Elastic wave device and communication device

Abstract

The present invention reduces spurious emissions. Provided is an elastic wave device comprising: a support substrate with a cavity formed therein; a piezoelectric substrate located above the support substrate and covering the cavity; and IDT electrodes located above the piezoelectric substrate, wherein: the IDT electrodes include respective busbars, a plurality of electrode fingers, and a first region sandwiched between the busbars; the cavity and the entire interlacing area where the plurality of electrode fingers interlace overlap in a planar perspective; the first region includes a low sound speed region that extends in the direction along which the electrode fingers are arranged; and the periphery of the cavity and the low sound speed region overlap in a planar perspective.

Description

Acoustic wave device and communication device

[0001] The present disclosure relates to acoustic wave devices.

[0002] Patent Document 1 listed below discloses an example of the configuration of an acoustic wave device having a membrane structure.

[0003] Japanese Patent Publication No. 2012-257019

[0004] In order to solve the above problems, an elastic wave device according to one aspect of the present disclosure includes a support substrate in which a cavity is formed, a piezoelectric substrate located on the support substrate and covering the cavity, and an IDT electrode located on the piezoelectric substrate, wherein the IDT electrode has a bus bar, a plurality of electrode fingers, and a first region sandwiched between the bus bars, wherein the cavity and the entire intersection region where the plurality of electrode fingers intersect overlap in a planar perspective view, the first region has a low acoustic velocity region extending in the arrangement direction of the electrode fingers, and the outer edge of the cavity and the low acoustic velocity region overlap in a planar perspective view.

[0005] 1 is a plan view of a portion of an elastic wave device according to a first embodiment. FIG. 2 is a cross-sectional view of the elastic wave device according to the first embodiment. FIG. 3 is a graph showing frequency characteristics when the outer edge is positioned at the end of a bus bar. FIG. 4 is a graph showing frequency characteristics when the outer edge is positioned below the inside of a bus bar. FIG. 5 is a graph showing frequency characteristics when the outer edge is positioned below the inside of a dummy electrode finger. FIG. 6 is a graph showing frequency characteristics when the outer edge is positioned at the end of an intersection region. FIG. 7 is a graph showing frequency characteristics when the outer edge is positioned at the end of a low acoustic velocity region. FIG. 8 is a graph showing a transverse mode index as a function of the amount of silicon penetration in the elastic wave device according to the first embodiment. FIG. 9 is a graph showing an average phase value from the resonant frequency to the anti-resonant frequency as a function of the amount of silicon penetration in the elastic wave device according to the first embodiment. FIG. 10 is a cross-sectional view of an elastic wave device according to a third embodiment. FIG. 11 is a graph showing a transverse mode index as a function of the amount of silicon penetration in the elastic wave device according to the third embodiment. 10 is a cross-sectional view of an elastic wave device according to a fourth embodiment. FIG. 11 is a graph showing a transverse mode index as a function of the amount of silicon penetration in an elastic wave device according to the fourth embodiment. FIG. 12 is a graph showing a phase average value of the resonant frequency to the anti-resonant frequency as a function of the amount of silicon penetration in an elastic wave device according to the fourth embodiment. FIG. 13 is a graph showing a transverse mode index as a function of the amount of silicon penetration in an elastic wave device according to the fifth embodiment. FIG. 14 is a graph showing a phase average value of the resonant frequency to the anti-resonant frequency as a function of the amount of silicon penetration in an elastic wave device according to the fifth embodiment. FIG. 15 is a graph showing a transverse mode index as a function of the amount of silicon penetration in an elastic wave device according to the sixth embodiment. FIG. 16 is a graph showing a phase average value of the resonant frequency to the anti-resonant frequency as a function of the amount of silicon penetration in an elastic wave device according to the sixth embodiment. FIG. 17 is a graph showing a transverse mode index as a function of the width of a busbar in an elastic wave device according to the seventh embodiment. FIG. 18 is a plan view of an elastic wave device according to the seventh embodiment.10 is a graph showing the transverse mode index T as a function of the amount of silicon penetration in an elastic wave device according to embodiment 8. FIG. 11 is a graph showing the average phase from the resonant frequency to the anti-resonant frequency as a function of the amount of silicon penetration in an elastic wave device according to embodiment 8. FIG. 12 is a diagram illustrating a schematic configuration of a communication device according to embodiment 9. FIG. 13 is a plan view of one period of an IDT electrode in a general elastic wave device. FIG. 14 is a cross-sectional view of a general elastic wave device. FIG. 15 is a diagram showing the frequency characteristics of a general elastic wave device according to comparative example 1. FIG. 16 is a diagram showing the frequency characteristics of an elastic wave device according to comparative example 2.

