Elastic wave resonator, elastic wave filter, and communication device

Abstract

Provided is an elastic wave resonator comprising a piezoelectric layer and an IDT electrode. The piezoelectric layer is piezoelectric. The IDT electrode is positioned on a first surface of the piezoelectric layer, and comprises a plurality of electrode fingers aligned in a first direction. The entire plurality of electrode fingers is positioned in an electrode finger arrangement region. The distance in the first direction from one side of one electrode finger to said one side of an electrode finger adjacent to the one electrode finger is defined as the pitch of the one electrode finger. The electrode finger arrangement region comprises a first region where the pitches of all of the electrode fingers differ from each other. The elastic wave resonator is configured to enable usage of plate waves or bulk waves as elastic waves that propagate through the electrode finger arrangement region.

Description

Acoustic wave resonator, acoustic wave filter and communication device

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

[0002] A surface acoustic wave resonator is known in which a voltage is applied to an IDT (interdigital transducer) electrode, which is composed of multiple electrode fingers provided on the surface of a piezoelectric substrate, to generate an acoustic wave that propagates through the piezoelectric body. The IDT electrode has a configuration with gradation regions in which the electrode finger pitch gradually decreases at both ends. This configuration allows for a surface acoustic wave resonator with small ripples.

[0003] JP 2012-138964 A

[0004] An elastic wave resonator according to one embodiment of the present invention includes a piezoelectric layer and an IDT electrode. The piezoelectric layer has piezoelectricity. The IDT electrode is located on a first surface of the piezoelectric layer and includes a plurality of electrode fingers arranged in a first direction. The plurality of electrode fingers are all located in an electrode finger arrangement region. The distance in the first direction from one side of an electrode finger to the one side of an electrode finger adjacent to the electrode finger is defined as the pitch of the electrode finger. The electrode finger arrangement region includes a first region in which the pitches of all the electrode fingers are different from one another. The elastic wave resonator is configured to utilize a plate wave or a bulk wave as the elastic wave propagating through the electrode finger arrangement region.

[0005] An acoustic wave resonator according to one embodiment of the present invention includes a piezoelectric layer and an IDT electrode. The piezoelectric layer has piezoelectricity. The IDT electrode is located on a first surface of the piezoelectric layer and has a plurality of electrode fingers arranged in a first direction. The plurality of electrode fingers are all located in an electrode finger arrangement region. The distance from one side of one electrode finger to the one side of an electrode finger adjacent to the one electrode finger in the first direction is defined as the pitch of the electrode finger. When the electrode finger arrangement region is divided into thirds in the first direction, the pitch of the electrode fingers in a central region increases toward the one side.

[0006] An acoustic wave filter according to one embodiment of the present invention is a ladder-type acoustic wave filter having a plurality of series arm resonators connected in series and a parallel arm resonator connected in parallel to the series arm resonators. The plurality of series resonators include any of the acoustic wave resonators described above and a second acoustic wave resonator. The anti-resonance frequency of the second acoustic wave resonator is closer to the passband of the acoustic wave filter than the anti-resonance frequency of the first acoustic wave resonator. Among the pitches of the electrode fingers of an IDT electrode included in the acoustic wave resonator, the largest pitch is defined as P1max and the smallest pitch is defined as P1min. Among the pitches of the electrode fingers of an IDT electrode included in the second acoustic wave resonator, the largest pitch is defined as P2max and the smallest pitch is defined as P2min. (P2max - P2min) is smaller than (P1max - P1min).

[0007] An acoustic wave filter according to one embodiment of the present invention is a ladder-type acoustic wave filter including a series arm resonator connected in series and a plurality of parallel arm resonators connected in parallel to the series arm resonator. The plurality of parallel arm resonators include any one of the acoustic wave resonators described above and a second acoustic wave resonator. The resonant frequency of the second acoustic wave resonator is closer to the passband of the acoustic wave filter than the resonant frequency of the first acoustic wave resonator. Among the pitches of the electrode fingers of an IDT electrode included in the acoustic wave resonator, the largest pitch is defined as P1max and the smallest pitch is defined as P1min. Among the pitches of the electrode fingers of an IDT electrode included in the second acoustic wave resonator, the largest pitch is defined as P2max and the smallest pitch is defined as P2min. (P2max - P2min) is smaller than (P1max - P1min).

[0008] An acoustic wave filter according to one embodiment of the present invention is an acoustic wave filter having any of the acoustic wave resonators described above, wherein the maximum phase of spurious emissions originating from the acoustic wave resonator and present in the passband of the acoustic wave filter is −70° or less.

[0009] A communication device according to one embodiment of the present invention includes an antenna, an acoustic wave filter connected to the antenna, and an IC connected to the acoustic wave filter, wherein the acoustic wave filter includes the acoustic wave resonator described above.

