Elastic wave device

Abstract

The elastic wave device (1) propagates elastic waves in the X-axis direction. The elastic wave device (1) includes: a piezoelectric substrate (2); and a first electrode finger (4b) disposed on the main surface (2a) of the piezoelectric substrate (2) and extending in the Y-axis direction. The elastic wave device (1) is configured such that the elastic wave sound speed is distributed from the center of the first electrode finger (4b) outwards in the Y-axis direction in the order of medium speed, low speed, and high speed. The elastic wave device (1) also includes a first dielectric (41) disposed between the piezoelectric substrate (2) and the front end of the first electrode finger (4b). The end face of the first dielectric (41) in the Y-axis direction has a first side surface (S1) and a second side surface (S2). The tilt angle of the first side surface (S1) is smaller than the tilt angle of the second side surface (S2).

Description

Technical Field

[0001] This disclosure relates to elastic wave devices utilizing a piston mode. Background Technology

[0002] Previously, in order to suppress unwanted waves, elastic wave devices utilizing piston modes were proposed. The so-called piston mode is a technique in which the sound speed (the propagation speed in the direction of elastic wave propagation) constituting the elastic wave is distributed from the center in a direction orthogonal to the direction of elastic wave propagation outwards in the order of medium sound speed, low sound speed, and high sound speed, thereby making the effective electromechanical coupling coefficient of modes other than the fundamental mode close to zero.

[0003] For example, U.S. Patent Publication No. 2017 / 0155373 (Patent Document 1) discloses an example of an elastic wave device utilizing a piston mode. This elastic wave device includes a piezoelectric substrate and IDT (Interdigital Transducer) electrodes formed on the piezoelectric substrate. The IDT electrodes have: a first busbar and a second busbar extending opposite each other in the elastic wave propagation direction; a plurality of first electrode fingers, one end connected to the first busbar, extending in a direction orthogonal to the elastic wave propagation direction; and a plurality of second electrode fingers, one end connected to the second busbar, extending in a direction orthogonal to the elastic wave propagation direction. The plurality of second electrode fingers are arranged to be inserted between the plurality of first electrode fingers. A dielectric is provided between the tip of each electrode finger and the piezoelectric substrate. Thus, an elastic wave device utilizing a piston mode is formed. Specifically, the elastic wave velocity in the first edge region containing the front ends of a plurality of first electrode fingers and the elastic wave velocity in the second edge region containing the front ends of a plurality of second electrode fingers are configured to be lower than the elastic wave velocity in the central region between the first edge region and the second edge region. Furthermore, the elastic wave velocity in the region outside the first edge region and the second edge region relative to the central region is configured to be higher than the elastic wave velocity in the central region.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: U.S. Publication No. 2017 / 0155373 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Patent Document 1 disclosed a structure in which the side surface of the dielectric (the end face in the extension direction of the electrode) is set as a planar shape perpendicular to the main surface of the piezoelectric substrate (hereinafter also referred to as "vertical shape"), or as a planar shape inclined to the main surface of the piezoelectric substrate (hereinafter also referred to as "conical shape").

[0009] When the sides of the dielectric are made into a vertical shape, it becomes easy to form a sharp difference in sound velocity between the central region and the first and second edge regions, thus making it easier to suppress stray modes. However, stress becomes more likely to act on the piezoelectric substrate around the dielectric, raising concerns that polarization reversal of the piezoelectric material contained in the piezoelectric substrate may easily occur.

[0010] On the other hand, when the side of the dielectric is made into a conical shape, the stress on the piezoelectric substrate acting around the dielectric can be relieved, making it less likely to generate polarization reversal. However, it becomes difficult to form a sharp sound velocity difference between the central region and the first and second edge regions, so there is concern that it will become difficult to suppress the generation of stray modes.

[0011] This disclosure was made to solve such a problem, and its purpose is to suppress the generation of stray modes while suppressing polarization reversal of the piezoelectric substrate in an elastic wave device utilizing a piston mode.

[0012] Technical solutions for solving the problem

[0013] The elastic wave device based on this disclosure includes a piezoelectric substrate, an IDT electrode disposed on the main surface of the piezoelectric substrate, a first dielectric, and a second dielectric. The IDT electrode has: a first busbar and a second busbar facing each other; a first electrode finger, one end connected to the first busbar and extending toward the second busbar; and a second electrode finger, one end connected to the second busbar and extending toward the first busbar. The first electrode finger and the second electrode finger are interlocked. The first dielectric is disposed between at least one of the leading end portion of the first electrode finger and at least one of the portions of the second electrode finger adjacent to the leading end portion of the first electrode finger and the piezoelectric substrate. The second dielectric is disposed between at least one of the leading end portion of the second electrode finger and at least one of the portions of the first electrode finger adjacent to the leading end portion of the second electrode finger and the piezoelectric substrate. The region containing the tip of the first electrode finger is designated as the first edge region, the region containing the tip of the second electrode finger is designated as the second edge region, the region between the first and second edge regions is designated as the central region, the region located outside the central region compared to the first edge region is designated as the first outer region, and the region located outside the central region compared to the second edge region is designated as the second outer region. In this configuration, the elastic wave velocity in the first and second edge regions is lower than the elastic wave velocity in the central region, and there are regions in the first and second outer regions where the elastic wave velocity is higher than the elastic wave velocity in the central region. At least one of the end faces of the first and second dielectrics in the direction of extension of the first and second electrode fingers has a first surface and a second surface that is farther from the piezoelectric substrate than the first surface. The tilt angle of the first surface relative to the main surface of the piezoelectric substrate is smaller than the tilt angle of the second surface relative to the main surface of the piezoelectric substrate.

[0014] Invention Effects

[0015] According to this disclosure, in an elastic wave device utilizing a piston mode, it is possible to suppress the generation of stray modes while suppressing polarization reversal of the piezoelectric substrate. Attached Figure Description

[0016] Figure 1 This is a top view (1) of the elastic wave device.

[0017] Figure 2 It is an elastic wave device Figure 1 Sectional view II-II in the middle.

[0018] Figure 3 This is an enlarged view of the side portion of the dielectric (Figure 1).

[0019] Figure 4 This is a diagram showing the structure of Comparative Model 1.

