Elastic wave resonator and communication device

Abstract

This elastic wave resonator includes: a piezoelectric layer having grooves in a first surface thereof and having piezoelectric properties; and a plurality of electrode fingers including first electrode fingers having at least a portion positioned within the grooves. In a cross-sectional view from an extension direction of the plurality of electrode fingers, a region of the first electrode fingers located in the grooves has a wide region and a narrow region having a narrower width than the wide region. Further, the elastic wave resonator excites at least one of plate waves or bulk waves as a 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 IDT (interdigital transducer) electrode positioned on the piezoelectric layer, and uses A1-mode plate waves as acoustic waves. The IDT electrode has multiple electrode fingers arranged in the propagation direction of the acoustic waves. The smaller the pitch of the multiple electrode fingers, the higher the resonance frequency. The acoustic wave device of Patent Document 1 can achieve resonance in a higher frequency range than conventional resonators, with a pitch equivalent to that of conventional resonators that use surface acoustic waves as their primary resonance.

[0003] International Publication No. 2020 / 100949

[0004] An elastic wave resonator according to an embodiment of the present disclosure includes a piezoelectric layer having a groove on a first surface and having piezoelectric properties, and a plurality of electrode fingers including a first electrode finger at least partially located within the groove. In a cross-sectional view taken along the direction in which the plurality of electrode fingers extend, a region of the first electrode finger located within the groove has a wide region and a narrow region that is narrower than the wide 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] 1 is a schematic cross-sectional view of an acoustic wave resonator according to an embodiment of the present disclosure. FIG. 3A and FIG. 3B are schematic cross-sectional views of electrode fingers of an acoustic wave resonator according to an embodiment of the present disclosure. FIG. 4 is a diagram illustrating simulation results of resonance characteristics of an acoustic wave resonator according to an embodiment of the present disclosure. FIG. 5A, FIG. 5B, and FIG. 5C are schematic cross-sectional views of electrode fingers of an acoustic wave resonator according to another embodiment of the present disclosure. FIG. 5A is a schematic cross-sectional view of an acoustic wave resonator according to another embodiment of the present disclosure. FIG. 7A and FIG. 7B are diagrams illustrating simulation results of frequency characteristics for an example of the present disclosure. FIG. 8A and FIG. 8B are diagrams illustrating simulation results of frequency characteristics for an example of the present disclosure. FIG. 9A and FIG. 9B are diagrams illustrating simulation results of frequency characteristics for an example of the present disclosure. FIG. 10A and FIG. 10B are diagrams illustrating simulation results of frequency characteristics for an example of the present disclosure. FIG. 1 is a diagram schematically illustrating a duplexer as an example of use of an acoustic wave resonator according to an embodiment of the present disclosure. FIG. 2 is a block diagram illustrating a configuration of a main part of a communication device as an example of use of 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 accompanied by an orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis. 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 extension direction of the electrode fingers 412 (described later). The Z-axis is defined to be perpendicular to the upper surface 2 a of the piezoelectric layer 2 (described later). Note that the orthogonal coordinate system used in this disclosure is an example, and the X-axis, Y-axis, and Z-axis directions may be defined in directions different from those of the orthogonal coordinate system used in this disclosure. For convenience, in this disclosure, the terms upper surface and lower surface may be used, with the Z-axis direction being the up-down direction.

[0009] The embodiments of the acoustic wave resonator according to the present disclosure are merely examples, and therefore, different embodiments may be partially substituted for each other, or different embodiments may be partially combined.

[0010] 1 is a schematic cross-sectional view of an elastic wave resonator 1 according to an embodiment of the present disclosure, taken along the Y-axis direction. As shown in FIG. 1 , the elastic wave resonator 1 according to an 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. The lower surface 2b is located opposite the upper surface 2a. 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] The piezoelectric layer 2 contains a material having piezoelectricity. For example, lithium tantalate (LiTaO ３ ; hereinafter referred to as LT) single crystal and lithium niobate (LiNbO ３ (hereinafter referred to as LN) single crystals.

[0013] The piezoelectric layer 2 has piezoelectricity, and when a high-frequency signal is applied to the IDT electrode 4, an elastic wave is excited that propagates through the piezoelectric layer 2. 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.

