Elastic wave device

Abstract

Provided is an elastic wave device capable of suppressing spurs in a Rayleigh mode without causing the value of a fractional bandwidth to be too large. An elastic wave device (1) is provided with a support substrate (3), a silicon oxide layer (4) provided on the support substrate (3), a lithium niobate layer (5) provided on the silicon oxide layer (4), and an IDT electrode (6) provided on the lithium niobate layer (5). When the wavelength defined by the electrode finger pitch of the IDT electrode (6) is lambda, the thickness of the silicon oxide layer (4) is 0 lambda or more. The thickness of the IDT electrode (6) is represented by TIDT [lambda], the density of the IDT electrode (6) is represented by [rho] [g / cm3], the duty ratio of the IDT electrode (6) is represented by duty, the cutting angle of the lithium niobate layer (5) is represented by LNcut [degree], the thickness of the lithium niobate layer (5) is represented by TLN [lambda], the thickness of the silicon oxide layer (4) is represented by TSiO2 [lambda], the fractional bandwidth in the SH mode is represented by BW [%], and the electromechanical coupling coefficient in the Rayleigh mode is represented by ksaw2 [%]. TIDT, [rho], duty, LNcut, TLN, and TSiO2 are values within the range in which BW derived from formula 1 is 12% or less and ksaw2 derived from formula 2 is 0.1% or less.

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 portable phones, etc. An example of a surface acoustic wave device is disclosed in the following patent document 1. In the surface acoustic wave device described in patent document 1, a supporting substrate, a high acoustic velocity film, a low acoustic velocity film, and a lithium niobate film are stacked. An IDT (Interdigital Transducer) electrode is provided on the lithium niobate film. When the cutting angle of the lithium niobate film is 30°Y-cut, the thickness of the lithium niobate film is set to be less than 0.42λ. In addition, λ is set to the wavelength of the fundamental mode of the SH-type surface wave.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent No. 5850137 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] However, in the elastic wave device described in Patent Document 1, the spurious emission of the Rayleigh mode cannot be sufficiently suppressed. Moreover, in the elastic wave device using the lithium niobate film, the fractional bandwidth value tends to become large. When the fractional bandwidth value is too large, for example, when the elastic wave device is used in a filter device, the steepness near the end of the high-frequency side or the low-frequency side of the passband will not become sufficiently high.

[0008] An object of the present invention is to provide an elastic wave device that can suppress spurious emission in a Rayleigh mode without increasing the value of the fractional bandwidth too much.

[0009] Technical solutions to solve problems

[0010] In a broad aspect of the elastic wave device according to the present invention, the device comprises a support substrate, a silicon oxide layer provided on the support substrate, a lithium niobate layer provided on the silicon oxide layer, and an IDT electrode provided on the lithium niobate layer, wherein when a wavelength defined by an electrode finger pitch of the IDT electrode is λ, the thickness of the silicon oxide layer is greater than or equal to 0λ, and when a thickness of the IDT electrode is λ, the thickness of the IDT electrode is less than or equal to 0λ. IDT [λ], the density of the IDT electrode is set to ρ [g / cm 3 ], the duty ratio of the IDT electrode is set to duty, the cutting angle of the lithium niobate layer is set to LNcut [°], and the thickness of the lithium niobate layer is set to T LN[λ], the thickness of the silicon oxide layer is set to T SiO2 [λ], the fractional bandwidth of the SH mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%], the T IDT , the ρ, the duty, the LNcut, the T LN And the T SiO2 The BW derived from the following formula 1 is less than 12% and the ksaw2 derived from the following formula 2 is less than 0.1%.

[0011] [Formula 1]

[0012] Equation 1

[0013]

[0014] [Formula 2]

[0015] Equation 2

[0016] .