[0020] Figure 5 This is a diagram (Figure 1) showing the structure of comparative model 2.

[0021] Figure 6 This is a graph showing the simulation results of comparison model 1.

[0022] Figure 7 Figure 1 shows the simulation results of Comparison Model 2.

[0023] Figure 8 This is a graph showing the simulation results of the model disclosed in this publication.

[0024] Figure 9 It is a magnified view of the side portion of the dielectric (Figure 2).

[0025] Figure 10 This is a figure showing the simulation results of this deformable model 1.

[0026] Figure 11 Figure 2 shows the simulation results of comparison model 2.

[0027] Figure 12 It is a magnified view of the side portion of the dielectric (Figure 3).

[0028] Figure 13 This is a figure showing the simulation results of this deformed model 2.

[0029] Figure 14 This is a top view (2) of the elastic wave device.

[0030] Figure 15 This is a cross-sectional view of an elastic wave device.

[0031] Figure 16 This is a figure showing an example of the simulation results of the sound velocity difference between the central region B and the first edge region A1. Detailed Implementation

[0032] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, the same or equivalent parts in the drawings will be labeled with the same reference numerals, and their descriptions will not be repeated.

[0033] Figure 1 This is a top view of the elastic wave device 1 based on this embodiment. Figure 2 It is elastic wave device 1 Figure 1 Sectional view II-II in the middle.

[0034] The elastic wave device 1 includes a piezoelectric substrate 2, an IDT electrode 3, a plurality of first dielectrics 41 and 51, a plurality of second dielectrics 42 and 52, and reflectors 6A and 6B. The IDT electrode 3 and the reflectors 6A and 6B are disposed on the main surface 2a of the piezoelectric substrate 2.

[0035] Furthermore, the direction of elastic wave propagation in the elastic wave device 1 will be referred to as the X-axis direction, the normal direction of the main surface 2a of the piezoelectric substrate 2 will be referred to as the Z-axis direction, and the direction orthogonal to both the X-axis and Z-axis directions will be referred to as the Y-axis direction. The X-axis direction is an example of the "first direction," and the Y-axis direction is an example of the "second direction."

[0036] The IDT electrode 3 has a first bus bar 4a and a plurality of first electrode fingers 4b, and a second bus bar 5a and a plurality of second electrode fingers 5b. The first bus bar 4a and the second bus bar 5a are configured to extend in the X-axis direction and are opposite to each other.

[0037] Each of the plurality of first electrode fingers 4b has one end connected to a first busbar 4a, and each of the plurality of first electrode fingers 4b extends toward a second busbar 5a in the Y-axis direction. Each of the plurality of second electrode fingers 5b has one end connected to a second busbar 5a, and each of the plurality of second electrode fingers 5b extends toward a first busbar 4a in the Y-axis direction. The plurality of first electrode fingers 4b and the plurality of second electrode fingers 5b are configured to interlock with each other.

[0038] The IDT electrode 3 is an aluminum electrode. However, the material of the IDT electrode 3 is not limited to the aforementioned material. The IDT electrode 3 may also comprise a stacked metal film. When an alternating voltage is applied to the IDT electrode 3, the elastic wave is excited and propagates in the X-axis direction.

[0039] Reflectors 6A and 6B are respectively disposed on both sides of IDT electrode 3 in the X-axis direction. Each of reflectors 6A and 6B has multiple electrode fingers 6b. Reflectors 6A and 6B contain the same material as IDT electrode 3.

[0040] In this embodiment, the piezoelectric substrate 2 has a laminated structure in which piezoelectric films are stacked on a support substrate. Specifically, as shown in the figure... Figure 2 As shown, the piezoelectric substrate 2 is constructed by sequentially stacking a piezoelectric layer 21, a low-velocity layer 22, and a high-velocity support substrate 23 from the side closest to the IDT electrode 3 toward the side furthest from the IDT electrode 3.

[0041] The piezoelectric layer 21 includes a piezoelectric film comprising lithium tantalate (LiTaO3). The piezoelectric layer 21 may, for example, comprise a 50° Y-cut X-propagating LiTaO3 piezoelectric single crystal or piezoelectric ceramic (a lithium tantalate single crystal or ceramic cut with a plane rotated 50° from the Y-axis as the normal, and a single crystal or ceramic in which elastic waves propagate in the X-axis direction). For example, when the wavelength determined by the electrode finger spacing of the IDT electrode 3 is set as λ, the thickness of the piezoelectric layer 21 is 3.5λ or less.

[0042] The high-velocity acoustic support substrate 23 is a substrate that supports the piezoelectric layer 21 and the low-velocity acoustic layer 22. The high-velocity acoustic support substrate 23 also has a higher velocity of bulk waves compared to elastic waves such as surface waves and boundary waves propagating in the piezoelectric layer 21. The high-velocity acoustic support substrate 23 functions to confine elastic waves within the portion where the piezoelectric layer 21 and the low-velocity acoustic layer 22 are stacked, preventing leakage to areas below the high-velocity acoustic support substrate 23. The thickness of the high-velocity acoustic support substrate 23 is, for example, 120 μm.

[0043] The low-velocity layer 22 is a film in which the velocity of the bulk wave propagating in the piezoelectric layer 21 is lower than that of the elastic wave propagating in the piezoelectric layer 21, and it is disposed between the piezoelectric layer 21 and the high-velocity support substrate 23. The thickness of the low-velocity layer 22 is, for example, 670 nm. Due to this stacked structure of the piezoelectric substrate 2 and the property that the energy of the elastic wave is essentially concentrated in the low-velocity medium, leakage of the elastic wave energy to the IDT electrode 3 can be suppressed. According to this stacked structure, compared to a structure using a single layer of the piezoelectric substrate 2, the resonant frequency and the Q value at the anti-resonant frequency can be significantly improved. That is, a surface acoustic wave resonator with a high Q value can be constructed, and therefore, a filter with low insertion loss can be constructed using this elastic wave resonator.

[0044] The low-velocity layer 22 may contain materials primarily composed of glass, silicon oxynitride, tantalum oxide, or compounds of silicon oxide with added fluorine, carbon, or boron. Furthermore, the material of the low-velocity layer 22 need to be any material with relatively low sound velocity.

