Elastic wave device

Abstract

Provided is an elastic wave device that is less likely to be surge-breakdown. A dielectric film (4) is provided so as to cover an IDT electrode (3) having: a first edge region (E1), a second edge region (E2), which are low sound velocity regions; and a first high sound velocity region (H1), a second high sound velocity region (H2), which are provided further outward than a crossing width region adjacent to a first electrode finger (13) and a second electrode finger (14) in an elastic wave propagation direction, and the thickness of the dielectric film (4) on the first edge region (E1), the second edge region (E2) is set to be thicker than the thickness of the dielectric film (4) on the first high sound velocity region (H1), the second high sound velocity region (H2).

Description

TECHNICAL FIELD

[0001] The present application relates to an elastic wave device having an IDT electrode provided with a low sound velocity region lower in sound velocity than a central region. BACKGROUND

[0002] Conventionally, an elastic wave device utilizing a piston mode is known. For example, in the elastic wave device described in Patent Literature 1 below, a first electrode finger connected to one potential and a second electrode finger connected to another potential have a portion overlapping each other in an elastic wave propagation direction. The portion overlapping each other is a cross width region, and the cross width region has a central region located at the center in the extension direction of the first electrode finger and the second electrode finger, and a first low sound velocity region and a second low sound velocity region disposed on the outer sides of the central region. In the first low sound velocity region and the second low sound velocity region, the sound velocity is made lower than the central region. Further, in the extension direction of the first electrode finger and the second electrode finger, a first high sound velocity region and a second high sound velocity region are respectively provided on the outer sides than the first low sound velocity region and the second low sound velocity region. By having such a sound velocity relationship, a piston mode is generated.

[0003] In addition, in the first low sound velocity region and the second low sound velocity region, the width of the electrode finger, which is the size of the electrode finger in the elastic wave propagation direction, is set to be larger than the width of the electrode finger in the central region. Thereby, it is possible to seek low sound velocity.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: International Publication No. 2014 / 192755 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In the first low sound velocity region and the second low sound velocity region, the width of the first electrode finger and the second electrode finger is made wide. Therefore, in the first low sound velocity region and the second low sound velocity region, the gap in the elastic wave propagation direction between the first electrode finger and the second electrode finger is narrow. Therefore, there is a problem that it is easy to generate surge breakdown in this portion.

[0009] An object of the present application is to provide an elastic wave device in which surge breakdown is less likely to occur.

[0010] TECHNICAL SOLUTION FOR SOLVING THE PROBLEMS

[0011] The elastic wave device according to the present application is characterized by comprising: a piezoelectric substrate; an IDT electrode provided on the piezoelectric substrate; and a dielectric film provided so as to cover the IDT electrode, the IDT electrode having: a first bus bar; a second bus bar provided so as to face the first bus bar; a plurality of first electrode fingers having one end connected to the first bus bar; and a plurality of second electrode fingers having one end connected to the second bus bar, the plurality of first electrode fingers and the plurality of second electrode fingers being alternately and oppositely arranged so as to overlap each other when viewed in a direction in which an elastic wave propagates, an area in which the first electrode fingers and the second electrode fingers overlap each other being set as a cross width area, in this case, the cross width area having: a central area located at a center in an extension direction of the first electrode fingers and the second electrode fingers; and a first edge area and a second edge area located outside the first electrode fingers and the second electrode fingers in the extension direction of the central area, a width of the first electrode fingers and the second electrode fingers in the first edge area and the second edge area being set to be wider than a width of the first electrode fingers and the second electrode fingers in the central area, the elastic wave device having: a first high sound velocity area and a second high sound velocity area respectively arranged outside the first electrode fingers and the second electrode fingers in the extension direction of the first edge area and the second edge area, a thickness of the dielectric film on the first edge area and the second edge area being set to be thicker than a thickness of the dielectric film on the first high sound velocity area and the second high sound velocity area.

[0012] Effects of the Invention

[0013] In the elastic wave device according to the present application, surge breakdown is less likely to occur. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 Fig. 1 is a side sectional view of an elastic wave device according to a first embodiment of the present application.

