WO2024190677A1

WO2024190677A1 - Elastic wave resonator and communication device

Info

Publication number: WO2024190677A1
Application number: PCT/JP2024/009073
Authority: WO
Inventors: 直史笠松
Original assignee: 京セラ株式会社
Priority date: 2023-03-15
Filing date: 2024-03-08
Publication date: 2024-09-19

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

Elastic wave resonator and communication device

This disclosure relates to an elastic wave resonator, which is an electronic component that utilizes elastic waves, and a communication device that includes the elastic wave resonator.

Patent Document 1 below discloses an elastic wave device that has a piezoelectric layer and an IDT (interdigital transducer) electrode located on the piezoelectric layer, and uses an A1 mode plate wave as the elastic wave. The IDT electrode has multiple electrode fingers arranged at a pitch p. The smaller the pitch p, the higher the resonant frequency. The elastic 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.

International Publication No. 2020/100949

An elastic wave resonator according to one 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 a first region overlapping with the electrode fingers and a second region not overlapping with the electrode fingers in a planar view. 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.

A communication device according to one embodiment of the present disclosure has 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.

FIG. 1 is a schematic cross-sectional view of an elastic wave resonator according to an embodiment of the present disclosure. FIG. 2 is a schematic plan view of an elastic wave resonator according to an embodiment of the present disclosure. FIG. 1 is a schematic cross-sectional view of an elastic wave resonator according to an embodiment of the present disclosure. 11A and 11B are diagrams illustrating simulation results of resonance characteristics of an elastic wave resonator according to an embodiment of the present disclosure. 13A and 13B are diagrams illustrating simulation results of resonance characteristics of an elastic wave resonator according to a comparative example. 6A and 6B are diagrams showing changes in spurious intensity when the total value of the thickness of the first region and the electrode fingers is changed relative to the thickness of the second region. 13 is a diagram showing changes in frequency and phase of each resonance when the total value of the thickness of the first region and the electrode fingers is changed relative to the thickness of the second region. FIG. 11 is a schematic cross-sectional view of an elastic wave resonator according to another embodiment of the present disclosure. FIG. 11A and 11B are diagrams illustrating simulation results of resonance characteristics of an elastic wave resonator according to an embodiment of the present disclosure. 13A and 13B are diagrams illustrating simulation results of resonance characteristics of an elastic wave resonator according to a comparative example. 13 is a diagram showing changes in frequency and phase of each resonance when the total value of the thickness of the first region and the electrode fingers is changed relative to the thickness of the second region. FIG. 12A and 12B are schematic cross-sectional views of an acoustic wave resonator according to another embodiment of the present disclosure. 13A and 13B are schematic cross-sectional views of an acoustic wave resonator according to another embodiment of the present disclosure. FIG. 1 is a diagram illustrating a duplexer as an example of a use of an elastic wave resonator according to an embodiment of the present disclosure. 1 is a block diagram showing a configuration of a main part of a communication device as an example of a use of an acoustic wave resonator according to an embodiment of the present disclosure.

Below, an elastic wave resonator and a communication device according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the figures used in the following description are schematic diagrams, and the dimensional ratios and the like in the drawings do not necessarily match those of the actual elastic wave resonator and communication device.

For convenience, the drawings may be accompanied by an orthogonal 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, either direction may be considered to be upward or downward. However, for convenience, the terms upper surface and lower surface may be used with the Z-axis direction being the up-down direction. Note that 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 below, the Y-axis is defined to be parallel to the upper surface of the piezoelectric layer 2 and perpendicular to the X-axis, and the Z-axis is defined to be perpendicular to the upper surface of the piezoelectric layer 2.

Note that each embodiment described in this specification is merely illustrative, and different embodiments may be partially substituted with each other. Also, different embodiments may be partially combined.

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

The piezoelectric layer 2 has an upper surface 2a and a lower surface 2b 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.

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

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 one 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 set according to the 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 of one embodiment of the present disclosure, the plate wave used as the main resonance is a Lamb wave.

