Elastic wave resonator and communication device

Abstract

To provide an elastic wave resonator having excellent filter characteristics.SOLUTION: An elastic wave resonator includes: a piezoelectric layer having piezoelectricity and including a first face and a second face opposite to the first face; an IDT electrode located on the first face and including a plurality of electrode fingers; and an acoustic reflective layer located on the second face side and including a low-acoustic-impedance layer having acoustic impedance lower than that of the piezoelectric layer. The elastic wave resonator satisfies a relationship of 0.14≤(Ra1 / T)×100, where Ra1 is an arithmetic average roughness of at least a portion of surfaces of the plurality of electrode fingers in plan view, and T is a thickness of the plurality of electrode fingers, and is configured to use, as main resonance, a Lamb wave excited by the IDT electrode and propagating through the piezoelectric layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] The present invention discloses an acoustic wave device including a support substrate, an acoustic reflection layer formed on the support substrate, a piezoelectric layer formed on the acoustic reflection layer, and an IDT electrode formed on the upper or lower surface of the piezoelectric layer, and the acoustic reflection layer includes a low acoustic impedance layer and a high acoustic impedance layer having a higher acoustic impedance than the low acoustic impedance layer. With this configuration, plate waves propagating in the piezoelectric layer are reflected by the acoustic reflection layer, and the acoustic wave energy is trapped in the piezoelectric layer, allowing the plate waves to propagate through the piezoelectric layer with high energy intensity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5648695 Summary of the Invention [Problem to be solved by the invention]

[0004] In the acoustic wave device described in Patent Document 1, the acoustic reflection layer confines not only the main mode acoustic waves but also unwanted waves that cause spurious responses in the piezoelectric layer, resulting in increased spurious response intensity. [Means for solving the problem]

[0005] (1) An elastic wave resonator according to one embodiment of the present invention comprises a piezoelectric layer having piezoelectricity and having a first surface and a second surface opposite to the first surface, an IDT electrode located on the first surface and having a plurality of electrode fingers, and an acoustic reflection layer located on the second surface side and including a low acoustic impedance layer having an acoustic impedance lower than that of the piezoelectric layer, wherein the elastic wave resonator satisfies the relationship 0.14≦(Ra1 / T)×100, where Ra1 is the arithmetic mean roughness of at least a portion of the surface of the plurality of electrode fingers in a planar view, and T is the thickness of the plurality of electrode fingers, and is configured to utilize, as a primary resonance, a Lamb wave excited by the IDT electrode and propagating through the piezoelectric layer.

[0006] (2) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described above in (1), and has Ra1 of 0.20 nm or more.

[0007] (3) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in (1) or (2) above, wherein the acoustic reflection layer further includes a high acoustic impedance layer having a higher acoustic impedance than the low acoustic impedance layer, and the acoustic reflection layer is configured by alternately stacking a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers.

[0008] (4) An elastic wave resonator according to an embodiment of the present invention is the elastic wave resonator according to any one of (1) to (3) above, further comprising a support having a void that is located on the surface opposite to the first surface of the piezoelectric layer and that is covered by the piezoelectric layer with an internal space provided at a position that overlaps with a plurality of electrode fingers in a plan view. The substrate may further comprise a substrate, and the low acoustic impedance layer may be a gas present in the gap.

[0009] (5) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (4) above, which further satisfies the relationship (Ra1 / T)×100≦8.6.

[0010] (6) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (5) above, which further satisfies the relationship (Ra1 / T)×100≦1.4.

[0011] (7) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (6) above, which further satisfies the relationship (Ra1 / T)×100≦0.93.

[0012] (8) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (7) above, wherein Ra1 is 12 nm or less.

[0013] (9) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (8) above, in which Ra1 is 2.0 nm or less.

[0014] (10) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (9) above, wherein Ra1 is 1.3 nm or less.

[0015] (11) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator described in any one of (1) to (10) above, in which the Lamb wave is in the A1 mode.

[0016] (12) An elastic wave resonator according to one embodiment of the present invention is an elastic wave resonator as set forth in any one of (1) to (11) above, in which the thickness of the piezoelectric layer is 2λ or less, where λ is defined as twice the repeat pitch of multiple electrode fingers.

[0017] (13) An elastic wave resonator according to one embodiment of the present invention is an elastic wave resonator as described in any one of (1) to (12) above, wherein the first thickness of the piezoelectric layer in a portion that overlaps with a plurality of electrode fingers in a planar view is greater than the second thickness of the piezoelectric layer in a portion that does not overlap with a plurality of electrode fingers in a planar view.

[0018] (14) An elastic wave resonator according to one embodiment of the present invention is an elastic wave resonator as described in any one of (1) to (13) above, in which, when the arithmetic mean roughness of the first surface of the piezoelectric layer in a portion that does not overlap with the plurality of electrode fingers in a planar view is Ra2, Ra2 is greater than Ra1.

