Elastic wave device, communication device, piezoelectric substrate, and method for manufacturing piezoelectric substrate

Abstract

The purpose of the present invention is to improve performance of an elastic wave device. This elastic wave device comprises: a piezoelectric substrate including a monocrystal piezoelectric body, and having a first surface; and a plurality of IDT electrodes positioned on the first surface. The piezoelectric substrate has a first region and a second region thicker than the first region. On the first surface side, the crystallinity of the second region is higher than the crystallinity of the first region. The plurality of IDT electrodes include a first IDT electrode positioned in the first region and a second IDT electrode positioned in the second region. The elastic wave device has a series resonator and a parallel resonator constituting a ladder-type filter. The series resonator has the first IDT electrode, and the parallel resonator has the second IDT electrode.

Description

Acoustic wave device, communication device, piezoelectric substrate, and method for manufacturing piezoelectric substrate

[0001] The following disclosure relates to acoustic wave devices.

[0002] Patent Document 1 listed below discloses an example of the configuration of an elastic wave device.

[0003] Japan Special Table No. 2018-506930

[0004] An elastic wave device according to one aspect of the present disclosure is an elastic wave device including a piezoelectric substrate having a first surface including a single-crystal piezoelectric body, and a plurality of IDT electrodes located on the first surface, wherein the piezoelectric substrate has a first region and a second region thicker than the first region, and on the first surface side, the crystallinity of the second region is higher than that of the first region, and the plurality of IDT electrodes include a first IDT electrode located on the first region and a second IDT electrode located on the second region, and the elastic wave device has series resonators and parallel resonators that form a ladder-type filter, and the series resonators have the first IDT electrode, and the parallel resonators have the second IDT electrode.

[0005] An elastic wave device according to one aspect of the present disclosure is an elastic wave device including a piezoelectric substrate including a single-crystal piezoelectric body and having a first surface, and a plurality of IDT electrodes located on the first surface, wherein the piezoelectric substrate has a first region and a second region thicker than the first region, and on the first surface side, the surface roughness of the second region is smaller than the surface roughness of the first region, and the plurality of IDT electrodes include a first IDT electrode located on the first region and a second IDT electrode located on the second region, and the elastic wave device has series resonators and parallel resonators that form a ladder-type filter, and the series resonators have the first IDT electrode, and the parallel resonators have the second IDT electrode.

[0006] A piezoelectric substrate according to one aspect of the present disclosure includes a single-crystal piezoelectric material and has a first surface, the piezoelectric substrate having a first region and a second region that is thicker than the first region, and on the first surface side, the crystallinity of the second region is higher than the crystallinity of the first region.

[0007] A piezoelectric substrate according to one aspect of the present disclosure includes a single-crystal piezoelectric body and has a first surface, the piezoelectric substrate having a first region and a second region that is thicker than the first region, and on the first surface side, the surface roughness of the second region is smaller than the surface roughness of the first region.

[0008] A method for manufacturing a piezoelectric substrate according to one aspect of the present disclosure is a method for manufacturing a piezoelectric substrate including a single-crystal piezoelectric body, and includes the steps of forming a first region by dry etching and forming a second region thicker than the first region by CMP finishing.

[0009] 1 shows an example of a configuration of an elastic wave device according to a first embodiment; 2 shows an example of a frequency filter having a series resonator and a parallel resonator; 3 shows a schematic plan view of an elastic wave device according to a first embodiment; 4 shows an enlarged view of the vicinity of a first region in the elastic wave device according to the first embodiment; 5 shows an example of a rocking curve in the

[111] direction for an IDT electrode; 6 shows an example of a TEM image; 7 shows an example of the results of an EDS analysis; 8 shows an example of the results of an FFT analysis of a TEM image; 9 shows an example of a surface state obtained by surface treatment of a piezoelectric body; 10 shows an example of a configuration of an elastic wave device according to a second embodiment; 11 shows an example of a configuration of a communication device according to a third embodiment.