[0006] It is desirable to achieve filter characteristics with reduced spurious emissions in an acoustic wave device having a membrane structure.

[0007] [Embodiment 1] An elastic wave device according to embodiment 1 will be described below. For ease of explanation, components having the same functions as those described in embodiment 1 will be denoted by the same reference numerals in the following embodiments, and their description will not be repeated. For simplicity, descriptions of well-known technical matters will also be omitted as appropriate. Unless otherwise specified, the components, materials, and numerical values ​​described in this specification are merely examples. Therefore, for example, unless otherwise specified, the positional relationship of each component is not limited to the example shown in each figure. Furthermore, the illustrations of each component are not necessarily to scale.

[0008] (Comparative Example: Structure of General IDT Electrode 600) Prior to describing the first embodiment, a general acoustic wave device will be described. FIG. 29 is a plan view of one period of IDT electrode 600 in general acoustic wave device 100. Therefore, IDT electrode 600 is arranged in the arrangement direction of the electrode fingers (Y direction). FIG. 30 is a cross-sectional view of general acoustic wave device 100.

[0009] In the elastic wave device 100, silicon 3 is partially formed on a support portion 2 made of various materials. The material of the support portion 2 may be, for example, silicon or another material. When the support portion 2 is silicon, it may be bonded to the silicon 3 or may be formed integrally. The support portion 2 may not be present and the support portion 2 may be supported by the silicon 3. The region of the support portion 2 where silicon 3 is not formed is a cavity 4. The support portion 2 may have an opening in a region that overlaps with the cavity 4 in a plan view. The support portion 2 and silicon 3 may collectively be referred to as a support substrate. In the elastic wave device 100, a piezoelectric substrate 5 is further formed on top of the silicon 3 and cavity 4, and the piezoelectric substrate 5 covers the cavity 4. The piezoelectric substrate 5 is made of 105°Y-XLiNb ３ It is formed by 105°Y-XLiNb ３ is a 105° rotated Y-cut X-propagation LiNb ３ Also called.

[0010] In acoustic wave device 100, an IDT electrode 600 is formed in a region above piezoelectric substrate 5 that corresponds to cavity 4. IDT electrode 600 includes bus bars 61 a and 61 b, electrode fingers 62 a and 62 b, and dummy electrode fingers 63 a and 63 b (both referred to as second electrode fingers), to which different potentials are applied. Hereinafter, when the respective potentials are not taken into consideration, these will be referred to as bus bars 61, electrode fingers 62, and dummy electrode fingers 63. IDT electrode 600 excites A1-mode Lamb acoustic waves in piezoelectric substrate 5.

[0011] The IDT electrode 600 may excite a bulk acoustic wave in the piezoelectric substrate 5. A thickness-shear mode bulk wave may also be excited.

[0012] In the IDT electrode 600, electrode fingers 62 and dummy electrode fingers 63 are alternately connected to bus bars 61. The electrode fingers 62 are long in the X direction, and the dummy electrode fingers 63 are short in the X direction. The electrode fingers 62a and dummy electrode fingers 63b face each other, and the electrode fingers 62b and dummy electrode fingers 63a face each other. The region sandwiched between the bus bars 61 is referred to as a first region 60. Therefore, the electrode fingers 62 and dummy electrode fingers 63 exist in the first region 60.

[0013] The region where the electrode fingers 62a and 62b intersect is an intersection region 64. For example, a plate wave is excited in the piezoelectric substrate 5 in the intersection region 64 by the IDT electrode 600 to which an AC current is applied to the electrode fingers 62a and 62b.

[0014] The distance from the top end of the electrode finger 62a to the top end of the electrode finger 62b in the crossing region 64 is called the pitch PT, and the ratio of the width of the electrode finger 62 to the pitch PT is called the duty D.

[0015] Comparative Example 1: Frequency Characteristics of General IDT Electrode 600 Fig. 31 is a diagram showing the frequency characteristics of a general acoustic wave device 100 in accordance with Comparative Example 1. In Fig. 31 , the horizontal axis represents frequency and the vertical axis represents phase. In acoustic wave device 100, the phase may be constant at 90°.

