阅读说明：本技术 弹性波装置 (Elastic wave device ) 是由 三村昌和 于 2018-03-28 设计创作，主要内容包括：本发明提供一种利用了板波S0模式且低损耗的弹性波装置。一种弹性波装置(1),具备：压电体(5),直接或间接地设置在支承基板(2)上,由铌酸锂构成；以及IDT电极(6),直接或间接地设置在压电体(5)上,在将由IDT电极(6)的电极指间距决定的弹性波的波长设为λ时,压电体(5)的厚度为1λ以下,利用了在压电体(5)中传播的板波S0模式,所述铌酸锂的欧拉角为(0°±10°,θ,90°±10°),其中,θ为0°以上且180°以下。(The invention provides an elastic wave device using a plate wave S0 mode and having low loss. An elastic wave device (1) is provided with: a piezoelectric body (5) which is provided directly or indirectly on the support substrate (2) and is composed of lithium niobate; and an IDT electrode (6) that is provided directly or indirectly on the piezoelectric body (5), wherein the thickness of the piezoelectric body (5) is 1 λ or less, and the Euler angle of the lithium niobate is (0 ° ± 10 °, θ, 90 ° ± 10 °), where θ is 0 ° or more and 180 ° or less, by utilizing the S0 mode propagating in the piezoelectric body (5), when λ is the wavelength of an elastic wave determined by the electrode finger pitch of the IDT electrode (6).)

1. An elastic wave device is provided with:

A support substrate;

A piezoelectric body which is provided directly or indirectly on the support substrate and is made of lithium niobate; and

An IDT electrode directly or indirectly provided on the piezoelectric body,

A plate wave SO mode propagating in the piezoelectric body is utilized,

The thickness of the piezoelectric body is 1 lambda or less, where lambda is a wavelength of an elastic wave determined by an electrode finger pitch of the IDT electrode,

The Euler angle of the lithium niobate is (0 DEG + -10 DEG, theta, 90 DEG + -10 DEG),

The Euler angle θ is in the range of 0 ° or more and 180 ° or less.

2. The elastic wave device according to claim 1,

The Euler angle θ is in the range of 7 ° or more and 66 ° or less.

3. The elastic wave device according to claim 2,

The thickness of the piezoelectric body normalized by the wavelength λ of the elastic wave is defined as T_LNThe thickness of the IDT electrode normalized by the wavelength λ of the elastic wave is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_Althe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ rho/rho_Alin this case, T × r satisfies the following formula (1),

T×r≥0.1821×T_LN ²+0.1055×T_LN+0.0082 formula (1).

4. The elastic wave device according to claim 1,

The Euler angle θ is in a range of 67 ° or more and 104 ° or less.

5. The elastic wave device according to claim 4,

The thickness of the piezoelectric body normalized by the wavelength λ of the elastic wave is defined as T_LNthe thickness of the IDT electrode normalized by the wavelength λ of the elastic wave is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ rho/rho_AlIn this case, T × r satisfies the following expression (2),

T×r≥0.5902×T_LN ²-0.2133×T_LN+0.0248 formula (2).

6. The elastic wave device according to claim 1,

The Euler angle theta is in a range of 116 DEG or more and 137 DEG or less.

7. The elastic wave device according to claim 6,

Will usethe thickness of the piezoelectric body normalized by the wavelength λ of the elastic wave is T_LNThe thickness of the IDT electrode normalized by the wavelength λ of the elastic wave is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ rho/rho_AlIn this case, T × r satisfies the following formula (3),

T×r≥0.6307×T_LN ²-0.0858×T_LN+0.0110 formula (3).

8. The elastic wave device according to any one of claims 1 to 7,

the support substrate and the piezoelectric body have a hollow between them at a position where the IDT electrode is provided, in a plan view.

9. the elastic wave device according to any one of claims 1 to 7,

the support substrate is made of a high sound velocity material having a sound velocity of a bulk wave propagating therein higher than a sound velocity of an elastic wave propagating through the piezoelectric body.

10. The elastic wave device according to any one of claims 1 to 7,

Further provided with: and a layer made of a high acoustic velocity material, which is laminated between the support substrate and the piezoelectric body, and in which the acoustic velocity of a bulk wave propagating through the high acoustic velocity material is higher than the acoustic velocity of an elastic wave propagating through the piezoelectric body.

11. The elastic wave device according to claim 9 or 10,

Further provided with: and a low acoustic velocity material layer which is laminated between the high acoustic velocity material and the piezoelectric body and in which the acoustic velocity of a bulk wave propagating through the piezoelectric body is lower than that of an elastic wave propagating through the piezoelectric body.

12. The elastic wave device according to any one of claims 1 to 7,

Further provided with: an acoustic reflection layer provided between the support substrate and the piezoelectric body and supporting the piezoelectric body,

The acoustic reflection layer has a low acoustic impedance layer having a relatively low acoustic impedance and a high acoustic impedance layer having a relatively high acoustic impedance.

Technical Field

The present invention relates to an elastic wave device using an elastic wave of a plate wave SO mode.

Background

patent document 1 below discloses an elastic wave device using plate waves. In the elastic wave device described in patent document 1, a thin piezoelectric body is laminated on a support substrate via an acoustic reflection layer. An IDT electrode is provided on the piezoelectric body. Patent document 1 describes: when lithium niobate is used as the piezoelectric material and SO mode is used as the plate wave, the euler angle of lithium niobate is preferably (90 °, 90 °, 25 ° to 40 °).