In one embodiment of the present disclosure, the propagation mode of the plate wave or bulk wave excited as the main 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 main resonance. For example, if the piezoelectric layer 2 is LT, the A1 mode of the Lamb wave can be effectively used as the main resonance by setting the Euler angles (φ, θ, ψ) to (0°±10°, 0° to 55°, 0°±10°) or a crystallographically equivalent angle. In addition, if the piezoelectric layer 2 is LT, the Euler angles may be particularly (0°±10°, 24°±10°, 0°±10°) or a crystallographically equivalent angle. If the piezoelectric layer 2 is LN, the A1 mode of the Lamb wave can be effectively used as the main resonance by setting the Euler angles (φ, θ, ψ) to (0°±10°, 0° to 55°, 0°±10°) or a crystallographically equivalent angle. In addition, when the piezoelectric layer 2 is LN, the Euler angles may be particularly (0°±10°, 30°±10°, 0°±10°) or a crystallographically equivalent angle. Specifically, in one embodiment of the present disclosure, the propagation mode of the Lamb wave used as the main resonance is the A1 mode, and the Euler angles (φ, θ, ψ) of LN are (0°, 30°, 0°).

The primary resonance refers to, for example, the resonance with the smallest minimum impedance value (or, from another point of view, the impedance at the resonant frequency) among multiple resonances with different resonant frequencies that occur in the elastic wave resonator 1. In addition, when a specific elastic wave (e.g., a plate wave) is used as the primary resonance, it means, for example, that the specific elastic wave is the main component of the elastic wave that is causing the primary resonance. The main component is, for example, a component that occupies 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 has the above-mentioned value (each may be less than the above-mentioned lower limit).

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. There is no particular lower limit, 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 in any combination. Specifically, in one embodiment of the present disclosure, the thickness of the piezoelectric layer 2 is 0.153λ.

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, and for example, the thickness of the support substrate 3 may be thicker than the thickness of the piezoelectric layer 2.

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 materials for such a support substrate 3 include sapphire (Al ₂ O ₃ ), silicon carbide (SiC), and silicon (Si). Specifically, in one embodiment of the present disclosure, the support substrate 3 is Si.

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 trapped in the piezoelectric layer 2.

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

2 is a plan view of an elastic wave resonator 1 according to an embodiment of the present disclosure, viewed from the Z-axis direction. As shown in FIG. 2, the IDT electrode 4 has a comb-shaped electrode 41. The comb-shaped electrode 41 includes a plurality of electrode fingers 412. The comb-shaped 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.

The comb-shaped electrode 41 may also include a plurality of dummy electrode fingers 413. The plurality of dummy electrode fingers 413 include, 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.

In addition, in this disclosure, "opposing" does not necessarily mean that the opposing surfaces are parallel to each other; for example, one surface may be tilted toward the other surface.

The length 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 length of the electrode fingers 412 in the Y-axis direction (or, from another perspective, the cross width) changes depending on the position in the X-axis direction.

The repeat pitch (repetition interval) of the multiple electrode fingers 412 is P, and the width of the electrode fingers 412 is W. P and W are designed appropriately according to the desired frequency characteristics. In FIG. 2, P is constant, but is not limited to this example. For example, P may be designed to gradually increase, or may be designed to have multiple types of pitch in stages. If 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.

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

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

The thickness of the electrode fingers 412 of the IDT electrode 4 is defined as T. In one embodiment of the present disclosure, T is constant, but is not limited to this example. For example, T may vary depending on the electrode finger 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, among the multiple electrode fingers 412, or T may be defined as the thickness of the thickest electrode finger 412. Furthermore, T may vary depending on the part of the electrode finger 412 being measured. In such a case, T may be defined as the average value of the thicknesses measured at any number of points on the electrode fingers 412, or T may be defined as the thickness of the thickest part of the electrode fingers 412.

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

When a high-frequency signal is applied to the IDT electrode 4, an elastic wave with a wavelength λ defined as twice the pitch P, which is the repetition interval of the multiple electrode fingers 412, is excited and propagates through the piezoelectric layer 2. The resonance frequency fr of the elastic wave resonator 1 is roughly equivalent to the frequency of the elastic wave used as the main resonance among the excited elastic 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 crossing width, the film thickness, etc.

Note that, unlike the above, the dependence of the resonance frequency fr on the pitch P may be low, as in the case of bulk waves propagating in the thickness direction of the piezoelectric layer 2. Furthermore, λ when defining the thickness of the piezoelectric layer 2 only needs to be twice the pitch P, and may deviate from the wavelength of the elastic wave excited as the main resonance.

The elastic wave resonator 1 in one embodiment of the present disclosure may further include (or may not include) a pair of reflectors 42 located on the upper surface 2a 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 reflector 42 includes 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.

