Elastic wave resonator and communication device

Abstract

This elastic wave resonator comprises a piezoelectric layer having piezoelectric properties, and an IDT electrode. The IDT electrode has a plurality of electrode fingers and is in direct or indirect contact with the piezoelectric layer. In plan view, the piezoelectric layer has a first region that overlaps the electrode fingers, and a second region that does not overlap the electrode fingers. The total of the thickness of the piezoelectric layer in the first region and the thickness of the electrode fingers is no more than 1.28 times the thickness of the piezoelectric layer in the second region. The elastic wave resonator excites at least one of plate waves or bulk waves as main resonance.

Description

Acoustic wave resonator and communication device

[0001] The present disclosure relates to an acoustic wave resonator, which is an electronic component that utilizes acoustic waves, and a communication device including the acoustic wave resonator.

[0002] Patent Document 1 below discloses an acoustic wave device that has a piezoelectric layer and an interdigital transducer (IDT) electrode positioned on the piezoelectric layer, and uses an A1 mode plate wave as an acoustic wave. The IDT electrode has multiple electrode fingers arranged at a pitch p. The smaller the pitch p, the higher the resonance frequency. The acoustic wave device of Patent Document 1 can achieve resonance in a higher frequency range than conventional devices, with a pitch p equivalent to that of conventional devices.

[0003] International Publication No. 2020 / 100949

[0004] An elastic wave resonator according to an embodiment of the present disclosure includes a piezoelectric layer having piezoelectric properties and an IDT electrode. The IDT electrode has a plurality of electrode fingers and is in direct or indirect contact with the piezoelectric layer. The piezoelectric layer has, in a planar view, a first region overlapping with the electrode fingers and a second region not overlapping with the electrode fingers. The sum of the thickness of the piezoelectric layer in the first region and the thickness of the electrode fingers is 1.28 times or less the thickness of the piezoelectric layer in the second region. The elastic wave resonator excites at least one of a plate wave and a bulk wave as a primary resonance.

[0005] A communication device according to an embodiment of the present disclosure includes an antenna, an acoustic wave filter connected to the antenna, and an integrated circuit (IC) connected to the acoustic wave filter. The acoustic wave filter includes the acoustic wave resonator described above.

[0006] 6A and 6B are diagrams illustrating changes in spurious intensity when the total thickness of the first region and the electrode fingers is changed relative to the thickness of the second region. 6B are diagrams illustrating changes in frequency and phase of each resonance when the total thickness of the first region and the electrode fingers is changed relative to the thickness of the second region. 6A and ... 1 is a block diagram illustrating a configuration of a main part of a communication device as an example of using an acoustic wave resonator according to an embodiment of the present disclosure;

[0007] An acoustic wave resonator and a communication device according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that the drawings used in the following description are schematic diagrams, and the dimensional ratios and the like in the drawings do not necessarily correspond to those of the actual acoustic wave resonator and communication device.

[0008] For convenience, the drawings may be illustrated with a Cartesian coordinate system consisting of an X-axis, a Y-axis, and a Z-axis. In the elastic wave resonator 1 according to an embodiment of the present disclosure, any direction may be considered to be up or down. However, for convenience, the terms top surface and bottom surface may be used, with the Z-axis direction being the up or down direction. The X-axis is defined to be parallel to the propagation direction of an elastic wave used as the main resonance among the elastic waves propagating through the piezoelectric layer 2 (described later). The Y-axis is defined to be parallel to the top surface of the piezoelectric layer 2 and perpendicular to the X-axis. The Z-axis is defined to be perpendicular to the top surface of the piezoelectric layer 2.

[0009] It should be noted that the embodiments described in this specification are merely examples, and different embodiments may be partially substituted for each other. Also, different embodiments may be partially combined.

[0010] 1 is a schematic cross-sectional view of an acoustic wave resonator 1 according to an embodiment of the present disclosure. As shown in FIG. 1 , the acoustic wave resonator 1 according to the embodiment of the present disclosure includes a piezoelectric layer 2, a support substrate 3, an acoustic reflection layer 5, and an IDT electrode 4.

[0011] The piezoelectric layer 2 has an upper surface 2a and a lower surface 2b that are perpendicular to the Z axis, with the Z axis being the up-down direction. For example, the upper surface 2a may be called the first surface, and the lower surface 2b may be called the second surface. An acoustic reflection layer 5 and a support substrate 3, which will be described later, are located on the lower surface 2b side of the piezoelectric layer 2. An IDT electrode 4, which will be described later, is located on the upper surface 2a side of the piezoelectric layer 2.

[0012] Various materials having piezoelectricity can be used for the piezoelectric layer 2. Examples of the material having piezoelectricity include lithium tantalate (LiTaO ３ ; hereinafter referred to as LT) single crystal and lithium niobate (LiNbO ３ (hereinafter referred to as LN) single crystal. In one embodiment of the present disclosure, specifically, the piezoelectric layer 2 is made of LN single crystal.