Prior art documents

Patent document

Patent document 1: WO 2012/086441A 1

disclosure of Invention

Problems to be solved by the invention

In an elastic wave device using an elastic wave of a plate wave SO mode as described in patent document 1, when the euler angle is set to (90 °, 90 °, 25 ° to 40 °), the loss may be increased due to the influence of the energy flow angle.

The present invention aims to reduce loss in an elastic wave device using an elastic wave in a plate wave SO mode.

Means for solving the problems

An elastic wave device according to the present invention includes: a support substrate; a piezoelectric body which is provided directly or indirectly on the support substrate and is made of lithium niobate; and an IDT electrode that is provided directly or indirectly on the piezoelectric body, and that uses a plate wave SO mode propagating through the piezoelectric body, wherein the thickness of the piezoelectric body is 1 λ or less, the Euler angle of the lithium niobate is (0 ° ± 10 °, θ, 90 ° ± 10 °), and θ of the Euler angle is in a range of 0 ° or more and 180 ° or less, where λ is a wavelength of an elastic wave determined by an electrode finger pitch of the IDT electrode.

in the elastic wave device according to the present invention, it is preferable that θ of the euler angle is in a range of 7 ° or more and 66 ° or less. In this case, the electromechanical coupling coefficient of the plate wave SO mode can be increased.

In the elastic wave device according to the present invention, it is preferable that a thickness obtained by normalizing a thickness of the piezoelectric body with a wavelength λ of the elastic wave is T_LNThe thickness of the IDT electrode normalized by the wavelength lambda of the elastic wave is T, and the IDT electrode is formedρ represents the density of the metal of (2), and ρ represents the density of Al_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ rho/rho_AlIn this case, T × r satisfies the following formula (1).

T×r≥0.1821×T_LN ²+0.1055×T_LN+0.0082 type (1)

In this case, the position of the spurious signal can be shifted out of the desired frequency band.

In the elastic wave device according to the present invention, θ of the euler angle is preferably in a range of 67 ° or more and 104 ° or less. In this case, the electromechanical coupling coefficient of the spurious mode can be reduced.

In the present invention, it is preferable that a thickness obtained by normalizing a thickness of the piezoelectric body with a wavelength λ of the elastic wave is T_LNThe thickness of the IDT electrode normalized by the wavelength λ of the elastic wave is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ rho/rho_AlIn this case, T × r satisfies the following expression (2).

T×r≥0.5902×T_LN ²-0.2133×T_LN+0.0248 type (2)

In this case, the position of the spurious signal can be shifted out of the desired frequency band.

In the elastic wave device according to the present invention, θ of the euler angle is preferably in a range of 116 ° or more and 137 ° or less. In this case, the electromechanical coupling coefficient of the plate wave SO mode can be increased.

in the present invention, it is preferable that a thickness obtained by normalizing a thickness of the piezoelectric body with a wavelength λ of the elastic wave is T_LNThe thickness of the IDT electrode normalized by the wavelength λ of the elastic wave is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ rho/rho_Alin this case, T × rSatisfies the following formula (3).

T×r≥0.6307×T_LN ²-0.0858×T_LN+0.0110 type (3)

in this case, the position of the spurious signal can be shifted out of the desired frequency band.

in the elastic wave device according to the present invention, the support structure of the piezoelectric body is not particularly limited as long as the piezoelectric body is supported SO that the plate wave SO mode is enclosed in the piezoelectric body.

In a specific aspect of the elastic wave device according to the present invention, the support substrate and the piezoelectric body have a hollow between them at a position where the IDT electrode is provided, in a plan view.

In another specific aspect of the elastic wave device according to the present invention, the support substrate is made of a high-sound-velocity material in which a sound velocity of a bulk wave (bulk wave) propagating therethrough is higher than a sound velocity of an elastic wave propagating through the piezoelectric body.

In another specific aspect of the elastic wave device according to the present invention, the elastic wave device further includes: and a layer made of a high acoustic velocity material, which is laminated between the support substrate and the piezoelectric body, and in which the acoustic velocity of a bulk wave propagating through the high acoustic velocity material is higher than the acoustic velocity of an elastic wave propagating through the piezoelectric body.

In another specific aspect of the elastic wave device according to the present invention, the elastic wave device further includes: and a low acoustic velocity material layer which is laminated between the high acoustic velocity material and the piezoelectric body and in which the acoustic velocity of a bulk wave propagating through the piezoelectric body is lower than that of an elastic wave propagating through the piezoelectric body.

In another specific aspect of the elastic wave device according to the present invention, the elastic wave device further includes: and an acoustic reflection layer provided between the support substrate and the piezoelectric body and supporting the piezoelectric body, the acoustic reflection layer having a low acoustic impedance layer having a relatively low acoustic impedance and a high acoustic impedance layer having a relatively high acoustic impedance.

Effects of the invention

According to the present invention, in an elastic wave device using an elastic wave in a plate wave SO mode, loss can be reduced.

drawings

Fig. 1 is a front cross-sectional view of an elastic wave device according to a first embodiment of the present invention.

Fig. 2 is a schematic diagram for explaining a plate wave SO mode propagating in the piezoelectric body.

Fig. 3 is a graph showing the relationship between θ and power flow angle PFA of the euler angle in example 1.