[0010] [Embodiment 1] Embodiment 1 will be described below. For convenience of explanation, components having the same functions as those described in Embodiment 1 will be denoted by the same reference numerals in the following embodiments, and their descriptions will not be repeated. For brevity, descriptions of well-known technical matters will be omitted as appropriate. Each component, material, and numerical value described in this specification is merely exemplary unless there is a contradiction in the content. Therefore, unless there is a contradiction in the content, for example, the positional relationship and connection relationship of each component are not limited to the examples in each figure. Furthermore, each figure is not necessarily drawn to scale. In this specification, unless there is a particular contradiction, the notation "A to B" for two numbers A and B means "greater than or equal to A and less than or equal to B."

[0011] (Configuration Example of Elastic Wave Device 100) Fig. 1 shows a configuration example of an elastic wave device 100 according to a first embodiment. Fig. 1 shows a schematic front view of the layer structure of the elastic wave device 100. The elastic wave device 100 according to the first embodiment includes a plurality of elastic wave resonators 1. The elastic wave resonators 1 are also referred to as elastic wave elements.

[0012] For convenience of explanation, the present specification introduces a Cartesian coordinate system (D1-D2-D3 coordinate system) shown in FIG. 1 . The D1 direction in the example of embodiment 1 is the propagation direction of an elastic wave propagating within piezoelectric substrate 4 of elastic wave device 100. In the example of embodiment 1, multiple electrode fingers 32 in elastic wave device 100 are arranged in the D1 direction. The D1 direction may also be referred to as a first direction.

[0013] The D2 direction is an example of a direction intersecting the D1 direction. In the example of embodiment 1, the electrode fingers 32 extend in the D2 direction. The D2 direction may also be referred to as the second direction. The D3 direction is the thickness direction of each portion of the acoustic wave device 100. In this specification, the positive direction of the D3 direction is described as the upward direction. Therefore, the negative direction of the D3 direction is the downward direction. The D3 direction may also be referred to as the third direction.

[0014] The elastic wave device 100 includes a series resonator 1S and a parallel resonator 1P as a plurality of elastic wave resonators 1. The series resonators 1S and the parallel resonators 1P can be connected to each other to form any frequency filter. For the sake of clarity, the example in FIG. 1 shows one series resonator 1S and one parallel resonator 1P.

[0015] The acoustic wave device 100 includes a piezoelectric substrate 4 including a single crystal piezoelectric material. Examples of the material of the piezoelectric material include lithium tantalate (LiTaO ３ :LT) or lithium niobate (LiNbO ３ In the first embodiment, the piezoelectric substrate 4 is mainly an LN layer.

[0016] The cut angle of the piezoelectric body can be set appropriately. As an example, the cut angle of LN may be set to 100° to 120°. The cut angle in this specification refers to the Y-cut X-propagation cut angle. The X-axis and Y-axis are the crystal orientation axes of the piezoelectric body.

[0017] For example, "100° Y-cut X-propagating LN" means "an LN cut by a plane having the X-axis as the central axis and an axis rotated 100° from the Y-axis as the normal, when the X-axis direction is the propagation direction of the elastic wave." The X-axis and Y-axis may be related to the D1 to D3 directions. For example, the direction of the X-axis may coincide with the D1 direction. However, the X-axis and Y-axis do not have to be related to the D1 to D3 directions.

[0018] The piezoelectric substrate 4 has a first surface S1. In the first embodiment, the first surface S1 is a surface that supports an IDT (Interdigital Transduce) electrode 3, which will be described below. The piezoelectric substrate 4 has a first region REG1 and a second region REG2 that is different from the first region REG1. In the example of FIG. 1, the thickness of the second region REG1 is greater than the thickness of the first region REG1. Therefore, the piezoelectric substrate 4 in the example of FIG. 1 has a step portion DS that connects the first region REG1 and the second region REG2.

[0019] The first region REG1 and the second region REG can be formed by performing a predetermined surface treatment on the piezoelectric body. As an example, the first region REG1 can be formed by performing dry etching on a part of the piezoelectric body. An example of dry etching is trimming using Ar ions (hereinafter referred to as Ar ion trimming).

[0020] On the other hand, the second region REG may be formed by performing a surface treatment other than dry etching on another portion of the piezoelectric body. This makes it possible to obtain the second region REG having a surface condition different from that of the first region REG1. As an example, the second region REG2 may be formed by performing a CMP (Chemical Mechanical Polishing) finish on another portion of the piezoelectric body.

