WO2023002790A1 - Elastic wave device - Google Patents

Abstract

Provided is an elastic wave device capable of suppressing unwanted waves at a frequency lower than and around a resonance frequency.　An elastic wave device 10 of the present invention comprises: a support member including a support substrate; a piezoelectric layer 14 provided on the support member and comprising a lithium niobate layer or a lithium tantalate layer; and an IDT electrode 11 provided on the piezoelectric layer 14 and having a pair of bus bars (first and second bus bars 26, 27) and a plurality of electrode fingers (first and second electrode fingers 28, 29). The support member is provided with an acoustic reflecting portion. The acoustic reflecting portion overlaps at least a part of the IDT electrode 11 in plan view. If the thickness of the piezoelectric layer 14 is d and the distance between the centers of adjacent electrode fingers is p, d/p is 0.5 or less. Some of the plurality of electrode fingers are connected to one of the bus bars of the IDT electrode 11. The remaining electrode fingers of the plurality of electrode fingers are connected to the other bus bar. A plurality of electrode fingers connected to one bus bar and a plurality of electrode fingers connected to the other bus bar are interdigitated. If a direction in which adjacent electrode fingers oppose each other is defined as an electrode finger opposing direction, the adjacent electrode fingers overlap each other in an intersecting region F when viewed from the electrode finger opposing direction. If the direction of extension of the plurality of electrode fingers is defined as an electrode finger extending direction, the intersecting region F includes a central region H and a pair of edge regions (first and second edge regions E1, E2) disposed so as to sandwich the central region H in the electrode finger extending direction. At least one mass-adding film 24 is provided in at least the edge regions. If the dimension of the mass-adding film 24 along the electrode finger extending direction is defined as the length of the mass-adding film 24, and arbitrary two points in the electrode finger opposing direction in a portion in which the mass-adding film 24 is located are defined as a first point O1 and a second point O2, the length of the mass-adding film 24 is different between the first point O1 and the second point O2 of at least one group thereof.

Description

Acoustic wave device

The present invention relates to elastic wave devices.

Conventionally, elastic wave devices have been widely used in filters for mobile phones. In recent years, there has been proposed an elastic wave device using a thickness-shear mode bulk wave, as described in Patent Document 1 below. In this elastic wave device, a piezoelectric layer is provided on a support. A pair of electrodes is provided on the piezoelectric layer. The paired electrodes face each other on the piezoelectric layer and are connected to different potentials. By applying an AC voltage between the electrodes, a thickness-shear mode bulk wave is excited.

U.S. Patent No. 10491192

In an elastic wave device that utilizes thickness-shear mode bulk waves, such as that described in Patent Document 1, unnecessary waves are generated at frequencies that are lower than and near the resonance frequency. Therefore, electrical characteristics may deteriorate.

An object of the present invention is to provide an elastic wave device capable of suppressing unwanted waves at frequencies lower than and near the resonance frequency.

An elastic wave device according to the present invention includes a support member including a support substrate, a piezoelectric layer provided on the support member and being a lithium niobate layer or a lithium tantalate layer, and a piezoelectric layer provided on the piezoelectric layer. and an IDT electrode having a pair of busbars and a plurality of electrode fingers, an acoustic reflection portion being provided in the support member, and the acoustic reflection portion being, in plan view, at least one of the IDT electrodes. where d is the thickness of the piezoelectric layer and p is the center-to-center distance between the adjacent electrode fingers, d/p is 0.5 or less, and one of the bus bars of the IDT electrodes has Some of the plurality of electrode fingers are connected, the rest of the plurality of electrode fingers are connected to the other bus bar, and the other electrode fingers are connected to the one bus bar. A plurality of electrode fingers and the plurality of electrode fingers connected to the other bus bar are inserted into each other, and the direction in which the adjacent electrode fingers face each other is defined as the electrode finger facing direction. When viewed from the direction, a region where the adjacent electrode fingers overlap is an intersecting region. and a pair of edge regions arranged so as to sandwich a central region in the extending direction of the electrode fingers, at least one mass addition film being provided in at least the edge regions, the electrode of the mass addition film When the length of the mass addition film is the length of the mass addition film along the finger extending direction, and two arbitrary points in the electrode finger facing direction of the portion where the mass addition film is positioned are the first point and the second point, The lengths of the mass addition film at at least one set of first and second points are different from each other.

According to the present invention, it is possible to provide an elastic wave device capable of suppressing unwanted waves at frequencies lower than and near the resonance frequency.

FIG. 1 is a schematic plan view of an elastic wave device according to a first embodiment of the invention. FIG. 2 is a schematic cross-sectional view taken along line II in FIG. FIG. 3 is a schematic plan view of an elastic wave device of a first comparative example. FIG. 4 is a diagram showing phase characteristics in the first embodiment of the present invention and the first comparative example. FIG. 5 is a diagram showing the relationship between the length of the mass addition film in the edge region and the phase characteristics. FIG. 6 is an enlarged view of FIG. 5 around 4000 MHz. FIG. 7 is a schematic plan view of an elastic wave device according to a modification of the first embodiment of the invention. FIG. 8 is a schematic plan view of an elastic wave device according to a second embodiment of the invention. FIG. 9 is a schematic plan view of an elastic wave device of a reference example. FIG. 10 is a diagram showing the relationship between the length of the mass addition film in the gap region and the phase characteristics. FIG. 11 is an enlarged view of FIG. 10 around 4000 MHz. FIG. 12 is a schematic plan view of an elastic wave device according to a first modification of the second embodiment of the invention. FIG. 13 is a schematic plan view of an elastic wave device according to a second modification of the second embodiment of the invention. FIG. 14 is a schematic plan view of an elastic wave device according to a third embodiment of the invention. 15 is a schematic cross-sectional view taken along line II in FIG. 14. FIG. FIG. 16 is a schematic plan view of an elastic wave device according to a fourth embodiment of the invention. FIG. 17 is a schematic plan view of an elastic wave device according to a fifth embodiment of the invention. FIG. 18 is a schematic cross-sectional view along the II line in FIG. 17 FIG. 19 is a schematic plan view of an elastic wave device according to a sixth embodiment of the invention. FIG. 20 is a schematic plan view of an elastic wave device according to a modification of the sixth embodiment of the invention. FIG. 21(a) is a schematic perspective view showing the external appearance of an elastic wave device that utilizes a thickness-shear mode bulk wave, and FIG. 21(b) is a plan view showing an electrode structure on a piezoelectric layer. FIG. 22 is a cross-sectional view of a portion taken along line AA in FIG. 21(a). FIG. 23(a) is a schematic front cross-sectional view for explaining a Lamb wave propagating through a piezoelectric film of an acoustic wave device, and FIG. FIG. 2 is a schematic front cross-sectional view for explaining bulk waves in a mode; FIG. 24 is a diagram showing amplitude directions of bulk waves in the thickness shear mode. FIG. 25 is a diagram showing resonance characteristics of an elastic wave device that utilizes bulk waves in a thickness-shear mode. FIG. 26 is a diagram showing the relationship between d/p and the fractional bandwidth of the resonator, where p is the center-to-center distance between adjacent electrodes and d is the thickness of the piezoelectric layer. FIG. 27 is a plan view of an acoustic wave device that utilizes thickness shear mode bulk waves. FIG. 28 is a diagram showing the resonance characteristics of the elastic wave device of the reference example in which spurious appears. FIG. 29 is a diagram showing the relationship between the fractional bandwidth and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious. FIG. 30 is a diagram showing the relationship between d/2p and metallization ratio MR. FIG. 31 is a diagram showing a map of fractional bandwidth with respect to Euler angles (0°, θ, ψ) of LiNbO ₃ when d/p is brought infinitely close to 0. FIG. FIG. 32 is a front cross-sectional view of an elastic wave device having an acoustic multilayer film.