[0016] As shown in Figure 31 , the phase drops sharply, for example, near approximately 5590 MHz and approximately 5655 MHz. Such undesired sudden changes in phase with respect to frequency are sometimes referred to as spurious. Spurious emissions occur in elastic wave device 100. Below, we will demonstrate the advantages of elastic wave devices based on the configurations of the present disclosure using Figure 31 as a comparison.

[0017] (Comparative Example 2: Frequency Characteristics When Silicon 3 Invades Below IDT Electrode 600) In the elastic wave device of Comparative Example 2, the cavity 4 is smaller than that of elastic wave device 100, and the silicon 3 invades below the IDT electrode 600. That is, the outer edge 4 a of the cavity 4 is located below the IDT electrode 600. In the elastic wave device of Comparative Example 2, the duty of the electrode fingers is constant from the base to the tip. The dummy electrode fingers also have the same duty as the electrode fingers. Such an elastic wave device is also referred to as a non-duty offset resonator or a normal resonator.

[0018] FIG. 32 is a diagram illustrating the frequency characteristics of the elastic wave device of Comparative Example 2. In the upper graph of FIG. 32 , the horizontal axis represents frequency and the vertical axis represents phase. The solid line represents the frequency characteristics when silicon 3 penetrates below IDT electrode 600 in the elastic wave device of Comparative Example 2, and the dashed line represents the frequency characteristics when silicon 3 does not penetrate below IDT electrode 600 in the elastic wave device of Comparative Example 2. The schematic diagram at the bottom of FIG. 32 is a schematic diagram illustrating the penetration depth of silicon 3. In the case of the solid line, the penetration depth of silicon 3 is 0.5 μm. 0.5 μm corresponds to ⅓ of the thickness of the bus bar.

[0019] As shown in FIG. 32, the frequency characteristics of Comparative Example 2 are not significantly different from those of Comparative Example 1, and it is clear that spurious signals are generated.

[0020] (Configuration of IDT Electrode 6) Next, the shape of the IDT electrode according to the first embodiment will be explained, and then it will be shown that the IDT electrode can reduce spurious signals.

[0021] 1 is a plan view of a portion of an elastic wave device 1 in accordance with Preferred Embodiment 1. The elastic wave device 1 differs from the elastic wave device 100 in that an IDT electrode 6 is provided instead of the IDT electrode 600.

[0022] The IDT electrode 6 includes bus bars 61 a and 61 b, electrode fingers 62 a and 62 b, dummy electrode fingers 63 a and 63 b, and widened portions 65 a and 65 b (also referred to as widened portion 65), to which different potentials are applied. Widened portion 65 is located near bus bar 61 in the first region 60.

[0023] Further, the widened portion 65 located near the bus bar 61 may be present within a range of one wavelength from the end of the crossing region 64 on the bus bar side, or within a range of the pitch PT.

[0024] In the IDT electrode 6, the widened portions 65 and the dummy electrode fingers 63 are alternately connected to the bus bar 61, and the electrode fingers 62 are connected to the widened portions 65. The electrode fingers 62 and the dummy electrode fingers 63 still face each other.

[0025] The ratio of the width of the widened portion 65 to the pitch PT is called the offset duty OD, and the offset duty OD is greater than the duty D. In other words, the width of the widened portion 65 in the Y direction (the direction in which the electrode fingers are arranged) is greater (widened) than the width of the electrode fingers 62 in the Y direction. Also, the length of the widened portion 65 in the X direction (the direction in which the electrode fingers extend) is longer than the length of the dummy electrode fingers 63. An IDT electrode 6 having such widened portions 65 is called a duty offset resonator. Also, the dummy electrode fingers (second electrode fingers) 63 have a width greater than the average width of the electrode fingers 62.

[0026] The region of the widened portion 65 that extends in the arrangement direction of the electrode fingers 62 is referred to as the low acoustic velocity region 66. Because the offset duty OD of the widened portion 65 is greater than the duty D of the electrode fingers 62, the weight per unit area of ​​the widened portion 65 is greater than that of the electrode fingers 62. Therefore, the acoustic velocity of the low acoustic velocity region 66 is lower than that of the electrode fingers 62 in the first region 60.

