WO2023013741A1

WO2023013741A1 - Elastic wave device

Info

Publication number: WO2023013741A1
Application number: PCT/JP2022/030013
Authority: WO
Inventors: 翔永友
Original assignee: 株式会社村田製作所
Priority date: 2021-08-04
Filing date: 2022-08-04
Publication date: 2023-02-09

Abstract

The present invention suppresses leakage of elastic waves. This elastic wave device comprises: a support member equipped with a support substrate which is thick in a first direction; and an IDT electrode that has a piezoelectric layer provided in the first direction of the support member, a plurality of first electrode fingers provided on a main surface of the piezoelectric layer and extending in a second direction intersecting the first direction, a first busbar electrode to which the plurality of first electrode fingers are connected, a plurality of second electrode fingers lying opposite any of the plurality of first electrode fingers in a third direction orthogonal to the second direction and extending in the second direction, and a second busbar electrode to which the plurality of second electrode fingers are connected. The present invention has, in plan view in the first direction, a non-piezoelectric region containing a non-piezoelectric body in a gap region between at least one of the first electrode fingers and the second busbar electrode, or between at least one of the second electrode fingers and the first busbar electrode.

Description

Acoustic wave device

The present disclosure relates to elastic wave devices.

Patent Document 1 describes an elastic wave device.

JP 2012-257019 A

In the elastic wave device shown in Patent Document 1, leakage of elastic waves may occur in the direction in which the electrode fingers extend.

The present disclosure is intended to solve the above-described problems, and aims to suppress leakage of elastic waves.

An elastic wave device according to one aspect includes a support member including a support substrate having a thickness in a first direction, a piezoelectric layer provided in the first direction of the support member, a main surface of the piezoelectric layer provided, a plurality of first electrode fingers extending in a second direction intersecting the first direction; a first busbar electrode to which the plurality of first electrode fingers are connected; an IDT electrode having a plurality of second electrode fingers facing any one of the plurality of first electrode fingers and extending in the second direction; and a second busbar electrode to which the plurality of second electrode fingers are connected; a gap between at least one first electrode finger and the second busbar electrode or between at least one second electrode finger and the first busbar electrode in plan view in the first direction The region has a non-piezoelectric region containing non-piezoelectric material.

According to the present disclosure, elastic wave leakage can be suppressed.

1A is a perspective view showing an elastic wave device according to a first embodiment; FIG. FIG. 1B is a plan view showing the electrode structure of the first embodiment. FIG. 2 is a cross-sectional view of a portion along line II-II of FIG. 1A. FIG. 3A is a schematic cross-sectional view for explaining Lamb waves propagating through the piezoelectric layer of the comparative example. FIG. 3B is a schematic cross-sectional view for explaining a thickness-shear primary mode bulk wave propagating through the piezoelectric layer of the first embodiment. FIG. 4 is a schematic cross-sectional view for explaining the amplitude direction of a thickness-shear primary mode bulk wave propagating in the piezoelectric layer of the first embodiment. FIG. 5 is an explanatory diagram showing an example of resonance characteristics of the elastic wave device of the first embodiment. In the elastic wave device of the first embodiment, FIG. 2 is an explanatory diagram showing the relationship between , and the fractional band. FIG. FIG. 7 is a plan view showing an example in which a pair of electrodes are provided in the elastic wave device of the first embodiment. FIG. 8 is a reference diagram showing an example of resonance characteristics of the elastic wave device of the first embodiment. FIG. 9 shows the ratio bandwidth when a large number of elastic wave resonators are configured in the elastic wave device of the first embodiment, and the phase rotation amount of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. is an explanatory diagram showing the relationship between. FIG. 10 is an explanatory diagram showing the relationship between d/2p, metallization ratio MR, and fractional bandwidth. FIG. 11 is an explanatory diagram showing a map of the fractional band with respect to the Euler angles (0°, θ, ψ) of LiNbO ₃ when d/p is infinitely close to 0. FIG. FIG. 12 is a modification of the first embodiment, and is a cross-sectional view of a portion taken along line II-II of FIG. 1A. FIG. 13 is a partially cutaway perspective view for explaining the elastic wave device according to the embodiment of the present disclosure. 14 is a plan view showing an example of the elastic wave device according to the first embodiment; FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 14. FIG. FIG. 16 is an explanatory diagram showing an example of admittance characteristics of the elastic wave device according to the first embodiment. FIG. 17 is a plan view showing an example of the elastic wave device according to the second embodiment. 18 is a cross-sectional view taken along line XVIII-XVIII of FIG. 17. FIG.

Below, embodiments of the present disclosure will be described in detail based on the drawings. Note that the present disclosure is not limited by this embodiment. It should be noted that each embodiment described in the present disclosure is an exemplary one, and among different embodiments, a modification that allows partial replacement or combination of configurations, and the first embodiment after the second embodiment A description of matters common to the embodiment will be omitted, and only different points will be described. In particular, similar actions and effects due to similar configurations will not be mentioned sequentially for each embodiment.

(First embodiment)
1A is a perspective view showing an elastic wave device according to a first embodiment; FIG. FIG. 1B is a plan view showing the electrode structure of the first embodiment.

The elastic wave device 1 of the first embodiment has a piezoelectric layer 2 made of LiNbO ₃ . The piezoelectric layer 2 may consist of LiTaO ₃ . The cut angle of LiNbO ₃ and LiTaO ₃ is Z-cut in the first embodiment. The cut angles of LiNbO ₃ and LiTaO ₃ may be rotated Y-cut or X-cut. Preferably, the Y-propagation and X-propagation ±30° propagation orientations are preferred.

Although the thickness of the piezoelectric layer 2 is not particularly limited, it is preferably 50 nm or more and 1000 nm or less in order to effectively excite the thickness shear primary mode.

The piezoelectric layer 2 has a first main surface 2a and a second main surface 2b facing each other in the Z direction.

Electrode fingers

3 and 4 are provided on the first main surface 2a.