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

It should be noted that each embodiment described in this specification is an example, and partial replacement or combination of configurations is possible between different embodiments.

FIG. 1 is a schematic plan view of an elastic wave device according to the first embodiment of the invention. FIG. 2 is a schematic cross-sectional view taken along line II in FIG.

As shown in FIG. 1, the acoustic wave device 10 has a piezoelectric substrate 12 and an IDT electrode 11. As shown in FIG. 2, the piezoelectric substrate 12 has a support member 13 and a piezoelectric layer 14 . In this embodiment, the support member 13 includes a support substrate 16 and an insulating layer 15 . An insulating layer 15 is provided on the support substrate 16 . A piezoelectric layer 14 is provided on the insulating layer 15 . However, the support member 13 may be composed of only the support substrate 16 .

The piezoelectric layer 14 has a first main surface 14a and a second main surface 14b. The first main surface 14a and the second main surface 14b face each other. Of the first principal surface 14a and the second principal surface 14b, the second principal surface 14b is located on the support member 13 side.

As the material of the support substrate 16, for example, semiconductors such as silicon, ceramics such as aluminum oxide, and the like can be used. As a material for the insulating layer 15, any suitable dielectric such as silicon oxide or tantalum oxide can be used. The piezoelectric layer 14 may be, for example, a lithium niobate layer, such as a LiNbO3 layer, or a lithium tantalate layer _, such as a _LiTaO3 layer.

As shown in FIG. 2, the support member 13 is provided with a hollow portion 10a. More specifically, the insulating layer 15 is provided with a recess. A piezoelectric layer 14 is provided on the insulating layer 15 so as to close the recess. Thereby, the hollow portion 10a is configured. However, the cavity 10 a may be provided over the insulating layer 15 and the support substrate 16 or may be provided only in the support substrate 16 . Note that the hollow portion 10 a may be a through hole provided in the support member 13 .

An IDT electrode 11 is provided on the first main surface 14a of the piezoelectric layer 14. As shown in FIG. The elastic wave device 10 of the present embodiment is an elastic wave resonator configured to be able to use bulk waves in a thickness-shear mode such as a primary thickness-shear mode. However, the elastic wave device of the present invention may be a filter device having a plurality of elastic wave resonators, a multiplexer, or the like.

At least a portion of the IDT electrode 11 overlaps the hollow portion 10a of the support member 13 in plan view. In this specification, "planar view" means viewing from a direction corresponding to the upper direction in FIG. In FIG. 2, for example, of the support substrate 16 and the piezoelectric layer 14, the piezoelectric layer 14 side is the upper side.

As shown in FIG. 1, the IDT electrode 11 has a pair of busbars and a plurality of electrode fingers. A pair of busbars is specifically a first busbar 26 and a second busbar 27 . The first busbar 26 and the second busbar 27 face each other. The plurality of electrode fingers are specifically a plurality of first electrode fingers 28 and a plurality of second electrode fingers 29 . One ends of the plurality of first electrode fingers 28 are each connected to the first bus bar 26 . One ends of the plurality of second electrode fingers 29 are each connected to the second bus bar 27 . The plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 are interleaved with each other. The IDT electrode 11 may be composed of a single-layer metal film, or may be composed of a laminated metal film.

In the following, the first electrode finger 28 and the second electrode finger 29 may be simply referred to as electrode fingers. When the direction in which a plurality of electrode fingers extends is defined as the electrode finger extending direction, and the direction in which adjacent electrode fingers face each other is defined as the electrode finger facing direction, in the present embodiment, the electrode finger extending direction and the electrode finger facing direction are Orthogonal.

In the elastic wave device 10, d/p is 0.5 or less, where d is the thickness of the piezoelectric layer 14 and p is the center-to-center distance between adjacent electrode fingers. As a result, thickness-shear mode bulk waves are preferably excited.

By the way, the hollow portion 10a of the support member 13 shown in FIG. 2 is the acoustic reflection portion in the present invention. The acoustic reflector can effectively confine the energy of the elastic wave to the piezoelectric layer 14 side. An acoustic multilayer film, which will be described later, may be provided as the acoustic reflector.

Returning to FIG. 1, the IDT electrode 11 has an intersecting region F. The intersecting region F is a region where adjacent electrode fingers overlap each other when viewed from the direction in which the electrode fingers are opposed. The intersection region F has a central region H and a pair of edge regions. A pair of edge regions is specifically a first edge region E1 and a second edge region E2. The first edge region E1 and the second edge region E2 are arranged so as to sandwich the central region H in the extending direction of the electrode fingers. The first edge region E1 is located on the first bus bar 26 side. The second edge region E2 is located on the second busbar 27 side.

The IDT electrode 11 has a pair of gap regions. A pair of gap regions are located between the intersection region F and a pair of busbars. A pair of gap regions is specifically a first gap region G1 and a second gap region G2. The first gap region G1 is located between the first busbar 26 and the first edge region E1. The second gap region G2 is located between the second busbar 27 and the second edge region E2.

In this embodiment, the elastic wave device 10 has a pair of mass adding films 24 . One mass addition film 24 of the pair of mass addition films 24 is provided over the first edge region E1 and the first gap region G1. The other mass addition film 24 is provided over the second edge region E2 and the second gap region G2. Each mass addition film 24 has a strip shape. Each mass addition film 24 is provided on the first main surface 14a of the piezoelectric layer 14 so as to cover the plurality of electrode fingers. Each mass addition film 24 is also provided on the portion between the electrode fingers on the first main surface 14a.

By providing the mass addition film 24, a low sound velocity region is formed in each edge region. The low sound velocity region is a region in which the sound velocity is lower than the sound velocity in the central region H. A central region H and a low-frequency region are arranged in this order from the inner side to the outer side of the IDT electrode 11 in the electrode finger extending direction. Thereby, the piston mode is established and the transverse mode can be suppressed.

It should be noted that the elastic wave device of the present invention utilizes thickness-shear mode bulk waves instead of surface acoustic waves. In this case, even if the mass addition film 24 is provided in each gap region, the piston mode can be suitably established.

In this embodiment, each mass addition film 24 extends from each edge region to each gap region. However, each mass addition film 24 may be provided only in each edge region. In the elastic wave device of the present invention, the mass adding film 24 should be provided at least in the edge region. More specifically, the mass adding film 24 may be provided in at least one of the first edge region E1 and the second edge region E2.

As shown in FIG. 1, of the edge portion on the side of the central region H and the edge portion on the side of the first bus bar 26 in the mass addition film 24 provided in the first edge region E1, the edge portion on the side of the central region H is The edge portion extends obliquely with respect to the facing direction of the electrode fingers. On the other hand, the edge portion of the mass addition film 24 on the side of the first bus bar 26 extends parallel to the electrode finger facing direction. Therefore, when the length of the mass addition film 24 is defined as the dimension of the mass addition film 24 along the extending direction of the electrode fingers, the length of the mass addition film 24 is not uniform. More specifically, in this embodiment, the length of the mass adding film 24 increases from one side to the other side of the electrode finger facing direction. The same applies to the mass addition film 24 provided in the second edge region E2. In addition, the aspect in which the length of the mass addition film 24 is not uniform is not limited to the above.