[0027] (Frequency Characteristics for Each Cross-Sectional Shape of IDT Electrode 6) In the comparative example, the IDT electrode 600 is disposed above the region corresponding to the cavity 4, but this is not limited to this. Specifically, in the elastic wave device 1 according to the first embodiment, the silicon 3 extends below the IDT electrode 6, and the outer edge 4 a is located below the IDT electrode 6. As will be described below, in the elastic wave device 1, the outer edge 4 a of the cavity 4 and the low acoustic velocity region 66 overlap in a planar perspective view.

[0028] FIG. 2 is a cross-sectional view of an elastic wave device 1 according to a first embodiment. Unlike FIG. 30 , silicon 3 penetrates below an IDT electrode 6 in FIG. This penetration amount is designated as silicon penetration amount x, where x is the distance from the end of bus bar 61 outside first region 60 to outer edge 4 a of cavity 4. Silicon penetration amount x is a variable, and the frequency characteristics of the elastic wave device were simulated while adjusting the silicon penetration amount x. For the IDT electrode 6, the duty D was set to 0.5 and the offset duty OD was set to 0.6.

[0029] Fig. 3 shows the frequency characteristics when the position of outer edge 4a coincides with the end of bus bar 61. Fig. 4 shows the frequency characteristics when outer edge 4a is located below the interior of bus bar 61. Fig. 5 shows the frequency characteristics when outer edge 4a is located below the interior of dummy electrode finger 63. Fig. 6 shows the frequency characteristics when outer edge 4a is located at the end of intersection region 64. Fig. 7 shows the frequency characteristics when outer edge 4a is located at the end of widened portion 65.

[0030] In the upper graphs of Figures 3 to 7, the dashed lines represent the frequency characteristics for Comparative Example 1, and the solid lines represent the respective cases. The schematic diagrams at the bottom of Figures 3 to 7 are schematic diagrams showing the penetration amount of silicon 3. As shown in Figures 3 to 7, the frequency characteristics change depending on the penetration amount x of silicon 3 below the IDT electrode 6.

[0031] As shown in FIGS. 3 to 7, it can be seen that spurious signals can be reduced from when the position of the outer edge 4a coincides with the end of the bus bar 61 to when it is located at the end of the low sound velocity region.

[0032] (Introduction of Transverse Mode Index) A transverse mode index T is introduced to quantify the frequency characteristics according to the amount x of silicon penetration into the silicon 3 below the IDT electrode 6. The transverse mode index T can be expressed by the following equation. Here, P is the phase, f is the frequency, and Δf is the difference between the anti-resonance frequency fa and the resonance frequency fr.

[0033] Since dP / df is the phase gradient, the transverse mode index T is the absolute value of the gradient per unit frequency within the passband. Therefore, the larger the transverse mode index T, the less flat the phase characteristics are within the passband, indicating the presence of significant spurious signals. The inventors searched for a region where the transverse mode index T is small.

[0034] (Frequency Characteristics) Fig. 8 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in the elastic wave device 1 according to Embodiment 1. Fig. 9 shows the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in the elastic wave device 1 according to Embodiment 1. The dashed lines in Figs. 8 and 9 represent values ​​in a comparative example, and the solid lines represent values ​​in the elastic wave device 1 according to Embodiment 1. Figs. 8 and 9 summarize the frequency characteristics in Figs. 3 to 7 for each index in a single graph.

[0035] As shown in Fig. 8 , the transverse mode index T is sufficiently small compared to the comparative example until the outer edge 4a is positioned at the end of the low acoustic velocity region 66. Furthermore, as shown in Fig. 9 , the average phase angle is also sufficiently close to 90° until the outer edge 4a is positioned at the end of the low acoustic velocity region 66. Therefore, in the elastic wave device 1 according to embodiment 1, the frequency characteristics are sufficiently good until the outer edge 4a is positioned at the end of the low acoustic velocity region 66.

[0036] (Summary) We investigated whether the frequency characteristics change when silicon 3 penetrates below the duty offset resonator having a low acoustic velocity region 66, such as the elastic wave device 1 according to embodiment 1. Specifically, we investigated the case where the outer edge 4 a is located within the first region 60, from the end of the bus bar 61 outside the first region 60.

[0037] As a result, it was found that the duty offset resonator has sufficiently good frequency characteristics when the outer edge 4a (the edge relative to the cavity 4) is located from the end of the bus bar 61 in the low acoustic velocity region 66 to the end of the low acoustic velocity region 66. Furthermore, it was found from Figures 3 to 7 that spurious emissions can be reduced.

