Elastic wave device

Abstract

An elastic wave device capable of improving a Q value and hardly deteriorating resonance characteristics even when miniaturization is promoted. An elastic wave device (1) of the present invention includes a piezoelectric film (2) including lithium niobate or lithium tantalate, first and second bus bar electrodes (6, 7) disposed on the piezoelectric film (2) and opposed to each other, and first and second electrode fingers (8, 9) connected at one end to the first and second bus bar electrodes (6, 7). A bulk wave using a thickness shear primary mode is used. A first gap (G1) is disposed between the first bus bar electrode (6) and the second electrode finger (9). A second gap (G2) is disposed between the second bus bar electrode (7) and the first electrode finger (8). In a case where a center-to-center distance of adjacent first and second electrode fingers (8, 9) is p, a length of at least one of the first and second gaps (G1, G2) in a direction in which the first and second electrode fingers (8, 9) extend is 0.92p or more.

Description

[0001] This application is a divisional application of the invention patent application filed on March 29, 2021, with application number 202180025103.1 (PCT international application number PCT / JP2021 / 013328) and entitled "Elastic Wave Device". Technical Field

[0002] This invention relates to elastic wave devices. Background Technology

[0003] Conventionally, elastic wave devices utilizing plate waves propagating in a piezoelectric film comprising LiNbO3 or LiTaO3 are known. For example, Patent Document 1 disclosed below discloses an elastic wave device utilizing a Lamb wave as a plate wave. Here, the piezoelectric substrate comprises LiNbO3 or LiTaO3. An IDT electrode is provided on the upper surface of the piezoelectric substrate. A voltage is applied between multiple electrode fingers of the IDT electrode connected to one potential and multiple electrode fingers connected to another potential. This excites a Lamb wave. Reflectors are provided on both sides of the IDT electrode. Thus, an elastic wave resonator utilizing a plate wave is constructed.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-257019 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] To achieve miniaturization of the elastic wave device, reducing the number of electrode fingers is considered. However, reducing the number of electrode fingers lowers the Q value. On the other hand, when the distance between the electrode fingers of the IDT electrode and the busbar is too short, unwanted waves are generated due to their interference, which degrades the resonance characteristics.

[0009] The purpose of this invention is to provide an elastic wave device that can improve the Q value and whose resonance characteristics are difficult to deteriorate even when miniaturization is promoted.

[0010] means for solving problems

[0011] In a general aspect of the elastic wave device of the present invention, the elastic wave device comprises: a piezoelectric film including lithium niobate or lithium tantalate; a first busbar electrode and a second busbar electrode disposed on the piezoelectric film and facing each other; and a first electrode finger and a second electrode finger disposed on the piezoelectric film, one end of the first electrode finger being connected to the first busbar electrode, and one end of the second electrode finger being connected to the second busbar electrode. The elastic wave device utilizes a thickness shearing single-mode volume wave. When the direction in which the first electrode finger and the second electrode finger extend is defined as a first direction and the direction orthogonal to the first direction is defined as a second direction, the first electrode finger and the second electrode finger are facing each other in the second direction. A first gap is disposed between the first busbar electrode and the second electrode finger, and a second gap is disposed between the second busbar electrode and the first electrode finger. When the center-to-center distance between adjacent first electrode fingers and second electrode fingers is defined as p, the length of the first gap and the second gap along the first direction is 0.92p or more.

[0012] In another broad aspect of the elastic wave device of the present invention, the elastic wave device comprises: a piezoelectric film including lithium niobate or lithium tantalate; a first busbar electrode and a second busbar electrode disposed on the piezoelectric film and facing each other; and a first electrode finger and a second electrode finger disposed on the piezoelectric film, one end of the first electrode finger being connected to the first busbar electrode, and one end of the second electrode finger being connected to the second busbar electrode. When the thickness of the piezoelectric film is set as d and the center-to-center distance between adjacent first electrode fingers and second electrode fingers is set as p, d / p is 0.5 or less. When the direction in which the first electrode fingers and second electrode fingers extend is set as a first direction and the direction orthogonal to the first direction is set as a second direction, the first electrode fingers and second electrode fingers are facing each other in the second direction. A first gap is disposed between the first busbar electrode and the second electrode finger, and a second gap is disposed between the second busbar electrode and the first electrode finger. The length of the first gap and the second gap along the first direction is 0.92p or more.