Here, the electrode finger 3 is an example of the "first electrode finger" and the electrode finger 4 is an example of the "second electrode finger". In FIGS. 1A and 1B , the multiple electrode fingers 3 are multiple “first electrodes” connected to the first busbar electrodes 5 . A plurality of electrode fingers 4 are a plurality of “second electrodes” connected to second busbar electrodes 6 . The plurality of electrode fingers 3 and the plurality of electrode fingers 4 are interdigitated with each other. Thus, an IDT (Interdigital Transducer) electrode including electrode fingers 3 , electrode fingers 4 , first busbar electrodes 5 , and second busbar electrodes 6 is configured.

The

electrode fingers

3 and 4 have a rectangular shape and a length direction. The electrode finger 3 and the electrode finger 4 adjacent to the electrode finger 3 face each other in a direction perpendicular to the length direction. Both the length direction of the

electrode fingers

3 and 4 and the direction orthogonal to the length direction of the

electrode fingers

3 and 4 are directions that intersect the thickness direction of the piezoelectric layer 2 . Therefore, it can be said that the electrode finger 3 and the electrode finger 4 adjacent to the electrode finger 3 face each other in the direction intersecting the thickness direction of the piezoelectric layer 2 . In the following description, the thickness direction of the piezoelectric layer 2 is defined as the Z direction (or first direction), the length direction of the

electrode fingers

3 and 4 is defined as the Y direction (or second direction), and the electrode fingers 3 and electrode fingers 4 may be described as the X direction (or the third direction).

Further, the length direction of the

electrode fingers

3 and 4 may be interchanged with the direction orthogonal to the length direction of the

electrode fingers

3 and 4 shown in FIGS. 1A and 1B. That is, in FIGS. 1A and 1B, the

electrode fingers

3 and 4 may extend in the direction in which the first busbar electrodes 5 and the second busbar electrodes 6 extend. In that case, the first busbar electrode 5 and the second busbar electrode 6 extend in the direction in which the

electrode fingers

3 and 4 extend in FIGS. 1A and 1B. A pair of structures in which the electrode fingers 3 connected to one potential and the electrode fingers 4 connected to the other potential are adjacent to each other are arranged in a direction perpendicular to the length direction of the

electrode fingers

3 and 4. Multiple pairs are provided.

Here, the electrode finger 3 and the electrode finger 4 are adjacent to each other, not when the electrode finger 3 and the electrode finger 4 are arranged so as to be in direct contact, but when the electrode finger 3 and the electrode finger 4 are arranged with a gap therebetween. It refers to the case where the When the electrode finger 3 and the electrode finger 4 are adjacent to each other, there are electrodes connected to the hot electrode and the ground electrode, including

other electrode fingers

3 and 4, between the electrode finger 3 and the electrode finger 4. is not placed. The logarithms need not be integer pairs, but may be 1.5 pairs, 2.5 pairs, or the like.

The center-to-center distance, that is, the pitch, between the

electrode fingers

3 and 4 is preferably in the range of 1 μm or more and 10 μm or less. Further, the center-to-center distance between the

electrode fingers

3 and 4 means the center of the width dimension of the electrode fingers 3 in the direction orthogonal to the length direction of the electrode fingers 3 and the distance orthogonal to the length direction of the electrode fingers 4 . It is the distance connecting the center of the width dimension of the electrode finger 4 in the direction of

Furthermore, when at least one of the

electrode fingers

3 and 4 is plural (when there are 1.5 or more pairs of electrodes when the

electrode fingers

3 and 4 are paired as a pair of electrode pairs), the electrode fingers 3. The center-to-center distance of the electrode fingers 4 refers to the average value of the center-to-center distances of adjacent electrode fingers 3 and electrode fingers 4 among 1.5 or more pairs of electrode fingers 3 and electrode fingers 4 .

Also, the width of the

electrode fingers

3 and 4, that is, the dimension in the facing direction of the

electrode fingers

3 and 4 is preferably in the range of 150 nm or more and 1000 nm or less. Note that the center-to-center distance between the

electrode fingers

3 and 4 is the distance between the center of the dimension (width dimension) of the electrode finger 3 in the direction perpendicular to the length direction of the electrode finger 3 and the length of the electrode finger 4. It is the distance connecting the center of the dimension (width dimension) of the electrode finger 4 in the direction orthogonal to the direction.

Also, in the first embodiment, since the Z-cut piezoelectric layer is used, the direction orthogonal to the length direction of the

electrode fingers

3 and 4 is the direction orthogonal to the polarization direction of the piezoelectric layer 2 . This is not the case when a piezoelectric material with a different cut angle is used as the piezoelectric layer 2 . Here, "perpendicular" is not limited to being strictly perpendicular, but substantially perpendicular (the angle formed by the direction perpendicular to the length direction of the electrode fingers 3 and electrode fingers 4 and the polarization direction is, for example, 90° ± 10°).

A support substrate 8 is laminated on the second main surface 2b side of the piezoelectric layer 2 with an intermediate layer 7 interposed therebetween. The intermediate layer 7 and the support substrate 8 have a frame shape and, as shown in FIG. 2,

openings

7a and 8a. A space (air gap) 9 is thereby formed.

The space 9 is provided so as not to disturb the vibration of the excitation region C of the piezoelectric layer 2 . Therefore, the support substrate 8 is laminated on the second main surface 2b with the intermediate layer 7 interposed therebetween at a position not overlapping the portion where at least one pair of

electrode fingers

3 and 4 are provided. Note that the intermediate layer 7 may not be provided. Therefore, the support substrate 8 can be directly or indirectly laminated to the second main surface 2b of the piezoelectric layer 2 .

The intermediate layer 7 is made of silicon oxide. However, the intermediate layer 7 can be formed of an appropriate insulating material other than silicon oxide, such as silicon nitride and alumina.

The support substrate 8 is made of Si. The plane orientation of the surface of Si on the piezoelectric layer 2 side may be (100), (110), or (111). Preferably, high-resistance Si having a resistivity of 4 kΩ or more is desirable. However, the support substrate 8 can also be constructed using an appropriate insulating material or semiconductor material. Materials for the support substrate 8 include, for example, aluminum oxide, lithium tantalate, lithium niobate, piezoelectric materials such as crystal, alumina, magnesia, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, and steer. Various ceramics such as tight and forsterite, dielectrics such as diamond and glass, and semiconductors such as gallium nitride can be used.

