Elastic wave device

Abstract

An elastic wave device is provided, capable of handling high frequencies and improving linearity. The elastic wave device (1) includes a piezoelectric layer (4), a first electrode (51), and a second electrode (52). The first electrode (51) and the second electrode (52) are positioned opposite each other in a direction (D2) intersecting the thickness direction (D1) of the piezoelectric layer (4). The elastic wave device (1) utilizes a thickness-sheared first-order mode bulk wave. The material of the piezoelectric layer (4) is lithium niobate or lithium tantalate. The piezoelectric layer (4) is disposed on a first main surface (21) of a silicon substrate (2). The elastic wave device (1) also has a trapping region (10). The trapping region (10) is disposed on the second main surface (42) side of the piezoelectric layer (4).

Description

Technical Field

[0001] This invention generally relates to elastic wave devices, and more specifically, to elastic wave devices having a piezoelectric layer. Background Technology

[0002] Previously, a surface acoustic wave device comprising a support substrate, a low-velocity sound film, a piezoelectric thin film, and an IDT electrode was known (see, for example, Patent Document 1).

[0003] The material of the supporting substrate is, for example, silicon. The material of the low-velocity film is, for example, silicon oxide. The material of the piezoelectric film is, for example, LiTaO3.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2015 / 098678 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The surface acoustic wave (SAW) device disclosed in Patent Document 1 is difficult to handle further high frequencies. In addition, the SAW device disclosed in Patent Document 1 sometimes suffers from a decrease in linearity due to high-order harmonic distortion, IMD (intermodulation distortion), etc.

[0009] The purpose of this invention is to provide an elastic wave device that can cope with high frequencies and improve linearity.

[0010] Methods for solving problems

[0011] An elastic wave device according to one aspect of the present invention includes a piezoelectric layer, a first electrode, and a second electrode. The first electrode and the second electrode are opposed to each other in a direction intersecting the thickness direction of the piezoelectric layer. The elastic wave device utilizes thickness shearing of a first-order mode bulk wave. The elastic wave device further includes a silicon substrate. The silicon substrate has a first main surface and a second main surface opposed to each other. The piezoelectric layer is made of lithium niobate or lithium tantalate. The piezoelectric layer is disposed on the first main surface of the silicon substrate. The elastic wave device further includes a trapping region disposed on the silicon substrate.

[0012] An elastic wave device according to one aspect of the present invention includes a piezoelectric layer, a first electrode, and a second electrode. The first electrode and the second electrode are opposed to each other in a direction intersecting the thickness direction of the piezoelectric layer. The first electrode and the second electrode are adjacent electrodes. In the elastic wave device, when the distance between the center lines of the first electrode and the second electrode is defined as p in any cross-section along the thickness direction of the piezoelectric layer and the thickness of the piezoelectric layer is defined as d, d / p is 0.5 or less. The elastic wave device further includes a silicon substrate. The silicon substrate has a first main surface and a second main surface opposed to each other. The material of the piezoelectric layer is lithium niobate or lithium tantalate. The piezoelectric layer is disposed on the first main surface of the silicon substrate. The elastic wave device also has a trapping region disposed on the silicon substrate.

[0013] Invention Effects

[0014] In the elastic wave device of the present invention described above, it is possible to handle high frequencies and improve linearity. Attached Figure Description

[0015] Figure 1 This is a top view of the elastic wave device according to Embodiment 1.

[0016] Figure 2 Regarding the aforementioned elastic wave device Figure 1 A sectional view along line AA.

[0017] Figure 3 Regarding the aforementioned elastic wave device Figure 1 BB line section view.

[0018] Figure 4 This is a three-dimensional view of a section of the aforementioned elastic wave device.

[0019] Figure 5 This is a top view of the main part of the aforementioned elastic wave device.

[0020] Figure 6A This is an explanatory diagram of Lamb. Figure 6B This is an illustration of the volume wave of the first-order mode of thickness shear.

[0021] Figure 7 This is an explanatory diagram of the operation of the elastic wave device in Embodiment 1.

[0022] Figure 8 This is an explanatory diagram of the structural model of an elastic wave device in reference mode.

[0023] Figure 9A This is a coordinate graph showing the relationship between the relative bandwidth of the thickness shear mode and the [thickness of the piezoelectric layer] / [distance between the centerlines of the two paired electrodes] for the above construction model. Figure 9BThis is a coordinate graph showing the relationship between the relative bandwidth of the thickness shear mode and [thickness of the piezoelectric layer] / [distance between the centerlines of the paired electrodes] based on the above structural model. Figure 9A The magnified coordinate graph of the horizontal axis in the range of 0 to 0.2.

[0024] Figure 10 This is a graph showing the relationship between the relative bandwidth of the thickness shear mode and the normalized spurious level for the above-described construction model.

[0025] Figure 11 This is the impedance-frequency characteristic diagram of the above-described model.

[0026] Figure 12 This is a diagram illustrating the distribution of relative bandwidth in the combination of [thickness of the piezoelectric layer] / [distance between the centerlines of the two paired electrodes] and construction parameters, based on the above construction model.

[0027] Figure 13 This is a cross-sectional view of another structural example of the elastic wave device according to Embodiment 1.

[0028] Figure 14 This is a top view of the elastic wave device of Embodiment 1, a variation of Embodiment 1.

[0029] Figure 15 This is the equivalent circuit diagram of the aforementioned elastic wave device.

[0030] Figure 16 This is a top view of the elastic wave device of Embodiment 1, Variation 2.

[0031] Figure 17 This is a top view of the elastic wave device of variation 3 of embodiment 1.

[0032] Figure 18 This is a cross-sectional view of the elastic wave device according to Embodiment 2.

[0033] Figure 19 This is a top view of the elastic wave device according to Embodiment 2.

[0034] Figure 20 Regarding the aforementioned elastic wave device Figure 19 A sectional view along line AA.

[0035] Figure 21 Regarding the aforementioned elastic wave device Figure 19 BB line section view.

[0036] Figure 22 This is a top view of the elastic wave device of Modification 1 of Embodiment 2.

[0037] Figure 23This is a top view of the elastic wave device of Embodiment 2, Variation 2.

[0038] Figure 24 This is a top view of the elastic wave device of variation 3 of embodiment 2.

[0039] Figure 25 This is a cross-sectional view of the elastic wave device of variation 4 of embodiment 2.

[0040] Figure 26 This is a top view of the elastic wave device of variation 5 of embodiment 2.

[0041] Figures 27A to 27D This is a cross-sectional view showing another shape of a pair of electrodes in an elastic wave device.

[0042] Figures 28A-28C This is a cross-sectional view showing another structural example of the above-mentioned elastic wave device. Detailed Implementation

[0043] The following implementation methods, etc., refer to Figures 1-8 Figures 13, 14, and 16-28C are schematic diagrams. The size or thickness ratio of each component in the figure may not necessarily reflect the actual size ratio.

[0044] (Implementation Method 1)

[0045] The following is for reference Figures 1-5 The elastic wave device 1 of Embodiment 1 will be described.

[0046] (1.1) Overall structure of the elastic wave device

[0047] like Figure 1 As shown, the elastic wave device 1 of Embodiment 1 includes a piezoelectric layer 4, a first electrode 51, and a second electrode 52. As... Figure 2As shown, the first electrode 51 and the second electrode 52 are positioned opposite each other in a direction D2 (hereinafter referred to as the second direction D2) that intersects the thickness direction D1 (hereinafter also referred to as the first direction D1) of the piezoelectric layer 4. The elastic wave device 1 is an elastic wave device that utilizes a thickness shear first-order mode bulk wave. The second direction D2 is orthogonal to the polarization direction PZ1 of the piezoelectric layer 4. The thickness shear first-order mode bulk wave is a bulk wave that propagates in the thickness direction D1 of the piezoelectric layer 4 through thickness shear vibration of the piezoelectric layer 4, and is a bulk wave with a number of segments equal to 1 in the thickness direction D1 of the piezoelectric layer 4. The thickness shear vibration is excited by the first electrode 51 and the second electrode 52. The thickness shear vibration is excited in the piezoelectric layer 4 in a defined region 45 between the first electrode 51 and the second electrode 52 when viewed from the thickness direction D1. In the elastic wave device 1, if the second direction D2 is orthogonal to the polarization direction PZ1 of the piezoelectric layer 4, the electromechanical coupling coefficient (hereinafter also referred to as the coupling coefficient) of the bulk wave of the first-order mode of thickness shear is relatively large. Here, "orthogonal" is not limited to the case of strict orthogonality, but can also be approximately orthogonal (the angle between the second direction D2 and the polarization direction PZ1 is, for example, 90°±10°).

[0048] like Figure 1 and 2 As shown, the elastic wave device 1 includes a plurality of first electrodes 51 and a plurality of second electrodes 52. That is, when the first electrodes 51 and the second electrodes 52 are configured as a pair of electrode groups, the elastic wave device 1 has multiple pairs of electrode groups of first electrodes 51 and second electrodes 52. In the elastic wave device 1, the plurality of first electrodes 51 and the plurality of second electrodes 52 are arranged alternately, one at a time, in the second direction D2. Figure 1 As shown, the elastic wave device 1 further includes a first wiring portion 61 connected to a first electrode 51 and a second wiring portion 62 connected to a second electrode 52. The first wiring portion 61 is connected to a first terminal T1. The second wiring portion 62 is connected to a second terminal T2, which is different from the first terminal T1. Multiple first electrodes 51 are connected to the first wiring portion 61. Multiple second electrodes 52 are connected to the second wiring portion 62.

[0049] like Figure 2As shown, the elastic wave device 1 includes a silicon substrate 2, a piezoelectric layer 4, a plurality of first electrodes 51, and a plurality of second electrodes 52. The piezoelectric layer 4 is disposed on the silicon substrate 2. As an example, the piezoelectric layer 4 is disposed on the silicon substrate 2 with a silicon oxide film 7 in between. The plurality of first electrodes 51 and the plurality of second electrodes 52 are disposed on the piezoelectric layer 4. The elastic wave device 1 has an elastic wave resonator 5 including the first electrodes 51, the second electrodes 52, and the piezoelectric layer 4 as a resonator. The silicon substrate 2 includes at least a portion of a cavity 26 opposite a portion of the piezoelectric layer 4. The cavity 26 overlaps with the plurality of first electrodes 51 and the plurality of second electrodes 52 when viewed from the thickness direction D1 of the piezoelectric layer 4. Here, the cavity 26 overlaps with the plurality of first electrodes 51, the plurality of second electrodes 52, and a plurality of defined regions 45 when viewed from the thickness direction D1 of the piezoelectric layer 4. The plurality of defined regions 45 are the portions between adjacent first electrodes 51 and second electrodes 52. It should be noted that "adjacent" to the first electrode 51 and the second electrode 52 means that the first electrode 51 and the second electrode 52 are placed opposite each other with a gap between them.

[0050] The elastic wave device 1 also has a trapping region 10 that suppresses the movement of charges (see reference). Figures 2-4 ).

[0051] (1.2) Components of an elastic wave device

[0052] Next, the constituent elements of the elastic wave device 1 will be described with reference to the accompanying drawings.

[0053] (1.2.1) Silicon substrate

[0054] like Figure 2 As shown, the silicon substrate 2 supports the piezoelectric layer 4. In the elastic wave device 1 of Embodiment 1, the silicon substrate 2 supports the piezoelectric layer 4, a plurality of first electrodes 51, and a plurality of second electrodes 52 through a silicon oxide film 7.

[0055] The silicon substrate 2 has a first main surface 21 and a second main surface 22 that are opposite each other. The first main surface 21 and the second main surface 22 are opposite each other in the thickness direction of the silicon substrate 2. The thickness direction of the silicon substrate 2 is along the thickness direction D1 of the piezoelectric layer 4. When viewed from the thickness direction D1 of the piezoelectric layer 4, the outer periphery of the silicon substrate 2 is rectangular, but not limited to this, for example, it can also be square.

[0056] The thickness of the silicon substrate 2 is, for example, 100 μm or more and 500 μm or less. The silicon substrate 2 is formed using a monocrystalline silicon substrate having a first main surface and a second main surface that are opposite each other. The orientation of the first main surface of the monocrystalline silicon substrate can be, for example, a (100) surface, a (110) surface, or a (111) surface. The propagation orientation of the bulk wave described above can be set without being restricted by the orientation of the monocrystalline silicon substrate. The resistivity of the monocrystalline silicon substrate is, for example, 1 kΩcm or more, preferably 2 kΩcm or more, and more preferably 4 kΩcm or more.