[0013] Invention Effects

[0014] The elastic wave device according to the present invention can improve the Q value even when miniaturization is promoted, and the resonance characteristics are difficult to deteriorate. Attached Figure Description

[0015] Figure 1 (a) is a perspective view showing the appearance of the elastic wave device according to the first embodiment of the present invention. Figure 1 (b) is a top view showing the electrode structure on the piezoelectric film.

[0016] Figure 2 It is along Figure 1 A partial sectional view of line AA in (a).

[0017] Figure 3 (a) is a schematic front cross-sectional view illustrating the propagation of a Lamb wave through a piezoelectric film in a conventional elastic wave device. Figure 3 (b) is a schematic front cross-sectional view illustrating a thickness shear primary mode of a bulk wave propagating in a piezoelectric film in an elastic wave device according to an embodiment of the present invention.

[0018] Figure 4 This is a diagram showing the amplitude direction of the body wave in the first-order thickness shear mode.

[0019] Figure 5 This is a graph showing the relationship between d / p and the fractional bandwidth of the resonator when the average distance between the centers of adjacent first and second electrode fingers is set as p and the thickness of the piezoelectric film is set as d.

[0020] Figure 6 This is a graph showing the impedance-frequency characteristics of the first and second gaps when their lengths along the first direction are 0.31p to 1.54p.

[0021] Figure 7 yes Figure 6 Enlarged image.

[0022] Figure 8 This is a graph showing the impedance-frequency characteristics of the first and second gaps when their lengths along the first direction are 1.54p to 9.23p.

[0023] Figure 9 This is a top view showing the electrode structure of the elastic wave device according to the second embodiment of the present invention.

[0024] Figure 10 This is a graph showing the impedance-frequency characteristics of the first and second gaps when their lengths along the first direction are 0.31p to 1.54p.

[0025] Figure 11 This is a graph showing the frequency characteristics of attenuation when the length of the first gap and the second gap along the first direction is 0.31p to 1.54p.

[0026] Figure 12 This is a reference diagram illustrating an example of the resonant characteristics of an elastic wave device according to an embodiment of the present invention.

[0027] Figure 13 This is a graph showing the relationship between fractional bandwidth and the size of normalized spurious signals.

[0028] Figure 14 This is a graph showing the relationship between d / 2p, metallization rate (MR), and fractional bandwidth.

[0029] Figure 15 This is a graph of the fractional bandwidth mapping in LiNbO3 with Euler angles (0°, θ, ψ) such that d / p approaches 0. Detailed Implementation

[0030] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0031] It should be noted that the embodiments described in this specification are illustrative, and it is indicated in advance that partial substitutions or combinations of structures can be made between different embodiments.

[0032] Figure 1 (a) is a perspective view showing the appearance of the elastic wave device according to the first embodiment of the present invention. Figure 1 (b) is a top view showing the electrode structure on the piezoelectric film in the first embodiment.

[0033] like Figure 1 As shown in (a), the elastic wave device 1 has a piezoelectric film 2. The piezoelectric film 2 has a first main surface 2a and a second main surface 2b. The first main surface 2a and the second main surface 2b are opposite to each other. In this embodiment, the piezoelectric film 2 is a lithium niobate film. More specifically, the piezoelectric film 2 is a LiNbO3 film. It should be noted that the material of the piezoelectric film 2 is not limited to the above; for example, lithium tantalate such as LiTaO3 can also be used. The thickness of the piezoelectric film 2 is preferably 40 nm or more and 1000 nm or less.

[0034] A functional electrode 5 is disposed on the first main surface 2a of the piezoelectric film 2. For example... Figure 1 As shown in (b), the functional electrode 5 has a plurality of electrode fingers. The plurality of electrode fingers are arranged in a direction intersecting the thickness direction of the piezoelectric film 2. The plurality of electrode fingers includes multiple pairs of first electrode fingers 8 and second electrode fingers 9. Furthermore, the functional electrode 5 has a first busbar electrode 6 and a second busbar electrode 7. The first busbar electrode 6 and the second busbar electrode 7 are opposite to each other. One end of each of the plurality of first electrode fingers 8 is connected to the first busbar electrode 6. The other end of each of the plurality of first electrode fingers 8 is opposite to the second busbar electrode 7. One end of each of the plurality of second electrode fingers 9 is connected to the second busbar electrode 7. The other end of each of the plurality of second electrode fingers 9 is opposite to the first busbar electrode 6. The first electrode fingers 8 and the second electrode fingers 9 extend in parallel. The plurality of first electrode fingers 8 and the plurality of second electrode fingers 9 are inserted alternately into each other.