[0010] FIG. 1 is a schematic cross-sectional view of an elastic wave resonator according to an embodiment of the present invention. FIG. 2 is a plan view of an elastic wave resonator according to an embodiment of the present invention. FIG. 3 is a plan view of an elastic wave resonator according to an embodiment of the present invention. FIG. 4 is a diagram showing resonance characteristics of an elastic wave resonator according to an embodiment of the present invention. FIG. 5 is another diagram showing resonance characteristics of an elastic wave resonator according to an embodiment of the present invention. FIG. 6 is yet another diagram showing resonance characteristics of an elastic wave resonator according to an embodiment of the present invention. FIG. 7 is a diagram showing the pitch difference required to express a frequency difference of 50 MHz in a resonator having an anti-resonance frequency of 4600 MHz to 4950 MHz. FIG. 8 is a schematic cross-sectional view of an elastic wave resonator according to another embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of an elastic wave resonator according to yet another embodiment of the present invention. FIG. 10 is a diagram schematically showing an elastic wave filter as an example of use of the elastic wave resonator according to an embodiment of the present invention. FIG. 11 is a block diagram showing the configuration of a main part of a communication device as an example of use of the elastic wave resonator according to an embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0012] For convenience, the drawings may be illustrated with an orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis. In the elastic wave resonator 1 according to the present invention, any 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. The X-axis is defined to be parallel to the propagation direction of a SAW (Surface Acoustic Wave) propagating along the upper surface of the piezoelectric layer 2 (described later). The Y-axis is defined to be parallel to the upper surface of the piezoelectric layer 2 and perpendicular to the X-axis. The Z-axis is defined to be perpendicular to the upper surface of the piezoelectric layer 2.

[0013] It should be noted that the embodiments described in this specification are merely examples, and different embodiments may be partially substituted for each other. Also, different embodiments may be partially combined.

[0014] FIG. 1 is a schematic cross-sectional view of an elastic wave resonator 1 according to one embodiment of the present invention.

[0015] 1, an elastic wave resonator 1 according to one embodiment of the present invention includes a piezoelectric layer 2, a support substrate 3, and an IDT electrode 4. The support substrate 3 and the piezoelectric layer 2 are laminated in this order.

[0016] The support substrate 3 supports the piezoelectric layer 2 laminated thereon, and the material of the support substrate 3 is not particularly limited as long as it has a certain strength. For example, if the support substrate 3 is made of a material with a smaller linear expansion coefficient than the piezoelectric layer 2, it is possible to reduce deformation of the piezoelectric layer 2 due to temperature changes, thereby reducing changes in resonance characteristics due to temperature changes. Furthermore, the material of the support substrate 3 may be a material whose shear wave acoustic velocity is higher than that of the elastic wave propagating through the piezoelectric layer 2. When a material whose shear wave acoustic velocity is higher than that of the elastic wave propagating through the piezoelectric layer 2 is selected as the material of the support substrate 3, it is possible to confine the elastic waves within the piezoelectric layer 2, and it is possible to provide an elastic wave resonator 1 with excellent frequency characteristics.

[0017] Such materials include, for example, sapphire (Al ２ O ３ In this embodiment, an example in which Si is used as the support substrate 3 will be described.

[0018] The thickness of the support substrate 3 is not particularly limited, but is, for example, thicker than the thickness of the piezoelectric layer 2 described below.

[0019] 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. The aforementioned support substrate 3 is located on the lower surface 2b side. The lower surface 2b and the support substrate 3 may be in direct contact with each other, or indirectly via, for example, an intermediate layer and a multilayer film layer 5 (described later). The lower surface 2b and the support substrate 3 may also be in indirectly in contact with each other via an adhesive layer (not shown). The IDT electrode 4 (described later) is located on the upper surface 2a side.

[0020] The piezoelectric layer 2 is made of, for example, lithium tantalate (LiTaO ３ a piezoelectric single crystal substrate made of lithium niobate (LiNbO ３ A piezoelectric single crystal substrate made of LN (hereinafter referred to as LN) crystal can be used. In this embodiment, specifically, the piezoelectric layer 2 is made of 120° Y-cut-X-propagation LN.

[0021] When a high-frequency signal is applied to the IDT electrode 4 (described later), an elastic wave is excited that propagates through the piezoelectric layer 2 in the propagation direction of the elastic wave. The propagation direction may be any direction, for example, along the upper and lower surfaces of the piezoelectric layer 2 and / or along the thickness direction of the piezoelectric layer 2. In the elastic wave resonator 1 of this embodiment, the excited elastic waves include plate waves and bulk waves. The elastic wave resonator 1 may use plate waves or bulk waves as the main mode.

[0022] The type of elastic wave used is not particularly limited. For example, the plate wave may be a Lamb wave. For example, the bulk wave may be an SH wave or a thickness shear wave. Furthermore, the propagation mode of the plate wave used is not particularly limited. Specifically, in this embodiment, the plate wave is an A1 mode Lamb wave.

