Elastic wave device

Abstract

Provided is an elastic wave device capable of suppressing spurious caused by high-order modes. The elastic wave device (1) includes: a support substrate (2); a piezoelectric film directly or indirectly laminated to the support substrate (2); and an IDT electrode (7) formed on the piezoelectric film, the piezoelectric film having: a first piezoelectric film (5) having a front surface on the support substrate (2) side and a back surface on the IDT electrode (7) side; and a second piezoelectric film (6) laminated to the first piezoelectric film (5) and having a back surface on the support substrate (2) side and a front surface on the IDT electrode (7) side, wherein when a wavelength determined by an electrode finger pitch of the IDT electrode (7) is λ, a total film thickness of a thickness of the first piezoelectric film (5) and a thickness of the second piezoelectric film (6) is 1λ or less.

Description

Technical Field

[0001] This invention relates to an elastic wave device having a piezoelectric film. Background Technology

[0002] In the past, various elastic wave devices using piezoelectric films have been proposed. For example, in the elastic wave device described in Patent Document 1 below, a high-velocity acoustic component, a low-velocity acoustic film, and a piezoelectric film are sequentially stacked on a support substrate. An IDT electrode is provided on the piezoelectric film.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: WO2012 / 086639 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] When a bandpass filter is constructed using an elastic wave device as described in Patent Document 1, spurious signals caused by higher-order modes sometimes occur in the frequency band outside the passband.

[0008] The purpose of this invention is to provide an elastic wave device capable of suppressing stray high-order modes.

[0009] Technical solutions for solving the problem

[0010] The elastic wave device of the present invention comprises: a support substrate; a piezoelectric film directly or indirectly laminated on the support substrate; and an IDT electrode formed on the piezoelectric film, the piezoelectric film having: a first piezoelectric film having a front side on the support substrate side and a negative side on the IDT electrode side; and a second piezoelectric film laminated with the first piezoelectric film having a negative side on the support substrate side and a front side on the IDT electrode side, wherein when the wavelength determined by the electrode finger spacing of the IDT electrode is set as λ, the total thickness of the first piezoelectric film and the second piezoelectric film is 1λ or less.

[0011] Invention Effects

[0012] According to the elastic wave device of the present invention, it is possible to suppress spurious signals caused by higher-order modes outside the passband when the device is configured as a filter. Attached Figure Description

[0013] Figure 1 (a) is a front sectional view of the elastic wave device according to the first embodiment of the present invention. Figure 1 (b) is a schematic top view showing the electrode structure of the elastic wave device.

[0014] Figure 2This is a diagram showing the impedance characteristics of the elastic wave device of the first embodiment as a resonator.

[0015] Figure 3 This is a diagram showing the phase characteristics of the elastic wave device as a resonator in the first embodiment and the first comparative example.

[0016] Figure 4 This is a graph showing the relationship between the total thickness of the first LiTaO3 film and the second LiTaO3 film and the maximum value of the phase of the frequency position of the response where higher-order modes appear.

[0017] Figure 5 It is Figure 4 The phase magnification of the vertical axis is shown in the figure.

[0018] Figure 6 This is a graph showing the relationship between the maximum value of the stray phase and the combined thickness of the first LiTaO3 film and the second LiTaO3 film being fixed at 0.4 μm = 0.2λ, and the thickness of the first LiTaO3 film being varied to 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm or 0.3 μm.

[0019] Figure 7 The graph shows the relationship between the cutting angle of the Y-cut LiTaO3 film and the impedance ratio in the impedance characteristics of the elastic wave device. The elastic wave device fixes the total thickness of the first LiTaO3 film and the second LiTaO3 film, which are composed of Y-cut LiTaO3 films, at 0.4 μm = 0.2λ, and sets the thickness of the first LiTaO3 film to 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm or 0.35 μm.

[0020] Figure 8 This is a graph showing the relationship between the film thickness of the first LiTaO3 film and the total film thickness of the first and second LiTaO3 films, and the cutting angle of the LiTaO3 film that can effectively suppress stray particles.

[0021] Figure 9 This is a diagram showing the phase characteristics of the elastic wave device as a resonator in the second embodiment and the second comparative example.