[0017] In another broad aspect of the elastic wave device according to the present invention, the elastic wave device comprises a supporting substrate, a silicon oxide layer provided on the supporting substrate, a lithium niobate layer provided on the silicon oxide layer, and an IDT electrode provided on the lithium niobate layer and containing AlCu, wherein when a wavelength defined by an electrode finger pitch of the IDT electrode is λ, a thickness of the silicon oxide layer is greater than or equal to 0λ, and when a thickness of the IDT electrode is T IDT [λ], the duty ratio of the IDT electrode is set to duty, the cutting angle of the lithium niobate layer is set to LNcut [°], and the thickness of the lithium niobate layer is set to T LN [λ], the thickness of the silicon oxide layer is set to T SiO2 [λ], the fractional bandwidth of the SH mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%], the T IDT , the duty, the LNcut, the T LN And the T SiO2 The BW derived from the following formula 3 is less than 12% and the ksaw2 derived from the following formula 4 is less than 0.1%.

[0018] [Formula 3]

[0019] Equation 3

[0020]

[0021] [Formula 4]

[0022] Equation 4

[0023] .

[0024] Effects of the Invention

[0025] According to the elastic wave device according to the present invention, it is possible to suppress spurious emission in the Rayleigh mode without making the value of the fractional bandwidth too large. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0027] Figure 2 It is a plan view of the elastic wave device according to the first embodiment of the present invention.

[0028] Figure 3 The figure shows the T when LNcut is 45°. LN and T SiO2 A diagram showing the relationship with BW in SH mode.

[0029] Figure 4 The figure shows the T when LNcut is 45°. LN and T SiO2 Plot of the relationship with KSAW2 of the Rayleigh mode.

[0030] Figure 5 It is a diagram showing the phase characteristics in the first embodiment of the present invention and a comparative example.

[0031] Figure 6 It shows T SiO2 A plot of versus the normalized frequency that produces higher order modes.

[0032] Figure 7 This is a circuit diagram of a filter device according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0033] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings to make the present invention clear.

[0034] In addition, it should be noted that each embodiment described in this specification is an example, and some structures can be replaced or combined among different embodiments.

[0035] Figure 1 It is a front cross-sectional view of the elastic wave device according to the first embodiment of the present invention.

[0036] The elastic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 has a supporting substrate 3, a silicon oxide layer 4, and a lithium niobate layer 5. The silicon oxide layer 4 is provided on the supporting substrate 3. The lithium niobate layer 5 is provided on the silicon oxide layer 4. In the present embodiment, the silicon oxide used in the silicon oxide layer 4 is SiO2. However, the composition of the silicon oxide used in the silicon oxide layer 4 is not limited to SiO2.

[0037] IDT electrode 6 is provided on lithium niobate layer 5. Acoustic waves are excited by applying an AC voltage to IDT electrode 6. Acoustic wave device 1 is a surface acoustic wave resonator configured to utilize the SH mode as a main mode. In acoustic wave device 1, the Rayleigh mode becomes a spurious mode.

[0038] Figure 2 is a top view of the elastic wave device according to the first embodiment. Figure 1 It is along Figure 2 The cross-sectional view of line II in FIG. Figure 2 In the figure, a dielectric film described later is omitted.

[0039] A pair of reflectors 7A and 7B are provided on both sides of the elastic wave propagation direction of the IDT electrode 6 on the lithium niobate layer 5. The IDT electrode 6 has a first bus bar 16 and a second bus bar 17 and a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. The first bus bar 16 and the second bus bar 17 are opposed to each other. One end of the plurality of first electrode fingers 18 is respectively connected to the first bus bar 16. One end of the plurality of second electrode fingers 19 is respectively connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interlaced with each other.

[0040] In the following, the first electrode finger 18 and the second electrode finger 19 are sometimes simply recorded as electrode fingers. In the present embodiment, the direction in which the plurality of electrode fingers extend is orthogonal to the direction in which the elastic wave propagates. The dimension of the electrode finger along the direction in which the elastic wave propagates is set to the width of the electrode finger. Furthermore, the wavelength specified by the electrode finger pitch of the IDT electrode 6 is set to λ. Specifically, the wavelength λ is twice the electrode finger pitch. In addition, the electrode finger pitch is the center-to-center distance between adjacent first electrode fingers 18 and second electrode fingers 19.