[0023] Just to be clear, the Lamb wave mainly comprises a component (P component) in the arrangement direction (propagation direction) of the electrode fingers 412 and / or a component (SV component) in the thickness direction of the piezoelectric layer 2. The A1 mode refers to a first-order asymmetric mode (A mode) (one node in the thickness direction). The SH wave mainly comprises a component (SH component) in a direction perpendicular to the arrangement direction (propagation direction) of the electrode fingers 412 and horizontal to the surface of the piezoelectric layer 2. The thickness shear wave slides different portions (e.g., the upper and lower surfaces) in the thickness direction of the piezoelectric layer 2 in directions along the upper and lower surfaces of the piezoelectric layer 2 and propagates in the thickness direction of the piezoelectric layer 2. The thickness shear wave may have any order, for example, first order (one node in the thickness direction).

[0024] The thickness of the piezoelectric layer 2 may be set appropriately as long as it is a thickness that allows the use of plate waves. For example, in this embodiment, the thickness of the piezoelectric layer 2 is 2λ or less, where λ is a value described later.

[0025] 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. Various conductive materials such as Al, Cu, Pt, Mo, Au, or alloys thereof can be used as the material for the IDT electrode 4, and the IDT electrode 4 may be made of a laminate of multiple layers. When the IDT electrode 4 is made of a laminate of multiple layers, a base layer (not shown) may be interposed at the interface between the layers. In this embodiment, the IDT electrode 4 is specifically made of Al.

[0026] 2 is a schematic diagram showing the shape of the IDT electrode 4 when viewed in plan from the Z-axis direction. As shown in FIG. 2, the IDT electrode 4 includes a pair of comb-shaped electrodes 41.

[0027] The comb-shaped electrode 41 (41a and 41b) includes, for example, a bus bar 411 (411a and 411b) and a plurality of electrode fingers 412 (412a and 412b) extending from the bus bar 411, and the electrode fingers 412a connected to one bus bar 411a and the electrode fingers 412b connected to the other bus bar 411b are arranged to interdigitate with each other. The comb-shaped electrode 41 may also include a plurality of dummy electrode fingers 413 (413a and 413b) between the plurality of electrode fingers 412, which protrude from one bus bar 411 and face the electrode fingers 412 extending from the other bus bar 411.

[0028] The lengths of the electrode fingers 412 in the Y-axis direction may be set appropriately depending on the required electrical characteristics, etc. For example, the lengths of the electrode fingers 412 in the Y-axis direction are equal to each other. The IDT electrode 4 may be apodized, in which the lengths of the electrode fingers 412 in the Y-axis direction (or, from another perspective, the overlap width) vary depending on the position in the propagation direction.

[0029] The acoustic wave resonator 1 may further include a pair of reflectors 42 on the upper surface of the piezoelectric layer 2. The pair of reflectors 42 are located on both sides of the IDT electrode 4 in the propagation direction of the acoustic wave. 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] The thickness of the plurality of electrode fingers 412 in the Z-axis direction may be set appropriately depending on the required electrical characteristics, etc. For example, the thickness of the plurality of electrode fingers 412 in the Z-axis direction may be constant.

[0031] 1, the width of one electrode finger 412a in the X-axis direction is defined as the width (w) of the electrode finger 412a. The distance from one side of the electrode finger 412a to one side of the electrode finger 412b adjacent to the electrode finger 412a is defined as the pitch (p) of the electrode fingers 412a. The duty d of the electrode fingers 412a represents the ratio of the width to the pitch of the electrode fingers 412a. In other words, the duty d of the electrode fingers 412a can be expressed as width / pitch (w / p).

[0032] The plurality of electrode fingers 412 are arranged at intervals based on a predetermined pitch. Furthermore, the resonant frequency of the elastic waves excited by the elastic wave resonator 1 among the elastic waves propagating through the piezoelectric layer 2 depends on the pitch of the electrode fingers 412.

[0033] In the acoustic wave resonator 1 according to this preferred embodiment, as shown in Fig. 2 , the electrode fingers 412 of the IDT electrode 4 are all located within the electrode finger arrangement region 7 in a plan view. In other words, the electrode finger arrangement region 7 is a region in which the electrode fingers 412 are all located in a plan view. For convenience, the electrode finger arrangement region 7 is indicated by a dotted line in Fig. 2 . In this preferred embodiment, the electrode finger arrangement region 7 includes at least one first region 71.

[0034] In this embodiment, the pitches of all the electrode fingers 412 located in the first region 71 are different from one another. Specifically, in FIG. 2 , the pitches P1 to P6 of all the electrode fingers located in the first region 71 are different from one another. In this way, the pitches of the electrode fingers 412 are different from one another, which reduces resonance of various unwanted waves, including second and third harmonic waves, and can reduce the occurrence of spurious signals.