The plurality of electrode fingers 3, electrode fingers 4, first busbar electrodes 5, and second busbar electrodes 6 are made of appropriate metals or alloys such as Al and AlCu alloys. In the first embodiment, the electrode fingers 3, the electrode fingers 4, the first busbar electrodes 5, and the second busbar electrodes 6 have a structure in which an Al film is laminated on a Ti film. Note that an adhesion layer other than the Ti film may be used.

When driving, an AC voltage is applied between the multiple electrode fingers 3 and the multiple electrode fingers 4 . More specifically, an AC voltage is applied between the first busbar electrode 5 and the second busbar electrode 6 . As a result, it is possible to obtain resonance characteristics using a thickness-shear primary mode bulk wave excited in the piezoelectric layer 2 .

Further, in the elastic wave device 1, when the thickness of the piezoelectric layer 2 is d, and the center-to-center distance between any one of the plurality of pairs of

electrode fingers

3 and 4 adjacent to each other is p, d/p is set to 0.5 or less. As a result, the thickness-shear primary mode bulk wave is effectively excited, and good resonance characteristics can be obtained. More preferably, d/p is 0.24 or less, in which case even better resonance characteristics can be obtained.

When at least one of the electrode fingers 3 and the electrode fingers 4 is plural as in the first embodiment, that is, when the electrode fingers 3 and the electrode fingers 4 form a pair of electrodes, the electrode fingers 3 and the electrode fingers When there are 1.5 pairs or more of 4, the center-to-center distance p between the

adjacent electrode fingers

3 and 4 is the average distance between the center-to-center distances between the

adjacent electrode fingers

3 and 4 .

Since the acoustic wave device 1 of the first embodiment has the above configuration, even if the logarithms of the

electrode fingers

3 and 4 are reduced in an attempt to reduce the size, the Q value is unlikely to decrease. This is because the resonator does not require reflectors on both sides, and the propagation loss is small. The reason why the above reflector is not required is that the bulk wave of the thickness-shlip primary mode is used.

FIG. 3A is a schematic cross-sectional view for explaining Lamb waves propagating through the piezoelectric layer of the comparative example. FIG. 3B is a schematic cross-sectional view for explaining a thickness-shear primary mode bulk wave propagating through the piezoelectric layer of the first embodiment. FIG. 4 is a schematic cross-sectional view for explaining the amplitude direction of a thickness-shear primary mode bulk wave propagating in the piezoelectric layer of the first embodiment.

FIG. 3A shows an acoustic wave device as described in Patent Document 1, in which Lamb waves propagate through the piezoelectric layer. As shown in FIG. 3A, waves propagate through the piezoelectric layer 201 as indicated by arrows. Here, the piezoelectric layer 201 has a first principal surface 201a and a second principal surface 201b, and the thickness direction connecting the first principal surface 201a and the second principal surface 201b is the Z direction. . The X direction is the direction in which the

electrode fingers

3 and 4 of the IDT electrodes are aligned. As shown in FIG. 3A, in the Lamb wave, the wave propagates in the X direction as shown. Since it is a plate wave, although the piezoelectric layer 201 vibrates as a whole, the wave propagates in the X direction, so reflectors are arranged on both sides to obtain resonance characteristics. Therefore, wave propagation loss occurs, and when miniaturization is attempted, that is, when the number of logarithms of the

electrode fingers

3 and 4 is reduced, the Q value is lowered.

On the other hand, as shown in FIG. 3B, in the acoustic wave device of the first embodiment, since the vibration displacement is in the thickness sliding direction, the wave is generated between the first main surface 2a and the second main surface 2a of the piezoelectric layer 2. It propagates almost in the direction connecting the surface 2b, that is, in the Z direction, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Further, since resonance characteristics are obtained by propagating waves in the Z direction, no reflector is required. Therefore, no propagation loss occurs when propagating to the reflector. Therefore, even if the number of electrode pairs consisting of the

electrode fingers

3 and 4 is reduced in an attempt to promote miniaturization, the Q value is unlikely to decrease.

As shown in FIG. 4, the amplitude direction of the bulk wave of the primary thickness-shear mode is the first region 251 included in the excitation region C (see FIG. 1B) of the piezoelectric layer 2 and the first region 251 included in the excitation region C (see FIG. 1B). 2 area 252 is reversed. FIG. 4 schematically shows bulk waves when a voltage is applied between the electrode fingers 3 so that the electrode fingers 4 have a higher potential than the electrode fingers 3 . The first region 251 is a region of the excitation region C between the virtual plane VP1 that is perpendicular to the thickness direction of the piezoelectric layer 2 and bisects the piezoelectric layer 2 and the first main surface 2a. The second region 252 is a region of the excitation region C between the virtual plane VP1 and the second main surface 2b.

In the elastic wave device 1, at least one pair of electrodes consisting of the

electrode fingers

3 and 4 is arranged. It is not always necessary to have a plurality of pairs of electrode pairs. That is, it is sufficient that at least one pair of electrodes is provided.

For example, the electrode finger 3 is an electrode connected to a hot potential, and the electrode finger 4 is an electrode connected to a ground potential. However, the electrode finger 3 may be connected to the ground potential and the electrode finger 4 to the hot potential. In the first embodiment, the at least one pair of electrodes are, as described above, electrodes connected to a hot potential or electrodes connected to a ground potential, and no floating electrodes are provided.

FIG. 5 is an explanatory diagram showing an example of resonance characteristics of the elastic wave device of the first embodiment. The design parameters of the acoustic wave device 1 that obtained the resonance characteristics shown in FIG. 5 are as follows.

Piezoelectric layer 2: _LiNbO3 with Euler angles (0°, 0°, 90°)
Thickness of piezoelectric layer 2: 400 nm

Length of excitation region C (see FIG. 1B): 40 μm
Number of electrode pairs consisting of electrode fingers 3 and 4: 21 pairs Center-to-center distance (pitch) between electrode fingers 3 and 4: 3 μm
Width of electrode fingers 3 and 4: 500 nm
d/p: 0.133

　Middle layer 7: Silicon oxide film with a thickness of 1 μm

Support substrate 8: Si

The excitation region C (see FIG. 1B) is a region where the

electrode fingers

3 and 4 overlap when viewed in the X direction perpendicular to the length direction of the

electrode fingers

3 and 4. . The length of the excitation region C is the dimension along the length direction of the

electrode fingers

3 and 4 of the excitation region C. As shown in FIG. Here, the excitation region C is an example of the "intersection region".