[0014] In one embodiment of the present disclosure, the type and propagation mode of the plate wave or bulk wave excited as the primary resonance are not particularly limited and may be set according to the desired frequency characteristics. The Euler angles (φ, θ, ψ) of the piezoelectric single crystal contained in 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. Examples of types of plate waves include Lamb waves and SH waves. Examples of propagation modes of Lamb waves include the A1 mode, which is an asymmetric mode, and the S mode, which is a symmetric mode. 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 one embodiment of the present disclosure, the elastic wave excited as the primary resonance is the A1 mode of a Lamb wave, which is a plate wave.

[0015] For example, when the piezoelectric layer 2 is made of LT, the Euler angles (φ, θ, ψ) of the LT can be set to (0°±10°, 0° to 55°, 0°±10°) or a crystallographically equivalent angle, thereby effectively utilizing the A1 mode of the Lamb wave as the primary resonance. With reference to Examples 1 and 2 described below, the angles may be set to (0°±10°, 30°±10°, 0°±10°) or a crystallographically equivalent angle. When the piezoelectric layer 2 is made of LN, the Euler angles (φ, θ, ψ) of the LN can be set to (0°±10°, 0° to 55°, 0°±10°) or a crystallographically equivalent angle, thereby effectively utilizing the A1 mode of the Lamb wave as the primary resonance. With reference to Examples 3 and 4 described below, the angles may be set to (0°±10°, 35°±10°, 0°±10°) or a crystallographically equivalent angle.

[0016] 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).

[0017] The thickness of the piezoelectric layer 2 may be λ or less, expressed using a wavelength λ described below. By setting the thickness of the piezoelectric layer 2 to λ or less, at least one of the plate wave and the bulk wave can be effectively used as the main resonance. The thickness of the piezoelectric layer 2 may also be 0.5λ or less. In this case, at least one of the plate wave and the bulk wave can be more effectively used as the main resonance. Furthermore, the thickness may be 0.4λ or less or 0.3λ or less. There is no particular restriction on the lower limit, and the piezoelectric layer 2 may be made as thin as possible. For example, the thickness of the piezoelectric layer 2 may be 0.05λ or more, 0.10λ or more, or 0.15λ or more. The above lower limit and upper limit may be arbitrarily combined.

[0018] 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.

[0019] 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 ), silicon carbide (SiC), and silicon (Si).

[0020] The acoustic reflection layer 5 is located on the lower surface 2b side of the piezoelectric layer 2 (in direct or indirect contact with it), 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, and therefore the excited elastic waves can be effectively confined in the piezoelectric layer 2.

[0021] The acoustic reflection layer 5 may be composed of a single layer or multiple layers. For example, the acoustic reflection layer 5 may be composed of multiple low acoustic impedance layers 51 and multiple high acoustic impedance layers 52 alternately stacked. 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, elastic waves leaking from the lower surface 2b 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.

[0022] 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 ), tungsten (W), molybdenum (Mo) and zirconium oxide (ZrO ２ ) etc. can be mentioned as examples.

[0023] 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.

[0024] FIG. 2 is a plan view of an 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 arranged 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 electrode fingers 412 and are connected to the electrode fingers 412. In other words, the electrode fingers 412 extend from the bus bars 411. The electrode fingers 412 are arranged such that the electrode fingers 412a connected to one bus bar 411a and the electrode fingers 412b connected to the other bus bar 411b interdigitate with each other. Note that in the embodiment illustrated in FIG. 2 , the arrangement direction of the electrode fingers 412 is the X-axis direction, and the extension direction of the electrode fingers 412 is the Y-axis direction.

[0025] The comb-shaped electrode 41 may include a plurality of dummy electrode fingers 413 located between the respective electrode fingers 412. The plurality of dummy electrode fingers 413 includes 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. Note that in the present disclosure, "facing" does not necessarily require that the opposing surfaces be parallel to each other, and the opposing surfaces may be inclined.

[0026] The length of the electrode fingers 412 in the extension direction may be set appropriately depending on the required electrical characteristics, etc. For example, the lengths of the electrode fingers 412 in the extension direction are equal to each other. Note that the IDT electrode 4 may be apodized, in which the length of the electrode fingers 412 in the extension direction varies depending on the position in the X-axis direction.