[0019] (15) An elastic wave resonator according to one embodiment of the present invention is the elastic wave resonator according to any one of the above (1) to (14), wherein Ra1 is a value of the surface roughness of the plurality of electrode fingers in a plan view. It is the arithmetic mean roughness.

[0020] (16) A communication device according to one embodiment of the present invention has an antenna, an acoustic wave filter connected to the antenna, and an IC connected to the acoustic wave filter, and the acoustic wave filter includes an acoustic wave resonator according to any one of (1) to (15) above. [Effects of the Invention]

[0021] According to the above configuration, it is possible to provide an elastic wave resonator and a communication device having excellent frequency characteristics. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of an elastic wave resonator according to a preferred embodiment of the present invention. [Figure 2] 1 is a schematic plan view of an elastic wave resonator according to a preferred embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view of an elastic wave resonator according to a preferred embodiment of the present invention. [Figure 4]10A and 10B are diagrams illustrating simulation results of resonance characteristics of an elastic wave resonator according to one embodiment of the present invention and a comparative example. [Figure 5] FIG. 10 is a graph showing the change in average |S| when the arithmetic mean roughness of the surface of the electrode finger is changed. [Figure 6] 10 is a diagram showing changes in the phase of spurious signals located on the higher frequency side than the main resonance when the arithmetic mean roughness of the electrode finger surfaces is changed relative to the thickness of the electrode fingers. [Figure 7] FIG. 10 is a schematic cross-sectional view of an elastic wave resonator according to another preferred embodiment of the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view of an elastic wave resonator according to another preferred embodiment of the present invention. [Figure 9] FIG. 10 is a schematic cross-sectional view of an elastic wave resonator according to another preferred embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view of an elastic wave resonator according to another preferred embodiment of the present invention. [Figure 11] FIG. 10 is a schematic plan view of an elastic wave resonator according to another preferred embodiment of the present invention. [Figure 12] 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 invention. [Figure 13] 1 is a block diagram showing a configuration of a main part of a communication device as an example of using an elastic wave resonator according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] An acoustic wave resonator and a communication device according to an embodiment of the present invention 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.

[0024] For convenience, the drawings may be illustrated with a Cartesian coordinate system consisting of an X-axis, a Y-axis, and a Z-axis. In the elastic wave resonator 1 according to an embodiment of the present 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 an elastic wave used as the primary resonance among the elastic waves propagating through the piezoelectric layer 2 (described later). The Y-axis is defined to be parallel to the top surface of the piezoelectric layer 2 and perpendicular to the X-axis. The Z-axis is defined to be perpendicular to the top surface of the piezoelectric layer 2.

[0025] 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.

[0026] 1 is a schematic cross-sectional view of an acoustic wave resonator 1 according to one embodiment of the present invention. As shown in FIG. 1, the acoustic wave resonator 1 according to one embodiment of the present invention includes a piezoelectric layer 2, an acoustic reflection layer 5, a support substrate 3, and an IDT electrode 4.

[0027] 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. 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.

[0028] Various piezoelectric materials can be used for the piezoelectric layer 2. Examples of piezoelectric materials include a single crystal of lithium tantalate (LiTaO3; hereinafter referred to as LT) and a single crystal of lithium niobate (LiNbO3; hereinafter referred to as LN). In this embodiment, specifically, the piezoelectric layer 2 is made of a single crystal of LT.

[0029] The piezoelectric layer 2 has piezoelectric properties, and when a high-frequency signal is applied to the IDT electrode 4 (described later), an elastic wave propagating through the piezoelectric layer 2 is excited. The type of elastic wave to be used as the main resonance may be determined according to desired frequency characteristics, etc. For example, the elastic wave used as the main resonance may be a plate wave. Examples of plate waves include Lamb waves and SH waves. The elastic wave used as the main resonance may also be a mixture of multiple types of elastic waves. Specifically, in the elastic wave resonator 1 of the embodiment, the elastic wave used as the main resonance includes a Lamb wave.

[0030] The thickness of the piezoelectric layer 2 may be appropriately designed depending on the desired frequency characteristics and the type of elastic wave used as the primary resonance. Specifically, in this embodiment, the thickness of the piezoelectric layer 2 is 2λ or less, expressed using a wavelength λ described below. By setting the thickness of the piezoelectric layer 2 to 2λ or less, for example, Lamb waves can be effectively used as the primary resonance.

[0031] Furthermore, in a plan view, the thickness of the piezoelectric layer 2 in the region overlapping with the IDT electrode 4 (described later) may be constant. With such a configuration, for example, when Lamb waves are used as the main resonance, the loss of Lamb wave resonance is reduced, and an elastic wave resonator 1 with good frequency characteristics can be provided. Note that the thickness of the piezoelectric layer 2 being constant does not necessarily mean that it is strictly constant, and some variation is allowed within a range that does not significantly affect the characteristics of the elastic waves propagating through the piezoelectric layer 2.