[0035] In this specification, λ is defined as twice the largest pitch among the pitches of the multiple electrode fingers located in the first region. λ is generally used as a symbol representing wavelength. However, in the elastic wave resonator 1, the wavelength of the plate wave may or may not be equal to λ. For example, the wavelength of the A1 mode Lamb wave tends to be relatively close to λ. On the other hand, the wavelength of the thickness shear wave depends on λ, but its dependence on the thickness of the piezoelectric layer 2 is relatively large, and it is not necessarily close to λ.

[0036] In this embodiment, the electrode finger arrangement region 7 may also include a second region 72. The pitch of all electrode fingers 412 located in the second region 72 is the same. In this specification, "constant pitch" does not necessarily mean that the pitch is strictly constant, but rather allows for some variation within a range that can be called a manufacturing error. The range that can be called a manufacturing error refers to, for example, a range of 1.5% or less of the average pitch of the electrode fingers 412 located in that region. However, even if the difference in pitch between adjacent electrodes is 1.5% or less, if it is clear that a constant pitch is not intended when comprehensively determining the pitch change trend in the region including the adjacent electrodes, the adjacent electrodes do not need to be considered to be constant.

[0037] The electrode fingers 412 located on the boundary between the first region 71 and the second region 72 may be interpreted as being included in both the first region and the second region. Similarly, the electrode fingers 412 located on the boundary between a central region (described later) and the regions on both sides of the central region may be interpreted as being included in the central region.

[0038] The elastic wave resonator 1 of this embodiment uses a plate wave as the main mode. The resonance characteristics of the plate wave are highly dependent on the thickness of the piezoelectric layer 2. On the other hand, the resonance of the plate wave is less affected by differences in the pitch of the electrode fingers 412. Therefore, in this embodiment, the elastic wave resonator 1 uses a plate wave, and all of the electrode fingers 412 located in the first region 71 have different pitches. This makes it possible to maintain relatively good resonance in the main mode due to the plate wave while effectively reducing resonance in spurious modes due to unwanted waves. Note that using a plate wave as the main mode means that the main mode of the elastic wave excited by the IDT electrode 4 is a plate wave.

[0039] 2, the first region 71 may occupy half or more of the area of ​​the electrode finger arrangement region 7. With such a configuration, the region where the pitch of the electrode fingers 412 is different becomes dominant, and it is possible to more effectively reduce the occurrence of spurious signals with large phases.

[0040] 2 , the vicinity of the center of the electrode finger arrangement region 7 in the arrangement direction of the electrode fingers 412 may belong to the first region 71. Note that the vicinity of the center refers to, for example, the central region when the electrode finger arrangement region 7 is divided into three equal parts in the arrangement direction of the electrode fingers 412.

[0041] 3, the entire electrode finger arrangement region 7 may belong to the first region 71. With this configuration, the proportion of the region where spurious emissions are reduced becomes even larger, and spurious emissions can be reduced more effectively.

[0042] 4A to 4C are diagrams comparing the resonance characteristics of elastic wave resonator 1 according to one embodiment of the present invention with those of an elastic wave resonator according to a comparative example. Fig. 4A is a diagram showing the overall resonance characteristics, Fig. 4B is a diagram showing an enlarged view of resonance due to the main mode, and Fig. 4C is a diagram showing an enlarged view of resonance due to the spurious mode. In the diagrams, the solid line shows the characteristics of the embodiment, and the dotted line shows the characteristics of the comparative example.

[0043] The elastic wave resonator 1 according to one embodiment of the present invention and the elastic wave resonator according to a comparative example are designed as follows: Example (piezoelectric layer: LN, IDT electrode: Al, pitch: 2.12 μm to 2.42 μm, duty d: 0.3) Comparative example (piezoelectric layer: LN, IDT electrode: Al, pitch: 2.18 μm, duty d: 0.3)

[0044] In the design values ​​of the above embodiment, the pitch of 2.12 μm to 2.42 μm means that the pitch increases continuously in one direction from 2.12 μm to 2.42 μm. Since the pitches are different values, in this embodiment, the entire electrode finger arrangement region 7 belongs to the first region 71.

[0045] 4A to 4C , the elastic wave resonator 1 according to the embodiment of the present invention has reduced resonance due to spurious modes compared to the elastic wave resonator according to the comparative example, while the resonance due to the main mode has smaller loss than the spurious modes, and still maintains favorable characteristics.

[0046] The pitches of the electrode fingers 412 located in the first region 71 are not particularly limited as long as they are different from one another. For example, the pitches of the electrode fingers 412 located in the first region 71 may increase by the same amount or rate in the first direction (the arrangement direction of the electrode fingers 412).