[0041] In this specification, the duty ratio is used as an indicator of the width of the first electrode finger 18 and the second electrode finger 19 relative to the width of the area between the centers of the adjacent first electrode finger 18 and the second electrode finger 19. More specifically, the duty ratio is the ratio of the width of the portion of the first electrode finger 18 and the second electrode finger 19 provided in the above-mentioned area to the dimension of the above-mentioned area along the propagation direction of the elastic wave. In addition, in the present embodiment, both the electrode finger pitch and the electrode finger width are fixed. In this case, the duty ratio of each of the above-mentioned areas in the IDT electrode 6 is the value obtained by dividing the electrode finger width by the electrode finger pitch. In this way, when the duty ratio is fixed, it is simply recorded below as the duty ratio of the IDT electrode 6.

[0042] In the present embodiment, the IDT electrode 6, the reflector 7A, and the reflector 7B include a single-layer metal film. Specifically, the IDT electrode 6 and each reflector include Al. However, the materials of the IDT electrode 6 and each reflector are not limited to the above. Alternatively, the IDT electrode 6 and each reflector may also include a stacked metal film. In addition, in this specification, the so-called component containing a certain material includes a case where a trace amount of impurities is contained to the extent that the electrical characteristics of the elastic wave device will not be significantly deteriorated.

[0043] Return to Figure 1 A dielectric film 8 is provided on the lithium niobate layer 5 so as to cover the IDT electrode 6. The dielectric film 8 is provided so that the IDT electrode 6 is not easily damaged. In the present embodiment, the dielectric film 8 includes silicon oxide. The thickness of the dielectric film 8 is 30 nm. However, the material and thickness of the dielectric film 8 are not limited to the above. In addition, the dielectric film 8 may not be provided.

[0044] Hereinafter, the thickness of the IDT electrode 6 is referred to as T IDT [λ], the density of the IDT electrode 6 is ρ [g / cm 3 ], the duty ratio of the IDT electrode 6 is set to duty. The cutting angle of the lithium niobate layer 5 is set to LNcut [°], and the thickness of the lithium niobate layer 5 is set to T LN [λ], the thickness of the silicon oxide layer 4 is set to T SiO2 [λ]. The fractional bandwidth of the SH mode as the main mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%]. In addition, when the resonant frequency is set to fr and the anti-resonant frequency is set to fa, the fractional bandwidth is represented by (|fa-fr| / fr)×100[%]. More specifically, the cut angle of the lithium niobate layer 5 is the cut angle when expressed in the rotation Y cut X propagation.

[0045] This embodiment is characterized in that T IDT ,ρ,duty,LNcut,TLN and T SiO2 The value is within the range where BW derived from the following equation 1 is 12% or less and ksaw2 derived from the following equation 2 is 0.1% or less. This makes it possible to suppress Rayleigh mode spurious without making the fractional bandwidth value too large. The details are described below.

[0046] Formula 1 is T IDT ,ρ,duty,LNcut,T LN and T SiO2 The relationship between T and BW. IDT ,ρ,duty,LNcut,T LN and T SiO2 The relationship between ksaw2 and equation 1 and equation 2 are as follows.

[0047] [Formula 5]

[0048] Equation 5

[0049]

[0050] [Formula 6]

[0051] Equation 6

[0052]

[0053] Equations 1 and 2 were derived by performing simulations on an elastic wave device having the same laminated structure as that of Embodiment 1. The materials of the components of the elastic wave device involved in the simulations are as follows.