[0032] The propagation mode of the elastic waves used in the elastic wave resonator 1 according to one embodiment of the present invention is not particularly limited and may be set according to the desired frequency characteristics. The Euler angles (φ, θ, ψ) of the piezoelectric single crystal used for the piezoelectric layer 2 may be appropriately designed according to the type and propagation mode of the elastic waves used as the primary resonance. For example, if the piezoelectric layer 2 is made of LT, the A1 mode of Lamb waves can be effectively used as the primary resonance by setting the Euler angles (φ, θ, ψ) to (0°±10°, 0° to 55°, 0°±10°). Furthermore, if the piezoelectric layer 2 is made of LN, the A1 mode of Lamb waves can be effectively used as the primary resonance by setting the Euler angles (φ, θ, ψ) to (0°±10°, 0° to 55°, 0°±10°). Specifically, in this embodiment, the propagation mode of the Lamb wave used as the main resonance is the A1 mode, and the Euler angles (φ, θ, ψ) of the LT are (0°, 24°, 0°).

[0033] The support substrate 3 is located on the underside of the piezoelectric layer 2 and the acoustic reflection layer 5, which will be described later, and supports the piezoelectric layer 2 and the acoustic reflection layer 5. 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.

[0034] The material of the support substrate 3 is not particularly limited. For example, the material of the support substrate 3 may be a material with 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 materials for the support substrate 3 include sapphire (Al2O3), silicon carbide (SiC), and silicon (Si). In the embodiment, specifically, the support substrate 3 is Si.

[0035] The acoustic reflection layer 5 is located between the piezoelectric layer 2 and the support substrate 3. The acoustic reflection layer 5 has at least a low acoustic impedance layer 51. The acoustic impedance of the low acoustic impedance layer 51 is lower than the acoustic impedance of the piezoelectric layer 2. By thus locating the low acoustic impedance layer 51 on the lower surface 2b side of the piezoelectric layer 2, the acoustic waves propagating through the piezoelectric layer 2 are reflected by the low acoustic impedance layer 51 and confined within the piezoelectric layer 2, thereby reducing leakage of the acoustic waves from the lower surface 2b side. An example of such a low acoustic impedance layer 51 is silicon oxide (SiO2). In this embodiment, the low acoustic impedance layer 51 is specifically made of SiO2.

[0036] 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. The IDT electrode 4 can be made of various conductive materials, such as aluminum (Al), copper (Cu), platinum (Pt), molybdenum (Mo), gold (Au), or alloys thereof. The IDT electrode 4 may also be made by laminating multiple layers made of the various conductive materials described above. When the IDT electrode 4 is made by laminating multiple layers, an underlayer may be interposed at the interface between the layers. In this embodiment, the IDT electrode 4 is made of Al.

[0037] 2 shows a schematic diagram of the shape of the IDT electrode 4 when the acoustic wave resonator 1 according to this embodiment is viewed in plan from the Z-axis direction. As shown in FIG. 2, the IDT electrode 4 includes a pair of interdigital transducers 41.

[0038] The comb-shaped electrode 41 includes, for example, a pair of bus bars 411 and a plurality of electrode fingers 412 extending from the bus bars 411. The plurality of 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. The comb-shaped electrode 41 may also include a plurality of dummy electrode fingers 413. The dummy electrode fingers 413 protrude from one bus bar 411 between the plurality of electrode fingers 412 and face the electrode fingers 412 extending from the other bus bar 411.

[0039] 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. Note that the IDT electrode 4 may be apodized, in which the lengths of the electrode fingers 412 in the Y-axis direction (or, from another perspective, the overlap width) vary depending on the position in the X-axis direction.

[0040] The repetition interval of the electrode fingers 412 is defined as the pitch P, and the width of the electrode fingers 412 is defined as the width W. The pitch P and the width W are designed appropriately according to the desired frequency characteristics. In FIG. 2, the repetition interval of the electrode fingers 412 is constant, but this is not limiting. For example, the repetition interval of the electrode fingers 412 may be designed to gradually increase, or may be designed to have multiple repetition intervals in stages. When there are multiple repetition intervals of the electrode fingers 412, the average value of the repetition intervals may be defined as the pitch P, or the largest pitch may be defined as the pitch P.

[0041] When a high-frequency signal is applied to the IDT electrode 4, an acoustic wave with a wavelength λ, which is defined as twice the pitch P of the electrode fingers 412, is excited and propagates through the piezoelectric layer 2. The resonance frequency fr of the acoustic wave resonator 1 is approximately equal to the frequency of the acoustic wave used as the main resonance among the excited acoustic waves. The anti-resonance frequency fa is determined by the resonance frequency fr and the capacitance ratio, which is mainly determined by the piezoelectric layer 2 and can be adjusted by the number of electrode fingers 412, the overlap width, the film thickness, etc.