[0013] The piezoelectric layer 2 has piezoelectric properties, and when a high-frequency signal is applied to the IDT electrode 4, an elastic wave propagating through the piezoelectric layer 2 is excited. In an embodiment of the present disclosure, the elastic wave excited as the main resonance is at least one of a plate wave and a bulk wave. Which type of elastic wave, a plate wave or a bulk wave, is used as the main resonance may be determined depending on desired frequency characteristics, etc. Examples of types of plate waves include Lamb waves and SH waves. Examples of types of bulk waves include those that propagate in the planar direction of the piezoelectric layer 2 and those that propagate in the thickness direction of the piezoelectric layer 2. Specifically, in the elastic wave resonator 1 according to an embodiment of the present disclosure, the plate wave used as the main resonance is a Lamb wave.

[0014] In one embodiment of the present disclosure, the propagation mode of the plate wave or bulk wave excited as the primary resonance is not particularly limited and may be set according to the desired frequency characteristics. The Euler angles (φ, θ, ψ) of the piezoelectric single crystal used as the piezoelectric layer 2 may be appropriately designed according to the type and propagation mode of the plate wave or bulk wave used as the primary resonance. For example, if the piezoelectric layer 2 is LT, the Euler angles (φ, θ, ψ) can be set to (0°±10°, 0° to 55°, 0°±10°) or a crystallographically equivalent angle to effectively utilize the A1 mode of the Lamb wave as the primary resonance. Furthermore, if the piezoelectric layer 2 is LT, the Euler angles may be (0°±10°, 24°±10°, 0°±10°) or a crystallographically equivalent angle to the Euler angles. If the piezoelectric layer 2 is made of LN, the A1 mode of Lamb waves can be effectively utilized as the primary resonance by setting the Euler angles (φ, θ, ψ) to (0°±10°, 0° to 55°, 0°±10°) or crystallographically equivalent angles thereto. Furthermore, if the piezoelectric layer 2 is made of LN, the Euler angles may be particularly (0°±10°, 30°±10°, 0°±10°) or crystallographically equivalent angles thereto. Specifically, in one embodiment of the present disclosure, the propagation mode of Lamb waves utilized as the primary resonance is the A1 mode, and the Euler angles (φ, θ, ψ) of LN are (0°, 30°, 0°).

[0015] The primary resonance refers to, for example, the smallest minimum impedance value (or, from another perspective, the impedance at the resonant frequency) among multiple resonances occurring in the elastic wave resonator 1 that have different resonant frequencies. Furthermore, when a specific elastic wave (e.g., a plate wave) is used as the primary resonance, it means that the specific elastic wave is the primary component of the elastic wave that is causing the primary resonance. The primary component is, for example, a component that accounts for 50% or more or 80% or more of the energy of the elastic wave at the resonant frequency. When both a plate wave and a bulk wave are used as the primary resonance, it is sufficient that the total energy of both waves has the above-mentioned value (each may be below the above-mentioned lower limit).

[0016] The thickness of the piezoelectric layer 2, expressed using a wavelength λ described below, may be λ or less, 0.50λ or less, 0.30λ or less, or 0.20λ or less. By setting the thickness of the piezoelectric layer 2 to λ or less, for example, plate waves can be effectively used as the main resonance. The lower limit is not particularly limited, and the piezoelectric layer 2 may be made as thin as possible. The thickness of the piezoelectric layer 2 may be, for example, 0.05λ or more, 0.10λ or more, or 0.15λ or more. The above lower limit and upper limit may be combined arbitrarily. Specifically, in one embodiment of the present disclosure, the thickness of the piezoelectric layer 2 is 0.153λ.

[0017] The support substrate 3 is located on the lower surface 2b side of the piezoelectric layer 2. The thickness of the support substrate 3 is not particularly limited. For example, the thickness of the support substrate 3 may be thicker than the thickness of the piezoelectric layer 2.

[0018] The material of the support substrate 3 is not particularly limited. For example, the material of the support substrate 3 may be a material having a smaller linear expansion coefficient than that of the piezoelectric layer 2. By using such a material for the support substrate 3, it is possible to reduce deformation of the piezoelectric layer 2 due to temperature changes and reduce changes in the resonance characteristics of the acoustic wave resonator 1 due to temperature changes. Examples of such a material for the support substrate 3 include sapphire (Al ２ O ３ Examples of suitable materials include silicon carbide (SiC) and silicon (Si). Specifically, in one embodiment of the present disclosure, the support substrate 3 is made of Si.

[0019] The acoustic reflection layer 5 is located on the lower surface 2b side of the piezoelectric layer 2, and is located between the piezoelectric layer 2 and the support substrate 3. The acoustic impedance of the acoustic reflection layer 5 is different from the acoustic impedance of the piezoelectric layer 2. In this case, a difference in acoustic impedance occurs between the piezoelectric layer 2 and the acoustic reflection layer 5, so that the excited elastic waves can be effectively confined in the piezoelectric layer 2.