[0054] Support substrate: Material…Si, Surface orientation…(111)

[0055] Silicon oxide layer: Material…SiO2

[0056] Lithium niobate layer: Material…LiNbO3

[0057] IDT electrode: Material…Al

[0058] Formula 1 was derived by changing the design parameters within the following range. The wavelength λ was set to 5 μm. ρ is the density of Al [g / cm 3 ], 2.699 g / cm 3 However, as the value of ρ in Formula 1, the following metal density [g / cm 3 ]. Cu: 8.96; Ag: 10.05; Au: 19.32; Pt: 21.4; W: 19.3; Ti: 4.54; Ni: 8.9; Cr: 7.19; Mo: 10.28.

[0059] T IDT :0.04λ or more and 0.16λ or less

[0060] LNcut: 25° or more and 70° or less

[0061] T LN :0.06λ or more and 0.7λ or less

[0062] T SiO2 :0λ or more and 0.6λ or less

[0063] Duty: 0.4 or more and 0.6 or less

[0064] Depend on Figure 3 as well as Figure 4 The T when LNcut is 45° is shown. LN and T SiO2 Example of relationship with BW and ksaw2.

[0065] Figure 3 The figure shows the case of rotating Y cut 45° X propagation (LNcut=45°), T LN and T SiO2 A diagram showing the relationship with BW in SH mode. Figure 4 The figure shows the T when LNcut is 45°. LN and T SiO2 Plot of the relationship with KSAW2 of the Rayleigh mode.

[0066] like Figure 3 As shown, it can be seen that BW depends on T LN and T SiO2 Similarly, if Figure 4 As shown, it can be seen that ksaw2 depends on T LN and T SiO2 In the case of different LNcut, T LN and T SiO2 The relationship with BW and ksaw2 also becomes different. The equations showing the relationship between them are the above equations 1 and 2.

[0067] In the first embodiment, T IDT ,ρ,duty,LNcut,T LN and T SiO2 The BW derived from Formula 1 is within a range of 12% or less. This can prevent the fractional bandwidth of the SH mode from being too large. IDT ,ρ,duty,LNcut,T LN and T SiO2The ksaw2 derived from equation 2 becomes a value within a range of 0.1% or less. According to this, the spurious emission of the Rayleigh mode can be suppressed. This effect is shown by comparing the first embodiment and the comparative example. The design parameters of the elastic wave device of the first embodiment involved in this comparison are as follows.

[0068] Support substrate: Material…Si, Surface orientation…(111)

[0069] Silicon oxide layer: Materials…SiO2, T SiO2 …0.1λ

[0070] Lithium niobate layer: Material…LiNbO3, LNcut…45°, T LN : 0.6λ

[0071] IDT electrode: Material…Al, ρ…2.699g / cm 3 、T IDT …0.08λ, duty…0.5, wavelength λ…5μm

[0072] The design parameters of the comparative example are as follows: LNcut is 25°, T LN The same as the first embodiment except that it is 0.2λ. In the design parameters of the comparative example, BW derived from equation 1 is not less than 12%, and ksaw2 derived from equation 2 is not less than 0.1%. In the first embodiment and the comparative example, the phase characteristics are compared.

[0073] Figure 5 It is a diagram showing the phase characteristics in the first embodiment and the comparative example.

[0074] like Figure 5 As shown in the figure, in the comparative example, spurious Rayleigh mode is generated around 600MHz. In contrast, it can be seen that almost no spurious Rayleigh mode is generated in the first embodiment. Moreover, it can be seen that in the first embodiment, the frequency band from the resonant frequency to the antiresonant frequency of the main mode is narrower than that in the comparative example. Therefore, it can be seen that in the first embodiment, the value of the fractional bandwidth of the main mode is smaller than that in the comparative example.

[0075] As described above, in the first embodiment, the fractional bandwidth of the main mode can be kept from being too large and the spurious emission of the Rayleigh mode can be suppressed. Accordingly, when the elastic wave device 1 of the first embodiment is used in a filter device, good filter characteristics can be obtained. More specifically, the fractional bandwidth is small in the elastic wave device 1. Thus, the steepness of the end of the high-frequency side or the low-frequency side of the passband of the filter device can be improved. In this specification, high steepness means that the change in frequency is small relative to the change in a certain fixed attenuation near the end of the passband. In addition, the influence of the spurious emission of the Rayleigh mode on the filter characteristics can be suppressed.