[0042] In acoustic wave resonator 1 according to this preferred embodiment, the thickness of multiple electrode fingers 412 is defined as thickness T. The thickness of electrode finger 412 refers to the distance from the end of electrode finger 412 on the piezoelectric substrate side in the Z-axis direction to surface 71, which will be described later. The thickness of electrode finger 412 does not need to be strictly constant; for example, the thickness may be measured at several points near the center of electrode finger 412 in the X-axis direction, and the average of these values ​​may be defined as thickness T.

[0043] The acoustic wave resonator 1 in this preferred embodiment may further include a pair of reflectors 42 on the upper surface 2a of the piezoelectric layer 2. The pair of reflectors 42 are located on both sides of the interdigital electrode 41 in the X-axis direction. The reflector 42 includes a pair of reflector bus bars 421 facing each other and a plurality of strip electrodes 422 extending between the pair of reflector bus bars 421.

[0044] FIG. 3 is a schematic diagram illustrating a cross section of an acoustic wave resonator 1 according to this embodiment. In this embodiment, if the arithmetic mean roughness of a surface 71 of the plurality of electrode fingers 412 of the IDT electrode 4 is defined as Ra1, Ra1 is greater than 0 nm. In other words, the surface 71 of the electrode fingers 412 has a predetermined roughness. Note that in this specification, the arithmetic mean roughness refers to the arithmetic mean roughness (Ra) defined in JIS B 0601:2013. Note that the surface 71 refers to the surface of the electrode fingers 412 located opposite the piezoelectric layer 2.

[0045] In the elastic wave resonator 1 of this embodiment, the low acoustic impedance layer 51 located on the lower surface 2b side of the piezoelectric layer 2 confines not only the elastic waves used for the main resonance but also unwanted elastic waves that cause spurious emissions within the piezoelectric layer 2. Therefore, in the elastic wave resonator 1 of this embodiment, the surface 71 of the electrode fingers 412 has a predetermined roughness, so that, for example, unwanted waves confined within the piezoelectric layer 2 propagate through the electrode fingers 412 and are scattered when reflected by the surface 71, thereby reducing spurious emissions. Note that the effects of the elastic wave resonator 1 of this embodiment are not limited to those described above.

[0046] Furthermore, in the elastic wave resonator 1 according to this embodiment, the surface 71 of the electrode fingers 412 has a predetermined roughness, which, for example, causes the weight of the electrode fingers to vary from part to part of the electrode fingers 412, thereby shifting the frequency of the excited unwanted waves, thereby reducing spurious emissions. While the resonance characteristics of Lamb waves depend on the thickness of the piezoelectric layer 2, they are less affected by the design of the electrode fingers 412. Therefore, when the elastic wave resonator 1 according to this embodiment uses Lamb waves as the primary resonance, for example, spurious emissions can be reduced more effectively. Note that the effects of the elastic wave resonator 1 according to this embodiment are not limited to those described above.

[0047] 4A is a graph showing simulated resonance characteristics in the frequency range of 4100 MHz to 5700 MHz of elastic wave resonators in Example 1, in which the Ra1 value is 0.8 nm, Example 2, in which the Ra1 value is 1.4 nm, and Example 3, in which the Ra1 value is 6.8 nm. Also shown in FIG. 4A is the simulated resonance characteristics of an elastic wave resonator in Comparative Example 1, in which the Ra1 value is 0 nm, as a comparative example.

[0048] 4B to 4D show enlarged views of the resonance characteristics shown in FIG. 4A, particularly the resonance characteristics of the main resonance. FIG. 4B is a diagram comparing the resonance characteristics of the main resonance of Example 1 and Comparative Example 1. FIG. 4C is a diagram comparing the resonance characteristics of the main resonance of Example 2 and Comparative Example 1. FIG. 4D is a diagram comparing the resonance characteristics of the main resonance of Example 3 and Comparative Example 1.

[0049] As shown in FIGS. 4B to 4D, Examples 1 to 3, in which Ra1 is greater than 0 nm, can reduce spurious emissions within the main resonance band compared to Comparative Example 1, in which Ra1 is 0 nm. Furthermore, Examples 1 to 3 can reduce spurious emissions located on the high-frequency side of the main resonance compared to Comparative Example 1. This can reduce spurious signals.

[0050] 4E is a diagram showing the resonance characteristics of Example 2 and Comparative Example 1 using a Smith chart. In the Smith chart, two intersections of the graph with a first center line extending horizontally of the circle indicate the resonance characteristics at the resonance frequency (fr) and the anti-resonance frequency (fa), respectively. In addition, in the Smith chart, the graph portion located above the first center line of the circle indicates the resonance characteristics within the band.