[0021] Therefore, in the first embodiment, a case is illustrated in which the first region REG1 is a region that has been dry-etched, and the second region REG2 is a region that has been finished by CMP. As is clear from the above, the manufacturing method of the piezoelectric substrate 4 can include the steps of forming the first region REG1 by dry etching and forming the second region REG2 by CMP. The manufacturing method can further include the step of forming a step portion DS.

[0022] By forming the first region REG1 and the second region REG2 according to this manufacturing method, for example, the crystallinity of the second region REG2 on the first surface S1 side can be higher than the crystallinity of the first region REG1. This is because CMP finishing is a surface treatment that is less likely to destroy the crystalline structure of the processing object (e.g., a piezoelectric body) than Ar ion trimming.

[0023] Furthermore, by forming the first region REG1 and the second region REG2 according to this manufacturing method, the surface roughness of the second region REG2 on the first surface S1 side can be smaller than the surface roughness of the first region REG1. The relationship between the surface treatment technique and the surface roughness will be described later (see FIG. 9).

[0024] The acoustic wave device 100 includes a plurality of IDT electrodes 3. The IDT electrodes 3 excite acoustic waves. For this reason, the IDT electrodes 3 are also referred to as excitation electrodes. In the first embodiment, the IDT electrodes 3 are configured to excite plate waves.

[0025] The multiple IDT electrodes 3 are each located on the first surface S1. Each of the multiple acoustic wave resonators 1 has an individual IDT electrode 3. In other words, in the acoustic wave device 100, the individual IDT electrodes 3 constitute the individual acoustic wave resonators 1.

[0026] Each IDT electrode 3 has a plurality of electrode fingers 32. In the example of embodiment 1, each of the plurality of electrode fingers 32 is located on the first surface S1 of the piezoelectric substrate 4 and is spaced apart from one another in the direction D1. Specifically, each of the plurality of electrode fingers 32 is alternately and repeatedly located on the first surface S1 at a generally constant interval (pitch) in the direction D1.

[0027] The acoustic wave device 100 includes a first IDT electrode 3 a and a second IDT electrode 3 b that is different from the first IDT electrode 3 a as the multiple IDT electrodes 3. In the example of FIG. 1 , the first IDT electrode 3 a is located on a first region REG1, while the second IDT electrode 3 b is located on a second region REG2.

[0028] In the first embodiment, the series resonator 1S has the first IDT electrode 3a, and the parallel resonator 1P has the second IDT electrode 3b. In other words, the first IDT electrode 3a constitutes the series resonator 1S, and the second IDT electrode 3b constitutes the parallel resonator 1P.

[0029] 1 , the acoustic wave device 100 may include a support substrate 6 that supports each component of the acoustic wave device 100. Examples of materials for the support substrate 6 include Si. The acoustic wave device 100 may include an acoustic reflection film 5 located below the piezoelectric substrate 4. The acoustic reflection film 5 may be located between the piezoelectric substrate 4 and the support substrate 6.

[0030] 1 has a laminated structure of low acoustic impedance layers 5 a and high acoustic impedance layers 5 b. As an example, the acoustic reflecting film 5 may be a multilayer film in which the low acoustic impedance layers 5 a and the high acoustic impedance layers 5 b are alternately laminated.

[0031] For example, the low acoustic impedance layer 5a may have an acoustic impedance lower than that of the piezoelectric substrate 4. Examples of the low acoustic impedance layer 5a include SiO ２ On the other hand, the high acoustic impedance layer 5b only needs to have a higher acoustic impedance than the low acoustic impedance layer 5a. Examples of materials for the high acoustic impedance layer 5b include HfO ２ Examples include:

[0032] In the example of Fig. 1, a unit consisting of one low acoustic impedance layer 5a and one high acoustic impedance layer 5b is represented as a laminate unit UN. In the example of Fig. 1, the acoustic reflecting film 5 has two laminate units UN. Therefore, the acoustic reflecting film 5 in Fig. 1 has two low acoustic impedance layers 5a and two high acoustic impedance layers 5b.

[0033] 2 shows an example of a frequency filter FIL including a series resonator 1S and a parallel resonator 1P. In the first embodiment, an example is shown in which the elastic wave device 100 includes the frequency filter FIL. In the example of FIG. 2, the frequency filter FIL is configured as a ladder filter by two series resonators 1S and one parallel resonator 1P.

