Elastic wave device

Abstract

The purpose of the present invention is to provide an elastic wave device capable of suppressing deterioration of electrical characteristics.　An elastic wave device 10 according to the present invention includes: a support substrate 3; an intermediate layer 5 provided on the support substrate 3; a piezoelectric layer 6 provided on the intermediate layer 5; and an IDT electrode 7 provided on the piezoelectric layer 6 and having a plurality of electrode fingers. When the thickness of the portion of the piezoelectric layer 6 where the IDT electrode 7 is provided is d, and the distance between the centers of the adjacent electrode fingers is p, d / p is 0.5 or less. A cavity part 2a is provided between the piezoelectric layer 6 and the support substrate 3. The cavity part 2a overlaps the IDT electrode 7 in a plan view. The elastic wave device 10 further includes any one film of a silicon nitride film 4, an amorphous silicon film, and a polycrystalline silicon film, at least a part of which is provided between the support substrate 3 and the intermediate layer 5, and which faces the piezoelectric layer 6 across at least one of the cavity part 2a and the intermediate layer 5.

Description

Elastic Wave Device

[0001] The present invention relates to an acoustic wave device.

[0002] Acoustic wave devices have been widely used in filters for mobile phones and the like. Recently, an acoustic wave device using thickness-shear mode bulk waves has been proposed, as described in Patent Document 1 below. In this acoustic wave device, an intermediate layer is provided on a support substrate. A piezoelectric layer is provided on the intermediate layer. A functional electrode is provided on the piezoelectric layer. The functional electrode has multiple pairs of electrode fingers. The paired electrode fingers face each other on the piezoelectric layer and are connected to different potentials. By applying an AC voltage between the electrode fingers, thickness-shear mode bulk waves are excited.

[0003] The intermediate layer has a recess. The piezoelectric layer covers the recess. This provides a space between the piezoelectric layer and the support substrate. The space is located in a portion that overlaps with the functional electrode in a plan view.

[0004] International Publication No. 2022 / 210809

[0005] In Patent Document 1, silicon oxide is cited as an example of a material for the intermediate layer, and Si is cited as an example of a material for the support substrate. When a support substrate and an intermediate layer made of such materials are stacked, a low-resistance layer may be formed due to charges contained in the intermediate layer or charges captured by interface states at the interface of the support substrate.

[0006] However, in the acoustic wave device of Patent Document 1, a cavity is provided between the support substrate and the portion of the piezoelectric layer where the functional electrode is provided. That is, a cavity is provided between the support substrate and the portion where thickness-shear mode bulk waves are generated. Therefore, even if a low-resistivity layer is formed, it is thought that the effect on the electrical characteristics of the acoustic wave device is suppressed. However, the present inventors have found that even when a cavity is provided, the formation of a low-resistivity layer may still degrade the electrical characteristics of the acoustic wave device.

[0007] An object of the present invention is to provide an acoustic wave device capable of suppressing deterioration of electrical characteristics.

[0008] The elastic wave device according to the present invention includes a support substrate, an intermediate layer provided on the support substrate, a piezoelectric layer provided on the intermediate layer, and an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, wherein d / p is 0.5 or less, where d is the thickness of a portion of the piezoelectric layer where the IDT electrode is provided, and p is the center-to-center distance between adjacent electrode fingers. The elastic wave device further includes one of a silicon nitride film, an amorphous silicon film, and a polycrystalline silicon film, the cavity overlapping the IDT electrode in a planar view, at least a portion of the cavity overlapping the support substrate and the intermediate layer, and facing the piezoelectric layer with at least one of the cavity and the intermediate layer sandwiched therebetween.

[0009] According to an acoustic wave device according to a preferred embodiment of the present invention, deterioration of electrical characteristics can be suppressed.