[0045] As the high-speed support substrate 23, various ceramics such as aluminum nitride, aluminum oxide, silicon carbide, silicon, sapphire, lithium tantalate, lithium niobate, quartz, etc., bauxite, zirconium oxide, cordierite, mullite, block talc, magnesium olivine, etc., magnesium oxide diamond, or materials with the above materials as the main components, or materials with mixtures of the above materials as the main components, can be used.

[0046] Alternatively, the hypersonic support substrate 23 may also have a structure in which a support substrate and a hypersonic film are stacked, and the speed of sound of the bulk waves propagating in the hypersonic film is higher than that of elastic waves such as surface waves and boundary waves propagating in the piezoelectric layer 21. In this case, the support substrate can be made of piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, and quartz; various ceramics such as alumina, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite; dielectric materials such as glass; semiconductor materials such as silicon and gallium nitride; and resin substrates. Furthermore, the hypersonic film can be made of a wide variety of hypersonic materials such as aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, DLC film, diamond, dielectrics mainly composed of the above materials, and dielectrics mainly composed of mixtures of the above materials.

[0047] Alternatively, the piezoelectric substrate 2 may also contain piezoelectric single crystals other than lithium tantalate (LiTaO3), such as lithium tantalate (LiTaO3) or lithium niobate (LiNbO3). The piezoelectric substrate 2 may also be a substrate of a piezoelectric body without a supporting substrate.

[0048] The first dielectric 41 is disposed at the front end of the first electrode finger 4b. Figure 1 The first dielectric 51 is disposed between the end of the second electrode finger 5b in the positive Y-axis direction (shown as the end of the first electrode finger 4b) and the piezoelectric substrate 2. The portion of the second electrode finger 5b adjacent to the front end of the first electrode finger 4b in the X-axis direction (hereinafter also referred to as the "adjacent portion of the second electrode finger 5b") is disposed between the first dielectric 51 and the piezoelectric substrate 2. Additionally, in Figure 1 An example is shown in which the first dielectrics 41 and 51 are configured not to intersect the XZ plane passing through the front end of the first electrode finger 4b, but the first dielectrics 41 and 51 may also be configured to intersect the XZ plane passing through the front end of the first electrode finger 4b.

[0049] The second dielectric 52 is disposed at the front end of the second electrode finger 5b. Figure 1 The second dielectric 42 is disposed between the end of the first electrode finger 4b in the negative Y-axis direction (shown as the end in the negative Y-axis direction) and the piezoelectric substrate 2. The portion of the first electrode finger 4b adjacent to the front end of the second electrode finger 5b in the X-axis direction (hereinafter also referred to as the "adjacent portion of the first electrode finger 4b") is disposed between the first electrode finger 4b and the piezoelectric substrate 2. Furthermore, in Figure 1 An example is shown in which the second dielectrics 42 and 52 are configured not to intersect the XZ plane passing through the front end of the second electrode finger 5b, but the second dielectrics 42 and 52 may also be configured to intersect the XZ plane passing through the front end of the second electrode finger 5b.

[0050] Hereinafter, the region containing the front ends of multiple first electrode fingers 4b and extending in the X-axis direction is defined as "first edge region A1", and the region containing the front ends of multiple second electrode fingers 5b and extending in the X-axis direction is defined as "second edge region A2". Furthermore, in the first edge region A1, in addition to the front ends of the multiple first electrode fingers 4b, it also includes adjacent portions of the multiple second electrode fingers 5b. Similarly, in the second edge region A2, in addition to the front ends of the multiple second electrode fingers 5b, it also includes adjacent portions of the multiple first electrode fingers 4b.

[0051] Therefore, the area between the first edge region A1 and the second edge region A2 is defined as "central region B", the area that is outside the first edge region A1 relative to the central region B is defined as "first outer region C1", and the area that is outside the second edge region A2 relative to the central region B is defined as "second outer region C2".

[0052] Furthermore, the “first edge region A1”, “second edge region A2”, “central region B”, “first outer region C1”, and “second outer region C2” in this embodiment can respectively correspond to the “first edge region”, “second edge region”, “central region”, “first outer region”, and “second outer region” of this disclosure.

[0053] In the elastic wave device 1 based on this embodiment, a first dielectric 41 and 51 are disposed in the first edge region A1, and a second dielectric 42 and 52 are disposed in the second edge region A2. As a result, the elastic wave sound velocity Va in the first edge region A1 and the second edge region A2 becomes lower than the elastic wave sound velocity Vb in the central region B, and the elastic wave sound velocity Vc in the first outer region C1 and the second outer region C2 becomes higher than the elastic wave sound velocity Vb in the central region B. That is, the elastic wave sound velocity is configured to be distributed from the central region B towards the two outer sides in the Y-axis direction in the order of medium sound velocity Vb, low sound velocity Va, and high sound velocity Vc. In this way, in the elastic wave device 1 based on this embodiment, stray noise caused by the transverse mode can be suppressed using a piston mode, and the fundamental mode can be propagated efficiently.

[0054] Furthermore, the relationship between the various sound speeds is Va < Vb < Vc. The relationship between the various sound speeds described above is shown in... Figure 1 Additionally, it shows that the speed of sound changes with direction. Figure 1 It becomes higher on the left side of the middle.

[0055] <Side shape of the dielectric>

[0056] The side shapes of each dielectric (first dielectric 41, 51 and second dielectric 42, 52) in this embodiment will be described below. As described above, in this embodiment, the first dielectrics 41 and 51 disposed in the first edge region A1 are disposed between the front end of the first electrode finger 4b and the adjacent portion of the second electrode finger 5b and the piezoelectric substrate 2. Furthermore, the second dielectrics 42 and 52 disposed in the second edge region A2 are disposed between the front end of the second electrode finger 5b and the adjacent portion of the first electrode finger 4b and the piezoelectric substrate 2.

[0057] In the configuration described above, if the sides (end faces in the Y-axis direction) of each dielectric 41, 51, 42, 52 are set to a simple vertical shape, it becomes easy to form a sharp sound velocity difference between each edge region A1, A2 and the central region B, and between each edge region A1, A2 and each outer region C1, C2, thus making it easier to suppress stray modes. However, stress becomes more likely to act on the piezoelectric substrate 2 surrounding each dielectric 41, 51, 42, 52, so there is a concern that polarization reversal may easily occur in the piezoelectric film of the piezoelectric substrate 2.