FIG. 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 when viewed from a plane in the Z-axis direction, and the second region 22 is a region that does not overlap with the electrode fingers 412 when viewed from a plane in 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.

L1 does not necessarily have to be strictly constant. If L1 is not constant, for example, L1 may represent the thickness of the thickest part of the first region 21, 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 overlaps with the electrode finger 412 in a plan view.

L2 does not necessarily have to be strictly constant. If L2 is not constant, for example, the thickness of the thickest part 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 412a and 412b in a plan view.

The elastic wave resonator 1 according to an embodiment of the present disclosure uses at least one of plate waves and bulk waves as the main resonance. The resonance characteristics of plate waves and bulk waves are highly dependent on the thickness of the piezoelectric layer 2. Since the IDT electrode 4 protrudes from the top surface 2a of the piezoelectric layer 2, when the piezoelectric layer 2 and the IDT electrode 4 are regarded as an integral 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 may occur due to the 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 occurrence of spurious caused by the vibration of the electrode fingers 412 can be reduced. The amount of protrusion 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.

FIG. 4 is a diagram showing the simulation results of the frequency characteristics of the elastic wave resonator 1 in Example 1 of the present disclosure. FIG. 5 is a diagram showing the simulation results of the frequency characteristics of an elastic wave resonator as 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 the electrode fingers 412 from the top surface 2a in the Z-axis direction is smaller in Example 1 than in Comparative Example 1.

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. The most dominant vibration mode of spurious S1 had the greatest vibration intensity in the part of electrode finger 412. The most dominant vibration mode of spurious S2 had the greatest vibration intensity in the part of electrode finger 412. The most dominant vibration mode of spurious S3 had the greatest vibration intensity in the part of piezoelectric layer 2 where electrode finger 412 was not located.

Therefore, it was found that the spurious noises S1 and S2 are most predominantly caused by a vibration mode in which the electrode fingers 412 vibrate, and the spurious noise S3 is most predominantly caused by a vibration mode unrelated to the vibration of the electrode fingers 412. In other words, the spurious noises S1 and S2 are caused by the vibration of the electrode fingers 412, and the spurious noise S3 is not caused by the vibration of the electrode fingers 412.

As can be seen from FIG. 4, in Example 1, the spurious S1 and spurious 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 with excellent frequency characteristics can be provided.

In addition, in an 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, so that the occurrence of spurious signals caused by vibration of the electrode fingers 412 can be reduced.

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

As shown in Figures 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 caused by the vibration of the electrode fingers 412 is significantly reduced. Therefore, in the case of a configuration that 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.

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

7, the smaller the value of (L1+T)/L2 is, the smaller the phase of the spurious S1 near 5525 MHz and the spurious 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)
With this configuration, the amount of protrusion of the electrode fingers 412 is further reduced, so that the occurrence of spurious signals caused by vibration of the electrode fingers 412 can be further reduced.

For example, in an 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, so that the occurrence of spurious signals caused by vibration of the electrode fingers 412 can be further reduced.

FIG. 8 is an enlarged view of a part of a schematic cross-sectional view of an elastic wave resonator 1 according to an embodiment of the present disclosure. In the embodiment shown in FIG. 8, a groove is formed on the upper surface 2a of the piezoelectric layer 2, and at least a part of the electrode fingers 412 is located inside the groove. 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. In this configuration, the amount of protrusion of the electrode fingers 412 from the upper surface 2a 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 value compared to when the thickness of the electrode fingers 412 is reduced.

FIG. 9 is a diagram showing the results of a simulation of the frequency characteristics of the elastic wave resonator 1 in Example 2 of the present disclosure. FIG. 10 is a diagram showing the results of a simulation of the frequency characteristics of an elastic wave resonator as 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 the 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 the electrode fingers 412 is 120 nm. Therefore, the protrusion amount of the electrode fingers 412 from the top surface 2a in the Z-axis direction is smaller in Example 2 than in Comparative Example 2. Furthermore, in Example 2, the protrusion amount of the electrode fingers 412 from the top surface 2a in the Z-axis direction is 100 nm or less.

As can be seen from FIG. 10, in Comparative Example 2, like Comparative Example 1, spurious S1 occurs near 5525 MHz, spurious S2 occurs near 7175 MHz, and spurious S3 occurs near 4370 MHz. The spurious S1 and spurious S2 are caused by the vibration of the electrode fingers 412, while the spurious S3 is not caused by the vibration of the electrode fingers 412.