[0035] Here, the direction in which the first electrode finger 8 and the second electrode finger 9 extend is defined as the first direction y, and the direction orthogonal to the first direction y is defined as the second direction x. In the second direction x, the first electrode finger 8 and the second electrode finger 9 are opposite each other. Both the first direction y and the second direction x are directions that intersect the thickness direction of the piezoelectric film 2. Therefore, the first electrode finger 8 and the second electrode finger 9 can also be said to be opposite each other in a direction that intersects the thickness direction of the piezoelectric film 2.

[0036] The first electrode finger 8 and the second electrode finger 9 are connected to different potentials. When viewed from the second direction x, the overlapping area of ​​an adjacent pair of first electrode fingers 8 and second electrode fingers 9 is the excitation region B. Figure 1 In (b), an excitation region B is shown as an example, but the region between the plurality of first electrode fingers 8 and the plurality of second electrode fingers 9 is also the excitation region B.

[0037] Here, the distance between the centers of adjacent first electrode fingers 8 and second electrode fingers 9 is defined as p. The distance between the centers of the first electrode fingers 8 and the second electrode fingers 9 is the distance connecting the center of the first electrode finger 8 in the second direction x and the center of the second electrode finger 9 in the second direction x.

[0038] like Figure 1 As shown in (b), a first gap G1 is disposed between the first busbar electrode 6 and the second electrode finger 9. A second gap G2 is disposed between the second busbar electrode 7 and the first electrode finger 8. In this embodiment, the lengths of the first gap G1 and the second gap G2 along the first direction y are 0.92p or more. The lengths of the first gap G1 and the second gap G2 along the first direction y are the same. It should be noted that the lengths of the first gap G1 and the second gap G2 along the first direction y may also be different. At least one of the first gap G1 and the second gap G2 may have a length of 0.92p or more along the first direction y.

[0039] The functional electrode 5 comprises a suitable metal or alloy such as Al or an AlCu alloy. In the AlCu alloy, Cu is preferably 1% by weight or more and 10% by weight or less. The functional electrode 5 may also comprise a stacked metal film. In this case, for example, a bonding layer may be provided. Examples of bonding layers include Ti layers and Cr layers.

[0040] Figure 2 It is along Figure 1 A partial sectional view of line AA in (a).

[0041] A support member 4 is stacked on the second main surface 2b of the piezoelectric film 2, separated by an insulating layer 3. The insulating layer 3 and the support member 4 have a frame-like shape. The insulating layer 3 has an opening 3a. The support member 4 has an opening 4a. This forms an air gap 10. The air gap 10 is provided to avoid hindering the vibration of the excitation region B of the piezoelectric film 2. The support member 4 does not overlap with at least one pair of first electrode fingers 8 and second electrode fingers 9 when viewed from above. It should be noted that the insulating layer 3 may not be provided. Therefore, the support member 4 can be stacked directly or indirectly on the second main surface 2b of the piezoelectric film 2.

[0042] The insulating layer 3 comprises silicon oxide. However, in addition to silicon oxide, suitable insulating materials such as silicon oxynitride and aluminum oxide can also be used. The support member 4 comprises Si. The orientation of the surface of the piezoelectric film 2 side of the Si constituting the support member 4 can be (100), (111), or (110). The Si used for the support member 4 is preferably a high resistivity of 4 kΩ or higher. However, the support member 4 can also be constructed using suitable insulating or semiconductor materials.

[0043] However, in this embodiment, no reflector is provided on the piezoelectric film 2. The elastic wave device 1 does not have a reflector. Alternatively, if the elastic wave device 1 has a reflector, the number of electrode fingers of the reflector can be reduced. This is because the elastic wave device 1 utilizes a thickness shear primary mode body wave.

[0044] The feature of this embodiment is that the elastic wave device 1 utilizes a thickness shear primary mode body wave, and the lengths of the first gap G1 and the second gap G2 along the first direction y are 0.92p or more. Therefore, even with miniaturization, the Q value can be improved, and the resonance characteristics are less prone to deterioration. The details of this effect will be explained below along with the details of the thickness shear primary mode.

[0045] like Figure 2 As shown, multiple pairs of adjacent first electrode fingers 8 and second electrode fingers 9 are arranged in the second direction x. This number of pairs does not need to be an integer; it can be 1.5 pairs, 2.5 pairs, etc. It should be noted that "adjacent" in the functional electrode 5 does not mean that the electrode fingers are configured to be in direct contact with each other, but rather that the electrode fingers are configured with a gap between them. Furthermore, when the first electrode finger 8 and the second electrode finger 9 are adjacent, no other signal electrodes or ground electrodes are disposed between the first electrode finger 8 and the second electrode finger 9.

