Elastic wave device

Abstract

Provided is an elastic wave device capable of suppressing ripples near a resonance frequency. The elastic wave device (1) comprises a piezoelectric substrate (2) and an IDT electrode (7) disposed on the piezoelectric substrate (2). The piezoelectric substrate (2) comprises a high acoustic velocity layer and a piezoelectric layer (6). The IDT electrode (7) comprises first and second bus bars (14, 15) and a plurality of first and second electrode fingers (16, 17) alternately inserted into each other. First and second envelopes (A1, A2) which are imaginary lines formed by connecting the respective front ends of the plurality of first and second electrode fingers (16, 17) extend obliquely relative to the propagation direction of the elastic wave. A first dielectric film (9a, 9b) is disposed in at least one of a plurality of first gaps (G1) between the plurality of first electrode fingers (16) and the second bus bar (15) and a plurality of second gaps (G2) between the plurality of second electrode fingers (17) and the first bus bar (14), and the density of the first dielectric film (9a, 9b) is higher than that of silicon oxide.

Description

Technical Field

[0001] The present invention relates to elastic wave devices. Background Art

[0002] In the past, elastic wave devices have been widely used in filters for mobile phones and the like. An example of an elastic wave device is disclosed in the following patent document 1. The elastic wave device has a laminated body formed by laminating a low-acoustic-velocity film and a piezoelectric film in sequence on a high-acoustic-velocity support substrate, and an IDT electrode provided on the piezoelectric film. Although the elastic wave device having the above-mentioned laminated body can improve the Q value, there is a problem of generating transverse mode ripples.

[0003] In Patent Document 1, in order to suppress transverse mode ripples, the IDT electrode is an inclined IDT electrode. The inclined IDT electrode is an IDT electrode in which an imaginary line, i.e., an envelope line, formed by connecting the front ends of a plurality of electrode fingers connected to one bus bar and an imaginary line, i.e., an envelope line, formed by connecting the front ends of a plurality of electrode fingers connected to another bus bar extend obliquely with respect to the propagation direction of the elastic wave.

[0004] Prior Art Literature

[0005] Patent Literature

[0006] Patent Document 1: International Publication No. 2016 / 208236 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, even if an inclined IDT electrode is used, when it is used in combination with the above-mentioned laminate, ripples may be generated near the resonance frequency.

[0009] An object of the present invention is to provide an elastic wave device capable of suppressing ripples near a resonance frequency.

[0010] Means for solving problems

[0011] The elastic wave device of the present invention comprises: a piezoelectric substrate; and an IDT electrode, which is arranged on the piezoelectric substrate, the piezoelectric substrate has a high acoustic velocity layer and a piezoelectric layer directly or indirectly arranged on the high acoustic velocity layer, the acoustic velocity of the body wave propagating in the high acoustic velocity layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer, the IDT electrode has a first bus bar and a second bus bar facing each other, a plurality of first electrode fingers connected to the first bus bar at one end, and a plurality of second electrode fingers connected to the second bus bar at one end and alternately inserted with the plurality of first electrode fingers. A first envelope, an imaginary line formed by connecting the front ends of the plurality of first electrode fingers, extends obliquely relative to the direction of propagation of the elastic wave, and a second envelope, an imaginary line formed by connecting the front ends of the plurality of second electrode fingers, extends obliquely relative to the direction of propagation of the elastic wave. A first dielectric film is provided in at least one of the plurality of first gaps between the plurality of first electrode fingers and the second bus bar and the plurality of second gaps between the plurality of second electrode fingers and the first bus bar on the piezoelectric substrate, and the density of the first dielectric film is higher than that of silicon oxide.

[0012] Effects of the Invention

[0013] According to the present invention, an elastic wave device capable of suppressing ripples near a resonance frequency can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0015] Figure 2 It is a plan view of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 3 FIG. 1 is a diagram showing the vicinity of the first gap of the IDT electrode in the first embodiment of the present invention and the Figure 2 A cross-sectional view of the section taken along line II in FIG.

[0017] Figure 4 This is a plan view for explaining a modified example of the IDT electrode of the elastic wave device according to the first embodiment.

[0018] Figure 5 is a plan view of an elastic wave device according to a first comparative example.

[0019] Figure 6 It is a diagram showing impedance characteristics in the first embodiment of the present invention and the first comparative example.

[0020] Figure 7 It is a diagram showing impedance characteristics near the resonance frequency in the first embodiment of the present invention and the first comparative example.

