Elastic wave device
By placing a dielectric film between the reflector electrode and the piezoelectric substrate or below the electrode finger in the elastic wave device, the propagation of Rayleigh waves is hindered, thus solving the problem of large response caused by Rayleigh waves and achieving effective suppression of Rayleigh waves and a compact design of the device.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- MURATA MFG CO LTD
- Filing Date
- 2021-04-20
- Publication Date
- 2026-07-10
AI Technical Summary
In existing technologies, the large response caused by Rayleigh waves leads to significant spurious emissions.
In an elastic wave device, a dielectric film is placed between the reflector electrode and the piezoelectric substrate, or below the electrode finger of the reflector electrode, to impede the propagation direction component of the Rayleigh wave and suppress the excitation of the Rayleigh wave.
It effectively suppresses the Rayleigh wave response, avoids the need for large-scale elastic wave devices, and keeps the capacitance constant.
Smart Images
Figure CN115428334B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an elastic wave device having an IDT electrode and a reflector electrode. Background Technology
[0002] In the elastic wave device described in Patent Document 1 below, a piezoelectric film is laminated on a support substrate. An IDT electrode and reflector electrodes disposed on both sides of the IDT electrode in the elastic wave propagation direction are provided on this piezoelectric film. In Patent Document 1, the intersection region of the IDT electrode has a central region and a first edge region and a second edge region disposed outside the central region in the direction in which the electrode fingers extend. A dielectric film is provided between the electrode fingers and the piezoelectric film in the first edge region and the second edge region.
[0003] Prior art literature
[0004] Patent documents
[0005] Patent Document 1: US2017 / 0155373A1 Summary of the Invention
[0006] The problem the invention aims to solve
[0007] In the invention described in Patent Document 1, although the resonance characteristics of SH waves can be utilized, there is a problem of large spurious emissions caused by Rayleigh waves due to the large response caused by Rayleigh waves.
[0008] The purpose of this invention is to provide an elastic wave device that suppresses the response caused by Rayleigh waves.
[0009] Technical solutions for solving the problem
[0010] The elastic wave device according to the first invention of this application includes: a piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; and a reflector electrode disposed on both sides of the elastic wave propagation direction of the IDT electrode, having a plurality of electrode fingers arranged at intervals. The elastic wave device further includes: a first dielectric film disposed between the reflector electrode and the piezoelectric substrate in the region where the plurality of electrode fingers of the reflector electrode are disposed and the intervals are.
[0011] The second invention relates to an elastic wave device comprising: a piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate; and a reflector electrode disposed on both sides of the elastic wave propagation direction of the IDT electrode, having a plurality of electrode fingers arranged at intervals. The elastic wave device further comprises: a first dielectric film disposed between the plurality of electrode fingers of the reflector electrode and the piezoelectric substrate, wherein the first dielectric film is not disposed in the entire region between the region where the reflector electrode is disposed and the piezoelectric substrate.
[0012] Hereinafter, the first invention and the second invention will be collectively referred to as the present invention.
[0013] Invention Effects
[0014] According to the present invention, an elastic wave device capable of suppressing the response caused by Rayleigh waves can be provided. Attached Figure Description
[0015] Figure 1 This is a top view of the elastic wave device according to the first embodiment of the present invention.
[0016] Figure 2(a) and Figure 2(b) are along Figure 1 The sectional views of lines AA and BB in the diagram.
[0017] Figure 3 This is a graph showing the phase-frequency characteristics of the elastic wave device of Embodiment 1 and Comparative Example 1.
[0018] Figure 4 It is Figure 3 The portion shown as C is enlarged and is a graph showing the phase-frequency characteristics of Example 1 and Comparative Example 1.
[0019] Figure 5 This is a top view of the elastic wave device according to the second embodiment of the present invention.
[0020] Figure 6 It is along Figure 5 A cross-sectional view of the DD line.
[0021] Figure 7 This is a graph showing the phase-frequency characteristics of the elastic wave devices of Embodiment 1, Embodiment 2 and Comparative Example 1.