Fig. 4 is a graph showing the relationship between ψ of the euler angle and power flow angle PFA of comparative example 1.

Fig. 5 is a graph showing a relationship between θ of the euler angle and the electromechanical coupling coefficient of the plate wave SO mode and the mode which becomes a stray wave in example 1.

Fig. 6 is a diagram showing resonance characteristics of the elastic wave device of example 2.

Fig. 7 is a diagram showing resonance characteristics of the elastic wave device of example 3.

fig. 8 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 30 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.10 λ.

Fig. 9 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 30 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.20 λ.

fig. 10 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 30 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.30 λ.

FIG. 11 is a graph showing the relationship between the lithium niobate film thickness and the Al film thickness at which the anti-resonance frequency Fa and the frequency SB at the upper end of the stop band coincide.

fig. 12 is a graph showing resonance characteristics of example 4 when the euler angle of lithium niobate is (0 °, 90 °, 90 °) and the Al film thickness is 0.03 λ.

Fig. 13 is a graph showing resonance characteristics of example 5 when the euler angle of lithium niobate is (0 °, 90 °, 90 °) and the Al film thickness is 0.005 λ.

Fig. 14 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 90 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.20 λ.

Fig. 15 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 90 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.30 λ.

Fig. 16 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 90 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.35 λ.

Fig. 17 is a graph showing the relationship between the lithium niobate film thickness and the Al film thickness in which the anti-resonance frequency Fa and the frequency SB at the upper end of the stop band coincide with each other when the euler angle of the lithium niobate is (0 °, 90 °, 90 °).

Fig. 18 is a graph showing resonance characteristics of example 6 in which the euler angle of lithium niobate is (0 °, 125 °, 90 °) and the Al film thickness is 0.04 λ.

Fig. 19 is a graph showing resonance characteristics of example 7 in which the euler angle of lithium niobate is (0 °, 125 °, 90 °) and the Al film thickness is 0.01 λ.

fig. 20 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 125 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.10 λ.

Fig. 21 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 125 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.20 λ.

Fig. 22 is a graph showing the relationship between the Al film thickness and the sound velocity at the resonance frequency Fr, the frequency SB at the upper end of the stop band, and the anti-resonance frequency Fa when the euler angle of lithium niobate is (0 °, 125 °, 90 °) and the thickness of the piezoelectric body made of lithium niobate is 0.30 λ.

Fig. 23 is a graph showing the relationship between the lithium niobate film thickness and the Al film thickness in which the anti-resonance frequency Fa and the frequency SB at the upper end of the stop band coincide with each other when the euler angle of the lithium niobate is (0 °, 125 °, 90 °).

Fig. 24 is a diagram showing resonance characteristics in the case where the number of stacked layers in the acoustic reflection layer is 3.

fig. 25 is a diagram showing resonance characteristics in the case where the number of stacked layers in the acoustic reflection layer is 4.

Fig. 26 is a diagram showing resonance characteristics in the case where the number of stacked layers in the acoustic reflection layer is 7.

fig. 27 is a graph showing the relationship between the number of laminations in the acoustic reflection layer and the impedance ratio.

Fig. 28 is a schematic front cross-sectional view for explaining an elastic wave device according to a second embodiment of the present invention.

Fig. 29 is a front cross-sectional view of an elastic wave device according to a third embodiment of the present invention.

Detailed Description

the present invention will be made clear by the following description of specific embodiments of the present invention with reference to the accompanying drawings.

Note that the embodiments described in the present specification are exemplary, and partial replacement or combination of the structures may be performed between different embodiments.

(first embodiment)

Fig. 1 is a front cross-sectional view of an elastic wave device according to a first embodiment of the present invention. In acoustic wave device 1, piezoelectric body 5 is indirectly laminated on support substrate 2. The piezoelectric body 5 may be directly laminated on the support substrate 2. An IDT electrode 6 and reflectors 7 and 8 are provided on the piezoelectric body 5. IDT electrode 6 and reflectors 7 and 8 are directly laminated on piezoelectric body 5, but may be indirectly laminated on piezoelectric body 5. Reflectors 7 and 8 are provided on both sides of the IDT electrode 6 in the propagation direction of the elastic wave. Thus, a single-port type elastic wave resonator is configured.

λ is a wavelength determined by the electrode finger pitch of the IDT electrode 6. Piezoelectric body 5 is made of lithium niobate, and has a thickness of 1 λ or less. The acoustic wave device 1 utilizes a plate wave SO mode propagating through the thin piezoelectric body 5. In elastic wave device 1 according to the present embodiment, the euler angle of lithium niobate constituting piezoelectric body 5 is (0 °, θ, 90 °).

Here, the plate wave is a general term for various waves excited by a piezoelectric thin plate having a film thickness of 1 λ or less, where λ is the wavelength of the plate wave to be excited. The method used to confine the wave is not critical as long as the wave is concentrated in the piezoelectric sheet. That is, a so-called membrane type (membrane type) support structure having a hollow space below the piezoelectric sheet may be provided. Further, a structure in which a layer reflecting the plate wave is present in the vicinity of the piezoelectric thin plate may be employed, and for example, as shown in patent document 1, a structure in which an acoustic reflection layer is present, or a structure in which the elastic wave is totally reflected by arranging a medium having a higher sound velocity of the bulk wave than that of the plate wave, that is, a high sound velocity material described later.