[0015] Figure 2 Fig. 1(a) is a plan view showing an IDT electrode of the elastic wave device according to the first embodiment of the present application, Figure 2 Fig. 1(b) is a schematic plan view of the elastic wave device according to the first embodiment of the present application.

[0016] Figure 3 Fig. 1(c) is a partially cutaway enlarged sectional view of the elastic wave device according to the first embodiment of the present application, as viewed from a direction indicated by an arrow B in Fig. 1(a). Figure 1 Fig. 1(c) is a partially cutaway enlarged sectional view of the elastic wave device according to the first embodiment of the present application, as viewed from a direction indicated by an arrow B in Fig. 1(a).

[0017] Figure 4 Fig. 2 is a graph showing an impedance characteristic of a resonator as the elastic wave device.

[0018] Figure 5is a partial cutaway plan view for illustrating an IDT electrode of an elastic wave device to which the second embodiment of the present application relates.

[0019] Figure 6 is a circuit diagram showing a ladder type filter using an elastic wave resonator constituted by the elastic wave device of the present application.

[0020] Figure 7 is a circuit diagram showing a band pass type filter using the elastic wave device of the present application.

[0021] Figure 8 is a front sectional view of a piezoelectric substrate used in the elastic wave device of the modified example of the present application. DETAILED DESCRIPTION

[0022] Hereinafter, specific embodiments of the present application will be described with reference to the drawings, thereby making the present application clear.

[0023] Note that each of the embodiments described in the present specification is illustrative, and partial substitution or combination of structures can be made among different embodiments.

[0024] Figure 1 is a side sectional view (along the Figure 2 A-A line of (b)) of the elastic wave device to which the first embodiment of the present application relates. Figure 2 (a) of is a plan view showing an IDT electrode of the elastic wave device to which the first embodiment of the present application relates, Figure 2 (b) of is a schematic plan view of the elastic wave device.

[0025] The elastic wave device 1 has a piezoelectric substrate 2. In the present embodiment, the piezoelectric substrate 2 contains a LiNbO3 single crystal. The piezoelectric substrate 2 can also contain other piezoelectric single crystals such as LiTaO3.

[0026] An IDT electrode 3 is provided on the piezoelectric substrate 2. A dielectric film 4 is laminated so as to cover the IDT electrode 3.

[0027] As shown in (b) of Figure 2 , reflectors 5, 6 are provided on both sides of the IDT electrode 3 in the elastic wave propagation direction. Thus, in the elastic wave device 1, an elastic wave resonator of a single port type is constituted.

[0028] Details of the IDT electrode 3 are shown in (a) of Figure 2 . The IDT electrode 3 has a first bus bar 11 and a second bus bar 12. The first bus bar 11 and the second bus bar 12 extend in the elastic wave propagation direction. The second bus bar 12 is spaced apart from and opposed to the first bus bar 11 in a direction orthogonal to the elastic wave propagation direction.

[0029] One end of each of the multiple first electrode fingers 13 is connected to the first busbar 11. One end of each of the multiple second electrode fingers 14 is connected to the second busbar 12. The multiple first electrode fingers 13 and the multiple second electrode fingers 14 are interleaved with each other. When the first electrode fingers 13 and the second electrode fingers 14 are observed in the direction of elastic wave propagation, the overlapping area is called the cross-width region. The dimension of this cross-width region along the extension direction of the first electrode fingers 13 and the second electrode fingers 14 is called the cross-width.

[0030] The first electrode finger 13 and the second electrode finger 14 have wide portions 13b and 14b at their front ends. Furthermore, a wide portion 14c is provided in the second electrode finger 14 at a position overlapping with the wide portion 13b in the direction of elastic wave propagation. The wide portion 13c is provided in the first electrode finger 13 at a position overlapping with the wide portion 14b in the direction of elastic wave propagation.

[0031] The regions where the wide portions 13c and 14b repeat along the direction of elastic wave propagation are designated as the first edge region E1, and the regions where the wide portions 13b and 14c repeat along the direction of elastic wave propagation are designated as the second edge region E2. Furthermore, the area between the first edge region E1 and the second edge region E2 is the central region C. That is, the cross-width region has the central region C and the first edge region E1 and the second edge region E2 located outside the extending direction of the first electrode finger 13 and the second electrode finger 14 in the central region C.