[0034] In the example of Fig. 2, one of the two series resonators 1S is designated as series resonator 1S-1, and the other is designated as series resonator 1S-2. In the example of Fig. 2, the two series resonators 1S are located in a series arm SL. The series resonator 1S-1 is connected to an input terminal Pin of the frequency filter FIL. On the other hand, the series resonator 1S-2 is connected to an output terminal Pout of the frequency filter FIL.

[0035] 2, the parallel resonator 1P is located in the parallel arm PL. The parallel arm PL extends from a node located between the series resonators 1S-1 and 1S-2 in the series arm SL to the ground terminal GND. Therefore, the parallel resonator 1P is connected to this node and the ground terminal GND.

[0036] Fig. 3 shows a schematic plan view of the elastic wave device 100. In the example of the elastic wave device 100 shown in Fig. 3, the first region REG1 is located on the outer edge of the elastic wave device 100. On the other hand, the second region REG2, which is thicker than the first region REG1, is located on the inner side of the elastic wave device 100.

[0037] 3, the first region REG1 surrounds the second region REG2. In this manner, the second region REG2 may be an island-type region surrounded by the first region REG1.

[0038] When the second region REG2 is an island-type region, for example, the risk of resist residue accumulating in the corners of the acoustic wave device 100 can be reduced during the process of forming the first region REG1 and the second region REG2.

[0039] 4 shows an enlarged view of the vicinity of first region REG1 in elastic wave device 100. IDT electrode 3 may contain Al as a primary component. Therefore, for example, IDT electrode 3 (more specifically, electrode fingers 32) may have an Al layer 35. The Al layer 35 may be any layer that contains Al as a primary component. Therefore, Al layer 35 may contain trace amounts of metal components other than Al. For example, Al layer 35 may contain a trace amount of Cu.

[0040] The IDT electrode 3 (more specifically, the electrode fingers 32) may have an underlayer 36 located between the Al layer 35 and the first surface S1. The underlayer 36 in the example of FIG. 4 is thinner than the Al layer 35. The material of the underlayer 36 may be Ti. Therefore, the underlayer 36 may be a Ti layer.

[0041] As will be described later, when the first region REG1 is formed by dry etching (e.g., Ar ion trimming) of the piezoelectric body, a heterogeneous layer may be generated in a part of the first region REG1. The heterogeneous layer can be distinguished from other regions belonging to the first region REG1 by differences in crystallinity. In this specification, the region other than the heterogeneous layer in the first region REG1 is referred to as the residual region. In the example of FIG. 4, reference numeral 4q denotes the heterogeneous layer, and reference numeral 4r denotes the residual region.

[0042] In this manner, the piezoelectric substrate 4 may have a heterogeneous layer 4q and a residual region 4r. As described above, the crystallinity of the heterogeneous layer 4q may be different from that of the residual region 4r. Therefore, the composition of the heterogeneous layer 4q may be different from that of the residual region 4r.

[0043] Therefore, for example, based on an image of the piezoelectric substrate 4 and its surroundings obtained by a certain analytical method, it is possible to determine whether or not a heterogeneous layer 4q exists in a part of the piezoelectric substrate 4. Examples of analytical methods include EDS (Energy Dispersive X-ray Spectroscopy) and TEM (Transmission Electron Microscope).

[0044] Region AR in Fig. 4 is an example of a region that includes part of the IDT electrode 3 and part of the piezoelectric substrate 4. Within region AR in the example of Fig. 4, part of the Al layer 35, part of the underlayer 36, part of the heterogeneous layer 4q, and part of the remaining region 4r are located.

[0045] (First Consideration) In the manufacturing process of acoustic wave device 100, after the piezoelectric substrate 4 is formed, the IDT electrode 3 is generally formed on the first surface S1 of the piezoelectric substrate 4. For this reason, it is thought that, for example, the surface condition of the piezoelectric substrate 4 may affect some properties of the IDT electrode 3. The inventors considered that the surface condition of the piezoelectric substrate 4 may affect the orientation of Al, which is the main component of the IDT electrode 3.

[0046] Therefore, as a first example, the inventors prepared LN with a cut angle of 105° that had not been subjected to Ar ion trimming as the piezoelectric substrate 4. Specifically, the inventors prepared LN with a cut angle of 105° that had been subjected to CMP finishing as the piezoelectric substrate 4.