In the following, arbitrary two points in the electrode finger facing direction of the portion where the mass addition film 24 is located are referred to as a first point O1 and a second point O2. Note that the first point O1 and the second point O2 shown in FIG. 1 are examples. A feature of this embodiment is that at least one mass addition film 24 is provided at least in the edge region, and the lengths of the mass addition film 24 at at least one pair of first point O1 and second point O2 are different from each other. There are different things. That is, in this embodiment, the length of the mass addition film 24 is not uniform. As a result, it is possible to suppress unnecessary waves having frequencies lower than the resonance frequency and located near the resonance frequency. The details will be shown below by comparing the present embodiment with the first comparative example.

As shown in FIG. 3, the first comparative example differs from the first embodiment in that the length of the mass addition film 104 is constant. The elastic wave device of the first comparative example also uses bulk waves in the thickness-shear mode, like the elastic wave device of the first embodiment. The phase characteristics of the elastic wave devices of the first embodiment and the first comparative example were compared.

FIG. 4 is a diagram showing phase characteristics in the first embodiment and the first comparative example.

As shown in FIG. 4, in the phase characteristics of the first comparative example, ripples caused by unwanted waves occur at frequencies lower than and near the resonance frequency. This unwanted wave is a unique unwanted wave in an acoustic wave device that utilizes bulk waves in the thickness-shear mode. In contrast, in the phase characteristics of the first embodiment, ripples that occur in the first comparative example are suppressed. From this, it can be seen that in the first embodiment, unnecessary waves can be suppressed at frequencies lower than and near the resonance frequency. In the following description, when an unwanted wave is simply described, it means an unwanted wave generated at a frequency lower than the resonance frequency and located near the resonance frequency, unless otherwise specified.

In the first embodiment, the length of the mass adding film 24 differs for each position in the electrode finger facing direction. As a result, the frequencies at which unwanted waves are generated can be dispersed, and the intensity of the unwanted waves can be reduced. Therefore, unwanted waves can be suppressed. Details of this effect are given below by referring to a second comparative example.

The second comparative example is different from the first embodiment in that the pair of mass addition films are provided only in the pair of edge regions and the length of the pair of mass addition films is constant. different from Here, a plurality of acoustic wave devices of the second comparative example were prepared, each having a different length of the mass addition film. The phase characteristics of each elastic wave device prepared were measured.

FIG. 5 is a diagram showing the relationship between the length of the mass addition film in the edge region and the phase characteristics. FIG. 6 is an enlarged view of FIG. 5 around 4000 MHz.

As shown in FIGS. 5 and 6, it can be seen that when the length of the mass addition film differs, the frequency at which ripples caused by unnecessary waves occur also differs. As shown in FIG. 1, in the first embodiment, one mass addition film 24 has two or more portions with different lengths. More specifically, in the first embodiment, the length of the mass adding film 24 changes continuously in the electrode finger facing direction. As a result, frequencies at which unwanted waves are generated can be dispersed, and the intensity of the unwanted waves can be reduced. Therefore, unwanted waves can be suppressed.

By the way, as shown in FIG. 1, the intersecting region F in the IDT electrode 11 of the acoustic wave device 10 includes a plurality of excitation regions C. More specifically, the excitation region C is the region between the centers of adjacent electrode fingers. Elastic waves are excited in a plurality of excitation regions C by applying an AC voltage to the IDT electrodes 11 . On the other hand, in an acoustic wave device that utilizes surface acoustic waves, the intersection region is one excitation region.

Unlike an acoustic wave device that uses surface acoustic waves, the acoustic wave device 10 that uses thickness-shear mode bulk waves is substantially equivalent to a configuration in which a plurality of resonators each having an excitation region C are connected in parallel. . Therefore, in the acoustic wave device 10, even if the length of the mass adding film 24 is not uniform in the direction in which the electrode fingers are opposed, the waveform of the frequency characteristics such as the phase characteristics is unlikely to collapse. Therefore, in the first embodiment, unnecessary waves can be suppressed without deteriorating electrical characteristics.

The portion where the mass addition film 24 is provided will be described in more detail below. As shown in FIG. 2, each of the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 has a first surface 11a, a second surface 11b, and a side surface 11c. The first surface 11a and the second surface 11b of each electrode finger face each other in the thickness direction of each electrode finger. Of the first surface 11a and the second surface 11b, the second surface 11b is the surface on the piezoelectric layer 14 side. A side surface 11c is connected to the first surface 11a and the second surface 11b. Hereinafter, unless otherwise specified, the side surface 11c of the electrode finger refers to the side surface 11c in the electrode finger facing direction.

The mass addition film 24 is provided on the first surfaces 11 a of the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 . More specifically, the mass addition film 24 is provided so as to cover the first surface 11 a and the side surface 11 c of the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 . As described above, in the first embodiment, the piezoelectric layer 14, the electrode fingers, and the mass addition film 24 are laminated in this order in the portions where the mass addition film 24 is provided on the electrode fingers. However, the mass adding film 24 may be provided between the piezoelectric layer 14 and the electrode fingers.

The mass adding film 24 may overlap with a plurality of electrode fingers in plan view, and may not overlap with all of the electrode fingers. However, the mass addition film 24 preferably overlaps all the electrode fingers in plan view. As a result, the piston mode can be established more reliably, and the transverse mode can be suppressed more reliably.

Returning to FIG. 1, the mass addition film 24 may be provided in at least one of the first edge region E1 and the second edge region E2. In the elastic wave device of the present invention, at least one mass adding film 24 should be provided. However, it is preferable that the mass addition film 24 is provided in both the first edge region E1 and the second edge region E2. Thereby, the transverse mode can be suppressed more reliably.

At least one dielectric selected from the group consisting of silicon oxide, tungsten oxide, niobium pentoxide, tantalum oxide and hafnium oxide is preferably used as the material of the mass addition film 24 . As a result, the piston mode can be established more reliably, and the transverse mode can be suppressed more reliably.

At least one mass addition film 24 is preferably provided over the edge region and the gap region. More preferably, all the mass adding films 24 are provided over the edge region and the gap region as in the first embodiment. As a result, it is possible to effectively suppress unwanted waves of frequencies lower than and near the resonance frequency.

The shape of the mass addition film 24 in plan view is a trapezoid. Therefore, the edge portion on the side of the first bus bar 26 and the edge portion on the side of the central region H of the mass addition film 24 provided in the first edge region E1 have a linear shape in plan view. . However, for example, the shape of both the edge portions of the mass adding film 24 in a plan view may be a curved shape. Alternatively, for example, the shape of both the edge portions of the mass addition film 24 in plan view may be a shape in which straight lines are connected, curved lines are connected, or a curved line and a straight line are connected. The same applies to the mass addition film 24 provided in the second edge region E2.

In the first embodiment, the length of the mass adding film 24 changes continuously in the electrode finger facing direction. However, the length of the mass addition film 24 at least one set of the first point O1 and the second point O2 should be different from each other. For example, in the modification of the first embodiment shown in FIG. 7, the length of the mass adding film 24A changes discontinuously in the electrode finger facing direction. More specifically, the mass addition film 24A has a plurality of stepped portions 24a. Portions of the mass addition film 24A having different lengths are connected to each other by the stepped portion 24a. The stepped portion 24a extends parallel to the extending direction of the electrode fingers. Each portion of the mass addition film 24A connected by the step portion 24a has a constant length. At least one stepped portion 24a may be provided. Also in this modified example, unwanted waves can be suppressed as in the first embodiment.

In the first embodiment, the length of each mass addition film 24 is not uniform in each edge region. On the other hand, the length of each mass addition film 24 is uniform in each gap region. However, each mass addition film 24 need not be uniform in each gap region. An example of this is illustrated by the second embodiment.

FIG. 8 is a schematic plan view of an elastic wave device according to the second embodiment.

