JPWO2010131606A1 - Boundary acoustic wave device - Google Patents

Abstract

In the boundary acoustic wave device, characteristics such as filter characteristics and resonator characteristics are improved. The boundary acoustic wave device 1 includes a first medium 21 made of a piezoelectric material, a second medium 22, a third medium 23, an IDT electrode 20, and a wiring electrode 24. The second medium 22 is formed on the first medium 21. The third medium 23 is formed on the second medium 22. The IDT electrode 20 is formed at the boundary between the first medium 21 and the second medium 22. The second medium 22 has a lower sound speed than the first and third media 21 and 23. The sound speed of the third medium 23 is higher than the sound speed of the first medium 21. The wiring electrode 24 is formed on the third medium 23 so as to at least partially overlap the IDT electrode 20 in plan view. The thickness of the third medium 23 is 0.7 times or more the wavelength of the boundary acoustic wave excited in the IDT electrode 20.

Description

  The present invention relates to a boundary acoustic wave device using a boundary acoustic wave, and more particularly to a three-medium type boundary acoustic wave device having first and second dielectric layers formed on a piezoelectric substrate.

  Conventionally, elastic wave devices have been used for RF filters and IF filters for mobile phones, VCO resonators, television VIF filters, and the like. As a surface acoustic wave device, a surface acoustic wave device using a surface acoustic wave has been generally used. However, in recent years, since it can be made smaller than a surface acoustic wave device, for example, the following patent document The boundary acoustic wave device as described in No. 1 has been used.

  FIG. 15 is a schematic cross-sectional view of the boundary acoustic wave device described in Patent Document 1. As shown in FIG. 15, the boundary acoustic wave device 100 includes a first medium layer 101. A second medium layer 102 is formed on the first medium layer 101. Further, a third medium layer 103 is formed on the second medium layer 102. Furthermore, a sound absorbing layer 104 is formed on the third medium layer 103. An IDT electrode 105 is formed at the boundary between the first medium layer 101 and the second medium layer 102. In addition, wiring electrodes 106 and 107 are formed on the boundary between the second medium layer 102 and the third medium layer 103 and on the boundary between the third medium layer 103 and the sound absorbing layer 104.

  The wiring electrodes 106 and 107 are drawn to the outer surface of the boundary acoustic wave device 100. The wiring electrodes 106 and 107 are formed so as to overlap the IDT electrode 105 in plan view. For this reason, a boundary acoustic wave apparatus can be reduced in size.

  In Patent Document 1, since the sound absorbing layer 104 is provided, the mode that becomes spurious is attenuated by the sound absorbing layer 104, and as a result, a plurality of spurious frequencies on the higher frequency side than the resonance frequency and on the higher frequency side of the pass band. It is described that the response can be effectively suppressed.

WO2005 / 066946 A1

  However, in the boundary acoustic wave device 100 described in Patent Document 1, the sound absorbing layer 104 is provided on the wiring electrodes 106 and 107. The higher-order mode that becomes a spurious is reflected by the wiring electrodes 106 and 107 provided between the sound absorbing layer 104 and the second medium 102 or the third medium 103, and cannot move to the sound absorbing layer 104. For this reason, the sound absorption layer 104 cannot act as a sound absorption medium.

  Accordingly, the energy of the higher order mode returns to the second and third medium layers 102 and 103 again, and becomes an unnecessary spurious.

  Therefore, the boundary acoustic wave device 100 formed so that the wiring electrodes 106 and 107 overlap with the IDT electrode 105 in a plan view has a problem that sufficiently good characteristics such as filter characteristics and resonator characteristics cannot be obtained. It was.

  The present invention has been made in view of such points, and an object thereof is to improve characteristics such as filter characteristics and resonator characteristics in the boundary acoustic wave device.

  The boundary acoustic wave device according to the present invention includes a first medium, a second medium, a third medium, an IDT electrode, and a wiring electrode. The first medium is made of a piezoelectric body. The second medium is formed on the first medium. The third medium is formed on the second medium. The IDT electrode is formed at the boundary between the first medium and the second medium. The second medium has a lower sound velocity than the first and third media. The sound speed of the third medium is higher than the sound speed of the first medium. The wiring electrode is formed on the third medium so as to at least partially overlap the IDT electrode in plan view. The thickness of the third medium is 0.7 times or more the wavelength of the boundary acoustic wave excited in the IDT electrode.