Fig. 2 is a schematic diagram for explaining a plate wave SO mode propagating in the piezoelectric body 5. In the plate wave SO mode, the main component of displacement in the piezoelectric body 5 is a direction parallel to the propagation direction of the elastic wave as indicated by an arrow, and there is no node in the thickness direction of the piezoelectric body 5.

In addition, in the lithium niobate used in the present application, a plate wave SO mode is excited at an acoustic velocity of 6000 to 7000 m/s. Here, the sound velocity is expressed by the product of the frequency of the excitation elastic wave and the wavelength of the elastic wave. The frequency of the excitation elastic wave is a frequency at which the elastic wave device operates. The frequency at which the elastic wave device operates is, for example, a frequency that becomes a pass Band in the case of a Band-pass Filter (Band-pass Filter), a frequency that becomes a stop Band in the case of a Band-stop Filter (Band-elimination Filter), and a resonance frequency in the case of an elastic wave resonator.

The wavelength of the elastic wave is a length determined by an electrode finger pitch of an IDT electrode formed on the surface of piezoelectric body 5 in the elastic wave device. That is, the center-to-center distance between adjacent electrode fingers connected to different potentials becomes λ/2. Therefore, λ is the center-to-center distance between the electrode fingers closest to the same potential. When the pitch of the electrode fingers in one IDT electrode changes, λ is determined in consideration of the average of the pitches in the IDT electrode.

Further, if the piezoelectric body 5 used in the elastic wave device is lithium niobate and the product of the frequency of the excitation elastic wave obtained as described above and the wavelength of the elastic wave is 6000 to 7000m/s, it is considered that the elastic wave device uses the plate wave SO mode.

The support structure 4 is configured to enclose a plate wave SO mode in the piezoelectric body 5. In the present embodiment, the support structure 4 includes the support substrate 2 and the acoustic reflection layer 3 laminated on the support substrate 2. A piezoelectric body 5 is provided on the acoustic reflection layer 3. The acoustic reflection layer 3 has low acoustic impedance layers 3a, 3c, 3e having relatively low acoustic impedance and high acoustic impedance layers 3b, 3d having relatively high acoustic impedance. The low acoustic impedance layers 3a, 3c, 3e and the high acoustic impedance layers 3b, 3d are alternately laminated in the thickness direction.

In the present embodiment, the low acoustic impedance layers 3a, 3c, 3e are made of SiO₂(silicon oxide). The high acoustic impedance layers 3b and 3d are made of Pt (platinum). However, the materials of the low acoustic impedance layers 3a, 3c, and 3e and the high acoustic impedance layers 3b and 3d are not limited thereto, and any suitable material can be used as long as the relative magnitude relationship of the acoustic impedances is satisfied.

The support substrate 2 is made of Si (silicon). The support substrate 2 can be formed using an appropriate material as long as it can support the acoustic reflection layer 3.

(second embodiment)

An elastic wave device according to a second embodiment will be described with reference to fig. 28. In an elastic wave device 11 according to a second embodiment shown in fig. 28, a cavity 11a is provided in a support substrate 4A. The piezoelectric body 5 is supported by the support substrate 4A such that a cavity 11a is present below the piezoelectric body 5. Therefore, since the cavity 11a is provided below the piezoelectric body 5, the plate wave SO mode excited in the piezoelectric body 5 is confined in the piezoelectric body 5.

(third embodiment)

In an elastic wave device 21 according to a third embodiment shown in fig. 29, the support substrate 4B is formed of a high sound velocity material layer in which the sound velocity of a bulk wave propagating therethrough is higher than the sound velocity of an elastic wave propagating through the piezoelectric body 5. In this way, when the support substrate 4B made of a high acoustic velocity material layer is used, the plate wave SO mode can be confined in the piezoelectric body 5, and the energy can be concentrated in the piezoelectric body 5.

Although the support substrate 4B is made of a high-sound-velocity material in the elastic wave device 21, the low-sound-velocity material layer 22 may be provided between the piezoelectric body 5 and the high-sound-velocity material as shown by a broken line in fig. 29. The low acoustic velocity material layer 22 is a layer made of a low acoustic velocity material in which the acoustic velocity of a bulk wave propagating therethrough is lower than the acoustic velocity of a plate wave SO mode.

Further, a high sound velocity material layer 23 shown by a one-dot chain line in fig. 29 may be further provided between the support substrate 4B and the low sound velocity material layer 22. In this case, the support substrate 4B may be made of a material other than the high-sound-velocity material.

The high sound velocity material and the low sound velocity material are not particularly limited as long as the sound velocity relationship is satisfied. For example, can be made of SiO₂And SiON, etc. form a low acoustic velocity material layer. Further, as for the high sound velocity material layer, Al can be used₂O₃And a dielectric, metal, semiconductor, or the like such as SiN, AlN, SiC, diamond-like carbon, diamond, or the like.

Further, the plurality of low sound velocity material layers and the plurality of high sound velocity material layers may be alternately stacked. That is, the number of stacked low-sound-velocity material layers and high-sound-velocity material layers is not particularly limited.

(example 1 and comparative example 1)

As follows, elastic wave devices of example 1 and comparative example 1, which are examples of the first embodiment, were produced, and the energy flow angle was determined.