[0022] Figure 8 It is Figure 7 The portion E in the diagram is enlarged and shows the phase-frequency characteristics of Example 1, Example 2, and Comparative Example 1.
[0023] Figure 9This is a graph showing the relationship between the cutting angle of the Y-cut LiTaO3 and the magnitude of the phase of the Rayleigh wave in an elastic wave device of embodiments and comparative examples in which niobium oxide and tungsten oxide are used as dielectric films.
[0024] Figure 10 This is a front cross-sectional view of a piezoelectric substrate showing a modified example.
[0025] Figure 11 This is a front sectional view used to illustrate a modified example of a piezoelectric substrate. Detailed Implementation
[0026] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.
[0027] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.
[0028] Figure 1 This is a top view of the elastic wave device according to the first embodiment of the present invention. Figures 2(a) and 2(b) are along... Figure 1 A cross-sectional view of lines AA and BB in the diagram.
[0029] The elastic wave device 1 includes a support substrate 2. The support substrate 2 contains Si. A silicon oxide film 3, serving as a low-velocity sound film, is disposed on the support substrate 2. A piezoelectric film 4 containing LiTaO3 is disposed on the silicon oxide film 3. That is, a piezoelectric substrate is formed by stacking the support substrate 2, the silicon oxide film 3, and the piezoelectric film 4. The piezoelectric material constituting the piezoelectric film 4 is not limited to LiTaO3; LiNbO3 or the like can also be used. In this embodiment, Y-cut LiTaO3 is used.
[0030] An IDT electrode 5 is disposed on the piezoelectric film 4. The IDT electrode 5 has multiple first electrode fingers 5a and multiple second electrode fingers 5b that are interleaved with each other.
[0031] The direction of elastic wave propagation is orthogonal to the directions in which the first electrode finger 5a and the second electrode finger 5b extend. Reflector electrodes 6 and 7 are arranged on both sides of the IDT electrode 5 along the elastic wave propagation direction. Reflector electrodes 6 and 7 are respectively configured to short-circuit the two ends of the multiple electrode fingers 6a and 7a.
[0032] The IDT electrode 5 and the reflector electrodes 6 and 7 contain metals such as Al, Mo, Cu, and W, or alloys based on these metals. Alternatively, the IDT electrode 5 and the reflector electrodes 6 and 7 may also contain a stacked metal film formed by stacking multiple metal films.
[0033] In the IDT electrode 5, the region where the first electrode finger 5a and the second electrode finger 5b overlap in the direction of elastic wave propagation is called an intersection region. This intersection region has a central region located in the direction in which the first electrode finger 5a and the second electrode finger 5b extend, and a first edge region and a second edge region located on either side of the central region in the same direction. Furthermore, dielectric films 8 and 9, serving as second dielectric films, are provided in the first edge region and the second edge region. The second dielectric films 8 and 9 are disposed between the IDT electrode 5 and the piezoelectric film 4. In this embodiment, the dielectric films 8 and 9 are composed of Ta2O5 films, which are tantalum oxide films. By providing dielectric films 8 and 9, the sound velocity in the first edge region and the second edge region is lower than that in the central region. This suppresses transverse mode ripple.
[0034] The elastic wave device 1 is characterized in that, in the reflector electrodes 6 and 7, between the reflector electrodes 6 and 7 and the piezoelectric film 4, there are dielectric films 10 and 11 serving as first dielectric films.
[0035] In this embodiment, dielectric films 10 and 11 are composed of Ta2O5 films, which are tantalum oxide films. However, the dielectric material constituting dielectric films 10 and 11 is not limited to this; an oxide selected from the group consisting of, for example, niobium oxide such as Nb2O3, tungsten oxide such as WO3, hafnium oxide such as Hf2O5, and cerium oxide such as CeO2 can be used.
[0036] In the elastic wave device 1, dielectric films 10 and 11 are provided, thereby suppressing the response caused by Rayleigh waves. This is made clear by showing the phase-frequency characteristics of Example 1 and Comparative Example 1.