[0047] The inventors formed a Ti layer with a thickness of 60 Å on the LN, and then further formed an Al layer with a thickness of 1500 Å on the Ti layer, thereby forming the IDT electrode 3. The inventors then measured the rocking curve of Al for the IDT electrode 3 using a thin film X-ray diffraction apparatus.

[0048] No significant peak was observed in the rocking curve of the first example, which indicates that no specific orientation of Al occurs in the IDT electrode 3 of the first example.

[0049] Next, as a second example, the inventors prepared another piezoelectric substrate 4, an LN substrate with a cut angle of 105° that had been subjected to Ar ion trimming. As in the first example, the inventors formed a Ti layer and an Al layer on the LN substrate to form an IDT electrode 3. Then, the inventors measured the rocking curve of Al for the IDT electrode 3.

[0050] Unlike the rocking curve in the first example, a significant peak was observed in the rocking curve in the second example, which indicates that a specific orientation occurs in the Al in the IDT electrode 3 in the first example.

[0051] FIG. 5 shows an example of a rocking curve in the

[111] direction of the IDT electrode 3 in the second example. The horizontal axis ω of the graph in FIG. 5 represents the incident angle of the X-ray with respect to the IDT electrode 3, which is the sample. The vertical axis of the graph represents the X-ray intensity as a measurement result. In the rocking curve in the example of FIG. 5, a peak exists at ω=18.8°. The half-width of the rocking curve is 5.3°. The rocking curve in FIG. 5 shows that Al is oriented in the

[111] direction in the IDT electrode 3 in the second example.

[0052] As described above, in the first embodiment, Al in the Al layer 35 of the IDT electrode 3 located on the first region REG1 (that is, the first IDT electrode 3a) can be oriented in the

[111] direction.

[0053] (Second Study) The inventors prepared another piezoelectric substrate 4, an LN substrate with a cut angle of 120° that had been subjected to Ar ion trimming. The inventors formed a Ti layer with a thickness of 60 Å on the LN substrate, and then formed an Al layer with a thickness of 1040 Å on the Ti layer, thereby forming an IDT electrode 3. The inventors then captured TEM images of the cross sections of the LN substrate and the IDT electrode 3. The TEM images correspond to the TEM image of the region AR in FIG. 4 described above.

[0054] Fig. 6 shows an example of a TEM image obtained in the second study. As shown in Fig. 6, the heterogeneous layer 4q in the TEM image is represented as a phase of a different color from the remaining region 4r in the TEM image. The thickness of the heterogeneous layer 4q in the example of Fig. 6 is about 2.7 nm.

[0055] Next, the inventors performed EDS analysis on the above-mentioned cross section. FIG. 7 shows an example of the results of EDS analysis in the second study. An example of an EDS image of the cross section is shown on the far left of FIG. 7. An example of a distribution map of O, Al, Ar, Ti, and Nb, among the elements in the cross section, is shown on the right side of the EDS image. The distribution map of a certain element is a contour diagram showing the density of the element at each position. Since it is difficult to detect Li, a light element, using EDS, a distribution map of Li is not shown in FIG. 7.

[0056] As shown in Fig. 7, the heterogeneous layer 4q in the EDS image is also represented as a phase of a different color from the remaining region 4r in the EDS image. In the distribution map in Fig. 7, the portion containing a large amount of Al corresponds to the Al layer, and the portion containing a large amount of Ti corresponds to the Ti layer.

[0057] As shown in Figure 7, the heterogeneous layer 4q contains Ar. The Ar in the heterogeneous layer 4q is derived from Ar ion trimming. As described above, Ar ion trimming is an example of a surface treatment that easily destroys the crystalline structure of the piezoelectric material (LN in the example of Figure 7) that is the treatment target. Therefore, the heterogeneous layer 4q can be formed as an amorphous layer.

[0058] The heterogeneous layer 4q may contain the same type of element as the piezoelectric body. In the example of FIG. 7, the heterogeneous layer 4q is LN, i.e., LiNbO ３ It contains O and Nb as elements of the same kind as those contained in LN. Both O and Nb are constituent elements of LN.