[0051] In a Smith chart, if the distance from the center of a circle to the graph is defined as |S|, then the better the resonance characteristics, the closer |S| is to the radius of the circle. In other words, the better the resonance characteristics, the closer the value of |S| is to 1. On the other hand, when spurious signals occur, |S| approaches 0. Therefore, in a Smith chart, the resonance characteristics can be evaluated by calculating the average |S|, which is the average value of |S| within a band. For example, the closer the average |S| is to 1, the smaller the influence of spurious signals and the better the resonance characteristics. In acoustic wave resonator 1 according to this embodiment, the resonance characteristics are evaluated by calculating the average |S| in the range of (fr-40 MHz) to (fa+40 MHz).

[0052] In the elastic wave resonator 1 according to this embodiment, the arithmetic mean roughness Ra1 of the surface 71 of the electrode finger 412 is greater than 0 nm, but may be, for example, 0.20 nm or greater. Fig. 5 is a graph showing the change in average |S| when the thickness T of the electrode finger 412 is 140 nm and the arithmetic mean roughness Ra1 of the surface 71 of the electrode finger 412 is changed from 0.010 nm to 15 nm in the elastic wave resonator 1 according to this embodiment. The horizontal axis represents the Ra1 value in logarithmic notation; for example, the larger the value on the horizontal axis, the larger the roughness of the surface 71 of the electrode finger 412. The vertical axis represents the average |S| in the range of (fr - 40 MHz) to (fa + 40 MHz); for example, the larger the value on the vertical axis, the better the resonance characteristics.

[0053] 5, when the value of Ra1 is 0.20 nm or more, the average |S| value is large and the resonance characteristics are good. Therefore, in the acoustic wave resonator 1 according to this embodiment, by setting Ra1 to 0.20 or more, spurious components can be reduced and good frequency characteristics can be obtained.

[0054] 5, thickness T of electrode finger 412 is 140 nm, and therefore, when the value of Ra1 (0.20 nm) is expressed as a ratio to thickness T of electrode finger 412, it becomes 0.14%. Therefore, acoustic wave resonator 1 according to this embodiment can reduce spurious and obtain good frequency characteristics when Ra1 and thickness T satisfy the relationship shown in formula (1) below.

[0055] 0.14≦(Ra1 / T)×100 (1) Furthermore, in the elastic wave resonator 1 according to this embodiment, Ra1 may be 12 nm or less. As shown in FIG. 5 , when the value of Ra1 exceeds 12 nm, the average |S| value decreases rapidly, and the resonance characteristics deteriorate. On the other hand, when the value of Ra1 is 12 nm or less, the average |S| value remains high. Therefore, in the elastic wave resonator 1 according to this embodiment, by setting Ra1 to 12 nm or less, spurious responses can be reduced and good frequency characteristics can be obtained.

[0056] 5, thickness T of electrode finger 412 is 140 nm, and therefore, when the value of Ra1 (12 nm) is expressed as a ratio to thickness T of electrode finger 412, it is 8.6%. Therefore, acoustic wave resonator 1 according to this embodiment can reduce spurious and obtain good frequency characteristics when Ra1 and thickness T satisfy the relationship shown in formula (2) below.

[0057] (Ra1 / T)×100≦8.6 (2) Furthermore, in the acoustic wave resonator 1 according to this embodiment, Ra1 may be 2.0 nm or less. FIG. 6 is a graph showing changes in the phase of spurious signals located on the higher frequency side than the main resonance when the value of Ra1 is changed relative to the thickness T. The horizontal axis represents the value of Ra1 in logarithmic notation. The vertical axis represents the phase of spurious signals located on the higher frequency side than the main resonance, with the magnitude of the spurious signals increasing as the value on the vertical axis increases. In other words, the magnitude of the spurious signals increases downward in FIG. 6, and the frequency characteristics deteriorate.

[0058] 6, when the value of Ra1 is 0.20 nm or more, the phase of the spurious signals located on the higher frequency side than the main resonance becomes small. On the other hand, when the value of Ra1 exceeds 2.0 nm, the phase of the spurious signals located on the higher frequency side than the main resonance becomes large. Therefore, in the elastic wave resonator 1 according to this embodiment, by setting Ra1 to 2.0 nm or less, the phase of the spurious signals located on the higher frequency side can be reduced, resulting in even better frequency characteristics.

[0059] 6, thickness T of electrode finger 412 is 140 nm, and therefore, when the value of Ra1 (2.0 nm) is expressed as a ratio to thickness T of electrode finger 412, it becomes 1.4%. Therefore, in acoustic wave resonator 1 according to this embodiment, when Ra1 and thickness T satisfy the relationship shown in formula (3) below, the phase of spurious components located on the high frequency side can be reduced, and better frequency characteristics can be obtained.

[0060] (Ra1 / T)×100≦1.4 (3) Furthermore, in the acoustic wave resonator 1 according to this embodiment, Ra1 may be 1.3 nm or less. When the value of Ra1 is 1.3 nm or less, the phase of the spurious component located on the higher frequency side than the main resonance can be further reduced, as shown in Fig. 6, thereby achieving better frequency characteristics.