[0058] On the other hand, if the sides of each dielectric 41, 51, 42, 52 are designed as simple conical shapes, the stress acting on the piezoelectric substrate 2 around each dielectric 41, 51, 42, 52 can be alleviated, thereby suppressing the polarization reversal of the piezoelectric substrate 2. However, it becomes difficult to form a sharp sound velocity difference between each edge region A1, A2 and the central region B, and between each edge region A1, A2 and each outer region C1, C2, thus raising concerns that it may become difficult to suppress the generation of stray modes.

[0059] Therefore, in this embodiment, the side shapes of each dielectric 41, 51, 42, 52 are set as follows: Figure 2 The shape shown. Additionally, in Figure 2 The side shape of the first dielectric 41 is shown representatively. The side shapes of each dielectric 41, 51, 42, and 52 are substantially the same; therefore, the side shape of the first dielectric 41 will be described representatively below.

[0060] like Figure 2 As shown, the first dielectric 41 has a first side surface S1 that is in contact with the piezoelectric substrate 2 and a second side surface S2 that is further away from the piezoelectric substrate 2 than the first side surface S1. Both the first side surface S1 and the second side surface S2 are planes extending in the X-axis direction. The first side surface S1 is an example of the "first surface" among the end faces of the first dielectric 41 in the Y-axis direction, and the second side surface S2 is an example of the "second surface" among the end faces of the first dielectric 41 in the Y-axis direction.

[0061] The tilt angle of the first side surface S1 relative to the main surface 2a of the piezoelectric substrate 2 (hereinafter also referred to as "the tilt angle of the first side surface S1") is smaller than the tilt angle of the second side surface S2 relative to the main surface 2a of the piezoelectric substrate 2 (hereinafter also referred to as "the tilt angle of the second side surface S2").

[0062] In addition, Figure 2 An example is shown where both the side surface in the positive Y-axis direction (the direction in which the I electrode extends, i.e., 4b) and the side surface in the negative Y-axis direction (the direction in which the second electrode extends, i.e., 5b) of the first dielectric 41 have a first side surface S1 and a second side surface S2. However, it is also possible that either the side surface in the positive Y-axis direction or the side surface in the negative Y-axis direction of the first dielectric 41 has a first side surface S1 and a second side surface S2.

[0063] Figure 3 This is an enlarged view of the side portion of the first dielectric 41. As described above, a first side surface S1 and a second side surface S2 are formed on the side surface of the first dielectric 41. Figure 3In the example shown, the tilt angle of the first side surface S1 is set to 15 degrees, and the tilt angle of the second side surface S2 is set to 90 degrees. Furthermore, the thickness (width in the Z-axis direction) of the first dielectric 41 is set to 50 nm, and the length in the Y-axis direction of the first side surface S1 is set to 20 nm. The upper surface (end face in the positive Z-axis direction) of the first dielectric 41 is parallel to the main surface 2a of the piezoelectric substrate 2. However, the values ​​of the tilt angle and length of each side surface are merely an example and are not limited to this.

[0064] In this embodiment, the tilt angle of the side surface of the first dielectric 41 is made different in the portion near the piezoelectric substrate 2 and the portion away from the piezoelectric substrate 2. That is, the tilt angle of the first side surface S1 near the piezoelectric substrate 2 is relatively reduced. As a result, the contact between the first dielectric 41 and the first electrode finger 4b can be improved, and the stress applied to the piezoelectric substrate 2 and the first electrode finger 4b can be reduced. Furthermore, the tilt angle of the second side surface S2 away from the piezoelectric substrate 2 is relatively increased. As a result, the regions where the sound velocity changes (more specifically, the regions where the sound velocity changes from the medium sound velocity Vb in the central region B to the low sound velocity Va in the first edge region A1, and the regions where the sound velocity changes from the low sound velocity Va in the first edge region A1 to the high sound velocity Vc in the first outer region C1) can be reduced, and a sharp sound velocity difference can be formed between the central region B and the first edge region A1, and between the first edge region A1 and the first outer region C1.

[0065] As described above, the side shapes of the dielectrics other than the first dielectric 41 (first dielectric 51, second dielectrics 42, 52) are substantially the same as the side shape of the first dielectric 41. Therefore, the same effect as the first dielectric 41 can be achieved in the dielectrics 51, 42, 52 other than the first dielectric 41. As a result, while creating a sharp difference in sound velocity between the central region B and each edge region A1, A2, and between each edge region A1, A2 and each outer region C1, C2, the tightness of the dielectrics 41, 51, 42, 52 and each electrode finger 4b, 5b can be improved, thereby reducing the stress applied to the piezoelectric substrate 2 and each electrode finger 4b, 5b.

[0066] <Simulation results of stress>

[0067] To verify the aforementioned effects, the inventors of this application conducted simulations using the finite element method and calculated the stress (Von Mises stress) applied to the piezoelectric substrate 2 and the IDT electrode 3. In this simulation, the effects were verified by simulating the stress generated when the temperature changed from 25°C to 85°C.

[0068] In addition, in this verification, simulations of comparative model 1 and comparative model 2 were also performed, using the previously comparable structural models. Figure 4 This is a diagram showing the structure of Comparative Model 1. In Comparative Model 1, the sides of the dielectric are designed as a simple vertical shape. Figure 5 This is a diagram showing the structure of Comparative Model 2. In Comparative Model 2, the side surface of the dielectric is set as a simple conical shape with an inclination angle of 45 degrees.

[0069] In addition, in these simulations, tantalum oxide (Ta2O5) with a thickness of 50 nm was formed as a dielectric material on a piezoelectric substrate with 50° Y-cut X-propagating LiTaO3, and aluminum with a thickness of 150 nm was formed as an IDT electrode.

[0070] Figure 6 This is a graph showing the simulation results of comparison model 1. Figure 7 This is a graph showing the simulation results of comparison model 2. Figure 8 This is a diagram showing the simulation results of the model disclosed herein (elastic wave device 1 based on this embodiment).