[0037] As an example 1, an elastic wave device 1 was manufactured with the following design parameters.
[0038] Support substrate 2: Si
[0039] Silicon oxide film 3: A SiO2 film with a thickness of 600 nm
[0040] Piezoelectric film 4: LiTaO3 cut at 50°Y, thickness = 600nm
[0041] IDT electrode 5 and reflector electrodes 6 and 7: Material is AlCu, electrode thickness = 140nm
[0042] The wavelength λ = 2 μm is determined by the distance between the electrode fingers of IDT electrode 5.
[0043] The number of electrode fingers of IDT electrode 5 is 100 pairs.
[0044] The size of the intersection area = 15λ
[0045] The dimension of the first electrode finger 5a and the second electrode finger 5b in the direction of extension of the first edge region and the second edge region is 350 nm.
[0046] The width of electrode 1 (5a) and electrode 2 (5b) is 500 nm.
[0047] The number of electrodes (6a) is 40.
[0048] The number of electrodes in electrode 7a is 40.
[0049] Electrode widths 6a and 7a are 500 nm.
[0050] Dielectric films 8 and 9 composed of Ta2O5 film: thickness = 30 nm
[0051] Ta₂O₅ films used as dielectric films 10 and 11: thickness = 30 nm
[0052] In addition, such as Figure 1 As shown, dielectric films 10 and 11 are configured to be located not only below electrode fingers 6a and 7a in reflector electrodes 6 and 7, but also in the interval region between electrode fingers 6a and 6a and the interval region between electrode fingers 7a and 7a.
[0053] As a comparative example 1, except that the dielectric films 10 and 11 described above are not provided, the elastic wave device of comparative example 1 is constructed in the same way as that of embodiment 1 described above.
[0054] exist Figure 3 In the diagram, the phase-frequency characteristics of Example 1 are shown in solid lines, and the phase-frequency characteristics of Comparative Example 1 are shown in dashed lines. Figure 3 In the vicinity of 1900MHz to 1990MHz, a response of the SH wave, which is the dominant mode utilized, appears. Moreover, a response caused by Rayleigh waves appears near 1400MHz.
[0055] Figure 4 It is Figure 3 The portion shown as C in the diagram is enlarged and represents a graph illustrating the phase-frequency characteristics of Example 1 and Comparative Example 1. Figure 4 In the diagram, solid lines represent the results of Example 1, while dashed lines represent the results of Comparative Example 1. According to... Figure 4 It is clearly understood that, compared to Comparative Example 1, the response caused by Rayleigh waves can be suppressed in Example 1. That is, according to Example 1, spurious signals caused by Rayleigh waves can be effectively suppressed.
[0056] As mentioned above, it can be assumed that the response caused by Rayleigh waves can be suppressed by setting dielectric films 10 and 11 for the following reasons.
[0057] Rayleigh waves have propagation direction components and depth direction components. By providing the aforementioned dielectric films 10 and 11, the propagation direction component can be blocked, making it difficult to excite Rayleigh waves. This can be considered as suppressing the response caused by Rayleigh waves.
[0058] Furthermore, in this embodiment, the dielectric films 10 and 11 are not disposed in the portion where the IDT electrode 5 is provided. Therefore, the capacitance in the IDT electrode 5 will not decrease, thus avoiding the need for a large-scale elastic wave device.
[0059] Figure 5 This is a top view of the elastic wave device according to the second embodiment of the present invention. Figure 6 It is shown Figure 5 A sectional view of the portion along line DD.
[0060] In the elastic wave device 21, dielectric films 10 and 11 are disposed below electrode fingers 6a of reflector electrode 6 and below electrode fingers 7a of reflector electrode 7, but not in the interval regions between electrode fingers 6a and 7a. Furthermore, dielectric films 10 and 11 are not configured to protrude on either side of the elastic wave propagation direction of reflector electrodes 6 and 7. That is, dielectric films 10 and 11 are disposed only below electrode fingers 6a and 7a. Regarding other structures, elastic wave device 21 is the same as elastic wave device 1. Therefore, descriptions of the same parts are omitted by using the same reference numerals.