[0021] Figure 8 It is a front cross-sectional view of an elastic wave device according to a first modified example of the first embodiment of the present invention.

[0022] Fig. 9 It is a front cross-sectional view of an elastic wave device according to a second modified example of the first embodiment of the present invention.

[0023] Fig.10 It is a front cross-sectional view of an elastic wave device according to a second embodiment of the present invention.

[0024] Fig.11 It is a cross-sectional view showing the vicinity of the first gap of the IDT electrode in the second embodiment of the present invention.

[0025] Fig.12 It is a plan view of an elastic wave device according to a third embodiment of the present invention.

[0026] Fig.13 It is a cross-sectional view showing the vicinity of the first gap of the IDT electrode in the third embodiment of the present invention.

[0027] Fig.14 It is a diagram showing impedance characteristics in the third embodiment of the present invention and the second comparative example.

[0028] Fig.15 It is a diagram showing impedance characteristics near the resonance frequency in the third embodiment of the present invention and the second comparative example. DETAILED DESCRIPTION

[0029] Hereinafter, the present invention will be made clear by describing specific embodiments of the present invention with reference to the accompanying drawings.

[0030] It should be noted that each embodiment described in this specification is an illustrative content, and it is intended that some structures can be replaced or combined between different embodiments.

[0031] Figure 1 It is a front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0032] The elastic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 has a supporting substrate 3, a high-acoustic-velocity film 4 provided on the supporting substrate 3, a low-acoustic-velocity film 5 provided on the high-acoustic-velocity film 4, and a piezoelectric layer 6 provided on the low-acoustic-velocity film 5. In the present embodiment, the piezoelectric layer 6 is a lithium tantalate film. More specifically, the piezoelectric layer 6 is composed of 50°YX-LiTaO3. It should be noted that the cutting angle of the piezoelectric layer 6 is not limited to the above, and the material of the piezoelectric layer 6 is not limited to the above. The piezoelectric layer 6 may also have a piezoelectric single crystal such as lithium niobate or an appropriate piezoelectric ceramic as a main component.

[0033] An IDT electrode 7 is provided on the piezoelectric layer 6 in the piezoelectric substrate 2. An elastic wave is excited by applying an AC voltage to the IDT electrode 7. A pair of reflectors 8a and 8b are provided on both sides of the IDT electrode 7 on the piezoelectric layer 6 in the direction of propagation of the elastic wave. Thus, the elastic wave device 1 of the present embodiment is an elastic wave resonator. However, the elastic wave device of the present invention may also be a filter device such as a ladder filter including an elastic wave resonator.

[0034] The low-acoustic-velocity film 5 is a film having a relatively low acoustic velocity. More specifically, the acoustic velocity of the bulk wave propagating through the low-acoustic-velocity film 5 is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer 6. The low-acoustic-velocity film 5 is made of SiO x The silicon oxide represented by is the main component. x is an arbitrary positive value. In the present embodiment, the low acoustic velocity film 5 is a SiO2 film. It should be noted that the material of the low acoustic velocity film 5 is not limited to the above, and for example, a material having silicon oxide, glass, silicon oxynitride, tantalum oxide, and a compound obtained by adding fluorine, carbon, and boron to silicon oxide as the main component can also be used.

[0035] In the elastic wave device 1, the high acoustic velocity layer in the present invention is the high acoustic velocity film 4. The high acoustic velocity layer is a layer with a relatively high acoustic velocity. More specifically, the acoustic velocity of the body wave propagating in the high acoustic velocity layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer 6. In the present embodiment, the high acoustic velocity film 4 as the high acoustic velocity layer is a silicon nitride film. It should be noted that the material of the high acoustic velocity film 4 is not limited to the above, for example, piezoelectric bodies such as lithium tantalate, lithium niobate, and crystal, alumina, zirconium oxide, cordierite, mullite, talc, forsterite and other ceramics, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, DLC (diamond-like carbon) film, silicon, sapphire, diamond, magnesium oxide, or a material with the above materials as the main component, or a material with a mixture of the above materials as the main component can also be used.

[0036] In this embodiment, the support substrate 3 is a silicon substrate. More specifically, the crystal orientation of the support substrate 3 is Si(100). The Euler angles ( θ, ψ) are Euler angles (0°, 0°, 45°). It should be noted that the crystal orientation of the support substrate 3 and the Euler angles ( θ, ψ) are not limited to the above, and the material of the support substrate 3 is also not limited to the above. As the material of the support substrate 3, for example, piezoelectric bodies such as lithium tantalate, lithium niobate, and crystal, various ceramics such as alumina, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, talc, and forsterite, glass, spinel, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, DLC film, silicon, sapphire, diamond, magnesium oxide, or materials containing the above materials as the main component, materials containing a mixture of the above materials as the main component, etc. can also be used.