[0027] The repetition interval of the electrode fingers 412 in the arrangement direction is defined as the pitch P. The pitch P is designed appropriately depending on the desired frequency characteristics. In FIG. 2 , the pitch P is constant, but this example is not limiting. For example, the pitch P may be designed to gradually increase, or may be designed to have multiple repetition intervals in stages. If there are multiple different repetition intervals, the pitch P may be defined as the average value of repetition intervals measured at 5 to 10 locations, or the largest repetition interval may be defined as the representative pitch P. The specific value of the pitch P is arbitrary. For example, the pitch P may be 0.5 μm or more, 1 μm or more, or 10 μm or less, 5 μm or less, or 2 μm or less. The above lower limit and upper limit examples may be combined arbitrarily. In one specific embodiment of the present disclosure, the pitch P of the electrode fingers 412 is 1.1 μm.

[0028] When a high-frequency signal is applied to the IDT electrode 4, an elastic wave having a wavelength λ defined as twice the pitch P, which is the repetition interval of the plurality of electrode fingers 412, is excited and propagates through the piezoelectric layer 2. Unlike the above, the wavelength λ may have low dependency on the pitch P, as in the case of a bulk wave that propagates in the thickness direction of the piezoelectric layer 2. Furthermore, λ, when defining the thickness of the piezoelectric layer 2, etc., may be twice the pitch P, and may be different from the wavelength of the elastic wave excited as the main resonance.

[0029] 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.

[0030] 3A and 3B are schematic cross-sectional views of the elastic wave resonator 1 according to an embodiment of the present disclosure taken along the Y-axis direction, illustrating an enlarged view of the electrode fingers 412. In other words, FIGS. 3A and 3B are cross-sectional views taken along the direction in which the electrode fingers 412 extend.

[0031] In the acoustic wave resonator 1 according to an embodiment of the present disclosure, the piezoelectric layer 2 has grooves 21 on its upper surface 2 a. At least a portion of the plurality of electrode fingers 412 is located within the grooves 21. All of the plurality of electrode fingers 412 may be located within the grooves 21, but this is not a limitation. For example, some electrode fingers 412 may be located within the grooves 21, while others may be located outside the grooves 21. Furthermore, the entire thickness (and / or volume) of the electrode fingers 412 located within the grooves 21 may be located within the grooves 21. This is not a limitation. For example, it is sufficient that at least a portion (e.g., a lower portion) of the thickness (and / or volume) of the electrode fingers 412 is located within the grooves 21. The region of the electrode fingers 412 located within the grooves 21 may be referred to as a buried region 45 to distinguish it from a protruding region 46, which will be described later.

[0032] As shown in FIG. 3A , the buried region 45 located in the groove 21 of the electrode finger 412 has a wide region 43 and a narrow region 44. The width of the electrode finger 412 in the narrow region 44 is narrower than the width of the electrode finger 412 in the wide region 43. In other words, if the width of the electrode finger 412 in the wide region 43 is T1 and the width of the electrode finger 412 in the narrow region 44 is T2, then T1 > T2. Note that T1 may be the width of any portion of the wide region 43, and T2 may be the width of any portion of the narrow region 44. For example, T1 may be the width of the widest portion of the wide region 43, and T2 may be the width of the narrowest portion of the narrow region 44. The "width" of the electrode finger 412 refers to the length of the electrode finger 412 in the X-axis direction.

[0033] Which parts of the electrode finger 412 are the narrow region 44 and which are the wide region 43 can be determined by comparing the widths of the parts to be measured. The narrow region 44 is a region narrower than the narrowest part of the wide region 43, and the wide region 43 is a region wider than the widest part of the narrow region 44. In other words, the entire wide region 43 is wider than the entire narrow region 44, and the entire narrow region 44 is narrower than the entire wide region 43. Note that the embedded region 45 of the electrode finger 412 may have multiple wide regions 43 or multiple narrow regions 44.

[0034] 3B , the specific cross-sectional shape of the electrode fingers 412 in the extension direction according to an embodiment of the present disclosure is a trapezoid, with the main surface located on the opening side of the groove 21 as an upper base 451, the main surface located on the bottom side of the groove 21 as a lower base 452, and the side surfaces as legs 453. In this way, when the cross-sectional shape of the electrode fingers 412 in the extension direction is trapezoidal, the narrow regions 44 are located closer to the lower surface 2 b of the piezoelectric layer 2 than the wide regions 43.