[0057] The first main surface 21 of the silicon substrate 2 includes a rough surface 211. The rough surface 211 is formed by roughening the first main surface of the monocrystalline silicon substrate. In the elastic wave device 1 of Embodiment 1, the entire area of ​​the first main surface 21 of the silicon substrate 2 is the rough surface 211. The rough surface 211 does not overlap with the elastic wave resonator 5 when viewed from the thickness direction D1 of the piezoelectric layer 4. The silicon substrate 2 has a body region 2B and a surface region 2S. The body region 2B is located on the side of the surface region 2S opposite to the piezoelectric layer 4 side. The surface region 2S is, for example, an amorphous silicon layer. The amorphous silicon layer is formed, for example, by degrading the lattice structure of the monocrystalline silicon substrate when roughening the first main surface of the monocrystalline silicon substrate. The surface region 2S includes the first main surface 21 of the silicon substrate 2. The thickness of the surface region 2S is, for example, 1 nm or more and 700 nm or less. The body region 2B is a monocrystalline silicon layer. The monocrystalline silicon layer is the remaining portion of the monocrystalline silicon substrate after the surface region 2S has been formed on it. The body region 2B includes the second main surface 22 of the silicon substrate 2. In the elastic wave device 1, the trapping region 10 includes the surface region 2S. The surface region 2S is not limited to an amorphous silicon layer, but may also be a polycrystalline silicon layer, for example. The surface region 2S can be formed, for example, by grinding a portion of the monocrystalline silicon substrate from the first main surface of the monocrystalline silicon substrate, but is not limited thereto. The surface region 2S may also be an amorphous silicon layer or a polycrystalline silicon layer deposited on the monocrystalline silicon substrate constituting the body region 2B. In the silicon substrate 2, when the surface region 2S is an amorphous silicon layer or a polycrystalline silicon layer deposited on the body region 2B, the first main surface 21 of the silicon substrate 2 may include a rough surface 211, or may not include a rough surface 211. In addition, the surface region 2S may also be formed, for example, by implanting ions of at least one element selected from the group consisting of argon, silicon, oxygen, and carbon from the first main surface of the monocrystalline silicon substrate. Alternatively, the surface region 2S can also be formed, for example, by irradiating the monocrystalline silicon substrate with radiation from the first main surface of the monocrystalline silicon substrate. When the surface region 2S is formed by ion implantation or radiation irradiation, the first main surface 21 of the silicon substrate 2 may or may not include a rough surface 211.

[0058] The silicon substrate 2 includes at least a portion of a cavity 26 opposite to the second main surface 42 of the piezoelectric layer 4. The cavity 26 is located on the side opposite to the first electrode 51 and the second electrode 52, separated by the piezoelectric layer 4. The cavity 26 overlaps with the elastic wave resonator 5 when viewed from the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1 of Embodiment 1, the cavity 26 is larger than the elastic wave resonator 5 when viewed from the thickness direction D1 of the piezoelectric layer 4, and overlaps the entire elastic wave resonator 5. In addition, in the elastic wave device 1 of Embodiment 1, the cavity 26 also overlaps with a portion of each of the first wiring portion 61 and the second wiring portion 62 when viewed from the thickness direction D1 of the piezoelectric layer 4. The opening shape of the cavity 26 when viewed from the thickness direction D1 of the piezoelectric layer 4 is rectangular, but not limited to this.

[0059] (1.2.2) Silicon oxide film

[0060] A silicon oxide film 7 is disposed between the first main surface 21 of the silicon substrate 2 and the piezoelectric layer 4. In the elastic wave device 1 of Embodiment 1, the silicon oxide film 7 overlaps the entire area of ​​the first main surface 21 of the silicon substrate 2 in the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1 of Embodiment 1, the entire area of ​​the first main surface 21 is a rough surface 211; therefore, the silicon oxide film 7 overlaps the rough surface 211 of the silicon substrate 2 when viewed from above in the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1 of Embodiment 1, the silicon substrate 2 and the piezoelectric layer 4 are bonded together with the silicon oxide film 7 in between.

[0061] The thickness of the silicon oxide film 7 is, for example, 0.1 μm or more and 10 μm or less.

[0062] (1.2.3) Piezoelectric layer

[0063] like Figure 2 As shown, the piezoelectric layer 4 has a first main surface 41 and a second main surface 42 facing each other. The first main surface 41 and the second main surface 42 are facing each other in the thickness direction D1 of the piezoelectric layer 4. The piezoelectric layer 4 is disposed on the first main surface 21 of the silicon substrate 2. Here, the piezoelectric layer 4 overlaps with the first main surface 21 and the void 26 of the silicon substrate 2 when viewed from the thickness direction D1. In the piezoelectric layer 4, the second main surface 42 of the first main surface 41 and the second main surface 42 is located on the silicon substrate 2 side. The first main surface 41 of the piezoelectric layer 4 is the main surface of the piezoelectric layer 4 on the side opposite to the silicon substrate 2 side. The second main surface 42 of the piezoelectric layer 4 is the main surface of the piezoelectric layer 4 on the silicon substrate 2 side.

[0064] In the elastic wave device 1, the distance between the first main surface 41 of the piezoelectric layer 4 and the silicon substrate 2 is longer than the distance between the second main surface 42 of the piezoelectric layer 4 and the silicon substrate 2. The material of the piezoelectric layer 4 is lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). The piezoelectric layer 4 is, for example, Z-cut LiNbO3 or Z-cut LiTaO3. Regarding the Euler angles of the piezoelectric layer 4... θ is 0°±10°. ψ is an arbitrary angle. From the viewpoint of improving the coupling coefficient, the piezoelectric layer 4 is preferably Z-cut LiNbO3 or Z-cut LiTaO3. The piezoelectric layer 4 can also be rotated Y-cut LiNbO3, rotated Y-cut LiTaO3, X-cut LiNbO3, or X-cut LiTaO3. The propagation orientation can be the Y-axis direction in the crystal axis (X, Y, Z) defined relative to the crystal structure of the piezoelectric layer 4, or the X-axis direction, or a direction rotated from the X-axis within ±90°. The piezoelectric layer 4 is a single crystal, but not limited to this; for example, it can also be a twin crystal or a ceramic.

[0065] The thickness of the piezoelectric layer 4 is, for example, 50 nm or more and 1000 nm or less, and for example, 400 nm.

[0066] The piezoelectric layer 4 has a defined region 45. The defined region 45 is a region that, when viewed from the thickness direction D1 of the piezoelectric layer 4, intersects both the first electrode 51 and the second electrode 52 in the direction opposite to each other in the piezoelectric layer 4, and is located between the first electrode 51 and the second electrode 52.

[0067] (1.2.4) Electrode

[0068] Multiple first electrodes 51 and multiple second electrodes 52 are disposed on the first main surface 41 of the piezoelectric layer 4.

[0069] In the elastic wave device 1, the paired first electrode 51 and second electrode 52 are at different potentials. In the elastic wave device 1, one of the paired first electrode 51 and second electrode 52 is an electrode that becomes a signal potential when an alternating voltage is applied, and the other is an electrode that becomes a ground potential.

[0070] In the elastic wave device 1, a plurality of first electrodes 51 and a plurality of second electrodes 52 are arranged alternately, spaced apart from each other. Therefore, adjacent first electrodes 51 and second electrodes 52 are separated. The distance between the centerlines of paired first electrodes 51 and second electrodes 52 is, for example, 1 μm or more and 10 μm or less; for example, it is 3 μm. A group of electrodes including a plurality of first electrodes 51 and a plurality of second electrodes 52 can be configured such that the plurality of first electrodes 51 and the plurality of second electrodes 52 are spaced apart in the second direction D2, or it can be configured such that the plurality of first electrodes 51 and the plurality of second electrodes 52 are not alternately spaced apart from each other. For example, it is also possible to have a region where one first electrode 51 and one second electrode 52 are arranged alternately, and a region where two of the first electrodes 51 or the second electrodes 52 are arranged in the second direction D2.

[0071] like Figure 1 As shown, the plurality of first electrodes 51 and the plurality of second electrodes 52, viewed from the thickness direction D1 of the piezoelectric layer 4, are elongated strips (straight lines) with a third direction D3 orthogonal to the second direction D2 as the long side and the second direction D2 as the width direction. The length of each of the plurality of first electrodes 51 is, for example, 20 μm, but is not limited thereto. The width H1 (first electrode width H1) of each of the plurality of first electrodes 51 is, for example, 50 nm or more and 1000 nm or less; as an example, it is 500 nm. The length of each of the plurality of second electrodes 52 is, for example, 20 μm, but is not limited thereto. The width H2 (second electrode width H2) of each of the plurality of second electrodes 52 is, for example, 50 nm or more and 1000 nm or less; as an example, it is 500 nm.

[0072] Each of the plurality of first electrodes 51 has a first electrode main portion 510. The first electrode main portion 510 is the portion of the first electrode 51 that intersects with the second electrode 52 in the direction in which the first electrode 51 and the second electrode 52 are facing each other. Furthermore, each of the plurality of second electrodes 52 has a second electrode main portion 520. The second electrode main portion 520 is the portion of the second electrode 52 that intersects with the first electrode 51 in the direction in which the first electrode 51 and the second electrode 52 are facing each other.

[0073] In the elastic wave device 1 of Embodiment 1, the width H1 of each of the plurality of first electrodes 51 is the same, but it is not limited to this and may be different. Similarly, in the elastic wave device 1 of Embodiment 1, the width H2 of each of the plurality of second electrodes 52 is the same, but it is not limited to this and may be different. In the elastic wave device 1 of Embodiment 1, the width H1 of the first electrode and the width H2 of the second electrode are the same, but it is not limited to this and the width H1 of the first electrode and the width H2 of the second electrode may be different.

[0074] Regarding the elastic wave device 1 in Embodiment 1, in Figure 1In the text, the number of the first electrode 51 and the second electrode 52 is described as 5, but the number of the first electrode 51 and the second electrode 52 is not limited to 5. It can also be 1, 2 to 4, 6 or more, or 50 or more.

[0075] The second direction D2, where adjacent first electrodes 51 and second electrodes 52 are positioned opposite each other, is preferably aligned with the polarization direction PZ1 of the piezoelectric layer 4 (refer to...). Figure 2 Orthogonal, but not limited to. For example, if the piezoelectric layer 4 is not a Z-cut piezoelectric material, the first electrode 51 and the second electrode 52 can also be positioned opposite each other in a direction orthogonal to the third direction D3, which is the long side direction. It should be noted that there are also cases where the first electrode 51 and the second electrode 52 are not rectangular. In this case, the third direction D3, which is the long side direction, can also be the long side direction of the circumscribed polygon that is external to the first electrode 51 and the second electrode 52 when viewed from above. It should be noted that the "circumscribed polygon that is external to the first electrode 51 and the second electrode 52" includes the following polygons: when the first wiring portion 61 is connected to the first electrode 51 and the second wiring portion 62 is connected to the second electrode 52, at least the portion of the first electrode 51 excluding the portion connected to the first wiring portion 61 and the portion of the second electrode 52 excluding the portion connected to the second wiring portion 62 are external to it.

[0076] like Figure 2 As shown, the plurality of first electrodes 51 each include a first main surface 511 and a second main surface 512 intersecting the thickness direction D1 of the piezoelectric layer 4, and two side surfaces 513, 514 intersecting the width direction of the first electrode 51. In each of the plurality of first electrodes 51, the second main surface 512 of the first main surface 511 and the second main surface 512 is located on the side of the first main surface 41 of the piezoelectric layer 4, and is in planar contact with the first main surface 41 of the piezoelectric layer 4.

[0077] Each of the plurality of second electrodes 52 includes a first main surface 521 and a second main surface 522 that intersect the thickness direction D1 of the piezoelectric layer 4, and two side surfaces 523, 523 that intersect the width direction of the second electrode 52. In each of the plurality of second electrodes 52, the second main surface 522 of the first main surface 521 and the second main surface 522 is located on the side of the first main surface 41 of the piezoelectric layer 4, and is in planar contact with the first main surface 41 of the piezoelectric layer 4.

[0078] The plurality of first electrodes 51 and the plurality of second electrodes 52 are conductive. The materials of each first electrode 51 and each second electrode 52 are, for example, Al (aluminum), Cu (copper), Pt (platinum), Au (gold), Ag (silver), Ti (titanium), Ni (nickel), Cr (chromium), Mo (molybdenum), W (tungsten), or alloys primarily composed of any of these metals. Alternatively, each first electrode 51 and each second electrode 52 may have a structure formed by stacking multiple metal films comprising these metals or alloys. Each first electrode 51 and each second electrode 52, for example, comprises a laminated film consisting of a bonding film and a main electrode film. The bonding film comprises a Ti film, and the main electrode film comprises an Al film or an AlCu film formed on the bonding film. The thickness of the bonding film is, for example, 10 nm. The thickness of the main electrode film is, for example, 80 nm. In the AlCu film, the concentration of Cu is preferably 1 wt% or more and 20 wt% or less.

[0079] (1.2.5) First wiring section and second wiring section

[0080] The first wiring section 61 includes a first busbar 611. The first busbar 611 is a conductor section used to make the plurality of first electrodes 51 have the same potential. The first busbar 611 is a long strip (straight line) with the second direction D2 as its long side direction. The first busbar 611 is connected to the plurality of first electrodes 51. The plurality of first electrodes 51 connected to the first busbar 611 extend toward the second busbar 621. In the elastic wave device 1, the first conductor section including the plurality of first electrodes 51 and the first busbar 611 has a comb-shaped shape when viewed from the thickness direction D1 of the piezoelectric layer 4. The first busbar 611 is integrally formed with the plurality of first electrodes 51, but is not limited thereto.

[0081] The second wiring section 62 includes a second busbar 621. The second busbar 621 is a conductor section used to make the plurality of second electrodes 52 have the same potential. The second busbar 621 is a long strip (straight line) with the second direction D2 as its long side direction. The second busbar 621 is connected to the plurality of second electrodes 52. The plurality of second electrodes 52 connected to the second busbar 621 extend toward the first busbar 611. In the elastic wave device 1, the second conductor section including the plurality of second electrodes 52 and the second busbar 621 has a comb-shaped shape when viewed from the thickness direction D1 of the piezoelectric layer 4. The second busbar 621 is integrally formed with the plurality of second electrodes 52, but is not limited thereto.