This embodiment differs from the first embodiment in the shape of each mass addition film 34 . Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

One of the mass addition films 34 of the pair of mass addition films 34 is provided over the entire first edge region E1. That is, the mass addition film 34 has a uniform length in the first edge region E1. Of the edge portion of the mass addition film 34 on the side of the first bus bar 26 and the edge portion on the side of the central region H, the edge portion on the side of the central region H extends parallel to the electrode finger facing direction. there is On the other hand, the mass addition film 34 is not uniform in length in the first gap region G1. More specifically, the edge portion of the mass addition film 34 on the side of the first bus bar 26 extends obliquely with respect to the electrode finger facing direction.

Similarly, the edge portion on the central region H side of the mass adding film 34 provided over the second edge region E2 and the second gap region G2 extends parallel to the electrode finger facing direction. The end edge portion of the mass addition film 34 on the side of the second bus bar 27 extends obliquely with respect to the electrode finger facing direction.

It will be shown below with reference to a reference example that unwanted waves can be suppressed in this embodiment as well as in the first embodiment. As shown in FIG. 9, in the elastic wave device of the reference example, one of the mass adding films 104 of the pair of mass adding films 104 is provided only in the first gap region G1. The other mass addition film 104 is provided only in the second gap region G2.

A plurality of elastic wave devices of reference examples were prepared, each having a different length of the mass addition film 104 . In each elastic wave device, the length of the mass adding film 104 is constant. The phase characteristics of each elastic wave device prepared were measured.

FIG. 10 is a diagram showing the relationship between the length of the mass addition film in the gap region and the phase characteristics. FIG. 11 is an enlarged view of FIG. 10 around 4000 MHz.

As shown in FIGS. 10 and 11, when the length of the mass addition film 34 in the gap region is different, the frequencies at which ripples caused by unwanted waves are generated are also different. As shown in FIG. 8, in this embodiment, the length of the mass adding film 34 is uniform in each edge region, but not uniform in each gap region. As a result, frequencies at which unwanted waves are generated can be dispersed, and the intensity of the unwanted waves can be reduced. Therefore, unwanted waves can be suppressed.

In this embodiment, each mass addition film 34 is provided over the entire gap region in the electrode finger facing direction. However, it is not limited to this. For example, in the first modification of the second embodiment shown in FIG. 12, a portion of one of the mass addition films 34A of the pair of mass addition films 34A is the first edge region E1 and the first edge region E1. It is provided over the gap region G1. Another part of the mass adding film 34A is provided only in the first edge region E1. The mass addition film 34A has a step portion 34a. A portion of the mass addition film 34A provided only in the first edge region E1 and a portion provided over the first edge region E1 and the first gap region G1 are connected by a step portion 34a. ing.

In the other mass addition film 34A, similarly, a portion provided only in the second edge region E2 and a portion provided over the second edge region E2 and the second gap region G2 are stepped portions. connected by Also in this modified example, unwanted waves can be suppressed as in the second embodiment.

In the second embodiment shown in FIG. 8, each mass adding film 34 is provided over the entire edge region. However, even when the mass addition film 34 is provided over the edge region and the gap region, the mass addition film 34 may be provided in a part of the edge region. For example, in a second modification of the second embodiment shown in FIG. 13, one of the mass addition films 34B of the pair of mass addition films 34B has a portion of the first edge region E1 and a portion of the first edge region E1. is provided in a part of the gap region G1. Both the edge portion of the mass addition film 34B on the side of the first bus bar 26 and the edge portion on the side of the central region H extend obliquely with respect to the facing direction of the electrode fingers.

The other mass addition film 34B is similarly provided in part of the second edge region E2 and part of the second gap region G2. Both the edge portion of the mass addition film 34B on the side of the second bus bar 27 and the edge portion on the side of the central region H extend obliquely with respect to the facing direction of the electrode fingers. Also in this modified example, unwanted waves can be suppressed as in the second embodiment.

FIG. 14 is a schematic plan view of an elastic wave device according to the third embodiment. 15 is a schematic cross-sectional view taken along line II in FIG. 14. FIG.

As shown in FIG. 14, this embodiment differs from the first embodiment in that a pair of mass addition films 24 are provided between the plurality of electrode fingers and the piezoelectric layer 14. FIG. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

More specifically, as shown in FIG. 15, one mass addition film 24 is located on the first edge region E1 so that the second surfaces 11b of the plurality of first electrode fingers 28 and the plurality of second electrodes 28 It is provided between the second surface 11 b of the finger 29 and the piezoelectric layer 14 . Although not shown, the mass adding film 24 is provided between the second surfaces 11b of the plurality of first electrode fingers 28 and the piezoelectric layer 14 also in the first gap region G1. Similarly, in the second edge region E2, the other mass addition film 24 has the second surfaces 11b of the plurality of first electrode fingers 28 and the second surfaces 11b of the plurality of second electrode fingers 29, It is provided between the piezoelectric layer 14 and the piezoelectric layer 14 . The mass adding film 24 is provided between the second surfaces 11b of the plurality of second electrode fingers 29 and the piezoelectric layer 14 also in the second gap region G2. In addition, in each edge region and each gap region, the mass addition film 24 is also provided on the first main surface 14a of the piezoelectric layer 14 between the electrode fingers.

Also in this embodiment, as in the first embodiment, the length of the mass adding film 24 is not uniform in each edge region. Therefore, unwanted waves can be suppressed. In addition, it is possible to establish the piston mode and suppress the lateral mode.

In the above-described first to third embodiments, the mass adding film is continuously provided so as to overlap the plurality of electrode fingers and the regions between the electrode fingers in plan view. However, it is not limited to this. For example, in each edge region, a plurality of mass adding films 24 may be provided so as to overlap the electrode fingers and not overlap the region between the electrode fingers in plan view. An example of this is illustrated by the fourth embodiment.

FIG. 16 is a schematic plan view of an elastic wave device according to the fourth embodiment.

This embodiment differs from the first embodiment in that a plurality of mass adding films 44 are provided in each edge region. This embodiment also differs from the first embodiment in that the mass addition film 44 is not provided between the electrode fingers on the first main surface 14a of the piezoelectric layer 14 in each edge region. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

In the first edge region E1, each mass addition film 44 is applied only to the first surface 11a of one first electrode finger 28 or only to the first surface 11a of one second electrode finger 29. is provided. A plurality of mass addition films 44 are arranged in the electrode finger facing direction. In the present embodiment, the length of each mass adding film 44 is increased from one side to the other side in the direction in which the electrode fingers are opposed. Specifically, among the three mass addition films 44 that are continuous in the electrode finger facing direction, two adjacent mass addition films 44 have the same length, and the length of the two mass addition films 44 and The length of the remaining one mass addition film 44 is different from each other. Thus, the length of the mass addition film 44 changes periodically in the first edge region E1.

Similarly, in the second edge region E2, each mass addition film 44 is formed only on the first surface 11a of one first electrode finger 28 or on the first surface 11a of one second electrode finger 29. It is provided only on the surface 11a. The length of each mass adding film 44 increases from one to the other in the direction in which the electrode fingers are opposed. Note that the period in which the length of the mass addition film 44 changes is not limited to the above. Alternatively, the length of the mass addition film 44 may not change periodically. In each edge region, at least two mass addition films 44 among the plurality of mass addition films 44 should have different lengths. In this case, the lengths of the mass addition film 44 at least one set of the first point O1 and the second point O2 are different from each other.

In this embodiment, the lengths of the plurality of mass adding films 44 are not uniform in each edge region. Therefore, unwanted waves can be suppressed as in the first embodiment. In addition, it is possible to establish the piston mode and suppress the lateral mode.

