Acoustic wave device

Abstract

To provide an acoustic wave device capable of easily adjusting a specific band without leading a change of a characteristic other than a main mode, and progressing a miniaturization.SOLUTION: An acoustic wave device 1 of the present invention, comprises: a piezoelectric layer 4; an IDT electrode 5 that is provided onto the piezoelectric layer 4, and includes a plurality of electrode fingers (a plurality of first electrode fingers 18 and a plurality of second electrode fingers); and a dielectric film 6 that is provided onto the piezoelectric layer 4 so as to cover the IDT electrode 5. When viewing it from a direction orthogonal to a direction where the plurality of electrode fingers is extended, a region where both of the adjacent electrode fingers are overlapped is an intersecting region. The acoustic wave device 1 further includes a thin film layer 7 that is at least partially embedded in the dielectric film 6, at least partially overlaps with the intersecting region in a planar view, and does not entirely overlap with the plurality of electrode fingers in a planar view, has a density higher than that of the dielectric film 6, and has a thickness thinner than the thickness of the plurality of electrode fingers. At different positions in a thickness direction of the dielectric film 6, the plurality of electrode fingers and the thin film layer 7 are positioned.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an elastic wave device.

Background Art

[0002] Conventionally, elastic wave devices have been widely used in filters for mobile phones and the like. In Patent Document 1 below, an example of an elastic boundary wave device as an elastic wave device is disclosed. In this elastic wave device, an insulating layer is provided on a piezoelectric substrate. Comb electrodes are provided on the interface between the piezoelectric substrate and the insulating layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the elastic wave device described in Patent Document 1 and the like, when miniaturization or adjustment of the specific bandwidth is performed, it is necessary to change the processing conditions and the design of the comb electrodes. However, when the processing conditions and the design of the comb electrodes are changed, the characteristics other than the main mode tend to change.

[0005] For example, in the case of the comb electrodes, when miniaturizing the elastic wave device by increasing the duty ratio, the difference between the frequency at which the main mode occurs and the frequency at which unnecessary waves occur also changes. Alternatively, when reducing the speed of sound of the elastic wave and miniaturizing the elastic wave device by increasing the thickness of the comb electrodes, the variation in the processing of the comb electrodes becomes large, and there is a risk that the yield will be low. In addition, when the processing conditions and the design of the comb electrodes are changed, the frequency at which unnecessary waves such as higher-order modes occur and the frequency of the stop band may change. Therefore, when the elastic wave device is used in a filter device or the like, the characteristics within the pass band of the filter device or the like may deteriorate.

[0006] An object of the present invention is to provide an elastic wave device that can easily adjust the specific bandwidth and promote miniaturization without causing changes in characteristics other than the main mode.

Means for Solving the Problems

[0007] The elastic wave device according to the present invention includes a piezoelectric layer, an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, and a dielectric film provided on the piezoelectric layer so as to cover the IDT electrode. When viewed from a direction orthogonal to the direction in which the plurality of electrode fingers extend, a region where adjacent electrode fingers overlap is a crossing region, at least a part of which is embedded in the dielectric film, and in a plan view, at least a part overlaps with the crossing region, and in a plan view, the whole does not overlap with the plurality of electrode fingers, and further includes a thin film layer having a density higher than that of the dielectric film and a thickness thinner than that of the plurality of electrode fingers, and the plurality of electrode fingers and the thin film layer are located at different positions in the thickness direction of the dielectric film.

Effects of the Invention

[0008] According to the elastic wave device of the present invention, the specific bandwidth can be easily adjusted and miniaturization can be promoted without causing changes in characteristics other than the main mode.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

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Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

[0011] It should be noted that each embodiment described in this specification is exemplary, and it is pointed out that partial substitution or combination of configurations is possible between different embodiments.

[0012] FIG. 1 is a schematic plan view of an elastic wave device according to a first embodiment of the present invention. In FIG. 1, a second dielectric film described later is omitted.

[0013] As shown in FIG. 1, the elastic wave device 1 includes a piezoelectric layer 4, an IDT electrode 5, a dielectric film 6, and a plurality of thin film layers 7. The IDT electrode 5 is provided on the piezoelectric layer 4. A dielectric film 6 is provided on the piezoelectric layer 4 so as to cover the IDT electrode 5. A plurality of thin film layers 7 are embedded in the dielectric film 6.

