Elastic wave device

Abstract

Provided is an elastic wave device with low loss. In an elastic wave device (1), an IDT electrode (6) and a reflector electrode (7, 8) are provided on a piezoelectric substrate (2), an area in which first electrode fingers (6c) and second electrode fingers (6d) of the IDT electrode (6) overlap in an elastic wave propagation direction is a crossover area (K), the crossover area (K) has a central area (C), and first edge areas (E1) and second edge areas (E2) on both sides of the central area (C), and a dielectric film (9, 10) is arranged to pass through the reflector electrode (7, 8) from the first edge areas (E1) and the second edge areas (E2) to an area outside the elastic wave propagation direction of the reflector electrode (7, 8).

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 the 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 extending direction of the electrode finger in the central region. A dielectric film is disposed between the electrode finger 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: US 2017 / 0155373 A1 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In the elastic wave device described in Patent Document 1, the acoustic discontinuity between the IDT electrode and the reflector electrode is relatively large. Therefore, there is a problem of energy scattering and increased loss.

[0008] The purpose of this invention is to provide an elastic wave device with low loss.

[0009] means for solving problems

[0010] The elastic wave device of the present invention comprises: a piezoelectric substrate; an IDT electrode disposed on the piezoelectric substrate, having first electrode fingers and second electrode fingers inserted alternately therein; and a reflector electrode disposed on both sides of the elastic wave propagation direction of the IDT electrode, having multiple electrode fingers. In the IDT electrode, when viewed along the elastic wave propagation direction, the area where the first electrode fingers and the second electrode fingers overlap is an intersection region. The intersection region has a central region and a first edge region and a second edge region disposed on both sides of the extension direction of the first electrode fingers and the second electrode fingers disposed in the central region. The elastic wave device further comprises a dielectric film configured to extend from the first edge region and the second edge region to a region outside the elastic wave propagation direction of the region where the reflector electrode is disposed.

[0011] Invention Effects

[0012] According to the present invention, a low-loss elastic wave device can be provided. Attached Figure Description

[0013] Figure 1 This is a top view of the elastic wave device according to the first embodiment of the present invention.

[0014] Figure 2 (a) and (b) are respectively along Figure 1 A cross-sectional view of lines AA and BB in the diagram.

[0015] Figure 3 This is a graph showing the relationship between the extension length of the dielectric film extending to the outer edge of the reflector and the energy leakage rate in the elastic wave device of the first embodiment.

[0016] Figure 4 This is a top view of the elastic wave device according to the second embodiment of the present invention.

[0017] Figure 5 This is a front sectional view showing the main parts of the elastic wave device according to the third embodiment of the present invention.

[0018] Figure 6 This is a front sectional view showing the main parts of the elastic wave device according to the fourth embodiment of the present invention.

[0019] Figure 7 This is a side sectional view used to illustrate the elastic wave device of the fifth embodiment of the present invention.

[0020] Figure 8 This is a front cross-sectional view used to illustrate a modified example of the piezoelectric substrate used in this invention. Detailed Implementation

[0021] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0022] 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.

[0023] Figure 1 This is a top view of the elastic wave device according to the first embodiment of the present invention. Figure 2 (a) and (b) are along Figure 1 A partial sectional view of lines AA and BB in the diagram.

[0024] The elastic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 has a support substrate 3 including Si, a low-velocity film 4 stacked on the support substrate 3 including silicon oxide as a low-velocity material, and a piezoelectric film 5 stacked on the low-velocity film 4.

[0025] Low-velocity sound materials refer to materials in which the speed of sound of the propagating bulk wave is lower than the speed of sound of the bulk wave propagating in the piezoelectric film 5. Examples of such low-velocity sound materials include silicon oxide. It should be noted that the material of the low-velocity sound film 4 is not limited to silicon oxide. The material of the low-velocity sound film 4 may also be, for example, silicon oxide, glass, silicon oxynitride, tantalum oxide, compounds obtained by adding fluorine, carbon or boron to silicon oxide, or materials with the above-mentioned materials as the main components.

[0026] In this embodiment, the support substrate 3 includes Si as a high-velocity acoustic material. A high-velocity acoustic material is a material in which the velocity of the propagating bulk wave is higher than the velocity of the elastic wave propagating in the piezoelectric film 5. In addition to Si, other high-velocity acoustic materials that can be used include alumina, silicon carbide, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, DLC (diamond-like carbon) film or diamond, and materials whose main components are the above-mentioned materials.