[0038] 10 is a cross-sectional view of an elastic wave device 1a according to a second embodiment. The elastic wave device 1a differs from the elastic wave device 1 in that a silicon dioxide (SiO ２ The difference is that the connection layer 7a is provided on the silicon 3 only, and is not present at the position of the cavity 4. The connection layer 7a has a thickness of about 0.1 μm.

[0039] Fig. 11 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in elastic wave device 1a according to embodiment 2. Fig. 12 is a graph showing the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in elastic wave device 1a according to embodiment 2. The dashed lines in Figs. 11 and 12 represent values ​​in Comparative Example 1, and the solid lines represent values ​​in elastic wave device 1a according to embodiment 2.

[0040] 11 , the transverse mode index T is sufficiently smaller than that of Comparative Example 1 until the outer edge 4 a is positioned at the end of the low acoustic velocity region 66. Furthermore, as shown in FIG. 12 , the phase average value is also sufficiently close to 90° until the outer edge 4 a is positioned at the end of the low acoustic velocity region 66. Therefore, in the elastic wave device 1 a according to Embodiment 2, the frequency characteristics are sufficiently good until the outer edge 4 a is positioned at the end of the low acoustic velocity region 66.

[0041] 13 is a cross-sectional view of an elastic wave device 1b according to embodiment 3. Elastic wave device 1b differs from elastic wave device 1 in that it includes a low-resistivity connection layer 7b between silicon 3 and piezoelectric substrate 5. Connection layer 7b is present only above silicon 3 and is not present at the position of cavity 4.

[0042] The low-resistivity layer is an interface that deteriorates the characteristics at the bonding interface. The low-resistivity layer is a compound of lithium, niobium, silicon, oxygen, etc. The low-resistivity layer has a thickness of about 2 nm and a resistivity of, for example, about 2.5 Ω cm at a frequency of about 5500 MHz.

[0043] Fig. 14 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in elastic wave device 1b according to embodiment 3. Fig. 15 shows the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in elastic wave device 1b according to embodiment 3. The dashed lines in Figs. 14 and 15 represent values ​​in Comparative Example 1, and the solid lines represent values ​​in elastic wave device 1b according to embodiment 3.

[0044] 14 , it can be seen that the transverse mode index T is sufficiently smaller than that of Comparative Example 1 until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66. Furthermore, as shown in FIG. 15 , it can be seen that the phase average value is also sufficiently close to 90° until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66. Therefore, it can be said that the frequency characteristics of the elastic wave device 1 b according to Embodiment 3 are sufficiently good until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66.

[0045] 16 is a cross-sectional view of an elastic wave device 1c according to embodiment 4. Elastic wave device 1c differs from elastic wave device 1 in that it includes an aluminum nitride (AlN) connection layer 7c between silicon 3 and piezoelectric substrate 5. Connection layer 7c is present only above silicon 3 and is not present at the position of cavity 4. Connection layer 7c has a thickness of approximately 0.1 μm.

[0046] Fig. 17 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in elastic wave device 1c according to embodiment 4. Fig. 18 shows the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in elastic wave device 1c according to embodiment 4. The dashed lines in Figs. 17 and 18 show the values ​​in Comparative Example 1, and the solid lines show the values ​​in elastic wave device 1c according to embodiment 4.

[0047] 17 , the transverse mode index T is sufficiently smaller than that of Comparative Example 1 until the outer edge 4 a is positioned at the end of the low acoustic velocity region 66. Furthermore, as shown in FIG. 18 , the phase average value is also sufficiently close to 90° until the outer edge 4 a is positioned at the end of the low acoustic velocity region 66. Therefore, in the elastic wave device 1 c according to Embodiment 4, the frequency characteristics are sufficiently good until the outer edge 4 a is positioned at the end of the low acoustic velocity region 66.

[0048] Fifth Preferred Embodiment In an elastic wave device 1d according to a fifth preferred embodiment, the offset duty OD of the IDT electrode 6 is increased to 0.7 compared to the elastic wave device 1. In other words, the weight of the low acoustic velocity region 66 is increased.

[0049] Fig. 19 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in the elastic wave device according to embodiment 5. Fig. 20 shows the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in the elastic wave device according to embodiment 5. The dashed lines in Figs. 19 and 20 show the values ​​in Comparative Example 1, and the solid lines show the values ​​in the elastic wave device according to embodiment 5.