[0037] In this embodiment, the elastic wave device 1 includes a piezoelectric substrate 2 including a laminated body in which a high acoustic velocity film 4, a low acoustic velocity film 5, and a piezoelectric layer 6 are sequentially laminated. Thus, the energy of the elastic wave can be effectively confined to the piezoelectric layer 6 side.

[0038] Figure 2 It is a top view of the elastic wave device according to the first embodiment.

[0039] The IDT electrode 7 includes a first bus bar 14 and a second bus bar 15 facing each other. The IDT electrode 7 includes a plurality of first electrode fingers 16 connected at one end to the first bus bar 14 and a plurality of second electrode fingers 17 connected at one end to the second bus bar 15. The plurality of first electrode fingers 16 and the plurality of second electrode fingers 17 are alternately inserted.

[0040] In addition, the IDT electrode 7 has a plurality of first dummy electrode fingers 18 connected at one end to the first bus bar 14. The plurality of first dummy electrode fingers 18 are respectively opposed to the plurality of second electrode fingers 17 via the second gaps G2. The IDT electrode 7 has a plurality of second dummy electrode fingers 19 connected at one end to the second bus bar 15. The plurality of second dummy electrode fingers 19 are respectively opposed to the plurality of first electrode fingers 16 via the first gaps G1.

[0041] Here, the first envelope A1, which is an imaginary line formed by connecting the front ends of the plurality of first electrode fingers 16, extends obliquely relative to the elastic wave propagation direction. Similarly, the second envelope A2, which is an imaginary line formed by connecting the front ends of the plurality of second electrode fingers 17, extends obliquely relative to the elastic wave propagation direction. In this way, the IDT electrode 7 is an inclined IDT electrode. The inclination angle of the direction in which the first envelope A1 and the second envelope A2 extend relative to the elastic wave propagation direction is not particularly limited, but in this embodiment, the inclination angle is 7.5°.

[0042] In this embodiment, the plurality of first gaps G1 are located between the plurality of first electrode fingers 16 and the plurality of second dummy electrode fingers 19. The plurality of second gaps G2 are located between the plurality of second electrode fingers 17 and the plurality of first dummy electrode fingers 18. The plurality of first gaps G1 may be located between the plurality of first electrode fingers 16 and the second bus bar 15, and the plurality of second gaps G2 may be located between the plurality of second electrode fingers 17 and the first bus bar 14.

[0043] The IDT electrode 7 is composed of a stacked metal film in which a Ti layer, an Al layer, and a Ti layer are stacked in sequence from the side of the piezoelectric substrate 2. In the present embodiment, the reflectors 8a and 8b are also composed of the same stacked metal film as the IDT electrode 7. It should be noted that the materials of the IDT electrode 7, the reflectors 8a, and the reflectors 8b and the number of metal layers are not limited to the above. Alternatively, the IDT electrode 7, the reflectors 8a, and the reflectors 8b may also be composed of a single-layer metal film.

[0044] Figure 3 FIG. 1 is a diagram showing the vicinity of the first gap of the IDT electrode in the first embodiment and the Figure 2 A cross-sectional view of the section taken along line II in FIG.

[0045] The first dielectric film 9a is provided in the plurality of first gaps G1 on the piezoelectric substrate 2. More specifically, the plurality of first dielectric films 9a are provided to reach the entirety of the plurality of first gaps G1. The plurality of first dielectric films 9a reach the first electrode fingers 16 and the second dummy electrode fingers 19. The first dielectric film 9a is continuously provided near the front end of the first electrode fingers 16 and near the front end of the first gaps G1 and the second dummy electrode fingers 19. It should be noted that the first dielectric film 9a only needs to be provided in at least a portion of the first gaps G1.

[0046] Similarly, the plurality of first dielectric films 9b are respectively provided to reach the entirety of the plurality of second gaps G2. The plurality of first dielectric films 9b reach the second electrode fingers 17 and the first dummy electrode fingers 18. More specifically, the first dielectric film 9b is continuously provided near the front end of the second electrode fingers 17, the second gaps G2, and the front end of the first dummy electrode fingers 18. It should be noted that the first dielectric film 9b only needs to be provided in at least a portion of the second gaps G2.