[0027] The piezoelectric film 5 includes lithium tantalate, but may also include other piezoelectric materials such as lithium niobate.

[0028] Because the piezoelectric substrate 2 has the above-described laminated structure, the elastic wave excited in the piezoelectric film 5 can be effectively contained within the piezoelectric film 5. An IDT electrode 6, and a first reflector electrode 7 and a second reflector electrode 8 disposed on both sides of the elastic wave propagation direction of the IDT electrode 6 are provided on the piezoelectric substrate 2.

[0029] The IDT electrode 6, the first reflector electrode 7, and the second reflector electrode 8 comprise suitable metals or alloys such as Al, Cu, Mo, and W.

[0030] The IDT electrode 6 has a first busbar 6a and a second busbar 6b ​​that are opposite to each other. One end of a plurality of first electrode fingers 6c is connected to the first busbar 6a. One end of a plurality of second electrode fingers 6d is connected to the second busbar 6b. The plurality of first electrode fingers 6c and the plurality of second electrode fingers 6d are inserted alternately.

[0031] The first reflector electrode 7 has multiple electrode fingers 7a. The two ends of the multiple electrode fingers 7a are short-circuited. The second reflector electrode 8 also has multiple electrode fingers 8a. The two ends of the multiple electrode fingers 8a are short-circuited.

[0032] In the elastic wave device 1, a one-port elastic wave resonator is constructed from the aforementioned IDT electrode 6, the first reflector electrode 7, and the second reflector electrode 8. An AC voltage is applied between the first electrode finger 6c and the second electrode finger 6d to excite the elastic wave. In this embodiment, the piezoelectric film 5 comprises LiTaO3, and the SH wave is excited as the dominant mode.

[0033] In the elastic wave device 1, the propagation direction of the elastic wave is orthogonal to the extension directions of the first electrode finger 6c and the second electrode finger 6d. When viewed along the elastic wave propagation direction, the area where the first electrode finger 6c and the second electrode finger 6d overlap is the intersection region K, which serves as the resonant region. This intersection region K has a central region C, and a first edge region E1 and a second edge region E2 disposed on both sides of the extension directions of the first electrode finger 6c and the second electrode finger 6d in the central region C.

[0034] In the elastic wave device 1, dielectric films 9 and 10 are provided in the first edge region E1 and the second edge region E2. The dielectric films 9 and 10 are films that add mass to the first edge region E1 and the second edge region E2. Preferably, a dielectric material selected from the group consisting of tantalum oxide, hafnium oxide, tungsten oxide, selenium oxide, and niobium oxide is used as the dielectric material for the dielectric film. In this embodiment, Ta2O5 is used as tantalum oxide.

[0035] like Figure 2 As shown in (a), in the central region C, there is no dielectric film between the first electrode finger 6c and the second electrode finger 6d and the piezoelectric substrate 2. In contrast, as... Figure 2 As shown in (b), in the first edge region E1, a dielectric film 9 is disposed between the first electrode finger 6c and the second electrode finger 6d, i.e., the IDT electrode 6 and the piezoelectric substrate 2. Furthermore, the dielectric film 9 is also located below the first reflector electrode 7 and the second reflector electrode 8. That is, the dielectric film 9 extends from between the IDT electrode 6 and the piezoelectric substrate 2 to between the reflector electrodes 7 and 8 and the piezoelectric substrate 2. Similarly, in the second edge region E2, a dielectric film 10 is also disposed between the first electrode finger 6c and the second electrode finger 6d, i.e., the IDT electrode 6 and the piezoelectric substrate 2. Furthermore, the dielectric film 10 is also located below the first reflector electrode 7 and the second reflector electrode 8.

[0036] Because of the dielectric films 9 and 10, the sound velocity in the first edge region E1 and the second edge region E2 is lower than the sound velocity in the central region C. Figure 1 The diagram illustrates the relationship between the sound velocity V1 in the central region C, the sound velocity V2 in the first edge region E1 and the second edge region E2, and the sound velocity V3 in the gap region outside the direction of the electrode fingers extending from the first edge region E1 and the second edge region E2. That is, in Figure 1 The right side of the elastic wave device 1 shows a scale where the speed of sound increases as it moves to the right. V3 > V1 > V2.

[0037] Therefore, in the elastic wave device 1, the ripple of the transverse mode can be suppressed by the aforementioned sound velocity difference.