[0022] Figure 10The graph shows the relationship between the cutting angle of the Y-cut LiNbO3 film and the impedance ratio in the impedance characteristics of the elastic wave device. The elastic wave device fixes the total thickness of the first LiNbO3 film and the second LiNbO3 film, which are composed of Y-cut LiNbO3 films, at 0.4 μm = 0.2λ, and sets the thickness of the first LiNbO3 film to 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm or 0.35 μm.

[0023] Figure 11 This is a graph showing the relationship between the film thickness of the first LiNbO3 film and the total film thickness of the first and second LiNbO3 films, and the cutting angle of the LiNbO3 film that can effectively suppress stray particles.

[0024] Figure 12 This is a front sectional view of the elastic wave device according to the second embodiment of the present invention. Detailed Implementation

[0025] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0026] 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.

[0027] Figure 1 (a) is a front sectional view of the elastic wave device according to the first embodiment of the present invention. Figure 1 (b) is a schematic top view showing its electrode construction.

[0028] The elastic wave device 1 has a support substrate 2. In this embodiment, the support substrate 2 contains Si. However, the material of the support substrate 2 is not particularly limited. In addition to Si, quartz, semiconductor, or insulators such as alumina or silicon nitride can also be used. Alternatively, Si with the (111) facet, Si with the (110) facet, or quartz can be used.

[0029] A high-velocity material layer 3 and a low-velocity film 4 are stacked on the support substrate 2.

[0030] A first LiTaO3 film 5, serving as a first piezoelectric film, and a second LiTaO3 film 6, serving as a second piezoelectric film, are stacked on the low-velocity sound film 4. In this embodiment, the piezoelectric film is constituted by the stack of the first LiTaO3 film 5 and the second LiTaO3 film 6. Furthermore, the piezoelectric film including the first LiTaO3 film 5 and the second LiTaO3 film 6 is indirectly stacked on the support substrate 2. An IDT electrode 7 and reflectors 8 and 9 are disposed on the second LiTaO3 film 6. A dielectric film 10 is stacked such that it covers the IDT electrode 7 and the reflectors 8 and 9. The IDT electrode 7 comprises a suitable metal or alloy. Preferably, the main electrode layer comprises an Al or AlCu alloy.

[0031] As described above, in the elastic wave device 1, the piezoelectric film includes a first LiTaO3 film 5 and a second LiTaO3 film 6. Here, the main surface 5a on the support substrate 2 side of the first LiTaO3 film 5 is negative, and the main surface 5b on the opposite side of the support substrate 2 is positive. In the second LiTaO3 film 6, the main surface 6a on the support substrate 2 side is positive, and the main surface 6b on the IDT electrode 7 side is negative. That is, the first LiTaO3 film 5 and the second LiTaO3 film 6 are stacked so that their front surfaces are in contact with each other.

[0032] Furthermore, in this invention, the positive and negative sides of the first and second piezoelectric films are expressions based on the polarity of the polarization of the first and second piezoelectric films. More preferably, the polarization direction of the first and second piezoelectric films are opposite directions.

[0033] To ensure the polarity of the first LiTaO3 film 5 and the second LiTaO3 film 6 is as described above, for example, the crystal orientation of the first LiTaO3 film 5 can be set to (0°, 138°, 0°) in Euler angle representation, and the crystal orientation of the second LiTaO3 film 6 can be set to (0°, -42°, 180°) in Euler angle representation. Furthermore, Euler angle representation... In this context, ψ represents the propagation angle ψ.

[0034] When the wavelength determined by the distance between the electrode fingers of the IDT electrode 7 is set to λ, the total film thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 is set to 1λ or less. Therefore, as will be described later, in the characteristics of the elastic wave device 1 as a resonator, spurious noise caused by higher-order modes can be effectively suppressed.

[0035] The first embodiment of the above-mentioned elastic wave device 1 was manufactured according to the following design parameters.

[0036] Support substrate 2: Si substrate on the (111) surface, with a propagation angle ψ set to 46°.

[0037] High-speed acoustic material layer 3: silicon nitride film, 300nm thick

[0038] Low-velocity film 4: Silicon oxide film, 300nm thick

[0039] First LiTaO3 film 5: Thickness 200nm

[0040] Second LiTaO3 film 6: Thickness 200nm

[0041] The IDT electrode 7 and reflectors 8 and 9 are formed from the side of the second LiTaO3 film 6 by a stacked film of Ti layer, AlCu layer, and Ti layer. The thickness is set as follows: the lower Ti layer = 12 nm, the AlCu layer = 100 nm, and the upper Ti layer = 4 nm.

