the tip of the electrode finger can be reduced, thereby constituting an elastic wave device utilizing a piston mode.

[0084] Figure 15 This is a front cross-sectional view showing the main parts of the elastic wave device according to the fourth embodiment of the present invention. In the elastic wave device 41, a first elastic wave resonator 42A and a second elastic wave resonator 42B are formed in the piezoelectric composite substrate 2. The electrode finger spacing of the IDT electrode 6A of the first elastic wave resonator 42A and the electrode finger spacing of the IDT electrode 6B of the second elastic wave resonator 42B are different. That is, the resonant frequencies of the first and second elastic wave resonators 42A and 42B are different. Even in this case, as mentioned above, since the optimal cutting angle of the LiTaO3 constituting the piezoelectric layer 5 is close, it is possible to effectively suppress ripple caused by Rayleigh waves in both the first and second elastic wave resonators 42A and 42B.

[0085] Furthermore, in the elastic wave device of the present invention, three or more elastic wave resonators may be configured in the same piezoelectric composite substrate. Even in this case, according to the present invention, by setting F(x) to 10 or less, the ripple caused by Rayleigh waves in each elastic wave resonator can be effectively suppressed.

[0086] Explanation of reference numerals in the attached figures

[0087] 1, 21, 31, 41: Elastic wave device;

[0088] 2: Piezoelectric composite substrate;

[0089] 3: Support base plate;

[0090] 4: Dielectric layer;

[0091] 5: Piezoelectric layer;

[0092] 5a: First main face;

[0093] 5b: 2nd main surface;

[0094] 6: First IDT electrode;

[0095] 6A, 6B: IDT electrodes;

[0096] 7, 8: Reflectors;

[0097] 22: Second IDT electrode;

[0098] 32: Conductive film;

[0099] 42A: First elastic wave resonator;

[0100] 42B: Second elastic wave resonator.

Claims

1. An elastic wave device, comprising: A piezoelectric composite substrate comprising a piezoelectric layer and a support substrate, the piezoelectric layer having a first main surface and a second main surface facing each other and comprising lithium tantalate, the piezoelectric layer being directly or indirectly laminated onto the support substrate from the first main surface side; and The first IDT electrode is disposed on the first main surface of the piezoelectric layer. The first IDT electrode comprises a metal film. Let λ be the wavelength determined by the distance between the electrode fingers of the first IDT electrode, let te be the thickness of the metal film of the first IDT electrode normalized to wavelength λ, and let tp be the thickness of the piezoelectric layer normalized to wavelength λ. Let te / tp = x, and let y be the average density of the metal film normalized to its total mass using the thickness te, where y is in g / cm³. 3 At this point, F(x) given by the following equation (1) is less than 10. F(x) = Ax 2 +Bx+C …Equation (1) Furthermore, in equation (1), A and B are represented by equations (2) and (3) below, and C = 19. A=1.0392y 2 +8.4182y-45.223 …Equation (2) B=0.0334y 2 -11.363y+28.984 …Equation (3).

2. The elastic wave device according to claim 1, wherein, The value of F(x) is 5 or less.

3. The elastic wave device according to claim 1 or 2, wherein, A conductive film is provided on the second main surface of the piezoelectric layer.

4. An elastic wave device, comprising: A piezoelectric composite substrate has a piezoelectric layer and a support substrate. The piezoelectric layer has a first main surface and a second main surface that are opposite to each other and contains lithium tantalate. The piezoelectric layer is directly or indirectly stacked on the support substrate from the first main surface side. A first IDT electrode is disposed on the first main surface of the piezoelectric layer; and The second IDT electrode is disposed on the second main surface of the piezoelectric layer, and is opposite to the first IDT electrode across the piezoelectric layer. The second IDT electrode comprises a metal film. Let λ be the wavelength determined by the distance between the electrode fingers of the second IDT electrode; let te be the thickness of the metal film of the second IDT electrode normalized to wavelength λ; let tp be the thickness of the piezoelectric layer normalized to wavelength λ; let te / tp = x; and let y be the average density of the metal film normalized to its total mass using the thickness te, where y is in g / cm³. 3 At this point, G(x) given by the following equation (4) is less than 10. G(x) = Ax 2 +Bx+C …Equation (4) Furthermore, in equation (4), A and B are represented by equations (5) and (6) below, and C = 19. A=0.0564y 2 +39.909y-29.023 …Equation (5) B=0.1407y 2 -11.875y+5.4093 … Equation (6).

5. The elastic wave device according to claim 1 or 4, wherein, The metal film constituting the first IDT electrode comprises a metal layer containing a metal with a density higher than Al.

6. The elastic wave device according to claim 5, wherein, The metal layer with a higher density than Al is the main metal layer of the metal film.

7. The elastic wave device according to claim 1 or 4, wherein, A dielectric layer is disposed between the support substrate and the first main surface of the piezoelectric layer, and the first IDT electrode is connected to the first main surface of the piezoelectric layer and embedded in the dielectric layer.

8. The elastic wave device according to claim 7, wherein, The dielectric layer comprises a material containing silicon oxide.

9. The elastic wave device according to claim 1 or 4, wherein, Two first IDT electrodes are disposed on the first main surface of the piezoelectric layer, and the electrode finger spacing of one of the two first IDT electrodes is set as P. A The electrode finger spacing of the other first IDT electrode is set to P. B At this time, the P A With the P B different.

10. The elastic wave device according to claim 1 or 4, wherein, The piezoelectric layer comprises lithium tantalate that is rotated Y-cut and X-propagated, with the cutting angle ranging from 40° to 60°.

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