[0014] The piezoelectric layer 4 has a first main surface 4a and a second main surface 4b. The first main surface 4a and the second main surface 4b face each other. An IDT electrode 5 and a dielectric film 6 are provided on the first main surface 4a.

[0015] As the material of the piezoelectric layer 4, for example, lithium tantalate, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate) can be used. As the material of the piezoelectric layer 4, it is preferable to use lithium tantalate or lithium niobate.

[0016] FIG. 2 is a schematic plan view showing the electrode configuration on the first main surface of the piezoelectric layer for explaining the configuration of the IDT electrode in the first embodiment.

[0017] The IDT electrode 5 has a pair of bus bars and a plurality of electrode fingers. Specifically, the pair of bus bars are a first bus bar 16 and a second bus bar 17. The first bus bar 16 and the second bus bar 17 face each other. The plurality of electrode fingers are specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One ends of the plurality of first electrode fingers 18 are each connected to the first bus bar 16. One ends of the plurality of second electrode fingers 19 are each connected to the second bus bar 17. The first electrode finger 18 and the second electrode finger 19 are connected to different potentials. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interposed with each other.

[0018] Pt is used as the material of the IDT electrode 5. Note that the material of the IDT electrode 5 is not limited to the above. Alternatively, the IDT electrode 5 may be made of a laminated metal film.

[0019] Hereinafter, the first bus bar 16 and the second bus bar 17 may be simply referred to as bus bars. The first electrode finger 18 and the second electrode finger 19 may be simply referred to as electrode fingers. The direction in which the plurality of electrode fingers extend is defined as the electrode finger extension direction, and the direction orthogonal to the electrode finger extension direction is defined as the electrode finger orthogonal direction.

[0020] Figure 3 is a schematic cross-sectional view showing the vicinity of one electrode finger along the line I-I in Figure 1.

[0021] The dielectric film 6 has a first dielectric film 6a and a second dielectric film 6b. The first dielectric film 6a is provided on the piezoelectric layer 4. The second dielectric film 6b is provided on the first dielectric film 6a. The material of the first dielectric film 6a and the material of the second dielectric film 6b are different from each other. In the present embodiment, the first dielectric film 6a is made of silicon oxide. The second dielectric film 6b is made of silicon nitride. Note that the materials of the first dielectric film 6a and the second dielectric film 6b are not limited to the above. In this specification, that a certain member is made of a certain material includes the case where a trace amount of impurities that do not significantly deteriorate the electrical characteristics of the elastic wave device is included.

[0022] In the present embodiment, the dielectric film 6 is a two-layer laminate. Note that the dielectric film 6 may be a laminate of three or more layers, or may be a single-layer dielectric film.

[0023] The thin film layer 7 has a first surface 7a, a second surface 7b, and a side surface 7c. The first surface 7a and the second surface 7b face each other in the thickness direction of the thin film layer 7. Of the first surface 7a and the second surface 7b, the second surface 7b is the surface on the piezoelectric layer 4 side. The side surface 7c is connected to the first surface 7a and the second surface 7b.

[0024] The thin film layer 7 is located within the dielectric film 6. Specifically, in the present embodiment, the surfaces other than the first surface 7a are covered with the first dielectric film 6a. On the other hand, the first surface 7a is covered with the second dielectric film 6b. In this way, the entire thin film layer 7 is embedded in the dielectric film 6. However, at least a part of the thin film layer 7 may be embedded in the dielectric film 6.

[0025] In this specification, when it is assumed that the entire thin film layer 7 is embedded in the dielectric film 6, all portions of all surfaces of the thin film layer 7 other than the first surface 7a are covered by the dielectric film 6, including the case where the first surface 7a is not covered by the dielectric film 6. On the other hand, for example, when a part of the side surface 7c of the thin film layer 7 is not covered by the dielectric film 6 and the first surface 7a is not covered by the dielectric film 6, it is assumed that not the entire thin film layer 7 but a part thereof is embedded in the dielectric film 6.