As can be seen from FIG. 9, in Example 2, the spurious S1 and spurious S2 caused by the 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 with excellent frequency characteristics can be provided.

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

As can be seen from FIG. 11, the phase of the spurious S1 near 5525 MHz and the spurious S2 near 7175 MHz decreases as the value of (L1+T)/L2 decreases. 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). With this configuration, the amount of protrusion of the electrode fingers 412 decreases, thereby reducing the occurrence of spurious noise caused by vibration of the electrode fingers 412.

In one 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 than the thickness of the second region 22. In other words, L1, L2, and T may satisfy formula (2). With such a configuration, the amount of protrusion of the electrode fingers 412 is further reduced, so that the occurrence of spurious noise caused by the vibration of the electrode fingers 412 can be further reduced. Also, 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 than the thickness of the second region 22. In other words, L1, L2, and T may satisfy formula (3). With such a configuration, the amount of protrusion of the electrode fingers 412 is further reduced, so that the occurrence of spurious noise caused by the vibration of the electrode fingers 412 can be further reduced.

In one 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 time (ideally 1.000... times) the latter. The former may also be 1.00 times or more 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-mentioned Example 2, (L1+T)/L2=462/460=1.004347....

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...). Also, for example, T may be 0.01 times or more, 0.10 times or more, or 0.20 times or more relative to L2, and may be 0.50 times or less, 0.40 times or less, 0.30 times or less, 0.20 times or 0.10 times or less. The above lower and upper limits may be combined in any way so long as no contradiction occurs.

In the elastic wave resonator 1 according to an embodiment of the present disclosure shown in FIG. 1, the acoustic reflection layer 5 is a single type of layer, but is not limited to this example. Other embodiments of the present disclosure are shown in FIG. 12A and FIG. 12B. For example, as another embodiment of the present disclosure, as shown in FIG. 12A, the acoustic reflection layer 5 may be configured 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 smaller than the acoustic impedance of the piezoelectric layer 2. The acoustic impedance of the high acoustic impedance layer 52 is larger than the acoustic impedance of the low acoustic impedance layer 51. With this configuration, the elastic wave leaking from the lower surface 2b side of the piezoelectric layer 2 is reflected toward the piezoelectric layer 2 at the interface between the low acoustic impedance layer 51 and the high acoustic impedance layer 52, so that the leakage of the elastic wave can be more effectively reduced.

An example of the low acoustic impedance layer 51 is silicon oxide (SiO ₂ ), and an example of the high acoustic impedance layer 52 is hafnium oxide (HfO ₂ ), tantalum oxide (Ta ₂ O ₅ ), zirconium oxide (ZrO ₂ ), and the like.

In addition, in the elastic wave resonator 1 according to one embodiment of the present disclosure shown in FIG. 1, an example has been shown in which the acoustic reflection layer 5 is a solid layer, but this is not limited to this example. 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.

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 when viewed in a plan view. 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 the 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.

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. Examples of such additional films and base films include _SiO2 . Such additional films and base films do not need to be taken into consideration when measuring the thicknesses of the electrode fingers 412 and the piezoelectric layer 2.

1 and 3 have been described as an example in which there is only one elastic wave resonator, but there may be multiple elastic wave resonators sharing 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, there may be an elastic wave resonator 11 and an elastic wave resonator 12 sharing the same piezoelectric layer 2, and for example, the pitch P11 of the multiple electrode fingers 412 of the elastic wave resonator 11 may be different from the pitch P12 of the multiple electrode fingers 412 of the elastic wave resonator 12. Also, as shown in FIG. 13A, the thickness T of the multiple electrode fingers 412 may be different between the elastic wave resonator 11 and the elastic wave resonator 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 the elastic wave resonators 11 and 12.

Also, as shown in FIG. 13B, the thickness of the 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.

(Example of use of elastic wave resonator 1: duplexer)
14 is a circuit diagram showing a schematic configuration of a duplexer 101 as an example of the use of the elastic wave resonator 1. As can be seen from the reference numerals shown in the upper left corner of the figure, in this figure, the comb-shaped electrode 41 is shown diagrammatically in a bifurcated fork shape, and the reflector 42 is represented by a single line bent at both ends.