[0042] The wavelength λ, determined by the distance between the electrode fingers of IDT electrode 7, is set to 2 μm, and the duty cycle of IDT electrode 7 is set to 0.5.

[0043] Dielectric film 10: Silicon oxide film, 35nm thick

[0044] In addition, as mentioned above, the total thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 is 400 nm, i.e., 0.2λ.

[0045] Furthermore, the cutting angles of the first LiTaO3 film 5 and the second LiTaO3 film 6 are both set to 42° Y cut. The main surface 5a of the first LiTaO3 film 5 is the negative side and the main surface 5b is the front side, while the main surface 6a of the second LiTaO3 film 6 is the front side and the main surface 6b is the negative side.

[0046] The impedance characteristics of the elastic wave device 1 configured as described above are shown in the figure. Figure 2 .like Figure 2 As shown, a large response caused by the SH mode, which is the dominant transverse wave, appears near 2000MHz. Furthermore, it can be observed that at higher frequencies than the response caused by the dominant mode, almost no spurious signals caused by higher-order modes appear.

[0047] Figure 3 This is a diagram showing the phase characteristics of the elastic wave device of the first embodiment and the elastic wave device of the first comparative example as a resonator. The solid line shows the results of the first embodiment, and the dashed line shows the results of the first comparative example.

[0048] In the first comparative example, the only difference from the first embodiment was that a LiTaO3 film with a thickness of 0.2λ was used instead of the first LiTaO3 film 5 and the second LiTaO3 film 6. Additionally, the side of the LiTaO3 film on the support substrate side was designated as the negative side, and the side on the IDT electrode side was designated as the positive side.

[0049] according to Figure 3It is clear that in the first comparative example, large spurious emissions caused by higher-order modes appeared near 4500MHz. In contrast, it is evident that in the first embodiment, the response caused by higher-order mode spurious emissions near 4500MHz became very small.

[0050] In addition, according to Figure 3 It is clearly understood that the response caused by the dominant mode near 2000MHz in the first embodiment is equivalent to the response in the first comparative example. Therefore, in the elastic wave device 1 of the first embodiment, the response of the dominant mode is sufficiently large.

[0051] Therefore, according to the first embodiment, stray noise caused by higher-order modes can be effectively suppressed without causing response degradation caused by the master mode.

[0052] As described above, while the reason for suppressing stray emissions caused by higher-order modes in the first embodiment is not clear, it can be considered that the higher-order modes are canceled out by stacking the first LiTaO3 film 5 and the second LiTaO3 film 6 with different polarities in a face-to-face contact manner. Furthermore, although the face-to-face contact is made in the first embodiment, the first LiTaO3 film 5 and the second LiTaO3 film 6 with different polarities can also be stacked in a negative-to-negative contact manner. That is, the first LiTaO3 film 5, which is the first piezoelectric film, can also be stacked on top of the second LiTaO3 film 6, which is the second piezoelectric film. In this case, the same effect can also be obtained.

[0053] However, it is preferable that the first piezoelectric film and the second piezoelectric film are stacked such that the front sides of the first piezoelectric film and the front sides of the second piezoelectric film are in contact. As a result, compared with the case where the negative sides are in contact with each other, the adhesion strength between the first piezoelectric film and the second piezoelectric film can be improved, and peeling between the first piezoelectric film and the second piezoelectric film is less likely to occur.

[0054] In this invention, regarding the stacking method of the first piezoelectric film and the second piezoelectric film, as described above, the second piezoelectric film can be stacked on the first piezoelectric film, or the first piezoelectric film can be stacked on the second piezoelectric film.

[0055] In the elastic wave device 1, spurious signals caused by higher-order modes can be suppressed. Therefore, for example, in the case of constructing a bandpass filter using multiple elastic wave devices 1, spurious signals caused by higher-order modes at higher frequencies than the passband can be effectively suppressed.

[0056] In the elastic wave device 1 of the first embodiment, various elastic wave devices were fabricated by making the thicknesses of the first LiTaO3 film 5 and the second LiTaO3 film 6 equal, but varying the total film thickness. The relationship between the total film thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 in these various elastic wave devices and the maximum value of the phase near 4500MHz where a higher-order mode response occurs is shown below. Figure 4 In addition, the total film thickness is varied in increments of 0.1 μm within the range of 0.2 μm or more and 1.2 μm or less.