[0010] FIG. 1 is a schematic front cross-sectional view of an elastic wave device according to a first preferred embodiment of the present invention. FIG. 2 is a schematic plan view of an elastic wave resonator according to the first preferred embodiment of the present invention. FIG. 3 is a schematic front cross-sectional view of an elastic wave device according to a modified preferred embodiment of the first preferred embodiment of the present invention. FIG. 4 is a schematic front cross-sectional view of an elastic wave device according to a first comparative example. FIG. 5 is a diagram showing phase characteristics in the first comparative example. FIG. 6 is a diagram showing phase characteristics in a modified preferred embodiment of the first preferred embodiment of the present invention. FIG. 7 is a schematic front cross-sectional view of an elastic wave device according to a second preferred embodiment of the present invention. FIG. 8 is a diagram showing the relationship between d / p and the fractional bandwidth of an elastic wave resonator. FIG. 9 is a diagram showing the relationship between the fractional bandwidth and the magnitude of normalized spurious signals in an elastic wave resonator. FIG. 10 is a diagram showing the relationship between d / p, the metallization ratio MR, and the fractional bandwidth. FIG. 11 is a diagram showing the relationship between d / p and the metallization ratio MR and the fractional bandwidth of a LiNbO resonator when d / p approaches 0. ３ FIG. 10 is a diagram showing a map of fractional bandwidths versus Euler angles (0°, θ, ψ) of the .lambda.

[0011] The present invention will be clarified below by describing specific embodiments of the present invention with reference to the drawings.

[0012] It should be noted that the embodiments described in this specification are merely examples, and partial substitution or combination of configurations is possible between different embodiments.

[0013] Fig. 1 is a schematic front cross-sectional view of an elastic wave device according to a first preferred embodiment of the present invention. In Fig. 1, an IDT (Interdigital Transducer) electrode, which will be described later, is shown as a simplified rectangle with two diagonal lines added. The same applies to the other schematic front cross-sectional views.

[0014] The elastic wave device 10 of this preferred embodiment is a filter device having a plurality of resonators. Specifically, the plurality of resonators of the elastic wave device 10 are all elastic wave resonators 1. However, this is not a limitation. The plurality of resonators of the elastic wave device 10 may include at least one elastic wave resonator 1.

[0015] An elastic wave device according to the present invention may be, for example, an element having a plurality of resonators including an elastic wave resonator and used as part of a filter device, or may be composed of only one elastic wave resonator.

[0016] The specific configuration of acoustic wave device 10 will be described below. As shown in FIG. 1 , acoustic wave device 10 includes a piezoelectric substrate 2 and a plurality of IDT electrodes 7. Piezoelectric substrate 2 is a substrate having piezoelectric properties. Specifically, piezoelectric substrate 2 includes a support substrate 3, a silicon nitride film 4, an intermediate layer 5, and a piezoelectric layer 6. The silicon nitride film 4 is provided on support substrate 3. The intermediate layer 5 is provided on silicon nitride film 4. The piezoelectric layer 6 is provided on intermediate layer 5.

[0017] In this embodiment, the support substrate 3 is a silicon substrate. The material of the support substrate 3 is not limited to silicon, and for example, quartz crystal or glass can also be used. In this embodiment, the intermediate layer 5 is a silicon oxide layer. The material of the intermediate layer 5 is not limited to silicon oxide, and for example, tantalum oxide can also be used. The piezoelectric layer 6 is, for example, LiNbO ３ Lithium niobate such as LiTaO ３ In this specification, when a certain component is made of a certain material, it also includes the case where a trace amount of impurities is contained to the extent that the electrical characteristics of the acoustic wave device are not significantly deteriorated.

[0018] A plurality of cavities 2a are provided in the intermediate layer 5. Specifically, each cavity 2a is a hollow portion provided in the intermediate layer 5. In the portion where the cavities 2a are provided, the silicon nitride film 4 and the piezoelectric layer 6 face each other with both the intermediate layer 5 and the cavities 2a sandwiched between them. However, the cavities 2a may be formed, for example, by a recess provided in the intermediate layer 5 being blocked by either the piezoelectric layer 6 or the silicon nitride film 4. Alternatively, the cavities 2a may be formed by a through-hole provided in the intermediate layer 5 being blocked by both the piezoelectric layer 6 and the silicon nitride film 4. Note that a portion of the cavities 2a may be connected to the outside via a through-hole or the like.

[0019] 1, in the portion where the cavity 2a is provided, the silicon nitride film 4 and the piezoelectric layer 6 face each other with both the intermediate layer 5 and the cavity 2a sandwiched between them. On the other hand, in the portion where the cavity 2a is not provided, the silicon nitride film 4 and the piezoelectric layer 6 face each other with the intermediate layer 5 sandwiched between them. As such, in this embodiment, the silicon nitride film 4 and the piezoelectric layer 6 face each other with at least the intermediate layer 5 sandwiched between them.