[0082] The first bus bar 611 and the second bus bar 621 are positioned opposite each other on the third direction D3.

[0083] The first wiring portion 61 and the second wiring portion 62 are conductive. The materials of the first wiring portion 61 and the second wiring portion 62 are, for example, Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W, or alloys primarily composed of any of these metals. Alternatively, the first wiring portion 61 and the second wiring portion 62 may have a structure formed by stacking multiple metal films comprising these metals or alloys. The first wiring portion 61 and the second wiring portion 62 may, for example, comprise a laminated film comprising a bonding film and a main wiring film. The bonding film comprises a Ti film, and the main wiring film comprises an Al film or an AlCu film formed on the bonding film. The thickness of the bonding film is, for example, 10 nm. The thickness of the main wiring film is, for example, 80 nm. In the AlCu film, the concentration of Cu is preferably 1 wt% or more and 20 wt% or less.

[0084] In the elastic wave device 1, from the viewpoint of reducing the resistance of the first busbar 611 and the second busbar 621, a metal film may be included on the main wiring film of each of the first busbar 611 and the second busbar 621. In addition, the thickness of each of the first wiring portion 61 and the second wiring portion 62 may be thicker than the thickness of the first electrode 51 and the second electrode 52.

[0085] (1.2.6) Captured Area

[0086] A trapping region 10 is disposed on the second main surface 42 side of the piezoelectric layer 4. The trapping region 10 is disposed on the silicon substrate 2. The trapping region 10 suppresses the movement of charge along the first main surface 21 of the silicon substrate 2. Here, in the elastic wave device 1 of Embodiment 1, the trapping region 10 suppresses the movement of charge near the interface between the first main surface 21 of the silicon substrate 2 and the silicon oxide film 7 along the first main surface 21 of the silicon substrate 2 between the first wiring portion 61 and the second wiring portion 62 when a potential difference exists between the first wiring portion 61 and the second wiring portion 62.

[0087] In the elastic wave device 1 of Embodiment 1, the trapping density of the surface region 2S included in the trapping region 10 is higher than the trapping density of the bulk region 2B. Here, trapping density is the trapping density of trapped charges (free charge carriers). Furthermore, in the trapping region 10, the carrier mobility of the surface region 2S is lower than that of the bulk region 2B. In the elastic wave device 1 of Embodiment 1, the voids 26 included in the silicon substrate 2 overlap with portions of the first wiring portion 61 and the second wiring portion 62 when viewed from the thickness direction D1 of the piezoelectric layer 4, and are included in the trapping region 10. That is, in the elastic wave device 1 of Embodiment 1, the trapping region 10 includes the surface region 2S of the silicon substrate 2 and the voids 26 of the silicon substrate 2.

[0088] (1.3) Manufacturing method of elastic wave device

[0089] In the manufacturing method of the elastic wave device 1, for example, after preparing a monocrystalline silicon substrate having a first main surface and a second main surface that are opposite to each other, the first to sixth steps are performed. In the first step, a silicon substrate 2 having a surface region 2S and a bulk region 2B is formed by roughening the first main surface of the monocrystalline silicon substrate. In the second step, a silicon oxide film 7 is formed on the first main surface 21 of the silicon substrate 2. In the third step, a piezoelectric substrate, which will become the basis of the piezoelectric layer 4, is bonded to the silicon substrate 2 through the silicon oxide film 7. In the fourth step, a piezoelectric layer 4 including a portion of the piezoelectric substrate is formed by thinning the piezoelectric substrate. In the fifth step, a plurality of first electrodes 51, a plurality of second electrodes 52, a first wiring portion 61, a second wiring portion 62, a first terminal T1, and a second terminal T2 are formed on the first main surface 41 of the piezoelectric layer 4. In the sixth step, a cavity 26 is formed from the second main surface 22 of the silicon substrate 2. In the fifth step described above, multiple first electrodes 51, multiple second electrodes 52, a first wiring portion 61, a second wiring portion 62, a first terminal T1, and a second terminal T2 are formed using photolithography, etching, and thin film formation techniques. Furthermore, in the sixth step described above, the predetermined area for forming the voids 26 in the silicon substrate 2 is etched using photolithography and etching techniques. In the sixth step, the silicon substrate 2 is etched using a silicon oxide film 7 as an etching barrier layer. Afterward, unwanted portions of the silicon oxide film 7 are etched away, thereby exposing a portion of the second main surface 42 of the piezoelectric layer 4. Additionally, when preparing the single-crystal silicon substrate, a single-crystal silicon wafer is prepared, and in the third step, the piezoelectric wafer is used as the piezoelectric substrate. In the method for manufacturing the elastic wave device 1, multiple elastic wave devices 1 (chips) are obtained by cutting a wafer comprising multiple elastic wave devices 1.

[0090] The manufacturing method of the elastic wave device 1 is just one example and is not particularly limited. For example, the piezoelectric layer 4 can also be formed using a film deposition technique. In this case, the manufacturing method of the elastic wave device 1 includes a step of forming a piezoelectric layer 4 instead of the third and fourth steps. The piezoelectric layer 4 formed by the film deposition technique can be, for example, a single crystal or a twin crystal. As a film deposition technique, CVD (Chemical Vapor Deposition) is cited as an example, but it is not limited to this.

[0091] (1.4) Operation and characteristics of elastic wave devices

[0092] The elastic wave device 1 of Embodiment 1 is an elastic wave device utilizing a first-order thickness shear mode volume wave. As described above, the first-order thickness shear mode volume wave is a volume wave propagating in the thickness direction D1 of the piezoelectric layer 4 through thickness shear vibration of the piezoelectric layer 4, and is a volume wave with a node number of 1 in the thickness direction D1 of the piezoelectric layer 4. The thickness shear vibration is excited by the first electrode 51 and the second electrode 52. The thickness shear vibration is excited in a defined region 45 between adjacent first electrodes 51 and second electrodes 52 in the piezoelectric layer 4 when viewed from the thickness direction D1. The thickness shear vibration can be confirmed, for example, by FEM (Finite Element Method). More specifically, for example, by using parameters of the piezoelectric layer 4 (material, Euler angle, and thickness, etc.), parameters of the first electrode 51 and the second electrode 52 (material, thickness, distance between the center lines of the first electrode 51 and the second electrode 52, etc.), the displacement distribution can be analyzed and the deformation can be analyzed by FEM, thereby confirming the thickness shear vibration. The Euler angles of piezoelectric layer 4 can be determined through analysis.

[0093] Here, refer to Figure 6A and 6B This is to illustrate the difference between the Lamb wave used in conventional elastic wave devices and the aforementioned first-order thickness shear mode volume wave.

[0094] Figure 6A This is a schematic front cross-sectional view illustrating the Lamb wave propagating in the piezoelectric film of a conventional elastic wave device, such as the surface acoustic wave device described in Patent Document 1. In conventional elastic wave devices, the elastic wave propagates in the piezoelectric film 400 as indicated by the arrow. Here, the piezoelectric film 400 has a first main surface 401 and a second main surface 402 that are opposite each other. Figure 6A In the diagram, the Z and X directions are shown differently from those of the piezoelectric thin film 400. Figure 6A In the diagram, the Z-direction is the thickness direction connecting the first principal surface 401 and the second principal surface 402 of the piezoelectric thin film 400. The X-direction is the direction in which the multiple electrode fingers of the IDT electrode are arranged. In Lamb waves, elastic waves are as follows: Figure 6A As shown, the plate wave propagates along the X-direction. Therefore, in conventional elastic wave devices, since the elastic wave propagates along the X-direction, two reflectors are placed on each side of the IDT electrode to obtain the desired resonance characteristics. However, in conventional elastic wave devices, propagation losses of the elastic wave occur, and thus, even with miniaturization, i.e., reducing the number of electrode finger pairs, the Q value decreases.

[0095] In contrast, in the elastic wave device 1 of Embodiment 1, the vibration displacement is in the thickness shear direction, therefore, as Figure 6BAs shown, the elastic wave propagates and resonates approximately along the Z-direction, which connects the first principal surface 41 and the second principal surface 42 of the piezoelectric layer 4. That is, the X-direction component of the elastic wave is significantly smaller than the Z-direction component. In the elastic wave device 1 of Embodiment 1, the resonance characteristic is obtained through the propagation of the elastic wave in the Z-direction, therefore, a reflector is not necessarily required. Therefore, in the elastic wave device 1 of Embodiment 1, no propagation loss occurs when the elastic wave propagates through a reflector. Therefore, in the elastic wave device 1 of Embodiment 1, even if the number of electrode pairs including the first electrode 51 and the second electrode 52 is reduced to promote miniaturization, it is difficult to cause a decrease in the Q value.

[0096] In the elastic wave device 1 of embodiment 1, such as Figure 7 As shown, the vibration width direction of the bulk wave of the first-order mode of thickness shear is opposite in the first region 451 and the second region 452 included in the defined region 45 of the piezoelectric layer 4. Figure 7 The diagram schematically illustrates a bulk wave when a voltage is applied between the first electrode 51 and the second electrode 52, making the second electrode 52 have a higher potential than the first electrode 51. The first region 451 is the region within the defined region 45 between a virtual plane VP1, orthogonal to the thickness direction D1 of the piezoelectric layer 4 and dividing the piezoelectric layer 4 into two parts, and the first main surface 41. The second region 452 is the region within the defined region 45 between the virtual plane VP1 and the second main surface 42.

[0097] Construction model 1r of an elastic wave device using a reference mode for a first-order volume wave with thickness shearing (referencing) Figure 8 The characteristics are simulated. Regarding the construction model 1r, the same labels are used for the same components as those in the elastic wave device 1 of embodiment 1, and the descriptions are omitted.

[0098] Model 1r differs from the elastic wave device 1 of Embodiment 1 in that it lacks the first wiring section 61, the second wiring section 62, and the trapping region 10. During simulation, the logarithm of the first electrode 51 and the second electrode 52 is set to infinity, and the piezoelectric layer 4 is set to rotate 120°, Y-cutting X-propagating LiNbO3.

[0099] In structural model 1r, the piezoelectric layer 4 is a film-like material, and its second principal surface 42 is in contact with air. In structural model 1r, at any cross-section along the thickness direction D1 of the piezoelectric layer 4 ( Figure 8In the model 1r, the distance between the center lines of adjacent first electrodes 51 and second electrodes 52 is defined as p, and the thickness of the piezoelectric layer 4 is defined as d. Furthermore, in the structural model 1r, viewed from the thickness direction D1 of the piezoelectric layer 4, the area of ​​the main portion 510 of the first electrode is defined as S1, the area of ​​the main portion 520 of the second electrode is defined as S2, the area of ​​the defined region 45 is defined as S0, and the structural parameter defined by (S1+S2) / (S1+S2+S0) is defined as MR. It should be noted that when at least one of multiple first electrodes 51 and second electrodes 52 is formed on the piezoelectric layer 4, the aforementioned distance between center lines p becomes the distance between the center lines of adjacent first electrodes 51 and second electrodes 52, respectively.

[0100] Figure 9A and 9B This is a coordinate graph showing the relationship between relative bandwidth and d / p when different potentials are applied to the first electrode 51 and the second electrode 52, based on the constructed model 1r. Figure 9A and 9B In the figure, the horizontal axis represents d / p, and the vertical axis represents the relative bandwidth. Figure 9A and 9B This refers to the case where the piezoelectric layer 4 is rotated 120° to cut the X-axis propagating LiNbO3, but the same trend occurs even with other cutting angles. Furthermore, in the structural model 1r of the elastic wave device, when the material of the piezoelectric layer 4 is LiTaO3, the relationship between the relative bandwidth and d / p also becomes... Figure 9A and 9B The same trend applies. Furthermore, in the construction model 1r of the elastic wave device, regardless of the logarithm of the first electrode 51 and the second electrode 52, the relationship between the relative bandwidth and d / p becomes... Figure 9A and 9B The same trend applies. Furthermore, in the structural model 1r of the elastic wave device, not limited to the case where the second principal surface 42 of the piezoelectric layer 4 is in contact with air, but also in the case where it is in contact with the acoustic reflection layer, the relationship between the relative bandwidth and d / p also becomes related to... Figure 9A and 9B The same trend.

[0101] according to Figure 9A It can be seen that in the structural model 1r of the elastic wave device, the relative bandwidth changes drastically with an inflection point of d / p = 0.5. In the structural model 1r of the elastic wave device, when d / p > 0.5, regardless of how d / p is varied within the range of 0.5 < d / p < 1.6, the coupling coefficient remains low, and the relative bandwidth is less than 5%. On the other hand, in the structural model 1r of the elastic wave device, when d / p ≤ 0.5, if d / p is varied within the range of 0 < d / p ≤ 0.5, the coupling coefficient can be increased, making the relative bandwidth greater than 5%.

[0102] Furthermore, in the construction model 1r of the elastic wave device, when d / p ≤ 0.24, if d / p is varied within the range of 0 < d / p ≤ 0.24, the coupling coefficient can be further improved, resulting in a larger relative bandwidth. Regarding the elastic wave device 1 of Embodiment 1, as... Figure 2 As shown, if in any cross section along the thickness direction D1 of the piezoelectric layer 4, the distance between the center lines of the first electrode 51 and the second electrode 52 is set as p, and the thickness of the piezoelectric layer 4 is set as d, then the relationship between its relative bandwidth and d / p also follows the same trend as the relationship between the relative bandwidth and d / p of the construction model 1r of the elastic wave device.