[0047] It should be noted that the first dummy electrode finger 18 and the second dummy electrode finger 19 may not be provided. Figure 4 As in the modified example of the IDT electrode 7 shown in FIG. 1 , the first dummy electrode finger 18 and the second dummy electrode finger 19 are not provided. Here, the plurality of first dielectric films 9a are provided so as to reach the second bus bar 15 from the first electrode finger 16 through the gap between the first electrode finger 16 and the second bus bar 15. Similarly, the first dielectric film 9b is provided so as to reach the first bus bar 14 from the second electrode finger 17 through the gap between the second electrode finger 17 and the first bus bar 14.

[0048] In this embodiment, the first dielectric film 9a is provided in all the first gaps G1, and the first dielectric film 9b is provided in all the second gaps G2. It should be noted that the first dielectric film 9a and the first dielectric film 9b do not need to be provided in all the first gaps G1 and the second gaps G2. The first dielectric film 9a or the first dielectric film 9b only needs to be provided in at least one of the plurality of first gaps G1 and the plurality of second gaps G2.

[0049] In this embodiment, the first dielectric film 9a and the first dielectric film 9b are tantalum pentoxide films. It should be noted that, without limitation to this, the density of the first dielectric film 9a and the first dielectric film 9b can be higher than the density of silicon oxide. It should be noted that in this specification, the silicon oxide used as a density comparison object is SiO2. In addition, the density of silicon oxide in this specification is 2.21×10 3 [kg / m 3 As the dielectric constituting the first dielectric film 9a and the first dielectric film 9b, for example, hafnium oxide, thorium oxide, or niobium nitride can also be used.

[0050] The present embodiment is characterized in that it has the following structure. 1) It has a piezoelectric substrate 2 and an inclined IDT electrode 7 provided on the piezoelectric substrate 2, and the piezoelectric substrate 2 includes a stacked body in which a high-acoustic-velocity film 4, a low-acoustic-velocity film 5, and a piezoelectric layer 6 are stacked in sequence. 2) A plurality of first dielectric films 9a and a plurality of first dielectric films 9b having a density higher than that of silicon oxide are provided in a plurality of first gaps G1 and a plurality of second gaps G2 of the IDT electrode 7. Thus, ripples near the resonance frequency can be suppressed. This is explained below by comparing the present embodiment with a comparative example.

[0051] It should be noted that if Figure 5 As shown, an elastic wave device 101 according to the first comparative example has the same structure as the elastic wave device 1 according to the first embodiment, except that the first dielectric film 9 a and the first dielectric film 9 b according to the first embodiment are not included.

[0052] An elastic wave device having the structure of the first embodiment and an elastic wave device of the first comparative example are produced. Here, the conditions of the elastic wave device having the structure of the first embodiment and the elastic wave device of the first comparative example are as follows. It should be noted that the wavelength described below is a wavelength specified by the electrode finger pitch of the IDT electrode. When observing the IDT electrode along the propagation direction of the elastic wave, the area where adjacent electrode fingers overlap is set as the intersection area of ​​the IDT electrode, and the length of the intersection area along the direction in which the electrode fingers extend is set as the intersection width. The length of the first gap along the direction in which the electrode fingers extend is set as the first gap width, and the length of the second gap along the direction in which the electrode fingers extend is set as the second gap width.

[0053] Piezoelectric layer: Material 50°YX-LiTaO3, film thickness 600nm

[0054] Low acoustic velocity membrane: Material: silicon oxide (SiO2), film thickness 673nm

[0055] High acoustic velocity membrane: Material: silicon nitride (SiN), film thickness: 900nm

[0056] Support substrate: Material: silicon (Si), crystal orientation: Si (100), Euler angle (0°, 0°, 45°)

[0057] The thickness of each metal layer of the IDT electrode is: the thickness of the Ti layer on the piezoelectric layer side is 12nm, the thickness of the Al layer is 100nm, and the thickness of the Ti layer is 4nm

[0058] Wavelength: 2μm

[0059] Cross width: 30μm

[0060] Number of IDT electrode finger pairs: 100 pairs

[0061] Tilt angle: 7.5°

[0062] First gap width and second gap width: 0.27 μm

[0063] The conditions for the first dielectric film constituting the elastic wave device of the first embodiment are as follows.

[0064] First dielectric film: Material: Tantalum pentoxide (Ta2O5), density 8.47×10 3 [kg / m 3 ], film thickness 30nm

[0065] The following Figure 6 and Figure 7 Impedance characteristics of each elastic wave device are shown.