Here, the phase velocity V of the elastic wave at a certain propagation angle psi is used_ψAnd phase velocities V of elastic waves at angles phi-delta and phi + delta that are offset from phi by a slight angle delta (rad)_ψ-δ、V_ψ+δAn arbitrary Euler angle is obtained by the following equationEnergy flow Angle of PFA.

PFA＝tan^-1((V_ψ+δ-V_ψ-δ)/(2×V_ψ×δ))

In example 1, the IDT electrode was made of Al, and the Al film thickness was set to 0.05 λ. The duty ratio of the IDT electrode was set to 0.50. The thickness of the piezoelectric body 5 is set to 0.2 λ. The thickness of the low acoustic impedance layers 3a, 3c, 3e is set to 0.14 λ, and the thickness of the high acoustic impedance layers 3b, 3d is set to 0.09 λ. In example 1, various elastic wave devices were produced with θ of euler angles (0 °, θ, 90 °) set to 0 °, 30 °, 60 °, 90 °, 120 °, 150 °, or 180 °. Fig. 3 shows a relationship between θ, which is an euler angle, and PFA, which is a power flow angle, in the elastic wave device. As shown in fig. 3, at euler angles (0 °, θ, 90 °), the power flow angles are all 0 ° regardless of the value of θ.

As comparative example 1, a plurality of elastic wave devices were produced in the same manner as in example 1, except that the euler angle of lithium niobate was changed to (90 °, 90 °, ψ) in a range of 25 ° to 44 °. Fig. 4 shows the relationship between ψ of euler angle and power flow angle PFA in comparative example 1. As is clear from fig. 4, in comparative example 1, the energy flow angle PFA is 0 ° in the vicinity of ψ 37 °. However, in the other region, the absolute value of the power flow angle PFA becomes large. Therefore, in the acoustic wave device of comparative example 1, when ψ is not 37 °, the power flow angle PFA does not become 0 °. Therefore, the direction of energy propagation of the elastic wave deviates from the direction perpendicular to the electrode fingers of the IDT electrode, and thus the loss increases. On the other hand, in example 1, as described above, it is understood that the energy flow angle PFA is 0 ° in all cases where θ is any value at the euler angles (0 °, θ, 90 °). Therefore, it is found that the direction of energy propagation of the elastic wave coincides with the direction perpendicular to the electrode fingers of the IDT electrode, and therefore, the loss can be reduced.

Fig. 5 is a diagram showing a relationship between θ of the euler angle, the electromechanical coupling coefficient of the plate wave SO mode, and the electromechanical coupling coefficient of a mode that is generated in the vicinity and becomes a stray in the elastic wave device of example 1 that can reduce the loss.

In addition, an electromechanical coupling coefficient K²The following formula (A) was used. In formula (a), Fr shows the resonance frequency and Fa shows the antiresonance frequency.

K²(pi/2) (Fr/Fa) { Cot (pi/2. (Fr/Fa) } formula (A)

The range of the euler angle θ is preferably such that the electromechanical coupling coefficient of the plate wave SO mode is large and the electromechanical coupling coefficient of the mode that becomes a stray is small. As such a range of θ, the following range can be cited from fig. 5. That is, θ of the euler angle is preferably in the range of 7 ° or more and 66 ° or less, or 116 ° or more and 137 ° or less. In this case, the electromechanical coupling coefficient K of the plate wave SO mode can be set²Is more than 7.5 percent. When the resonance frequency Fr and the antiresonance frequency Fa are obtained by using the formula (a), the relative bandwidth of the resonator is obtained by the following steps: (Fa-Fr)/Fr (%), then 7.5% of K²Corresponding to a relative bandwidth of the resonator of 3.2%. Since the relative bandwidth of a filter that can be manufactured using a certain resonator substantially matches the relative bandwidth of the resonator, if K is used²A resonator of 7.5% makes it possible to produce a filter in a frequency Band wider than LTE-Band2 having a relative bandwidth of 3.1%. More preferably, θ of the euler angle is in the range of 11 ° or more and 59 ° or less. In this case, the electromechanical coupling coefficient K can be set²Is more than 10 percent. 10% of K²Corresponding to a relative bandwidth of the resonator of 4.4%. Therefore, using this resonator makes it possible to produce a filter in a wider Band than LTE-Band3 having a relative bandwidth of 4.2%. Further preferably, θ of the euler angle is in a range of 21 ° or more and 44 ° or less. In this case, the electromechanical coupling coefficient K of the plate wave SO mode can be set²Is more than 15 percent. 15% of K²Corresponding to a relative bandwidth of the resonator of 6.9%. Therefore, using this resonator makes it possible to produce a filter in a wider Band than LTE-Band28 having a relative bandwidth of 6.2%.

On the other hand, in order to reduce the electromechanical coupling coefficient of the mode which becomes the spurious, θ of the euler angle is preferably in a range of 67 ° or more and 104 ° or less. In this case, a spurious mode can be setElectromechanical coupling coefficient K²is 1.0% or less, and the size of the stray can be sufficiently reduced. More preferably, θ of the euler angle is in a range of 73 ° or more and 96 ° or less. In this case, the electromechanical coupling coefficient K of the spurious mode can be set²The amount is 0.5% or less, and the size of the stray can be further reduced.

(examples 2 and 3)

An elastic wave device of example 2, which is an example of the first embodiment, was obtained in the same manner as in example 1, except that the euler angle of lithium niobate in the elastic wave device of example 1 was set to (0 °, 30 °, 90 °), and the film thickness of Al (aluminum) constituting the IDT electrode 6 was set to 0.06 λ.