[0046] When the elastic wave device 1 is driven, an alternating voltage is applied between the plurality of first electrode fingers 8 and the plurality of second electrode fingers 9. More specifically, an alternating voltage is applied between the first busbar electrode 6 and the second busbar electrode 7. As a result, a thickness shear primary mode bulk wave is excited in the piezoelectric film 2.

[0047] In the elastic wave device 1, when the thickness of the piezoelectric film 2 is set to d and the center-to-center distance between adjacent first electrode fingers 8 and second electrode fingers 9 is set to p, d / p is 0.5 or less. Therefore, the aforementioned thickness shear primary mode bulk wave is effectively excited, and good resonance characteristics can be obtained.

[0048] The elastic wave device 1 has the above-described structure and utilizes a thickness shear primary mode volume wave. Therefore, even if the number of pairs of the first electrode fingers 8 and the second electrode fingers 9 is reduced to achieve miniaturization, it is difficult to cause a decrease in the Q value.

[0049] In this embodiment, a Z-cut piezoelectric material is used in the piezoelectric film 2. Therefore, the second direction x becomes orthogonal to the polarization direction of the piezoelectric film 2. It should be noted that this is not a limitation if a piezoelectric material with other cut angles is used in the piezoelectric film 2.

[0050] Reference Figure 3 (a) and Figure 3 (b) explains the difference between the body wave of the thickness shear primary mode and the Lamb wave used previously.

[0051] Figure 3 (a) is a schematic front cross-sectional view illustrating the Lamb wave propagating in the piezoelectric film of the elastic wave device described in Patent Document 1. Here, the wave propagates in the piezoelectric film 201 as indicated by the arrow. Here, in the piezoelectric film 201, a first main surface 201a and a second main surface 201b are opposite each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the third direction z. The second direction x is the direction in which the electrode fingers of the IDT electrodes are arranged. Figure 3 As shown in (a), the Lamb wave propagates along the second direction x. Since the Lamb wave is a plate wave, although the piezoelectric film 201 vibrates as a whole, the wave propagates along the second direction x. Therefore, by placing reflectors on both sides of the IDT electrode in the second direction x, a resonant characteristic is obtained.

[0052] In contrast, such as Figure 3 As shown in (b), in the elastic wave device of the present invention, the vibration displacement is in the thickness shear direction. Therefore, the wave propagates almost along the third direction z and resonates. Therefore, the component of the wave in the second direction x is significantly smaller than the component in the third direction z. Moreover, since the resonant characteristic is obtained through the propagation of the wave in this third direction z, it is difficult to generate propagation loss even if the number of electrode fingers of the reflector is reduced. Furthermore, even if the number of electrode pairs including the first electrode finger 8 and the second electrode finger 9 is reduced in order to promote miniaturization, it is difficult to generate a decrease in the Q value.

[0053] It should be noted that, as Figure 4As shown, the amplitude direction of the bulk wave in the thickness shear primary mode is opposite in the first region 451 and the second region 452 contained in the excitation region of the piezoelectric film 2. Figure 4 The diagram schematically illustrates a body wave when a voltage is applied between the first electrode finger 8 and the second electrode finger 9, with the second electrode finger 9 having a higher potential than the first electrode finger 8. The first region 451 is the region between the virtual plane VP1, which is orthogonal to the thickness direction of the piezoelectric film 2 and divides the piezoelectric film 2 in two, and the first main surface 2a. The second region 452 is the region between the virtual plane VP1 and the second main surface 2b in the excitation region.

[0054] As described above, the elastic wave device 1 is equipped with multiple pairs of first electrode fingers 8 and second electrode fingers 9. The thickness shearing primary mode does not cause the wave to propagate along the second direction x; therefore, it is not necessary to provide multiple pairs of electrode pairs including first electrode fingers 8 and second electrode fingers 9. That is, providing at least one pair of first electrode fingers 8 and second electrode fingers 9 is sufficient.

[0055] In the elastic wave device 1, the first electrode finger 8 is an electrode connected to the signal potential, and the second electrode finger 9 is an electrode connected to the ground potential. However, it is also possible that the first electrode finger 8 is connected to the ground potential, and the second electrode finger 9 is connected to the signal potential. In this embodiment, as described above, at least one pair of electrode fingers is either connected to the signal potential or connected to the ground potential, and no floating electrode is provided.