[0020] However, as described above, the cavity 2a may be formed by blocking a through-hole provided in the intermediate layer 5 with both the piezoelectric layer 6 and the silicon nitride film 4. In this case, in the portion where the cavity 2a is provided, the silicon nitride film 4 and the piezoelectric layer 6 face each other with the cavity 2a in between, without sandwiching the intermediate layer 5. In the present invention, it is sufficient that the silicon nitride film 4 and the piezoelectric layer 6 face each other with at least one of the cavity 2a and the intermediate layer 5 in between.

[0021] In the present invention, the film corresponding to the silicon nitride film 4 may be an amorphous silicon film or a polycrystalline silicon film.

[0022] The piezoelectric layer 6 has a first main surface 6 a and a second main surface 6 b. The first main surface 6 a and the second main surface 6 b face each other. Of the first main surface 6 a and the second main surface 6 b, the second main surface 6 b is located on the support substrate 3 side.

[0023] A plurality of IDT electrodes 7 are provided on the first principal surface 6a of the piezoelectric layer 6. In a plan view, the plurality of IDT electrodes 7 overlap with the cavity portions 2a of the piezoelectric substrate 2. In this specification, a plan view refers to a view from a direction corresponding to the top in FIG. 1 along the stacking direction of the support substrate 3, the piezoelectric layer 6, and other layers in the piezoelectric substrate 2. In FIG. 1, for example, the piezoelectric layer 6 side is the top of the support substrate 3 side and the piezoelectric layer 6 side. Furthermore, in this specification, a plan view is synonymous with a view from the principal surface facing direction. The principal surface facing direction is the direction in which the first principal surface 6a and the second principal surface 6b of the piezoelectric layer 6 face each other. More specifically, the principal surface facing direction is, for example, the normal direction of the first principal surface 6a.

[0024] Each IDT electrode 7 overlaps a different cavity 2a in plan view. Note that a plurality of IDT electrodes 7 may overlap the same cavity 2a in plan view.

[0025] Each acoustic wave resonator 1 is composed of a piezoelectric substrate 2 and an IDT electrode 7. A specific configuration of the IDT electrode 7 will be described below.

[0026] 2 is a schematic plan view of the acoustic wave resonator according to the first preferred embodiment, in which a dielectric film and wiring, which will be described later, are omitted.

[0027] The IDT electrode 7 has a pair of bus bars and a plurality of electrode fingers. The pair of bus bars is specifically a first bus bar 16 and a second bus bar 17. The first bus bar 16 and the second bus bar 17 face each other. The plurality of electrode fingers is specifically a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. One end of each of the plurality of first electrode fingers 18 is connected to the first bus bar 16. One end of each of the plurality of second electrode fingers 19 is connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interdigitated with each other. The first electrode fingers 18 and the second electrode fingers 19 are connected to different potentials. The IDT electrode 7 may be made of a single-layer metal film or may be made of a laminated metal film.

[0028] Hereinafter, the first electrode fingers 18 and the second electrode fingers 19 may be collectively referred to simply as electrode fingers. The direction in which the electrode fingers extend is referred to as the electrode finger extension direction, and the direction perpendicular to the electrode finger extension direction is referred to as the electrode finger perpendicular direction.

[0029] The acoustic wave resonator 1 is configured to utilize thickness-shear mode bulk waves. More specifically, when viewed from the electrode finger orthogonal direction, the excitation region C is a region where adjacent electrode fingers overlap and between the centers of the adjacent electrode fingers. The acoustic wave resonator 1 includes multiple excitation regions C. In FIG. 2 , one of the multiple excitation regions C is indicated by a dashed dotted line. By applying an AC voltage to the IDT electrode 7, thickness-shear mode bulk waves are excited in each excitation region C. Note that the excitation region C is a region of the piezoelectric layer 6 that is defined based on the configuration of the IDT electrode 7.