[0020] The IDT electrode 4 is located on the upper surface 2a of the piezoelectric layer 2. The IDT electrode 4 is made of a conductive material. Examples of the material for the IDT electrode 4 include various conductive materials such as aluminum (Al), copper (Cu), platinum (Pt), molybdenum (Mo), gold (Au), and alloys thereof. The IDT electrode 4 may also be formed by stacking multiple layers made of the above-mentioned conductive materials. When the IDT electrode 4 is formed by stacking multiple layers, a diffusion prevention layer made of a metal such as titanium (Ti) or a dielectric may be interposed at the stacking interface. Of the multiple layers of the IDT electrode 4, the layer located on the piezoelectric layer 2 side may be a base layer made of a metal such as titanium (Ti) or a dielectric. In one embodiment of the present disclosure, the IDT electrode 4 is specifically made of Al.

[0021] 2 is a plan view of the acoustic wave resonator 1 according to an embodiment of the present disclosure, as viewed from the Z-axis direction. As shown in FIG. 2 , the IDT electrode 4 has an interdigital electrode 41. The interdigital electrode 41 includes a plurality of electrode fingers 412. The interdigital electrode 41 also includes a pair of bus bars 411 that are positioned in a direction intersecting the arrangement direction of the plurality of electrode fingers 412 and are connected to the plurality of electrode fingers 412. The plurality of electrode fingers 412 are arranged such that the plurality of electrode fingers 412a connected to one bus bar 411a and the plurality of electrode fingers 412b connected to the other bus bar 411b interdigitate with each other.

[0022] The comb-shaped electrode 41 may also include a plurality of dummy electrode fingers 413. The plurality of dummy electrode fingers 413 includes, between each of the plurality of electrode fingers 412, a plurality of dummy electrode fingers 413a connected to one bus bar 411a and facing the electrode fingers 412b extending from the other bus bar 411b, and a plurality of dummy electrode fingers 413b connected to one bus bar 411b and facing the electrode fingers 412a extending from the other bus bar 411a.

[0023] In the present disclosure, "facing" does not necessarily mean that the opposing surfaces are parallel to each other; for example, one surface may be tilted relative to the other surface.

[0024] The lengths of the electrode fingers 412 in the Y-axis direction may be set appropriately depending on the required electrical characteristics, etc. For example, the lengths of the electrode fingers 412 in the Y-axis direction are equal to each other. The IDT electrode 4 may be apodized, in which the lengths of the electrode fingers 412 in the Y-axis direction (or, from another perspective, the overlap width) vary depending on the position in the X-axis direction.

[0025] The repeat pitch (repetition interval) of the multiple electrode fingers 412 is defined as P, and the width of the electrode fingers 412 is defined as W. P and W are designed appropriately according to the desired frequency characteristics. In FIG. 2 , P is constant, but this is not limiting. For example, P may be designed to gradually increase, or may be designed to have multiple types of pitch in stages. When there are multiple pitches, P may be defined as the average value of pitches measured at 5 to 10 locations, or the largest pitch may be defined as P.

[0026] The specific value of P is arbitrary. For example, P may be 0.5 μm or more, or 1 μm or more, or may be 10 μm or less, 5 μm or less, or 2 μm or less. The above examples of the lower limit and upper limit may be combined arbitrarily. Note that, specifically, in one embodiment of the present disclosure, the repeat pitch of the electrode fingers 412 is 1.5 μm.

[0027] The W / P (Duty) is also arbitrary. For example, the Duty may be 0.2 or more, or 0.3 or more, or may be 0.6 or less, 0.5 or less, or 0.4 or less. The above examples of the lower limit and the upper limit may be combined arbitrarily. In one specific embodiment of the present disclosure, the Duty is 0.3.

[0028] The thickness of the electrode fingers 412 of the IDT electrode 4 is defined as T. In an embodiment of the present disclosure, T is constant, but is not limited to this example. For example, T may vary depending on the electrode fingers 412 being measured. In such a case, T may be defined as the average value of the thicknesses of the electrode fingers 412 located near both ends in the arrangement direction and the electrode fingers 412 located near the center, or T may be defined as the thickness of the thickest electrode finger 412. Furthermore, T may vary depending on the portion of the electrode finger 412 being measured. In such a case, T may be defined as the average value of thicknesses measured at any number of positions on the electrode fingers 412, or T may be defined as the thickness of the thickest portion of the electrode fingers 412.

[0029] The specific thickness of T is arbitrary. For example, T may be 1 nm or more or 2 nm or more, or may be 200 nm or less or 100 nm or less. The above examples of the lower limit and the examples of the upper limit may be arbitrarily combined.