[0056] However, in this embodiment, d / p is 0.5 or less. It should be noted that d / p is preferably 0.24 or less. In this case, better resonance characteristics can be obtained. (Refer to...) Figure 5 This needs to be explained.

[0057] By changing d / p, multiple elastic wave devices can be obtained. Figure 5 This is a graph showing the relationship between d / p and the fractional bandwidth of the resonator as an elastic wave device.

[0058] according to Figure 5 It is known that when d / p > 0.5, even with adjustments to d / p, the fractional bandwidth is less than 5%. Conversely, when d / p ≤ 0.5, varying d / p within this range allows for a fractional bandwidth exceeding 5%. Therefore, a resonator with a high coupling coefficient can be constructed. Furthermore, when d / p is below 0.24, the fractional bandwidth can be increased to over 7%. Based on this, adjusting d / p within this range yields a resonator with an even wider fractional bandwidth, enabling the realization of a resonator with a higher coupling coefficient. It should be noted that, for example, if the piezoelectric film 2 has a thickness deviation, a value obtained by averaging that thickness can also be used.

[0059] The center-to-center distance p between adjacent first electrode fingers 8 and second electrode fingers 9 is preferably 1 μm or more and 10 μm or less. When the dimension of the plurality of electrode fingers of the functional electrode 5 along the second direction x is set as the width, the width of the first electrode finger 8 and the second electrode finger 9 is preferably 50 nm or more and 1000 nm or less, respectively.

[0060] Here, as Figure 1 As shown in (b), in the first embodiment, the lengths of the first gap G1 and the second gap G2 along the first direction y are 0.92p or more. Therefore, even with miniaturization, the resonance characteristics are unlikely to deteriorate. This will be explained in detail below.

[0061] Multiple elastic wave devices were prepared by making the lengths of the first gap and the second gap different along the first direction. The impedance characteristics of these multiple elastic wave devices were measured. It should be noted that in each elastic wave device, the number of pairs of the first electrode fingers and the second electrode fingers is set to one. The design parameters of each prepared elastic wave device are as follows.

[0062] Piezoelectric film: Material…LiNbO3, thickness 400nm

[0063] The number of electrode pairs, including the first electrode finger and the second electrode finger, is 1 pair.

[0064] The lengths of the first and second gaps along the first direction are: 0.31p, 0.62p, 0.92p, 1.23p, 1.54p, 3.08p, 4.62p, 6.15p, or 9.23p.

[0065] Figure 6 This is a graph showing the impedance-frequency characteristics of the first and second gaps when their lengths along the first direction are 0.31p to 1.54p. Figure 7 yes Figure 6 Enlarged image. Figure 8 This is a graph showing the impedance-frequency characteristics of the first and second gaps when their lengths along the first direction are 1.54p to 9.23p.

[0066] like Figure 6 and Figure 7 As shown, it can be seen that compared to the case where the length of the first gap and the second gap along the first direction is 0.92p or more, the impedance characteristics deteriorate when the length is 0.62p. When the length is 0.31p, the impedance characteristics deteriorate further. Thus, it can be seen that when the length is shorter than 0.92p, the resonant characteristics deteriorate. On the other hand, it can be seen that when the length of the first gap and the second gap along the first direction is 0.92p or more, the impedance characteristics remain almost unchanged. Furthermore, as... Figure 8As shown, when the length of the first gap and the second gap along the first direction is 1.54p or more, the impedance characteristics do not change significantly.

[0067] Here, in order to miniaturize the elastic wave device, in addition to reducing the number of electrode fingers, the lengths of the first gap and the second gap along the second direction can also be shortened. For example... Figures 6-8 As shown, even if the lengths of the first gap and the second gap along the second direction are shortened to 0.92p, the resonance characteristics are difficult to deteriorate. In the first embodiment, the lengths of the first gap G1 and the second gap G2 along the first direction y are 0.92p or more. Based on this, in the first embodiment, a bulk wave of the thickness shearing primary mode is used. Therefore, even with the miniaturization of the elastic wave device 1, the Q value can be improved, and the resonance characteristics are difficult to deteriorate.

[0068] It should be noted that the lengths of the first gap G1 and the second gap G2 along the first direction y are preferably 9.2p or less, and more preferably 3p or less. This allows for appropriate miniaturization of the elastic wave device 1.

[0069] In the first embodiment, the front end of the second electrode finger 9 is separated from the first busbar electrode 6 by a first gap G1. The front end of the first electrode finger 8 is separated from the second busbar electrode 7 by a second gap G2. It should be noted that this is not a limitation; the first gap G1 can be disposed between the first busbar electrode 6 and the second electrode finger 9. The second gap G2 can be disposed between the second busbar electrode 7 and the first electrode finger 8. Examples other than the first embodiment with this structure are shown below.