[0103] In addition, by Figure 9A It can be seen that when d / p ≤ 0.10, if d / p is varied within the range of 0 < d / p ≤ 0.10, the coupling coefficient can be further increased, making the relative bandwidth even larger.

[0104] Figure 9B It is Figure 9A A magnified portion of the coordinate graph. For example... Figure 9B As shown, the relative bandwidth changes with an inflection point of d / p = 0.096. Therefore, when d / p ≤ 0.096, if d / p is varied within the range of 0 < d / p ≤ 0.096, the coupling coefficient can be further increased compared to the case where 0.096 < d / p, resulting in a larger relative bandwidth. Additionally, as... Figure 9B As shown, the relative bandwidth changes with inflection points of d / p = 0.072 and 0.048. If 0.048 ≤ d / p ≤ 0.072, the change in coupling coefficient caused by the change in d / p can be suppressed, and the relative bandwidth can be made to be approximately a fixed value.

[0105] Figure 10 In the construction model 1r of the elastic wave device using the thickness shear mode reference method, a graph is plotted showing the spurious levels in the frequency band between the resonant frequency and the anti-resonant frequency when the thickness d of the piezoelectric layer 4, the distance p between the center lines of the first electrode 51 and the second electrode 52, the width H1 of the first electrode, and the width H2 of the second electrode are changed. Figure 10 In the diagram, the horizontal axis represents the relative bandwidth, and the vertical axis represents the normalized spurious level. The normalized spurious level is the value obtained by normalizing the spurious level by setting the spurious level in the relative bandwidth (e.g., 22%) to 1, even if the thickness d of the piezoelectric layer 4, the distance p between the center lines of the first electrode 51 and the second electrode 52, the width H1 of the first electrode, and the width H2 of the second electrode are changed. Figure 10This is the case where Z-cut LiNbO3 is used as the piezoelectric layer 4, which can more appropriately excite the thickness shear mode; however, the same trend occurs with other cut angles. Furthermore, in the construction model 1r of the elastic wave device, when the material of the piezoelectric layer 4 is LiTaO3, the relationship between the normalized stray level and the relative bandwidth also becomes... Figure 10 The same trend applies. Furthermore, in the construction model 1r of the elastic wave device, regardless of the logarithm of the first electrode 51 and the second electrode 52, the relationship between the normalized spurious level and the relative bandwidth becomes... Figure 10 The same trend applies. Furthermore, in the structural model 1r of the elastic wave device, not limited to the case where the second principal surface 42 of the piezoelectric layer 4 is in contact with air, but also in the case where it is in contact with the acoustic reflection layer, the relationship between the normalized stray level and the relative bandwidth also becomes related to... Figure 10 The same trend.

[0106] according to Figure 10 It can be seen that when the relative bandwidth exceeds 17%, the normalized spurious level converges to 1. This means that when the relative bandwidth is above 17%, such as Figure 11 As illustrated by the frequency characteristics of the impedance, there are certain secondary resonances in the frequency band between the resonant frequency and the anti-resonant frequency. Figure 11 This refers to the frequency response of the impedance when Z-cut LiNbO3 with Euler angles of (0°, 0°, 90°) is used as the piezoelectric layer 4, and d / p = 0.08 and MR = 0.35 are set. Figure 11 In the image, the part of the secondary resonance is surrounded by a dashed line.

[0107] As described above, when the relative bandwidth exceeds 17%, even if the thickness d of the piezoelectric layer 4, the width H1 of the first electrode, and the width H2 of the second electrode are changed, a large amount of spurious emissions are still present in the frequency band between the resonant frequency and the anti-resonant frequency. Such spurious emissions are generated primarily by harmonics in the planar direction, mainly in the opposing directions of the first electrode 51 and the second electrode 52. Therefore, from the viewpoint of suppressing spurious emissions in the frequency band, the relative bandwidth is preferably 17% or less. The elastic wave device 1 of Embodiment 1 also shows the same trend as the construction model 1r of the elastic wave device regarding the relationship between the normalized spurious emission level and the relative bandwidth; therefore, the relative bandwidth is preferably 17% or less.

[0108] Figure 12 This indicates that, under the following conditions, a first distribution region DA1 with a relative bandwidth exceeding 17% and a second distribution region DA2 with a relative bandwidth below 17% are defined as follows: In the construction model 1r of the elastic wave device, Z-cut LiNbO3 is used as the piezoelectric layer 4, and the thickness d of the piezoelectric layer 4, the distance p between the centerlines of the first electrode 51 and the second electrode 52, the width H1 of the first electrode, and the width H2 of the second electrode are varied. Figure 12 In the first distribution region DA1 and the second distribution region DA2, the point densities are made different, with the point density in the first distribution region DA1 being higher than the point density in the second distribution region DA2. Additionally, in... Figure 12 In the diagram, the approximate straight line DL1, representing the boundary between the first distribution region DA1 and the second distribution region DA2, is shown as a dashed line. The approximate straight line DL1 is represented by the formula MR = 1.75 × (d / p) + 0.075. Therefore, in the structural model 1r of the elastic wave device, by satisfying the condition MR ≤ 1.75 × (d / p) + 0.075, it is easy to make the relative bandwidth less than 17%. Figure 12 The case where Z-cut LiNbO3 is used as the piezoelectric layer 4, which can more appropriately excite the thickness shearing mode, is a common occurrence, but the same trend applies to other cutting angles. Furthermore, in the construction model 1r of the elastic wave device, when the material of the piezoelectric layer 4 is LiTaO3, the approximate straight line DL1 is also the same. Additionally, in the construction model 1r of the elastic wave device, the approximate straight line DL1 is the same regardless of the logarithm of the first electrode 51 and the second electrode 52. Furthermore, in the construction model 1r of the elastic wave device, the approximate straight line DL1 is the same not only when the second principal surface 42 of the piezoelectric layer 4 is in contact with air, but also when it is in contact with the acoustic reflection layer. Similar to the construction model 1r of the elastic wave device, the elastic wave device 1 of Embodiment 1 easily achieves a relative bandwidth of 17% or less by satisfying the condition MR ≤ 1.75 × (d / p) + 0.075. It should be noted that... Figure 12 In the diagram, the approximate line DL2 (hereinafter also referred to as the second approximate line DL2), which is shown as a dashed line distinct from the approximate line DL1 (hereinafter also referred to as the first approximate line DL1), represents the line used to reliably ensure that the relative bandwidth is below 17%. The second approximate line DL2 is represented by the formula MR = 1.75 × (d / p) + 0.05. Therefore, in the construction model 1r of the elastic wave device and the elastic wave device 1 of Embodiment 1, by satisfying the condition MR ≤ 1.75 × (d / p) + 0.05, it is possible to reliably ensure that the relative bandwidth is below 17%.

[0109] (1.5) Effect

[0110] The elastic wave device 1 of Embodiment 1 includes a piezoelectric layer 4, a first electrode 51, and a second electrode 52. The first electrode 51 and the second electrode 52 are positioned opposite each other in a direction D2 intersecting the thickness direction D1 of the piezoelectric layer 4. The elastic wave device 1 utilizes thickness shearing of a first-order mode bulk wave. The elastic wave device 1 also includes a silicon substrate 2. The silicon substrate 2 has a first main surface 21 and a second main surface 22 facing each other. The piezoelectric layer 4 is made of lithium niobate or lithium tantalate. The piezoelectric layer 4 is disposed on the first main surface 21 of the silicon substrate 2. The elastic wave device 1 also has a trapping region 10 disposed on the silicon substrate 2.

[0111] In the elastic wave device 1 of Embodiment 1 described above, it is possible to handle high frequencies and improve linearity.

[0112] In the elastic wave device 1 of Embodiment 1, the resonant frequency is not limited by the distance between the center lines of adjacent first electrodes 51 and second electrodes 52. The resonant frequency can be increased by reducing the thickness of the piezoelectric layer 4. Therefore, high-frequency operation can be achieved without increasing the planar size of the elastic wave device 1. Furthermore, in the surface acoustic wave device described in Patent Document 1, a sufficient Q value is sometimes not obtained when the number of electrode fingers of the IDT electrode is reduced. In contrast, in the elastic wave device 1 of Embodiment 1, a sufficient Q value can be obtained even by reducing the number of pairs of first electrodes 51 and second electrodes 52. Therefore, a sufficient Q value can be obtained while achieving miniaturization. Additionally, in the elastic wave device 1 of Embodiment 1, linearity can be improved by providing the trapping region 10.

[0113] Compared to the elastic wave device of the comparative example which has an interface between a single-crystal silicon substrate and a silicon oxide film but does not have a trapping region 10, the elastic wave device 1 of Embodiment 1 can improve linearity by suppressing the movement of charge along the first main surface 21 of the silicon substrate 2 through the trapping region 10.

[0114] Furthermore, the elastic wave device 1 of Embodiment 1 includes a piezoelectric layer 4, a first electrode 51, and a second electrode 52. The first electrode 51 and the second electrode 52 are opposed to each other in a direction D2 intersecting the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1, when the distance between the center lines of adjacent first electrodes 51 and second electrodes 52 is set as p and the thickness of the piezoelectric layer 4 is set as d in any cross-section along the thickness direction D1 of the piezoelectric layer 4, d / p is 0.5 or less. The elastic wave device 1 also includes a silicon substrate 2. The silicon substrate 2 has a first main surface 21 and a second main surface 22 that are opposed to each other. The material of the piezoelectric layer 4 is lithium niobate or lithium tantalate. The piezoelectric layer 4 is disposed on the first main surface 21 of the silicon substrate 2. The elastic wave device 1 also has a trapping region 10 disposed on the silicon substrate 2.

[0115] In the elastic wave device 1 of Embodiment 1 described above, it is possible to handle high frequencies and improve linearity.

[0116] Furthermore, in the elastic wave device 1 of Embodiment 1, the silicon substrate 2 includes a portion of a cavity 26 that exposes a portion of the second main surface 42 of the piezoelectric layer 4. It should be noted that "the silicon substrate 2 includes a portion of the cavity 26" means that a portion of the cavity 26 is surrounded by the silicon substrate 2. "The case where a portion of the cavity 26 is surrounded by the silicon substrate 2" is, for example, not limited to, the cases described later. Figure 13The case shown is that the void 26 is covered by the substrate 20 on the second main surface 22 side of the silicon substrate 2, but it also includes the case where the void 26 is not covered by the substrate 20 on the second main surface side of the silicon substrate 2. Here, a portion of the void 26 also serves as a gap 27 that overlaps with a portion of both the first wiring portion 61 and the second wiring portion 62 when viewed from above in the thickness direction D1 of the piezoelectric layer 4. Moreover, in the elastic wave device 1 of Embodiment 1, the trapping region 10 includes the aforementioned surface region 2S and the gap 27. Therefore, in the elastic wave device 1 of Embodiment 1, compared to the case where the trapping region 10 does not include the gap 27, linearity can be improved.

[0117] (Another structural example of the elastic wave device according to Embodiment 1)

[0118] In another structural example of the elastic wave device 1, for example, as shown in the example... Figure 13 As shown, other substrates 20 may also be stacked on the side of the silicon substrate 2 opposite to the piezoelectric layer 4, i.e., on the second main surface 22 of the silicon substrate 2, such that they overlap with the piezoelectric layer 4 when viewed from above in the thickness direction D1. Silicon is an example of the material used for these other substrates 20. In summary, in the elastic wave device 1, a second silicon substrate including the aforementioned other substrates 20 may be bonded to the second main surface 22 of the first silicon substrate 2. It should be noted that the silicon substrate 2 is not limited to being stacked with other substrates 20; it may also be integrally formed from a single substrate.

[0119] (Modification 1 of Implementation Method 1)

[0120] The following is for reference Figure 14 and 15 The elastic wave device 1a of Modified Example 1 will be described. It should be noted that, with respect to the elastic wave device 1a of Modified Example 1, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1 of Embodiment 1, and the description is omitted.

[0121] The elastic wave device 1a in Modification 1 is an elastic wave filter (here, a trapezoidal filter). The elastic wave device 1a has an input terminal 15, an output terminal 16, a plurality of (two) series-arm resonators RS1 disposed on a first path 12 connecting the input terminal 15 and the output terminal 16, and a plurality of (two) parallel-arm resonators RS2 disposed on each of a plurality of (two) second paths 13 and 14 connecting a plurality of (two) nodes N1, N2 on the first path 12 to ground (ground terminals 17, 18). Ground terminals 17 and 18 can also be combined into a single ground.

[0122] In the elastic wave device 1a, multiple series-arm resonators RS1 and multiple parallel-arm resonators RS2 are elastic wave resonators 5. Each of the multiple elastic wave resonators 5 includes multiple first electrodes 51 and multiple second electrodes 52, but is not limited to this; any resonator may include at least one first electrode 51 and one second electrode 52. In the elastic wave device 1a, the piezoelectric layer 4 is used in all of the multiple elastic wave resonators 5. The resonant frequency of the parallel-arm resonator RS2 is lower than the resonant frequency of the series-arm resonator RS1. In the elastic wave resonator 5 constituting the parallel-arm resonator RS2, for example, a silicon oxide film is provided on the first main surface 41 of the piezoelectric layer 4. On the other hand, in the elastic wave resonator 5 constituting the series-arm resonator RS1, a silicon oxide film is not provided on the first main surface 41 of the piezoelectric layer 4. In the elastic wave resonator 5 constituting the series-arm resonator RS1, a silicon oxide film may also be provided on the first main surface 41 of the piezoelectric layer 4. In this case, the thickness of the silicon oxide film of the elastic wave resonator 5 constituting the series arm resonator RS1 can be thinner than the thickness of the silicon oxide film of the elastic wave resonator 5 constituting the parallel arm resonator RS2.