[0032] In the IDT electrode 3, the first busbar 11 has a plurality of openings 11a arranged along the elastic wave propagation direction. An inner busbar portion 11b is provided on the side further along the cross-width region than the region where the plurality of openings 11a are provided. An outer busbar portion 11c is provided on the side further along the cross-width direction than the openings 11a. In addition, the cross-width direction is parallel to the extension direction of the first electrode finger 13 and the second electrode finger 14. The outer busbar portion 11c and the inner busbar portion 11b are connected by a connecting portion 11d. The connecting portion 11d is located between adjacent openings 11a. The connecting portion 11d is located on the extension of the first electrode finger 13 and the second electrode finger 14 in the extension direction.

[0033] Similar to the first busbar 11, the second busbar 12 also has multiple openings 12a, an inner busbar portion 12b, an outer busbar portion 12c, and a connecting portion 12d.

[0034] The regions with openings 11a and 12a are designated as the first hypersonic region H1 and the second hypersonic region H2.

[0035] The dimensions of the inner busbar portions 11b and 12b and the outer busbar portions 11c and 12c along the extension direction of the first electrode finger 13 and the second electrode finger 14 are defined as their widths. The widths of the inner busbar portions 11b and 12b are narrower than the widths of the outer busbar portions 11c and 12c.

[0036] exist Figure 2 The right side of (a) schematically shows the sound velocity in each region of IDT electrode 3. As indicated by arrow V, the sound velocity increases as you move to the right of the graph. Let the sound velocity in the central region C be V1, and the sound velocities in the first edge region E1 and the second edge region E2 be V2. V1 > V2.

[0037] Furthermore, the sound velocity of the gap regions G1 and G2 outside the first edge region E1 and the second edge region E2 is set to V3, the sound velocity of the inner busbar sections 11b and 12b is set to V4, the sound velocity of the first high-velocity region H1 and the second high-velocity region H2 with openings 11a and 12a is set to V5, and the sound velocity of the region with outer busbar sections 11c and 12c is set to V6. V2 < V3 < V5. Therefore, the first high-velocity region H1 and the second high-velocity region H2 with a sound velocity of V5 are located outside the low-velocity region formed by the first edge region E1, the second edge region E2, the gap regions G1 and G2, and the inner busbar sections 11b and 12b. Therefore, transverse mode ripples can be suppressed by the piston mode.

[0038] Furthermore, in the first edge region E1 and the second edge region E2, wide portions 13b, 13c, 14b, and 14c are provided to reduce the sound velocity V2. In addition, in this embodiment, as... Figure 1 As shown, the thickness of the dielectric film portion 4b on the first edge region E1 and the second edge region E2 is set to be thicker than the dielectric film portion 4a on the first high-speed sound region H1 and the second high-speed sound region H2. That is, the thickness of the dielectric film portion 4b is thicker than the thickness of the dielectric film portion 4a. The thickness of the dielectric film 4 on the first edge region E1 and the second edge region E2 is set to be ΔH thicker than the thickness of the dielectric film 4 on the first high-speed sound region H1 and the second high-speed sound region H2. Therefore, compared with the sound speed V2 of the first edge region E1 and the second edge region E2, the sound speed V5 of the first high-speed sound region H1 and the second high-speed sound region H2 can be further increased. That is, Figure 1 The greater the thickness difference AH of the dielectric film 4 shown, the greater the difference between the sound velocity V5 and the sound velocity V2.

[0039] In the elastic wave device 1, the difference in sound velocity ΔH between the thicknesses of the dielectric film 4 can be used to ensure the difference in sound velocity. Therefore, the difference between sound velocity V2 and sound velocity V5 can be increased without making the widths of the wide portions 13b, 13c, 14b, and 14c too large. Consequently, by utilizing the difference in thickness ΔH between the dielectric film 4, the gap (the dimension along the elastic wave propagation direction) between the first electrode finger 13 and the second electrode finger 14 in the first edge region E1 and the second edge region E2 can be increased to a certain extent. Therefore, transverse mode ripple can be suppressed by means of a piston mode while suppressing surge breakdown.