[0030] When the thickness of the portion of the piezoelectric layer 6 where the IDT electrode 7 is provided is d and the center-to-center distance between adjacent electrode fingers is p, d / p is 0.5 or less. This allows for suitable excitation of bulk waves in thickness-shear mode. Each elastic wave resonator 1 shown in FIG. 1 is configured to utilize bulk waves in thickness-shear mode. Note that the design parameters and thickness d of the IDT electrode 7 may differ among multiple elastic wave resonators 1 depending on the desired characteristics.

[0031] A plurality of wirings 13 are provided on the first main surface 6a of the piezoelectric layer 6. The plurality of IDT electrodes 7 are electrically connected to one another by the wirings 13. Each of the plurality of wirings 13 is made of a laminated metal film. Specifically, each of the plurality of wirings 13 has a first wiring layer 13a and a second wiring layer 13b. The first wiring layer 13a is provided on the first main surface 6a of the piezoelectric layer 6. The second wiring layer 13b is provided on the first wiring layer 13a. Note that the number of layers in the plurality of wirings 13 is not limited to two. Each of the plurality of wirings 13 may be made of a laminated metal film of three or more layers, or may be made of a single-layer metal film.

[0032] At least one of the wires 13 includes a pad portion 14. In this embodiment, the pad portion 14 is provided directly on the first main surface 6a of the piezoelectric layer 6. The pad portion 14 is made of the second wiring layer 13b. The pad portion 14 may also be made of a laminated metal film of the first wiring layer 13a and the second wiring layer 13b.

[0033] A pad electrode 15 is provided on the pad portion 14. A bump 9 is provided on the pad electrode 15. The bump 9 is made of Au. However, the material of the bump 9 is not limited to Au. Alternatively, a conductive adhesive or the like may be provided instead of the bump 9.

[0034] Note that at least one pad portion 14, at least one pad electrode 15, and at least one bump 9 are also provided in portions not shown. The acoustic wave device 10 is electrically connected to the outside via the wiring 13, the pad electrode 15, and the bump 9.

[0035] A dielectric film 8 is provided on the first main surface 6a of the piezoelectric layer 6 so as to cover the IDT electrodes 7. This protects the IDT electrodes 7. Therefore, the IDT electrodes 7 are less likely to be damaged. In this embodiment, the dielectric film 8 covers a portion of the first wiring layer 13a of the wirings 13. However, the dielectric film 8 does not necessarily have to be in contact with the first wiring layer 13a. Examples of materials that can be used for the dielectric film 8 include silicon oxide, silicon nitride, and silicon oxynitride. The dielectric film 8 does not necessarily have to be provided.

[0036] As shown in FIG. 1 , through holes are provided in a portion of the piezoelectric substrate 2 and the dielectric film 8 so as to reach the cavity 2a. Specifically, a through hole 5c is provided in the intermediate layer 5 in a portion between the cavity 2a and the piezoelectric layer 6. A through hole 6c is provided in the piezoelectric layer 6. A through hole 8c is provided in the dielectric film 8. A through hole, in which the through holes 5c, 6c, and 8c are connected, reaches the cavity 2a. Note that similar through holes are also provided in portions of the elastic wave device 10 (not shown). These through holes are provided to form the cavity 2a by etching during the manufacture of the elastic wave device 10. However, these through holes are not necessarily provided.

[0037] The present invention is characterized by the following configuration: 1) A cavity 2a is provided between the piezoelectric layer 6 and the support substrate 3, and the cavity 2a overlaps the IDT electrode 7 in a plan view. 2) A silicon nitride film 4 is provided between the support substrate 3 and the intermediate layer 5, and faces the piezoelectric layer 6 with at least one of the cavity 2a and the intermediate layer 5 sandwiched therebetween. Note that an amorphous silicon film or a polycrystalline silicon film may be provided instead of the silicon nitride film 4. This configuration can suppress deterioration of the electrical characteristics of the elastic wave device 10. Details of this configuration are described below by comparing a modified example of the first embodiment with a first comparative example.

[0038] Fig. 3 is a schematic front cross-sectional view of an elastic wave device according to a modified example of the first preferred embodiment of the present invention, and Fig. 4 is a schematic front cross-sectional view of an elastic wave device according to a first comparative example.