[0123] In the elastic wave device 1a, the silicon substrate 2 includes a portion of a cavity 26 that overlaps with a plurality of elastic wave resonators 5 when viewed from the thickness direction D1 of the piezoelectric layer 4, but is not limited thereto, and may also include a portion of each of the plurality of cavities 26 that overlap with the plurality of elastic wave resonators 5 one by one.

[0124] (Modification 2 of Implementation Method 1)

[0125] The following is for reference Figure 16 The elastic wave device 1j of Modified Example 2 will be described. Regarding the elastic wave device 1j of Modified Example 2, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1 of Embodiment 1, and the description is omitted.

[0126] In Modification 2, the elastic wave device 1j does not have the gap 27 of the elastic wave device 1 in Embodiment 1. The silicon substrate 2 and the silicon oxide film 7 overlap with portions of both the first wiring portion 61 and the second wiring portion 62 when viewed from the thickness direction D1 of the piezoelectric layer 4. Here, in Modification 2, the surface region 2S that overlaps with the entire area of ​​the silicon oxide film 7 overlaps with portions of both the first wiring portion 61 and the second wiring portion 62 when viewed from the thickness direction D1 of the piezoelectric layer 4. Therefore, in Modification 2, the surface region 2S included in the trapping region 10 is configured to overlap with multiple external connection terminals (input terminal 15, output terminal 16, ground terminals 17, 18) when viewed from above.

[0127] (Modification 3 of Implementation Method 1)

[0128] The following is for reference Figure 17 The elastic wave device 1b of Modified Example 3 will be described. Regarding the elastic wave device 1b of Modified Example 3, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1 of Embodiment 1, and the description is omitted.

[0129] The elastic wave device 1b of Modified Example 3 differs from the elastic wave device 1 of Embodiment 1 in that it also has two reflectors 8.

[0130] The two reflectors 8 are short-circuit gratings. Each reflector 8 is not intended to reflect bulk waves of the first shear mode, but rather to reflect unwanted surface acoustic waves propagating along the first principal surface 41 of the piezoelectric layer 4. One of the two reflectors 8 is located on the side of the first electrode 51 located at the end, opposite to the side of the second electrode 52, in the direction of propagation of the unwanted surface acoustic waves of the elastic wave device 1b. The remaining reflector 8 is located on the side of the second electrode 52 located at the end, opposite to the side of the first electrode 51, in the direction of propagation of the unwanted surface acoustic waves of the elastic wave device 1b.

[0131] Each reflector 8 has a plurality of (e.g., four) electrode fingers 81, one end of each electrode finger 81 being short-circuited to the other, and the other end being short-circuited to the other. The number of electrode fingers 81 in each reflector 8 is not particularly limited.

[0132] Each reflector 8 is conductive. The material of each reflector 8 is, for example, Al, Cu, Pt, Au, Ag, Ti, Ni, Cr, Mo, W, or an alloy primarily composed of any of these metals. Alternatively, each reflector 8 may have a structure formed by stacking multiple metal films comprising these metals or alloys. Each reflector 8, for example, includes a laminated film comprising a bonding film and a main electrode film. The bonding film comprises a Ti film formed on the piezoelectric layer 4, and the main electrode film comprises an Al film formed on the bonding film. The thickness of the bonding film is, for example, 10 nm. The thickness of the main electrode film is, for example, 80 nm.

[0133] Furthermore, in the elastic wave device 1b of Modified Example 2, each reflector 8 is a short-circuit grating, but it is not limited to this. For example, it can also be an open grating, a positive and negative reflection type grating, or a grating composed of a combination of a short-circuit grating and an open grating. In addition, the elastic wave device 1b has two reflectors 8, but it can also be a structure with only one of the two reflectors 8.

[0134] The two reflectors 8 in the elastic wave device 1b of Modified Example 2 can also be applied to the elastic wave device 1a of Modified Example 1. For example, they can also be set according to each elastic wave resonator 5 of the elastic wave device 1a of Modified Example 1.

[0135] (Implementation Method 2)

[0136] The following is for reference Figure 18 The elastic wave device 1c of Embodiment 2 will be described. Regarding the elastic wave device 1c of Embodiment 2, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1 of Embodiment 1, and descriptions are omitted.

[0137] The elastic wave device 1c of Embodiment 2 includes a silicon nitride film 11 as an insulating film, which is directly formed on the first main surface 21 of the silicon substrate 2. Therefore, the oxygen weight ratio of the insulating film is less than that of silicon oxide. The silicon nitride film 11 is a sputtered thin film formed by sputtering.

[0138] In the elastic wave device 1c of Embodiment 2, the silicon oxide film 7 is sandwiched between the silicon nitride film 11 and the piezoelectric layer 4, and is in contact with both the silicon nitride film 11 and the piezoelectric layer 4. Therefore, in the elastic wave device 1c of Embodiment 2, the silicon nitride film 11 and the surface region 2S are located between the silicon oxide film 7 and the bulk region 2B of the silicon substrate 2.

[0139] In the elastic wave device 1c of Embodiment 2, the trapping region 10 includes the surface region 2S of the silicon substrate 2.

[0140] In the elastic wave device 1c of Embodiment 2, the trapping region 10 is similar to that of the elastic wave device 1 of Embodiment 1, thus improving linearity.

[0141] In the elastic wave device 1c of embodiment 2, the silicon oxide film 7 is not a necessary component, and the silicon nitride film 11 and the piezoelectric layer 4 can also be connected.

[0142] Alternatively, in the elastic wave device 1c of embodiment 2, it may also be configured to remove the silicon nitride film 11 and form a silicon oxide film 7 by sputtering.

[0143] (Implementation Method 3)

[0144] The following is for reference Figures 19-21 The elastic wave device 1d according to Embodiment 3 will be described. Regarding the elastic wave device 1d of Embodiment 3, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1 of Embodiment 1, and the description is omitted.

[0145] like Figure 20 As shown, the elastic wave device 1d of Embodiment 3 differs from the elastic wave device 1 of Embodiment 1 in that it has an acoustic reflection layer 3 sandwiched between the silicon substrate 2 and the piezoelectric layer 4, and does not have the void 26 in the elastic wave device 1 of Embodiment 1. Furthermore, in the elastic wave device 1d of Embodiment 3, the silicon substrate 2 includes two gaps 27 (see reference 1) that overlap with portions of the first wiring portion 61 and the second wiring portion 62 when viewed from the thickness direction D1 of the piezoelectric layer 4. Figure 19 and 21 This is different from the elastic wave device 1 of Embodiment 1. The elastic wave device 1d of Embodiment 3 has two trapping regions 10. The two trapping regions 10 each include a gap 27. Each trapping region 10 is disposed on the silicon substrate 2 on the second main surface 42 side of the piezoelectric layer 4 to suppress the movement of charge along the first main surface 21 of the silicon substrate 2.

[0146] In the elastic wave device 1d of embodiment 3, an acoustic reflection layer 3 is disposed on the first main surface 21 of the silicon substrate 2, and a piezoelectric layer 4 is disposed on the acoustic reflection layer 3. In the elastic wave device 1d, the elastic wave resonator 5 includes a first electrode 51, a second electrode 52, and a piezoelectric layer 4. In the elastic wave device 1d, the elastic wave resonator 5 also has the aforementioned acoustic reflection layer 3.

[0147] The acoustic reflection layer 3 is positioned opposite to a plurality of first electrodes 51 and a plurality of second electrodes 52 in the thickness direction D1 of the piezoelectric layer 4.

[0148] The acoustic reflection layer 3 has the function of suppressing the leakage of bulk waves (the aforementioned thickness shear first-order mode bulk waves) excited by the first electrode 51 and the second electrode 52 into the silicon substrate 2. By including the acoustic reflection layer 3, the elastic wave device 1d can improve the containment effect of elastic wave energy into the piezoelectric layer 4. Therefore, compared with the case without the acoustic reflection layer 3, the elastic wave device 1d can reduce losses and improve the Q value.

[0149] The acoustic reflective layer 3 has a stacked structure in which multiple (three) low acoustic impedance layers 31 and multiple (two) high acoustic impedance layers 32 are arranged alternately in the thickness direction D1 of the piezoelectric layer 4. The acoustic impedance of the low acoustic impedance layer 31 is lower than that of the high acoustic impedance layer 32.

[0150] For ease of explanation, in the acoustic reflection layer 3, the two high acoustic impedance layers 32 are sometimes referred to as the first high acoustic impedance layer 321 and the second high acoustic impedance layer 322 in order of proximity to the first main surface 21 of the silicon substrate 2. Alternatively, the three low acoustic impedance layers 31 are sometimes referred to as the first low acoustic impedance layer 311, the second low acoustic impedance layer 312, and the third low acoustic impedance layer 313 in order of proximity to the first main surface 21 of the silicon substrate 2.

[0151] In the acoustic reflection layer 3, a first low acoustic impedance layer 311, a first high acoustic impedance layer 321, a second low acoustic impedance layer 312, a second high acoustic impedance layer 322, and a third low acoustic impedance layer 313 are arranged sequentially from the silicon substrate 2 side. Therefore, the acoustic reflection layer 3 can reflect bulk waves (thickness shear first-order mode bulk waves) from the piezoelectric layer 4 at the interfaces of the third low acoustic impedance layer 313 and the second high acoustic impedance layer 322, the second high acoustic impedance layer 322 and the second low acoustic impedance layer 312, the second low acoustic impedance layer 312 and the first high acoustic impedance layer 321, and the first high acoustic impedance layer 321 and the first low acoustic impedance layer 311, respectively.

[0152] The material of the plurality of high acoustic impedance layers 32 is, for example, Pt (platinum). The material of the plurality of low acoustic impedance layers 31 is, for example, silicon oxide. The thickness of each of the plurality of high acoustic impedance layers 32 is, for example, 94 nm. The thickness of each of the plurality of low acoustic impedance layers 31 is, for example, 188 nm. Since the two high acoustic impedance layers 32 are each formed of platinum, the acoustic reflection layer 3 also includes two conductive layers.

[0153] The material of the multiple high acoustic impedance layers 32 is not limited to Pt, but can also be metals such as W (tungsten) and Ta (tantalum). Furthermore, the material of the multiple high acoustic impedance layers 32 is not limited to metals, but can also be insulators.

[0154] Furthermore, the multiple high acoustic impedance layers 32 are not limited to being made of the same material; for example, they can also be made of different materials. Similarly, the multiple low acoustic impedance layers 31 are not limited to being made of the same material; for example, they can also be made of different materials.

[0155] Furthermore, the number of high acoustic impedance layers 32 and low acoustic impedance layers 31 in the acoustic reflection layer 3 is not limited to two or three; it can also be one, three or more, or four or more. Additionally, the number of high acoustic impedance layers 32 and low acoustic impedance layers 31 is not limited to being different; they can be the same, or the number of low acoustic impedance layers 31 can be one less than the number of high acoustic impedance layers 32. Furthermore, the thickness of each of the high acoustic impedance layers 32 and low acoustic impedance layers 31 is appropriately set according to the design frequency of the elastic wave device 1 and the materials used in the high acoustic impedance layers 32 and low acoustic impedance layers 31 respectively, so that good reflection is achieved in the acoustic reflection layer 3.

[0156] In the elastic wave device 1d of embodiment 3, the gap 27 is formed over the entire area of ​​the silicon substrate 2 and the acoustic reflection layer 3, exposing a portion of the second main surface 42 of the piezoelectric layer 4.

[0157] In the manufacturing method of the elastic wave device 1d, for example, after preparing a silicon substrate 2 having a first main surface 21 and a second main surface 22 facing each other, first to fifth processes are performed. In the first process, an acoustic reflection layer 3 is formed on the first main surface 21 of the silicon substrate 2. In the second process, a piezoelectric substrate, which will serve as the basis for a piezoelectric layer 4, is bonded to the silicon substrate 2 through the acoustic reflection layer 3. In the third process, a piezoelectric layer 4, including a portion of the piezoelectric substrate, is formed by thinning the piezoelectric substrate. In the fourth process, a plurality of first electrodes 51, a plurality of second electrodes 52, a first wiring portion 61, a second wiring portion 62, a first terminal T1, and a second terminal T2 are formed on the piezoelectric layer 4. In the fifth process, a gap 27 is formed by etching a portion of the silicon substrate 2 and the acoustic reflection layer 3 from the second main surface 22 of the silicon substrate 2. It should be noted that in the fifth process, a portion of the silicon substrate 2 may also be etched from the first main surface 21 of the silicon substrate 2. In the first to fifth processes, a silicon wafer is used as the silicon substrate 2. Furthermore, in the second process, a piezoelectric wafer is used as a piezoelectric substrate. In the manufacturing method of the elastic wave device 1d, multiple elastic wave devices 1d (chips) are obtained by cutting a wafer comprising multiple elastic wave devices 1d.