[0038] It should be noted that in the elastic wave device 1, the dielectric films 9 and 10 are positioned not only below the IDT electrode 6 in the first edge region E1 and the second edge region E2, but also extend beyond the first reflector electrode 7 and the second reflector electrode 8 from below the IDT electrode 6 to the outer side of the elastic wave propagation direction. Therefore, low loss is achieved in the elastic wave device 1. This will be explained in more detail.

[0039] As described in Patent Document 1, a piston-mode resonator is constructed by reducing the sound velocity in the first edge region E1 and the second edge region E2, thereby suppressing transverse mode ripple. However, in the elastic wave device of Patent Document 1, there is a problem that the sound discontinuity between the IDT electrode and the reflector electrode increases. More specifically, in the edge regions, the sound discontinuity between the IDT electrode and the reflector electrode, i.e., the difference in sound velocity or the difference in reflection coefficient, sometimes increases. Therefore, there is a problem that elastic wave scattering is more likely to occur, and the loss caused by scattering increases.

[0040] In contrast, in the elastic wave device 1, the dielectric films 9 and 10 are configured to extend from the IDT electrode 6, passing below the first reflector electrode 7 and the second reflector electrode 8, to the regions outside the first reflector electrode 7 and the second reflector electrode 8. Therefore, the acoustic discontinuities in the first edge region E1 and the second edge region E2 are mitigated. Consequently, elastic wave scattering is less likely to occur, thus suppressing losses caused by scattering. Therefore, a low-loss elastic wave device 1 can be provided.

[0041] It should be noted that in the elastic wave device 1, the dielectric films 9 and 10 are further configured not to reach the end edges 2a and 2b located on both sides of the elastic wave propagation direction of the piezoelectric substrate 2. Therefore, after conducting reliability tests such as reflow soldering tests or thermal shock tests, the following effect can be obtained: even if tensile stress is generated by the dielectric films 9 and 10, the end edges 2a and 2b of the piezoelectric substrate 2 are not prone to breakage, which is therefore preferred.

[0042] It should be noted that, in Figure 1 The illustration of the protective film on the top layer is omitted, but as shown in the image... Figure 2 As shown in (a) and (b), in the elastic wave device 1, the protective film 11 is configured to cover the IDT electrode 6, and cover Figure 2 The first reflector electrode 7 and the second reflector electrode 8 are not shown. The protective film 11 includes silicon oxide. However, the protective film 11 can be formed from various materials other than silicon oxide, such as silicon oxynitride, silicon nitride, etc.

[0043] In the elastic wave device 1, dielectric films 9 and 10 extend further outward from the outer edges of the first reflector electrode 7 and the second reflector electrode 8. The length of this outwardly extended portion is defined as the extension length L. Figure 3 The graph shows the relationship between the extension length L (μm) and the energy leakage rate. The energy leakage rate refers to the proportion of energy leaked to the outside from the energy generated by the excitation of the IDT electrode 6. When the leakage rate is low, the energy loss is small. That is, the loss through the frequency band can be reduced.

[0044] according to Figure 3 It is known that, compared to the case where the extension length is 0, the energy leakage rate is smaller when the extension length is set to 0.25μm or 0.375μm. Therefore, as with the elastic wave device 1, it is preferable that the dielectric films 9 and 10 extend to a position further outward than the outer edge of the first reflector electrode 7 and the second reflector electrode 8.

[0045] Figure 4 This is a top view of the elastic wave device according to the second embodiment of the present invention. In the elastic wave device 21, the dielectric films 9 and 10 are configured to reach the end edges 2a and 2b located on both sides of the elastic wave propagation direction of the piezoelectric substrate 2. Regarding other structures, the elastic wave device 21 is the same as the elastic wave device 1. Therefore, the same reference numerals are used for the same parts, and their description is omitted.

[0046] In the elastic wave device 21, dielectric films 9 and 10 are disposed in the first edge region E1 and the second edge region E2, thus enabling a piston-like configuration similar to that of the elastic wave device 1. Furthermore, the dielectric films 9 and 10 extend beyond the first reflector electrode 7 and the second reflector electrode 8 to regions outside the first reflector electrode 7 and the second reflector electrode 8. Therefore, low loss can be achieved similarly to that of the elastic wave device 1.