[0026] As shown in FIG. 2, the surface acoustic wave device 1 has an overlapping region A. The overlapping region A is a region where adjacent electrode fingers overlap when viewed from the direction orthogonal to the electrode fingers. The overlapping region A is a region of the piezoelectric layer 4 defined based on the configuration of the IDT electrode 5. However, it can also be said that the overlapping region A is a region of the IDT electrode 5 in showing the configuration of the IDT electrode 5.

[0027] As shown in FIG. 1, the plurality of thin film layers 7 overlap the overlapping region A in a plan view. Specifically, all portions of the plurality of thin film layers 7 overlap the overlapping region A in a plan view. Note that a part of the thin film layer 7 may reach a portion that does not overlap the overlapping region A in a plan view. In this specification, the plan view means viewing the surface acoustic wave device from a direction corresponding to above in FIG. 3. In FIG. 3, for example, of the first dielectric film 6a side and the second dielectric film 6b side, the second dielectric film 6b side is above.

[0028] In a plan view, the entire thin film layer 7 does not overlap the electrode fingers. Note that in a plan view, the thin film layer 7 is located between the electrode fingers. On the other hand, in a cross section along the direction orthogonal to the electrode fingers of the surface acoustic wave device 1 shown in FIG. 3, the thin film layer 7 is not located between the electrode fingers. More specifically, in this cross section, in the direction orthogonal to the electrode fingers, the thin film layer 7 and the electrode fingers do not overlap. Therefore, the thin film layer 7 is not in contact with the piezoelectric layer 4.

[0029] More specifically, each electrode finger has a first surface 5a, a second surface 5b, and a side surface 5c. The first surface 5a and the second surface 5b face each other in the thickness direction of the electrode finger. Among the first surface 5a and the second surface 5b, the second surface 5b is the surface on the piezoelectric layer 4 side. The side surface 5c is connected to the first surface 5a and the second surface 5b. The distance between the first main surface 4a of the piezoelectric layer 4 and the second surface 7b of the thin film layer 7 is longer than the distance between the first main surface 4a of the piezoelectric layer 4 and the first surface 5a of the electrode finger. Therefore, a plurality of electrode fingers and the thin film layer 7 are located at different positions in the thickness direction of the dielectric film 6.

[0030] The thickness of the thin film layer 7 is thinner than the thickness of the electrode finger. The thin film layer 7 is made of Pt. Note that the material of the thin film layer 7 is not limited to the above. It is sufficient that the density of the thin film layer 7 is higher than the density of the dielectric film 6. When the dielectric film 6 is a laminate, it is sufficient that the density of the thin film layer 7 is higher than the density of any layer of the dielectric film in the dielectric film 6. The thin film layer 7 may be made of a metal or may be made of a dielectric.

[0031] As shown in FIG. 2, a pair of reflectors 8A and 8B are provided on the first main surface 4a of the piezoelectric layer 4. More specifically, the reflectors 8A and 8B face each other with the IDT electrode 5 interposed therebetween in the direction orthogonal to the electrode finger. Each of the reflectors 8A and 8B has a plurality of reflector electrode fingers 8a. By applying an alternating voltage to the IDT electrode 5, an elastic wave used as a main mode is excited in the crossover region A. The elastic wave device 1 of the present embodiment is a surface acoustic wave device.

[0032] As shown in FIGS. 1 and 3, the feature of this embodiment is that it has the following configuration. 1) At least a part of the thin film layer 7 is embedded in the dielectric film 6, and in a plan view, at least a part of the thin film layer 7 overlaps with the crossing region A, and in a plan view, the whole of the thin film layer 7 does not overlap with a plurality of electrode fingers. 2) The density of the thin film layer 7 is higher than the density of the dielectric film 6, and the thickness of the thin film layer 7 is thinner than the thickness of the plurality of electrode fingers. 3) The plurality of electrode fingers and the thin film layer 7 are located at different positions in the thickness direction of the dielectric film 6. Thereby, the specific band can be easily adjusted without causing changes in characteristics other than the main mode, and the miniaturization of the elastic wave device 1 can be promoted. The specific band is represented by (|fa - fr| / fr)×100[%] when the resonance frequency is fr and the anti-resonance frequency is fa. The details of the above effects will be described below.