[0040] Figure 3 From Figure 1 A partially enlarged cross-sectional view of the first hypersonic region H1 of the elastic wave device 1, observed in the direction indicated by arrow B. A cross-section in the thickness direction of the connecting portion 11d is shown here.

[0041] In the first hypersonic region H1, the connecting portion 11d is periodically arranged along the elastic wave propagation direction. Therefore, in the dielectric film 4 that covers the connecting portion 11d, a raised portion 4c is formed above the connecting portion 11d. The height of the raised portion 4c is higher than the upper surface of the dielectric film 4 between the raised portions 4c. Therefore, because the raised portion 4c is periodically provided along the elastic wave propagation direction, the position of the upper stopband of the elastic wave resonator shifts towards the higher frequency side. (Refer to...) Figure 4 The resonance characteristics of the instrument are used to explain this.

[0042] Figure 4 This is a diagram showing the impedance characteristics of a resonator used as an elastic wave device. The lower end of the stopband is at the resonant frequency fr, and the upper end is at a position higher than the anti-resonant frequency fa. At the upper end of the stopband, ripple caused by the upper stopband appears in the resonant characteristics. Figure 4 The ripple indicated by arrow SB is this ripple.

[0043] In this embodiment, the structure has the aforementioned raised portion 4c periodically provided, so the ripple indicated by arrow SB moves further away from the anti-resonant frequency fa, that is, it moves towards a higher frequency side. Therefore, it is possible to reduce the influence of the ripple caused by the upper stopband on the resonance characteristics and the filter characteristics of the elastic wave filter using the elastic wave resonator.

[0044] In addition, Figure 1 In this structure, the dielectric film 4 has a dielectric film portion 4a with a relatively low height on its upper surface and a dielectric film portion 4b with a relatively high height on its upper surface. Furthermore, not only is the thickness of the dielectric film 4 set to be equal to that of dielectric film portion 4a in the first hypersonic region H1 and the second hypersonic region H2, but also on its outer side, the thickness of the dielectric film 4 is set to be equal to that of dielectric film portion 4a.Figure 2 The thickness of the dielectric film 4 on the outer busbar portions 11c and 12c of (a) does not need to be equal to the thickness of the dielectric film 4 on the first hypersonic region H1 and the second hypersonic region H2. That is, the thickness of the dielectric film 4 on the outer busbar portions 11c and 12c can be thicker or thinner than the dielectric film portion 4a.

[0045] Furthermore, the dielectric film 4 on the first edge region E1 and the second edge region E2 is a dielectric film portion 4b, but the thickness of the dielectric film 4 on the central region C does not need to be equal to the thickness of the dielectric film 4 on the first edge region E1 and the second edge region E2. The thickness of the dielectric film 4 on the central region C can be thicker or thinner than the dielectric film portion 4b. Preferably, to ensure the sound velocity difference, the thickness of the dielectric film 4 in the central region C is thinner than that of the dielectric film portion 4b. However, if the upper surface of the dielectric film 4 on the central region C is flush with the upper surface of the dielectric film 4 on the first edge region E1 and the second edge region E2, that is, if it is the structure of this embodiment, it is easy to manufacture.

[0046] Furthermore, regarding other regions, namely the gap regions G1 and G2 with a sound velocity of V3 and the regions with inner busbar portions 11b and 12b where the sound velocity is V4, the thickness of the dielectric film 4 does not need to be equal to that of the dielectric film portion 4b as in this embodiment. It can be thinner or thicker than the dielectric film portion 4b.

[0047] However, in the structure where dielectric film portions 4a and 4b of two different thicknesses are provided as in this embodiment, as mentioned above, the dielectric film 4 is easy to form.