[0039] An elastic wave device 10A according to a modification of the first embodiment shown in FIG. 3 is a two-port elastic wave resonator. In elastic wave device 10A, the layer structure of piezoelectric substrate 2A is the same as the layer structure of piezoelectric substrate 2 in the first embodiment. IDT electrodes 7A and 7B are provided on a first main surface 6a of a piezoelectric layer 6 of piezoelectric substrate 2A. IDT electrodes 7A and 7B overlap cavity 2a in a plan view.

[0040] 4 differs from the modified example of the first embodiment in that it does not include the silicon nitride film 4. The phase characteristics of the modified example of the first embodiment and the first comparative example were compared.

[0041] Fig. 5 is a diagram showing phase characteristics in a first comparative example, and Fig. 6 is a diagram showing phase characteristics in a modified example of the first embodiment.

[0042] As shown in Fig. 5, in the first comparative example, the phase is significantly different from -90° between 1250 MHz and 7500 MHz. In contrast, in the modified example of the first embodiment shown in Fig. 6, the phase is close to -90° between 1250 MHz and 7500 MHz. As such, in this modified example, deterioration of the electrical characteristics is suppressed. As in this modified example, deterioration of the electrical characteristics can also be suppressed in each elastic wave resonator 1 of the first embodiment shown in Fig. 1.

[0043] 4 , the acoustic wave device of the first comparative example has a cavity 2 a in the area overlapping with the IDT electrodes 7A and 7B in a plan view. In this case, the cavity 2 a blocks the path of electron movement between the IDT electrodes 7A and 7B and the support substrate 3. Therefore, even if a low-resistance layer is formed, it is thought that the effect on the electrical characteristics is suppressed when a thickness-shear mode bulk wave is excited.

[0044] In response to this, the present inventors have found that the formation of a low-resistance layer may cause charges accumulated in cavity 2 a to migrate through intermediate layer 5, thereby degrading the electrical characteristics of the acoustic wave resonator. Specifically, the present inventors have found that the degradation of the electrical characteristics of the first comparative example shown in FIG. 5 is caused by the above-described charge migration. In the first embodiment and its modifications shown in FIGS. 1 and 3 , silicon nitride film 4 is provided between support substrate 3 and intermediate layer 5. This can prevent a low-resistance layer from being formed between support substrate 3 and intermediate layer 5. This can prevent degradation of the electrical characteristics of the acoustic wave device.

[0045] 1, the IDT electrode 7 and the cavity 2a overlap in plan view, so that the energy of the elastic waves can be effectively confined to the piezoelectric layer 6. This effectively increases the Q value of each elastic wave resonator 1. Similarly, the Q value can be effectively increased in the modification of the first embodiment.

[0046] It should be noted that even when an amorphous silicon film or a polycrystalline silicon film is provided instead of the silicon nitride film 4, it is possible to prevent a low-resistance layer from being formed between the support substrate 3 and the intermediate layer 5. In the present invention, any one of the silicon nitride film 4, amorphous silicon film, and polycrystalline silicon film may be provided between the support substrate 3 and the intermediate layer 5, and may face the piezoelectric layer 6 with at least one of the cavity 2a and the intermediate layer 5 sandwiched therebetween. This makes it possible to prevent deterioration of the electrical characteristics and effectively increase the Q value.

[0047] FIG. 7 is a schematic front cross-sectional view of an elastic wave device according to a second preferred embodiment of the present invention.

[0048] This embodiment differs from the first embodiment in that the silicon nitride film 4 faces a cavity 22a in the piezoelectric substrate 22. In this embodiment, the cavity 22a is formed by providing the silicon nitride film 4 so as to close a recess provided in the intermediate layer 5. Except for the above points, the elastic wave device 20 of this embodiment has a similar configuration to the elastic wave device 10 of the first embodiment.

[0049] In a configuration in which silicon nitride film 4 is removed from the second embodiment, support substrate 3 and intermediate layer 5 are not stacked in the portion that overlaps IDT electrode 7 in a plan view. The inventors have found that even in this case, charges accumulated in cavity 2 a may move through the portion of intermediate layer 5 facing cavity 2 a, thereby degrading the electrical characteristics of the acoustic wave resonator.