In a specific aspect of the boundary acoustic wave device according to the present invention, the first medium is made of LiNbO ₃ , the second medium is made of silicon oxide, and the third medium is made of silicon nitride.

  In another specific aspect of the boundary acoustic wave device according to the present invention, the wiring electrode includes an external terminal electrode.

  In the present invention, the sound speed of the second medium is lower than the sound speed of the first and third media, and the thickness of the third medium is 0.7 times or more the wavelength of the boundary acoustic wave excited in the IDT electrode. Has been. For this reason, the higher order mode of the boundary acoustic wave generated in the IDT electrode can be confined in the second and third media so as not to exist on the surface of the third medium. For this reason, even when the wiring electrode is formed on the third medium so as to overlap the IDT electrode in plan view, the higher-order mode is not reflected by the wiring electrode. Therefore, it is possible to reduce the size of the boundary acoustic wave device while preventing the characteristic deterioration due to the higher order mode.

FIG. 1 is an equivalent circuit diagram of the boundary acoustic wave device. FIG. 2 is a schematic cross-sectional view of a part of the boundary acoustic wave device. FIG. 3A is a schematic plan view of a first boundary acoustic wave device manufactured in an experimental example. FIG. 3B is a schematic cross-sectional view of a part of the first boundary acoustic wave device manufactured in the experimental example. FIG. 4 is a schematic plan view of the second boundary acoustic wave device manufactured in the experimental example. FIG. 5 is a schematic plan view of a third boundary acoustic wave device manufactured in the experimental example. FIG. 6 is a graph showing filter characteristics of the first to third boundary acoustic wave devices. FIG. 7 is a graph showing the displacement distribution of the SH type boundary acoustic wave in the fourth boundary acoustic wave device. FIG. 8 is a graph showing the displacement distribution of the first higher-order mode in the fourth boundary acoustic wave device. FIG. 9 is a graph showing the displacement distribution of the second higher-order mode in the fourth boundary acoustic wave device. FIG. 10 is a graph showing the displacement distribution of the SH type boundary acoustic wave in the fifth boundary acoustic wave device. FIG. 11 is a graph showing the displacement distribution of the first higher-order mode in the fifth boundary acoustic wave device. FIG. 12 is a graph showing the displacement distribution of the second higher-order mode in the fifth boundary acoustic wave device. FIG. 13A is a schematic plan view of a boundary acoustic wave device in which an IDT electrode and a wiring electrode do not overlap in a plan view. FIG. 13B is a schematic plan view of the boundary acoustic wave device in which the IDT electrode and a part of the wiring electrode overlap in plan view. FIG. 14 is a schematic cross-sectional view of a boundary acoustic wave device according to a modification. FIG. 15 is a schematic cross-sectional view of the boundary acoustic wave device described in Patent Document 1. FIGS. 16A and 16B show a boundary acoustic wave device having a SiO ₂ / Au / LiNbO ₃ structure described in Patent Document 1, with a Au thickness of 0.05λ and a SiO ₂ film thickness of 1. It is a figure which shows the displacement distribution of each spurious mode when set to 0.5λ.

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

  FIG. 1 is an equivalent circuit diagram of the boundary acoustic wave device. FIG. 2 is a schematic cross-sectional view of a portion where the IDT electrode of the boundary acoustic wave device according to this embodiment is formed. In the present embodiment, the boundary acoustic wave device embodying the present invention will be described by taking the boundary acoustic wave device 1 as a boundary acoustic wave filter shown in FIG. 1 as an example. However, in the present invention, the boundary acoustic wave device is not limited to the boundary acoustic wave filter. The boundary acoustic wave device of the present invention may be, for example, a boundary acoustic wave resonator or a ladder type filter composed of a plurality of boundary acoustic wave resonators.

  In FIG. 1 and FIGS. 3 to 5 and 13 below, IDT electrodes and resonators are schematically shown.

  As shown in FIG. 1, the boundary acoustic wave device 1 includes an unbalanced input terminal 10 and first and second balanced output terminals 11a and 11b. A boundary acoustic wave filter unit 12 using a boundary acoustic wave is connected between the unbalanced input terminal 10 and the first and second balanced output terminals 11a and 11b. The boundary acoustic wave filter unit 12 is a 5IDT type longitudinally coupled resonator type boundary acoustic wave filter unit.