[0050] 19 , it can be seen that the transverse mode index T is sufficiently smaller than that of Comparative Example 1 until the position of outer edge 4 a is located at the end of low acoustic velocity region 66. Furthermore, as shown in FIG. 20 , it can be seen that the phase average value is also sufficiently close to 90° until the position of outer edge 4 a is located at the end of low acoustic velocity region 66. Therefore, it can be said that the frequency characteristics of the elastic wave device according to Embodiment 5 are sufficiently good until the position of outer edge 4 a is located at the end of low acoustic velocity region 66.

[0051] In the first and fifth embodiments, the only difference is the value of the offset duty OD, and the rest is the same, and good frequency characteristics can be obtained even when the offset duty OD is increased.

[0052] Sixth Preferred Embodiment In an elastic wave device 1e according to a sixth preferred embodiment, the offset duty OD of the IDT electrode 6 is increased to 0.8 compared to the elastic wave device 1. In other words, the weight of the low acoustic velocity region 66 is increased.

[0053] Fig. 21 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in the elastic wave device according to embodiment 6. Fig. 22 shows the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in the elastic wave device according to embodiment 6. The dashed lines in Figs. 21 and 22 represent values ​​in Comparative Example 1, and the solid lines represent values ​​in the elastic wave device according to embodiment 5.

[0054] 21 , it can be seen that the transverse mode index T is sufficiently smaller than that of Comparative Example 1 until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66. Furthermore, as shown in FIG. 22 , it can be seen that the phase average value is also sufficiently close to 90° until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66. Therefore, it can be said that the frequency characteristics of the elastic wave device according to Embodiment 5 are sufficiently good until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66.

[0055] In the first and sixth embodiments, the only difference is the value of the offset duty OD, and the rest is the same, and good frequency characteristics can be obtained even when the offset duty OD is increased.

[0056] Seventh Embodiment An elastic wave device 1 according to a seventh embodiment has a busbar 61 of an IDT electrode 6 with a different width. Fig. 23 is a graph showing the transverse mode index T as a function of the busbar width in an elastic wave device 1 according to the seventh embodiment. Fig. 24 is a graph showing the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the busbar width in an elastic wave device 1 according to the seventh embodiment. The silicon penetration depth x was set to the case where the dummy electrode fingers 63 were located below the tips thereof.

[0057] As shown in FIGS. 23 and 24, it was confirmed that changing the width of the busbar 61 had no effect on the transverse mode index T and the phase average value.

[0058] 25 is a plan view of an elastic wave device according to embodiment 8. The elastic wave device includes an IDT electrode 6f, which is a piston resonator, instead of the IDT electrode 6.

[0059] In the piston resonator, the electrode fingers 62 are widened at their bases where they contact the bus bar 61 and at their tips, which are widened portions 65 and 67, respectively. Furthermore, the piston resonator does not include dummy electrode fingers 63. Furthermore, the bus bar 61 is provided with an opening 68. The widened portions 67 and 68 are classified into widened portions 67a and 67b, and openings 68a and 68b, depending on the applied potential.

[0060] Fig. 26 is a graph showing the transverse mode index T as a function of the silicon penetration depth x in the elastic wave device according to embodiment 8. Fig. 27 shows the phase average value from the resonant frequency fr to the antiresonant frequency fa as a function of the silicon penetration depth x in the elastic wave device according to embodiment 8. The dashed lines in Figs. 26 and 27 show values ​​in a comparative example, and the solid lines show values ​​in the elastic wave device according to embodiment 8.

[0061] 26 , it can be seen that the transverse mode index T is sufficiently smaller than that of Comparative Example 1 until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66. Furthermore, as shown in FIG. 27 , it can be seen that the phase average value is also sufficiently close to 90° until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66. Therefore, it can be said that the frequency characteristics of the elastic wave device according to Embodiment 8 are sufficiently good until the position of the outer edge 4 a is located at the end of the low acoustic velocity region 66.

[0062] 28 is a diagram illustrating a schematic configuration of a communication device 151 according to a ninth embodiment. The communication device 151 is an application example of an elastic wave device according to an aspect of the present disclosure and performs wireless communication using radio waves. The communication device 151 may include one duplexer 101 as a transmit filter 109 and another duplexer 101 as a receive filter 111. Each of the two duplexers 101 may include an elastic wave device according to an aspect of the present disclosure (e.g., elastic wave devices 1, 1a to 1f). In this manner, the communication device 151 may include an elastic wave device according to an aspect of the present disclosure.