In the first embodiment, the inter-electrode distances of the electrode pairs consisting of the

electrode fingers

3 and 4 are all equal in a plurality of pairs. That is, the electrode fingers 3 and the electrode fingers 4 are arranged at equal pitches.

As is clear from FIG. 5, good resonance characteristics with a specific bandwidth of 12.5% are obtained in spite of having no reflector.

By the way, when the thickness of the piezoelectric layer 2 is d, and the center-to-center distance between the

electrode fingers

3 and 4 is p, in the first embodiment, d/p is 0.5 or less, more preferably 0. .24 or less. This will be explained with reference to FIG.

A plurality of elastic wave devices were obtained by changing d/2p in the same manner as the elastic wave device that obtained the resonance characteristics shown in FIG. In the elastic wave device of the first embodiment, FIG. 6 shows d/2p, where p is the center-to-center distance between adjacent electrodes or the average distance of the center-to-center distances, and d is the average thickness of the piezoelectric layer 2. It is an explanatory view showing the relationship with the fractional bandwidth as.

As shown in FIG. 6, when d/2p exceeds 0.25, that is, when d/p>0.5, even if d/p is adjusted, the fractional bandwidth is less than 5%. On the other hand, when d/2p≦0.25, that is, when d/p≦0.5, the specific bandwidth can be increased to 5% or more by changing d/p within that range. , that is, a resonator having a high coupling coefficient can be constructed. Further, when d/2p is 0.12 or less, that is, when d/p is 0.24 or less, the specific bandwidth can be increased to 7% or more. In addition, by adjusting d/p within this range, a resonator with a wider specific band can be obtained, and a resonator with a higher coupling coefficient can be realized. Therefore, by setting d/p to 0.5 or less, it is possible to construct a resonator having a high coupling coefficient using the thickness-shear primary mode bulk wave.

Note that at least one pair of electrodes may be one pair, and the above p is the center-to-center distance between

adjacent electrode fingers

3 and 4 in the case of one pair of electrodes. In the case of 1.5 pairs or more of electrodes, the average distance between the centers of

adjacent electrode fingers

3 and 4 should be p.

Also, for the thickness d of the piezoelectric layer 2, if the piezoelectric layer 2 has variations in thickness, a value obtained by averaging the thickness may be adopted.

FIG. 7 is a plan view showing an example in which a pair of electrodes are provided in the elastic wave device of the first embodiment. In elastic wave device 101 , a pair of electrodes having

electrode fingers

3 and 4 are provided on first main surface 2 a of piezoelectric layer 2 . Note that K in FIG. 7 is the intersection width. As described above, in the elastic wave device of the present disclosure, the number of pairs of electrodes may be one. Even in this case, if the above d/p is 0.5 or less, it is possible to effectively excite the bulk wave in the primary mode of thickness shear.

In the elastic wave device 1, preferably, the excitation region is an overlapping region of the plurality of

electrode fingers

3 and 4 when viewed in the direction in which any

adjacent electrode fingers

3 and 4 are facing each other. It is desirable that the metallization ratio MR of the

adjacent electrode fingers

3 and 4 with respect to the region C satisfies MR≦1.75(d/p)+0.075. In that case, spurious can be effectively reduced. This will be described with reference to FIGS. 8 and 9. FIG.

FIG. 8 is a reference diagram showing an example of resonance characteristics of the elastic wave device of the first embodiment. A spurious signal indicated by an arrow B appears between the resonance frequency and the anti-resonance frequency. Note that d/p=0.08 and the Euler angles of LiNbO ₃ (0°, 0°, 90°). Also, the metallization ratio MR was set to 0.35.

The metallization ratio MR will be explained with reference to FIG. 1B. In the electrode structure of FIG. 1B, when focusing on the pair of

electrode fingers

3 and 4, it is assumed that only the pair of

electrode fingers

3 and 4 are provided. In this case, the excitation region C is the portion surrounded by the dashed-dotted line. The excitation region C is a region where the

electrode fingers

3 and 4 overlap with the electrode fingers 4 when viewed in a direction perpendicular to the length direction of the

electrode fingers

3 and 4, that is, in a facing direction. a region where the electrode fingers 3 overlap each other; and a region between the

electrode fingers

3 and 4 where the

electrode fingers

3 and 4 overlap each other. The area of the

electrode fingers

3 and 4 in the excitation region C with respect to the area of the excitation region C is the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of the metallization portion to the area of the excitation region C.

When a plurality of pairs of

electrode fingers

3 and 4 are provided, the ratio of the metallization portion included in the entire excitation region C to the total area of the excitation region C should be MR.

FIG. 9 shows the ratio bandwidth when a large number of elastic wave resonators are configured in the elastic wave device of the first embodiment, and the phase rotation amount of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. is an explanatory diagram showing the relationship between. The ratio band was adjusted by changing the film thickness of the piezoelectric layer 2 and the dimensions of the

electrode fingers

3 and 4 in various ways. FIG. 9 shows the results when the piezoelectric layer 2 made of Z-cut LiNbO ₃ is used, but the same tendency is obtained when the piezoelectric layer 2 with other cut angles is used.

In the area surrounded by ellipse J in FIG. 9, the spurious is as large as 1.0. As is clear from FIG. 9, when the fractional band exceeds 0.17, that is, exceeds 17%, a large spurious with a spurious level of 1 or more changes the parameters constituting the fractional band, even if the passband appear within. That is, as in the resonance characteristics shown in FIG. 8, a large spurious component indicated by arrow B appears within the band. Therefore, the specific bandwidth is preferably 17% or less. In this case, by adjusting the film thickness of the piezoelectric layer 2 and the dimensions of the

electrode fingers

3 and 4, the spurious response can be reduced.