[0057] That is, the total film thickness was set to 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm or 1.2μm.

[0058] according to Figure 4 It is clear that if the total film thickness is 1 μm or less (equivalent to 0.5λ using the wavelength λ in this embodiment), the phase based on higher-order modes can be sufficiently reduced. More preferably, according to the... Figure 4 The vertical axis is magnified to show Figure 5 It is clear that if the total film thickness is 0.5 μm or less (which is 0.25λ if converted using the wavelength λ in this embodiment), spurious emissions can be suppressed more effectively. Therefore, the total film thickness is preferably 0.5λ or less, and more preferably 0.25λ or less. Furthermore, in cases where the value of λ is other than 2 μm, unlike in this embodiment, by setting the total film thickness to 0.5λ or less, and more preferably 0.25λ or less, the phase based on higher-order modes can also be sufficiently reduced.

[0059] If the combined thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 increases, the sound velocity of higher-order modes decreases, making it impossible to use the Si-containing support substrate 2 to cut off the volume wave sound velocity. Therefore, the response caused by higher-order modes can be considered to increase. Thus, as described above, the combined film thickness is set to 1 μm = 0.5λ or less.

[0060] Next, in the construction of the first embodiment described above, the total thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 is fixed at 0.4 μm = 0.2λ, and the thicknesses of the first LiTaO3 film 5 and the second LiTaO3 film 6 are set as shown in Table 1 below.

[0061] [Table 1]

[0062]

[0063] The maximum value of the stray phase near 4500MHz in the elastic wave device constructed as described above was obtained. Figure 6 This is a graph showing the relationship between the thickness (μm) of the first LiTaO3 film and the maximum phase value of strays caused by the aforementioned higher-order modes.

[0064] according to Figure 6It is clear that when the thickness of the first LiTaO3 film 5 on the lower side (the side closer to the support substrate among the first LiTaO3 film 5 and the second LiTaO3 film 6) is 0.2 μm or more, that is, when the thickness of the first LiTaO3 film 5 is thicker than the thickness of the second LiTaO3 film 6, higher-order modes can be suppressed more effectively.

[0065] Next, in the construction of the first embodiment, the total thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 is fixed at 0.4 μm = 0.2λ, and the thickness of the first LiTaO3 film 5 is set to 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, or 0.35 μm. Various Y-cut LiTaO3 films with different cutting angles are used as the first LiTaO3 film 5 and the second LiTaO3 film 6. Furthermore, the cutting angles of the first LiTaO3 film 5 and the second LiTaO3 film 6 are set to be equal.

[0066] Figure 7 This is a graph showing the relationship between the cutoff angle and the impedance ratio in the impedance characteristics of multiple elastic wave devices configured as described above. Here, the impedance ratio is the ratio of the impedance at the anti-resonant frequency of the dominant mode to the impedance at the resonant frequency. According to... Figure 7 It is known that even when the thickness of the first LiTaO3 film 5 is varied within a range of 0.05 μm or more and 0.35 μm or less at various cutting angles, the impedance ratio of the master mode remains approximately the same if the cutting angle is the same. Furthermore, it is known that if the cutting angle is -20° or more and +75° or less, the impedance ratio of the master mode can be increased to 80 dB or more. Therefore, it is preferable that the cutting angle of the Y-cut LiTaO3 film is -20° or more and +75° or less.

[0067] Figure 8 This is a graph showing the relationship between the film thickness ratio and the cutting angle that can suppress stray waves caused by Rayleigh waves when the total film thickness of the first LiTaO3 film 5 and the second LiTaO3 film 6 is fixed at 0.4 μm = 0.2λ in the first embodiment described above, and the film thickness ratio (%) of the first LiTaO3 film 5 relative to the total film thickness is varied. Figure 8 The dashed lines in the text are achieved by... Figure 8 The formula is obtained by approximating multiple plotted points in the equation. This formula becomes the following equation (1).

[0068] y = -0.0009955556x 3 +0.1552380952x 2 -4.6325396825x+78.5714285714… Equation (1)

[0069] Here, y is the cutting angle, and x is the proportion of the thickness of the first LiTaO3 film 5 mentioned above.