[0066] Figure 6 It is a diagram showing impedance characteristics in the first embodiment and the first comparative example. Figure 7 Graphs showing impedance characteristics near the resonant frequency in the first embodiment and the first comparative example. Figure 6 and Figure 7 In FIG. 1 , the solid line shows the result of the first embodiment, and the dotted line shows the result of the first comparative example.

[0067] In the first embodiment and the first comparative example, an inclined IDT electrode is used. Figure 6 As shown in Figure 1, the ripple between the resonant frequency and the anti-resonant frequency is suppressed. Figure 6 and Figure 7As shown by the arrow B, it can be seen that in the first comparative example, ripples are generated near the resonance frequency. In contrast, it can be seen that in the first embodiment, ripples near the resonance frequency are not generated. In this way, in the first embodiment, the ripples between the resonance frequency and the anti-resonance frequency can be suppressed, and the ripples near the resonance frequency can also be suppressed.

[0068] In the first comparative example, by having the same piezoelectric substrate 2 as the first embodiment, the elastic wave device can easily seal the unnecessary waves that may cause the ripples into the piezoelectric layer side together with the elastic waves used as the main mode. In addition, the first electrode finger 16 and the second dummy electrode finger 19 are separated by the first gap G1 and become discontinuous. Therefore, the sound velocity in the area where the IDT electrode 7 is provided has discontinuity near the first gap G1. Similarly, the sound velocity in the area where the IDT electrode 7 is provided has discontinuity near the second gap G2. The ripples in the first comparative example are considered to be caused by the modes sealed in the vicinity of the first gap G1 and the vicinity of the second gap G2 of the inclined IDT electrode 7.

[0069] In contrast, in the first embodiment, if Figure 2 As shown, a first dielectric film 9a is provided in the first gap G1. In addition, the density of the first dielectric film 9a is higher than the density of silicon oxide. Thus, the density of the first dielectric film 9a can be effectively made close to the density of the IDT electrode 7, or the density of the first dielectric film 9a can be made greater than the density of the IDT electrode 7. Thus, the state of mass addition in the first gap G1 can be effectively made close to the state of mass addition in the portion where the first electrode finger 16 and the second dummy electrode finger 19 are provided. Therefore, the sound velocity in the region where the first gap G1 is configured can be effectively made close to the sound velocity in the region where the first electrode finger 16 is provided and the region where the second dummy electrode finger 19 is provided. Therefore, the discontinuity of the first electrode finger 16 and the second dummy electrode finger 19 in the first gap G1 can be reduced.

[0070] Similarly, by providing the first dielectric film 9b in the second gap G2, the discontinuity between the second electrode finger 17 and the first dummy electrode finger 18 in the second gap G2 can be reduced. Therefore, the confinement of the mode in the first gap G1 and the second gap G2 can be suppressed. Therefore, the ripple near the resonance frequency can be suppressed.

[0071] The density of the first dielectric film 9a and the first dielectric film 9b is preferably equal to or higher than the density of the material of the IDT electrode 7. In this case, the state of mass addition in the first gap G1 can be made closer to the state of mass addition in the portion where the first electrode finger 16 and the second dummy electrode finger 19 are provided more reliably. In particular, when the density of the first dielectric film 9a and the first dielectric film 9b is greater than the density of the IDT electrode 7, even if the film thickness of the first dielectric film 9a is made thinner than the film thickness of the IDT electrode 7, the state of mass addition in the first gap G1 can be effectively made closer to the state of mass addition in the portion where the first electrode finger 16 and the second dummy electrode finger 19 are provided. Similarly, the state of mass addition in the second gap G2 can be made closer to the state of mass addition in the portion where the second electrode finger 17 and the first dummy electrode finger 18 are provided. Therefore, the confinement of the mode in the first gap G1 and the second gap G2 can be suppressed more reliably, and the ripple near the resonance frequency can be suppressed more reliably.

[0072] In the case where the IDT electrode 7 is composed of a stacked metal film, the average density of the stacked metal film can be compared with the density of the first dielectric film 9a and the first dielectric film 9b. The average density of the stacked metal film can be calculated as follows. In each metal layer of the stacked metal film, the value obtained by dividing the film thickness of the metal layer by the film thickness of the entire stacked metal film is calculated, that is, the film thickness ratio of the metal layer. Then, in each metal layer, the product of the film thickness ratio and the density is calculated. Then, the above products in all metal layers are added.