FIG. 10 is an explanatory diagram showing the relationship between d/2p, metallization ratio MR, and fractional bandwidth. In the elastic wave device 1 of the first embodiment, various elastic wave devices 1 with different d/2p and MR were configured, and the fractional bandwidth was measured. The hatched portion on the right side of the dashed line D in FIG. 10 is the area where the fractional bandwidth is 17% or less. The boundary between the hatched area and the non-hatched area is expressed by MR=3.5(d/2p)+0.075. That is, MR=1.75(d/p)+0.075. Therefore, preferably MR≤1.75(d/p)+0.075. In that case, it is easy to set the fractional bandwidth to 17% or less. More preferably, it is the area on the right side of MR=3.5(d/2p)+0.05 indicated by the dashed-dotted line D1 in FIG. That is, if MR≤1.75(d/p)+0.05, the fractional bandwidth can be reliably reduced to 17% or less.

FIG. 11 is an explanatory diagram showing a map of the fractional band with respect to the Euler angles (0°, θ, ψ) of LiNbO ₃ when d/p is infinitely close to 0. FIG. A hatched portion in FIG. 11 is a region where a fractional bandwidth of at least 5% or more is obtained. When the range of the area is approximated, it becomes the range represented by the following formulas (1), (2) and (3).

(0°±10°, 0° to 20°, arbitrary ψ) Equation (1)
(0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ² /900) ^1/2 ) or (0°±10°, 20° to 80°, [180 °-60° (1-(θ-50) ² /900) ^1/2 ] ~ 180°) Equation (2)
(0°±10°, [180°-30°(1-(ψ-90) ² /8100) ^1/2 ]~180°, arbitrary ψ) Equation (3)

Therefore, in the case of the Euler angle range of formula (1), formula (2), or formula (3), the fractional band can be sufficiently widened, which is preferable.

FIG. 12 is a modification of the first embodiment, and is a cross-sectional view of a portion taken along line II-II of FIG. 1A. In the acoustic wave device 41 , an acoustic multilayer film 42 is laminated on the second main surface 2 b of the piezoelectric layer 2 . The acoustic multilayer film 42 has a laminated structure of low

acoustic impedance layers

42a, 42c, 42e with relatively low acoustic impedance and high

acoustic impedance layers

42b, 42d with relatively high acoustic impedance. The low acoustic impedance layer is, for example, a layer of _SiO2 , and the high acoustic impedance layer is, for example, a metal layer such as W, Pt or a dielectric layer such as AlN, SiN. When the acoustic multilayer film 42 is used, the thickness-shear primary mode bulk wave can be confined in the piezoelectric layer 2 without using the space 9 in the elastic wave device 1 . Also in the acoustic wave device 41, by setting the above d/p to 0.5 or less, it is possible to obtain resonance characteristics based on bulk waves in the first-order thickness shear mode. In the acoustic multilayer film 42, the number of lamination of the low

acoustic impedance layers

42a, 42c, 42e and the high

acoustic impedance layers

42b, 42d is not particularly limited. At least one of the high

acoustic impedance layers

42b, 42d needs to be arranged farther from the piezoelectric layer 2 than the low

acoustic impedance layers

42a, 42c, 42e.

The low

acoustic impedance layers

42a, 42c, 42e and the high

acoustic impedance layers

42b, 42d can be made of appropriate materials as long as the acoustic impedance relationship is satisfied. Examples of materials for the low

acoustic impedance layers

42a, 42c, and 42e include silicon oxide and silicon oxynitride. Materials for the high acoustic impedance layers 42b and 42d include alumina, silicon nitride, and metals.

FIG. 13 is a partially cutaway perspective view for explaining the elastic wave device according to the embodiment of the present disclosure. In FIG. 13, the outer peripheral edge of the space portion 9 is indicated by a dashed line. The elastic wave device of the present disclosure may utilize plate waves. In this case, the elastic wave device 301 has

reflectors

310 and 311 as shown in FIG.

Reflectors

310 and 311 are provided on both sides of the

electrode fingers

3 and 4 of the piezoelectric layer 2 in the acoustic wave propagation direction. In the elastic wave device 301, a Lamb wave as a plate wave is excited by applying an AC electric field to the

electrode fingers

3 and 4 on the space 9. FIG. At this time, since the

reflectors

310 and 311 are provided on both sides, it is possible to obtain resonance characteristics due to Lamb waves as Lamb waves.

As described above, the elastic wave devices 1 and 101 use bulk waves in the primary mode of thickness shear. In the elastic wave devices 1 and 101, the first electrode finger 3 and the second electrode finger 4 are adjacent electrodes, the thickness of the piezoelectric layer 2 is d, and the center of the first electrode finger 3 and the second electrode finger 4 is d/p is set to 0.5 or less, where p is the distance between them. As a result, the Q value can be increased even if the elastic wave device is miniaturized.

In the elastic wave devices 1 and 101, the piezoelectric layer 2 is made of lithium niobate or lithium tantalate. The first principal surface 2a or the second principal surface 2b of the piezoelectric layer 2 has first electrode fingers 3 and second electrode fingers 4 facing each other in a direction intersecting the thickness direction of the piezoelectric layer 2. It is desirable to cover the finger 3 and the second electrode finger 4 with a protective film.

FIG. 14 is a plan view showing an example of the elastic wave device according to the first embodiment. 15 is a cross-sectional view taken along line XV-XV of FIG. 14. FIG. An acoustic wave device 1A according to the first embodiment includes a piezoelectric layer 2, IDT electrodes including

electrode fingers

3 and 4 and

busbar electrodes

5 and 6, and a support member.

The support member is a member provided with the support substrate 8 . In the first embodiment, the support member consists of a support substrate 8 . In the first embodiment, the piezoelectric layer 2 is provided on the support substrate 8 in the Z direction. Note that the support member may further include an intermediate layer 7 provided in the Z direction of the support substrate 8 . The support member has a space portion 9 at a position at least partially overlapping with the IDT electrode when viewed from above in the Z direction. In the example of FIG. 15, the space 9 is provided so as to penetrate the support substrate 8 in the Z direction, but this is only an example, and may be provided only on the piezoelectric layer 2 side of the support member.

The piezoelectric layer 2 is provided in the Z direction of the support member. In the first embodiment, the piezoelectric layer 2 is a layer containing piezoelectric lithium niobate and unavoidable impurities, and is, for example, single crystal Z-cut lithium niobate.