[0070] For y obtained from the approximation (1), preferably, if it is a value within any range of (y±10°)+180n (where n is an integer of 0, 1, 2, 3, ...) or (y±10°)-180n (where n is an integer of 0, 1, 2, 3, ...), it can more effectively suppress spurious waves caused by Rayleigh waves.

[0071] In the elastic wave device of the present invention, the first piezoelectric film and the second piezoelectric film may also be composed of LiNbO3 films. As a second embodiment, a structure using the first LiNbO3 film and the second LiNbO3 film instead of the first LiTaO3 film 5 and the second LiTaO3 film 6 will be described. The second embodiment was fabricated according to the following design parameters.

[0072] Support substrate: (111) Si substrate, with a propagation angle ψ set to 46°.

[0073] High-speed acoustic material layer: silicon nitride film, 300nm thick

[0074] Low-velocity sound film: silicon oxide film, 300nm thick

[0075] First LiNbO3 film: 200nm thick

[0076] Second LiNbO3 film: 200nm thick

[0077] The IDT electrode and reflector are formed from a stack of Ti layers, AlCu layers, and Ti layers starting from the second LiNbO3 film side. The thicknesses are set as follows: the lower Ti layer = 12 nm, the AlCu layer = 100 nm, and the upper Ti layer = 4 nm.

[0078] The wavelength λ, determined by the distance between the electrode fingers of the IDT electrode, is set to 2 μm, and the duty cycle of the IDT electrode is set to 0.5.

[0079] Dielectric film: Silicon oxide film, 30nm thick

[0080] In addition, as mentioned above, the combined thickness of the first LiNbO3 film and the second LiNbO3 film is 400 nm, i.e., 0.2λ.

[0081] Furthermore, the cutting angles of both the first LiNbO3 film and the second LiNbO3 film are set to 30° Y cut. The main surface of the first LiNbO3 film on the support substrate side is the front side, the main surface of the second LiNbO3 film side is the back side, the main surface of the second LiNbO3 film on the first LiNbO3 film side is the back side, and the main surface of the IDT electrode side is the front side.

[0082] Furthermore, for comparison, the elastic wave device of the second comparative example was fabricated in the same manner as the second embodiment described above, except that a single-layer 30°Y-cut LiNbO3 film with a thickness of 400 nm was used. Additionally, in the second comparative example, the side of the supporting substrate, which is the single-layer LiNbO3 film, was designated as the negative side, and the main side of the IDT electrode was designated as the positive side.

[0083] Figure 9 This is a diagram showing the phase characteristics of the elastic wave device of the second embodiment and the elastic wave device of the second comparative example as a resonator. The solid line shows the results of the second embodiment, and the dashed line shows the results of the second comparative example.

[0084] according to Figure 9 It is clear that in the second comparative example, large spurious emissions caused by higher-order modes appeared near 3400MHz, 6700MHz, and 7200MHz. In contrast, it is evident that in the second embodiment, the spurious-induced response in these frequency bands becomes very small. Furthermore, according to... Figure 9 It is clearly understood that the magnitude of the response caused by the dominant mode near 2000MHz in the second embodiment is equivalent to the response in the second comparative example. Therefore, in the elastic wave device of the second embodiment, the response of the dominant mode is sufficiently large. Thus, it is understood that in the second embodiment, it is also possible to suppress spurious signals caused by higher-order modes without degrading the response caused by the dominant mode.

[0085] Next, in the construction of the second embodiment, the total thickness of the first LiNbO3 film and the second LiNbO3 film is fixed at 0.4 μm = 0.2λ, and the thickness of the first LiNbO3 film is set to 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, or 0.35 μm. Various Y-cut LiNbO3 films with different cutting angles are used as the first and second LiNbO3 films. Furthermore, the cutting angles of the first and second LiNbO3 films are set to be equal.

[0086] Figure 10 This is a graph showing the relationship between the cutoff angle and the impedance ratio in the impedance characteristics of multiple elastic wave devices configured as described above. Here, the impedance ratio is the ratio of the impedance at the anti-resonant frequency of the dominant mode to the impedance at the resonant frequency. According to... Figure 10It is known that even when the thickness of the first LiNbO3 film varies within a range of 0.05 μm or more and 0.35 μm or less at different cutting angles, the impedance ratio of the master mode remains approximately the same if the cutting angle is the same. Furthermore, it is known that if the cutting angle is -20° or more and +90° or less, the impedance ratio of the master mode can be increased to 80 dB or more. Therefore, it is preferable that the cutting angle of the Y-cut LiNbO3 film is -20° or more and +90° or less.