  Specifically, the boundary acoustic wave filter unit 12 includes first to fifth IDT electrodes 13a to 13e and first to fifth IDT electrodes 13a to 13e arranged along the propagation direction of the boundary acoustic wave. And reflectors (not shown) disposed on both sides of the formed region in the elastic wave propagation direction. One side of each of the first, third, and fifth IDT electrodes 13 a, 13 c, and 13 e is connected to the unbalanced input terminal 10. On the other hand, the other side of each of the first, third and fifth IDT electrodes 13a, 13c and 13e is connected to a ground electrode. One side of each of the second and fourth IDT electrodes 13b and 13d is connected to a ground electrode. The other side of the fourth IDT electrode 13d is connected to the first balanced output terminal 11a. The other side of the second IDT electrode 13b is connected to the second balanced output terminal 11b.

  A boundary acoustic wave resonator 14 as a series trap is connected between one side of each of the first, third, and fifth IDT electrodes 13 a, 13 c, and 13 e and the unbalanced input terminal 10. The boundary acoustic wave resonator 14 includes an IDT electrode and reflectors disposed on both sides of the IDT electrode in the elastic wave propagation direction.

  As shown in FIG. 1, a parallel capacitor 15 is connected between the connection point on one side of each of the first, third, and fifth IDT electrodes 13a, 13c, and 13e and the ground potential. Yes. The parallel capacitor 15 is composed of a pair of comb electrodes that are inserted into each other.

  There is a parallel trap between the connection point between the second IDT electrode 13b and the second balanced output terminal 11b and the connection point between the fourth IDT electrode 13d and the first balanced output terminal 11a. The boundary acoustic wave resonator 16 is connected. The boundary acoustic wave resonator 16 includes an IDT electrode and reflectors disposed on both sides of the IDT electrode in the elastic wave propagation direction.

  Next, a specific configuration of the boundary acoustic wave device 1 will be described in detail with reference to FIG. 2 is a cross-sectional view of a portion where one of the IDT electrodes such as the first to fifth IDT electrodes 13a to 13e included in the boundary acoustic wave device 1 is formed. In FIG. The IDT electrode is referred to by reference numeral “20”.

As shown in FIG. 2, the boundary acoustic wave device 1 is a so-called three-medium type boundary acoustic wave device. The boundary acoustic wave device 1 includes a first medium 21. The first medium 21 is a piezoelectric substrate made of a piezoelectric body. The piezoelectric body used for forming the first medium 21 is not particularly limited, and can be appropriately selected according to the characteristics required for the boundary acoustic wave device 1. Specific examples of the piezoelectric body include, for example, LiNbO ₃ and LiTaO ₃ .

  On the first medium 21, the IDT electrode 20 described above is formed.

  A second medium 22 is formed on the first medium 21 so as to cover the IDT electrode 20. That is, the IDT electrode 20 is formed at the boundary between the first medium 21 and the second medium 22.

  A third medium 23 is formed on the second medium 22. The sound speed of the second medium 22 is lower than the sound speed of the first and third media 21 and 23. The speed of sound of the third medium 23 is higher than the speed of sound of the first medium 21.

The material of the second and third media 22 and 23 is not particularly limited as long as the sound velocity of the second medium 22 is slower than the sound velocity of the first and third media 21 and 23. For example, the second and third media 22 and 23 can be formed of a dielectric. Specifically, for example, the second medium 22 is formed of silicon oxide such as SiO _2, the third medium 23 can be formed of silicon nitride, such as SiN.

  The thickness of the second medium 22 is not particularly limited, and can be appropriately set according to characteristics required for the boundary acoustic wave device 1. On the other hand, the thickness of the third medium 23 is 0.7 times or more the wavelength (λ) of the boundary acoustic wave excited in the IDT electrode 20.

  In the present embodiment, the protective film 25 is formed on the third medium 23. This protective film 25 is a protective film for protecting a wiring electrode 24 described later. The protective film 25 can be formed of polyimide, for example.

  In addition, the boundary acoustic wave device 1 includes a wiring electrode 24 connected to the IDT electrode 20. The wiring electrode 24 is formed at the boundary between the first medium 21 and the second medium 22 and the boundary between the third medium 23 and the protective film 25, and the second medium 22 and the third medium. It is not formed at the boundary. That is, the wiring electrode 24 is formed only on the third medium 23 except for the boundary between the first medium 21 and the second medium 22 where the IDT electrode 20 is formed. At least a part of the wiring electrode 24 overlaps the IDT electrode 20 in plan view.