[0073] It should be noted that the density of the first dielectric film 9a and the first dielectric film 9b is preferably greater than the density of the first electrode fingers 16 and the second electrode fingers 17. Thus, even when the metal layer constituting the first electrode fingers 16 and the second electrode fingers 17 is different from the metal layer constituting the first bus bar 14 and the second bus bar 15, the above-mentioned discontinuity in the first gap G1 and the second gap G2 can be more reliably reduced.

[0074] The first dielectric film 9a is preferably provided to reach the entire first gap G1. Thus, the discontinuity between the first electrode finger 16 and the second dummy electrode finger 19 can be further reduced. Similarly, the first dielectric film 9b is preferably provided to reach the entire second gap G2. Thus, the discontinuity between the second electrode finger 17 and the first dummy electrode finger 18 can be further reduced. Therefore, the ripple near the resonance frequency can be further suppressed.

[0075] Furthermore, the first dielectric film 9a preferably reaches the entire first gap G1 and reaches the first electrode finger 16 and the second dummy electrode finger 19. Similarly, the first dielectric film 9b preferably reaches the entire second gap G2 and reaches the second electrode finger 17 and the first dummy electrode finger 18. Thus, when manufacturing the elastic wave device 1, even if the first dielectric film 9a is misaligned, the first dielectric film 9a can be more reliably arranged to reach the entire first gap G1. Similarly, the first dielectric film 9b can be more reliably arranged to reach the entire second gap G2. Therefore, the ripple near the resonance frequency can be more reliably and further suppressed.

[0076] The piezoelectric substrate 2 of the first embodiment is a laminated body formed by laminating a support substrate 3, a high acoustic velocity film 4, a low acoustic velocity film 5, and a piezoelectric layer 6 in sequence, but is not limited thereto. The first and second modified examples of the first embodiment having the same structure as the first embodiment except for the piezoelectric substrate are shown below. In the first and second modified examples, ripples near the resonance frequency can also be suppressed in the same manner as in the first embodiment.

[0077] Figure 8 The piezoelectric substrate 22 in the first modified example shown has a high-acoustic-velocity supporting substrate 23, a low-acoustic-velocity film 5 provided on the high-acoustic-velocity supporting substrate 23, and a piezoelectric layer 6 provided on the low-acoustic-velocity film 5. In this modified example, the high-acoustic-velocity layer in the present invention is the high-acoustic-velocity supporting substrate 23. The piezoelectric layer 6 is indirectly provided on the high-acoustic-velocity supporting substrate 23 via the low-acoustic-velocity film 5.

[0078] The high acoustic velocity support substrate 23 is a silicon substrate. It should be noted that the material of the high acoustic velocity support substrate 23 is not limited to the above, and aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, crystal, alumina, zirconium oxide, cordierite, mullite, talc, forsterite, magnesium oxide, DLC or diamond, etc., or a medium containing the above materials as a main component can also be used.

[0079] The elastic wave device of this modification has a piezoelectric substrate 22 which is a stacked body formed by stacking a high acoustic velocity supporting substrate 23, a low acoustic velocity film 5, and a piezoelectric layer 6 in this order. Therefore, the energy of the elastic wave can be confined to the piezoelectric layer 6 side as in the first embodiment.

[0080] Fig. 9 The piezoelectric substrate 24 in the second modification shown includes a high-acoustic-velocity support substrate 23 and a piezoelectric layer 6 provided directly on the high-acoustic-velocity support substrate 23. In this modification as well, the energy of elastic waves can be confined to the piezoelectric layer 6 side as in the first embodiment.

[0081] Fig.10It is a front cross-sectional view of the elastic wave device according to the second embodiment. Fig.11 2 is a cross-sectional view showing the vicinity of the first gap of the IDT electrode in the second embodiment. Fig.11 Shown along with Figure 2 The section corresponding to the II line in FIG.

[0082] like Fig.10 and Fig.11 As shown, the present embodiment is different from the first embodiment in that a second dielectric film 39 is provided on the piezoelectric substrate 2 so as to cover the IDT electrode 7, the first dielectric film 9a, and the first dielectric film 9b. Except for the above point, the elastic wave device of the present embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0083] The second dielectric film 39 is not particularly limited, but is a silicon oxide film in this embodiment. More specifically, the second dielectric film 39 is a SiO2 film. The second dielectric film 39 can be used as a protective film, for example. Thus, the IDT electrode 7 is less likely to be damaged.