In the portion where each mass addition film 44 is provided, the piezoelectric layer 14, the electrode fingers and the mass addition film 44 are laminated in this order. However, as in the third embodiment, the plurality of mass addition films 44 includes the second surfaces 11b of the plurality of first electrode fingers 28 and the second surfaces 11b of the plurality of second electrode fingers 29, It may be provided between the piezoelectric layer 14 and the piezoelectric layer 14 .

For example, at least one mass addition film 44 among the plurality of mass addition films 44 may be provided over the first edge region E1 and the first gap region G1. Similarly, at least one mass addition film 44 among the plurality of mass addition films 44 may be provided over the second edge region E2 and the second gap region G2.

Each mass addition film 44 contacts only the first electrode finger 28 or only the second electrode finger 29 . In this case, the mass addition film 44 may be made of metal.

In this embodiment, the mass adding film 44 is provided directly on the first surfaces 11a of the plurality of electrode fingers. Alternatively, in the above-described first to third embodiments, the mass adding film is provided directly between the electrode fingers on the first main surface 14a of the piezoelectric layer 14. FIG. However, even if the mass addition film is indirectly provided on the first surface 11a of the plurality of electrode fingers and the portion between the electrode fingers on the first main surface 14a of the piezoelectric layer 14 via the dielectric film. good. An example of this is illustrated by the fifth embodiment.

FIG. 17 is a schematic plan view of an elastic wave device according to the fifth embodiment. 18 is a schematic cross-sectional view taken along line II in FIG. 17. FIG.

As shown in FIGS. 17 and 18, this embodiment differs from the first embodiment in that a dielectric film 53 is provided so as to cover the IDT electrodes 11 . As shown in FIG. 17, the length of the mass adding film 54 is also different from the first embodiment in that it changes discontinuously in the electrode finger facing direction. Note that the shape of the mass addition film 54 provided in each edge region in the present embodiment in plan view is the same as the shape of the mass addition film in the modified example of the first embodiment. However, this embodiment differs from the first embodiment and its modification in that each mass addition film 54 is provided only in each edge region. Furthermore, this embodiment differs from the first embodiment in that the mass addition film 54 is made of metal. Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

One of the pair of mass addition films 54 is provided on the dielectric film 53 in the first edge region E1. Similarly, the other mass addition film 54 is provided on the dielectric film 53 in the second edge region E2. In each edge region, a mass addition film 54 is indirectly provided through a dielectric film 53 on the first surface 11a of the plurality of electrode fingers and the portion between the electrode fingers on the first main surface 14a of the piezoelectric layer 14. is provided. Each mass adding film 54 is continuously provided so as to overlap the plurality of electrode fingers and the regions between the electrode fingers in plan view.

For example, silicon oxide, silicon nitride, or silicon oxynitride can be used for the dielectric film 53 . Each mass addition film 54 is made of a suitable metal. However, each mass addition film 54 may be made of an appropriate dielectric.

Even when the dielectric film 53 is provided as in this embodiment, at least one mass adding film 54 may be provided over the edge region and the gap region.

FIG. 19 is a schematic plan view of an elastic wave device according to the sixth embodiment.

This embodiment differs from the first embodiment in that a plurality of mass adding films 64 are provided in each edge region. This embodiment also differs from the first embodiment in the position where the mass addition film 64 is provided in each edge region, and also in the shape and material of the mass addition film 64 . Except for the above points, the elastic wave device of this embodiment has the same configuration as the elastic wave device 10 of the first embodiment.

Note that in the present embodiment, the mass adding film 64 is provided integrally with the electrode fingers. Therefore, in FIG. 19, among the plurality of mass adding films 64, some of the mass adding films 64 indicated by reference numerals are indicated by dashed lines.

A plurality of mass addition films 64 are provided on the first main surface 14a of the piezoelectric layer 14 between the electrode fingers. More specifically, in the first edge region E1, the multiple mass addition films 64 are provided on the side surfaces 11c of the multiple first electrode fingers 28 and the side surfaces 11c of the multiple second electrode fingers 29. there is On the other hand, the plurality of mass addition films 64 are formed on the first surfaces 11a and the second surfaces 11b of the plurality of first electrode fingers 28 and the first surfaces 11a and the second surfaces 11b of the plurality of second electrode fingers 29 . is not provided on the surface 11b.

Similarly, in the second edge region E2, the multiple mass addition films 64 are provided on the side surfaces 11c of the multiple first electrode fingers 28 and the side surfaces 11c of the multiple second electrode fingers 29. On the other hand, the plurality of mass addition films 64 are formed on the first surfaces 11a and the second surfaces 11b of the plurality of first electrode fingers 28 and the first surfaces 11a and the second surfaces 11b of the plurality of second electrode fingers 29 . is not provided on the surface 11b.

More specifically, each mass addition film 64 is provided only on the side surface 11 c of one first electrode finger 28 or only on the side surface 11 c of one second electrode finger 29 . In this embodiment, one mass adding film 64 is provided on both side surfaces 11c of all first electrode fingers 28 and both side surfaces 11c of all second electrode fingers 29 in each edge region. ing. Both side surfaces 11c are a pair of side surfaces 11c of each electrode finger that are opposed to each other in the electrode finger facing direction. Note that the mass adding film 64 may be provided only on one side surface of one electrode finger.

The material and thickness of the plurality of mass adding films 64 are the same as the material and thickness of the plurality of first electrode fingers 28 and the plurality of second electrode fingers 29 . In this embodiment, the mass addition film 64 and the first electrode finger 28 or the second electrode finger 29 are integrally provided. Therefore, the width of the electrode finger is widened in the portion where the mass addition film 64 is provided. As a result, the width of the edge regions of the electrode fingers provided with the mass adding films 64 on the side surfaces 11c is wider than the width thereof in the central region H. As shown in FIG. Also in this case, each edge region constitutes a low sound velocity region. Therefore, the piston mode is established and the lateral mode can be suppressed. The width of the electrode finger is the dimension along the direction in which the electrode finger faces the electrode finger.

The plurality of mass addition films 64 need only be provided on the side surfaces 11c of the electrode fingers, and the plurality of mass addition films 64 need not be provided on all the side surfaces 11c of the electrode fingers. However, it is preferable that the plurality of mass adding films 64 are provided on the side surfaces 11c of all the electrode fingers as in this embodiment. As a result, the piston mode can be established more reliably, and the transverse mode can be suppressed more reliably.

In this embodiment, in the first edge region E1, the mass addition film 64 provided on one side surface 11c of one electrode finger and the mass addition film 64 provided on the other side surface 11c Same as length. However, the length of the mass addition film 64 provided on the side surface 11c of one of the adjacent first electrode fingers 28 and the length of the mass addition film 64 provided on the side surface 11c of the other first electrode finger 28 It is different from the length of the mass adding membrane 64 . The length of the mass addition film 64 provided on the side surface 11c of one of the adjacent second electrode fingers 29 and the length of the mass addition film 64 provided on the side surface 11c of the other second electrode finger 29 The length of membrane 64 is different. The length of the mass adding film 64 provided on the side surface 11c of the first electrode finger 28 is the length of one of the two second electrode fingers 29 adjacent to the first electrode finger 28. It is the same length as the mass adding film 64 provided on the side surface 11 c of the electrode finger 29 . The same applies to the second edge region E2.