[0076] The cutting angle LNcut of the lithium niobate layer 5 is preferably 40° or more. Figure 3 As shown in FIG. 1 , the thickness T of the lithium niobate layer 5 can be increased to make the fractional bandwidth BW of the main mode less than 12%. LN and the thickness T of the silicon oxide layer 4 SiO2 range.

[0077] The thickness T of the lithium niobate layer 5 is LN Preferably, it is greater than 0.5λ. In this case, for example, Figure 3 as well as Figure 4 As shown, the fractional bandwidth BW of the SH mode, which is the main mode, and the value of the electromechanical coupling coefficient Ksaw2 of the Rayleigh mode can be reduced more reliably.

[0078] Here, the thickness T of the silicon oxide layer 4 in the elastic wave device 1 having the structure of the first embodiment is further set to SiO2 From this, T SiO2 The relationship between the frequency of the spurious high-order mode and the design parameters of the elastic wave device 1 in this simulation is T SiO2 In addition to Figure 5 The design parameters of the elastic wave device 1 involved in the comparison shown are the same.

[0079] The thickness T of the silicon oxide layer 4 is SiO2 The frequency is changed within a range of 0.02λ to 0.6λ. More specifically, it is changed in increments of 0.08λ within a range of 0.02λ to 0.1λ, and in increments of 0.1λ within a range of 0.1λ to 0.6λ. The frequency at which the high-order mode is generated is expressed as a normalized frequency normalized by the resonant frequency of the main mode.

[0080] Figure 6 It shows T SiO2 A plot of versus the normalized frequency that produces higher order modes.

[0081] like Figure 6 As shown, it can be seen that the thickness T of the silicon oxide layer 4 SiO2 The smaller the value of T, the higher the normalized frequency of the higher-order mode. SiO2 Preferably, it is less than 0.56λ. In this case, the frequency of the high-order mode can be made higher than the antiresonance frequency of the main mode more reliably. More specifically, Figure 6 The fractional bandwidth of the elastic wave device 1 with the relationship of is 8%. In this case, the antiresonant frequency normalized by the resonant frequency is 1.08. On the other hand, at T SiO2 When the thickness of T is less than 0.56λ, the normalized frequency of the high-order mode is greater than 1.08.SiO2 By setting it to 0.56λ or less, the frequency at which the high-order mode is generated can be easily made higher than the antiresonance frequency of the main mode.

[0082] In addition, T SiO2 More preferably, it is 0.34λ or less. In this case, in the elastic wave device 1, the frequency of the high-order mode can be made higher than the antiresonance frequency of the main mode more reliably. More specifically, in the elastic wave device 1 of the first embodiment, the fractional bandwidth BW derived from equation 1 is 12% or less. Therefore, the antiresonance frequency normalized by the resonant frequency is 1.12 or less. On the other hand, at T SiO2 When T is less than 0.34λ, the normalized frequency of the high-order mode is greater than 1.12. SiO2 By setting the value to 0.34λ or less, in the elastic wave device 1 having any fractional bandwidth and the structure of the first embodiment, it is easy to make the frequency at which a high-order mode is generated higher than the antiresonance frequency of the main mode.

[0083] In addition, T SiO2 In this case, when elastic wave device 1 having the structure of the first embodiment is used for parallel arm resonators and series arm resonators of a ladder filter, the frequency of the high-order mode generated in the parallel arm resonator can be more reliably made higher than the antiresonance frequency of the series arm resonator.