[0071] according to Figure 6 The simulation results of the comparison model 1 and Figure 7 The simulation results of Comparative Model 2 show that, compared to Comparative Model 1, which has a vertically oriented dielectric side surface, Comparative Model 2, with its conical dielectric side surface, applies less stress to the piezoelectric substrate and IDT electrodes, thus reducing the risk of polarization reversal in the piezoelectric substrate and IDT breakage. However, in Comparative Model 2, the sound velocity varies slowly corresponding to the tilt of the dielectric side surface; specifically, the sound velocity varies along the distance in the Y-axis direction of the dielectric side surface (approximately 70 nm, the square root of 2 multiplied by 50 nm). Therefore, compared to Comparative Model 1, it becomes disadvantageous from the perspective of suppressing stray modes (transverse modes).

[0072] In contrast, in the model disclosed herein, on the side of the first dielectric 41, only a first side surface S1 with a tilt angle of 15 degrees and a length of 20 nm is formed in the Y-axis direction, while the tilt angle of the other second side surfaces S2 is set to 90 degrees. Figure 8 The simulation results of the model shown in this disclosure are consistent with Figure 6 The simulation results of the comparison model 1 and Figure 7Comparing the simulation results of the comparative model 2, it can be seen that the stress applied to the piezoelectric substrate 2 is smaller in the model of this disclosure. Therefore, compared with comparative models 1 and 2, the polarization reversal of the piezoelectric substrate 2 is less likely to occur in the model of this disclosure. On the other hand, the region of sound velocity variation in the model of this disclosure is 20 nm, which is smaller than that in comparative model 2, where the side surface of the dielectric is cone-shaped. Therefore, compared with comparative model 2, transverse modes are also easier to suppress.

[0073] Furthermore, when the piezoelectric film of lithium tantalate in the piezoelectric substrate is sufficiently thick, there is a tendency for the aforementioned transverse mode to be less likely to occur. However, in a structure where a piezoelectric film of lithium tantalate (piezoelectric layer 21) is stacked on a support substrate (hypersonic support substrate 23) as in the piezoelectric substrate 2 of this embodiment, the piezoelectric film of lithium tantalate is thinner, and therefore transverse mode may occur. In addition, when the piezoelectric substrate includes a piezoelectric film of lithium niobate, transverse mode may occur even when the piezoelectric film is thick. However, in the above simulation, the purpose was to verify how the stress applied to the piezoelectric substrate 2 and the IDT electrode 3 changes by changing the side shape of the dielectric; therefore, the simulation was performed with the piezoelectric substrate 2 as a single layer of lithium tantalate.

[0074] As described above, the elastic wave device 1 based on this embodiment includes a piezoelectric substrate 2, an IDT electrode 3 disposed on the main surface 2a of the piezoelectric substrate 2, first dielectrics 41 and 51, and second dielectrics 42 and 52. The IDT electrode 3 has: a first bus bar 4a and a second bus bar 5a, which extend opposite each other in the X-axis direction (first direction); a first electrode finger 4b, one end of which is connected to the first bus bar 4a and extends toward the second bus bar 5a in the Y-axis direction (second direction); and a second electrode finger 5b, one end of which is connected to the second bus bar 5a and extends toward the first bus bar 4a in the Y-axis direction (second direction), and is disposed adjacent to the first electrode finger 4b.

[0075] The first dielectrics 41 and 51 are respectively disposed between the front end of the first electrode finger 4b and the piezoelectric substrate 2, and between the adjacent portion of the second electrode finger 5b and the piezoelectric substrate 2. The second dielectrics 42 and 52 are respectively disposed between the front end of the second electrode finger 5b and the piezoelectric substrate 2, and between the adjacent portion of the first electrode finger 4b and the piezoelectric substrate 2.

[0076] The elastic wave velocity in the first edge region A1 and the second edge region A2 is lower than that in the central region B, and the elastic wave velocity in the first outer region C1 and the second outer region C2 is higher than that in the central region B.

[0077] The sides (end faces in the Y-axis direction) of the first dielectric 41, 51 and the second dielectric 42, 52 have a first side surface S1 that is in contact with the piezoelectric substrate 2 and a second side surface S2 that is further away from the piezoelectric substrate 2 than the first side surface S1. The tilt angle of the first side surface S1 is smaller than the tilt angle of the second side surface S2.

[0078] In this way, by relatively reducing the tilt angle of the first side surface S1, the stress applied to the piezoelectric substrate 2 can be reduced. Furthermore, by relatively increasing the tilt angle of the second side surface S2, which is farther away from the piezoelectric substrate 2, a sharp sound velocity difference can be formed between the central region B and each edge region A1, A2, and between the central region B and each outer region C1, C2. As a result, the generation of stray modes can be suppressed while suppressing polarization reversal of the piezoelectric substrate 2.

[0079] <Variation Example 1>

[0080] In the elastic wave device 1 based on the above-described embodiment, an example of forming a first side surface S1 and a second side surface S2 on the sides of each dielectric 41, 51, 42, 52 is described.

[0081] In contrast, in the elastic wave device 1A based on this modified example 1, in addition to the first side surface S1 and the second side surface S2, a third side surface S3 is further formed on the side surfaces of each dielectric 41, 51, 42, and 52, which is further away from the piezoelectric substrate 2 than the second side surface S2. The third side surface S3 is an example of the "third surface" among the end faces of each dielectric 41, 51, 42, and 52 in the Y-axis direction. The tilt angle of the third side surface S3 relative to the main surface 2a of the piezoelectric substrate 2 (hereinafter also simply referred to as the "tilt angle of the third side surface S3") is smaller than the tilt angle of the second side surface S2. Furthermore, the shapes of each side surface of each dielectric 41, 51, 42, and 52 based on this modified example 1 are substantially the same. Therefore, the first dielectric 41 having the side surface shape based on this modified example 1 will be referred to as "the first dielectric 41A" below, and the side surface shape of the first dielectric 41A will be described representatively.

[0082] Figure 9 This is an enlarged view of the side portion of the first dielectric 41A based on this modified example 1. In this modified example 1, the tilt angles of the first side surface S1 and the second side surface S2 are set to 15 degrees and 90 degrees, respectively, as in the embodiment described above. Furthermore, the tilt angle of the third side surface S3 is set to 15 degrees. In addition, the thickness (width in the Z-axis direction) of the first dielectric 41A is set to 50 nm, and the lengths of the first side surface S1 and the third side surface S3 in the Y-axis direction are each set to 20 nm. The values ​​of the tilt angles and lengths of each side surface are merely examples and are not limited thereto.