[0033] In this embodiment, the thin film layer 7 is embedded in the dielectric film 6 so as to overlap with the crossing region A in a plan view, and the density of the thin film layer 7 is higher than the density of the dielectric film 6. Thereby, mass can be suitably added to the crossing region A. Thereby, the electromechanical coupling coefficient of the main mode can be increased. The larger the electromechanical coupling coefficient is, the smaller the value of the specific band is. Therefore, by adjusting the thickness and density of the thin film layer 7 and adjusting the mass added to the crossing region A, the specific band of the main mode can be easily adjusted. Thereby, the specific band can be easily adjusted without changing the processing conditions and design of the IDT electrode 5.

[0034] In addition, due to the addition of mass by the thin film layer 7, the sound velocity of the sound wave propagating on the surface of the piezoelectric layer 4 becomes lower. Thereby, the sound velocity of the main mode can be lowered. Here, when the sound velocity is v, the frequency is f, and the wavelength is λ0, the relationship f = v / λ0 holds. When obtaining a desired frequency f, when the sound velocity v becomes lower, the wavelength λ0 becomes shorter.

[0035] In the elastic wave device 1, the wavelength is defined by the electrode finger pitch. When this wavelength is λ and the electrode finger pitch is p, λ = 2p. In the present embodiment, since the addition of mass by the thin film layer 7 can lower the sound velocity of the main mode, the wavelength λ can be shortened. As a result, the electrode finger pitch p can be narrowed. Therefore, the IDT electrode 5 can be miniaturized, and the overall size reduction of the elastic wave device 1 can be promoted.

[0036] Note that in this specification, the electrode finger pitch is the distance in the direction orthogonal to the electrode fingers between the centers of adjacent electrode fingers. On the other hand, in this specification, the distance between adjacent electrode fingers is the distance in the direction orthogonal to the electrode fingers between the closer edge portions of adjacent electrode fingers.

[0037] In the present embodiment, in a plan view, the thin film layer 7 does not overlap the electrode fingers. A plurality of electrode fingers and the thin film layer 7 are located at different positions in the thickness direction of the dielectric film 6. By these, even when the thin film layer 7 is made of metal, the influence of the thin film layer 7 itself on the electrical characteristics of the elastic wave device 1 can be suppressed. On the other hand, by the addition of mass by the thin film layer 7, the specific bandwidth can be adjusted, and the electrode finger pitch p can be narrowed. As described above, in the present embodiment, the specific bandwidth of the main mode can be easily adjusted without causing changes in characteristics other than the main mode, and the size reduction of the elastic wave device 1 can be promoted.

[0038] Hereinafter, the effects in the first embodiment will be specifically shown. As a comparative example, an elastic wave device different from the first embodiment in that it does not have a thin film layer was prepared. In the first embodiment and the comparative example, the impedance frequency characteristics were compared. The design parameters of the elastic wave device 1 of the first embodiment are as follows. Here, the dimension along the electrode finger extending direction in the crossover region A is defined as the crossover width. The width of the thin film layer 7 is the dimension along the direction orthogonal to the electrode fingers of the thin film layer 7.

[0039] Thin film layer: Material... Pt, Thickness... 100 nm, Width... 1 μm The first dielectric film: Material... SiO 2 , Thickness... 1805 nm The second dielectric film: Material... SiN, Thickness... 40 nm Overlap width: 72 μm Electrode finger pitch: 2.4 μm Distance between adjacent electrode fingers: 1.3 μm Electrode fingers: Material... Pt, Thickness... 500 nm Number of pairs of electrode fingers: 80 pairs Duty ratio of IDT electrodes: 0.45 Number of pairs of reflector electrode fingers: 10 pairs Duty ratio of reflector: 0.45

[0040] The design parameters in the comparative example were the same as those in the first embodiment, except that no thin film layer was provided.

[0041] FIG. 4 is a diagram showing the impedance frequency characteristics in the first embodiment and the comparative example.

[0042] As shown in FIG. 4, in the first embodiment, it can be seen that the difference between the resonance frequency and the anti-resonance frequency is smaller than that in the comparative example. That is, in the first embodiment, the value of the specific bandwidth is smaller than that in the comparative example. Specifically, the specific bandwidth in the first embodiment is 7.5%, and the specific bandwidth in the comparative example is 7.9%. When these are converted as the area ratio of the IDT electrodes, the area of the IDT electrodes in the first embodiment is 0.995 times the area of the IDT electrodes in the comparative example. Thus, in the first embodiment, miniaturization of the surface acoustic wave device can be promoted.