[0035] In a configuration in which the buried region 45 of the electrode fingers 412 has a wide region 43 and a narrow region 44, as in the embodiment of the present disclosure, the pitch P1 of the electrode fingers 412 in the wide region 43 can be made different from the pitch P2 of the electrode fingers 412 in the narrow region 44. Note that the aforementioned pitch P is a parameter that is not affected by the width of the electrode fingers 412, and is, for example, the distance between the centers of adjacent electrode fingers 412. The pitches P1 and P2 are parameters that are affected by the width of the electrode fingers 412, and are, for example, the distance (spacing) between the side surfaces of adjacent electrode fingers 412.

[0036] Generally, when the pitches (e.g., P1 and P2) of the electrode fingers 412 vary in the thickness direction, both the main mode, which is the primary resonance, and the spurious modes, which are unwanted waves, are less likely to resonate, and the phase intensity of both modes is reduced. However, in one embodiment of the present disclosure, at least one of a plate wave and a bulk wave, whose frequency characteristics are less affected by differences in pitch, is used as the primary resonance. Therefore, even if the pitch P1 of the electrode fingers 412 in the wide region 43 and the pitch P2 of the electrode fingers 412 in the narrow region 44 are different, the effect on the frequency characteristics of the primary resonance can be reduced. Therefore, according to one embodiment of the present disclosure, it is possible to effectively reduce spurious modes while maintaining good frequency characteristics of the primary resonance.

[0037] Because the effects of the wide region 43 and the narrow region 44 can be qualitatively explained as described above, the specific values ​​of the width and thickness of the electrode fingers 412 and the width and thickness of the grooves 21 are arbitrary. For example, T1 / P and / or T2 / P may be 0.05 or more, 0.2 or more, or 0.3 or more, or 0.6 or less, 0.5 or less, or 0.3 or less. Any combination of the above upper and lower limits may be used so long as no contradiction occurs. Furthermore, for example, the thickness of the electrode fingers 412 and / or the depth of the grooves 21 may be 0.005λ or more, 0.01λ or more, 0.02λ or more, or 0.04λ or more, or 0.5λ or less, 0.3λ or less, or 0.1λ or less, provided that they are equal to or less than the thickness of the piezoelectric layer 2 (or less than the thickness of the piezoelectric layer 2). Any combination of the above lower and upper limits may be used. The thicker the electrode fingers 412 are, the more easily the above-described structure and effects of the electrode fingers 412 can be realized.

[0038] 4 shows simulation results of the frequency characteristics of the elastic wave resonator 1 according to an embodiment of the present disclosure. The solid line indicates the simulation results of Example 1 shown in FIGS. 1 and 3 , and the dotted line indicates the simulation results of the comparative example. In Example 1, the side surfaces of the electrode fingers 412 are inclined, and the cross-sectional shape of the buried regions 45 of the electrode fingers 412 is trapezoidal, as shown in FIG. 3 . In the comparative example, the side surfaces of the electrode fingers 412 are not inclined, and the cross-sectional shape of the buried regions 45 is rectangular.

[0039] 4, the spurious components occurring in the vicinity of 6000 MHz to 6500 MHz are reduced in the example compared to the comparative example. Meanwhile, the main resonance characteristics located in the vicinity of 5400 MHz to 5800 MHz are not significantly affected. Thus, according to one embodiment of the present disclosure, an elastic wave resonator having excellent frequency characteristics can be provided.

[0040] The cross-sectional shape of the buried region 45 of the electrode finger 412 and the positional relationship between the wide region 43 and the narrow region 44 can be designed as appropriate. Figures 5A to 5C show an elastic wave resonator 1 according to another example of the present disclosure.

[0041] 1, the narrow region 44 is located closer to the lower surface 2b of the piezoelectric layer 2 than the wide region 43. However, this is not limiting. For example, in the example shown in FIG. 5A, the narrow region 44 is located closer to the upper surface 2a of the piezoelectric layer 2 than the wide region 43.