The splitter 101 has, for example, a transmit filter 105 that filters the transmit signal from the transmit terminal 103 and outputs it to the antenna terminal 102, and a receive filter 106 that filters the receive signal from the antenna terminal 102 and outputs it to the receive terminal 104.

Furthermore, the transmit filter 105 and the receive filter 106 are configured, for example, as ladder-type filters in which multiple resonators are connected in a ladder configuration. 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 that connect the series arm to a reference potential.

For example, the elastic wave resonator 1 in one embodiment of the present disclosure may be used as at least one of the series resonators or parallel resonators in the transmit filter 105 and the receive filter 106.

FIG. 14 is merely one example of the configuration of the splitter 101, and the splitter 101 is not limited to the configuration 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 elastic wave filters, but this configuration is not limiting. For example, either the transmit filter 105 or the receive filter 106 may be an elastic wave filter that uses an elastic wave resonator 1, and the other may be an LC filter that includes one or more inductors and one or more capacitors.

Note that although the above description has been given of a case in which splitter 101 includes transmit filter 105 and receive filter 106, splitter 101 is not limited to this configuration. For example, splitter 101 may be a diplexer or a multiplexer including three or more filters.

(Example of use of elastic wave resonator 1: communication device)
15 is a block diagram showing a main part of a communication device 111 as an example of a use of the acoustic wave resonator 1 and the duplexer 101. The communication device 111 includes the duplexer 101, and performs wireless communication using radio waves.

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 of the carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 113 to produce a transmission signal TS. Unnecessary 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 the transmission terminal 103. The transmission filter 105 then removes unnecessary components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from the antenna terminal 102 to the antenna 112. The antenna 112 converts the input transmission signal TS into a wireless signal and transmits it.

In addition, 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 it 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 become a received information signal RIS.

The transmitted information signal TIS and the received information signal RIS may be low-frequency signals containing appropriate information, for example, analog audio signals or digitized audio signals. The passband of the wireless 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. Although the circuit method shown in FIG. 15 is a direct conversion method, it is not limited to this example and may be, for example, a double superheterodyne method. Also, FIG. 15 shows only the essential parts in a schematic manner, and a low-pass filter or an isolator may be added at an appropriate position, and the position of an amplifier may be changed.

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: Gap 101: Splitter 102: Antenna terminal 103: Transmitting terminal 104: Receiving terminal 111: Communication device 112: Antenna 113: RF-IC
114: Amplifier 115: Bandpass filter

Claims

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;
a sum of a thickness of the piezoelectric layer in the first region and a thickness of the electrode fingers is 1.28 times or less a 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.
a sum of a thickness of the piezoelectric layer in the first region and a thickness of the electrode fingers is greater than a thickness of the piezoelectric layer in the second region;
2. The elastic wave resonator according to claim 1.
a sum of a thickness of the piezoelectric layer in the first region and a thickness of the electrode fingers is 1.20 times or less as large as a thickness of the piezoelectric layer in the second region;
3. The elastic wave resonator according to claim 1 or 2.
a sum of a thickness of the piezoelectric layer in the first region and a thickness of the electrode fingers is 1.07 times or less as large as a thickness of the piezoelectric layer in the second region;
The elastic wave resonator according to claim 1 .
When twice the repetition interval of the plurality of electrode fingers is defined as λ, a thickness of the piezoelectric layer in the first region and a thickness of the piezoelectric layer in the second region are equal to or less than λ.
The elastic wave resonator according to claim 1 .
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 .
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 finger is located inside the groove.
The elastic wave resonator according to claim 1 .
An acoustic reflection layer is provided in direct or indirect contact with the piezoelectric layer.
The elastic wave resonator according to claim 1 .
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 .
Further comprising a support substrate in direct or indirect contact with the piezoelectric layer,
a gap is provided between the piezoelectric layer and the support substrate;
the gap 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 .
The piezoelectric layer is
The material contains lithium tantalate and has Euler angles of (0°±10°, 24°±10°, 0°±10°) or equivalent angles;
or lithium niobate, and the Euler angles are (0°±10°, 30°±10°, 0°±10°) or equivalent angles;
the low acoustic impedance layer comprises silicon oxide;
The high acoustic impedance layer comprises hafnium oxide.
The elastic wave resonator according to claim 8 .
The antenna,
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.
Communications equipment.