[0030] When a high-frequency signal is applied to the IDT electrode 4, an acoustic wave having a wavelength λ defined by twice the pitch P, which is the repetition interval of the electrode fingers 412, is excited and propagates through the piezoelectric layer 2. The resonance frequency fr of the acoustic wave resonator 1 is approximately equal to the frequency of the acoustic wave used as the main resonance among the excited acoustic waves. The anti-resonance frequency fa is determined by the resonance frequency fr and the capacitance ratio. The capacitance ratio is determined mainly by the piezoelectric layer 2 and is adjusted by the number of electrode fingers 412, the overlap width, the film thickness, etc.

[0031] Unlike the above, the dependency of the resonance frequency fr on the pitch P may be low, as in the case of a bulk wave propagating in the thickness direction of the piezoelectric layer 2. Furthermore, λ when defining the thickness of the piezoelectric layer 2 may be twice the pitch P, and may be different from the wavelength of the elastic wave excited as the main resonance.

[0032] The elastic wave resonator 1 according to an embodiment of the present disclosure may (or may not) further include a pair of reflectors 42 located on the upper surface 2 a side of the piezoelectric layer 2. For example, the pair of reflectors 42 are located on both sides of the comb-shaped electrode 41 in the X-axis direction. The reflectors 42 include a pair of reflector bus bars 421 facing each other and a plurality of strip electrodes 422 extending between the pair of reflector bus bars 421.

[0033] 3 is an enlarged view of a portion of a schematic cross-sectional view of an elastic wave resonator 1 according to an embodiment of the present disclosure. The piezoelectric layer 2 has a first region 21 and a second region 22. The first region 21 is a region that overlaps with the electrode fingers 412 in a planar view from the Z-axis direction, and the second region 22 is a region that does not overlap with the electrode fingers 412 in a planar view from the Z-axis direction. The thickness of the piezoelectric layer 2 in the first region 21 in the Z-axis direction is defined as L1, and the thickness of the piezoelectric layer 2 in the second region 22 in the Z-axis direction is defined as L2.

[0034] L1 does not necessarily have to be strictly constant. When L1 is not constant, for example, the thickness of the thickest portion of the first region 21 may be used as L1, or L1 may be defined as the average thickness of the piezoelectric layer 2 measured at any number of points in the first region 21 that overlap with the electrode fingers 412 in a plan view.

[0035] L2 does not necessarily have to be strictly constant. When L2 is not constant, for example, the thickness of the thickest portion of the second region 22 may be used as L2, or L2 may be defined as the average thickness of the piezoelectric layer 2 measured at any number of points in the second region 22 sandwiched between the electrode fingers 412 a and 412 b in a plan view.

[0036] The acoustic wave resonator 1 according to an embodiment of the present disclosure utilizes at least one of plate waves and bulk waves as the primary resonance. The resonance characteristics of plate waves and bulk waves are significantly dependent on the thickness of the piezoelectric layer 2. Because the IDT electrode 4 protrudes toward the top surface 2a of the piezoelectric layer 2, when the piezoelectric layer 2 and the IDT electrode 4 are considered as an integrated film, the thickness of the film differs between the portion where the IDT electrode 4 is located and the portion where the IDT electrode 4 is not located. In this case, new spurious signals may be generated due to vibration of the electrode fingers 412 of the protruding IDT electrode 4. Therefore, by reducing the amount of protrusion of the electrode fingers 412 from the top surface 2a, the generation of spurious signals due to vibration of the electrode fingers 412 can be reduced. The protrusion amount can be rephrased as the length of the electrode fingers 412 protruding from the first surface (top surface 2a) in the first direction (Z-axis direction) or the height of the electrode fingers 412 from the first surface.

[0037] 4 is a diagram showing a simulation result of the frequency characteristics of elastic wave resonator 1 according to Example 1 of the present disclosure. FIG. 5 is a diagram showing a simulation result of the frequency characteristics of an elastic wave resonator according to Comparative Example 1. In Example 1, L1 and L2 are both 460 nm, and T is 2 nm. In Comparative Example 1, L1 and L2 are both 460 nm, and T is 120 nm. Therefore, the amount of protrusion of electrode fingers 412 from top surface 2 a in the Z-axis direction is smaller in Example 1 than in Comparative Example 1.

[0038] As can be seen from Figure 5, in Comparative Example 1, spurious S1 occurs near 5525 MHz, spurious S2 occurs near 7175 MHz, and spurious S3 occurs near 4370 MHz. The vibration modes of each of spurious S1, S2, and S3 were analyzed. Among the vibration modes of spurious S1, the most dominant vibration mode had the greatest vibration intensity in the part of electrode finger 412. Among the vibration modes of spurious S2, the most dominant vibration mode had the greatest vibration intensity in the part of electrode finger 412. Among the vibration modes of spurious S3, the most dominant vibration mode had the greatest vibration intensity in the part of piezoelectric layer 2 where electrode finger 412 was not located.