[0050] In contrast, in the second embodiment, the silicon nitride film 4 is provided between the support substrate 3 and the intermediate layer 5, and faces the piezoelectric layer 6 with at least one of the cavity 2 a and the intermediate layer 5 sandwiched therebetween. As a result, in the second embodiment, as in the first embodiment, deterioration of the electrical characteristics of the elastic wave device 20 can be suppressed. In addition, the Q value can be effectively increased.

[0051] A preferred configuration of the present invention will be described below with reference to Fig. 1. However, the following preferred configuration can also be applied to configurations of the present invention other than the first embodiment.

[0052] The stress of silicon nitride film 4 is preferably −300 MPa or more and 50 MPa or less. Acoustic wave device 10 is obtained, for example, by dividing a wafer having a plurality of acoustic wave elements formed thereon. The wafer is divided into a plurality of piezoelectric substrates 2. Therefore, the wafer used in manufacturing acoustic wave device 10 has silicon nitride film 4, just like piezoelectric substrate 2. Furthermore, when the stress of silicon nitride film 4 is within the above range, warping of the wafer can be suppressed. Therefore, wafers can be transported efficiently during the manufacturing process of acoustic wave device 10, thereby improving productivity.

[0053] In addition, when the stress of silicon nitride film 4 is −300 MPa or more and 50 MPa or less, it is easy to control the stress in acoustic wave device 10 as a whole.

[0054] The thickness of silicon nitride film 4 is preferably 30 nm or more and 250 nm or less. This more reliably ensures that the stress of silicon nitride film 4 is −300 MPa or more and 50 MPa or less. The thickness of silicon nitride film 4 is more preferably 50 nm or more and 250 nm or less, and even more preferably 50 nm or more and 200 nm or less. In this case, productivity can be more reliably improved. In addition, stress can be more easily controlled throughout acoustic wave device 10.

[0055] Furthermore, because silicon nitride film 4 itself has high strength, when the thickness of silicon nitride film 4 is within the above range, the strength of elastic wave device 10 can be sufficiently high even when the height of elastic wave device 10 is reduced by reducing the thickness of support substrate 3 or a component other than support substrate 3. Note that the Si / N composition ratio in silicon nitride film 4 is desirably 0.95 or greater. This facilitates control of film thickness and stress. Here, the Si / N composition ratio is the composition ratio of elements, i.e., the composition ratio of Si to N.

[0056] In the first and second embodiments, where d is the thickness of the portion of the piezoelectric layer 6 where the IDT electrode 7 is provided and p is the center-to-center distance between adjacent electrode fingers, d / p is 0.5 or less. It is preferable that d / p is 0.24 or less. This allows thickness-shear mode bulk waves to be more effectively excited and enables the value of the fractional bandwidth of the elastic wave resonator to be sufficiently large. The fractional bandwidth is expressed as (|fa-fr| / fr)×100[%], where fr is the resonant frequency and fa is the antiresonant frequency.

[0057] FIG. 8 is a graph showing the relationship between d / p and the bandwidth ratio of an elastic wave resonator.

[0058] As is clear from Figure 8, when d / p > 0.5, the fractional bandwidth is less than 5%. In contrast, when d / p ≤ 0.5, the fractional bandwidth can be increased to 5% or more. This increases the electromechanical coupling coefficient of the thickness-shear mode bulk wave. When d / p ≤ 0.24, the fractional bandwidth can be increased to 7% or more. This effectively increases the electromechanical coupling coefficient of the thickness-shear mode bulk wave.

[0059] When the metallization ratio of the electrode fingers to the excitation region C is MR, it is preferable to satisfy MR≦1.75(d / p)+0.075. In this case, the value of the fractional bandwidth of the acoustic wave resonator does not become too large, and spurious emissions between the resonant frequency and the antiresonant frequency can be suppressed. Details of this are described below.

[0060] In this specification, the metallization ratio MR of the electrode fingers to the excitation region C is the ratio of the portion of the piezoelectric layer 6 that is covered with the metal constituting the electrode fingers to the excitation region C in a plan view. Specifically, the metallization ratio MR is the ratio of the area of ​​the first electrode fingers 18 and the second electrode fingers 19 in the excitation region C to the area of ​​the excitation region C in a plan view. When the width of the electrode fingers located in the excitation region C is constant, the metallization ratio MR can also be calculated by dividing the sum of the widths of the electrode fingers located in the excitation region C by the dimension of the excitation region C in the direction perpendicular to the electrode fingers. The width of the electrode fingers is the dimension of the electrode fingers in the direction perpendicular to the electrode fingers.