[0047] For example, if there is variation in the amount or rate of increase in the pitch of the multiple electrode fingers 412 located in the first region 71, a portion with a small pitch difference will be included, and the intensity of the spurious at the frequency corresponding to that portion will be large. On the other hand, if the pitches of the multiple electrode fingers 412 increase by the same amount or rate, the pitch differences will be uniform, and the waveform of the resonance due to the spurious mode can be effectively broadened. This can reduce the impact on the pass characteristics of the filter, for example.

[0048] 5 is a diagram showing the pitch difference required to express a frequency difference of 50 MHz in a resonator having an antiresonant frequency of 4600 MHz to 4950 MHz. The vertical axis represents the value of 100×(Pmax−Pmin) / Pmax, where Pmax is the largest pitch among the plurality of electrode fingers 412 located in the first region 71, and Pmin is the smallest pitch. The horizontal axis represents the value of the duty d of the electrode fingers 412 located in the first region 71. Each plot represents the change in LN thickness in the range of 0.47 μm to 0.5 μm.

[0049] For example, the pitch of the electrode fingers 412 located in the first region 71 may be 100×(Pmax−Pmin) / Pmax≧3.0. With this configuration, the difference between the maximum pitch and the minimum pitch of the electrode fingers 412 located in the first region 71 becomes 50 MHz or more, so that the resonant waveform due to the spurious mode can be broadened more effectively. This can reduce the influence on the pass characteristics of the filter, for example.

[0050] In the elastic wave resonator 1 according to one embodiment of the present invention, the piezoelectric layer 2 is described as being made of 120° Y-cut, X-propagating LN. However, this is not limiting. The Euler angles of the piezoelectric layer 2 may be set as appropriate. For example, the Euler angles of the piezoelectric layer 2 may be (0°, θ + (α × 180), 0°) (θ is any value in the range of 0° to 180°, and α is an integer between 0 and 2). When the piezoelectric layer 2 has such an Euler angle, the A1 mode of Lamb waves can be effectively utilized. Furthermore, for example, the piezoelectric layer 2 may be made of Z-cut LN or LT. In this case, thickness shear waves can be effectively utilized, for example.

[0051] In the elastic wave resonator 1 according to one embodiment of the present invention, the thickness of the piezoelectric layer 2 overlapping the first region 71 may be constant in plan view. This configuration reduces the resonance loss of the plate waves used, thereby providing an elastic wave resonator 1 with excellent filter characteristics. Note that the thickness of the piezoelectric layer 2 being constant does not necessarily mean that the thickness is strictly constant; some variation is permitted within a range that does not significantly affect the characteristics of the elastic waves propagating through the piezoelectric layer 2.

[0052] In the elastic wave resonator 1 according to one embodiment of the present invention, the support substrate 3 has the configuration shown in Fig. 1 , but is not limited to this example. For example, as in another embodiment shown in Fig. 6A , the support substrate 3 may have a void 8 on its upper surface. In this case, the piezoelectric layer 2 covers the void 8 of the support substrate 3 in a plan view, leaving a space inside the void 8. The size and depth of the void 8 may be set as appropriate.

[0053] 1 shows an example in which the piezoelectric layer 2 and the support substrate 3 are in direct contact with each other in the elastic wave resonator 1 according to one embodiment of the present invention, but the present invention is not limited to this example. The lower surface 2 b of the piezoelectric layer 2 and the support substrate 3 may be in direct contact with each other, or may be indirectly in contact with each other via, for example, an intermediate layer and an adhesive layer (not shown).

[0054] As such an intermediate layer, silicon oxide (SiO ２ ), silicon nitride (Si ３ N ４ ), aluminum oxide (Al２ O ３ By providing such an insulating intermediate layer, it is possible to reduce the generation of unnecessary potential and unnecessary capacitance, thereby improving the electrical characteristics of the elastic wave resonator 1.

[0055] Furthermore, both an adhesive layer and an intermediate layer may be located between the piezoelectric layer 2 and the support substrate 3. For example, when both an adhesive layer and an intermediate layer are located between the piezoelectric layer 2 and the support substrate 3, the adhesive layer is located between the support substrate 3 and the intermediate layer. An example of such an adhesive layer is amorphous silicon.

[0056] As another example, an alumina film (not shown) may be further disposed between the intermediate layer and the piezoelectric layer 2. The presence of such an alumina film can reduce leakage of elastic waves from the piezoelectric layer 2 to the support substrate 3 side, thereby improving the frequency characteristics of the elastic wave resonator 1.