[0063] In the communication device 151, a transmission information signal TIS containing information to be transmitted may be modulated and frequency-raised (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 153, and converted into a transmission signal TS. A band-pass filter 155 may remove unnecessary components from the TS outside the transmission passband. Next, the TS after removing the unnecessary components may be amplified by an amplifier 157 and input to the transmission filter 109.

[0064] The transmission filter 109 may remove unnecessary components outside the transmission passband from the input transmission signal TS. The transmission filter 109 may output the TS after removing the unnecessary components to the antenna 159 via an antenna terminal (e.g., the above-mentioned TCin). The antenna 159 may convert the TS, which is an electrical signal input thereto, into radio waves as a wireless signal and transmit the radio waves to the outside of the communication device 151.

[0065] Furthermore, the antenna 159 may convert the received external radio waves into a received signal RS, which is an electrical signal, and input the RS to the receiving filter 111 via the antenna terminal. The receiving filter 111 may remove unnecessary components outside the receiving passband from the input RS. The receiving filter 111 may output the received signal RS after the unnecessary components have been removed to the amplifier 161. The output RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unnecessary components outside the receiving passband from the amplified RS. The RS after the unnecessary components have been removed may be frequency-downgraded and demodulated by the RF-IC 153, and converted into a received information signal RIS.

[0066] The TIS and RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the TIS and RIS may be analog audio signals or digitized audio signals. The passband of the wireless signals may be set appropriately and may comply with various known standards.

[0067] In the first to eighth embodiments, the low acoustic velocity region 66 is defined by the length of the widened portion 65 in the extension direction of the electrode fingers, but this is not limited to this. Specifically, instead of the widened portion 65, the low acoustic velocity region 66 may be defined by adding an additional film on the electrode fingers 62 to increase the weight of at least a portion of the electrode fingers 62. In other words, the frequency characteristics of the acoustic wave device can be improved by creating the low acoustic velocity region 66 by increasing the weight per unit length of the electrode fingers.

[0068] [Summary] An elastic wave device according to aspect 1 of the present disclosure includes a support substrate having a cavity formed therein, a piezoelectric substrate located on the support substrate and covering the cavity, and an IDT electrode located on the piezoelectric substrate, the IDT electrode having a pair of bus bars and a plurality of electrode fingers provided in a first region sandwiched between the pair of bus bars, the entire intersection region in the first region being arranged to overlap with the cavity in a planar perspective view, the first region being a region in which the acoustic velocity of elastic waves in the arrangement direction of the plurality of electrode fingers is lower than in at least some other regions in the first region, and including a low acoustic velocity region extending in the arrangement direction, and the outer edge of the cavity overlaps with the low acoustic velocity region in a planar perspective view.

[0069] According to the above configuration, it is possible to reduce spurious signals and improve frequency characteristics.

[0070] According to a second aspect of the present disclosure, in the elastic wave device of the first aspect, the low acoustic velocity region may be configured by providing widened portions in the plurality of electrode fingers.

[0071] According to the above configuration, the electrode finger may have a low acoustic velocity region, and the low acoustic velocity region has an increased width.

[0072] According to a third aspect of the present disclosure, in the elastic wave device of the first or second aspect, the low acoustic velocity region may be configured by providing an additional film on the plurality of electrode fingers.

[0073] According to the above configuration, the electrode finger may have a low acoustic velocity region, and the low acoustic velocity region has an additional film.

[0074] An elastic wave device according to aspect 4 of the present disclosure may be configured such that, in any one of aspects 1 to 3, the low acoustic velocity region is configured by providing a second electrode finger that faces the electrode finger in the extension direction of the electrode finger and has a width greater than the average width of the electrode finger.

[0075] According to the above configuration, the low acoustic velocity region may include the second electrode finger.

[0076] An elastic wave device according to a fifth aspect of the present disclosure is any one of the first to fourth aspects, wherein the low acoustic velocity region may be a portion of a region in the vicinity of the pair of bus bars.

[0077] According to the above configuration, the low acoustic velocity region can be located in the vicinity of the bus bar.

[0078] According to a sixth aspect of the present disclosure, in the elastic wave device of any one of the second to fifth aspects, the widened portions may be provided on tip sides of the electrode fingers.

[0079] According to the above configuration, the low acoustic velocity region can be positioned on the tip side of the electrode finger.