[0039] Therefore, it was found that the spurious components S1 and S2 are most dominant in a vibration mode in which the electrode fingers 412 vibrate, and the spurious component S3 is most dominant in a vibration mode unrelated to the vibration of the electrode fingers 412. In other words, the spurious components S1 and S2 are caused by the vibration of the electrode fingers 412, while the spurious component S3 is not caused by the vibration of the electrode fingers 412.

[0040] 4 , in Example 1, the spurious emissions S1 and S2 caused by vibration of the electrode fingers 412 can be reduced compared to Comparative Example 1. Therefore, according to one embodiment of the present disclosure, an elastic wave resonator having excellent frequency characteristics can be provided.

[0041] Furthermore, in one embodiment of the present disclosure, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be 1.28 times or less the thickness of the second region 22. In other words, L1, L2, and T may satisfy the following formula (1): (L1 + T)≦1.28×L2 (1) With this configuration, the amount of protrusion of the electrode fingers 412 is reduced, thereby reducing the occurrence of spurious signals due to vibration of the electrode fingers 412.

[0042] 6A and 6B show the change in spurious intensity when the total thickness of the first region 21 and the electrode fingers 412 is changed relative to the thickness of the second region 22 in one embodiment of the present disclosure. The horizontal axis represents the value of (L1 + T) / L2, and the vertical axis represents the phase (°) of the spurious. The spurious phase shown in FIG. 6A is the phase of the spurious S1, and the spurious phase shown in FIG. 6B is the phase of the spurious S2.

[0043] 6A and 6B , in one embodiment of the present disclosure, when the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 is 1.28 times or less the thickness of the second region 22, the phase of the spurious components caused by the vibration of the electrode fingers 412 is significantly reduced. Therefore, when the configuration satisfies formula (1), an elastic wave resonator with excellent frequency characteristics can be provided. Note that the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be more than 1 time the thickness of the second region 22.

[0044] 7 shows the changes in the frequency and phase of each resonance when the total thickness of the first region 21 and the electrode fingers 412 is changed relative to the thickness of the second region 22 in the embodiment shown in FIG. 3. The horizontal axis represents the value of (L1 + T) / L2, the vertical axis represents frequency (MHz), and the color shading represents the phase (°) of each resonance. Note that in FIG. 7, the simulation was performed with L1 = L2 = 460 nm.

[0045] 7 , the smaller the value of (L1 + T) / L2 is, the smaller the phase of the spurious signal S1 near 5525 MHz and the spurious signal S2 near 7175 MHz is. For example, in one embodiment of the present disclosure, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be 1.20 times or less the thickness of the second region 22. In other words, L1, L2, and T may satisfy the following formula (2): (L1 + T)≦1.20×L2 (2) This configuration further reduces the amount of protrusion of the electrode fingers 412, thereby further reducing the occurrence of spurious signals due to vibration of the electrode fingers 412.

[0046] For example, in one embodiment of the present disclosure, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be 1.07 times or less the thickness of the second region 22. In other words, L1, L2, and T may satisfy the following formula (3): (L1 + T)≦1.07×L2 (3) With this configuration, the amount of protrusion of the electrode fingers 412 is further reduced, thereby further reducing the occurrence of spurious signals due to vibration of the electrode fingers 412.

[0047] 8 is a partially enlarged schematic cross-sectional view of an elastic wave resonator 1 according to an embodiment of the present disclosure. In the embodiment illustrated in FIG. 8 , grooves are formed in the upper surface 2 a of the piezoelectric layer 2, and at least a portion of the electrode fingers 412 is located inside the grooves. In other words, the thickness of the piezoelectric layer 2 in the second region 22 is greater than the thickness of the piezoelectric layer 2 in the first region 21. With this configuration, the amount of protrusion of the electrode fingers 412 from the upper surface 2 a can be reduced without reducing the thickness of the electrode fingers 412. Therefore, an elastic wave resonator with excellent frequency characteristics can be provided while reducing the electrical resistance compared to a case where the thickness of the electrode fingers 412 is reduced.

[0048] FIG. 9 is a graph showing simulation results of the frequency characteristics of elastic wave resonator 1 according to Example 2 of the present disclosure. FIG. 10 is a graph showing simulation results of the frequency characteristics of an elastic wave resonator according to Comparative Example 2. In Example 2, L1 is 336 nm, L2 is 460 nm, T is 126 nm, and the protrusion amount (L1 + T - L2) of electrode fingers 412 is 2 nm. In Comparative Example 2, L1 is 454 nm, L2 is 460 nm, T is 126 nm, and the protrusion amount (L1 + T - L2) of electrode fingers 412 is 120 nm. Therefore, the protrusion amount of electrode fingers 412 from top surface 2 a in the Z-axis direction is smaller in Example 2 than in Comparative Example 2. Furthermore, in Example 2, the protrusion amount of electrode fingers 412 from top surface 2 a in the Z-axis direction is 100 nm or less.