[0070] Figure 9 This is a top view showing the electrode structure of the elastic wave device according to the second embodiment.

[0071] This embodiment differs from the first embodiment in that the functional electrode 15 has a plurality of first dummy electrode fingers 18 and a plurality of second dummy electrode fingers 19. Apart from the above aspects, the elastic wave device of this embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0072] One end of each of the plurality of first dummy electrode fingers 18 is connected to the first busbar electrode 6. The plurality of first dummy electrode fingers 18 are respectively opposed to the plurality of second electrode fingers 9. In this embodiment, a first gap G1 is also disposed between the first busbar electrode 6 and the second electrode fingers 9. However, the front end of each of the first dummy electrode fingers 18 is separated from the first gap G1 and is opposed to the front end of each of the second electrode fingers 9.

[0073] One end of each of the plurality of second dummy electrode fingers 19 is connected to the second busbar electrode 7. The plurality of second dummy electrode fingers 19 are respectively opposed to the plurality of first electrode fingers 8. In this embodiment, a second gap G2 is also disposed between the second busbar electrode 7 and the first electrode fingers 8. However, the front end of each of the second dummy electrode fingers 19 is separated from the second gap G2 and is opposed to the front end of the first electrode fingers 8.

[0074] In this embodiment, the elastic wave device also utilizes a thickness shearing primary mode body wave, and the lengths of the first gap G1 and the second gap G2 along the first direction y are also 0.92p or more. Therefore, even with the miniaturization of the elastic wave device, the Q value can be improved, and the resonance characteristics are less prone to deterioration.

[0075] It should be noted that even if the widths of the first dummy electrode finger 18 and the second dummy electrode finger 19 differ within the range of 0.15 μm to 0.3 μm, the characteristics of the main mode do not change significantly. Similarly, even if the lengths of the first dummy electrode finger 18 and the second dummy electrode finger 19 along the first direction y differ within the range of 1 μm to 5 μm, the characteristics of the main mode do not change significantly.

[0076] Here, multiple elastic wave devices were prepared by making the lengths of the first gap G1 and the second gap G2 different along the first direction y. The impedance characteristics of these multiple elastic wave devices were measured. It should be noted that in each elastic wave device, the number of pairs of the first electrode fingers and the second electrode fingers is set to one. The design parameters of each elastic wave device are as follows.

[0077] Piezoelectric film: Material…LiNbO3, thickness 400nm

[0078] The number of electrode pairs, including the first electrode finger and the second electrode finger, is 1 pair.

[0079] The center-to-center distance p between the first and second electrode fingers is 3.25 μm.

[0080] The lengths of the first and second dummy electrode fingers along the first direction are: 3 μm.

[0081] The lengths of the first and second gaps along the first direction are: 0.31p, 0.62p, 0.92p, 1.23p, or 1.54p.

[0082] Figure 10 This is a graph showing the impedance-frequency characteristics of the first and second gaps when their lengths along the first direction are 0.31p to 1.54p.

[0083] like Figure 10As shown, compared to the cases where the length along the first direction of the first gap and the second gap is 0.92p or more, the impedance characteristics deteriorate when the length is 0.62p. When the length is 0.31p, the impedance characteristics deteriorate further. Thus, it can be seen that when the length is shorter than 0.92p, the resonant characteristics deteriorate. Figure 9 In the embodiment shown, the lengths of the first gap G1 and the second gap G2 along the first direction y are 0.92p or more, so the resonance characteristics are difficult to deteriorate.

[0084] Figure 11 This is a graph showing the frequency characteristics of attenuation when the length of the first gap and the second gap along the first direction is 0.31p to 1.54p.

[0085] like Figure 11 As shown, when the length of the first gap and the second gap along the first direction is 0.31p, a large ripple is generated at the frequency indicated by arrow C. In contrast, when the length is 0.92p or greater, the ripple is suppressed. Figure 9 In the embodiment shown, the lengths of the first gap G1 and the second gap G2 along the first direction y are 0.92p or more, thus suppressing ripple.

[0086] Furthermore, in this invention, the metallization rate MR of the adjacent first electrode finger 8 and second electrode finger 9 in the excitation region B is expected to satisfy MR ≤ 1.75 (d / p) + 0.075. In this case, stray emissions can be effectively reduced. (Refer to...) Figure 12 and Figure 13 This needs to be explained.