As shown in FIG. 19, in each edge region, the length of the mass adding film 64 provided on the side surface 11c of the first electrode finger 28 increases from one side to the other side in the electrode finger opposing direction. Similarly, in each edge region, the length of the mass adding film 64 provided on the side surface 11c of the second electrode finger 29 increases from one to the other in the electrode finger facing direction. In each edge region, the length of the mass addition film 64 provided on the side surface 11c of at least one electrode finger should be different from the length of the mass addition film 64 provided on the side surface 11c of the other electrode fingers. Just do it. In this case, the lengths of the mass addition film 64 at at least one set of the first point O1 and the second point O2 are different from each other.

In this embodiment, the lengths of the plurality of mass adding films 64 are not uniform in each edge region. Therefore, unwanted waves can be suppressed as in the first embodiment.

In this embodiment, the length of the mass addition film 64 is changed periodically. However, the direction of change in the length of the mass addition film 64 is one direction. Note that the direction of change in the length of the mass addition film 64 is not limited to the above. For example, in the modification of the sixth embodiment shown in FIG. 20, the length of the mass adding film 64 provided on the side surface 11c of the first electrode finger 28 increases from one side to the other side in the electrode finger facing direction. A lengthened portion and a shortened portion are provided. Also in this case, unwanted waves can be suppressed as in the sixth embodiment.

The details of the thickness slip mode will be explained below. "Electrodes" in the IDT electrodes to be described later correspond to electrode fingers in the present invention. The supporting member in the following examples corresponds to the supporting substrate in the present invention. In the following description, the term "a certain member is made of a certain material" includes the case where a minute amount of impurity is included to such an extent that the electrical characteristics of the acoustic wave device are not significantly degraded.

FIG. 21(a) is a schematic perspective view showing the external appearance of an elastic wave device that utilizes thickness-shear mode bulk waves, and FIG. 21(b) is a plan view showing an electrode structure on a piezoelectric layer, FIG. 22 is a cross-sectional view of a portion taken along line AA in FIG. 21(a).

The acoustic wave device 1 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, but may be rotational Y-cut or X-cut. Although the thickness of the piezoelectric layer 2 is not particularly limited, it is preferably 40 nm or more and 1000 nm or less, more preferably 50 nm or more and 1000 nm or less, in order to effectively excite the thickness-shear mode. The piezoelectric layer 2 has first and second major surfaces 2a and 2b facing each other. Electrodes 3 and 4 are provided on the first main surface 2a. Here, the electrode 3 is an example of the "first electrode" and the electrode 4 is an example of the "second electrode". In FIGS. 21( a ) and 21 ( b ), the multiple electrodes 3 are multiple first electrode fingers connected to the first bus bar 5 . The multiple electrodes 4 are multiple second electrode fingers connected to the second bus bar 6 . The plurality of electrodes 3 and the plurality of electrodes 4 are interleaved with each other. Electrodes 3 and 4 have a rectangular shape and a length direction. The electrode 3 and the adjacent electrode 4 face each other in a direction perpendicular to the length direction. Both the length direction of the electrodes 3 and 4 and the direction orthogonal to the length direction of the electrodes 3 and 4 are directions crossing the thickness direction of the piezoelectric layer 2 . Therefore, it can be said that the electrode 3 and the adjacent electrode 4 face each other in the direction crossing the thickness direction of the piezoelectric layer 2 . Moreover, the length direction of the electrodes 3 and 4 may be interchanged with the direction orthogonal to the length direction of the electrodes 3 and 4 shown in FIGS. 21(a) and 21(b). That is, in FIGS. 21(a) and 21(b), the electrodes 3 and 4 may extend in the direction in which the first busbar 5 and the second busbar 6 extend. In that case, the first busbar 5 and the second busbar 6 extend in the direction in which the electrodes 3 and 4 extend in FIGS. 21(a) and 21(b). A plurality of pairs of structures in which an electrode 3 connected to one potential and an electrode 4 connected to the other potential are adjacent to each other are provided in a direction perpendicular to the length direction of the electrodes 3 and 4. there is Here, when the electrodes 3 and 4 are adjacent to each other, it does not mean that the electrodes 3 and 4 are arranged so as to be in direct contact with each other, but that the electrodes 3 and 4 are arranged with a gap therebetween. point to When the electrodes 3 and 4 are adjacent to each other, no electrodes connected to the hot electrode or the ground electrode, including the other electrodes 3 and 4, are arranged between the electrodes 3 and 4. FIG. The logarithms need not be integer pairs, but may be 1.5 pairs, 2.5 pairs, or the like. The center-to-center distance or pitch between the electrodes 3 and 4 is preferably in the range of 1 μm or more and 10 μm or less. Moreover, the width of the electrodes 3 and 4, that is, the dimension of the electrodes 3 and 4 in the facing direction is preferably in the range of 50 nm or more and 1000 nm or less, more preferably in the range of 150 nm or more and 1000 nm or less. Note that the center-to-center distance between the electrodes 3 and 4 means the distance between the center of the dimension (width dimension) of the electrode 3 in the direction orthogonal to the length direction of the electrode 3 and the distance between the center of the electrode 4 in the direction orthogonal to the length direction of the electrode 4. It is the distance connecting the center of the dimension (width dimension) of

In addition, since the Z-cut piezoelectric layer is used in the elastic wave device 1 , the direction perpendicular to the length direction of the electrodes 3 and 4 is the direction perpendicular 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 is substantially perpendicular (the angle formed by the direction perpendicular to the length direction of the electrodes 3 and 4 and the polarization direction is, for example, 90° ± 10°). within the range).

A supporting member 8 is laminated on the second main surface 2b side of the piezoelectric layer 2 with an insulating layer 7 interposed therebetween. The insulating layer 7 and the support member 8 have a frame shape and, as shown in FIG. 22, have through holes 7a and 8a. A cavity 9 is thereby formed. The cavity 9 is provided so as not to disturb the vibration of the excitation region C of the piezoelectric layer 2 . Therefore, the support member 8 is laminated on the second main surface 2b with the insulating layer 7 interposed therebetween at a position not overlapping the portion where at least one pair of electrodes 3 and 4 are provided. Note that the insulating layer 7 may not be provided. Therefore, the support member 8 can be directly or indirectly laminated to the second main surface 2b of the piezoelectric layer 2 .

The insulating layer 7 is made of silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon oxynitride and alumina can be used. The support member 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). It is desirable that the Si constituting the support member 8 has a high resistivity of 4 kΩcm or more. However, the support member 8 can also be constructed using an appropriate insulating material or semiconductor material.

Materials for the support member 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 electrodes 3, 4 and the first and second bus bars 5, 6 are made of appropriate metals or alloys such as Al, AlCu alloys. In this embodiment, the electrodes 3 and 4 and the first and second bus bars 5 and 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 electrodes 3 and the multiple electrodes 4 . More specifically, an AC voltage is applied between the first busbar 5 and the second busbar 6 . As a result, it is possible to obtain resonance characteristics using bulk waves in the thickness-shear mode excited in the piezoelectric layer 2 . Further, in the acoustic wave device 1, d/p is 0.0, where d is the thickness of the piezoelectric layer 2 and p is the center-to-center distance between any one of the pairs of electrodes 3 and 4 adjacent to each other. 5 or less. Therefore, the thickness-shear 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.

Since the elastic wave device 1 has the above configuration, even if the logarithm of the electrodes 3 and 4 is reduced in an attempt to reduce the size, the Q value is unlikely to decrease. This is because the propagation loss is small even if the number of electrode fingers in the reflectors on both sides is reduced. Moreover, the fact that the number of electrode fingers can be reduced is due to the fact that bulk waves in the thickness-shear mode are used. The difference between the Lamb wave used in the elastic wave device and the bulk wave in the thickness shear mode will be described with reference to FIGS. 23(a) and 23(b).