Here, in an elastic wave device that utilizes bulk elastic waves in the primary mode of thickness shear, there is a possibility that the elastic waves will leak on the surface of the piezoelectric layer 2 . Elastic wave leakage increases in the direction in which the

electrode fingers

3 and 4 extend (Y direction). Further, when the piezoelectric layer 2 is Z-cut and the second Euler angle θ is -15° or more and +15° or less, more elastic waves may leak.

The present inventors have found that in an elastic wave device that utilizes a thickness-shear first-order bulk elastic wave, an elastic wave leakage mode is generated outside the intersection region C in the Y direction, and the first bus bar electrode 5 or the second bus bar electrode 5 It was found that an elastic wave leakage mode occurs outside the busbar electrodes 6 in the Y direction. As a result of extensive research, the inventors of the present invention found that the leakage of elastic waves can be suppressed by providing the non-piezoelectric region 20 in the gap region. The gap region refers to a region between the first electrode fingers 3 and the second busbar electrodes 6 in the Y direction or between the second electrode fingers 4 and the first busbar electrodes 5 in the Y direction. The non-piezoelectric region 20 will be described below.

The non-piezoelectric region 20 is a region including the non-piezoelectric body 21 when viewed in plan in the Z direction. More specifically, the non-piezoelectric region 20 is a region composed of the non-piezoelectric body 21 and the portion of the piezoelectric layer 2 that overlaps the non-piezoelectric body 21 in plan view in the Z direction. In the first embodiment, the non-piezoelectric region 20 is a region made of a non-piezoelectric material 21 . A non-piezoelectric region 20 is in the gap region. In the first embodiment, the non-piezoelectric region 20 is in the region between the

busbar electrodes

5, 6 and the intersection region C in the Y direction. As a result, excitation of elastic waves in the gap region is inhibited, so leakage of elastic waves can be suppressed.

The non-piezoelectric material 21 is a material that does not exhibit piezoelectricity at all, or a material with low piezoelectricity. More specifically, the non-piezoelectric material 21 refers to a material whose absolute value of the piezoelectric constant _e15 is 50% or less with respect to the piezoelectric layer 2 in the intersection region C. In the first embodiment, the non-piezoelectric body 21 is provided so as to penetrate the piezoelectric layer 2 in the Z direction.

In the first embodiment, the non-piezoelectric material 21 is a material similar to that of the piezoelectric layer 2 in the intersection region C and having lower crystallinity and orientation than the piezoelectric layer 2, such as non-single crystal lithium niobate. . Here, non-single crystal refers to polycrystal, amorphous, or a crystal in an intermediate state between polycrystal and amorphous. Thereby, the electromechanical coupling coefficient of the non-piezoelectric body 21 can be made smaller than the electromechanical coupling coefficient of the piezoelectric layer 2 . Therefore, since the piezoelectricity and orientation of the material depend on the electromechanical coupling coefficient, the piezoelectricity and orientation of the non-piezoelectric body 21 can be made smaller than those of the piezoelectric layer 2 . Thereby, the piezoelectricity of the non-piezoelectric body 21 can be suppressed, and the leakage of elastic waves can be further suppressed.

The non-piezoelectric material 21 is preferably non-oriented. In this case, the electromechanical coupling coefficient of the non-piezoelectric body 21 can be made smaller than the electromechanical coupling coefficient of the piezoelectric layer 2 more reliably. Therefore, the piezoelectric constant of the non-piezoelectric body 21 can be made smaller than the piezoelectric constant of the piezoelectric layer 2 more reliably.

It should be noted that the non-piezoelectric material 21 is not limited to the amorphous material of the same kind as the piezoelectric layer 2 . The non-piezoelectric material 21 may be, for example, a material obtained by partially reversing the polarization of the material of the piezoelectric layer 2 . In this case, the piezoelectricity of the non-piezoelectric body 21 can be suppressed. Also, the non-piezoelectric material 21 may be made of a material different from that of the piezoelectric layer 2 . The non-piezoelectric body 21 may be, for example, lithium niobate that is damaged by ion implantation of a specific element. Here, the specific element is, for example, hydrogen, helium, or the like. In this case, the non-piezoelectric material 21 can be non-single-crystal, so that the piezoelectricity of the non-piezoelectric material 21 can be suppressed.

FIG. 16 is an explanatory diagram showing an example of admittance characteristics of the elastic wave device according to the first embodiment. In FIG. 16 , the example is the elastic wave device 1A according to the first embodiment, and the comparative example is the elastic wave device without the non-piezoelectric region 20 . As shown in FIG. 16, the elastic wave device according to the example has a narrower peak width at the resonance frequency than the elastic wave device according to the comparative example, so propagation loss is suppressed, and elastic wave leakage is suppressed. found to be suppressed.

As described above, the acoustic wave device 1A according to the first embodiment includes a support member including the support substrate 8 having a thickness in the first direction, the piezoelectric layer 2 provided in the first direction of the support member, and the piezoelectric layer 2 provided in the first direction. A plurality of first electrode fingers 3 provided on the main surface (first main surface 2a) of the layer 2 and extending in a second direction intersecting the first direction; , a plurality of second electrode fingers 4 facing any one of the plurality of first electrode fingers 3 in a third direction orthogonal to the second direction and extending in the second direction, and a plurality of second electrode fingers 4 and an IDT electrode having a second busbar electrode 6 to which is connected, and when viewed in the first direction, between at least one first electrode finger 3 and the second busbar electrode 6 A non-piezoelectric region 20 containing a non-piezoelectric body 21 is provided in the gap region between one second electrode finger 4 and the first busbar electrode 5 .

As a result, the excitation of elastic waves in the gap region is inhibited, and the generation of modes of leakage of elastic waves is suppressed, so that leakage of elastic waves can be suppressed.

In addition, the non-piezoelectric region 20 overlaps the first electrode finger 3 or the second electrode finger 4 when viewed in plan in the first direction. Even in this case, leakage of elastic waves can be suppressed.

Further, it is arranged so as to form a space portion 9 at a position at least partially overlapping with the IDT electrode when viewed in plan in the first direction. As a result, the thickness-shear primary mode bulk wave can be confined within the piezoelectric layer 2 .