[0087] Figure 11 This is a graph showing the relationship between the film thickness ratio and the cutting angle that can suppress stray waves caused by Rayleigh waves when the total film thickness of the first LiNbO3 film and the second LiNbO3 film are fixed at 0.4 μm = 0.2λ in the second embodiment described above, and the film thickness ratio (%) of the first LiNbO3 film relative to the total film thickness is varied. Figure 11 The dashed lines in the text are achieved by... Figure 11 The formula is obtained by approximating multiple plotting points in the equation. This formula becomes the following equation (2).

[0088] y = 0.0091x 2 +0.3543x+24.5… Equation (2)

[0089] Here, y is the cutting angle, and x is the proportion of the thickness of the first LiNbO3 film mentioned above.

[0090] For y obtained from the approximation (2), preferably, if it is a value within any range of (y±10°)+180n (where n is an integer of 0, 1, 2, 3, ...) or (y±10°)-180n (where n is an integer of 0, 1, 2, 3, ...), it can more effectively suppress spurious waves caused by Rayleigh waves.

[0091] Figure 12 This is a front cross-sectional view of the elastic wave device according to the second embodiment of the present invention. In the elastic wave device 21, an insulating film 22 is laminated between the first piezoelectric film 5 and the second piezoelectric film 6. For example, an oxide film can be used as the insulating film 22. The other structures of the elastic wave device 21 are the same as those of the elastic wave device 1. Similarly, the insulating film 22 can also be laminated between the first piezoelectric film 5 and the second piezoelectric film 6, as in the elastic wave device 21.

[0092] Furthermore, in the elastic wave device 1, the high-velocity acoustic material layer 3 is composed of a silicon nitride film, and the low-velocity acoustic film 4 is composed of a silicon oxide film, but their materials are not particularly limited. For example, various high-velocity materials can be used as the high-velocity acoustic material layer 3, where the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the first and second piezoelectric films. Examples of such high-velocity materials include AlN, Al2O3, and diamond films.

[0093] Furthermore, the low-velocity film 4 can also be made of a low-velocity material in which the velocity of the propagating bulk wave is lower than the velocity of the bulk wave propagating in the first and second piezoelectric films. Examples of such low-velocity materials include silicon oxide and silicon oxynitride.

[0094] Furthermore, the materials constituting the IDT electrode 7 and reflectors 8 and 9 are not limited to Ti / AlCu / Ti laminates; various metals or alloys can be used. Additionally, the IDT electrode 7 and reflectors 8 and 9 may also be composed of a single-layer metal film instead of a laminated metal film.

[0095] The material of the dielectric film 10 is not limited to silicon oxide; various dielectrics such as silicon oxynitride can be used.

[0096] In the elastic wave device 1, the high-velocity material layer 3 is disposed on the support substrate 2, but the high-velocity material layer 3 can also be integrated with the support substrate 2 by means of high-velocity material.

[0097] Alternatively, the low-velocity film 4 can be omitted, and the high-velocity material layer 3 can be directly laminated on the first piezoelectric film. Therefore, when the support substrate is composed of a high-velocity material layer, the first piezoelectric film can also be directly laminated on the support substrate.

[0098] Explanation of reference numerals in the attached figures

[0099] 1: Elastic wave device;

[0100] 2: Support base plate;

[0101] 3: High-speed sound material layer;

[0102] 4: Low-velocity membrane;

[0103] 5: The first LiTaO3 film;

[0104] 6: The second LiTaO3 membrane;

[0105] 5a, 5b, 6a, 6b: Main face;

[0106] 7: IDT electrode;

[0107] 8, 9: Reflectors;

[0108] 10: Dielectric film;

[0109] 21: Elastic wave device;

[0110] 22: Insulating film.