[0083] The inventors of this application also performed the same simulation as the above-described embodiment on the elastic wave device 1A based on this modified example 1, and calculated the stress applied to the piezoelectric substrate 2.

[0084] Figure 10 This is a figure showing the simulation results of this modified model 1 (elastic wave device 1A based on this modified example 1). Figure 11 This is a diagram showing the simulation results of the aforementioned Comparative Model 2, where the side surface shape is set to a simple conical shape.

[0085] Will Figure 10 The simulation results of the deformable model 1 shown are consistent with... Figure 11 Comparing the simulation results of the comparative model 2, it can be seen that in this modified model 1, the stress applied to the piezoelectric substrate 2 is smaller, and polarization reversal is less likely to occur. Furthermore, it can be seen that by setting a third side surface S3 with a smaller tilt angle than the second side surface S2 on the side farther away from the piezoelectric substrate 2, the stress on the first electrode finger 4bA near the upper end of the side surface of the first dielectric 41A is slightly reduced.

[0086] On the other hand, this modified model 1 can suppress the region of sound velocity variation to 40 nm (the sum of the lengths of the first side surface S1 and the third side surface S3 in the Y-axis direction), which reduces the region of sound velocity variation compared to the comparative model 2, which sets the sides of the dielectric to a simple conical shape. Therefore, it can be seen that, compared to the comparative model 2, the transverse mode is also easier to suppress.

[0087] As described above, it can also be modified so that, in addition to the first side surface S1 and the second side surface S2, a third side surface S3 with a smaller tilt angle than the second side surface S2 is provided on the side of each dielectric material that is farther away from the piezoelectric substrate 2 than the second side surface S2. By modifying it in this way, the same effect as the above-described embodiment can be achieved. Furthermore, by providing the third side surface S3, the stress acting on the electrode fingers around the third side surface S3 is also reduced.

[0088] <Variation Example 2>

[0089] In the elastic wave device 1 based on the above-described embodiment and the elastic wave device 1A based on modified example 1, the tilt angle of the second side surface S2 is set to 90 degrees, but the tilt angle of the second side surface S2 may also be set to less than 90 degrees.

[0090] Figure 12This is an enlarged view of the side portion of the first dielectric 41 in the elastic wave device 1B based on this Modified Example 2. Furthermore, the shapes of the sides of each dielectric 41, 51, 42, and 52 in the elastic wave device 1B based on this Modified Example 2 are substantially the same. Therefore, the first dielectric 41 having the side shape based on this Modified Example 2 will be referred to as "first dielectric 41B" below, and the side shape of the first dielectric 41B will be described representatively.

[0091] The first dielectric 41B based on this Modification Example 2 changes the second side surface S2 of the first dielectric 41A based on Modification Example 1 to a second side surface S2a. That is, a first side surface S1, a second side surface S2a, and a third side surface S3 are formed on the side surface of the first dielectric 41B. The tilt angle of the first side surface S1 and the tilt angle of the third side surface S3 are set to 15 degrees, just like in Modification Example 1. In addition, the thickness (width in the Z-axis direction) of the first dielectric 41B is set to 50 nm, and the lengths of the first side surface S1 and the third side surface S3 in the Y-axis direction are each set to 20 nm. Furthermore, similar to Comparative Model 2, the length of the side surface of the first dielectric 41B in the Y-axis direction (the distance in the Y-axis direction between the lower end of the first side surface S1 and the upper end of the third side surface S3) is set to the square root of 50 nm (approximately 70 nm). As a result, the tilt angle of the second side S2a, which connects the upper end of the first side S1 and the lower end of the third side S3, becomes less than 90 degrees.

[0092] The inventors of this application also performed the same simulation as the above-described embodiment on the elastic wave device 1B based on this modified example 2, and calculated the stress applied to the piezoelectric substrate 2.

[0093] Figure 13 This is a figure showing the simulation results of this modified model 2 (elastic wave device 1B based on this modified example 2).

[0094] Will Figure 13 The simulation results of the deformed model 2 shown are consistent with Figure 11 Comparing the simulation results of the comparative model 2, it can be seen that in this modified model 2, the stress applied to the piezoelectric substrate 2 is smaller, and polarization reversal is less likely to occur. Furthermore, in this modified model 2, by setting the tilt angle of the third side surface S3 to less than 90 degrees, the stress acting on the first electrode finger 4bB around the third side surface S3 is also slightly reduced.

[0095] On the other hand, the region of sound velocity variation in this modified model 2 is approximately 70 nm, which can be suppressed to a level roughly the same as that of the comparative model 2. Thus, compared to the comparative model 2, the increase in transverse mode can be suppressed.

[0096] As described above, the tilt angle of the second side S2 can also be set to less than 90 degrees. This allows for a more appropriate reduction in the stress acting on the electrode fingers while achieving the same effect as the embodiments described above.

[0097] <Variation Example 3>

[0098] In the above embodiment, an example in which the first dielectric 41 and 51 are provided on the front end of the first electrode finger 4b and the adjacent portion of the second electrode finger 5b in the first edge region A1 is described.

[0099] However, as long as a sound velocity distribution based on a piston pattern is formed, a portion of the first dielectric 41, 51 disposed in the first edge region A1 may be omitted. For example, the first dielectric 41 may be disposed at the leading end of the first electrode finger 4b, and the first dielectric 51 may not be disposed at the adjacent portion of the second electrode finger 5b. Conversely, the first dielectric 51 may be disposed at the adjacent portion of the second electrode finger 5b, and the first dielectric 41 may not be disposed at the leading end of the first electrode finger 4b.

[0100] Similarly, in the above embodiment, an example in which the second dielectric 42, 52 is provided on the front end of the second electrode finger 5b and the adjacent portion of the first electrode finger 4b in the second edge region A2 is described.

[0101] However, as long as a sound velocity distribution based on a piston pattern is formed, a portion of the second dielectric 42, 52 disposed in the second edge region A2 may be omitted. For example, the second dielectric 52 may be disposed at the leading end of the second electrode finger 5b, and the second dielectric 42 may not be disposed at the adjacent portion of the first electrode finger 4b. Alternatively, the second dielectric 42 may be disposed at the adjacent portion of the first electrode finger 4b, and the second dielectric 52 may not be disposed at the leading end of the second electrode finger 5b.