[0048] Figure 5This is a partially cut top view illustrating the IDT electrode of the elastic wave device according to the second embodiment of the present invention. In the elastic wave device of the second embodiment, the IDT electrode has a first busbar 21 and a second busbar 22 without openings. One end of a plurality of first electrode fingers 23 is connected to the first busbar 21. One end of a plurality of second electrode fingers 24 is connected to the second busbar 22. Similar to the first embodiment, the first electrode fingers 23 have a central region C and wide portions 23b and 23c. The second electrode fingers 24 also have a central region C and wide portions 24b and 24c. Thus, a central region C and a first edge region E1 and a second edge region E2 are formed. Furthermore, a second hypersonic region H2 is formed in the gap region between the front end of the first electrode finger 23 and the second busbar 22. In addition, a first hypersonic region H1 is formed in the gap region between the front end of the second electrode finger 24 and the first busbar 21. Let the speed of sound in the central region C be V11, the speed of sound in the first edge region E1 and the second edge region E2 be V12, and the speed of sound in the first high-speed sound region H1 and the second high-speed sound region H2 be V13. V11 > V12 and V12 < V13.

[0049] Thus, the construction of the IDT electrode using the piston mode is not limited to the construction with openings 11a and 12a shown in the first embodiment. In the second embodiment, it is the same as the first embodiment except that the IDT electrode is constructed as described above. Therefore, a dielectric film is provided to cover the IDT electrode. Furthermore, the thickness of the dielectric film on the first edge region E1 and the second edge region E2 is set to be thicker than the thickness of the dielectric film on the first hypersonic region H1 and the second hypersonic region H2. Therefore, similar to the first embodiment, it is possible to provide an elastic wave device that is less prone to surge breakdown.

[0050] The elastic wave device of the present invention can be widely used in various bandpass filters, etc.

[0051] Figure 6 This is a circuit diagram showing a trapezoidal filter using an elastic wave resonator constructed from the elastic wave device of the present invention. The trapezoidal filter 31 has multiple series arm resonators S1 to S4 and multiple parallel arm resonators P1 to P4. The series arm resonators S1 to S4 and the parallel arm resonators P1 to P4 are each constructed from an elastic wave resonator. At least one of these elastic wave resonators can utilize the elastic wave device of the present invention. Therefore, transverse mode ripple can be suppressed, and surge breakdown can be effectively suppressed.

[0052] Furthermore, in the elastic wave device 1 according to the first embodiment, the ripple at the upper end of the stopband can be shifted to the higher frequency side. Therefore, if the parallel arm resonators P1 to P4 are used in the trapezoidal filter, the impact on the passband can be further reduced, which is preferable.

[0053] Figure 7 This is a circuit diagram showing a bandpass filter using the elastic wave device of the present invention. Here, an elastic wave resonator 33 is connected in series with the longitudinally coupled resonator type filter 32, and an elastic wave resonator 34 is connected between the series arm and the ground potential. The elastic wave device of the present invention can also be used with such a longitudinally coupled resonator type filter 32, elastic wave resonators 33 and 34.

[0054] Figure 8 This is a front cross-sectional view illustrating the piezoelectric substrate used in the elastic wave device of a modified embodiment of the present invention. In the modified elastic wave device, a high-velocity material layer 43 and a low-velocity material layer 44 are stacked on the support substrate 42. A piezoelectric film 45 is stacked on the low-velocity material layer 44. A piezoelectric substrate 46 having such a stacked structure may also be used.

[0055] Furthermore, the high-velocity material layer 43 is composed of a high-velocity material in which the speed of propagating bulk waves is higher than the speed of propagating elastic waves in the piezoelectric film 45. The low-velocity material layer 44 is composed of a low-velocity material in which the speed of propagating bulk waves is lower than the speed of propagating bulk waves in the piezoelectric film 45.

[0056] As high-velocity materials, a wide variety of materials can be used, including alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, andalusite, blocky talc, forsterite, magnesium oxide, DLC (diamond-like carbon) films or diamond, media mainly composed of the above materials, and media mainly composed of mixtures of the above materials. Furthermore, as low-velocity materials, a wide variety of materials can be used, including silicon oxide, glass, silicon oxynitride, tantalum oxide, compounds with added fluorine, carbon, boron, hydrogen, or silanol groups to silicon oxide, and media mainly composed of the above materials.

[0057] Alternatively, the support substrate 42 and the hypersonic material layer 43 can be integrated to form a substrate made of hypersonic material.

[0058] In this invention, a piezoelectric substrate 46 can also be used. In addition, a structure in which an acoustic reflection film having a high acoustic impedance layer and a low acoustic impedance layer are stacked between the piezoelectric film and the substrate can also be used.