[0049] 10, in Comparative Example 2, spurious emissions S1 occur near 5525 MHz, spurious emissions S2 occur near 7175 MHz, and spurious emissions S3 occur near 4370 MHz, similar to Comparative Example 1. The spurious emissions S1 and S2 are caused by vibration of the electrode fingers 412, while the spurious emissions S3 are not caused by vibration of the electrode fingers 412.

[0050] 9 , in Example 2, the spurious emissions S1 and S2 caused by vibration of the electrode fingers 412 can be reduced compared to Comparative Example 2. Therefore, according to one embodiment of the present disclosure, an elastic wave resonator having excellent frequency characteristics can be provided.

[0051] 11 shows the changes in the frequency and phase of each resonance when the total thickness of the first region 21 and the electrode fingers 412 is changed relative to the thickness of the second region 22 in the embodiment shown in FIG. 8 . The horizontal axis represents the value of (L1 + T) / L2, the vertical axis represents frequency (MHz), and the color shading represents the phase (°) of each resonance. Note that in FIG. 11 , the simulation was performed with L2 = 460 nm and T = 160 nm.

[0052] 11 , the smaller the value of (L1 + T) / L2 is, the smaller the phase of the spurious component S1 near 5525 MHz and the spurious component S2 near 7175 MHz is. For example, in one embodiment of the present disclosure, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be 1.28 times or less the thickness of the second region 22. In other words, L1, L2, and T may satisfy formula (1). This configuration reduces the amount of protrusion of the electrode fingers 412, thereby reducing the occurrence of spurious components due to vibration of the electrode fingers 412.

[0053] In the embodiment shown in FIG. 8 , for example, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be 1.20 times or less the thickness of the second region 22. In other words, L1, L2, and T may satisfy formula (2). With this configuration, the protrusion amount of the electrode fingers 412 is further reduced, thereby further reducing the occurrence of spurious signals due to vibration of the electrode fingers 412. Furthermore, for example, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be 1.07 times or less the thickness of the second region 22. In other words, L1, L2, and T may satisfy formula (3). With this configuration, the protrusion amount of the electrode fingers 412 is further reduced, thereby further reducing the occurrence of spurious signals due to vibration of the electrode fingers 412.

[0054] In the embodiment shown in FIG. 8 , for example, the sum of the thickness of the first region 21 and the thickness of the electrode fingers 412 may be greater than the thickness of the second region 22. In other words, the former may be greater than 1 times (ideally 1.000 times) the latter. The former may also be 1.00 times or greater than the latter. In this case, 1.00 may include 0.995 or 1.004 (a measurement value that is rounded to 1.00). In the above-described second embodiment, (L1 + T) / L2 = 462 / 460 = 1.004347...

[0055] In one embodiment shown in FIG. 8 , the ratio of T to L2 (T / L2) is arbitrary. For example, T / L2 is greater than 0 (ideally 0.000...). Furthermore, for example, T may be set to 0.01 times or more, 0.10 times or more, or 0.20 times or more relative to L2, or 0.50 times or less, 0.40 times or less, 0.30 times or less, 0.20 times or less, or 0.10 times or less. The above lower and upper limits may be arbitrarily combined as long as no contradiction occurs.

[0056] In the elastic wave resonator 1 according to an embodiment of the present disclosure shown in FIG. 1 , the acoustic reflection layer 5 is formed of a single layer, but this is not limiting. Other embodiments of the present disclosure are shown in FIGS. 12A and 12B . For example, as shown in FIG. 12A , the acoustic reflection layer 5 may be formed by alternately stacking a plurality of low acoustic impedance layers 51 and a plurality of high acoustic impedance layers 52. The acoustic impedance of the low acoustic impedance layer 51 is lower than the acoustic impedance of the piezoelectric layer 2. The acoustic impedance of the high acoustic impedance layer 52 is higher than the acoustic impedance of the low acoustic impedance layer 51. With this configuration, elastic waves leaking from the lower surface 2 b of the piezoelectric layer 2 are reflected toward the piezoelectric layer 2 at the interface between the low acoustic impedance layer 51 and the high acoustic impedance layer 52, thereby more effectively reducing the leakage of elastic waves.

[0057] Such a low acoustic impedance layer 51 may be made of silicon oxide (SiO ２ ) and the like. The high acoustic impedance layer 52 may be made of hafnium oxide (HfO ２ ), tantalum oxide (Ta ２ O ５ ) and zirconium oxide (ZrO ２ ) etc. can be mentioned as examples.

[0058] 1 according to an embodiment of the present disclosure, the acoustic reflection layer 5 is a solid layer, but this is not limiting. For example, as another embodiment of the present disclosure, a void 53 may be provided between the piezoelectric layer 2 and the support substrate 3, as shown in FIG. 12B . In other words, the acoustic reflection layer 5 may be a gas present in the void 53.