[0061] 6, thickness T of electrode finger 412 is 140 nm, and therefore, when the value of Ra1 (1.3 nm) is expressed as a ratio to thickness T of electrode finger 412, it is 0.93%. Therefore, acoustic wave resonator 1 according to this embodiment can further reduce spurious and obtain better frequency characteristics when Ra1 and thickness T satisfy the relationship shown in formula (4) below.

[0062] (Ra1 / T)×100≦0.93 (4) 1 shows an example in which the piezoelectric layer 2 and the acoustic reflection layer 5 are in direct contact with each other, but the present invention is not limited to this example. For example, in another embodiment of the present invention, the lower surface 2b of the piezoelectric layer 2 and the acoustic reflection layer 5 may be in indirect contact with each other via an intermediate layer, an adhesive layer, or the like.

[0063] Examples of such intermediate layers include insulating materials such as silicon nitride (Si3N4) and aluminum oxide (Al2O3). By providing an insulating intermediate layer, it is possible to reduce the generation of unnecessary potential and unnecessary capacitance, thereby improving the electrical characteristics of the acoustic wave resonator 1. Examples of adhesive layers include amorphous silicon. Both the adhesive layer and the intermediate layer may be present, or only one of them may be present.

[0064] In the elastic wave resonator 1 according to one embodiment of the present invention shown in Fig. 1, the acoustic reflection layer 5 has only one low acoustic impedance layer 51, but this is not limiting. For example, as another embodiment of the present invention, as shown in Fig. 7A, the acoustic reflection layer 5 may have a plurality of low acoustic impedance layers 51 and a plurality of layers each having an acoustic impedance higher than that of the low acoustic impedance layer 51. The high acoustic impedance layers 52 may be alternately stacked.

[0065] By configuring the acoustic reflection layer 5 in this manner, acoustic waves leaking from the lower surface 2b side 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 acoustic waves. Examples of such high acoustic impedance layer 52 include hafnium oxide (HfO2), tantalum oxide (Ta2O5), and zirconium oxide (ZrO2).

[0066] Although the acoustic wave resonator 1 according to one embodiment of the present invention shown in FIG. 1 has been described as an example in which the low acoustic impedance layer 51 of the acoustic reflection layer 5 is a solid layer, this is not limiting. For example, as another embodiment of the present invention, as shown in FIG. 7B , the low acoustic impedance layer 51 may be a gas present in a void 8 provided in the support substrate 3. The void 8 is on the piezoelectric layer 2 side of the support substrate 3 and is located at a position overlapping with the plurality of electrode fingers 412 in plan view. The void 8 is covered by the piezoelectric layer 2, leaving an internal space in which a gas is present. The gas may be ordinary air or an inert gas such as nitrogen or argon.

[0067] By configuring the low acoustic impedance layer 51 in this manner, the gas present in the voids 8 acts as an acoustic reflection layer, effectively reducing the leakage of acoustic waves from the lower surface 2b side of the piezoelectric layer 2. The size and depth of the voids 8 may be set as appropriate.

[0068] In the acoustic wave resonator 1 according to one embodiment of the present invention shown in FIG. 3 , the thickness of the piezoelectric layer 2 is constant. However, this is not limiting. The thickness of the piezoelectric layer 2 may vary. For example, in another embodiment of the present invention, as shown in FIG. 8 , the thickness L1 of the first region 21 of the piezoelectric layer 2 may be greater than the thickness L2 of the second region 22 of the piezoelectric layer 2. The first region refers to the region of the piezoelectric layer 2 that overlaps with the electrode fingers 412 in a planar view. The second region refers to the region of the piezoelectric layer 2 that does not overlap with the electrode fingers 412 in a planar view. Note that the thickness of the piezoelectric layer 2 may gradually change at the boundary between the first region 21 and the second region 22.

[0069] In an acoustic wave resonator 1 according to a preferred embodiment of the present invention, the arithmetic mean roughness of the upper surface 2 a of the piezoelectric layer 2 may be set as appropriate. For example, in another preferred embodiment of the present invention, as shown in Fig. 9 , the arithmetic mean roughness Ra2 of the upper surface 2 a in the second region 22 of the piezoelectric layer 2 may be rougher than the arithmetic mean roughness Ra1 of the surfaces 71 of the electrode fingers 412. With this configuration, unwanted waves trapped in the piezoelectric layer 2 are scattered when reflected by the upper surface 2 a in the second region 22, thereby reducing spurious emissions.