[0061] Fig. 9 is a diagram showing the relationship between the relative bandwidth of an elastic wave resonator and the magnitude of normalized spurious. Fig. 9 shows the results of measuring the amount of phase rotation of spurious every time the relative bandwidth is changed by changing the thickness of the piezoelectric layer and the dimensions of the electrode fingers. The normalized magnitude of spurious in Fig. 9 is specifically a value obtained by normalizing the amount of phase rotation of the spurious impedance by 180°. The results shown in Fig. 9 are for a Z-cut LiNbO ３ Although this is the result when a piezoelectric layer made of this material was used, the same tendency is observed when a piezoelectric layer having another cut angle is used.

[0062] In the region surrounded by ellipse E in Figure 9, the normalized magnitude of the spurious response between the resonant frequency and the anti-resonant frequency is 1.0. If the bandwidth fraction of the elastic wave resonator exceeds 17%, the normalized magnitude of the spurious response may be 1.0 or more. For this reason, it is preferable that the bandwidth fraction be 17% or less. This makes it possible to suppress the spurious response between the resonant frequency and the anti-resonant frequency.

[0063] 10 is a diagram showing the relationship between d / p, metallization ratio MR, and bandwidth fraction, in which the bandwidth fraction is calculated for each of different d / p and metallization ratio MR.

[0064] In Figure 10, the hatched area is the area where the fractional bandwidth is 17% or less. The boundary between this hatched area and the non-hatched area is roughly represented by dashed line G. Dashed line G is represented by MR = 1.75(d / p) + 0.075. It is preferable that MR ≤ 1.75(d / p) + 0.075. In this case, it is easy to keep the fractional bandwidth at 17% or less.

[0065] On the other hand, the dashed-dotted line G1 in Figure 10 indicates the boundary where the slope of the change in metallization ratio MR with respect to the change in d / p is the same as that of the dashed line G, and where the fractional bandwidth is 17% or less over the entire range. The dashed-dotted line G1 is represented by MR = 1.75(d / p) + 0.05. It is more preferable that MR ≤ 1.75(d / p) + 0.05. In this case, the fractional bandwidth can be more reliably kept at 17% or less.

[0066] FIG. 11 shows the results of LiNbO when d / p approaches 0. ３ 11 is a map of the fractional bandwidth with respect to Euler angles (0°, θ, ψ) of the optical fiber 10. The hatched area in FIG. 11 is a region where a fractional bandwidth of at least 5% or more can be obtained, and the range of this region can be approximated as the ranges expressed by the following formulas (1), (2), and (3).

[0067] (0°±10°, 0° to 20°, any 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°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0068] It is preferable that the Euler angles (φ, θ, ψ) of the lithium niobate constituting the piezoelectric layer 6 are within the range of the above formula (1), formula (2), or formula (3). This allows the relative bandwidth of the elastic wave resonator to be sufficiently wide. The same applies when the piezoelectric layer 6 is made of lithium tantalate.

[0069] Examples of embodiments of the acoustic wave device according to the present invention will be described below.

[0070] <1> An elastic wave device comprising: a support substrate; an intermediate layer provided on the support substrate; a piezoelectric layer provided on the intermediate layer; and an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, wherein d / p is 0.5 or less, where d is the thickness of a portion of the piezoelectric layer where the IDT electrode is provided, and p is the center-to-center distance between adjacent electrode fingers; a cavity provided between the piezoelectric layer and the support substrate, the cavity overlapping the IDT electrode in a planar view, at least a portion of the cavity being provided between the support substrate and the intermediate layer, and facing the piezoelectric layer with at least one of the cavity and the intermediate layer sandwiched therebetween; and further comprising one of a silicon nitride film, an amorphous silicon film, and a polycrystalline silicon film.

[0071] <2> The acoustic wave device according to <1>, further comprising the silicon nitride film, the silicon nitride film having a thickness of 30 nm or more and 250 nm or less.

[0072] <3> The acoustic wave device according to <1> or <2>, further comprising the silicon nitride film, wherein the stress of the silicon nitride film is −300 MPa or more and 50 MPa or less.