[0059] The void 53 is located on the lower surface 2b side of the piezoelectric layer 2, at a position overlapping the first region 21 and the second region 22 in a plan view. A gas is present in the void 53. The gas may be air or an inert gas such as nitrogen or argon. With this configuration, the gas present in the void 53 acts as an acoustic reflection layer, effectively reducing leakage of elastic waves from the lower surface 2b side of the piezoelectric layer 2. The size and depth of the void 53 may be set as appropriate.

[0060] As another embodiment of the present disclosure, the acoustic wave resonator 1 may include an insulating additional film located above the IDT electrode 4 in the Z-axis direction. As another embodiment of the present disclosure, the acoustic wave resonator 1 may include an insulating base film located below the IDT electrode 4 in the Z-axis direction. Such an additional film and base film may include SiO ２ These additional films and undercoating films do not need to be taken into consideration when measuring the thicknesses of the electrode fingers 412 and the piezoelectric layer 2.

[0061] 1 and 3 have been described as examples in which there is only one acoustic wave resonator, but multiple acoustic wave resonators may be provided that share the same piezoelectric layer 2. Another embodiment of the present disclosure is shown in FIGS. 13A and 13B . In another embodiment of the present disclosure, acoustic wave resonators 11 and 12 may be provided that share the same piezoelectric layer 2. For example, the pitch P11 of the multiple electrode fingers 412 of acoustic wave resonator 11 may be different from the pitch P12 of the multiple electrode fingers 412 of acoustic wave resonator 12. Furthermore, as shown in FIG. 13A , the thickness T of the multiple electrode fingers 412 may be different between acoustic wave resonators 11 and 12. In this case, the relationship between T, L1, and L2 may satisfy any one of the relationships shown in formulas (1) to (3) in at least one of acoustic wave resonators 11 and 12.

[0062] 13B , the thickness of piezoelectric layer 2 may be different between elastic wave resonators 11 and 12. In other words, either or both of L1 and L2 may be different between elastic wave resonators 11 and 12. In this case, the relationship between T, L1, and L2 may satisfy any of the relationships in formulas (1) to (3) in at least one of elastic wave resonators 11 and 12.

[0063] 14 is a circuit diagram schematically illustrating the configuration of a duplexer 101, which is an example of the use of the acoustic wave resonator 1. As can be seen from the reference numerals in the upper left corner of the figure, the comb-like electrode 41 is schematically illustrated as a two-pronged fork, and the reflector 42 is represented by a single line bent at both ends.

[0064] The duplexer 101 has, for example, a transmit filter 105 that filters a transmit signal from a transmit terminal 103 and outputs the signal to an antenna terminal 102, and a receive filter 106 that filters a receive signal from the antenna terminal 102 and outputs the receive signal to a receive terminal 104.

[0065] The transmit filter 105 and the receive filter 106 are each configured as a ladder filter in which a plurality of resonators are connected in a ladder configuration, for example. That is, the transmit filter 105 has one or more series resonators connected in series between the transmit terminal 103 and the antenna terminal 102, and one or more parallel resonators connecting the series arm of the series resonator to a reference potential.

[0066] For example, the acoustic wave resonator 1 according to an embodiment of the present disclosure may be used as at least one of the series resonators and the parallel resonators included in the transmitting filter 105 and the receiving filter 106 .

[0067] 14 is merely one example of the configuration of the duplexer 101, and the duplexer 101 is not limited to the configuration shown in FIG. 14. For example, the transmit filter 105 may be configured as a multimode filter. Also, in FIG. 14, both the transmit filter 105 and the receive filter 106 are acoustic wave filters, but this configuration is not limiting. For example, one of the transmit filter 105 and the receive filter 106 may be an acoustic wave filter that uses the acoustic wave resonator 1, and the other may be an LC filter that includes one or more inductors and one or more capacitors.

[0068] Although the description has been given of a case in which the duplexer 101 includes the transmit filter 105 and the receive filter 106, the duplexer 101 is not limited to this configuration. For example, the duplexer 101 may be a diplexer or a multiplexer including three or more filters.

[0069] 15 is a block diagram showing a main part of a communication device 111 as an example of using the acoustic wave resonator 1 and the duplexer 101. The communication device 111 includes the duplexer 101 and performs wireless communication using radio waves.

[0070] In the communication device 111, a transmission information signal TIS containing information to be transmitted is modulated and frequency-raised (converted to a high-frequency signal with a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 113 to produce a transmission signal TS. Unwanted components outside the transmission passband are removed from the transmission signal TS by a bandpass filter 115a, amplified by an amplifier 114a, and input to a transmission terminal 103. The transmission filter 105 then removes unwanted components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from the antenna terminal 102 to an antenna 112. The antenna 112 converts the input transmission signal TS into a radio signal and transmits it.