[0070] In the acoustic wave resonator 1 according to one embodiment of the present invention shown in FIG. 3 , the side surfaces 72 of the electrode fingers 412 are perpendicular to the upper surface 2 a of the piezoelectric layer 2, but this is not limiting. For example, in another embodiment of the present invention, the side surfaces 72 of the electrode fingers 412 may be inclined in the X-axis direction, as shown in FIG. 10 . In this case, the cross section of the electrode fingers 412 perpendicular to the Y-axis has a trapezoidal shape. The side surfaces 72 refer to surfaces that connect the surfaces of the electrode fingers 412 facing the piezoelectric layer 2 to the surface 71.

[0071] 10, the roughness of the side surface 72 is omitted, but the arithmetic mean roughness Ra3 of the side surface 72 may be set appropriately. For example, the arithmetic mean roughness Ra3 of the side surface 72 may be the same as the arithmetic mean roughness Ra1 of the surface 71.

[0072] In the elastic wave resonator 1 according to one embodiment of the present invention, the surface 71 of all of the plurality of electrode fingers 412 has a predetermined roughness. However, the present invention is not limited to this example. The surface 71 of only some of the plurality of electrode fingers 412 may have a predetermined roughness. 11A, the surfaces 71 of only the electrode fingers 412 (hatched portions) located near both ends in the arrangement direction (X-axis direction) among the plurality of electrode fingers 412 may have a predetermined roughness. In this case, the arithmetic mean roughness of the surfaces 71 of the electrode fingers 412 located near the center in the X-axis direction among the plurality of electrode fingers 412 is different from the arithmetic mean roughness of the surfaces 71 of the electrode fingers 412 located near both ends. With this configuration, it is possible to effectively reduce spurious emissions while suppressing deterioration in the characteristics of the main resonance.

[0073] Although the elastic wave resonator 1 according to one embodiment of the present invention has been described with reference to an example in which the entire surface 71 of one electrode finger 412 has a predetermined roughness, this is not limiting. The surface 71 of only a portion of the electrode finger 412 may have a predetermined roughness. For example, as another embodiment of the present invention, as shown in FIG. 11B , in an intersection region 9 where an electrode finger 412 intersects with an adjacent electrode finger 412, the surface 71 near both ends (hatched portions) in the extension direction (Y-axis direction) may have a predetermined roughness. In this case, the arithmetic mean roughness of the surface 71 near the center in the Y-axis direction in the intersection region of the electrode fingers 412 is different from the arithmetic mean roughness of the surface 71 near both ends. This configuration effectively reduces spurious emissions while suppressing deterioration of the main resonance characteristics.

[0074] (Example of use of acoustic wave resonator 1: duplexer) 12 is a circuit diagram schematically illustrating the configuration of a duplexer 101 as an example of the use of acoustic wave resonator 1. As can be seen from the symbols in the upper left corner of the figure, in this figure, comb-shaped electrode 41 is schematically illustrated as a two-pronged fork shape, and reflector 42 is represented by a single line bent at both ends.

[0075] 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.

[0076] For example, the acoustic wave resonator 1 according to an embodiment of the present disclosure may be used as at least one of the transmit filter 105 and the receive filter 106. Alternatively, the acoustic wave resonator 1 may be used as both the transmit filter 105 and the receive filter 106.

[0077] The transmit filter 105 and the receive filter 106 are each configured, for example, as a ladder filter in which a plurality of resonators are connected in a ladder configuration. That is, the transmit filter 105 has a plurality of resonators (or one resonator) connected in series between the transmit terminal 103 and the antenna terminal 102, and a plurality of resonators (or one resonator) (parallel arm) connecting the series line (series arm) to a reference potential.

[0078] 12 is merely an example of the configuration of duplexer 101, and is not limited to the configuration shown in FIG. 12. For example, transmit filter 105 may be configured as a multimode filter. Also, in FIG. 12, both transmit filter 105 and receive filter 106 are acoustic wave filters, but this configuration is not limiting. For example, one of transmit filter 105 and receive filter 106 may be an acoustic wave filter using acoustic wave resonator 1, and the other may be an LC filter including one or more inductors and one or more capacitors.

[0079] Although the description has been given of a case in which demultiplexer 101 includes transmit filter 105 and receive filter 106, demultiplexer 101 is not limited to this configuration. For example, demultiplexer 101 may be a diplexer or a multiplexer including three or more filters.

[0080] In addition, as a filter constituting branching filter 101, an elastic wave resonator is used instead of elastic wave resonator 1. A child 11 may also be used.

[0081] (Example of use of acoustic wave resonator 1: communication device) 13 is a block diagram showing a main part of a communication device 111 as an example of using acoustic wave resonator 1 (branching filter 101). Communication device 111 includes branching filter 101 and performs wireless communication using radio waves.

[0082] In 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 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 branching filter 101 (transmission terminal 103). Branching filter 101 (transmission filter 105) then removes unwanted components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from antenna terminal 102 to antenna 112. Antenna 112 converts the input electrical signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

[0083] Furthermore, in the communication device 111, a radio signal (radio wave) received by the antenna 112 is converted by the antenna 112 into an electric signal (received signal RS) and input to the duplexer 101 (antenna terminal 102). The duplexer 101 (receive filter 106) removes unnecessary components outside the receive passband from the input received signal RS and outputs the signal from the receive terminal 104 to the amplifier 114b. The output received signal RS is amplified by the amplifier 114b, and the 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 become a received information signal RIS.