An acoustic wave device similar to that of example 2 was obtained as example 3, except that the Al film thickness was set to 0.02 λ.

Fig. 6 is a diagram showing resonance characteristics of an elastic wave device according to example 2, and fig. 7 is a diagram showing resonance characteristics of an elastic wave device according to example 3.

In each of the elastic wave devices of example 2 and example 3, the euler angles of lithium niobate were (0 °, 30 °, 90 °). Therefore, in the elastic wave devices according to examples 2 and3, the electromechanical coupling coefficient of the plate wave SO mode is large, as in the elastic wave device according to example 1. Therefore, even when the elastic wave devices of examples 2 and3 were used, a wide band-pass filter could be produced.

However, as is clear from fig. 7, in embodiment 3, a spurious occurs between the resonance frequency and the antiresonance frequency. On the other hand, as shown in fig. 6, in example 2, the stray is shifted to a frequency side higher than the anti-resonance frequency. That is, no spurious occurs in a frequency band that is a frequency band between the resonance frequency and the antiresonance frequency. Therefore, according to example 2, more favorable resonance characteristics can be obtained than in example 3.

As a result of diligent study on the stray, the inventors of the present application have found that the stray is generated due to the frequency mismatch between the open (open) and short (short) stopband upper ends of the IDT electrodes when the symmetry of the piezoelectric body 5 is broken. Therefore, the stray can be shifted to a frequency higher than the anti-resonance frequency by increasing the reflection coefficient per electrode finger and increasing the width of the stop band. As a result of studies on this point, the inventors of the present application have found that the reflection coefficient per electrode finger can be increased and the stray light can be shifted to the high frequency side by increasing the film thickness of the IDT electrode 6 and reducing the film thickness of the lithium niobate constituting the piezoelectric body 5.

Fig. 8 to 10 show changes in the resonance frequency Fr, the frequency SB at the upper end of the stopband, the anti-resonance frequency Fa, and the sound velocity when the Al film thickness and the thickness of the piezoelectric body made of lithium niobate are changed in the structure of example 2 using lithium niobate having an euler angle of (0 °, 30 °, 90 °). Fig. 8 shows the results when lithium niobate having an euler angle of (0 °, 30 °, 90 °) was used and the thickness of the piezoelectric body made of lithium niobate was 0.10 λ. Fig. 9 shows the results when lithium niobate having euler angles (0 °, 30 °, 90 °) was used and the thickness of the piezoelectric body made of lithium niobate was 0.20 λ. Fig. 10 shows the results when lithium niobate having euler angles (0 °, 30 °, 90 °) was used and the thickness of the piezoelectric body made of lithium niobate was 0.30 λ.

Referring to fig. 8, the Al film having the anti-resonance frequency Fa and the frequency SB at the upper end of the stop band is 0.020 λ. In fig. 9, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.037 λ. In fig. 10, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.0555 λ.

Fig. 11 is a graph showing the relationship between the lithium niobate film thickness and the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band, as shown in fig. 8 to 10.

As is clear from fig. 11, when the Al film thickness is y (λ) and the lithium niobate film thickness is x (λ), if y is 0.1821x²On the curve represented by +0.1055x +0.0082, the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band. Therefore, if T is used_AlDenotes y and is represented by T_LNWhen x is represented, the curve can be represented by the following formula (4).

T_Al＝0.1821×T_LN ²+0.1055×T_LN+0.0082 type (4)

therefore, as described above, by increasing the thickness of the IDT electrode 6 and reducing the thickness of the lithium niobate film constituting the piezoelectric body 5, the reflection coefficient per electrode finger can be increased to shift the stray light to the high frequency side, and therefore, the Al film thickness is made thicker than T represented by the above expression (4)_AlThick, the effect of strays can be reduced.

The reflectance of each electrode finger is approximately proportional to the mass loading caused by the electrode. Therefore, when the IDT electrode is formed using a metal having a higher density than Al, the thickness of the electrode film for obtaining the same reflection coefficient becomes thinner than that when the IDT electrode is formed using Al. The thickness of the IDT electrode normalized by the wavelength λ is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ ρ/ρ_AlIn this case, the following formula (5) may be satisfied.

T×r≥0.1821×T_LN ²+0.1055×T_LN+0.0082 type (5)

Therefore, in the present invention, the above formula (5) is preferably satisfied. This can further reduce the influence of the stray.

(examples 4 and 5)

In example 4, an elastic wave device was produced in the same manner as in example 1, except that parameters of the elastic wave device were changed as follows.

Piezoelectric body 5: lithium niobate with Euler angle of (0 degree, 90 degree)

The thickness of Al film constituting the IDT electrode 6 was 0.03 λ

Duty ratio of 0.50

The thickness of the piezoelectric body 5 is 0.2 λ

As for the acoustic reflection layer, SiO with a thickness of 0.14 λ was used as the low acoustic impedance layers 3a, 3c, and 3e in the same manner as in example 1₂And (3) a membrane. As the high acoustic impedance layers 3b and 3d, a Pt film having a thickness of 0.09 λ was used. The support substrate 2 is Si.

For comparison, an acoustic wave device of example 5 was obtained in the same manner as in example 4, except that the Al film thickness was 0.005 λ.