[0073] <4> The acoustic wave device according to any one of <1> to <3>, wherein the intermediate layer is a silicon oxide layer.

[0074] <5> The acoustic wave device according to any one of <1> to <4>, wherein the support substrate is a silicon substrate.

[0075] <6> The acoustic wave device according to any one of <1> to <5>, wherein d / p is 0.24 or less.

[0076] <7> An elastic wave device according to any one of <1> to <6>, wherein, when a direction perpendicular to the direction in which the plurality of electrode fingers extend is defined as an electrode finger perpendicular direction, adjacent electrode fingers overlap in the electrode finger perpendicular direction, and the region between the centers of adjacent electrode fingers is an excitation region, and when the metallization ratio of the electrode fingers to the excitation region is defined as MR, MR≦1.75(d / p)+0.075 is satisfied.

[0077] <8> The acoustic wave device according to any one of <1> to <7>, wherein the piezoelectric layer is made of lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (0°±10°, 0° to 20°, any ψ) ... formula (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°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] to 180°, any ψ) ...Equation (3)

[0078] REFERENCE SIGNS LIST 1... Acoustic wave resonator 2, 2A... Piezoelectric substrate 2a... Cavity 3... Support substrate 4... Silicon nitride film 5... Intermediate layer 5c... Through hole 6... Piezoelectric layer 6a, 6b... First and second principal surfaces 6c... Through hole 7, 7A, 7B... IDT electrode 8... Dielectric film 8c... Through hole 9... Bump 10, 10A... Acoustic wave device 13... Wiring 13a, 13b... First and second wiring layers 14... Pad portion 15... Pad electrode 16, 17... First and second bus bars 18, 19... First and second electrode fingers 20... Acoustic wave device 22... Piezoelectric substrate 22a... Cavity C... Excitation region

Claims

1. An elastic wave device comprising: a support substrate; an intermediate layer provided on the support substrate; a piezoelectric layer provided on the intermediate layer; and an IDT electrode provided on the piezoelectric layer and having a plurality of electrode fingers, wherein d / p is 0.5 or less, where d is the thickness of a portion of the piezoelectric layer where the IDT electrode is provided and p is the center-to-center distance between adjacent electrode fingers; a cavity is provided between the piezoelectric layer and the support substrate, and the cavity overlaps with the IDT electrode in a planar view; and the device further comprises at least a portion of a silicon nitride film, an amorphous silicon film, or a polycrystalline silicon film, the cavity being provided between the support substrate and the intermediate layer and facing the piezoelectric layer with at least one of the cavity and the intermediate layer sandwiched therebetween.

2. The acoustic wave device according to claim 1, comprising the silicon nitride film, the silicon nitride film having a thickness of 30 nm or more and 250 nm or less.

3. The acoustic wave device according to claim 1 or 2, comprising the silicon nitride film, wherein the stress of the silicon nitride film is −300 MPa or more and 50 MPa or less.

4. The acoustic wave device according to claim 1, wherein the intermediate layer is a silicon oxide layer.

5. The acoustic wave device according to any one of claims 1 to 4, wherein the supporting substrate is a silicon substrate.

6. The elastic wave device according to any one of claims 1 to 5, wherein d / p is 0.24 or less.

7. An elastic wave device according to any one of claims 1 to 6, wherein, when a direction perpendicular to the direction in which the multiple electrode fingers extend is defined as an electrode finger orthogonal direction, a region in which adjacent electrode fingers overlap in the electrode finger orthogonal direction and a region between the centers of adjacent electrode fingers is an excitation region, and when a metallization ratio of the electrode fingers to the excitation region is MR, MR satisfies MR≦1.75(d / p)+0.

075.

8. The elastic wave device according to any one of claims 1 to 7, wherein the piezoelectric layer is made of lithium niobate or lithium tantalate, and the Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2), or formula (3): (0°±10°, 0° to 20°, any ψ) ... formula (1) (0°±10°, 20° to 80°, 0° to 60° (1-(θ-50) ２ / 900) １／２ ) or (0°±10°, 20°~80°, [180°-60°(1-(θ-50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°-30°(1-(ψ-90) ２ / 8100) １／２ ] ~ 180°, any ψ) ... Equation (3)

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