[0043] As shown in FIG. 3, in the first embodiment, the first surface 7a of the thin film layer 7 is exposed from the first dielectric film 6a. However, the first surface 7a of the thin film layer 7 may be covered by the first dielectric film 6a. Alternatively, the entire second surface 7b of the thin film layer 7 and a part of the side surface 7c may be covered by the first dielectric film 6a, and the remaining part of the side surface 7c of the thin film layer 7 and the entire first surface 7a may be covered by the second dielectric film 6b.

[0044] In the first embodiment, in a plan view, one thin film layer 7 is located at each portion between all electrode fingers. All portions of each thin film layer 7 overlap the crossing region A in a plan view. Further, the dimension along the extending direction of the electrode fingers of each thin film layer 7 is the same as the crossing width. Note that the configuration of the plurality of thin film layers 7 is not limited thereto. In the following, first to third modified examples of the first embodiment, which differ from the first embodiment only in the arrangement or dimension of the thin film layer 7, are shown. Also in the first to third modified examples, similar to the first embodiment, the specific bandwidth can be easily adjusted without causing changes in characteristics other than the main mode, and miniaturization can be promoted.

[0045] In the first modified example shown in FIG. 5, in a plan view, the thin film layer 7 is located at the portions between a plurality of electrode fingers, and the thin film layer 7 is not located at least at one portion between the electrode fingers. All portions of each thin film layer 7 overlap the crossing region in a plan view. Note that in FIG. 5, the thin film layer 7 is shown with hatching. The same applies to FIG. 6.

[0046] However, as in the first embodiment, it is preferable that the thin film layer 7 is located at all portions between the electrode fingers in a plan view. Thereby, mass can be effectively added to the crossing region. In addition, the uniformity of the added mass can be increased.

[0047] In the second modified example shown in FIG. 6, at least one thin film layer 7 has a portion overlapping the crossing region and a portion overlapping a portion outside the crossing region in a plan view. The thin film layer 7 overlaps the first bus bar 16 in a plan view. On the other hand, the end portion of the thin film layer 7 on the side of the second bus bar 17 overlaps the crossing region in a plan view. However, the thin film layer 7 may overlap both the first bus bar 16 and the second bus bar 17 in a plan view. Alternatively, when the end portion of the thin film layer 7 in the extending direction of the electrode fingers overlaps a portion outside the crossing region in a plan view, the end portion may overlap a portion between the bus bar and the crossing region in a plan view.

[0048] In the third modification example shown in FIG. 7, in plan view, the two thin film layers 7 overlap the portion between the same electrode fingers. The two thin film layers 7 that overlap the portion between the same electrode fingers in plan view are arranged side by side in the direction orthogonal to the electrode fingers. Note that, for example, in plan view, three or more thin film layers 7 may overlap the portion between the same electrode fingers.

[0049] In the first embodiment, the dielectric film 6 is a laminate. However, the dielectric film 6 may be a single-layer film. For example, in the fourth modification example of the first embodiment shown in FIG. 8, the dielectric film 6A is a single-layer film. Note that the dielectric film 6A corresponds to the first dielectric film 6a in the first embodiment. The dielectric film 6A is provided so as to cover the IDT electrode 5 on the piezoelectric layer 4. All portions of the second surface 7b and the side surface 7c of the thin film layer 7 are covered with the dielectric film 6A. On the other hand, the first surface 7a of the thin film layer 7 is exposed from the dielectric film 6A. Also in this modification example, similar to the first embodiment, the ratio bandwidth can be easily adjusted without causing changes in characteristics other than the main mode, and miniaturization can be promoted.

[0050] In this modification example, the entire thin film layer 7 is embedded in the dielectric film 6A. Note that, for example, a part of the thin film layer 7 may be embedded in the dielectric film 6A. Specifically, all of the second surface 7b of the thin film layer 7 and a part of the side surface 7c may be covered with the dielectric film 6A, and the remaining part of the side surface 7c of the thin film layer 7 and the entire first surface 7a may be exposed from the dielectric film 6A. Also in this case, the ratio bandwidth can be easily adjusted without causing changes in characteristics other than the main mode, and miniaturization can be promoted.