Fig. 12 is a diagram showing resonance characteristics of the elastic wave device of example 4. Fig. 13 is a graph showing resonance characteristics of example 5.

As is clear from fig. 13, in embodiment 5, a spurious occurs between the resonance frequency and the antiresonance frequency. In contrast, in example 4, as shown in fig. 12, the stray is located on the higher frequency side than the anti-resonance frequency.

In example 4, various elastic wave devices were also fabricated by fixing the euler angle of lithium niobate at (0 °, 90 °, 90 °), and changing the Al film thickness and the thickness of the piezoelectric body made of lithium niobate. The sound velocity at the resonance frequency Fr, the anti-resonance frequency Fa, and the frequency SB at the upper end of the stop band in these elastic wave devices was determined. Fig. 14 shows the results when the thickness of the piezoelectric body made of lithium niobate was 0.20 λ. Fig. 15 shows the results when the thickness of the piezoelectric body made of lithium niobate was 0.30 λ. Fig. 16 shows the results when the thickness of the piezoelectric body made of lithium niobate was 0.35 λ. In FIG. 14, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.0065 λ. In fig. 15, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.0125 λ. In fig. 16, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.023 λ. These results were plotted instead of the curves shown in fig. 17. Fig. 17 shows the relationship between the lithium niobate film thickness and the Al film thickness in example 4, that is, in the case where lithium niobate having an euler angle of (0 °, 90 °, 90 °) is used, and the anti-resonance frequency Fa agrees with the frequency SB at the upper end of the stopband. When the lithium niobate film thickness is x (λ) and the Al film thickness is y (λ), the available y of the curve shown in fig. 17 is 0.5902x²-0.2133x + 0.0248.

Therefore, the Al film thickness is set to T_Aland the film thickness of lithium niobate is set as T_LNIn the case of (3), the above curve may be represented by T_Al＝0.5902×T_LN ²-0.2133×T_LN+ 0.0248.

Therefore, as described above, the IDT electrode 6 can be configured by increasing the film thicknessSince the reflection coefficient per electrode finger can be increased and the stray can be shifted to the high frequency side by making the lithium niobate film thickness of piezoelectric body 5 thin, the Al film thickness is made thicker than T expressed by equation (6)_AlThick, the effect of strays can be reduced.

The reflectance of each electrode finger is approximately proportional to the mass loading caused by the electrode. Therefore, when the IDT electrode is formed using a metal having a higher density than Al, the thickness of the electrode film for obtaining the same reflection coefficient becomes thinner than that when the IDT electrode is formed using Al. The thickness of the IDT electrode normalized by the wavelength λ is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_AlThe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ ρ/ρ_AlIn this case, the following formula (6) may be satisfied.

T×r≥0.5902×T_LN ²-0.2133×T_LN+0.0248 type (6)

This can further reduce the influence of the stray.

(examples 6 and 7)

In example 6, an elastic wave device was produced in the same manner as in example 1, except that parameters of the elastic wave device were changed as follows.

Piezoelectric body 5: lithium niobate with Euler angle of (0 degree, 125 degree, 90 degree)

The thickness of Al film constituting the IDT electrode 6 was 0.04 λ

Duty ratio of 0.50

The thickness of the piezoelectric body 5 is 0.2 λ

As for the acoustic reflection layer, SiO with a thickness of 0.14 λ was used as the low acoustic impedance layers 3a, 3c, and 3e in the same manner as in example 1₂And (3) a membrane. As the high acoustic impedance layers 3b and 3d, a Pt film having a thickness of 0.09 λ was used. The support substrate 2 is Si.

An acoustic wave device of example 7 was obtained in the same manner as in example 6, except that the Al film thickness was 0.01 λ.

Fig. 18 is a diagram showing resonance characteristics of the elastic wave device of example 6. Fig. 19 is a graph showing resonance characteristics of example 7.

As is clear from fig. 19, in example 7, a spurious occurred between the resonance frequency and the antiresonance frequency. In contrast, in example 6, as shown in fig. 18, the stray is located on the higher frequency side than the anti-resonance frequency.

In example 6, various elastic wave devices were also fabricated by fixing the euler angle of lithium niobate at (0 °, 125 °, 90 °), and changing the Al film thickness and the thickness of the piezoelectric body made of lithium niobate. The sound velocity at the resonance frequency Fr, the anti-resonance frequency Fa, and the frequency SB at the upper end of the stop band in these elastic wave devices was determined. Fig. 20 shows the results when the thickness of the piezoelectric body made of lithium niobate was 0.10 λ. Fig. 21 shows the result when the thickness of the piezoelectric body made of lithium niobate was 0.20 λ. Fig. 22 shows the results when the thickness of the piezoelectric body made of lithium niobate was 0.30 λ. In fig. 20, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.0080 λ. In fig. 21, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.0198 λ. In FIG. 22, the Al film thickness at which the anti-resonance frequency Fa coincides with the frequency SB at the upper end of the stop band is 0.041 λ. These results were plotted instead of the curves shown in fig. 23. Fig. 23 shows the relationship between the lithium niobate film thickness and the Al film thickness in example 6, that is, in the case where lithium niobate having an euler angle of (0 °, 125 °, 90 °) is used, and the anti-resonance frequency Fa agrees with the frequency SB at the upper end of the stopband. When the lithium niobate film thickness is x (λ) and the Al film thickness is y (λ), the available y of the curve shown in fig. 23 is 0.6307x²-0.0858x + 0.0110.