[0047] However, dielectric films 9 and 10 are configured to reach the end edges 2a and 2b. In this invention, dielectric films 9 and 10 may also be configured to reach the end edges 2a and 2b in this manner.

[0048] Figure 5 This is a front sectional view showing the main parts of the elastic wave device according to the third embodiment. Figure 5 In the middle, it is shown that... Figure 2 (b) The corresponding portion. That is, a cross-sectional structure of the first edge region is shown. In the elastic wave device 31, the dielectric film 9 is configured to cover the first electrode finger 6c and the second electrode finger 6d in the first edge region, that is, it is disposed on the upper surface of the IDT electrode 6. Thus, in the present invention, the dielectric film used to reduce the sound velocity in the first edge region and the second edge region can also be configured to cover the electrode fingers of the IDT electrode or the reflector electrode.

[0049] Figure 6 This is a front sectional view showing the main parts of the elastic wave device according to the fourth embodiment. Figure 6 It is also shown in the middle. Figure 2 The cross-sectional structure of the first edge region is shown in (b). In the elastic wave device 41, the dielectric film 9 is laminated on the upper surface of the protective film 11. Thus, the dielectric film 9 can also be configured to cover the first electrode finger 6c and the second electrode finger 6d as well as the protective film 11 in the first edge region. In this case, a dielectric film is also formed in the second edge region.

[0050] Figure 7 This is a side sectional view of the elastic wave device according to the fifth embodiment. Figure 7 The image shows a cross-section extending in the elastic wave device 51 in a direction orthogonal to the direction of elastic wave propagation, that is, a cross-section extending along the direction of the second electrode finger 6d of the IDT electrode 6.

[0051] In the elastic wave device 51, an IDT electrode 6 is provided on the piezoelectric substrate 2. Figure 7 The figure shows the first bus bar 6a, the second electrode finger 6d, and the second bus bar 6b.

[0052] In the elastic wave device 51, a protective film 52 is configured to cover the aforementioned IDT electrode 6. The protective film 52 comprises a suitable insulator such as silicon oxide or silicon oxynitride.

[0053] The aforementioned protective film 52 can also be a frequency temperature characteristic adjustment film used to adjust frequency temperature characteristics.

[0054] A dielectric film 53 is further laminated on the aforementioned protective film 52. In this dielectric film 53, an upwardly protruding portion is provided in the portion corresponding to the first edge region E1 and the second edge region E2. This protruding portion constitutes the dielectric films 9 and 10 as mass-adding films.

[0055] Thus, by adding mass to a portion equivalent to the first edge region E1 and the second edge region E2, low-speed sounding is achieved.

[0056] In the elastic wave device 51, the dielectric films 9 and 10 are configured, similarly to those in the first to fourth embodiments, to extend beyond the first and second reflector electrodes to the region outside the elastic wave propagation direction of the first and second reflector electrodes. Therefore, similar to the elastic wave device 1, low loss can be achieved.

[0057] It should be noted that in the elastic wave device 51, the piezoelectric substrate 2 comprises a single piezoelectric element. As such a piezoelectric element, a piezoelectric single crystal such as lithium tantalate or lithium niobate can be used. In this invention, a piezoelectric substrate 2 comprising a single piezoelectric element can also be used.

[0058] In the elastic wave device 1, a laminate comprising a support substrate 3 (Si), a low-velocity film 4, and a piezoelectric film 5 is used as the piezoelectric substrate 2. However, a high-velocity material layer comprising a high-velocity material can also be provided between the support substrate 3 and the low-velocity film 4. In this case, the support substrate 3 can also be composed of an insulating material other than the high-velocity material or a semiconductor material. It should be noted that in the elastic wave device 1, the support substrate 3 comprises Si and is integrated with the high-velocity material layer.

[0059] Alternatively, in this invention, the following methods can also be used: Figure 8 The piezoelectric substrate 2A is shown. In the piezoelectric substrate 2A, an acoustic reflection film 74 is stacked between the support substrate 3 and the piezoelectric film 5. The acoustic reflection film 74 has a structure in which low acoustic impedance layers 74a, 74c, and 74e with relatively low acoustic impedance and high acoustic impedance layers 74b, 74d, and 74f with relatively high acoustic impedance are alternately stacked. There is no particular limitation on the number of stacked layers. When the piezoelectric substrate 2A with such an acoustic reflection film 74 is used, the energy of elastic waves can be effectively blocked within the piezoelectric film 5.