[0059] Explanation of reference numerals in the attached figures

[0060] 1: Elastic wave device;

[0061] 2: Piezoelectric substrate;

[0062] 3: IDT electrode:

[0063] 4: Dielectric film;

[0064] 4a, 4b: Dielectric film portion;

[0065] 4c: bulge;

[0066] 5, 6: Reflectors;

[0067] 11, 12: Busbar 1 and Busbar 2;

[0068] 11a, 12a: Openings;

[0069] 11b, 12b: Inner busbar section;

[0070] 11c, 12c: Outer busbar section;

[0071] 11d, 12d: Connecting parts;

[0072] 13, 14: First electrode finger, second electrode finger;

[0073] 13b, 13c, 14b, 14c: Wide section;

[0074] 21, 22: Busbar 1 and Busbar 2;

[0075] 23, 24: First electrode finger, second electrode finger;

[0076] 23b, 23c, 24b, 24c: Wide section;

[0077] 31: Trapezoidal filter;

[0078] 32: Longitudinal Coupled Resonator Type Filter;

[0079] 33, 34: Elastic wave resonators;

[0080] 42: Support base plate;

[0081] 43: High-speed acoustic material layer;

[0082] 44: Low-velocity material layer;

[0083] 45: Piezoelectric film;

[0084] 46: Piezoelectric substrate.

Claims

1. An elastic wave device, comprising: piezoelectric substrate; IDT electrodes are disposed on the piezoelectric substrate; and A dielectric film is configured to cover the IDT electrode. The IDT electrode has: First busbar; The second busbar is configured to be opposite to the first busbar; Multiple first electrode fingers, one end of which is connected to the first bus bar; and Multiple second electrode fingers, one end of which is connected to the second bus bar. The plurality of first electrode fingers and the plurality of second electrode fingers are interlocked and interleaved with each other. The overlapping area between the first electrode finger and the second electrode finger when viewed in the direction of elastic wave propagation is defined as the cross-width region. In this case, The intersection width region has: The central region is located at the center of the extending direction of the first electrode finger and the second electrode finger; and The first edge region and the second edge region are located outside the extending direction of the first electrode finger and the second electrode finger in the central region. In the first edge region and the second edge region, the width of the first electrode finger and the second electrode finger are set to be wider than the width of the first electrode finger and the second electrode finger in the central region. It has: a first hypersonic region and a second hypersonic region, respectively disposed outside the extending direction of the first electrode finger and the second electrode finger in the first edge region and the second edge region. The thickness of the dielectric film in the first edge region and the second edge region is set to be thicker than the thickness of the dielectric film in the first high-speed sound region and the second high-speed sound region. The first busbar and the second busbar extend in the direction of elastic wave propagation and have: The inner busbar section is connected to either the first electrode finger or the second electrode finger; and The outer busbar portion is positioned further outward in the extending direction of the first electrode finger and the second electrode finger than the inner busbar portion. In the first busbar and the second busbar, a plurality of openings are provided in the region between the inner busbar portion and the outer busbar portion, arranged along the direction of elastic wave propagation. Adjacent openings are connected by connecting portions that link the inner busbar portion and the outer busbar portion. The first high-speed sound region is the area between the inner busbar portion and the outer busbar portion of the first busbar. The second hypersonic region is the area between the inner and outer busbar portions of the second busbar. In the thickness direction section of the connecting portion, the dielectric film on the first high-velocity region and the second high-velocity region has a raised portion above the connecting portion, and the raised portion is periodically arranged along the elastic wave propagation direction in the first high-velocity region and the second high-velocity region.

2. The elastic wave device according to claim 1, wherein, The first edge region and the second edge region constitute a low sound speed region where the sound speed is lower than that of the central region.

3. The elastic wave device according to claim 2, wherein, The thickness of the dielectric film in the low-sound-velocity region is equal to the thickness of the dielectric film in the central region. The upper surface of the dielectric film in the low-sound-velocity region is flush with the upper surface of the dielectric film in the central region.

4. The elastic wave device according to any one of claims 1 to 3, wherein, The piezoelectric substrate is a piezoelectric single crystal substrate.

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