[0051] However, it is preferable that the entire thin film layer 7 is embedded in the dielectric film 6A. Thereby, the thin film layer 7 is less likely to be damaged. More preferably, as in the first embodiment shown in FIG. 3, the thin film layer 7 is located within the dielectric film 6. That the thin film layer 7 is located within the dielectric film 6 means that all surfaces of the thin film layer 7 are covered with the dielectric film 6. In this case, the thin film layer 7 is even less likely to be damaged.

[0052] In the first embodiment, the material of the thin film layer 7 is the same as the material of the electrode fingers. Thereby, the types of materials to be used can be reduced, and the productivity of the surface acoustic wave device 1 can be increased. In addition, since the material of the thin film layer 7 is made of metal, it is easy to increase the density of the material of the thin film layer 7, and it is easy to suitably add mass to the crossover region A.

[0053] Note that the electrode fingers may be made of a laminated metal film. For example, in the fifth modification of the first embodiment shown in FIG. 9, each electrode finger of the IDT electrode 5A includes metal layers 13a, 13b, 13c, and 13d as a plurality of metal layers. From the piezoelectric layer 4 side, the metal layer 13a, the metal layer 13b, the metal layer 13c, and the metal layer 13d are laminated in this order. In this case, the first surface 5a of the electrode finger is the surface of the metal layer 13d far from the piezoelectric layer 4. The second surface 5b is the surface of the metal layer 13a on the piezoelectric layer 4 side. However, when the electrode finger includes a plurality of metal layers, the number of layers of the plurality of metal layers is not limited to four layers.

[0054] In this modification, the material of the thin film layer 7 is the same as the material of any one of the plurality of metal layers. When the material of the thin film layer 7 is the same as at least part of the material of the electrode fingers as in this modification and the first embodiment, the productivity of the surface acoustic wave device can be increased, and mass can be suitably added to the crossover region. Note that the material of the thin film layer 7 does not necessarily have to be the same as the material of any metal layer of the electrode fingers. For example, the density of the thin film layer 7 may be higher than the density of any metal layer.

[0055] Also in this modification, similar to the first embodiment, the fractional bandwidth can be easily adjusted without causing changes in characteristics other than the main mode, and miniaturization can be advanced.

[0056] Incidentally, in the above, an example of the design parameters of the elastic wave device 1 according to the first embodiment was shown. Each parameter may be, for example, within the following ranges. The electrode finger pitch may be 0.62 μm or more and 3 μm or less. The distance between adjacent electrode fingers may be 0.31 μm or more and 1.5 μm or less. The thickness of the thin film layer 7 may be in the range of 10 nm or more and 300 nm or less. The width of the thin film layer 7 may be in the range of 0.31 μm or more and 1.5 μm or less.

[0057] FIG. 10 is a schematic front cross-sectional view showing the vicinity of one electrode finger in the second embodiment.

[0058] This embodiment is different from the first embodiment in that the piezoelectric layer 4 and the support substrate 23 are laminated to form a piezoelectric substrate 22. The piezoelectric substrate 22 is a substrate having piezoelectricity. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 1 of the first embodiment.

[0059] Also in this embodiment, similar to the first embodiment, at least a part of the thin film layer 7 is embedded in the dielectric film 6, and in plan view, at least a part of the thin film layer 7 overlaps the crossing region, and in plan view, the entire thin film layer 7 does not overlap a plurality of electrode fingers. The density of the thin film layer 7 is higher than the density of the dielectric film 6, and the thickness of the thin film layer 7 is thinner than the thickness of the electrode fingers. A plurality of electrode fingers and the thin film layer 7 are located at different positions in the thickness direction of the dielectric film 6. Thereby, the specific band can be easily adjusted without causing changes in characteristics other than the main mode, and the miniaturization of the elastic wave device can be promoted.

[0060] In the piezoelectric substrate 22, the piezoelectric layer 4 is directly provided on the support substrate 23. However, it is not limited thereto. For example, the piezoelectric substrate 22A in the modification of the second embodiment shown in FIG. 11 has a support substrate 23, an intermediate layer 25, and a piezoelectric layer 4. The intermediate layer 25 is provided on the support substrate 23. The piezoelectric layer 4 is provided on the intermediate layer 25. Thus, the piezoelectric layer 4 is indirectly provided on the support substrate 23 via the intermediate layer 25. In this modification, the intermediate layer 25 is a single-layer dielectric layer. As the material of the intermediate layer 25, for example, a dielectric such as silicon oxide, tantalum oxide, or silicon nitride can be used. Note that the intermediate layer 25 may be a laminate including a plurality of dielectric layers.