Therefore, the Al film thickness is set to T_AlAnd the film thickness of lithium niobate is set as T_LNIn the case of (3), the above curve may be represented by T_Al＝0.6307×T_LN ²-0.0858×T_LN+ 0.0110.

Therefore, as described above, by increasing the thickness of the IDT electrode 6 and reducing the thickness of the lithium niobate film constituting the piezoelectric body 5, the reflection coefficient per electrode finger can be increased to shift the stray light to the high frequency side, and therefore, the Al film thickness is made thicker than T represented by formula (7)_AlIs thick, can be reducedThe effect of small spurs.

The reflectance of each electrode finger is approximately proportional to the mass loading caused by the electrode. Therefore, when the IDT electrode is formed using a metal having a higher density than Al, the thickness of the electrode film for obtaining the same reflection coefficient becomes thinner than that when the IDT electrode is formed using Al. The thickness of the IDT electrode normalized by the wavelength λ is represented by T, the density of the metal constituting the IDT electrode is represented by ρ, and the density of Al is represented by ρ_Althe density ratio of the metal constituting the IDT electrode to Al is defined as r ═ ρ/ρ_Alin this case, the following formula (7) may be satisfied.

T×r≥0.6307×T_LN ²-0.0858×T_LN+0.0110 type (7)

This can reduce the influence of the stray.

(example 8)

In elastic wave device 1 according to the first embodiment, an elastic wave device according to example 8 was produced as follows, with the design parameters set forth below. Here, the number of layers of the acoustic reflection layer 3 is changed.

Piezoelectric body 5: lithium niobate with Euler angle of (0 degree, 30 degree, 90 degree)

The thickness of the IDT electrode 6 made of Al is 0.06 λ

Duty ratio of 0.50

The thickness of the piezoelectric body 5 is 0.2 λ

Supporting substrate ═ Si

In the acoustic reflection layer, SiO is alternately laminated₂A low acoustic resistance layer having a thickness of 0.14 λ and a high acoustic resistance layer made of Pt having a thickness of 0.09 λ. The number of layers is 3, 4, or 7. In the 3-layer laminated structure, a low acoustic impedance layer, a high acoustic impedance layer, and a low acoustic impedance layer are laminated in this order from the piezoelectric body 5 side. In the 4-layer structure, the low acoustic impedance layer, the high acoustic impedance layer, the low acoustic impedance layer, and the high acoustic impedance layer are laminated in this order from the piezoelectric body 5 side. Of the 7 layers, the low acoustic impedance layer, the high acoustic impedance layer, and the low acoustic impedance layer were layered in this order from the piezoelectric body 5 sideAnd (5) stacking.

Fig. 24 is a diagram showing resonance characteristics of an elastic wave device in which the number of stacked layers in the acoustic reflection layer is 3. Fig. 25 is a diagram showing resonance characteristics of an elastic wave device in which the number of stacked layers in the acoustic reflection layer is 4. Fig. 26 is a diagram showing resonance characteristics of an elastic wave device in which the acoustic reflection layer is 7 layers.

As is clear from comparison of fig. 24 to 26, in the case where the acoustic reflection layer is 3 layers, the impedance curves at the resonance frequency and the antiresonance frequency are blunt. On the other hand, when the acoustic reflection layer is 4 layers or more, the peaks of the impedance at the resonance frequency and the antiresonance frequency become sharp.

Fig. 27 is a graph showing the relationship between the number of laminations in the acoustic reflection layer and the impedance ratio. It is known that the impedance ratio, that is, the ratio of the impedance at the antiresonant frequency to the impedance at the resonant frequency becomes large in the case of 4 layers or more. Therefore, the number of layers of the acoustic reflection layer is preferably 4 or more. Accordingly, the elastic wave of the plate wave SO mode is sufficiently reflected by the acoustic reflection layer, and the plate wave SO mode is considered to be effectively confined in the piezoelectric body 5.

Although the case of a single-port acoustic wave resonator has been described in embodiments 1 to 8, the present invention is not limited to a single-port acoustic wave resonator, and can be applied to other acoustic wave devices such as a longitudinally coupled resonator.

Further, LiNbO in the present invention₃euler angle ofAs long as it is crystallographically equivalent. For example, LiNbO is known from the literature (journal of the Japanese society for acoustics, 36, 3, 1980, pages 140 to 145)₃is a crystal belonging to a trigonal 3m point group, and therefore the following formula holds.

F(φ，θ，φ)＝F(60°+φ，-θ，φ)

＝F(60°-φ，-θ，180°-φ)

＝F(φ，180°+θ，180°-φ)

＝F(φ，θ，180°+φ)

Here, F is any elastic wave characteristic such as electromechanical coupling coefficient, propagation loss, TCF, PFA, or the like.

Description of the reference numerals

1: an elastic wave device;

2: a support substrate;

3: an acoustic reflective layer;

3a, 3c, 3 e: a low acoustic impedance layer;

3b, 3 d: a high acoustic impedance layer;

4: a support structure;

4A, 4B: a support substrate;

5: a piezoelectric body;

6: an IDT electrode;

7. 8: a reflector;

11. 21: an elastic wave device;

11 a: a void;

22: a layer of low acoustic velocity material;

23: a layer of high acoustic velocity material.