[0158] The manufacturing method of the elastic wave device 1d is one example and is not particularly limited. For example, the piezoelectric layer 4 can also be formed using a film deposition technique. In this case, the manufacturing method of the elastic wave device 1d includes a step of forming a film of the piezoelectric layer 4 instead of the second and third steps. The piezoelectric layer 4 formed by the film deposition technique can be, for example, a single crystal or a twin crystal. As a film deposition technique, CVD is an example, but it is not limited to this.

[0159] The elastic wave device 1d of Embodiment 3, like the elastic wave device 1 of Embodiment 1, utilizes a thickness-sheared first-order mode bulk wave. Therefore, in the elastic wave device 1d of Embodiment 3, the resonant frequency is not limited by the distance between the center lines of adjacent first electrodes 51 and second electrodes 52. The resonant frequency can be increased by reducing the thickness of the piezoelectric layer 4. Thus, high-frequency operation can be achieved without increasing the planar dimensions of the elastic wave device 1d. Furthermore, like the elastic wave device 1 of Embodiment 1, the linearity of the elastic wave device 1d of Embodiment 3 can be improved by having a trapping region 10.

[0160] The elastic wave device 1d has a trapping region 10 that overlaps with at least a portion of the first wiring portion 61 in the thickness direction D1 of the piezoelectric layer 4, and a trapping region 10 that overlaps with at least a portion of the second wiring portion 62 in the thickness direction D1 of the piezoelectric layer 4. However, as long as at least one of the trapping regions 10 is present, the linearity can be improved.

[0161] Furthermore, in the elastic wave device 1d of Embodiment 3, unwanted waves can be suppressed by the acoustic reflection layer 3 within the elastic wave resonator 5. Additionally, in the elastic wave device 1d of Embodiment 3, the piezoelectric layer 4 is made of LiNbO3 or LiTaO3, and the low acoustic impedance layer 31 is made of silicon oxide. Here, the frequency-temperature characteristics of LiNbO3 and LiTaO3 each have negative slopes, while the frequency-temperature characteristics of silicon oxide have positive slopes. Therefore, in the elastic wave device 1d of Embodiment 3, the absolute value of the TCF (Temperature Coefficient of Frequency) can be reduced, and the frequency-temperature characteristics can be improved.

[0162] (Modification 1 of Implementation Method 3)

[0163] The following is for reference Figure 22 The elastic wave device 1e of Modification 1 of Embodiment 3 will be described. Regarding the elastic wave device 1e of Modification 1, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1d of Embodiment 3, and the description is omitted.

[0164] The elastic wave device 1e of Modification 1 of Embodiment 3 is similar to the elastic wave device 1a of Modification 1 of Embodiment 1 as an elastic wave filter (here, a trapezoidal filter). The elastic wave device 1e has an input terminal 15, an output terminal 16, a plurality of (two) series-arm resonators RS1 disposed on a first path 12 connecting the input terminal 15 and the output terminal 16, and a plurality of (two) parallel-arm resonators RS2 disposed on each of a plurality of (two) second paths 13 and 14 connecting a plurality of (two) nodes N1 and N2 on the first path 12 to ground (ground terminals 17 and 18). Ground terminals 17 and 18 can also be combined into a single ground.

[0165] In the elastic wave device 1e of Modified Example 1, multiple series-arm resonators RS1 and multiple parallel-arm resonators RS2 are elastic wave resonators 5. Each of the multiple elastic wave resonators 5 includes a first electrode 51 and a second electrode 52. In the elastic wave device 1e, the piezoelectric layer 4 is used in all of the multiple elastic wave resonators 5. Additionally, in the elastic wave device 1e, the acoustic reflection layer 3 is used in all of the multiple elastic wave resonators 5. The resonant frequency of the parallel-arm resonator RS2 is lower than the resonant frequency of the series-arm resonator RS1. Here, the elastic wave resonator 5 constituting the parallel-arm resonator RS2, for example, has a silicon oxide film provided on the first main surface 41 of the piezoelectric layer 4; on the other hand, the elastic wave resonator 5 constituting the series-arm resonator RS1 does not have a silicon oxide film on the first main surface 41 of the piezoelectric layer 4. In the elastic wave resonator 5 constituting the series arm resonator RS1, a silicon oxide film may also be provided on the first main surface 41 of the piezoelectric layer 4. In this case, the thickness of the silicon oxide film of the elastic wave resonator 5 constituting the series arm resonator RS1 can be thinner than the thickness of the silicon oxide film of the elastic wave resonator 5 constituting the parallel arm resonator RS2.

[0166] In the elastic wave device 1e of Modified Example 1, the acoustic reflection layer 3 is used in multiple elastic wave resonators 5, but the high acoustic impedance layer 32 closest to the piezoelectric layer 4 (the second high acoustic impedance layer 322) among the multiple high acoustic impedance layers 32 can also be separated according to each elastic wave resonator 5. Furthermore, in the elastic wave device 1e of Modified Example 1, it is preferable if the first high acoustic impedance layer 321 is separated according to each elastic wave resonator 5.

[0167] In the elastic wave device 1e of Modified Example 1, gaps 27 are formed in portions of the first wiring section 61 and the second wiring section 62, which are respectively connected to multiple elastic wave resonators 5, such that they overlap when viewed from above in the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1e of Modified Example 1, gaps 27 do not overlap with multiple external connection terminals (input terminal 15, output terminal 16, ground terminals 17, 18) when viewed from above in the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1e of Modified Example 1, when viewed from above in the thickness direction D1 of the piezoelectric layer 4, a large portion of the first path 12 overlaps with gaps 27, and a large portion of each of the second paths 13, 14 overlaps with gaps 27. In the elastic wave device 1e of Modified Example 1, gaps 27 overlapping with the second wiring section 62 connected to the series arm resonator RS1 and gaps 27 overlapping with the second wiring section 62 connected to the parallel arm resonator RS2 are connected together. Therefore, in the elastic wave device 1e of Modified Example 1, the movement of charge along the first main surface 21 of the silicon substrate 2 can be further suppressed. Since the elastic wave device 1e of Modified Example 1 has a trapping region 10, linearity can be improved.

[0168] (Modification 2 of Implementation Method 3)

[0169] The following is for reference Figure 23 The elastic wave device 1f of Modification 2 of Embodiment 3 will be described. Regarding the elastic wave device 1f of Modification 2, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1e of Modification 1 of Embodiment 3, and the description is omitted.

[0170] Compared to the elastic wave device 1e of Modified Example 1, the elastic wave device 1f of Modified Example 2 has a smaller overlapping area with the gap 27 in each of the second paths 13 and 14 when viewed from the thickness direction D1 of the piezoelectric layer 4. In the elastic wave device 1f of Modified Example 2, the gap 27 overlapping with the second wiring portion 62 connected to the series arm resonator RS1 and the gap 27 overlapping with the second wiring portion 62 connected to the parallel arm resonator RS2 are separated. Compared to the elastic wave device 1e of Modified Example 1, the elastic wave device 1f of Modified Example 2 can improve mechanical strength.

[0171] (Modification 3 of Implementation Method 3)

[0172] The following is for reference Figure 24 The elastic wave device 1g of Modification 3 of Embodiment 3 will be described. Regarding the elastic wave device 1g of Modification 3, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1e of Modification 1 of Embodiment 3, and the description is omitted.

[0173] Modification 3's elastic wave device 1g has a gap 28 formed in a region different from the gap 27 of Modification 1's elastic wave device 1e. Gap 28, like gap 27, is formed over the entire area of ​​the silicon substrate 2 and the acoustic reflection layer 3. At least a portion of gap 28, viewed from the thickness direction D1 of the piezoelectric layer 4, lies within predetermined distances L11 and L12 from the region overlapping with a portion of at least one of the first wiring portion 61 and the second wiring portion 62. The predetermined distances L11 and L12 are the distances between the first electrode 51 and the second electrode 52 and the silicon substrate 2. The trapping region 10 includes gap 28.

[0174] Since the elastic wave device 1g of modified example 3 has a trapping region 10, its linearity can be improved.

[0175] (Modification 4 of Implementation Method 3)

[0176] The following is for reference Figure 25 The elastic wave device 1h of Modification 4 of Embodiment 3 will be described. Regarding the elastic wave device 1h of Modification 4, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1d of Embodiment 3, and the description is omitted.

[0177] The elastic wave device 1h in Modification Example 4 differs from the elastic wave device 1d in Embodiment 3 in that the materials of the low acoustic impedance layers 31 and the high acoustic impedance layers 32 in the acoustic reflection layer 3 are different dielectrics. The material of each low acoustic impedance layer 31 is, for example, silicon oxide. The material of each high acoustic impedance layer 32 is, for example, any one of silicon nitride, aluminum nitride, aluminum oxide, and tantalum oxide.

[0178] The elastic wave device 1h in Modification 4 does not have the gap 27 of the elastic wave device 1d in Embodiment 3. In the elastic wave device 1h of Modification 4, the silicon substrate 2 includes a surface region 2S that overlaps with a portion of at least one of the first wiring portion 61 and the second wiring portion 62 when viewed from above in the thickness direction D1 of the piezoelectric layer 4. The surface region 2S only needs to overlap with a portion of at least one of the first wiring portion 61 and the second wiring portion 62.

[0179] In the elastic wave device 1h of Variation 4 of Embodiment 3, the silicon substrate 2, like the silicon substrate 2 of the elastic wave device 1 of Embodiment 1, includes a body region 2B and a surface region 2S. The surface region 2S is, for example, an amorphous silicon layer. The surface region 2S includes a portion of the first main surface 21 of the silicon substrate 2. The first main surface 21 of the silicon substrate 2 includes a rough surface 211 in the surface region 2S. The surface region 2S is not formed in the region that overlaps with the elastic wave resonator 5 when viewed from the thickness direction D1 of the piezoelectric layer 4.

[0180] In the elastic wave device 1h of Modification 4 of Embodiment 3, the trapping region 10 includes the surface region 2S. Since the elastic wave device 1h of Modification 4 of Embodiment 3 has the trapping region 10, linearity can be improved.

[0181] (Modification 5 of Implementation Method 3)

[0182] The following is for reference Figure 26 The elastic wave device 1i of Modification 5 of Embodiment 3 will be described. Regarding the elastic wave device 1i of Modification 5, the same reference numerals are used for the same constituent elements as those of the elastic wave device 1d of Embodiment 3, and the description is omitted.

[0183] The elastic wave device 1i of Modification 5 of Embodiment 3 is similar to the elastic wave device 1b of Modification 2 of Embodiment 1 (see reference). Figure 17 It also has two reflectors 8, which is different from the elastic wave device 1d in embodiment 3. The structure of each reflector 8 is the same as that of each reflector 8 in elastic wave device 1b.

[0184] The above-described embodiments 1 to 3 are merely one embodiment among many of the various embodiments of the present invention. Embodiments 1 to 3 described above are acceptable as long as they achieve the objectives of the present invention, and various modifications can be made according to design, etc.

[0185] For example, in the elastic wave device 1 of Embodiment 1, the piezoelectric layer 4 is bonded to the silicon substrate 2 through the silicon oxide film 7, but the silicon oxide film 7 is not an essential component.

[0186] In addition, in the elastic wave device 1 of Embodiment 1, the cavity 26 is formed to penetrate the silicon substrate 2 along the thickness direction of the silicon substrate 2, but it is not limited to this. It may not penetrate the silicon substrate 2, but may be formed by the internal space of the recess formed on the first main surface 21 of the silicon substrate 2.

[0187] Furthermore, in the elastic wave devices 1 to 1j, the cross-sectional shape of the first electrode 51 and the second electrode 52 is rectangular, but not limited to this. Here, the cross-sectional shape is, for example, the shape in the cross-section along the thickness direction D1 and the second direction D2 of the piezoelectric layer 4. The first electrode 51 and the second electrode 52 may also be, for example, as shown in... Figures 27A-27D As shown in any of the figures, the shape is such that the width at the bottom is wider than the width at the top. Therefore, it is possible to achieve this without increasing the size of the first main surface 511 of the first electrode 51 (see Figure 51). Figure 2 ) and the first main surface 521 of the second electrode 52 (refer to Figure 2 In the state of the width of ), increase the capacitance between the adjacent first electrode 51 and second electrode 52.

[0188] Figure 27A The first electrode 51 and the second electrode 52 shown have a portion with a substantially fixed width at the upper end and a portion with a gradually increasing width at the lower end. Furthermore, Figure 27B The first electrode 51 and the second electrode 52 shown are trapezoidal in cross-section. Additionally, Figure 27C The first electrode 51 and the second electrode 52 shown are shaped with extended ends, and their two sides in the width direction are curved surfaces. Furthermore, Figure 27D The first electrode 51 and the second electrode 52 shown have a trapezoidal section on the upper end side and a trapezoidal section on the lower end side that is wider than the trapezoidal section on the upper end side.

[0189] In addition, such as Figures 28A-28C As shown in any of the figures, the elastic wave devices 1-1j may also include a dielectric film 9 covering the first main surface 41 of the piezoelectric layer 4, the first electrode 51 on the first main surface 41, and the second electrode 52 on the first main surface 41. By including the dielectric film 9, the elastic wave devices 1-1j can increase the capacitance between adjacent first electrodes 51 and second electrodes 52. Figure 28A In this process, the thickness of the dielectric film 9 is thinner than the thickness of the first electrode 51 and the second electrode 52, and the surface of the dielectric film 9 has an uneven shape along the shape of the substrate. Figure 28B In this process, the surface of the dielectric film 9 is planarized to become planar. Figure 28CIn the process, the thickness of the dielectric film 9 is greater than the thickness of the first electrode 51 and the second electrode 52, and the surface of the dielectric film 9 has an uneven shape along the shape of the substrate.