[0059] 7, the oxygen content of the foreign layer 4q is smaller than that of the remaining region 4r, suggesting that Ar ion trimming can cause local depletion of O in the LN.

[0060] 8 shows an example of the results of FFT (Fast Fourier Transform) analysis of the TEM image of region AR. In FIG. 8, examples of the results of FFT analysis are shown for each of regions F1 to F3 in the TEM image.

[0061] Region F1 belongs to the Al layer. The upper right corner of Figure 8 shows the results of FFT analysis of region F1. The results indicate that the Al in the Al layer is oriented in a specific direction. This corresponds to the experimental result above, which shows that the Al is oriented in the

[111] direction.

[0062] Region F2 belongs to the Ti layer. The left side of Figure 8 shows the results of FFT analysis of region F2. The results show that Ti in the Ti layer is oriented in a specific direction.

[0063] Region F3 belongs to the remaining region 4r. The results of FFT analysis of region F3 are shown in the lower right of Fig. 8. The results show that the LNs belonging to the remaining region 4r are oriented in a specific direction.

[0064] (Example of surface state obtained by surface treatment of piezoelectric body) Figure 9 shows an example of the surface state obtained by surface treatment of piezoelectric body. The piezoelectric body in the example of Figure 9 is LT. However, the results shown in the example of Figure 9 are thought to also apply to LN.

[0065] FIG. 9 illustrates CMP finishing and Ar ion trimming as surface treatment techniques. The inventors performed CMP finishing or Ar ion trimming on a 2 μm-thick piezoelectric body and a 10 μm-thick piezoelectric body, respectively. FIG. 9 shows three-dimensional images representing the surface condition of each piezoelectric body after each surface treatment. As can be seen from the three-dimensional images, when CMP finishing is used, the surface roughness of the piezoelectric body can be significantly reduced compared to when Ar ion trimming is used.

[0066] FIG. 9 shows several parameters quantitatively indicating the surface roughness of a piezoelectric body for both CMP finishing and Ar ion trimming. As an example, let us focus on Ra (a parameter indicating the arithmetic mean roughness of the surface) in FIG. 9. In the example of FIG. 9, the Ra obtained by CMP finishing is 0.2 nm. On the other hand, the Ra obtained by Ar ion trimming is 1.2 nm.

[0067] Thus, the Ra obtained by CMP finishing can be less than 0.2 times (i.e., 1 / 5 times) the Ra obtained by Ar ion trimming. In the example of Figure 9, the Ra obtained by CMP finishing is equal to 1 / 6 times the Ra obtained by Ar ion trimming.

[0068] As described above, in the example of embodiment 1, the first region REG1 is a dry-etched region, and the second region REG2 is a CMP-finished region. The second region REG2 is thicker than the first region REG1. Therefore, the first region REG1 corresponds to the combination of "Ar ion trimming, piezoelectric body thickness 2 μm" in the example of FIG. 9. On the other hand, the second region REG2 corresponds to the combination of "CMP-finished, piezoelectric body thickness 10 μm" in the example of FIG. 9.

[0069] In this specification, the Ra of the surface of the first region REG1 on the first surface S1 side is denoted as Ra1. The Ra of the surface of the second region REG2 on the first surface S1 side is denoted as Ra2. As can be understood from the above description of Figure 9, in the example of embodiment 1, Ra2 can be smaller than 0.2 times Ra1.

[0070] As described above, the surface treatment method for the piezoelectric body affects the surface condition of the piezoelectric body. Based on this, the inventors speculate that, for example, the surface roughness of the piezoelectric body may affect the orientation of Al in the IDT electrode 3 formed on the piezoelectric body.

[0071] (Effects) According to the first embodiment, the first region of the piezoelectric substrate can be formed by, for example, dry etching (typically, Ar ion trimming). Meanwhile, the second region, which is thicker than the first region, can be formed by, for example, CMP finishing. By forming the first region and the second region in this manner, the crystallinity of the second region can be made higher than the crystallinity of the first region on the first surface side of the piezoelectric substrate.

[0072] As described above, the first IDT electrode in the first embodiment is an IDT electrode of a series resonator that constitutes a ladder filter. Generally, a series resonator is required to have higher power durability than a parallel resonator. Therefore, in the first embodiment, the first IDT electrode is formed on the first region.