[0060] It should be noted that the low acoustic impedance materials constituting the low acoustic impedance layers 74a, 74c, and 74e and the high acoustic impedance materials constituting the high acoustic impedance layers 74b, 74d, and 74f can be combinations of appropriate materials that satisfy the above acoustic impedance relationship.

[0061] Explanation of reference numerals in the attached figures

[0062] 1, 21, 31, 41, 51… elastic wave device;

[0063] 2, 2A…piezoelectric substrate;

[0064] 2a, 2b... edge;

[0065] 3...support base plate;

[0066] 4…low-velocity membrane;

[0067] 5…piezoelectric film;

[0068] 6…IDT electrode;

[0069] 6a, 6b... First busbar, Second busbar;

[0070] 6c, 6d… First electrode finger, second electrode finger;

[0071] 7, 8… First reflector electrode, second reflector electrode;

[0072] 7a, 8a… electrode references;

[0073] 9, 10… dielectric film;

[0074] 11, 52… protective film;

[0075] 53…dielectric film;

[0076] 74…acoustic reflective membrane;

[0077] 74a, 74c, 74e… low acoustic impedance layers;

[0078] 74b, 74d, 74f... High acoustic impedance layers.

Claims

1. An elastic wave device, comprising: piezoelectric substrate; An IDT electrode, disposed on the piezoelectric substrate, has alternating first electrode fingers and second electrode fingers; and The reflector electrodes, positioned on either side of the elastic wave propagation direction of the IDT electrodes, have multiple electrode fingers. In the IDT electrode, when viewed along the elastic wave propagation direction, the area where the first electrode finger and the second electrode finger overlap is an intersection region. The intersection region has a central region and a first edge region and a second edge region on both sides of the extension direction of the first electrode finger and the second electrode finger disposed in the central region. The elastic wave device also includes a dielectric film, which is configured to extend from the first edge region and the second edge region to the region outside the elastic wave propagation direction where the reflector electrode is disposed.

2. The elastic wave device according to claim 1, wherein, The dielectric film is configured to not reach the end of the piezoelectric substrate outside the direction of elastic wave propagation of the reflector electrode.

3. The elastic wave device according to claim 1, wherein, The dielectric film is positioned to reach the end of the piezoelectric substrate outside the direction of elastic wave propagation of the reflector electrode.

4. The elastic wave device according to any one of claims 1 to 3, wherein, The dielectric film is configured to extend from between the IDT electrode and the piezoelectric substrate to between the reflector electrode and the piezoelectric substrate.

5. The elastic wave device according to any one of claims 1 to 3, wherein, The dielectric film is configured to extend from the IDT electrode to the reflector electrode.

6. The elastic wave device according to any one of claims 1 to 3, wherein, The elastic wave device also includes a protective film that is configured to cover the IDT electrode.

7. The elastic wave device according to any one of claims 1 to 3, wherein, The dielectric film includes a dielectric selected from the group consisting of tantalum oxide, hafnium oxide, tungsten oxide, selenium oxide and niobium oxide.

8. The elastic wave device according to any one of claims 1 to 3, wherein, The sound speed in the first edge region and the second edge region is lower than the sound speed in the central region.

9. The elastic wave device according to any one of claims 1 to 3, wherein, The piezoelectric substrate has a supporting substrate and a piezoelectric film directly or indirectly stacked on the supporting substrate.

10. The elastic wave device according to claim 9, wherein, The piezoelectric substrate further comprises a high-velocity acoustic material layer, which is disposed between the piezoelectric film and the supporting substrate, wherein the velocity of sound of the bulk wave propagating in the high-velocity acoustic material layer is higher than the velocity of sound of the elastic wave propagating in the piezoelectric film.

11. The elastic wave device according to claim 10, wherein, The support substrate includes the high-velocity material, and the high-velocity material layer is integrated with the support substrate.

12. The elastic wave device according to claim 10 or 11, wherein, The elastic wave device further comprises a low-velocity membrane including a low-velocity material, the low-velocity membrane being disposed between the high-velocity material layer and the piezoelectric membrane, wherein the velocity of the volume wave propagating on the low-velocity membrane is lower than the velocity of the volume wave propagating on the piezoelectric membrane.

13. The elastic wave device according to claim 9, wherein, The piezoelectric substrate also includes an acoustic reflection film stacked between the piezoelectric film and the supporting substrate.

14. The elastic wave device according to claim 13, 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.

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