  As shown in FIG. 2, the wiring electrode 24 includes a bump electrode 26 as an external terminal electrode exposed from the protective film 25.

  In the present embodiment, as described above, the second and third media 22 and 23 are formed on the first medium 21, and the thickness of the third medium 23 is excited in the IDT electrode 20. It is set to 0.7 times or more of the wavelength (λ) of the boundary acoustic wave. For this reason, the higher order mode of the boundary acoustic wave generated in the IDT electrode 20 can be confined in the second and third media 22 and 23 so as not to exist on the surface of the third media. That is, in this embodiment, not only the fundamental mode but also the higher order mode does not reach the surface of the third medium 23. Therefore, characteristics such as filter characteristics and resonator characteristics are not deteriorated due to the change in the shape of the higher-order mode by the wiring electrode 24 formed on the third medium 23.

  Hereinafter, this effect will be described in more detail based on specific examples.

  First, the wiring electrode 24 is provided on the second medium 22 without providing the third medium 23, and the wiring electrode 24 and the IDT electrode on the second medium 22 do not overlap in plan view. The boundary acoustic wave device (for GSM900 reception filter, passband: 925 MHz to 960 MHz) similar to the boundary acoustic wave device 1 shown in FIG. 1 and FIG. It was produced with the design parameters.

  FIG. 3A is a schematic plan view of the first boundary acoustic wave device. FIG. 3B is a schematic cross-sectional view of a part of the first boundary acoustic wave device.

  In FIG. 3A and the following FIGS. 4, 5, and 13, members having substantially the same function as those of the above-described embodiment are referred to by common reference numerals. 3 to 5 and 13, reference numeral 17 denotes a ground electrode.

First medium 21: LiNbO _{3 with a} cut angle of 15 °
IDT electrode 20: Ti film (thickness 10 nm (0.0029λ)) / Pt film (thickness 10 nm (0.0029λ)) / Au film (thickness 130 nm (0.037λ)) / Pt from the first medium side Film (thickness 10 nm (0.0029λ)) / Ti film (thickness 10 nm (0.0029λ)) / NiCr film (thickness 10 nm (0.0029λ))
Wavelength (λ) determined by the pitch of the electrode fingers of the IDT electrode 20: about 3.5 μm
Duty of IDT electrode 20: 0.60
Second medium 22: SiO ₂ (thickness 5500 nm (1.57λ))
Wiring electrode 24: Ti film (thickness 20 nm (0.0057λ)) / AlCu film (thickness 1000 nm (0.29λ)) / Ti film (thickness 50 nm (0.014λ)) / from the second medium 22 side / Pt film (thickness 20 nm (0.0057λ))
Protective film 25: polyimide film (thickness 7000 nm, 2.0λ)

  4 except that the dummy electrodes 30 are formed on all the IDT electrodes 20 in the boundary acoustic wave filter 13 and the boundary acoustic wave resonators 14 and 16 as in the first boundary acoustic wave device. A second boundary acoustic wave device shown in FIG.

  Further, the third boundary acoustic wave device shown in FIG. 5 was produced in the same manner as the first boundary acoustic wave device except that the dummy electrode 30 was formed only on the IDT electrode of the boundary acoustic wave filter portion. .

  The filter characteristics of the first to third boundary acoustic wave devices were measured. The measurement results are shown in FIG. In FIG. 6, the data indicated by “A” represents the filter characteristics of the first boundary acoustic wave device. Data indicated by “B” represents the filter characteristics of the second boundary acoustic wave device. Data indicated by “C” represents the filter characteristics of the third boundary acoustic wave device.

  As shown in FIG. 6, when only the second medium 22 having a thickness of 1.57λ is formed and the third medium 23 is not formed, the dummy electrode 30 is positioned on the IDT electrode 20. , Out-of-band spurious components located in the regions X1 and X2 indicated by dotted lines in FIG. 6 tend to increase.

Next, in order to investigate the cause of the out-of-band spurious, the present inventors have formed a SiO ₂ film (second medium 22) having a thickness of 0.6λ on a LiNbO ₃ substrate having a cut angle of 15 °. And a fourth boundary acoustic wave device in which a SiN film (third medium 23) having a thickness of 2.4λ is formed on a LiNbO ₃ substrate having a cut angle of 15 ° and a thickness of 0.6λ. A fifth boundary acoustic wave device in which a certain SiO ₂ film, a SiN film having a thickness of 2.4λ, and a wiring electrode (thickness: 0.1λ) made of Al are formed, and the displacement distribution of the boundary acoustic wave is measured. did. In the fourth and fifth boundary acoustic wave devices, the IDT electrode (thickness: 0.06λ) was formed of Au.