Further, the supporting member includes, on the piezoelectric layer 2 side, one or more low

acoustic impedance layers

42a, 42c, and 42e having an acoustic impedance lower than that of the piezoelectric layer 2 and one or more high

acoustic impedance layers

42a, 42c, and 42e having an acoustic impedance higher than that of the piezoelectric layer 2. It has an acoustic reflection layer (acoustic multilayer film 42) including acoustic impedance layers 42b and 42d. As a result, the thickness-shear primary mode bulk wave can be confined within the piezoelectric layer 2 .

In a preferred embodiment, the piezoelectric layer 2 is a single crystal material, and the non-piezoelectric body 21 is a polycrystalline single crystal material, an amorphous single crystal material, or a single crystal material into which ions of a specific element are implanted. It is a material that has been As a result, the electromechanical coupling coefficient of the non-piezoelectric body 21 can be made smaller than the electromechanical coupling coefficient of the piezoelectric layer 2 , and the piezoelectricity and orientation of the non-piezoelectric body 21 can be made smaller than those of the piezoelectric layer 2 . can. Thereby, the piezoelectricity of the non-piezoelectric body 21 can be suppressed, and the leakage of elastic waves can be further suppressed.

The piezoelectric layer 2 is Z-cut, and the second Euler angle θ of the piezoelectric layer 2 is -15° or more and 15° or less. Even in this case, leakage of elastic waves can be suppressed.

As a desirable aspect, the thickness of the piezoelectric layer 2 is the center-to-center distance between the adjacent first electrode fingers 3 and the second electrode fingers 4 among the plurality of first electrode fingers 3 and the plurality of second electrode fingers 4. It is 2p or less when p. Thereby, the acoustic wave device 1 can be miniaturized and the Q value can be increased.

As a preferred embodiment, the piezoelectric layer 2 contains lithium niobate or lithium tantalate. As a result, it is possible to provide an elastic wave device capable of obtaining good resonance characteristics.

As a desirable aspect, it is configured to be able to use bulk waves in the thickness-shlip mode. As a result, it is possible to provide an elastic wave device with a high coupling coefficient and good resonance characteristics.

As a desirable mode, the thickness of the piezoelectric layer 2 is d, and the center-to-center distance between the adjacent first electrode fingers 3 and second electrode fingers 4 among the plurality of first electrode fingers 3 and the plurality of second electrode fingers 4 is p. , d/p≦0.5. Thereby, the acoustic wave device 1 can be miniaturized and the Q value can be increased.

As a more desirable aspect, d/p is 0.24 or less. Thereby, the acoustic wave device 1 can be miniaturized and the Q value can be increased.

As a desirable mode, the region where the first electrode fingers 3 and the second electrode fingers 4 overlap when viewed in the third direction is the excitation region C, and the first electrode fingers 3 and the second electrode fingers 3 with respect to the excitation region C When the metallization ratio of finger 4 is MR, MR≦1.75(d/p)+0.075 is satisfied. In this case, the fractional bandwidth can be reliably set to 17% or less.

As a preferred embodiment, the piezoelectric layer 2 is made of lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate satisfy the following formula (1), formula (2) or It is in the range of formula (3). In this case, the fractional bandwidth can be widened sufficiently.

(0°±10°, 0° to 20°, arbitrary ψ) Equation (1)
(0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ² /900) ^1/2 ) or (0°±10°, 20° to 80°, [180 °-60° (1-(θ-50)2/900) ^1/2 ] ~ 180°) Equation (2)
(0°±10°, [180°-30°(1-(ψ-90) ² /8100) ^1/2 ]~180°, arbitrary ψ) Equation (3)

(Second embodiment)
FIG. 17 is a plan view showing an example of the elastic wave device according to the second embodiment. 18 is a cross-sectional view taken along line XVIII-XVIII of FIG. 17. FIG. An elastic wave device 1B according to the second embodiment differs from the first embodiment in that a non-piezoelectric region 20B contains a piezoelectric material. An elastic wave device 1B according to the second embodiment will be described below with reference to the drawings. In addition, about the structure similar to 1 A of elastic wave apparatuses which concern on 1st Embodiment, the code|symbol is attached|subjected and description is abbreviate|omitted.

The elastic wave device 1B has a non-piezoelectric region 20B in the region between the

busbar electrodes

5, 6 and the intersection region C in the Y direction. In the second embodiment, the non-piezoelectric regions 20B are spaced apart in the X direction so as not to overlap the

electrode fingers

3 and 4 when viewed in plan in the first direction.

As shown in FIG. 18, in the second embodiment, the non-piezoelectric region 20B includes a region made of the non-piezoelectric body 21B and a region of the piezoelectric layer 2 that overlaps the non-piezoelectric body 21B when viewed in plan in the Z direction. Consists of In this case, the piezoelectric constant _e15 in the region overlapping the non-piezoelectric body 21B is 50% or more of the piezoelectric constant _e15 of the piezoelectric material in the intersecting region C when viewed in plan in the Z direction. Even in this case, leakage of elastic waves can be suppressed.

In the second embodiment, the non-piezoelectric material 21 is a protective film made of a dielectric material, such as silicon oxide. In this case, the non-piezoelectric body 21 is provided at a position that does not overlap with the intersection region C when viewed from above in the Z direction. In the example of FIG. 18, the non-piezoelectric body 21 is provided in the gap region. Here, when the thickness of the non-piezoelectric body 21B is ds and the thickness of the piezoelectric layer 2 is dp, ds is larger than dp. That is, the thickness ds of the non-piezoelectric body 21B is less than 50% of the thickness (ds+dp) of the non-piezoelectric region 20B. As a result, the coupling coefficient of the gap region is significantly reduced compared to the coupling coefficient of the piezoelectric layer 2 in the intersection region C. FIG. As a result, excitation of elastic waves in the gap region is inhibited, and leakage of elastic waves can be suppressed.

As described above, in the elastic wave device 1B according to the second embodiment, the non-piezoelectric regions 20B are spaced apart in the third direction. Even in this case, leakage of elastic waves can be suppressed.

Also, the non-piezoelectric body 21B contains silicon oxide. Even in this case, leakage of elastic waves can be suppressed.

As a desirable mode, the non-piezoelectric body 21B is laminated on the piezoelectric layer 2, and the thickness ds of the non-piezoelectric body 21B is greater than the thickness dp of the piezoelectric layer 2. As a result, the coupling coefficient of the gap region is significantly reduced compared to the coupling coefficient of the intersection region C. FIG. As a result, excitation of elastic waves in the gap region is inhibited, and leakage of elastic waves can be suppressed.