[0087] Figure 12 This is a reference diagram illustrating an example of the resonant characteristics of an elastic wave device according to an embodiment of the present invention. The spurious signal indicated by arrow E occurs between the resonant frequency and the anti-resonant frequency. It should be noted that here, d / p is set to 0.08, and the Euler angles of LiNbO3 are set to (0°, 0°, 90°). Furthermore, the metallization rate MR is set to 0.35.

[0088] Reference Figure 1 (b) explains the metallization rate MR. Figure 1In the electrode configuration of (b), only one pair of first electrode fingers 8 and second electrode fingers 9 are provided. In this case, the portion enclosed by the single-dot dashed line is called the excitation region B. Specifically, the excitation region B includes the regions described in 1) to 3) below: 1) The region of the first electrode finger 8 that overlaps with the second electrode finger 9 in the second direction y. 2) The region of the second electrode finger 9 that overlaps with the first electrode finger 8 in the second direction y. 3) The region between the first electrode finger 8 and the second electrode finger 9 in the second direction y that overlaps with both the first electrode finger 8 and the second electrode finger 9. Furthermore, the area of ​​the first electrode finger 8 and the second electrode finger 9 within the excitation region B, relative to the area of ​​the excitation region B, is called the metallization rate MR. That is, the metallization rate MR is the ratio of the area of ​​the metallized portion to the area of ​​the excitation region B.

[0089] It should be noted that when multiple pairs of first electrode fingers 8 and second electrode fingers 9 are provided, the ratio of the metallized portion contained in the entire excitation region B to the total area of ​​the excitation region B can be set as MR.

[0090] Figure 13 This is a graph showing the relationship between the fractional bandwidth and the normalized spurious magnitude when multiple elastic wave resonators are constructed according to the present invention. The spurious magnitude is the magnitude of the spurious phase rotation normalized by 180 degrees. It should be noted that various changes and adjustments have been made to the thickness of the piezoelectric film or the dimensions of the electrode fingers regarding the fractional bandwidth. Furthermore, Figure 13 This is the result when using a Z-cut piezoelectric film including LiNbO3, but the same trend is also observed when using piezoelectric films with other cut angles.

[0091] exist Figure 13 In the region enclosed by ellipse J, the stray energy increases to 1.0. According to... Figure 13 It is known that when the fractional bandwidth exceeds 0.17, that is, exceeds 17%, even if the parameters constituting the fractional bandwidth are changed, large spurious emissions with a spurious emission level of 1 or higher will still appear in the passband. Therefore, the fractional bandwidth is preferably 17% or less. In this case, spurious emissions can be reduced by adjusting the thickness of the piezoelectric film 2, the size of the first electrode finger 8, the second electrode finger 9, etc.

[0092] Figure 14 This is a graph showing the relationship between d / 2p, metallization rate (MR), and fractional bandwidth. The fractional bandwidth was measured for various elastic wave devices constructed according to the present invention with different d / 2p and MR. Figure 14The area indicated by the shaded line to the right of the dashed line D is the region with a fractional bandwidth of 17% or less. The boundary between this shaded region and the unshaded region is represented by MR = 3.5(d / 2p) + 0.075. That is, MR = 1.75(d / p) + 0.075. Therefore, it is preferable that MR ≤ 1.75(d / p) + 0.075. In this case, it is easier to make the fractional bandwidth 17% or less. More preferably... Figure 14 The region to the right of the dashed line D1 in the diagram is MR = 3.5(d / 2p) + 0.05. More preferably, MR ≤ 1.75(d / p) + 0.05. This allows the fractional bandwidth to be more reliably below 17%.

[0093] Figure 15 This is a graph showing the fractional bandwidth of the Euler angles (0°, θ, ψ) of LiNbO3 relative to the case where d / p is infinitely close to 0. Figure 15 The area shown by the shading is the region with a fractional bandwidth of at least 5%, and when approximating the range of this region, it becomes the range represented by the following equations (1), (2) and (3).

[0094] (0°±10°, 0°~20°, any ψ)... Equation (1)

[0095] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50))) 2 / 900) 1 / 2 [180°]...Equation (2)

[0096] (0°±10°, [180°-30° (1-(ψ-90) 2 / 8100) 1 / 2 [~180°, any ψ)... Equation (3)

[0097] Therefore, within the range of Euler angles in equations (1), (2), or (3) above, it is preferable to be able to sufficiently expand the fractional bandwidth.