[0042] 1 , the cross-sectional shape of the embedded region 45 of the electrode finger 412 is trapezoidal, with the main surface located on the bottom side of the groove 21 as the base and the side surfaces as legs, but this is not limited to this example. For example, in the example shown in Fig. 5B , the cross-sectional shape of the embedded region 45 of the electrode finger 412 is a combination of a rectangular wide region 43 and a rectangular narrow region 44. In the example shown in Fig. 5B , the narrow region 44 is located closer to the lower surface 2b of the piezoelectric layer 2 than the wide region 43.

[0043] In the embodiment shown in FIG. 1 , the entire electrode finger 412 is located within the groove 21, but this is not limiting. For example, in the example shown in FIG. 5C , part of the electrode finger 412 may be located within the groove 21 and part may be located outside the groove 21. The region of the electrode finger 412 located outside the groove 21 is defined as a protruding region 46. The width of the protruding region 46 can be set as appropriate. For example, the width of the protruding region 46 may be larger or smaller than the width of the narrow region 44 in the embedded region 45.

[0044] Furthermore, the length of the protruding region 46 in the Z-axis direction may be smaller than the length of the buried region 45. In other words, the amount by which the protruding region 46 protrudes from the piezoelectric layer 2 may be smaller than the amount of embedding in the buried region 45. In this case, the effect of reducing spurious signals in the buried region 45 is more effectively achieved.

[0045] Furthermore, in the elastic wave resonator 1 according to an embodiment of the present disclosure shown in FIG. 1 , the acoustic reflection layer 5 is an example of a solid layer, but this is not limiting. For example, as another embodiment of the present disclosure, as shown in FIG. 6 , a void 53 may be located between the piezoelectric layer 2 and the support substrate 3. A gas is present in the void 53. The gas may be air or an inert gas such as nitrogen or argon. The support substrate 3 may be in direct or indirect contact with the piezoelectric layer 2.

[0046] The voids 53 are located at positions overlapping with the plurality of electrode fingers 412 when viewed from above in the Z-axis direction. With this configuration, the gas present in the voids 53 acts as an acoustic reflection layer, effectively reducing leakage of elastic waves from the lower surface 2b of the piezoelectric layer 2. The size and depth of the voids 53 may be set as appropriate.

[0047] 3B , when the cross-sectional shape of the electrode fingers 412 in the extension direction according to an embodiment of the present disclosure is trapezoidal, the angle θ between the upper base 451 and the leg 453 may be any value less than 90°. As the angle θ increases, the difference between the width of the electrode fingers 412 in the wide region 43 and the width of the electrode fingers 412 in the narrow region 44 increases. As a result, the difference between the pitch P1 of the electrode fingers 412 in the wide region 43 and the pitch P2 of the electrode fingers 412 in the narrow region 44 also increases, thereby more effectively reducing spurious emissions.

[0048] For example, the angle θ between the upper base 451 and the leg 453 may be greater than 35° and less than 90°. FIGS. 7A and 7B are diagrams illustrating simulation results of frequency characteristics when the angle θ is changed for Example 1 and Example 2, which are embodiments of the present disclosure. The vertical axis of FIGS. 7A and 7B represents the fractional bandwidth Δf (%) of the main resonance, and the horizontal axis represents the angle θ (°). In this specification, the fractional bandwidth Δf is defined as (fa-fr)×100 / fr, where fr is the resonance frequency of the elastic wave resonator 1 and fa is the antiresonance frequency. The larger the fractional bandwidth Δf of the main resonance, the wider the band width as a filter, resulting in improved frequency characteristics.

[0049] 7A shows the simulation results of the frequency characteristics of Example 1. FIG. 7B shows the simulation results of the frequency characteristics of Example 2. Example 1 is the embodiment shown in FIG. 1, in which an acoustic reflection layer 5 formed by laminating a low acoustic impedance layer 51 and a high acoustic impedance layer 52 is present on the lower surface 2b side of the piezoelectric layer 2. Example 2 is the embodiment shown in FIG. 6, in which a void 53 is present on the lower surface 2b side of the piezoelectric layer 2. The piezoelectric layer 2 in both Examples 1 and 2 is LT. The design details of Examples 1 and 2 are described below.

[0050] Conditions common to Examples 1 and 2 (piezoelectric layer: LT, piezoelectric layer Euler angles: (0°, 31°, 0°), piezoelectric layer thickness: 0.40 μm, IDT electrode: Al, pitch P: 1.1 μm, T1 / P: 0.5, electrode thickness: 0.13 μm, support substrate: Si) Example 1 (low acoustic impedance layer: SiO ２ , high acoustic impedance layer: HfO ２ Example 2 (with gap) The width T1 and the electrode thickness were kept constant, and the width T2 was changed to change the angle θ.