[0190] Furthermore, in the elastic wave devices 1 to 1j, the cross-sectional shape of the first electrode 51 and the cross-sectional shape of the second electrode 52 may be different. Here, the cross-sectional shape is, for example, the shape in the cross-section along the thickness direction D1 and the second direction D2 of the piezoelectric layer 4.

[0191] In addition, in the elastic wave devices 1 to 1j, the elastic wave resonator 5 has a plurality of first electrodes 51 and a plurality of second electrodes 52, but is not limited thereto, and may have at least one first electrode 51 and one second electrode 52.

[0192] Furthermore, when the elastic wave filter is configured as in the elastic wave device 1a of Modified Example 1 of Embodiment 1, the shapes of the first electrode 51 and the second electrode 52 may differ for each elastic wave resonator 5. Additionally, the shapes of the first electrode 51 and the second electrode 52 may differ in the elastic wave resonator 5 that constitutes the series arm resonator RS1 and the elastic wave resonator 5 that constitutes the parallel arm resonator RS2.

[0193] Furthermore, the first electrode 51 and the second electrode 52 are not limited to being straight when viewed from the thickness direction D1 of the piezoelectric layer 4. For example, the first electrode 51 and the second electrode 52 may also be curved, or may have a shape that includes both straight and curved portions.

[0194] (Way)

[0195] Based on the embodiments described above, the following methods are disclosed in this specification.

[0196] The elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) of the first type includes a piezoelectric layer (4), a first electrode (51), and a second electrode (52). The first electrode (51) and the second electrode (52) are opposed in a direction (D2) intersecting the thickness direction (D1) of the piezoelectric layer (4). The elastic wave device (1; 1a) utilizes a thickness-sheared first-order mode bulk wave. The elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) also includes a silicon substrate (2). The silicon substrate (2) has a first main surface (21) and a second main surface (22) that are opposed to each other. The material of the piezoelectric layer (4) is lithium niobate or lithium tantalate. The piezoelectric layer (4) is disposed on the first main surface (21) of the silicon substrate (2). The elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) also has a trapping region (10) disposed on the silicon substrate (2).

[0197] In the elastic wave device of the first type (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j), it is possible to cope with high frequency and improve linearity.

[0198] The second type of elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) includes a piezoelectric layer (4), a first electrode (51), and a second electrode (52). The first electrode (51) and the second electrode (52) are opposite each other in a direction (D2) intersecting the thickness direction (D1) of the piezoelectric layer (4). The first electrode (51) and the second electrode (52) are adjacent electrodes. In the elastic wave device (1; 1a), when the distance between the center lines of the first electrode (51) and the second electrode (52) is set as p in any cross-section along the thickness direction (D1) of the piezoelectric layer (4) and the thickness of the piezoelectric layer (4) is set as d, d / p is 0.5 or less. The elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) also includes a silicon substrate (2). The silicon substrate (2) has a first main surface (21) and a second main surface (22) facing each other. The piezoelectric layer (4) is made of lithium niobate or lithium tantalate. The piezoelectric layer (4) is disposed on the first main surface (21) of the silicon substrate (2). The elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) also has a trapping region (10) disposed on the silicon substrate (2).

[0199] In the second type of elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j), it is possible to cope with high frequencies and improve linearity.

[0200] The elastic wave device of the third method (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) is based on the second method, wherein d / p is 0.24 or less.

[0201] In the third-party elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j), the relative bandwidth can be made larger.

[0202] The fourth type of elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) is based on the third type, wherein the first electrode (51) has a first electrode main portion (510), and the second electrode (52) has a second electrode main portion (520). The first electrode main portion (510) intersects the second electrode (52) in a direction (D2) opposite to the first electrode (51) and the second electrode (52). The second electrode main portion (520) intersects the first electrode (51) in a direction (D2) opposite to the first electrode (51) and the second electrode (52). The piezoelectric layer (4) has a defined region (45). The specified region (45) is the area located between the first electrode (51) and the second electrode (52) in the piezoelectric layer (4) in the direction (D2) opposite to the first electrode (51) and the second electrode (52) when viewed from the thickness direction (D1) of the piezoelectric layer (4). The elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) satisfies the following condition: MR≤1.75×(d / p)+0.075. Here, S1 is the area of ​​the main part of the first electrode (510) when viewed from the thickness direction (D1) of the piezoelectric layer (4). S2 is the area of ​​the main part of the second electrode (520) when viewed from the thickness direction (D1) of the piezoelectric layer (4). S0 is the area of ​​a defined region (45) as viewed from the thickness direction (D1) of the piezoelectric layer (4). MR is a structural parameter defined by (S1+S2) / (S1+S2+S0).

[0203] In the fourth type of elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j), spurious emissions within the frequency band can be suppressed.

[0204] The fifth type of elastic wave device (1; 1a; 1h; 1i; 1j) is based on any one of the first to fourth types, wherein at least a portion of the first main surface (21) of the silicon substrate (2) is a rough surface (211). The silicon substrate (2) has a bulk region (2B) and a surface region (2S) including the rough surface (211). The trapping region (10) includes the surface region (2S).

[0205] The sixth type of elastic wave device (1; 1a; 1h; 1i; 1j) is based on any one of the first to fourth types, wherein the silicon substrate (2) has a bulk region (2B) and a surface region (2S) including a first main surface (21) of the silicon substrate (2). The surface region (2S) is an amorphous silicon layer. The trapping region (10) includes the surface region (2S).

[0206] The elastic wave device of the seventh type (1; 1a; 1h; 1i; 1j) is based on any one of the first to fourth types, wherein the silicon substrate (2) has a bulk region (2B) and a surface region (2S) including a first main surface (21) of the silicon substrate (2). The surface region (2S) is a polycrystalline silicon layer. The trapping region (10) includes the surface region (2S).

[0207] The elastic wave device of the eighth embodiment (1; 1a; 1h; 1i) is based on the fifth embodiment, wherein the rough surface (211) does not overlap with the elastic wave resonator (5) including the first electrode (51) and the second electrode (52) and a portion of the piezoelectric layer (4) when viewed from the thickness direction (D1).

[0208] The elastic wave device (1c) of the ninth type is based on any one of the first to fifth types and the eighth type, wherein the trapping region (10) includes an insulating film (silicon nitride film 11) formed directly on the first main surface (21) of the silicon substrate (2). The oxygen weight ratio of the insulating film (silicon nitride film 11) is less than that of silicon oxide.

[0209] The elastic wave device (1c) of the tenth type is based on any one of the first to fifth types and the eighth type, wherein the trapping region (10) includes an insulating film (silicon nitride film 11) formed directly on the first main surface (21) of the silicon substrate (2). The insulating film is a silicon nitride film (11).

[0210] The eleventh type of elastic wave device (1c) is based on the ninth or tenth type, wherein the insulating film (silicon nitride film 11) does not overlap with the elastic wave resonator (5) when viewed from the thickness direction (D1) of the piezoelectric layer (4). The elastic wave resonator (5) includes a first electrode (51) and a second electrode (52), as well as a portion of the piezoelectric layer (4).

[0211] In the eleventh type of elastic wave device (1c), compared with the case where the insulating film (silicon nitride film 11) overlaps with the elastic wave resonator (5), the Q value of the resonance characteristic of the elastic wave resonator (5) can be improved.

[0212] The twelfth type of elastic wave device (1; 1a; 1b; 1c) is based on any one of the first to eleventh types, wherein the silicon substrate (2) includes at least a portion of a cavity (26) disposed on the side opposite to the first electrode (51) and the second electrode (52) separated by a piezoelectric layer (4). The cavity (26) overlaps with the entire region of the elastic wave resonator (5) when viewed from the thickness direction (D1) of the piezoelectric layer (4). The elastic wave resonator (5) includes the first electrode (51), the second electrode (52), and a portion of the piezoelectric layer (4).

[0213] The elastic wave device of the thirteenth type (1; 1a; 1b; 1c; 1d; 1e; 1f; 1i) according to any one of the first to twelfth types, further comprising a first wiring portion (61) and a second wiring portion (62). The first wiring portion (61) is connected to a first electrode (51). The second wiring portion (62) is connected to a second electrode (52). The silicon substrate (2) includes at least a portion of a void (27). The void (27) overlaps with a portion of at least one of the first wiring portion (61) and the second wiring portion (62) when viewed from the thickness direction (D1) of the piezoelectric layer (4). The trapping region (10) includes the void (27).

[0214] The fourteenth type of elastic wave device (1d; 1e; 1f; 1i) according to any one of the first to fifth types and the eighth type, further includes a first wiring portion (61), a second wiring portion (62), and an acoustic reflection layer (3). The first wiring portion (61) is connected to a first electrode (51). The second wiring portion (62) is connected to a second electrode (52). The acoustic reflection layer (3) is disposed between a first main surface (21) of the silicon substrate (2) and a piezoelectric layer (4). The acoustic reflection layer (3) has at least one high acoustic impedance layer (32) and at least one low acoustic impedance layer (31). The acoustic impedance of the at least one low acoustic impedance layer (31) is lower than that of the at least one high acoustic impedance layer (32). The silicon substrate (2) includes at least a portion of a void (27). The void (27) overlaps with a portion of at least one of the first wiring portion (61) and the second wiring portion (62) when viewed from the thickness direction (D1) of the piezoelectric layer (4). The trapped area (10) includes the gap (27).

[0215] The elastic wave device (1g) of the fifteenth type is based on any one of the first to fifth types and the eighth type, wherein it further includes a first wiring portion (61) and a second wiring portion (62). The first wiring portion (61) is connected to the first electrode (51). The second wiring portion (62) is connected to the second electrode (52). The silicon substrate (2) includes at least a portion of a void (28). The void (28) includes a portion located within a predetermined distance (L11, L12) from the region overlapping a portion of at least one of the first wiring portion (61) and the second wiring portion (62) when viewed from the thickness direction (D1) of the piezoelectric layer (4). The predetermined distance (L11, L12) is the distance between the first electrode (51) and the second electrode (52) and the silicon substrate (2). The trapping region (10) includes the void (28).

[0216] The elastic wave device of the sixteenth embodiment (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) is based on any one of the thirteenth to fifteenth embodiments, wherein it includes a plurality of first electrodes (51) and a plurality of second electrodes (52). The plurality of first electrodes (51) and the plurality of second electrodes (52) are arranged alternately, one of each. The plurality of first electrodes (51) are connected to a first wiring section (61). The plurality of second electrodes (52) are connected to a second wiring section (62).

[0217] In the elastic wave device of the sixteenth type (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j), the Q value can be further improved.

[0218] The elastic wave device of the seventeenth type (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) is based on any one of the first to sixteenth types, and further includes a silicon oxide film (7). The silicon oxide film (7) is disposed between the silicon substrate (2) and the piezoelectric layer (4).

[0219] The eighteenth type of elastic wave device (1a; 1e; 1f; 1g; 1j) is based on any one of the first to seventeenth types, wherein it is an elastic wave filter having multiple elastic wave resonators (5). The multiple elastic wave resonators (5) are resonators including a first electrode (51) and a second electrode (52). The piezoelectric layer (4) is used in multiple elastic wave resonators (5).

[0220] The nineteenth type of elastic wave device (1; 1a; 1b; 1c; 1d; 1e; 1f; 1g; 1h; 1i; 1j) is based on any one of the first to eighteenth types, wherein the piezoelectric layer (4) has a first main surface (41) and a second main surface (42) facing each other. The first main surface (41) of the piezoelectric layer (4) is the main surface of the piezoelectric layer (4) opposite to the silicon substrate (2) side. The second main surface (42) of the piezoelectric layer (4) is the main surface of the piezoelectric layer (4) on the silicon substrate (2) side. The first electrode (51) and the second electrode (52) are facing each other on the first main surface (41) of the piezoelectric layer (4).