[0098] Explanation of reference numerals in the attached figures

[0099] 1…elastic wave device;

[0100] 2…piezoelectric film;

[0101] 2a…First main face;

[0102] 2b…Second main face;

[0103] 3…Insulation layer;

[0104] 3a…opening;

[0105] 4…supporting components;

[0106] 4a…opening;

[0107] 5…functional electrodes;

[0108] 6, 7… First busbar electrode, second busbar electrode;

[0109] 8, 9… First electrode indicator, second electrode indicator;

[0110] 10… air gap;

[0111] 15…functional electrodes;

[0112] 18, 19… First dummy electrode finger, second dummy electrode finger;

[0113] 201… piezoelectric film;

[0114] 201a, 201b... First main face, second main face;

[0115] 451, 452… First area, Second area;

[0116] B…incentive region;

[0117] G1, G2... First gap, second gap;

[0118] VP1… Virtual plane.

Claims

1. An elastic wave device, comprising: Piezoelectric films, including lithium niobate or lithium tantalate; The first busbar electrode and the second busbar electrode are disposed on the piezoelectric film and are opposite to each other; and A first electrode finger and a second electrode finger are disposed on the piezoelectric film. One end of the first electrode finger is connected to the first busbar electrode, and one end of the second electrode finger is connected to the second busbar electrode. The elastic wave device utilizes a thickness shear primary mode body wave. When the direction in which the first electrode finger and the second electrode finger extend is defined as the first direction, and the direction orthogonal to the first direction is defined as the second direction, the first electrode finger and the second electrode finger are positioned opposite each other in the second direction. A first gap is disposed between the first busbar electrode and the second electrode finger, and a second gap is disposed between the second busbar electrode and the first electrode finger. When the center-to-center distance between adjacent first electrode fingers and second electrode fingers is set as p, the length of at least one of the first gap and the second gap along the first direction is 0.92p or more.

2. The elastic wave device according to claim 1, wherein, The length of at least one of the first gap and the second gap along the first direction is 9.2p or less.

3. The elastic wave device according to claim 2, wherein, The length of at least one of the first gap and the second gap along the first direction is 3p or less.

4. The elastic wave device according to any one of claims 1 to 3, wherein, When the thickness of the piezoelectric film is set as d and the center-to-center distance between adjacent first electrode fingers and second electrode fingers is set as p, d / p is 0.24 or less.

5. The elastic wave device according to any one of claims 1 to 3, wherein, When viewed from the second direction, the overlapping area of ​​adjacent first electrode fingers and second electrode fingers is the excitation region. When the ratio of the area of ​​the first electrode fingers and second electrode fingers in the excitation region to the area of ​​the excitation region, i.e., the metallization rate, is set as MR, MR ≤ 1.75(d / p) + 0.075 is satisfied.

6. An elastic wave device, comprising: Piezoelectric films, including lithium niobate or lithium tantalate; The first busbar electrode and the second busbar electrode are disposed on the piezoelectric film and are opposite to each other; and A first electrode finger and a second electrode finger are disposed on the piezoelectric film. One end of the first electrode finger is connected to the first busbar electrode, and one end of the second electrode finger is connected to the second busbar electrode. When the thickness of the piezoelectric film is set as d and the center-to-center distance between adjacent first electrode fingers and second electrode fingers is set as p, d / p is 0.5 or less. When the direction in which the first electrode finger and the second electrode finger extend is defined as the first direction, and the direction orthogonal to the first direction is defined as the second direction, the first electrode finger and the second electrode finger are positioned opposite each other in the second direction. A first gap is disposed between the first busbar electrode and the second electrode finger, and a second gap is disposed between the second busbar electrode and the first electrode finger. The length of at least one of the first gap and the second gap along the first direction is 0.92p or more.

7. The elastic wave device according to claim 6, wherein, The length of at least one of the first gap and the second gap along the first direction is 9.2p or less.

8. The elastic wave device according to claim 7, wherein, The length of at least one of the first gap and the second gap along the first direction is 3p or less.

9. The elastic wave device according to any one of claims 6 to 8, wherein, When the thickness of the piezoelectric film is set as d and the center-to-center distance between adjacent first electrode fingers and second electrode fingers is set as p, d / p is 0.24 or less.

10. The elastic wave device according to any one of claims 6 to 8, wherein, When viewed from the second direction, the overlapping area of ​​adjacent first electrode fingers and second electrode fingers is the excitation region. When the ratio of the area of ​​the first electrode fingers and second electrode fingers in the excitation region to the area of ​​the excitation region, i.e., the metallization rate, is set as MR, MR ≤ 1.75(d / p) + 0.075 is satisfied.

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