[0061] Similar to the elastic wave device 21, in this invention, the dielectric films 10 and 11 can also be disposed only between the electrode fingers 6a and 7a of the reflector electrodes 6 and 7 and the piezoelectric film 4. In this case, the response caused by Rayleigh waves can also be effectively suppressed. This will be explained by comparing the phase-frequency characteristics of Example 2 with the phase-frequency characteristics of Example 1 and Comparative Example 1 described above.
[0062] The dielectric films 10 and 11 are disposed only below the electrode fingers 6a and 7a, and the other structures are the same as in Embodiment 1, which constitutes the elastic wave device of Embodiment 2.
[0063] Figure 7 This is a graph showing the phase-frequency characteristics of the elastic wave devices of Embodiment 1, Embodiment 2, and Comparative Example 1. Figure 8 It is Figure 7 The portion E in the diagram is enlarged and shows the phase-frequency characteristics of Example 1, Example 2, and Comparative Example 1.
[0064] exist Figure 7 as well as Figure 8In the diagram, the results of Example 1 are shown in solid lines, the results of Example 2 are shown in dashed lines, and the results of Comparative Example 1 are shown in dashed lines.
[0065] according to Figure 8 It is clearly understood that, in Example 2, similarly to Example 1, Rayleigh waves can be effectively suppressed compared to Comparative Example 1. Furthermore, in Example 2, the Rayleigh wave response can be further suppressed compared to Example 1.
[0066] As described above, in this invention, even when dielectric films 10 and 11 are provided only below the electrode fingers 6a and 7a of the reflector electrodes 6 and 7, the response caused by Rayleigh waves can be effectively suppressed. Furthermore, in this embodiment, it is not necessary to provide dielectric films 10 and 11 on the portion where the IDT electrode 5 is located. Therefore, the capacitance does not decrease, thus avoiding the need for a large-scale elastic wave device 21.
[0067] Furthermore, in the elastic wave device 21 according to the second embodiment, dielectric films 10 and 11 are not provided in the interval region between the reflector electrodes 6 and 7. Therefore, the reflection coefficient can be sufficiently ensured, thereby further reducing the response caused by Rayleigh waves.
[0068] In the first and second embodiments described above, the dielectric films 10 and 11 contain Ta2O5. However, in this invention, as mentioned above, other oxide dielectrics may also be used.
[0069] Figure 9 This is a graph showing the relationship between the cutting angle of Y-cut LiTaO3 and the magnitude of the Rayleigh wave phase when dielectric films containing Nb₂O₅ as niobium oxide and WO₃ as tungsten oxide are used as dielectric films 10 and 11. Additionally, in Figure 9 In the diagram, ○ indicates the results using Nb₂O₅, and Δ indicates the results using WO₃. Furthermore, in... Figure 9 In the diagram, × indicates the results of the aforementioned Comparative Example 1.
[0070] In addition, apart from different materials for the oxide dielectric and changes to the cutting angle, each elastic wave device was constructed in the same manner as in Example 1.
[0071] according to Figure 9 It is clearly understood that, within the range of LiTaO3 cut angles of 10° and 90°, the phase of the Rayleigh wave can be reduced by providing dielectric films 10 and 11 containing Nb2O5 or WO3, compared to Comparative Example 1, regardless of the specific case. In particular, it is understood that when the cut angle is 40° or less or 60° or more, the Rayleigh wave response can be suppressed more effectively compared to Comparative Example 1.
[0072] Furthermore, as shown in Figures 2(a) and 2(b), the elastic wave device 1 uses a piezoelectric substrate on which a low-velocity film composed of a silicon oxide film 3 and a piezoelectric film 4 are stacked on a support substrate 2 containing Si. In this case, the so-called low-velocity film refers to a film containing a low-velocity material in which the velocity of the propagating bulk wave is lower than the velocity of the bulk wave propagating in the piezoelectric film 4. As such a low-velocity material, silicon oxide, glass, silicon oxynitride, tantalum oxide, etc., can be used. In addition, compounds of silicon oxide with added fluorine, carbon, boron, etc., and media with the above materials as the main components can be used.