As a preferred embodiment, the non-piezoelectric region 20B further includes a portion of the piezoelectric layer 2 overlapping the non-piezoelectric body 21 in plan view in the first direction, and the non-piezoelectric body 21B has a thickness ds is greater than the thickness dp of a portion of the piezoelectric layer 2 . As a result, the coupling coefficient of the gap region is significantly reduced compared to the coupling coefficient of the intersection region C. FIG. As a result, excitation of elastic waves in the gap region is inhibited, and leakage of elastic waves can be suppressed.

It should be noted that the above-described embodiments are intended to facilitate understanding of the present disclosure, and are not intended to limit and interpret the present disclosure. This disclosure may be modified/modified without departing from its spirit, and this disclosure also includes equivalents thereof.

1, 1A, 1B, 41, 101, 301 elastic wave device 2 piezoelectric layer 2a first main surface 2b second main surface 3 electrode fingers (first electrode fingers)
4 electrode finger (second electrode finger)
5 busbar electrode (first busbar electrode)
6 busbar electrode (second busbar electrode)
7 intermediate layer 7a opening 8 supporting substrate 8a opening 9

space

20, 20B

non-piezoelectric regions

21, 21B non-piezoelectric body 42

acoustic multilayer films

42a, 42c, 42e low

acoustic impedance layers

42b, 42d high acoustic impedance layer 201 piezoelectric Layer 201a First main surface 201b Second main surface 251 First region 252

Second regions

310, 311 Reflectors ds, dp Thickness C Exciting region (intersection region)
VP1 virtual plane

Claims

a support member comprising a support substrate having a thickness in a first direction;
a piezoelectric layer provided in the first direction of the support member;
a plurality of first electrode fingers provided on the main surface of the piezoelectric layer and extending in a second direction intersecting the first direction; a first bus bar electrode to which the plurality of first electrode fingers are connected; a plurality of second electrode fingers facing any one of the plurality of first electrode fingers in a third direction orthogonal to the two directions and extending in the second direction; and a second electrode finger connected to the plurality of second electrode fingers. an IDT electrode having a busbar electrode,
In a gap region between at least one first electrode finger and the second busbar electrode or between at least one second electrode finger and the first busbar electrode when viewed in plan in the first direction, An acoustic wave device having a non-piezoelectric region containing a non-piezoelectric material.
The elastic wave device according to claim 1, wherein the non-piezoelectric region overlaps with the first electrode finger or the second electrode finger when viewed in the first direction.
The elastic wave device according to claim 1, wherein the non-piezoelectric regions are spaced apart in the third direction when viewed in plan in the first direction.
The elastic wave device according to any one of claims 1 to 3, arranged so as to form a space at a position at least partially overlapping with the IDT electrode when viewed in plan in the first direction.
The support member includes, on the piezoelectric layer side, one or more low acoustic impedance layers having an acoustic impedance lower than that of the piezoelectric layer and one or more high acoustic impedance layers having an acoustic impedance higher than that of the piezoelectric layer. 4. An acoustic wave device according to any one of claims 1 to 3, comprising an acoustic reflective layer comprising:
The piezoelectric layer is a single crystal material,
6. The non-piezoelectric material according to any one of claims 1 to 5, wherein the non-piezoelectric material is a material obtained by polycrystallizing the single crystal material, a material obtained by amorphizing the single crystal material, or a material obtained by implanting ions of a specific element into the single crystal material. The elastic wave device according to any one of claims 1 to 3.
The elastic wave device according to any one of claims 1 to 5, wherein the non-piezoelectric body contains silicon oxide.
The non-piezoelectric material is laminated on the piezoelectric layer,
The elastic wave device according to claim 7, wherein the thickness of said non-piezoelectric material is greater than the thickness of said piezoelectric layer.
The non-piezoelectric region further includes a portion of the piezoelectric layer that overlaps the non-piezoelectric body in plan view in the first direction,
The elastic wave device according to any one of claims 1 to 8, wherein the thickness of the non-piezoelectric material in the non-piezoelectric region is greater than the thickness of a portion of the piezoelectric layer.
The piezoelectric layer is Z-cut,
The elastic wave device according to any one of claims 1 to 9, wherein the second Euler angle θ of the piezoelectric layer is -15° or more and 15° or less.
The thickness of the piezoelectric layer is 2p, where p is the center-to-center distance between the first electrode fingers and the second electrode fingers that are adjacent to each other among the plurality of first electrode fingers and the plurality of second electrode fingers. The elastic wave device according to any one of claims 1 to 10, wherein:
The elastic wave device according to any one of claims 1 to 11, wherein the piezoelectric layer contains lithium niobate or lithium tantalate.
The acoustic wave device according to any one of claims 1 to 12, configured to be able to use bulk waves in thickness shear mode.
When the thickness of the piezoelectric layer is d, and the center-to-center distance between the first electrode fingers and the second electrode fingers adjacent to each other among the plurality of first electrode fingers and the plurality of second electrode fingers is p, The elastic wave device according to any one of claims 1 to 13, wherein d/p≤0.5.
The elastic wave device according to claim 14, wherein said d/p is 0.24 or less.
A region in which the first electrode finger and the second electrode finger overlap when viewed in the third direction is an excitation region, and the first electrode finger and the second electrode finger are metabolized with respect to the excitation region. The elastic wave device according to any one of claims 1 to 15, wherein MR≤1.75(d/p)+0.075 is satisfied when MR is a rise ratio.
The piezoelectric layer is lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate are given by the following formula (1), formula (2), or formula ( 17. The elastic wave device according to any one of claims 1 to 16, which falls within the range of 3).
(0°±10°, 0° to 20°, arbitrary ψ) Equation (1)
(0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) 2 /900) 1/2 ) or (0°±10°, 20° to 80°, [180 °-60° (1-(θ-50) 2 /900) 1/2 ] ~ 180°) Equation (2)
(0°±10°, [180°-30°(1-(ψ-90) 2 /8100) 1/2 ]~180°, arbitrary ψ) Equation (3)