FIG. 23(a) is a schematic front cross-sectional view for explaining a Lamb wave propagating through a piezoelectric film of an elastic wave device as described in Japanese Unexamined Patent Publication No. 2012-257019. Here, waves propagate through the piezoelectric film 201 as indicated by arrows. Here, in the piezoelectric film 201, the first main surface 201a and the second main surface 201b face each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z direction. is. The X direction is the direction in which the electrode fingers of the IDT electrodes are arranged. As shown in FIG. 23(a), the Lamb wave propagates in the X direction as shown. Since it is a plate wave, although the piezoelectric film 201 as a whole vibrates, since the wave propagates in the X direction, reflectors are arranged on both sides to obtain resonance characteristics. Therefore, a wave propagation loss occurs, and the Q value decreases when miniaturization is attempted, that is, when the logarithm of the electrode fingers is decreased.

On the other hand, as shown in FIG. 23(b), in the elastic wave device 1, since the vibration displacement is in the thickness slip direction, the wave is generated on the first principal surface 2a and the second principal surface of the piezoelectric layer 2. 2b, ie, the Z direction, and resonate. 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, propagation loss is unlikely to occur even if the number of electrode fingers of the reflector is reduced. Furthermore, even if the number of electrode pairs consisting of the electrodes 3 and 4 is reduced in an attempt to promote miniaturization, the Q value is unlikely to decrease.

Note that the amplitude direction of the bulk wave in the thickness-shear mode is opposite between the first region 451 included in the excitation region C of the piezoelectric layer 2 and the second region 452 included in the excitation region C, as shown in FIG. Become. FIG. 24 schematically shows a bulk wave when a voltage is applied between the electrodes 3 and 4 so that the potential of the electrode 4 is higher than that of the electrode 3 . The first region 451 is a region of the excitation region C between the first main surface 2a and a virtual plane VP1 that is perpendicular to the thickness direction of the piezoelectric layer 2 and bisects the piezoelectric layer 2 . The second region 452 is a region of the excitation region C between the virtual plane VP1 and the second main surface 2b.

As described above, in the acoustic wave device 1, at least one pair of electrodes consisting of the electrodes 3 and 4 is arranged. The number of electrode pairs need not be plural. That is, it is sufficient that at least one pair of electrodes is provided.

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

FIG. 25 is a diagram showing resonance characteristics of the elastic wave device shown in FIG. The design parameters of the elastic wave device 1 with this resonance characteristic are as follows.

Piezoelectric layer 2: LiNbO ₃ with Euler angles (0°, 0°, 90°), thickness = 400 nm.
When viewed in the direction orthogonal to the length direction of the electrodes 3 and 4, the length of the region where the electrodes 3 and 4 overlap, that is, the length of the excitation region C = 40 μm, the number of pairs of electrodes 3 and 4 = 21 pairs, center distance between electrodes = 3 µm, width of electrodes 3 and 4 = 500 nm, d/p = 0.133.
Insulating layer 7: Silicon oxide film with a thickness of 1 μm.
Support member 8: Si.

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

In this embodiment, the inter-electrode distances of the electrode pairs consisting of the electrodes 3 and 4 are all the same in a plurality of pairs. That is, the electrodes 3 and 4 were arranged at equal pitches.

As is clear from FIG. 25, good resonance characteristics with a fractional 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 electrodes 3 and 4 is p, in the present embodiment, d/p is more preferably 0.5 or less, as described above. is less than or equal to 0.24. This will be explained with reference to FIG.

A plurality of elastic wave devices were obtained by changing d/p in the same manner as the elastic wave device that obtained the resonance characteristics shown in FIG. FIG. 26 is a diagram showing the relationship between this d/p and the fractional bandwidth of the acoustic wave device as a resonator.

As is clear from FIG. 26, when d/p>0.5, even if d/p is adjusted, the specific bandwidth is less than 5%. On the other hand, when d/p≤0.5, the specific bandwidth can be increased to 5% or more by changing d/p within that range. can be configured. Further, 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 mode bulk wave.

FIG. 27 is a plan view of an elastic wave device that utilizes thickness-shear mode bulk waves. In elastic wave device 80 , a pair of electrodes having electrode 3 and electrode 4 is provided on first main surface 2 a of piezoelectric layer 2 . Note that K in FIG. 27 is the crossing width. As described above, in the elastic wave device of the present invention, the number of pairs of electrodes may be one. Even in this case, if d/p is 0.5 or less, bulk waves in the thickness-shear mode can be effectively excited.

In the elastic wave device 1, preferably, in the plurality of electrodes 3 and 4, the adjacent excitation region C is an overlapping region when viewed in the direction in which any of the adjacent electrodes 3 and 4 are facing each other. It is desirable that the metallization ratio MR of the mating electrodes 3, 4 satisfy MR≤1.75(d/p)+0.075. In that case, spurious can be effectively reduced. This will be described with reference to FIGS. 28 and 29. FIG. FIG. 28 is a reference diagram showing an example of resonance characteristics of the elastic wave device 1. As shown in FIG. 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. 21(b). In the electrode structure of FIG. 21(b), when focusing attention on the pair of electrodes 3 and 4, it is assumed that only the pair of electrodes 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 3 and the electrode 4 overlap each other when the electrodes 3 and 4 are viewed in a direction perpendicular to the length direction of the electrodes 3 and 4, i.e., in a facing direction. 3 and an overlapping area between the electrodes 3 and 4 in the area between the electrodes 3 and 4 . The area of the electrodes 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 electrodes are provided, MR may be the ratio of the metallization portion included in the entire excitation region to the total area of the excitation region.

FIG. 29 is a diagram showing the relationship between the fractional bandwidth and the amount of phase rotation of the spurious impedance normalized by 180 degrees as the magnitude of the spurious when a large number of acoustic wave resonators are configured according to this embodiment. be. The ratio band was adjusted by changing the film thickness of the piezoelectric layer and the dimensions of the electrodes. Also, FIG. 29 shows the results when a Z-cut LiNbO ₃ piezoelectric layer is used, but the same tendency is obtained when piezoelectric layers with other cut angles are used.

In the area surrounded by ellipse J in FIG. 29, the spurious is as large as 1.0. As is clear from FIG. 29, when the fractional band exceeds 0.17, that is, when it exceeds 17%, even if a large spurious with a spurious level of 1 or more changes the parameters constituting the fractional band, the passband appear within. That is, as in the resonance characteristics shown in FIG. 28, 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 electrodes 3 and 4, the spurious response can be reduced.

FIG. 30 is a diagram showing the relationship between d/2p, metallization ratio MR, and fractional bandwidth. In the elastic wave device described above, various elastic wave devices having different d/2p and MR were constructed, and the fractional bandwidth was measured. The hatched portion on the right side of the dashed line D in FIG. 30 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. 31 is a diagram showing a map of fractional bandwidth with respect to Euler angles (0°, θ, ψ) of LiNbO ₃ when d/p is brought infinitely close to 0. FIG. The hatched portion in FIG. 31 is a region where a fractional bandwidth of at least 5% or more is obtained, and when the range of the region is approximated, 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. The same applies when the piezoelectric layer 2 is a lithium tantalate layer.

FIG. 32 is a front cross-sectional view of an elastic wave device having an acoustic multilayer film.