[0051] 7A and 7B , when the angle θ is in the range of greater than 35° and less than 90°, the fractional bandwidth Δf is larger than when the angle θ is 90°. Therefore, when the angle θ is in the range of greater than 35° and less than 90°, the fractional bandwidth Δf can be increased while reducing spurious emissions, thereby improving the characteristics of the main resonance.

[0052] The angle θ may be in a range greater than 35° and less than 85°. In this case, the fractional bandwidth Δf can be increased even more effectively. The angle θ may be in a range greater than 35° and less than 80°. In this case, the fractional bandwidth Δf can be increased even more effectively. The angle θ may be in a range greater than 35° and less than 70°. In this case, the fractional bandwidth Δf can be increased even more effectively.

[0053] The angle θ between the upper base 451 and the leg 453 may be greater than 45° and less than 90°. FIGS. 8A and 8B are diagrams illustrating simulation results of frequency characteristics when the angle θ is changed for Example 1 and Example 2, which are embodiments of the present disclosure. The vertical axis of FIGS. 8A and 8B represents the peak-valley PV value of the main resonance, and the horizontal axis represents the angle θ (°). In this specification, PV is defined as the absolute value |Z| of the impedance at the antiresonance frequency fa of the elastic wave resonator 1 divided by the absolute value |Z| of the impedance at the resonant frequency fr. In other words, PV is defined as (|Z| at fa) / (|Z| at fr). The larger the PV of the main resonance, the better the steepness and loss characteristics of the filter, resulting in improved frequency characteristics.

[0054] 8A shows the simulation results of the frequency characteristics of Example 1. FIG. 8B shows the simulation results of the frequency characteristics of Example 2.

[0055] 8A and 8B, when the angle θ is in the range of greater than 45° and less than 90°, the PV becomes large, as if the angle θ were 90°. Therefore, when the angle θ is in the range of greater than 45° and less than 90°, the PV can be increased while reducing spurious components, thereby improving the characteristics of the main resonance.

[0056] The angle θ may be in a range greater than 45° and less than 85°. In this case, the PV can be increased even more effectively. The angle θ may be in a range greater than 45° and less than 80°. In this case, the PV can be increased even more effectively. The angle θ may be in a range greater than 45° and less than 70°. In this case, the PV can be increased even more effectively.

[0057] For example, the angle θ between the upper base 451 and the leg 453 may be greater than 55° and less than 90°. Figures 9A and 9B are diagrams showing simulation results of frequency characteristics when the angle θ is changed for Example 3 and Example 4, which are embodiments of the present disclosure. The vertical axis of Figures 9A and 9B represents the fractional bandwidth Δf (%) of the main resonance, and the horizontal axis represents the angle θ (°).

[0058] 9A shows the simulation results of the frequency characteristics of Example 3. FIG. 9B shows the simulation results of the frequency characteristics of Example 4. Example 3 is the embodiment shown in FIG. 1 , in which an acoustic reflection layer 5 formed by stacking a low acoustic impedance layer 51 and a high acoustic impedance layer 52 is present on the lower surface 2b side of the piezoelectric layer 2. Example 4 is the embodiment shown in FIG. 6 , in which a void 53 is present on the lower surface 2b side of the piezoelectric layer 2. The piezoelectric layer 2 in both Examples 3 and 4 is made of LN. Details of the design of Examples 3 and 4 are given below.

[0059] Conditions common to Examples 3 and 4 (piezoelectric layer: LN, piezoelectric layer Euler angles: (0°, 35°, 0°), piezoelectric layer thickness: 0.37 μm, IDT electrode: Al, pitch P: 1.1 μm, T1 / P: 0.5, electrode thickness: 0.11 μm, support substrate: Si) Example 3 (low acoustic impedance layer: SiO ２ , high acoustic impedance layer: HfO ２ Example 4 (with gap) The width T1 and the electrode thickness were kept constant, and the width T2 was changed to change the angle θ.