[0084] In this embodiment, as in the first embodiment, the first dielectric film 9a is provided in the first gap G1, and the first dielectric film 9b is provided in the second gap G2. This can suppress ripples near the resonance frequency.

[0085] Fig.12 It is a plan view of an elastic wave device according to a third embodiment. Fig.13 FIG. 1 is a cross-sectional view showing the vicinity of the first gap of the IDT electrode in the third embodiment. Fig.12 The second dielectric film is omitted. Fig.13 Shown along with Figure 2 The section corresponding to the part of line II in FIG.

[0086] like Fig.12 and Fig.13 As shown, the difference between the present embodiment and the first embodiment is that the first dielectric film 9a reaches between the first electrode finger 16 and the second dummy electrode finger 19 and the piezoelectric substrate 2. More specifically, the first dielectric film 9a reaches between the first electrode finger 16 and the piezoelectric substrate 2, and reaches between the second dummy electrode finger 19 and the piezoelectric substrate 2. In addition, the difference between the present embodiment and the first embodiment is that the first dielectric film 9b reaches between the second electrode finger 17 and the first dummy electrode finger 18 and the piezoelectric substrate 2. Except for the above points, the elastic wave device of the present embodiment has the same structure as the elastic wave device of the second embodiment.

[0087] like Fig.13As shown, in this embodiment, the second dielectric film 39 is also provided on the piezoelectric substrate 2 so as to cover the IDT electrode 7, the first dielectric film 9a, and the first dielectric film 9b.

[0088] Here, an elastic wave device having the structure of the third embodiment and an elastic wave device of a second comparative example were prepared. The elastic wave device of the second comparative example has the same structure as the third embodiment except that first dielectric films 9 a and 9 b are not provided.

[0089] The conditions for the elastic wave device having the structure of the third embodiment and the elastic wave device of the second comparative example are as follows.

[0090] Piezoelectric layer: Material 50°YX-LiTaO3, film thickness 600nm

[0091] Low acoustic velocity membrane: Material: silicon oxide (SiO2), film thickness 673nm

[0092] High acoustic velocity membrane: Material: silicon nitride (SiN), film thickness: 900nm

[0093] Support substrate: Material: silicon (Si), crystal orientation: Si (100), Euler angle (0°, 0°, 45°)

[0094] The thickness of each metal layer of the IDT electrode is: the thickness of the Ti layer on the piezoelectric layer side is 12nm, the thickness of the Al layer is 100nm, and the thickness of the Ti layer is 4nm

[0095] Wavelength: 2μm

[0096] Cross width: 30μm

[0097] Number of IDT electrode finger pairs: 100 pairs

[0098] Tilt angle: 7.5°

[0099] First gap width and second gap width: 0.27 μm

[0100] Second dielectric film: material SiO2, film thickness 35nm

[0101] The conditions for the first dielectric film of the elastic wave device having the structure of the third embodiment are as follows.

[0102] First dielectric film: Material: Tantalum pentoxide (Ta2O5), film thickness 30nm

[0103] The following Fig.14 and Fig.15 Impedance characteristics of each elastic wave device are shown.

[0104] Fig.14It is a diagram showing impedance characteristics in the third embodiment and the second comparative example. Fig.15 : is a graph showing the impedance characteristics near the resonant frequency in the third embodiment and the second comparative example. Fig.14 and Fig.15 In FIG. 1 , the solid line shows the result of the third embodiment, and the dotted line shows the result of the second comparative example.

[0105] like Fig.14 and Fig.15 As shown by the arrow C, it can be seen that in the second comparative example, ripples are generated near the resonance frequency. In contrast, it can be seen that in the third embodiment, ripples are not generated near the resonance frequency. In this way, in the third embodiment, ripples near the resonance frequency can be suppressed. In addition, when manufacturing the elastic wave device of the third embodiment, even if the first dielectric film 9a is misaligned, the first dielectric film 9a can be more reliably configured to reach the entire first gap G1. Similarly, the first dielectric film 9b can be more reliably configured to reach the entire second gap G2. Therefore, ripples near the resonance frequency can be suppressed more reliably and more effectively.

[0106] In addition, if Fig.14 As shown, in the third embodiment and the second comparative example, the resonant frequency is about the same. On the other hand, it can be seen that the anti-resonant frequency of the third embodiment is located at a higher frequency side than the anti-resonant frequency of the second comparative example. Fig.12 The first dielectric film 9a shown reaches between the first electrode fingers 16 and the second dummy electrode fingers 19 and the piezoelectric substrate 2, and the first dielectric film 9b reaches between the second electrode fingers 17 and the first dummy electrode fingers 18 and the piezoelectric substrate 2. This can widen the relative bandwidth.