[0102] <Variation Example 4>

[0103] In the above embodiments, an example was described in which the first dielectric 41 and 51 were independently provided at the front end of the first electrode finger 4b and the adjacent portion of the second electrode finger 5b in the first edge region A1.

[0104] However, the dielectric material disposed at the front end of the first electrode finger 4b and the adjacent portion of the second electrode finger 5b is not necessarily limited to being disposed separately, but may also be disposed integrally.

[0105] Similarly, in the above embodiments, an example is described in which the second dielectric 52, 42 are independently provided at the front end of the second electrode finger 5b and the adjacent portion of the first electrode finger 4b in the second edge region A2.

[0106] However, the dielectric material disposed at the front end of the second electrode finger 5b and the adjacent portion of the first electrode finger 4b is not necessarily limited to being disposed separately, but may also be disposed integrally.

[0107] Figure 14 This is a top view of the elastic wave device 1C based on this modified example 4. Figure 14 The elastic wave device 1C shown above will... Figure 1 The first dielectric 41 and 51 of the elastic wave device 1 shown are changed to "first dielectric 40", and the second dielectric 42 and 52 of the elastic wave device 1 are changed to "second dielectric 50". The other structures of the elastic wave device 1C are the same as those of the elastic wave device 1 described above, so detailed descriptions will not be repeated here.

[0108] The first dielectric 40 is configured to extend integrally over a wide range, including the front end of the first electrode finger 4b included in the first edge region A1 and the adjacent portion of the second electrode finger 5b, the portion of the second electrode finger 5b included in the first outer region C1, and the second busbar 5a.

[0109] The second dielectric 50 is configured to extend integrally over a wide range including the front end of the second electrode finger 5b included in the second edge region A2 and the adjacent portion of the first electrode finger 4b, the portion of the first electrode finger 4b included in the second outer region C2, and the first busbar 4a.

[0110] Even with the first dielectric 40 and the second dielectric 50, stray emissions can be suppressed using a piston mode. That is, in the elastic wave device 1C based on this modified example 4, the elastic wave velocity in the first edge region A1 and the second edge region A2 is lower than the elastic wave velocity in the central region B, and there are regions in the first outer region C1 and the second outer region C2 where the elastic wave velocity is higher than that in the central region B. Thus, the elastic wave velocity is distributed from the central region B towards the two outer sides in the Y-axis direction in the order of medium velocity, low velocity, and high velocity. Therefore, in the elastic wave device 1C based on this modified example 4, stray emissions can also be suppressed using a piston mode. Furthermore, the first dielectric 40 and the second dielectric 50 only need to be provided in the first edge region A1 and the second edge region A2, respectively, or they may not need to be provided in the regions including a portion of the first outer region C1 and the second outer region C2.

[0111] <Variation 5>

[0112] In the elastic wave device 1 based on the above-described embodiment, a protective film may also be provided covering the upper surface (end face in the positive Z-axis direction) of the IDT electrode 3.

[0113] Figure 15This is a cross-sectional view of the elastic wave device 1D based on this modified example 5. Figure 15 The elastic wave device 1D shown above will... Figure 2 The first dielectric 41 and the first electrode finger 4b of the elastic wave device 1 shown are changed to "first dielectric 41D" and "first electrode finger 4bD" respectively, and a protective film 60 is further added to cover the upper surface (end face in the positive Z-axis direction) of the IDT electrode 3. Additionally, although in Figure 15 Although not shown, in the elastic wave device 1D, the dielectrics 51, 42, 52 other than the first dielectric 41, as well as the second electrode finger 5b, are also modified in the same way as the first dielectric 41D and the first electrode finger 4bD. The other structures of the elastic wave device 1D are the same as those of the elastic wave device 1 described above, so detailed descriptions will not be repeated here.

[0114] The first dielectric 41D will contain the above-mentioned Figure 2 The second side S2 of the first dielectric 41 shown is changed to "second side S2d". The tilt angle of the second side S2d is greater than the tilt angle of the first side S1 (about 15 degrees) but less than 90 degrees (in Figure 15 In the example shown, the angle is approximately 50 degrees. That is, the second side surface S2d of the first dielectric 41D is not flat and is inclined relative to the main surface 2a of the piezoelectric substrate 2.

[0115] The first dielectric 41D is disposed between the front end of the first electrode finger 4bD and the piezoelectric substrate 2. Because the second side surface S2d of the first dielectric 41D is inclined relative to the main surface 2a of the piezoelectric substrate 2, the portion of the upper surface of the second side surface S2d of the first electrode finger 4bD is also inclined relative to the main surface 2a of the piezoelectric substrate 2.

[0116] The protective film 60 is formed to cover the upper surface (end face in the positive Z-axis direction) of the first dielectric 41D. Therefore, in the protective film 60, the portion of the upper surface of the second side surface S2d of the first dielectric 41D is also inclined relative to the main surface 2a of the piezoelectric substrate 2. Thus, the protective film 60 has a flat portion that is flat relative to the main surface 2a of the piezoelectric substrate 2 and an inclined portion that is inclined relative to the main surface 2a of the piezoelectric substrate 2. The inclined portion of the protective film 60 is formed at the boundary portion with the central region B in the first edge region A1 and at the boundary portion with the first outer region C1 in the first edge region A1.

[0117] In addition, although Figure 15 Not shown, but the inclined portion of the protective film 60 is also formed at the boundary portion with the central region B in the second edge region A2, and at the boundary portion with the second outer region C2 in the second edge region A2.

[0118] In this structure, in the protective film 60 based on this modified example 5, the thickness d2 of the inclined portion of the protective film 60 is thinner than the thickness (dimension in the Z-axis direction) d1 of the flat portion (d2 < d1). In this way, by making the thickness d2 of the inclined portion of the protective film 60 thinner than the thickness d1 of the flat portion, a more abrupt sound velocity difference can be formed between the central region B and the first edge region A1, and between the first edge region A1 and the first outer region C1.