[0084] More specifically, in the series arm resonator and the parallel arm resonator constituting the passband of the ladder filter, the resonant frequency of the parallel arm resonator is lower than the resonant frequency of the series arm resonator. Therefore, it is possible that a high-order mode of the parallel arm resonator is generated between the resonant frequency and the anti-resonant frequency of the series arm resonator. In the parallel arm resonator, by setting the normalized frequency of the high-order mode to be generated to be greater than 1.15, the frequency of the high-order mode can be made higher than the anti-resonant frequency of the series arm resonator. Here, in the elastic wave device 1 of the first embodiment, at T SiO2 When λ is less than 0.12λ, the normalized frequency of the high-order mode is 1.15 or more. SiO2 By setting the value to 0.12λ or less, the frequency at which the high-order mode is generated can be made higher than the antiresonance frequency of the series arm resonator.

[0085] In addition, in T SiO2 When the value is 0.02λ, the normalized frequency of the high-order mode can be increased to 1.16 or more.

[0086] In the elastic wave device 1 according to the first embodiment, the thickness T of the silicon oxide layer 4 is SiO2It only needs to be 0λ or more. When the thickness of the silicon oxide layer 4 is 0λ, the structure of the piezoelectric substrate 2 is the same as the structure in which the lithium niobate layer 5 is directly stacked on the supporting substrate 3 .

[0087] In the first embodiment, the IDT electrode includes a single-layer metal film. However, the IDT electrode may be a stack of a plurality of electrode layers. In this case, if the thickness of each electrode layer is t1, t2, ..., t n , then the thickness of the IDT electrode becomes T IDT =Σt n At this time, if the density of each electrode layer is set to ρ1, ρ2, ..., ρ n , then the density of the IDT electrode becomes Σ(ρ n ×t n ) / Σt n On the other hand, when each electrode layer includes an alloy, if the density of the elements constituting the alloy is ρ1, ρ2, ..., ρ n , set the concentration to p1, p2, ..., p n [%], then density = Σ(ρ n ×p n ). In addition, n in the formula using Σ is a natural number having a value greater than or equal to 1 and less than or equal to the number of stacking layers.

[0088] When the IDT electrode is a stack of multiple electrode layers, the n ×t n ) / Σt n The obtained density is used as ρ in equations 1 and 2. On the other hand, when the electrode layer of the IDT electrode is an alloy layer, the density calculated according to Σ(ρ n ×p n ) is used as ρ in equations 1 and 2. In the case where the IDT electrode is a laminate of alloy layers, it is sufficient to use Σ(ρ n ×t n ) / Σt n and Σ(ρ n ×p n ) is enough.

[0089] The structure of the second embodiment will be described below. The second embodiment differs from the first embodiment only in the materials of the IDT electrode and each reflector. Therefore, in the description of the second embodiment, the drawings and reference numerals used in the description of the first embodiment are used.

[0090] The IDT electrode 6 and each reflector in the second embodiment are made of AlCu. More specifically, in this embodiment, the IDT electrode 6 and each reflector are made of AlCu. This embodiment is characterized in thatIDT 、duty、LNcut、T LN and T SiO2 The value is set within a range where BW derived from the following equation 3 is 12% or less and ksaw2 derived from the following equation 4 is 0.1% or less. This makes it possible to suppress Rayleigh mode spurious without making the fractional bandwidth value too large.

[0091] Formula 3 is T IDT 、duty、LNcut、T LN and T SiO2 The relationship between T and BW. IDT 、duty、LNcut、T LN and T SiO2 The relationship between ksaw2 and ksaw2 is as follows. Equations 3 and 4 are derived in the same manner as when equations 1 and 2 are derived. Specifically, equations 3 and 4 are derived by simulation in an elastic wave device having the same stacked structure as that of the second embodiment.

[0092] [Formula 7]

[0093] Equation 7

[0094]

[0095] [Formula 8]

[0096] Equation 8

[0097]

[0098] As described above, the elastic wave device according to the present invention can be used in a filter device. An example of this is shown below.

[0099] Figure 7 This is a circuit diagram of a filter device according to a third embodiment.