[0107] Description of Reference Numerals

[0108] 1…Elastic wave device;

[0109] 2… piezoelectric substrate;

[0110] 3...support base plate;

[0111] 4…High sound velocity membrane;

[0112] 5…Low sound velocity membrane;

[0113] 6… piezoelectric layer;

[0114] 7…IDT electrode;

[0115] 8a, 8b…reflector;

[0116] 9a, 9b ... a first dielectric film;

[0117] 14, 15…first bus bar, second bus bar;

[0118] 16, 17…first electrode finger, second electrode finger;

[0119] 18, 19 ... first dummy electrode finger, second dummy electrode finger; 22 ... piezoelectric substrate;

[0120] 23 ... high acoustic velocity support substrate;

[0121] 24… piezoelectric substrate;

[0122] 39 ... a second dielectric film;

[0123] 101…Elastic wave device.

Claims

1. An elastic wave device comprising: a piezoelectric substrate; and An IDT electrode is provided on the piezoelectric substrate, The piezoelectric substrate comprises a high acoustic velocity layer and a piezoelectric layer directly or indirectly provided on the high acoustic velocity layer. The acoustic velocity of the body wave propagating in the high acoustic velocity layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer. The IDT electrode includes a first bus bar and a second bus bar facing each other, a plurality of first electrode fingers connected to the first bus bar at one end, and a plurality of second electrode fingers connected to the second bus bar at one end and alternately inserted with the plurality of first electrode fingers. A first envelope line formed by connecting the front ends of the plurality of first electrode fingers extends obliquely with respect to the propagation direction of the elastic wave, and a second envelope line formed by connecting the front ends of the plurality of second electrode fingers extends obliquely with respect to the propagation direction of the elastic wave. A first dielectric film is provided in at least one of the plurality of first gaps between the plurality of first electrode fingers and the second bus bar and the plurality of second gaps between the plurality of second electrode fingers and the first bus bar on the piezoelectric substrate, The density of the first dielectric film is higher than that of silicon oxide, The first dielectric film is not continuously provided in the plurality of first gaps across the second electrode fingers in the elastic wave propagation direction, and is not continuously provided in the plurality of second gaps across the first electrode fingers in the elastic wave propagation direction.

2. The elastic wave device according to claim 1, wherein: The density of the first dielectric film is equal to or greater than the density of the IDT electrode.

3. The elastic wave device according to claim 1 or 2, wherein: The IDT electrode has a plurality of first dummy electrode fingers connected to the first bus bar at one end and a plurality of second dummy electrode fingers connected to the second bus bar at one end. The plurality of first gaps are respectively located between the plurality of first electrode fingers and the plurality of second dummy electrode fingers, and the plurality of second gaps are respectively located between the plurality of second electrode fingers and the plurality of first dummy electrode fingers.

4. The elastic wave device according to claim 1 or 2, wherein: The first dielectric film reaches the entire first gap or the second gap where the first dielectric film is provided.

5. The elastic wave device according to claim 3, wherein: The first dielectric film provided in the first gap reaches the entire first gap and reaches the first electrode finger and the second dummy electrode finger. The first dielectric film provided in the second gap reaches the entire second gap and reaches the second electrode fingers and the first dummy electrode fingers.

6. The elastic wave device according to claim 3, wherein: The first dielectric film provided in the first gap reaches the entire first gap and reaches between the first electrode finger and the second dummy electrode finger and the piezoelectric substrate. The first dielectric film provided in the second gap reaches the entire second gap and reaches between the second electrode fingers and the first dummy electrode fingers and the piezoelectric substrate.

7. The elastic wave device according to claim 1 or 2, wherein: A second dielectric film is provided on the piezoelectric substrate so as to cover the IDT electrode and the first dielectric film.

8. The elastic wave device according to claim 1 or 2, wherein: The piezoelectric substrate has a low acoustic velocity film provided between the high acoustic velocity layer and the piezoelectric layer. The acoustic velocity of the bulk wave propagating through the low-acoustic-velocity film is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer.

9. The elastic wave device according to claim 1 or 2, wherein: The high acoustic velocity layer is a high acoustic velocity supporting substrate.

10. The elastic wave device according to claim 1 or 2, wherein: The piezoelectric substrate further includes a supporting substrate. The high acoustic velocity layer is a high acoustic velocity film provided on the supporting substrate.

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