[0221] Explanation of reference numerals in the attached figures

[0222] 1, 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i Elastic wave devices;

[0223] 1r Construct the model;

[0224] 2. Silicon substrate;

[0225] 21 First main face;

[0226] 211 Rough surface;

[0227] 22 Second main face;

[0228] 26. Hollow;

[0229] 27. Gaps;

[0230] 28. Gaps;

[0231] 2B body region;

[0232] 2S surface area;

[0233] 3. Sound-reflecting layer;

[0234] 31. Low acoustic impedance layer;

[0235] 311 First low acoustic impedance layer (silicon oxide film);

[0236] 312 Second low acoustic impedance layer;

[0237] 313 Third low acoustic impedance layer;

[0238] 32. High acoustic impedance layer;

[0239] 321 First high acoustic impedance layer;

[0240] 322 Second high acoustic impedance layer;

[0241] 4. Piezoelectric layer;

[0242] 41 First main face;

[0243] 42 Second main face;

[0244] 45. Designated area;

[0245] 451 First Region;

[0246] 452 Second Zone;

[0247] 5. Elastic wave resonator;

[0248] 51 First electrode;

[0249] 510 First electrode main part;

[0250] 511 First Main Face;

[0251] 512 Second main face;

[0252] 513 Side view;

[0253] 52 Second electrode;

[0254] 520 Second electrode main part;

[0255] 521 First main face;

[0256] 522 Second main face;

[0257] 523 Side view;

[0258] 61 First Wiring Department;

[0259] 611 First busbar;

[0260] 62 Second Wiring Section;

[0261] 621 Second busbar;

[0262] 7. Silicon oxide film;

[0263] 8. Reflectors;

[0264] 81 Electrode finger;

[0265] 9. Dielectric film;

[0266] 10. Captured areas;

[0267] 11. Silicon nitride film (insulating film);

[0268] 12. First path;

[0269] 13. Second path;

[0270] 14. Second path;

[0271] 15 Input terminals;

[0272] 16 Output terminals;

[0273] 17. Grounding terminal;

[0274] 18. Grounding terminal;

[0275] 20 substrate;

[0276] 400 piezoelectric film;

[0277] 401 First Main Page;

[0278] 402 Second Main Face;

[0279] D1 Thickness direction (first direction);

[0280] D2 Second direction;

[0281] D3 third direction;

[0282] DA1 First Distribution Region;

[0283] DA2 second distribution region;

[0284] DL1 is an approximate straight line (the first approximate straight line);

[0285] DL2 approximates a straight line (the second approximate straight line);

[0286] HB1 is the protruding dimension;

[0287] HB2 is the protruding dimension;

[0288] HC1 protruding dimensions;

[0289] HC2 protruding dimensions;

[0290] L11 specifies the distance;

[0291] L12 specifies the distance;

[0292] MR construction parameters;

[0293] N1 node;

[0294] N2 node;

[0295] PZ1 polarization direction;

[0296] RS1 series arm resonator;

[0297] RS2 parallel arm resonator;

[0298] VP1 Virtual plane;

[0299] d. Thickness of the piezoelectric layer;

[0300] p is the distance between center lines.

Claims

1. An elastic wave device, comprising: piezoelectric layer; and The first electrode and the second electrode are positioned opposite each other in a direction that intersects the thickness direction of the piezoelectric layer. The elastic wave device utilizes thickness shearing of first-order mode volume waves. in, The elastic wave device also includes a silicon substrate having a first main surface and a second main surface that are opposite each other. The piezoelectric layer is made of lithium niobate or lithium tantalate. The piezoelectric layer is disposed on the first main surface of the silicon substrate. The elastic wave device also has a trapping region disposed on the silicon substrate. At least a portion of the first main surface of the silicon substrate is a rough surface. The silicon substrate has: Body region; and Including the surface area of ​​the rough surface, The trapped area includes the surface area.

2. The elastic wave device according to claim 1, wherein, The surface region includes the first main surface of the silicon substrate. The surface region is an amorphous silicon layer.

3. The elastic wave device according to claim 1, wherein, The surface region includes the first main surface of the silicon substrate. The surface region is a polycrystalline silicon layer.

4. The elastic wave device according to claim 1, wherein, The rough surface, viewed from the thickness direction of the piezoelectric layer, does not overlap with the elastic wave resonator, which includes a portion of the piezoelectric layer and the first and second electrodes.

5. The elastic wave device according to claim 1, wherein, The trapping region includes an insulating film that is formed directly on the first main surface of the silicon substrate. The oxygen weight ratio of the insulating film is less than that of silicon oxide.

6. The elastic wave device according to claim 1, wherein, The trapping region includes an insulating film that is formed directly on the first main surface of the silicon substrate. The insulating film is a silicon nitride film.

7. The elastic wave device according to claim 5 or 6, wherein, The insulating film, viewed from the thickness direction of the piezoelectric layer, does not overlap with the elastic wave resonator, which includes a portion of the piezoelectric layer and the first and second electrodes.

8. The elastic wave device according to any one of claims 1 to 6, wherein, The silicon substrate includes at least a portion of a cavity disposed on the side opposite to the first electrode and the second electrode, separated by the piezoelectric layer. The void, viewed from above along the thickness of the piezoelectric layer, overlaps with the entire region of the elastic wave resonator, which includes a portion of the piezoelectric layer and the first and second electrodes.

9. The elastic wave device according to any one of claims 1 to 6, wherein, The elastic wave device also includes: A first wiring portion, which is connected to the first electrode; and The second wiring section is connected to the second electrode. The silicon substrate includes at least a portion of a gap that overlaps with a portion of at least one of the first wiring portion and the second wiring portion when viewed from the thickness direction of the piezoelectric layer. The trapped area includes the gap.

10. The elastic wave device according to claim 1 or 4, wherein, The elastic wave device also includes: A first wiring portion is connected to the first electrode; A second wiring portion, which is connected to the second electrode; and An acoustic reflection layer is disposed between the first main surface of the silicon substrate and the piezoelectric layer. The acoustic reflective layer has the following characteristics: At least one high acoustic impedance layer; as well as At least one low acoustic impedance layer, the acoustic impedance of which is lower than that of the at least one high acoustic impedance layer. The silicon substrate includes at least a portion of a gap that overlaps with a portion of at least one of the first wiring portion and the second wiring portion when viewed from the thickness direction of the piezoelectric layer. The trapped area includes the gap.

11. The elastic wave device according to claim 1 or 4, wherein, The elastic wave device also includes: A first wiring portion, which is connected to the first electrode; and The second wiring section is connected to the second electrode. The silicon substrate includes at least a portion of a gap disposed on the side opposite to the first electrode and the second electrode, separated by the piezoelectric layer. The gap includes a portion located within a predetermined distance from the area overlapping a portion of at least one of the first wiring portion and the second wiring portion, when viewed from the thickness direction of the piezoelectric layer. The specified distance is the distance between the first electrode and the second electrode and the silicon substrate. The trapped area includes the gap.

12. The elastic wave device according to claim 9, wherein, The elastic wave device includes a plurality of first electrodes and a plurality of second electrodes. The plurality of first electrodes and the plurality of second electrodes are arranged alternately, one of each. The plurality of first electrodes are connected together with the first wiring portion. The plurality of second electrodes are connected together with the second wiring section.

13. The elastic wave device according to any one of claims 1 to 6, wherein, The elastic wave device also includes a silicon oxide film disposed between the silicon substrate and the piezoelectric layer.

14. The elastic wave device according to any one of claims 1 to 6, wherein, The elastic wave device is an elastic wave filter equipped with multiple elastic wave resonators. The plurality of elastic wave resonators are resonators that include the first electrode and the second electrode, respectively. The piezoelectric layer is used in multiple elastic wave resonators.

15. The elastic wave device according to any one of claims 1 to 6, wherein, The piezoelectric layer has a first principal surface and a second principal surface that are opposite each other. The first main surface of the piezoelectric layer is the main surface of the piezoelectric layer opposite to the silicon substrate side. The second main surface of the piezoelectric layer is the main surface on the silicon substrate side of the piezoelectric layer. The first electrode and the second electrode are positioned opposite each other on the first main surface of the piezoelectric layer.

16. An elastic wave device, comprising: piezoelectric layer; and The first electrode and the second electrode are positioned opposite each other in a direction that intersects the thickness direction of the piezoelectric layer. The first electrode and the second electrode are adjacent to each other. In any cross-section along the thickness direction of the piezoelectric layer, if the distance between the centerlines of the first electrode and the second electrode is set to p, and the thickness of the piezoelectric layer is set to d, d / p is below 0.5 in, The elastic wave device also includes a silicon substrate having a first main surface and a second main surface that are opposite each other. The piezoelectric layer is made of lithium niobate or lithium tantalate. The piezoelectric layer has a first main surface and a second main surface that are opposite to each other, and is disposed on the first main surface of the silicon substrate. The elastic wave device also has a trapping region disposed on the silicon substrate.

17. The elastic wave device according to claim 16, wherein, The d / p ratio is below 0.

24.

18. The elastic wave device according to claim 17, wherein, The first electrode has a first electrode main portion, which intersects the second electrode in a direction opposite to the first electrode. The second electrode has a second electrode main portion, which intersects the first electrode in a direction opposite to the first electrode. The piezoelectric layer has a defined region that, when viewed from above along the thickness direction of the piezoelectric layer, is located between the first electrode and the second electrode in the direction in which the first electrode and the second electrode are opposite each other. Viewed from above along the thickness direction of the piezoelectric layer, Let the area of ​​the main part of the first electrode be S1. Let the area of ​​the main part of the second electrode be S2. Let the area of ​​the specified region be S0. When the construction parameters specified by (S1+S2) / (S1+S2+S0) are set as MR, The elastic wave device satisfies the following conditions. The condition is MR ≤ 1.75 × (d / p) + 0.

075.

19. The elastic wave device according to any one of claims 16 to 18, wherein, At least a portion of the first main surface of the silicon substrate is a rough surface. The silicon substrate has: Body region; and Including the surface area of ​​the rough surface, The trapped area includes the surface area.

20. The elastic wave device according to any one of claims 16 to 18, wherein, The silicon substrate has: Body region; and The surface region includes the first main surface of the silicon substrate. The surface region is an amorphous silicon layer. The trapped area includes the surface area.

21. The elastic wave device according to any one of claims 16 to 18, wherein, The silicon substrate has: Body region; and The surface region includes the first main surface of the silicon substrate. The surface region is a polycrystalline silicon layer. The trapped area includes the surface area.

22. The elastic wave device according to claim 19, wherein, The rough surface, viewed from the thickness direction of the piezoelectric layer, does not overlap with the elastic wave resonator, which includes a portion of the piezoelectric layer and the first and second electrodes.

23. The elastic wave device according to claim 16, wherein, The trapping region includes an insulating film that is formed directly on the first main surface of the silicon substrate. The oxygen weight ratio of the insulating film is less than that of silicon oxide.

24. The elastic wave device according to claim 16, wherein, The trapping region includes an insulating film that is formed directly on the first main surface of the silicon substrate. The insulating film is a silicon nitride film.

25. The elastic wave device according to claim 23 or 24, wherein, The insulating film, viewed from the thickness direction of the piezoelectric layer, does not overlap with the elastic wave resonator, which includes a portion of the piezoelectric layer and the first and second electrodes.

26. The elastic wave device according to any one of claims 16 to 18, wherein, The silicon substrate includes at least a portion of a cavity disposed on the side opposite to the first electrode and the second electrode, separated by the piezoelectric layer. The void, viewed from above along the thickness of the piezoelectric layer, overlaps with the entire region of the elastic wave resonator, which includes a portion of the piezoelectric layer and the first and second electrodes.

27. The elastic wave device according to any one of claims 16 to 18, wherein, The elastic wave device also includes: A first wiring portion, which is connected to the first electrode; and The second wiring section is connected to the second electrode. The silicon substrate includes at least a portion of a gap that overlaps with a portion of at least one of the first wiring portion and the second wiring portion when viewed from the thickness direction of the piezoelectric layer. The trapped area includes the gap.

28. The elastic wave device according to any one of claims 16 to 18, wherein, The elastic wave device also includes: A first wiring portion is connected to the first electrode; A second wiring portion, which is connected to the second electrode; and An acoustic reflection layer is disposed between the first main surface of the silicon substrate and the piezoelectric layer. The acoustic reflective layer has the following characteristics: At least one high acoustic impedance layer; as well as At least one low acoustic impedance layer, the acoustic impedance of which is lower than that of the at least one high acoustic impedance layer. The silicon substrate includes at least a portion of a gap that overlaps with a portion of at least one of the first wiring portion and the second wiring portion when viewed from the thickness direction of the piezoelectric layer. The trapped area includes the gap.

29. The elastic wave device according to any one of claims 16 to 18, wherein, The elastic wave device also includes: A first wiring portion, which is connected to the first electrode; and The second wiring section is connected to the second electrode. The silicon substrate includes at least a portion of a gap disposed on the side opposite to the first electrode and the second electrode, separated by the piezoelectric layer. The gap includes a portion located within a predetermined distance from the area overlapping a portion of at least one of the first wiring portion and the second wiring portion, when viewed from the thickness direction of the piezoelectric layer. The specified distance is the distance between the first electrode and the second electrode and the silicon substrate. The trapped area includes the gap.

30. The elastic wave device according to claim 27, wherein, The elastic wave device includes a plurality of first electrodes and a plurality of second electrodes. The plurality of first electrodes and the plurality of second electrodes are arranged alternately, one of each. The plurality of first electrodes are connected together with the first wiring portion. The plurality of second electrodes are connected together with the second wiring section.

31. The elastic wave device according to any one of claims 16 to 18, wherein, The elastic wave device also includes a silicon oxide film disposed between the silicon substrate and the piezoelectric layer.

32. The elastic wave device according to any one of claims 16 to 18, wherein, The elastic wave device is an elastic wave filter equipped with multiple elastic wave resonators. The plurality of elastic wave resonators are resonators that include the first electrode and the second electrode, respectively. The piezoelectric layer is used in multiple elastic wave resonators.

33. The elastic wave device according to any one of claims 16 to 18, wherein, The piezoelectric layer has a first principal surface and a second principal surface that are opposite each other. The first main surface of the piezoelectric layer is the main surface of the piezoelectric layer opposite to the silicon substrate side. The second main surface of the piezoelectric layer is the main surface on the silicon substrate side of the piezoelectric layer. The first electrode and the second electrode are positioned opposite each other on the first main surface of the piezoelectric layer.

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