[0071] Furthermore, in the communication device 111, a radio signal received by the antenna 112 is converted by the antenna 112 into a received signal RS and input to the antenna terminal 102. The receiving filter 106 removes unnecessary components outside the receiving passband from the input received signal RS and outputs the signal from the receiving terminal 104 to the amplifier 114b. The output received signal RS is amplified by the amplifier 114b, and unnecessary components outside the receiving passband are removed by the bandpass filter 115b. The received signal RS is then frequency-downshifted and demodulated by the RF-IC 113 to generate a received information signal RIS.

[0072] The transmit information signal TIS and the receive information signal RIS may be low-frequency signals containing appropriate information, such as analog audio signals or digitized audio signals. The passband of the radio signal may be set as appropriate, and in one embodiment of the present disclosure, a relatively high-frequency passband is also possible. The modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. While FIG. 15 illustrates a direct conversion system as an example of the circuit system, this is not limited to this example and may also be, for example, a double superheterodyne system. Furthermore, FIG. 15 schematically illustrates only the essential parts; low-pass filters or isolators may be added at appropriate positions, and the positions of amplifiers and other components may be changed.

[0073] 1: Acoustic wave resonator 2: Piezoelectric layer 2a: Upper surface 2b: Lower surface 21: First region 22: Second region 3: Support substrate 4: IDT electrode 41: Comb-shaped electrode 411: Bus bar 412: Electrode finger 42: Reflector 5: Acoustic reflection layer 51: Low acoustic impedance layer 52: High acoustic impedance layer 53: Air gap 101: Branching filter 102: Antenna terminal 103: Transmitting terminal 104: Receiving terminal 111: Communication device 112: Antenna 113: RF-IC 114: Amplifier 115: Bandpass filter

Claims

1. a piezoelectric layer having piezoelectricity; an IDT electrode having a plurality of electrode fingers and in direct or indirect contact with the piezoelectric layer; Equipped with the piezoelectric layer has, in a plan view, a first region overlapping with the electrode fingers and a second region not overlapping with the electrode fingers; the sum of the thickness of the piezoelectric layer in the first region and the thickness of the electrode fingers is 1.28 times or less the thickness of the piezoelectric layer in the second region; Exciting at least one of a plate wave and a bulk wave as a main resonance; Elastic wave resonator.

2. a sum of the thickness of the piezoelectric layer in the first region and the thickness of the electrode fingers is greater than a thickness of the piezoelectric layer in the second region; The elastic wave resonator according to claim 1 .

3. the sum of the thickness of the piezoelectric layer in the first region and the thickness of the electrode fingers is 1.20 times or less the thickness of the piezoelectric layer in the second region; The elastic wave resonator according to claim 2 .

4. the sum of the thickness of the piezoelectric layer in the first region and the thickness of the electrode fingers is 1.07 times or less the thickness of the piezoelectric layer in the second region; The elastic wave resonator according to claim 2 .

5. where λ is defined as twice the repetition interval of the plurality of electrode fingers, the thickness of the piezoelectric layer in the first region and the thickness of the piezoelectric layer in the second region are λ or less. The elastic wave resonator according to claim 1 .

6. the piezoelectric layer has a first surface located on the IDT electrode side, the height of the electrode fingers from the first surface is 100 nm or less; The elastic wave resonator according to claim 1 .

7. the piezoelectric layer has a first surface located on the IDT electrode side and a groove portion formed in the first surface, At least a part of the electrode fingers is located inside the groove. The elastic wave resonator according to claim 1 .

8. an acoustic reflection layer in direct or indirect contact with the piezoelectric layer; The elastic wave resonator according to claim 1 .

9. The acoustic reflection layer is a plurality of low acoustic impedance layers having an acoustic impedance lower than that of the piezoelectric layer; and a plurality of high acoustic impedance layers having an acoustic impedance higher than that of the plurality of low acoustic impedance layers. The elastic wave resonator according to claim 8 .

10. Further provided is a support substrate that is in direct or indirect contact with the piezoelectric layer, a gap located between the piezoelectric layer and the support substrate; the void overlaps with the first region and the second region in a plan view of the piezoelectric layer; The elastic wave resonator according to claim 1 .

11. The piezoelectric layer is The material contains lithium tantalate and has Euler angles of (0°±10°, 24°±10°, 0°±10°) or equivalent angles; Or, the material contains lithium niobate, and the Euler angles are (0°±10°, 30°±10°, 0°±10°) or equivalent angles, the low acoustic impedance layer includes silicon oxide; the high acoustic impedance layer comprises hafnium oxide; The elastic wave resonator according to claim 8 .

12. An upper surface of the piezoelectric layer in the second region is located closer to the lower surface of the piezoelectric layer in the thickness direction of the piezoelectric layer than upper surfaces of the electrode fingers in the first region. The elastic wave resonator according to claim 7 .

13. The antenna and an acoustic wave filter connected to the antenna; an IC connected to the acoustic wave filter, The acoustic wave filter includes the acoustic wave resonator according to claim 1. Communication equipment.