[0061] Also in this modification, similar to the second embodiment, the ratio bandwidth can be easily adjusted without causing changes in characteristics other than the main mode, and the miniaturization of the elastic wave device can be promoted.

[0062] Hereinafter, examples of the form of the elastic wave device according to the present invention will be collectively described.

[0063] <1> An elastic wave device comprising a piezoelectric layer, an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, and a dielectric film provided on the piezoelectric layer so as to cover the IDT electrode, wherein when viewed from a direction orthogonal to the direction in which the plurality of electrode fingers extend, a region where adjacent electrode fingers overlap is a crossing region, at least a part of which is embedded in the dielectric film, and in plan view, at least a part overlaps with the crossing region, and in plan view, the whole does not overlap with the plurality of electrode fingers, and further comprising a thin film layer having a density higher than that of the dielectric film and a thickness thinner than that of the plurality of electrode fingers, and the plurality of electrode fingers and the thin film layer are located at different positions in the thickness direction of the dielectric film.

[0064] <2>The dielectric film has a first dielectric film provided on the piezoelectric layer and a second dielectric film provided on the first dielectric film, and the material of the first dielectric film is different from the material of the second dielectric film. The elastic wave device according to <1>.

[0065] <3>The entire thin film layer is embedded in the dielectric film. The elastic wave device according to <1> or <2>.

[0066] <4>The material of the thin film layer is the same as the material of at least a part of the electrode fingers. The elastic wave device according to any one of <1> to <3>.

[0067] <5>The electrode fingers have a plurality of metal layers, and the material of the thin film layer is the same as the material of any one of the plurality of metal layers. The elastic wave device according to <4>.

[0068] <6>Further comprising a support substrate, and the piezoelectric layer is provided on the support substrate. The elastic wave device according to any one of <1> to <5>.

Explanation of Reference Numerals

[0069] 1... Elastic wave device 4... Piezoelectric layer 4a, 4b... First and second main surfaces 5, 5A... IDT electrodes 5a, 5b... First and second surfaces 5c... Side surface 6, 6A... Dielectric films 6a, 6b... First and second dielectric films 7... Thin film layer 7a, 7b... First and second surfaces 7c... Side surface 8A, 8B... Reflectors 8a... Reflector electrode fingers 13a to 13d... Metal layers 16, 17... First and second bus bars 18, 19... First and second electrode fingers 22, 22A... Piezoelectric substrates 23... Support substrate 25…Intermediate layer A…Intersection area

Claims

1. A piezoelectric layer, an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, a dielectric film provided on the piezoelectric layer so as to cover the IDT electrode, comprising: when viewed from a direction orthogonal to the direction in which the plurality of electrode fingers extend, a region where adjacent electrode fingers overlap is a crossover region, at least a part of which is embedded in the dielectric film, in plan view, at least a part of which overlaps with the crossover region, and in plan view, the whole does not overlap with the plurality of electrode fingers, having a density higher than that of the dielectric film and a thickness thinner than the thickness of the plurality of electrode fingers, further comprising a thin film layer, An elastic wave device in which the plurality of electrode fingers and the thin film layer are located at different positions in the thickness direction of the dielectric film.

2. The dielectric film has a first dielectric film provided on the piezoelectric layer and a second dielectric film provided on the first dielectric film, The elastic wave device according to claim 1, wherein the material of the first dielectric film and the material of the second dielectric film are different from each other.

3. The elastic wave device according to claim 1, wherein the whole of the thin film layer is embedded in the dielectric film.

4. The elastic wave device according to claim 1, wherein the material of the thin film layer is the same as the material of at least a part of the electrode fingers.

5. The electrode fingers have a plurality of metal layers, The elastic wave device according to claim 4, wherein the material of the thin film layer is the same as the material of any one of the plurality of metal layers.

6. further comprising a support substrate, The elastic wave device according to claim 1, wherein the piezoelectric layer is provided on the support substrate.

Images