In the acoustic wave device 81 , an acoustic multilayer film 82 is laminated on the second main surface 2 b of the piezoelectric layer 2 . The acoustic multilayer film 82 has a laminated structure of low acoustic impedance layers 82a, 82c, 82e with relatively low acoustic impedance and high acoustic impedance layers 82b, 82d with relatively high acoustic impedance. When the acoustic multilayer film 82 is used, the thickness shear mode bulk wave can be confined in the piezoelectric layer 2 without using the cavity 9 in the elastic wave device 1 . Also in the elastic wave device 81, by setting d/p to 0.5 or less, it is possible to obtain resonance characteristics based on bulk waves in the thickness-shear mode. In the acoustic multilayer film 82, the number of lamination of the low acoustic impedance layers 82a, 82c, 82e and the high acoustic impedance layers 82b, 82d is not particularly limited. At least one of the high acoustic impedance layers 82b, 82d should be arranged farther from the piezoelectric layer 2 than the low acoustic impedance layers 82a, 82c, 82e.

The low acoustic impedance layers 82a, 82c, 82e and the high acoustic impedance layers 82b, 82d can be made of appropriate materials as long as the acoustic impedance relationship is satisfied. Examples of materials for the low acoustic impedance layers 82a, 82c, 82e include silicon oxide and silicon oxynitride. Materials for the high acoustic impedance layers 82b and 82d include alumina, silicon nitride, and metals.

In the elastic wave devices of the first to sixth embodiments and modifications, for example, an acoustic multilayer film 82 shown in FIG. 32 may be provided between the support substrate and the piezoelectric layer. In this case, low acoustic impedance layers and high acoustic impedance layers may be alternately laminated in the acoustic multilayer film 82 . The acoustic multilayer film 82 may be an acoustic reflector in the elastic wave device.

In the elastic wave devices of the first to sixth embodiments and modifications using thickness shear mode bulk waves, as described above, d/p is preferably 0.5 or less, and 0.24 The following are more preferable. Thereby, even better resonance characteristics can be obtained. Furthermore, in the crossover regions of the elastic wave devices of the first to sixth embodiments and modifications using thickness shear mode bulk waves, MR≤1.75(d/p)+0. 075 is preferred. In this case, spurious can be suppressed more reliably.

The piezoelectric layer in the elastic wave devices of the first to sixth embodiments and modifications using thickness-shear mode bulk waves is preferably a lithium niobate layer or a lithium tantalate layer. The Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the above formula (1), formula (2), or formula (3). is preferred. In this case, the fractional bandwidth can be widened sufficiently.

REFERENCE SIGNS LIST 1 elastic wave device 2 piezoelectric layers 2a, 2b first and second main surfaces 3, 4 electrodes 5, 6 first and second bus bars 7 insulating layer 7a through hole 8 supporting member 8a Through hole 9 Hollow portion 10 Acoustic wave device 10a Hollow portion 11 IDT electrodes 11a, 11b First and second surfaces 11c Side surface 12 Piezoelectric substrate 13 Supporting member 14 Piezoelectric layers 14a, 14b First and second main surfaces 15 Insulating layer 16 Supporting substrates 24 and 24A Mass adding film 24a Stepped portions 26 and 27 First and second bus bars 28 and 29 First and second electrodes Fingers 34, 34A, 34B Mass adding film 34a Step portion 44 Mass adding film 53 Dielectric films 54, 64 Mass adding films 80, 81 Elastic wave device 82 Acoustic multilayer films 82a, 82c, 82e Low Acoustic impedance layers 82b, 82d High acoustic impedance layer 104 Mass addition film 201 Piezoelectric films 201a, 201b First and second main surfaces 451, 452 First and second regions B Arrow C Excitation region E1 , E2 First and second edge regions F Crossing regions G1 and G2 First and second gap regions H Central regions O1 and O2 First and second points VP1 Virtual plane

Claims (14)

1. a support member including a support substrate;
   a piezoelectric layer provided on the support member and being a lithium niobate layer or a lithium tantalate layer;
   an IDT electrode provided on the piezoelectric layer and having a pair of bus bars and a plurality of electrode fingers;
   with
   an acoustic reflection portion is provided on the support member, and the acoustic reflection portion overlaps at least a portion of the IDT electrode in a plan view;
   where d is the thickness of the piezoelectric layer and p is the center-to-center distance between the adjacent electrode fingers, d/p is 0.5 or less,
   Some of the plurality of electrode fingers are connected to one bus bar of the IDT electrode, and the remaining electrode fingers of the plurality of electrode fingers are connected to the other bus bar, the plurality of electrode fingers connected to one of the bus bars and the plurality of electrode fingers connected to the other bus bar are inserted into each other,
   A direction in which the adjacent electrode fingers face each other is defined as an electrode finger facing direction, and a region where the adjacent electrode fingers overlap each other when viewed from the electrode finger facing direction is an intersecting region. When the extending direction is defined as the electrode finger extending direction, the crossing area has a central area and a pair of edge areas arranged to sandwich the central area in the electrode finger extending direction,
   At least one mass addition film is provided in at least the edge region, and the length of the mass addition film is defined as a dimension along the electrode finger extending direction of the mass addition film. When arbitrary two points in the electrode finger facing direction are defined as a first point and a second point, the length of the mass addition film at at least one set of the first point and the second point is Acoustic wave devices that are different from each other.
2. The elastic wave device according to claim 1, wherein the at least one mass addition film is provided in each of at least both of the edge regions.
3. Each of the plurality of electrode fingers has a first surface and a second surface facing each other, and the second surface of the first surface and the second surface is the surface on the piezoelectric layer side. 3. The acoustic wave device according to claim 1, wherein said at least one mass adding film is provided on said first surface of said plurality of electrode fingers.
4. Each of the plurality of electrode fingers has a first surface and a second surface facing each other, and the second surface of the first surface and the second surface is the surface on the piezoelectric layer side. 3. The acoustic wave device according to claim 1, wherein said at least one mass adding film is provided between said second surface of said plurality of electrode fingers and said piezoelectric layer.
5. 3. The elasticity according to claim 1, wherein a dielectric film is provided on said piezoelectric layer so as to cover said IDT electrodes, and said at least one mass adding film is provided on said dielectric film. wave equipment.
6. The elastic wave device according to claim 5, wherein the mass addition film is made of metal.
7. 6. The mass addition film according to any one of claims 1 to 5, wherein at least one dielectric selected from the group consisting of silicon oxide, tungsten oxide, niobium pentoxide, tantalum oxide and hafnium oxide is used. Elastic wave device according to.
8. 8. The mass-applying film according to claim 1, wherein the mass-applying film is continuously provided so as to overlap the plurality of electrode fingers and regions between the electrode fingers in a plan view. Elastic wave device.
9. each of the plurality of electrode fingers has a first surface and a second surface facing each other and a side surface connected to the first surface and the second surface; and the second surface of the second surfaces is a surface on the piezoelectric layer side,
   A plurality of the mass addition films are provided on the side surfaces of the electrode fingers, the plurality of mass addition films are made of metal, and the width of the electrode fingers is widened at portions where the mass addition films are provided. The acoustic wave device according to claim 1 or 2, wherein
10. 2. A region located between said crossing region and said pair of bus bars is a pair of gap regions, and said at least one mass adding film is provided over said edge region and said gap region. 10. The elastic wave device according to any one of 1 to 9.
11. The elastic wave device according to any one of claims 1 to 10, wherein the acoustic reflection portion is a hollow portion provided in the support member.
12. The elastic wave device according to any one of claims 1 to 11, wherein d/p is 0.24 or less.
13. 13. The method according to claim 1, wherein MR≦1.75(d/p)+0.075 is satisfied, where MR is a metallization ratio of the plurality of electrode fingers to the intersecting region. Elastic wave device.
14. Euler angles (φ, θ, ψ) of the lithium niobate layer or the lithium tantalate layer as the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3). Item 14. The elastic wave device according to any one of items 1 to 13.
    (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)

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