  FIG. 7 is a graph showing the displacement distribution of the SH type boundary acoustic wave in the fourth boundary acoustic wave device. FIG. 8 is a graph showing the displacement distribution of the first higher-order mode in the fourth boundary acoustic wave device. FIG. 9 is a graph showing the displacement distribution of the second higher-order mode in the fourth boundary acoustic wave device.

  FIG. 10 is a graph showing the displacement distribution of the SH type boundary acoustic wave in the fifth boundary acoustic wave device. FIG. 11 is a graph showing the displacement distribution of the first higher-order mode in the fifth boundary acoustic wave device. FIG. 12 is a graph showing the displacement distribution of the second higher-order mode in the fifth boundary acoustic wave device.

  Here, the first higher-order mode is a higher-order mode mainly composed of the Y component, and the second higher-order mode is a higher-order mode mainly composed of the Z component.

  7 to 12, the horizontal axis is the displacement, and the vertical axis is the depth (λ) when the surface of the first medium is a reference) (0). “Δ” represents the displacement in the elastic wave propagation direction (X), and “◯” represents the displacement in the direction (Z) perpendicular to the elastic wave propagation direction (X) on the surface of the first medium 21. "X" represents the displacement in the thickness direction (Y) perpendicular to the direction (X) and the direction (Z).

  From the results shown in FIG. 7, it can be seen that the SH type boundary acoustic wave (fundamental mode) is confined in the second medium 22 and hardly oozes into the third medium 23. From the result shown in FIG. 10, similarly, in the case where the wiring electrode is provided on the third medium 23, the SH type boundary acoustic wave is confined in the second medium 22. It can be seen that the medium 23 hardly oozes out.

  From the results shown in FIGS. 8 and 11, the first higher-order mode is also confined in the second medium 22 regardless of the presence or absence of the wiring electrode, and almost oozes out into the third medium 23. I understand that it is not.

  In contrast, the results shown in FIGS. 9 and 12 show that the second higher-order mode oozes into the third medium 23 regardless of the presence or absence of the wiring electrode. Specifically, the second higher-order mode oozes to a depth of 1.3λ. For this reason, taking into account that the thickness of the second medium 22 is 0.6λ, the second higher-order mode has oozed out to the portion of the third medium 23 having a depth of 0.7λ. I understand. For this reason, when the third medium 23 is not provided or the thickness of the third medium 23 is less than 0.7λ, the wiring medium 24 is positioned above the IDT electrode 20. A second higher mode is reached. Then, it is considered that out-of-band spurious is generated due to deformation and reflection of the second higher-order mode at the wiring electrode 24.

  The displacement distribution of the higher-order mode when the third medium 23 is not provided is shown in Patent Document 1, for example, as shown in FIG.

FIGS. 16A and 16B show a boundary acoustic wave device having a SiO ₂ / Au / LiNbO ₃ structure described in Patent Document 1, with a Au thickness of 0.05λ and a SiO ₂ film thickness of 1. It is a figure which shows the displacement distribution of each spurious mode when set to 0.5λ.

  As shown in FIG. 16, a high-order mode displacement exists up to the surface of the second medium 22. Therefore, if the wiring electrode 24 is provided on the surface of the second medium 22 and the wiring electrode 24 on the second medium 22 and the IDT electrode overlap in plan view, the higher-order mode is Out-of-band spurious occurs due to deformation and reflection.

  As a method for suppressing out-of-band spurious, it is conceivable to form the wiring electrode 24 so that the IDT electrode 20 and the wiring electrode 24 do not overlap in the height direction, as shown in FIG. However, when the IDT electrode 20 and the wiring electrode 24 are not overlapped in a plan view, for example, as shown in FIG. 13B in which the IDT electrode 20 and a part of the wiring electrode 24 are overlapped in a plan view. In comparison, the size of the boundary acoustic wave device is increased. Therefore, it is difficult to achieve both suppression of out-of-band spurious and miniaturization of the boundary acoustic wave device.