[0119] Figure 16 This is a figure illustrating an example of the simulation results for the sound velocity difference between the central region B and the first edge region A1 when using the elastic wave device 1D based on this modified example 5. Additionally, in Figure 16 In the example shown, as a comparative example with respect to this modified example 5, the simulation results are shown by a single-dot dashed line when the thickness d1 of the flat portion of the protective film 60 is the same as the thickness d2 of the inclined portion.

[0120] according to Figure 16 The simulation results shown demonstrate that, compared to the comparative example (dashed line) where the thickness d1 of the flat portion and the thickness d2 of the inclined portion of the protective film 60 are the same, in this modified example 5 (solid line), where the thickness d2 of the inclined portion of the protective film 60 is thinner than the thickness d1 of the flat portion, the change in sound velocity difference between the central region B and the first edge region A1 is more abrupt. Therefore, in this disclosure, stray noise caused by the transverse mode can be suppressed more effectively, and the fundamental mode can propagate more efficiently.

[0121] Furthermore, in this modified example 5, the inclined portion of the protective film 60 is formed in all four boundary portions: the boundary portion of the first edge region A1 with the central region B, the boundary portion of the first edge region A1 with the first outer region C1, the boundary portion of the second edge region A2 with the central region B, and the boundary portion of the second edge region A2 with the second outer region C2. However, the inclined portion of the protective film 60 in this modified example 5 is not necessarily limited to being formed in all four boundary portions; it is sufficient that it is formed in at least one of the four boundary portions.

[0122] Furthermore, in the elastic wave device 1D based on this modified example 5, the first dielectric 41D has a first side surface S1 and a second side surface S2d. However, the first dielectric 41D is not necessarily limited to having both the first side surface S1 and the second side surface S2d. For example, the first dielectric 41D can be modified such that the first side surface S1 is omitted, becoming a dielectric in which the entire side surface (end face in the Y-axis direction) is formed by the second side surface S2d. The same modification can also be made in the dielectrics 51, 42, and 52 other than the first dielectric 41D.

[0123] The features described above in the embodiments and in variations 1 to 5 can be appropriately combined without causing contradictions.

[0124] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not restrictive. The scope of this disclosure is not shown by the description of the above embodiments, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

[0125] Explanation of reference numerals in the attached figures

[0126] 1, 1A, 1B, 1C: Elastic wave device; 2: Piezoelectric substrate; 2a: Main surface; 3: IDT electrode; 4a: First busbar; 4b, 4bA, 4bD: First electrode finger; 5a: Second busbar; 5b: Second electrode finger; 6A, 6B: Reflector; 6b: Electrode finger; 21: Piezoelectric layer; 22: Low-velocity layer; 23: High-velocity support substrate; 41, 41A, 41B, 41D; 51, 40: First dielectric; 42, 52, 50: Second dielectric; 60: Protective film; A1: First edge region; A2: Second edge region; B: Central region; C1: First outer region; C2: Second outer region.

Claims

1. An elastic wave device, comprising: Piezoelectric substrate; An IDT electrode is disposed on the main surface of the piezoelectric substrate; The first dielectric; and Second dielectric, The IDT electrode has: The first and second busbars are positioned opposite each other; The first electrode finger has one end connected to the first busbar and extends toward the second busbar; and The second electrode finger has one end connected to the second busbar and extends toward the first busbar. The first electrode finger and the second electrode finger are interlocked and interposed with each other. The first dielectric is disposed between at least one of the leading end portion of the first electrode finger and the portion of the second electrode finger adjacent to the leading end portion of the first electrode finger and the piezoelectric substrate. The second dielectric is disposed between at least one of the leading end portion of the second electrode finger and the portion of the first electrode finger adjacent to the leading end portion of the second electrode finger and the piezoelectric substrate. The region containing the tip of the first electrode finger is designated as the first edge region, the region containing the tip of the second electrode finger is designated as the second edge region, the region between the first edge region and the second edge region is designated as the central region, the region outside the first edge region relative to the central region is designated as the first outer region, and the region outside the second edge region relative to the central region is designated as the second outer region. In this configuration, the elastic wave velocity in the first edge region and the second edge region is lower than the elastic wave velocity in the central region, and there are regions in the first outer region and the second outer region where the elastic wave velocity is higher than the elastic wave velocity in the central region. At least one of the end faces of the first electrode finger in the extending direction and the end faces of the second electrode finger in the extending direction of the first dielectric and the second dielectric has a first surface and a second surface that is farther away from the piezoelectric substrate than the first surface. The tilt angle of the first surface relative to the main surface of the piezoelectric substrate is smaller than the tilt angle of the second surface relative to the main surface of the piezoelectric substrate.

2. The elastic wave device according to claim 1, wherein, At least one of the end faces of the first dielectric, the second dielectric, and the second electrode in the direction of extension of the first electrode fingers, further has a third surface that is farther away from the piezoelectric substrate than the second surface. The tilt angle of the third surface relative to the main surface of the piezoelectric substrate is smaller than the tilt angle of the second surface relative to the main surface of the piezoelectric substrate.

3. The elastic wave device according to claim 1 or 2, wherein, The tilt angle of the second surface relative to the main surface of the piezoelectric substrate is less than 90 degrees.

4. The elastic wave device according to claim 1 or 2, wherein, The piezoelectric substrate is composed of lithium tantalate.

5. The elastic wave device according to claim 1 or 2, wherein, The piezoelectric substrate has: piezoelectric film; A low-velocity layer is stacked on the opposite side of the IDT electrode relative to the piezoelectric film layer, and the velocity of the propagating volume wave is lower than the velocity of the elastic wave propagating in the piezoelectric film. as well as A high-velocity support substrate is stacked on the opposite side of the IDT electrode relative to the low-velocity layer, and the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the piezoelectric film.

6. The elastic wave device according to claim 1 or 2, wherein, It also has a protective film covering the IDT electrode. The protective film has the following characteristics: An inclined portion is formed in at least one of the boundary portion between the first edge region and the central region, the boundary portion between the first edge region and the first outer region, the boundary portion between the second edge region and the central region, and the boundary portion between the second edge region and the second outer region, and is inclined relative to the main surface of the piezoelectric substrate; as well as The flat portion, formed in the area other than the inclined portion, is flat relative to the main surface of the piezoelectric substrate. The thickness of the inclined portion of the protective film is thinner than the thickness of the flat portion of the protective film.

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