[0100] The filter device 20 is a ladder filter. The filter device 20 has a first signal terminal 22 and a second signal terminal 23, and a plurality of series arm resonators and a plurality of parallel arm resonators as a plurality of resonators. In the filter device 20 of this embodiment, the plurality of resonators are all elastic wave devices according to the present invention. However, it is sufficient that at least one resonator is an elastic wave device according to the present invention.

[0101] In the present embodiment, the first signal terminal 22 is an antenna terminal. The antenna terminal is connected to an antenna. The first signal terminal 22 and the second signal terminal 23 may be configured as, for example, electrode lands or wirings.

[0102] Specifically, the plurality of series arm resonators of the present embodiment are series arm resonators S1, series arm resonators S2, and series arm resonators S3. The plurality of series arm resonators are connected in series between the first signal terminal 22 and the second signal terminal 23. On the other hand, specifically, the plurality of parallel arm resonators of the present embodiment are parallel arm resonators P1 and parallel arm resonators P2. The parallel arm resonator P1 is connected between the connection point between the series arm resonator S1 and the series arm resonator S2 and the ground potential. The parallel arm resonator P2 is connected between the connection point between the series arm resonator S2 and the series arm resonator S3 and the ground potential.

[0103] However, the circuit structure of the filter device according to the present invention is not limited to the above. When the filter device is a ladder filter, the filter device only needs to have at least one series arm resonator and at least one parallel arm resonator. Alternatively, the filter device may also have a longitudinally coupled resonator type elastic wave filter. In this case, the filter device only needs to have at least one elastic wave device of the present invention as a series arm resonator or a parallel arm resonator.

[0104] In this embodiment, the elastic wave device according to the present invention is used as a series arm resonator and a parallel arm resonator. Therefore, in each resonator, the value of the fractional bandwidth can be reduced, and the spurious of the Rayleigh mode can be suppressed. Therefore, the steepness of the end in the passband can be improved, and the influence of the Rayleigh mode on the filter characteristics can be suppressed.

[0105] Preferably, at least one parallel arm resonator is an elastic wave device according to the present invention, and the thickness T of the silicon oxide layer is SiO2 In this case, as described above, the frequency of the high-order mode generated in the parallel arm resonator can be made higher than the antiresonance frequency of the series arm resonator.

[0106] Furthermore, even in a structure including another dielectric film between the silicon oxide layer and the support substrate, the effects of the present disclosure can be obtained.

[0107] Examples of aspects of the elastic wave device according to the present invention are summarized below.

[0108] <1> An elastic wave device comprises a support substrate, a silicon oxide layer provided on the support substrate, a lithium niobate layer provided on the silicon oxide layer, and an IDT electrode provided on the lithium niobate layer, wherein when a wavelength defined by an electrode finger pitch of the IDT electrode is λ, the thickness of the silicon oxide layer is greater than or equal to 0λ, and when a thickness of the IDT electrode is T IDT [λ], the density of the IDT electrode is set to ρ [g / cm 3], the duty ratio of the IDT electrode is set to duty, the cutting angle of the lithium niobate layer is set to LNcut [°], and the thickness of the lithium niobate layer is set to T LN [λ], the thickness of the silicon oxide layer is set to T SiO2 [λ], the fractional bandwidth of the SH mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%], the T IDT , the ρ, the duty, the LNcut, the T LN And the T SiO2 The BW derived from the following formula 1 is 12% or less, and the ksaw2 derived from the following formula 2 is 0.1% or less.

[0109] [Formula 9]

[0110] Equation 9

[0111]

[0112] [Formula 10]

[0113] Equation 10

[0114] .

[0115] <2> exist <1> In the elastic wave device described, the T SiO2 It is less than 0.56λ.

[0116] <3> exist <2> In the elastic wave device described, the T SiO2 It is less than 0.34λ.

[0117] <4> exist <3> In the elastic wave device described, the T SiO2 It is less than 0.12λ.