  On the other hand, as described above, since the second higher-order mode only oozes out to the portion of the third medium 23 having a depth of 0.7λ, By setting the thickness of the medium 23 to 0.7λ or more, the second higher-order mode can be prevented from reaching the surface of the third medium 23. Therefore, when the thickness of the third medium 23 is 0.7λ or more, out-of-band spurious is effectively suppressed even when the wiring electrode 24 is formed so as to overlap the IDT electrode 20 in plan view. Can do. That is, by setting the thickness of the third medium 23 to 0.7λ or more and forming the wiring electrode 24 on the surface of the third medium 23, both suppression of out-of-band spurious and miniaturization of the boundary acoustic wave device can be achieved. Can be planned.

  It should be noted that in the two-medium type boundary acoustic wave device in which the third medium is not provided, it is difficult to obtain the effect of suppressing the out-of-band spurious even when the second medium is thickened. This is because, in the two-medium type boundary acoustic wave device, there is no medium having a higher sound velocity than the second medium on the second medium, and therefore, in the higher-order mode, the entire medium in the thickness direction of the second medium is used. This is because the higher mode reaches the surface of the second medium even when the second medium is vibrated greatly and the thickness of the second medium is increased.

  On the other hand, in the so-called three-medium type boundary acoustic wave device provided with the high acoustic velocity third medium 23, as can be seen from the results shown in FIGS. The entirety of the first medium 21 formed by the body in the thickness direction vibrates greatly, and the sound speed of the second medium 22 is lowered. For this reason, although the higher order mode oozes out to the portion of the third medium 23 on the second medium 22 side, the higher order mode is attenuated in the third medium 23. Therefore, the higher-order mode does not reach the portion of the third medium 23 that is away from the second medium 22. Therefore, in the three-medium type boundary acoustic wave device, by setting the thickness of the third medium 23 to 0.7λ or more, the out-of-band spurious can be effectively suppressed as described above.

From the results shown in FIGS. 8, 9, 11, and 12, it can be seen that the higher mode oozes out toward the first medium 21. This is because the sound speed of the first medium 21 is slower than the sound speed of the third medium 23. That is, the higher-order mode can be oozed out to the LiNbO ₃ side by setting the sound speed of the higher-order mode to be higher than the fast transverse wave speed of LiNbO ₃ constituting the first medium 21. As a result, the surface of the third medium 23 does not vibrate. For this reason, it is possible to provide wiring on the surface of the third medium 23, and good characteristics can be realized.

(Modification)
In the example shown in FIG. 13B, two ground electrodes 17 are provided. However, as shown in FIG. 14, only one ground electrode 17 may be formed. By doing so, the boundary acoustic wave device can be further reduced in size.

DESCRIPTION OF SYMBOLS 1 ... Elastic boundary wave apparatus 10 ... Unbalanced input terminal 11a ... 1st balanced output terminal 11b ... 2nd balanced output terminal 12 ... Elastic boundary wave filter part 13 ... Elastic boundary wave filter 13a ... 1st IDT electrode 13b ... 2nd IDT electrode 13c ... 3rd IDT electrode 13d ... 4th IDT electrode 13e ... 5th IDT electrode 14 ... boundary acoustic wave resonator 15 ... parallel capacitance 16 ... boundary acoustic wave resonator 17 ... ground electrode 20 ... IDT electrode 21 ... first medium 22 ... second medium 23 ... third medium 24 ... wiring electrode 25 ... protective film 26 ... bump electrode 30 ... dummy electrode

Claims (3)

A first medium made of a piezoelectric body;
A second medium formed on the first medium;
A third medium formed on the second medium;
An IDT electrode formed at a boundary between the first medium and the second medium;
A boundary acoustic wave device including a wiring electrode, wherein the sound velocity of the second medium is lower than the sound velocity of the first and third media, and the sound velocity of the third medium is higher than the sound velocity of the first medium. There,
The wiring electrode is formed on the third medium so as to at least partially overlap the IDT electrode in a plan view.
A boundary acoustic wave device, wherein the thickness of the third medium is 0.7 times or more the wavelength of the boundary acoustic wave excited in the IDT electrode. 2. The boundary acoustic wave device according to claim 1, wherein the first medium is made of LiNbO ₃ , the second medium is made of silicon oxide, and the third medium is made of silicon nitride.   The boundary acoustic wave device according to claim 1, wherein the wiring electrode includes an external terminal electrode.

Images