[0060] 9A and 9B , when the angle θ is in the range of greater than 55° and less than 90°, the fractional bandwidth Δf becomes larger (or is the same) than when the angle θ is 90°. Therefore, when the angle θ is in the range of greater than 55° and less than 90°, the fractional bandwidth Δf can be increased while reducing spurious emissions, thereby improving the characteristics of the main resonance.

[0061] The angle θ may be in a range greater than 55° and less than 85°. In this case, the fractional bandwidth Δf can be increased even more effectively. The angle θ may be in a range greater than 55° and less than 80°. In this case, the fractional bandwidth Δf can be increased even more effectively. The angle θ may be in a range greater than 55° and less than 70°. In this case, the fractional bandwidth Δf can be increased even more effectively.

[0062] The angle θ between the upper base 451 and the leg 453 may be greater than 45° and less than 90°. Figures 10A and 10B are diagrams showing simulation results of frequency characteristics when the angle θ is changed for Example 3 and Example 4, which are embodiments of the present disclosure. The vertical axis of Figures 10A and 10B represents the PV value of the main resonance, and the horizontal axis represents the angle θ (°).

[0063] 10A shows the simulation results of the frequency characteristics of Example 3. FIG. 10B shows the simulation results of the frequency characteristics of Example 4.

[0064] 10A and 10B, when the angle θ is in the range of greater than 45° and less than 90°, the PV becomes large, as if the angle θ were 90°. Therefore, when the angle θ is in the range of greater than 45° and less than 90°, the PV can be increased while reducing spurious emissions, thereby improving the characteristics of the main resonance.

[0065] The angle θ may be in a range greater than 45° and less than 85°. In this case, the PV can be increased even more effectively. The angle θ may be in a range greater than 45° and less than 80°. In this case, the PV can be increased even more effectively. The angle θ may be in a range greater than 45° and less than 70°. In this case, the PV can be increased even more effectively.

[0066] Although not specifically shown, the applicant has confirmed through simulation calculations that the effect of reducing spurious signals can be obtained even when the pitch P is set to 5 μm and T1 / P is set to 0.06 under the conditions of Examples 1 to 4.

[0067] Note that a "trapezoid" does not necessarily have to be a trapezoid in the strict sense. For example, each corner of the trapezoid may be rounded. Furthermore, the upper base, lower base, and legs do not necessarily have to be strictly straight. For example, the upper base, lower base, and legs may be rounded curves. In this case, the angle θ between the upper base and the legs may be calculated as, for example, the angle between the tangent at the midpoint of the upper base and the tangent at the midpoint of the legs.

[0068] The trapezoid may also have a recess or protrusion in part. In this case, the angle θ between the upper base and the leg may be determined, for example, as the angle between a line that roughly overlaps the part of the upper base excluding the partial recess or protrusion, and a line that roughly overlaps the part of the leg excluding the partial recess or protrusion.

[0069] The cross-sectional shape of the electrode fingers 412 can be realized by various methods. For example, grooves 21 are formed in the piezoelectric layer 2, and the cross-sectional shape of the grooves 21 is formed into a desired shape, such as a trapezoid. Next, a metal layer that will become the electrode fingers 412 is formed. At this time, the metal layer fills the grooves 21, so that the cross-sectional shape of the electrode fingers 412 becomes the same as the cross-sectional shape of the grooves 21, and thus becomes a desired shape, such as a trapezoid. Various methods are also possible for forming the grooves 21 having a desired cross-sectional shape. For example, the grooves 21 may be formed by etching (e.g., wet etching). Then, a cross-sectional shape such as a trapezoid may be realized by utilizing the anisotropy of a single crystal with respect to etching or by sequentially performing etchings under different conditions. Alternatively, the grooves 21 may be formed by laser processing, for example. Then, a cross-sectional shape such as a trapezoid may be realized by utilizing a tapered or inversely tapered shape of laser light or by sequentially performing etchings under different conditions.

[0070] (Application Example of Elastic Wave Resonator 1: Duplexer) Fig. 11 is a circuit diagram schematically illustrating the configuration of a duplexer 101, which is an application example of elastic wave resonator 1. As can be seen from the reference numerals shown in the upper left of the figure, in Fig. 11, comb-like electrode 41 is schematically illustrated as a two-pronged fork shape, and reflector 42 is represented by a single line bent at both ends.

[0071] 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.

[0072] 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.