[0057] 6B shows a schematic cross-sectional view of an elastic wave resonator 1 according to yet another embodiment. In the embodiment shown in FIG. 6B, a multilayer film 5 may be located between the piezoelectric layer 2 and the support substrate 3. The multilayer film 5 is formed by alternately stacking low acoustic impedance layers 51 and high acoustic impedance layers 52. The acoustic impedance of the low acoustic impedance layer 51 is lower than the acoustic impedance of the piezoelectric layer 2, and the acoustic impedance of the high acoustic impedance layer 52 is higher than the acoustic impedance of the low acoustic impedance layer 51. For example, the low acoustic impedance layer 51 may be made of silicon oxide (SiO ２ ), and the high acoustic impedance layer 52 is hafnium oxide (HfO ２ )

[0058] In the acoustic wave resonator 1 according to one embodiment of the present invention, the duty d of the electrode fingers 412 located in the first region 71 may be constant. Because the pitches of the electrode fingers 412 located in the first region 71 are different from one another, when the value of the duty d of the electrode fingers 412 located in the first region 71 is constant, the possibility of spurious emissions due to unexpected resonance is reduced compared to when the duty d is different, and spurious emissions can be effectively reduced. For example, the value of the duty d of the electrode fingers 412 located in the first region 71 is 0.6 or less. Note that a constant value of the duty d does not necessarily mean that the value is strictly constant; some variation is allowed within a range of, for example, 0.01 or less.

[0059] In the acoustic wave resonator 1 according to one embodiment of the present invention, the thickness of the electrode fingers 412 located in the first region 71 may be constant, or may be set to a different thickness for each electrode finger 412 as appropriate.

[0060] In the acoustic wave resonator 1 according to a preferred embodiment of the present invention, the first region 71 may occupy more than half the area of ​​the electrode finger arrangement region 7. However, this is not limiting. For example, the number of electrode fingers 412 located in the first region 71 may be more than half the total number of the electrode fingers 412 located in the electrode finger arrangement region 7. With this configuration, the region where the pitch of the electrode fingers 412 is different becomes dominant, and the occurrence of spurious signals can be more effectively reduced.

[0061] There is no particular limitation on the specific number of electrode fingers 412 located in the first region 71. Theoretically, the number is three or more, forming a pitch of two or more, and in practice, the number may be, for example, five or more, ten or more, thirty or more, fifty or more, or one hundred or more.

[0062] In the elastic wave resonator 1 according to one embodiment of the present invention, the pitches of all the electrode fingers 412 in the first region 71 may be different from one another. However, this is not limiting. For example, when the electrode finger arrangement region 7 is divided into three equal parts, in the central region, the pitch of the electrode fingers 412 may increase toward one side in the first direction (the arrangement direction of the electrode fingers 412). In this case, the central region may include a portion where the pitch is constant. From another perspective, in part or all of the central region, the pitch may increase in stages (step-like) rather than continuously. Even in this case, the broadening effect and other effects can still be obtained.

[0063] The number of pitch changes in the central region is not particularly limited. Theoretically, the number of changes is 1 or more, and in practice, the number may be, for example, 5 or more, 10 or more, 30 or more, 50 or more, or 100 or more.

[0064] 7 is a circuit diagram schematically illustrating the configuration of an elastic wave filter 101 as an example of using the elastic wave resonator 1. As can be seen from the reference numerals in the upper left corner of the figure, the comb-like electrode 41 is represented by a two-pronged fork shape, and the reflector 42 is represented by a single line bent at both ends.

[0065] The acoustic wave filter 101 filters a signal input from an input terminal 102 and outputs the filtered signal to an output terminal 103 .

[0066] The acoustic wave filter 101 is configured as, for example, a ladder filter in which multiple resonators are connected in a ladder configuration. That is, the acoustic wave filter 101 has multiple (or one) resonators (series resonators) connected in series between an input terminal 102 and an output terminal 103, and multiple (or one) resonators (parallel resonators) connecting the series line to a reference potential.

[0067] At least one of the resonators included in the acoustic wave filter 101 of this preferred embodiment is the acoustic wave resonator 1 of this preferred embodiment. For convenience, a resonator formed of the acoustic wave resonator 1 will be referred to as a first acoustic wave resonator 11.

[0068] The acoustic wave filter 101 further includes a second acoustic wave resonator 12. For example, when the first acoustic wave resonator 11 and the second acoustic wave resonator 12 are series resonators, the anti-resonance frequency of the second acoustic wave resonator 12 may be closer to the pass band of the acoustic wave filter 101 than the anti-resonance frequency of the first acoustic wave resonator 11.

[0069] In the IDT electrode 4 of the first acoustic wave resonator 11, the largest pitch among the electrode fingers 412 located in the first region 71 is defined as P1max, and the smallest pitch among the electrode fingers of the IDT electrode 4 of the second acoustic wave resonator 12 is defined as P2max, and the smallest pitch among the electrode fingers of the IDT electrode 4 of the second acoustic wave resonator 12 is defined as P2min. In this case, the acoustic wave filter 101 may be designed so that (P2max-P2min) is smaller than (P1max-P1min).