Claims

1. An elastic wave device, comprising: support base plate; A piezoelectric film, directly or indirectly laminated onto the supporting substrate; and IDT electrodes are formed on the piezoelectric film. The piezoelectric film has the following characteristics: The first piezoelectric film has a front side facing the support substrate and a negative side facing the IDT electrode; and A second piezoelectric film is stacked on top of the first piezoelectric film, with the side facing the support substrate being the negative side and the side facing the IDT electrode being the positive side. When the wavelength determined by the electrode finger spacing of the IDT electrode is set as λ, the total thickness of the first piezoelectric film and the second piezoelectric film is less than 1λ. The polarization direction of the first piezoelectric film and the polarization direction of the second piezoelectric film are opposite.

2. The elastic wave device according to claim 1, wherein, The combined thickness of the first piezoelectric film and the second piezoelectric film is less than 0.5λ.

3. The elastic wave device according to claim 1, wherein, The combined thickness of the first piezoelectric film and the second piezoelectric film is less than 0.25λ.

4. The elastic wave device according to any one of claims 1 to 3, wherein, In the first piezoelectric film and the second piezoelectric film, the thickness of the piezoelectric film that is relatively closer to the support substrate is greater than the thickness of the piezoelectric film that is relatively farther from the support substrate.

5. The elastic wave device according to any one of claims 1 to 3, wherein, The first piezoelectric film and the second piezoelectric film are stacked such that the front side of the first piezoelectric film is in contact with the front side of the second piezoelectric film.

6. The elastic wave device according to any one of claims 1 to 3, wherein, The first piezoelectric film and the second piezoelectric film are LiTaO3 films.

7. The elastic wave device according to claim 6, wherein, The first and second piezoelectric films are Y-cut LiTaO3 films with a cutting angle of -20° or higher and +75° or lower.

8. The elastic wave device according to claim 6, wherein, The cutting angles of the first piezoelectric film and the second piezoelectric film are values ​​within the range of (y±10°)+180n or (y±10°)-180n, where n is an integer of 0, 1, 2, 3, ... When the film thickness of the piezoelectric film closer to the supporting substrate is set to x% relative to the total film thickness of the first and second piezoelectric films, y is a value that satisfies the following formula (1). y = -0.0009955556x 3 +0.1552380952x 2 -4.6325396825x + 78.5714285714... Equation (1).

9. The elastic wave device according to any one of claims 1 to 3, wherein, The first piezoelectric film and the second piezoelectric film are LiNbO3 films.

10. The elastic wave device according to claim 9, wherein, The first and second piezoelectric films are Y-cut LiNbO3 films with a cutting angle of -20° or higher and +90° or lower.

11. The elastic wave device according to claim 9, wherein, The cutting angles of the first piezoelectric film and the second piezoelectric film are values ​​within the range of (y±10°)+180n or (y±10°)-180n, where n is an integer of 0, 1, 2, 3, ... When the film thickness of the piezoelectric film closer to the support substrate is set to x% relative to the total film thickness of the first and second piezoelectric films, y is a value that satisfies the following formula (2). y = 0.0091x 2 +0.3543x+24.5… equation (2).

12. The elastic wave device according to any one of claims 1 to 3, wherein, It also includes: an insulating film, which is laminated between the first piezoelectric film and the second piezoelectric film.

13. The elastic wave device according to any one of claims 1 to 3, wherein, It also includes: a high-velocity acoustic material layer, stacked between the support substrate and the piezoelectric film, comprising a high-velocity acoustic material in which the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the first piezoelectric film and the second piezoelectric film.

14. The elastic wave device according to claim 13, wherein, The support substrate includes the hypersonic material, and the hypersonic material layer and the support substrate are integrated.

15. The elastic wave device according to claim 13, wherein, It also includes: a low-velocity film, stacked between the high-velocity material layer and the piezoelectric film, comprising a low-velocity material in which the velocity of the propagating volume wave is lower than the velocity of the volume wave propagating in the first and second piezoelectric films.

16. The elastic wave device according to any one of claims 1 to 3, wherein, It also has a dielectric film covering the IDT electrode.

17. The elastic wave device according to any one of claims 1 to 3, wherein, The IDT electrode has a main electrode layer comprising an Al or AlCu alloy.

18. The elastic wave device according to any one of claims 1 to 3, wherein, The support substrate comprises Si on the (111) side, Si on the (110) side, or quartz.

19. The elastic wave device according to any one of claims 1 to 3, wherein, The first piezoelectric film and the second piezoelectric film each contain lithium tantalate or lithium niobate.

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