[0073] 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 .

[0074] 11 is merely one example of the configuration of the duplexer 101, and the duplexer 101 is not limited to the configuration shown in FIG. 11 . For example, the transmit filter 105 may be configured as a multimode filter. Also, in FIG. 11 , 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 using the acoustic wave resonator 1, and the other may be an LC filter including one or more inductors and one or more capacitors.

[0075] 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.

[0076] 12 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.

[0077] In communication device 111, a transmission information signal TIS containing information to be transmitted is modulated and frequency-raised by RF-IC (Radio Frequency Integrated Circuit) 113 to generate a transmission signal TS. Unwanted components outside the transmission passband are removed from the transmission signal TS by bandpass filter 115a, amplified by amplifier 114a, and input to transmission terminal 103. Then, transmission filter 105 removes unwanted components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from antenna terminal 102 to antenna 112. Antenna 112 converts the input transmission signal TS into a radio signal and transmits it.

[0078] 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.

[0079] 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 the direct conversion method is illustrated in FIG. 12 as an example of the circuit method, this is not limited to this example and may be, for example, a double superheterodyne method. Furthermore, FIG. 12 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.

[0080] 1: Acoustic wave resonator 2: Piezoelectric layer 2a: Upper surface (first surface) 2b: Lower surface (second surface) 21: Groove 3: Support substrate 4: IDT electrode 41: Comb-shaped electrode 411: Bus bar 412: Electrode finger (first electrode finger) 42: Reflector 43: Wide region 44: Narrow region 45: Embedded region 46: Protruding region 451: Upper base 452: Lower base 453: Leg 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 a groove on a first surface and having piezoelectricity; a plurality of electrode fingers including a first electrode finger at least a portion of which is located within the groove; Equipped with a region of the first electrode finger located within the groove in a cross-sectional view taken along a direction in which the plurality of electrode fingers extend; the region of the first electrode finger having a wide region and a narrow region having a width narrower than that of the wide region; Exciting bulk waves as the dominant resonance, Elastic wave resonator.

2. the piezoelectric layer has a second surface located opposite the first surface, the narrow region is located closer to the second surface than the wide region; The elastic wave resonator according to claim 1 .

3. the first electrode finger has a trapezoidal shape in the cross-sectional view, with a surface located on the opening side of the groove as an upper base, a surface located on the bottom side of the groove as a lower base, and side surfaces as legs. The elastic wave resonator according to claim 1 .

4. In the cross-sectional view, the angle formed between the upper base and the leg is in the range of greater than 35° and less than 90°. The elastic wave resonator according to claim 3 .

5. In the cross-sectional view, the angle formed between the upper base and the leg is in the range of greater than 45° and less than 90°. The elastic wave resonator according to claim 3 .

6. In the cross-sectional view, the angle formed between the upper base and the leg is in the range of greater than 55° and less than 90°. The elastic wave resonator according to claim 3 .

7. the thickness of the piezoelectric layer is equal to or less than twice the repetition interval of the plurality of electrode fingers; The elastic wave resonator according to claim 1 .

8. the piezoelectric layer contains lithium tantalate or lithium niobate; 2. The elastic wave resonator according to claim 1.

9. Further provided is an acoustic reflection layer that is in direct or indirect contact with the piezoelectric layer, the acoustic reflection layer is formed by alternately stacking 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 1 .

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 gap overlaps with the plurality of electrode fingers in a planar perspective view from a direction perpendicular to the first surface; The elastic wave resonator according to claim 1 .

11. When the distance between the opposing side surfaces of adjacent electrode fingers is called a pitch, the pitch in the wide region and the pitch in the narrow region are different from each other. The elastic wave resonator according to claim 1 .

12. A piezoelectric layer having a groove on a first surface and having piezoelectricity; a plurality of electrode fingers including a first electrode finger at least a portion of which is located within the groove; Equipped with a region of the first electrode finger located within the groove in a cross-sectional view taken along a direction in which the plurality of electrode fingers extend; the region of the first electrode finger having a wide region and a narrow region having a width narrower than that of the wide region; Exciting plate waves as the main resonance, Elastic wave resonator.

13. Exciting the A1 mode Lamb wave as the main resonance, The elastic wave resonator according to claim 12.

14. 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 any one of claims 1 to 13. Communication equipment.