[0070] With this configuration, the second acoustic wave resonator 12 has a smaller pitch difference than the first acoustic wave resonator 11. Generally, a resonator with a smaller pitch difference has smaller resonance loss in the main mode than a resonator with a larger pitch difference. Therefore, by positioning the anti-resonance frequency of the second acoustic wave resonator 12, which has a smaller pitch difference than the first acoustic wave resonator 11, between the anti-resonance frequency of the first acoustic wave resonator 11 and the pass band of the acoustic wave filter 101, it is possible to reduce main mode loss in resonators located near the pass band of the filter. Therefore, an acoustic wave filter with very steep filter characteristics can be provided.

[0071] Furthermore, when the first acoustic wave resonator 11 and the second acoustic wave resonator 12 are parallel resonators, the resonant frequency of the second acoustic wave resonator 12 may be closer to the pass band of the acoustic wave filter 101 than the resonant frequency of the first acoustic wave resonator 11. In this case, the acoustic wave filter 101 may be designed so that (P2max−P2min) is smaller than (P1max−P1min).

[0072] With this configuration, the second acoustic wave resonator 12 has a smaller pitch difference than the first acoustic wave resonator 11. Therefore, the anti-resonance frequency of the second acoustic wave resonator 12, which has a smaller pitch difference than the first acoustic wave resonator 11, is located between the anti-resonance frequency of the first acoustic wave resonator 11 and the pass band of the acoustic wave filter 101, thereby reducing loss in the main mode of the resonator located near the pass band of the filter. This makes it possible to provide an acoustic wave filter with very steep filter characteristics.

[0073] Furthermore, when the acoustic wave filter 101 is a band elimination filter, the maximum phase of the spurious response originating from the first acoustic wave resonator 11 and present in the pass band of the acoustic wave filter 101 may be equal to or less than −70°. For example, the maximum phase of the spurious response originating from the first acoustic wave resonator 11 and present in the pass band of the acoustic wave filter 101 may be in the range of −80° to −70°.

[0074] With this configuration, spurious signals with small phases are positioned within the passband of the acoustic wave filter 101, thereby reducing the influence of spurious signals on the filter.

[0075] Although the acoustic wave filter 101 is a ladder filter in the above example, the present invention is not limited to this example. For example, the acoustic wave filter 101 may be a multimode filter (including a double-mode filter). The multimode filter includes a plurality of IDT electrodes 4 arranged in the propagation direction of acoustic waves and a pair of reflectors 42 arranged on both sides of the IDT electrodes 4.

[0076] 8 is a block diagram showing essential parts of a communication device 111 as an example of using the acoustic wave resonator 1 and the acoustic wave filter 101. The communication device 111 performs wireless communication using radio waves and includes a duplexer 116. The duplexer 116 includes a transmit filter 101a and a receive filter 101b. At least one of the transmit filter 101a and the receive filter 101b is formed by the acoustic wave filter 101. The output side of the transmit filter 101a and the input side of the receive filter 101b are both connected to an antenna 112.

[0077] 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 a carrier frequency) by an 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 a bandpass filter 115a, amplified by an amplifier 114a, and input to a branching filter 116 (transmission filter 101a). The branching filter 116 (transmission filter 101a) then removes unwanted components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS to an antenna 112. The antenna 112 converts the input electrical signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

[0078] Furthermore, in the communication device 111, a radio signal (radio wave) received by the antenna 112 is converted by the antenna 112 into an electrical signal (received signal RS) and input to the duplexer 116. The duplexer 116 (receive filter 101b) removes unnecessary components outside the receive passband from the input received signal RS and outputs the signal to the amplifier 114b. The output received signal RS is amplified by the amplifier 114b, and unnecessary components outside the receive 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 (baseband 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 this embodiment, a relatively high-frequency passband (e.g., 5 GHz or higher) 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 exemplified in FIG. 8 , other appropriate circuit methods may be used, such as a double superheterodyne method. Furthermore, FIG. 8 schematically illustrates only the essential components, and 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 2b: Lower surface 3: Support substrate 4: IDT electrode 41: Interdigital electrode 411: Bus bar 412: Electrode finger 42: Reflector 5: Multilayer film layer 7: Electrode finger arrangement region 71: First region 72: Second region 8: Gap 11: First acoustic wave resonator 12: Second acoustic wave resonator 101: Acoustic wave filter 102: Input terminal 103: Output terminal 111: Communication device 112: Antenna 113: RF-IC 114a, 114b: Amplifier 115a, 115b: Bandpass filter

Claims

1. A piezoelectric layer having piezoelectricity; an IDT electrode located on a first surface of the piezoelectric layer and having a plurality of electrode fingers arranged in a first direction; having the plurality of electrode fingers are entirely located in an electrode finger arrangement region, If the distance in the first direction from one side of one electrode finger to the one side of an electrode finger adjacent to the one electrode finger is defined as the pitch of the one electrode finger, the electrode finger arrangement region has a first region in which all the electrode fingers have different pitches; The electrode finger arrangement region is configured to utilize a plate wave or a bulk wave as an elastic wave propagating therethrough. Elastic wave resonator.