[0073] Furthermore, the support substrate 2 contains Si, and the support substrate 2 can contain various high-velocity acoustic materials containing Si. That is, it is sufficient as long as the high-velocity acoustic material layer is integrated with the support substrate. The so-called high-velocity acoustic material refers to a material in which the speed of sound of the propagating bulk wave is higher than the speed of sound of the elastic wave propagating in the piezoelectric film 4. Examples include alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) film or diamond, media mainly composed of the above materials, media mainly composed of mixtures of the above materials, and a wide variety of other materials.
[0074] Alternatively, a hypersonic material layer containing a hypersonic material can be disposed between the silicon oxide film 3 and the location indicated by the dashed line F in Figure 2(a). In this case, an insulator or semiconductor other than a hypersonic material can also be used as the support substrate 2.
[0075] Furthermore, in the elastic wave device 1, it is also possible to use Figure 10 The piezoelectric substrate shown is an acoustic reflective film 32 disposed between the support substrate 2 and the piezoelectric film 4 in the piezoelectric substrate 31. The acoustic reflective film 32 has low acoustic impedance layers 32a, 32c, and 32e with relatively low acoustic impedance and high acoustic impedance layers 32b, 32d, and 32f with relatively high acoustic impedance. Furthermore, the number of layers of the low acoustic impedance layers and the high acoustic impedance layers is not particularly limited.
[0076] Furthermore, in this invention, the following methods can also be used: Figure 11 The piezoelectric substrate 41 shown is composed of a single piezoelectric element. LiTaO3 and LiNbO3 can be used as such a piezoelectric element.
[0077] Explanation of reference numerals in the attached figures
[0078] 1: Elastic wave device;
[0079] 2: Support base plate;
[0080] 3: Silicon oxide film;
[0081] 4: Piezoelectric film;
[0082] 5: IDT electrode;
[0083] 5a, 5b: First electrode finger, second electrode finger;
[0084] 6, 7: Reflector electrodes;
[0085] 6a, 7a: Electrode references;
[0086] 8, 9, 10, 11: Dielectric film;
[0087] 21: Elastic wave device;
[0088] 31: Piezoelectric substrate;
[0089] 32: Acoustic reflector membrane;
[0090] 32a, 32c, 32e: Low acoustic impedance layers;
[0091] 32b, 32d, 32f: High acoustic impedance layers;
[0092] 41: Piezoelectric substrate.
Claims
1. An elastic wave device, comprising: piezoelectric substrate; An IDT electrode is disposed on the piezoelectric substrate; and The reflector electrodes, disposed on both sides of the elastic wave propagation direction of the IDT electrodes, have multiple electrode fingers arranged at intervals. The elastic wave device also includes: The first dielectric film is disposed between the reflector electrode and the piezoelectric substrate in the region where the plurality of electrode fingers of the reflector electrode are provided and the intervals therebetween, and does not overlap with the IDT electrode when viewed from above.
2. The elastic wave device according to claim 1, wherein, The IDT electrode has multiple first electrode fingers and multiple second electrode fingers that interlock with each other. The area where the first electrode fingers and the second electrode fingers overlap each other in the direction of elastic wave propagation is called an intersection region. The intersection region has a central region and first edge regions and second edge regions disposed on both sides of the central region in the direction in which the first electrode fingers and the second electrode fingers extend. The elastic wave device further comprises: a second dielectric film disposed between the IDT electrode and the piezoelectric substrate in the first edge region and the second edge region.
3. The elastic wave device according to claim 1 or 2, wherein, The first dielectric film comprises an oxide selected from the group consisting of tantalum oxide, niobium oxide, tungsten oxide, hafnium oxide, and cerium oxide.
4. The elastic wave device according to claim 1 or 2, wherein, The piezoelectric substrate includes a piezoelectric material, which is either LiNbO3 or LiTaO3.