[0118] <5> An elastic wave device comprises a support substrate, a silicon oxide layer provided on the support substrate, a lithium niobate layer provided on the silicon oxide layer, and an IDT electrode provided on the lithium niobate layer and containing AlCu, wherein when a wavelength defined by an electrode finger pitch of the IDT electrode is λ, the thickness of the silicon oxide layer is greater than or equal to 0λ, and when a thickness of the IDT electrode is T IDT [λ], the duty ratio of the IDT electrode is set to duty, the cutting angle of the lithium niobate layer is set to LNcut [°], and the thickness of the lithium niobate layer is set to T LN [λ], the thickness of the silicon oxide layer is set to T SiO2 [λ], the fractional bandwidth of the SH mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%], the TIDT , the duty, the LNcut, the T LN And the T SiO2 The BW derived from the following formula 3 is less than 12% and the ksaw2 derived from the following formula 4 is less than 0.1%.

[0119] [Formula 11]

[0120] Equation 11

[0121]

[0122] [Formula 12]

[0123] Equation 12

[0124] .

[0125] Description of Reference Numerals

[0126] 1…Elastic wave device

[0127] 2…Piezoelectric substrate

[0128] 3…Support base plate

[0129] 4…Silicon oxide layer

[0130] 5…Lithium niobate layer

[0131] 6…IDT electrode

[0132] 7A, 7B…Reflector

[0133] 8…Dielectric film

[0134] 16, 17…1st bus bar, 2nd bus bar

[0135] 18, 19…1st electrode finger, 2nd electrode finger

[0136] 20…Filter device

[0137] 22, 23…1st signal terminal, 2nd signal terminal

[0138] P1, P2…Parallel arm resonator

[0139] S1~S3...series arm resonator.

Claims

1. An elastic wave device comprising: support base plate; A silicon oxide layer is disposed on the supporting substrate; a lithium niobate layer disposed on the silicon oxide layer; and An IDT electrode is disposed on the lithium niobate layer, When the wavelength defined by the electrode finger pitch of the IDT electrode is λ, the thickness of the silicon oxide layer is 0λ or more, When the thickness of the IDT electrode is set to T IDT [λ], the density of the IDT electrode is set to ρ [g / cm 3 ], the duty ratio of the IDT electrode is set to duty, the cutting angle of the lithium niobate layer is set to LNcut [°], and the thickness of the lithium niobate layer is set to T LN [λ], the thickness of the silicon oxide layer is set to T SiO2 [λ], the fractional bandwidth of the SH mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%], the T IDT , the ρ, the duty, the LNcut, the T LN And the T SiO2 The BW derived from the following formula 1 is 12% or less, and the ksaw2 derived from the following formula 2 is 0.1% or less. [Formula 1] Equation 1 [Formula 2] Equation 2 。 2. The elastic wave device according to claim 1, wherein: The T SiO2 It is less than 0.56λ.

3. The elastic wave device according to claim 2, wherein: The T SiO2 It is less than 0.34λ.

4. The elastic wave device according to claim 3, wherein: The T SiO2 It is less than 0.12λ.

5. An elastic wave device comprising: support base plate; A silicon oxide layer is disposed on the supporting substrate; a lithium niobate layer disposed on the silicon oxide layer; and an IDT electrode disposed on the lithium niobate layer and comprising AlCu, When the wavelength defined by the electrode finger pitch of the IDT electrode is λ, the thickness of the silicon oxide layer is 0λ or more, When the thickness of the IDT electrode is set to T IDT [λ], the duty ratio of the IDT electrode is set to duty, the cutting angle of the lithium niobate layer is set to LNcut [°], and the thickness of the lithium niobate layer is set to T LN [λ], the thickness of the silicon oxide layer is set to T SiO2 [λ], the fractional bandwidth of the SH mode is set to BW[%], and the electromechanical coupling coefficient of the Rayleigh mode is set to ksaw2[%], the T IDT , the duty, the LNcut, the T LN And the T SiO2 The BW derived from the following formula 3 is less than 12% and the ksaw2 derived from the following formula 4 is less than 0.1%. [Formula 3] Equation 3 [Formula 4] Equation 4 。

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