2. the first region occupies half or more of the area of ​​the electrode finger arrangement region; 2. The elastic wave resonator according to claim 1.

3. a portion of the electrode finger arrangement region near a center in the first direction belongs to the first region; 2. The elastic wave resonator according to claim 1.

4. the entire electrode finger arrangement region belongs to the first region; 2. The elastic wave resonator according to claim 1.

5. the pitches of the electrode fingers located in the first region increase at the same increment or rate in the first direction; 2. The elastic wave resonator according to claim 1.

6. Among the pitches of the plurality of electrode fingers located in the first region, the largest pitch is denoted as Pmax and the smallest pitch is denoted as Pmin, 100×(Pmax−Pmin) / Pmax≧3.0; 2. The elastic wave resonator according to claim 1.

7. The elastic wave is a plate wave and is a Lamb wave A1 mode.

2. The elastic wave resonator according to claim 1.

8. The elastic wave is a bulk wave and a thickness shear wave.

2. The elastic wave resonator according to claim 1.

9. The width of one electrode finger in the first direction is defined as the width of the one electrode finger, If the width / pitch is defined as the duty d of one electrode finger, then A duty d of the plurality of electrode fingers located in the first region is constant.

2. The elastic wave resonator according to claim 1.

10. In the plurality of electrode fingers located in the first region, the duty d is 0.6 or less. The elastic wave resonator according to claim 9 .

11. The thickness of the plurality of electrode fingers located in the first region is constant.

2. The elastic wave resonator according to claim 1.

12. In a plan view, a thickness of the piezoelectric layer overlapping with the first region is constant.

2. The elastic wave resonator according to claim 1.

13. If λ is defined as twice the largest pitch among the pitches of the plurality of electrode fingers located in the first region, then The thickness of the piezoelectric layer is 2λ or less. The elastic wave resonator according to claim 12.

14. A piezoelectric layer having piezoelectricity; an IDT electrode located on a first surface of the piezoelectric layer and having a plurality of electrode fingers arranged in a first direction; having the plurality of electrode fingers are entirely located in an electrode finger arrangement region, If the distance in the first direction from one side of one electrode finger to the one side of an electrode finger adjacent to the one electrode finger is defined as the pitch of the one electrode finger, In a central region when the electrode finger arrangement region is divided into three equal parts in the first direction, the pitch of the electrode fingers becomes larger toward one side. Elastic wave resonator.

15. a plurality of series arm resonators including the elastic wave resonator according to any one of claims 1 to 14 and a second elastic wave resonator, the series arm resonators being connected in series; a parallel arm resonator connected in parallel to the series arm resonator; A ladder type acoustic wave filter having an anti-resonance frequency of the second acoustic wave resonator is located closer to a pass band of the acoustic wave filter than an anti-resonance frequency of the acoustic wave resonator; and Among pitches of a plurality of electrode fingers of an IDT electrode of the elastic wave resonator, the largest pitch is defined as P1max and the smallest pitch is defined as P1min, Among the pitches of the electrode fingers of the IDT electrode of the second acoustic wave resonator, the maximum pitch is defined as P2max and the minimum pitch is defined as P2min. (P2max-P2min) is smaller than (P1max-P1min) Elastic wave filters.

16. A series arm resonator connected in series; an elastic wave resonator according to any one of claims 1 to 14; and a plurality of parallel arm resonators including a second elastic wave resonator, the parallel arm resonators being connected in parallel to the series arm resonator; A ladder type acoustic wave filter having a resonant frequency of the second acoustic wave resonator is closer to a pass band of the acoustic wave filter than a resonant frequency of the acoustic wave resonator; Among pitches of a plurality of electrode fingers of an IDT electrode of the elastic wave resonator, the largest pitch is defined as P1max and the smallest pitch is defined as P1min, Among the pitches of the electrode fingers of the IDT electrode of the second acoustic wave resonator, the maximum pitch is defined as P2max and the minimum pitch is defined as P2min. (P2max-P2min) is smaller than (P1max-P1min) Elastic wave filters.

17. An elastic wave filter having the elastic wave resonator according to any one of claims 1 to 14, a maximum phase of a spurious component originating from the acoustic wave resonator and existing in a passband of the acoustic wave filter is −70° or less; Elastic wave filters.

18. The antenna, an acoustic wave filter connected to the antenna; an IC connected to the acoustic wave filter; The acoustic wave filter includes an acoustic wave resonator according to any one of claims 1 to 14. Communications equipment.