[0084] The transmission information signal TIS and the reception 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. Although the circuit method in FIG. 13 illustrates a direct conversion method, it is not limited to this example and may also be a double superheterodyne method, for example. Furthermore, FIG. 13 schematically illustrates only the essential parts, and low-pass filters or isolators may be added at appropriate positions, and the positions of amplifiers and the like may be changed. [Explanation of symbols]

[0085] 1: Elastic wave resonator 2: Piezoelectric layer 2a:Top surface 2b: Bottom surface 21:First area 22:Second area 3: Support substrate 4:IDT electrode 41:Comb-shaped electrode 411: Busbar 412: Electrode finger 42:Reflector 5: Acoustic reflective layer 51: Low acoustic impedance layer 52: High acoustic impedance layer 71: Surface 72: Side 8:Void 9: Intersection area 101: Duplexer 102: Antenna terminal 103: Transmit terminal 104: Receiving terminal 111:Communication equipment 112: Antenna 113: RF-IC 114: Amplifier 115: Bandpass filter

Claims

1. a piezoelectric layer having piezoelectricity and having a first surface and a second surface opposite to the first surface; an IDT electrode located on the first surface and having a plurality of electrode fingers; an acoustic reflection layer located on the second surface side and including a low acoustic impedance layer having an acoustic impedance lower than that of the piezoelectric layer; Equipped with When the arithmetic mean roughness of at least a part of the surfaces of the plurality of electrode fingers in a plan view is Ra1 and the thickness of the plurality of electrode fingers is T, The relationship 0.14≦(Ra1 / T)×100 is satisfied, a Lamb wave excited by the IDT electrode and propagating through the piezoelectric layer is utilized as a primary resonance. Elastic wave resonator.

2. a piezoelectric layer having piezoelectricity and having a first surface and a second surface opposite to the first surface; an IDT electrode located on the first surface and having a plurality of electrode fingers; an acoustic reflection layer located on the second surface side and including a low acoustic impedance layer having an acoustic impedance lower than that of the piezoelectric layer; Equipped with When the arithmetic mean roughness of at least a part of the surfaces of the plurality of electrode fingers in a plan view is defined as Ra1, Ra1 is 0.20 nm or more, a Lamb wave excited by the IDT electrode and propagating through the piezoelectric layer is utilized as a primary resonance. Elastic wave resonator.

3. the acoustic reflection layer further includes a high acoustic impedance layer having an acoustic impedance higher than that of the low acoustic impedance layer, The acoustic reflection layer is configured by alternately stacking a plurality of the low acoustic impedance layers and a plurality of the high acoustic impedance layers.

3. The elastic wave resonator according to claim 1.

4. The low acoustic impedance layer is a gas.

3. The elastic wave resonator according to claim 1.

5. Further satisfying the relationship of (Ra1 / T)×100≦8.6, 3. The elastic wave resonator according to claim 1.

6. Further satisfying the relationship of (Ra1 / T)×100≦1.4, 3. The elastic wave resonator according to claim 1.

7. Further satisfying the relationship of (Ra1 / T)×100≦0.93, 3. The elastic wave resonator according to claim 1.

8. The Ra1 is 12 nm or less.

3. The elastic wave resonator according to claim 1.

9. The Ra1 is 2.0 nm or less.

3. The elastic wave resonator according to claim 1.

10. The Ra1 is 1.3 nm or less.

3. The elastic wave resonator according to claim 1.

11. The Lamb wave is in A1 mode.

3. The elastic wave resonator according to claim 1.

12. When λ is defined as twice the repeat pitch of the plurality of electrode fingers, the thickness of the piezoelectric layer is 2λ or less.

3. The elastic wave resonator according to claim 1.

13. a first thickness of the piezoelectric layer at a portion overlapping with the plurality of electrode fingers in a plan view is greater than a second thickness of the piezoelectric layer at a portion not overlapping with the plurality of electrode fingers in a plan view; 3. The elastic wave resonator according to claim 1.

14. When the arithmetic mean roughness of the first surface of the piezoelectric layer in a portion that does not overlap with the plurality of electrode fingers in a plan view is Ra2, the Ra2 is larger than the Ra1.

3. The elastic wave resonator according to claim 1.

15. The Ra1 is the arithmetic mean roughness of the entire surface of the plurality of electrode fingers in a plan view.

3. The elastic wave resonator according to claim 1.

16. The antenna and an acoustic wave filter connected to the antenna; an IC connected to the acoustic wave filter, The acoustic wave filter includes the acoustic wave resonator according to claim 1 or 2. Communication equipment.

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