[0080] An elastic wave device according to a seventh aspect of the present disclosure is any one of the first to sixth aspects, wherein the distance from the low acoustic velocity region to the intersection region may be one wavelength or less.

[0081] According to the above configuration, the low sound velocity region can exist up to the vicinity of the intersection region.

[0082] An elastic wave device according to an eighth aspect of the present disclosure is any one of the first to seventh aspects, wherein the distance from the low acoustic velocity region to the intersection region may be within an attachment pitch of the plurality of electrode fingers.

[0083] According to the above configuration, the low sound velocity region can exist up to the vicinity of the intersection region.

[0084] An elastic wave device according to a ninth aspect of the present disclosure is any one of the first to eighth aspects, wherein the bus bar is configured by providing a gap portion.

[0085] According to the above configuration, the bus bar can be provided with a gap.

[0086] According to a tenth aspect of the present disclosure, in the elastic wave device of any one of the first to ninth aspects, the support substrate may be made of silicon.

[0087] According to the above configuration, silicon can be used as the support substrate.

[0088] An elastic wave device according to an eleventh aspect of the present disclosure is any one of the first to tenth aspects, wherein the IDT electrode excites an A1-mode Lamb wave.

[0089] According to the above configuration, the IDT electrode can excite an A1 mode Lamb wave acoustic wave.

[0090] An elastic wave device according to a twelfth aspect of the present disclosure may be a communication device including the elastic wave device of any one of the first to eleventh aspects.

[0091] According to the above configuration, the communication device can be filtered by the acoustic wave device.

[0092] [Additional Notes] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art could easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure.

[0093] REFERENCE SIGNS LIST 1, 1a to 1f, 100 Acoustic wave device 2 Support portion 3 Silicon 4 Cavity portion 4a Outer edge 5 Piezoelectric substrate 6, 6a to 6f, 600 IDT electrodes 7a to 7c Connection layer 60 First region 61, 61a, 61b Bus bar 62, 62a, 62b Electrode fingers 63, 63a, 63b Dummy electrode fingers 64 Intersection region 65, 65a, 65b, 67, 67a, 67b Widened portion 66 Low acoustic velocity region 68, 68a, 68b Opening 151 Communication device

Claims

1. A support substrate having a cavity formed therein; a piezoelectric substrate located on the support substrate and covering the cavity; an IDT electrode located on the piezoelectric substrate; The IDT electrode is A pair of bus bars; a plurality of electrode fingers provided in a first region sandwiched between the pair of bus bars; The first region is disposed so as to entirely overlap the cavity portion in a plan view, the first region includes a low acoustic velocity region extending in an arrangement direction of the plurality of electrode fingers, the low acoustic velocity region being a region in which an acoustic velocity of an acoustic wave in the arrangement direction of the plurality of electrode fingers is lower than that in at least a part of other regions in the first region, An elastic wave device, wherein an outer edge of the cavity and the low sound velocity region overlap in a planar perspective view.

2. The acoustic wave device according to claim 1 , wherein the low acoustic velocity region is formed by providing widened portions in the plurality of electrode fingers.

3. The acoustic wave device according to claim 1 , wherein the low acoustic velocity region is formed by providing an additional film on the plurality of electrode fingers.

4. The acoustic wave device according to claim 1 , wherein the low acoustic velocity region is configured by providing a second electrode finger that faces the electrode finger in the extension direction of the electrode fingers and has a width larger than an average width of the electrode fingers.

5. The acoustic wave device according to claim 1 , wherein the low acoustic velocity region is a portion of a region adjacent to the pair of bus bars.

6. The acoustic wave device according to claim 2 , wherein the widened portion is provided on a tip side of the electrode finger.

7. The acoustic wave device according to claim 1 , wherein a distance from the low acoustic velocity region to the intersection region is within one wavelength.

8. The acoustic wave device according to claim 1 , wherein a distance from the low acoustic velocity region to the intersection region is within an attachment pitch of the plurality of electrode fingers.

9. The acoustic wave device according to claim 1 , wherein the bus bar is configured by providing a gap.

10. The acoustic wave device according to claim 1 , wherein the support substrate is made of silicon.

11. The acoustic wave device according to claim 1 , wherein the IDT electrode excites an A1 mode Lamb wave acoustic wave.

12. A communication device comprising the acoustic wave device according to claim 1 .