5. The elastic wave device according to claim 1 or 2, wherein, The piezoelectric substrate has a supporting substrate and a piezoelectric film directly or indirectly stacked on the supporting substrate, wherein the piezoelectric film is LiNbO3 or LiTaO3.
6. The elastic wave device according to claim 5, wherein, The piezoelectric substrate further comprises: a high-velocity acoustic material layer disposed between the piezoelectric film and the supporting substrate, and comprising a high-velocity acoustic material in which the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the piezoelectric film.
7. The elastic wave device according to claim 6, wherein, It also includes: a low-velocity film disposed between the high-velocity material layer and the piezoelectric film, and comprising a low-velocity material in which the velocity of the propagating bulk wave is lower than the velocity of the bulk wave propagating in the piezoelectric film.
8. The elastic wave device according to claim 6 or 7, wherein, The hypersonic material layer is integrated with the supporting substrate.
9. The elastic wave device according to claim 5, wherein, The piezoelectric substrate further comprises: an acoustic reflective film, which is stacked between the piezoelectric film and the supporting substrate.
10. The elastic wave device according to claim 9, wherein, The acoustic reflective membrane has a low acoustic impedance layer with relatively low acoustic impedance and a high acoustic impedance layer with relatively high acoustic impedance.
11. An elastic wave device, comprising: piezoelectric substrate; An IDT electrode is disposed on the piezoelectric substrate; and The reflector electrodes, disposed on both sides of the elastic wave propagation direction of the IDT electrodes, have multiple electrode fingers arranged at intervals. The elastic wave device also includes: The first dielectric film is disposed between the plurality of electrodes of the reflector electrode and the piezoelectric substrate. The first dielectric film is not disposed in the entire region between the region where the reflector electrode is disposed and the piezoelectric substrate.
12. The elastic wave device according to claim 11, wherein, The IDT electrode has multiple first electrode fingers and multiple second electrode fingers that interlock with each other. The area where the first electrode fingers and the second electrode fingers overlap each other in the direction of elastic wave propagation is called an intersection region. The intersection region has a central region and first edge regions and second edge regions disposed on both sides of the central region in the direction in which the first electrode fingers and the second electrode fingers extend. The elastic wave device further comprises: a second dielectric film disposed between the IDT electrode and the piezoelectric substrate in the first edge region and the second edge region.
13. The elastic wave device according to claim 11 or 12, wherein, The first dielectric film comprises an oxide selected from the group consisting of tantalum oxide, niobium oxide, tungsten oxide, hafnium oxide, and cerium oxide.
14. The elastic wave device according to claim 11 or 12, wherein, The piezoelectric substrate includes a piezoelectric material, which is either LiNbO3 or LiTaO3.
15. The elastic wave device according to claim 11 or 12, wherein, The piezoelectric substrate has a supporting substrate and a piezoelectric film directly or indirectly stacked on the supporting substrate, wherein the piezoelectric film is LiNbO3 or LiTaO3.
16. The elastic wave device according to claim 15, wherein, The piezoelectric substrate further comprises: a high-velocity acoustic material layer disposed between the piezoelectric film and the supporting substrate, and comprising a high-velocity acoustic material in which the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the piezoelectric film.
17. The elastic wave device according to claim 16, wherein, It also includes: a low-velocity film disposed between the high-velocity material layer and the piezoelectric film, and comprising a low-velocity material in which the velocity of the propagating bulk wave is lower than the velocity of the bulk wave propagating in the piezoelectric film.
18. The elastic wave device according to claim 16 or 17, wherein, The hypersonic material layer is integrated with the supporting substrate.
19. The elastic wave device according to claim 15, wherein, The piezoelectric substrate further comprises: an acoustic reflective film, which is stacked between the piezoelectric film and the supporting substrate.
20. The elastic wave device according to claim 19, wherein, The acoustic reflective membrane has a low acoustic impedance layer with relatively low acoustic impedance and a high acoustic impedance layer with relatively high acoustic impedance.