[0073] As described above, the Al in the Al layer of the first IDT electrode can be oriented in, for example, the

[111] direction. That is, by forming the first IDT electrode on the first region, the Al orientation in the first IDT electrode can be improved. The improved Al orientation in the first IDT electrode contributes to improving the power durability of the first IDT electrode. Therefore, according to the first embodiment, a first IDT electrode with high power durability can be realized. As a result, the performance of the acoustic wave device can be improved.

[0074] On the other hand, the second IDT electrode in the first embodiment is an IDT electrode of a parallel resonator that constitutes a ladder-type filter. Parallel resonators do not require the same level of power durability as series resonators. Therefore, in the first embodiment, the second IDT electrode is formed on the second region.

[0075] By forming the first and second regions as described above, the surface roughness of the second region can be made smaller than that of the first region on the first surface side. The second region having a smaller surface roughness contributes to high definition of the second IDT electrode formed on the second region.

[0076] Second Embodiment Fig. 10 shows an example configuration of an elastic wave device 100V according to a second embodiment. Fig. 10 is a counterpart to Fig. 1. The elastic wave device 100V in Fig. 10 is an example configuration of a membrane-type elastic wave device. IDT electrode 3 in elastic wave device 100V may be configured to excite bulk waves, for example.

[0077] The elastic wave device 100V may include a membrane structure having a hollow portion MA surrounded by the piezoelectric substrate 4 and the support substrate 6. Unlike the elastic wave device 100 in the example of FIG. 1 , the elastic wave device 100V does not need to include the acoustic reflection film 5.

[0078] In the elastic wave device 100V, by forming the first IDT electrode on the first region, the first IDT electrode can have high power durability. Therefore, the performance of the elastic wave device according to the second embodiment can also be improved.

[0079] 11 illustrates a configuration example of a communication device 151 according to a third embodiment. The communication device 151 performs wireless communication using radio waves. The communication device 151 may include an acoustic wave device according to an aspect of the present disclosure (e.g., the acoustic wave device 100). For example, the transmit filter 109T and the receive filter 111R in FIG. 11 may each include the acoustic wave device 100 as a frequency filter.

[0080] In the communication device 151, a transmission information signal TIS containing information to be transmitted may be modulated and frequency-raised (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 153, and converted into a transmission signal TS. A bandpass filter 155 may remove unnecessary components from the TS outside the transmission passband. Next, the TS after removing the unnecessary components may be amplified by an amplifier 157 and then input to a transmission filter 109T.

[0081] The transmission filter 109T may remove unnecessary components outside the transmission passband from the transmission signal TS input via the transmission terminal. The transmission filter 109T may output the TS after removing the unnecessary components to the antenna 159 via the antenna terminal ANT. The antenna 159 can convert the TS, which is an electrical signal input to itself, into radio waves as a wireless signal and transmit the radio waves to the outside of the communication device 151.

[0082] The antenna 159 can also convert received external radio waves into a received signal RS, which is an electrical signal. The antenna 159 may input the RS to the receive filter 111R via the antenna terminal ANT. The receive filter 111R may remove unnecessary components outside the receive passband from the input RS. The receive filter 111R may output the received signal RS after the unnecessary components have been removed to the amplifier 161 via the receive terminal. The output RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unnecessary components outside the receive passband from the amplified RS. The RS after the unnecessary components have been removed may be frequency-downshifted and demodulated by the RF-IC 153, and converted into a received information signal RIS.

[0083] The TIS and RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the TIS and RIS may be analog or digitized audio signals. The passband of the radio signals may be set appropriately and may comply with any of various standards.

[0084] [Summary] An elastic wave device according to a first aspect of the present disclosure is an elastic wave device including a piezoelectric substrate that includes a single-crystal piezoelectric body and has a first surface, and a plurality of IDT electrodes located on the first surface, wherein the piezoelectric substrate has a first region and a second region that is thicker than the first region, and on the first surface side, the second region has higher crystallinity than the first region, and the plurality of IDT electrodes include a first IDT electrode located on the first region and a second IDT electrode located on the second region, and the elastic wave device has series resonators and parallel resonators that form a ladder-type filter, and the series resonators have the first IDT electrodes, and the parallel resonators have the second IDT electrodes.

[0085] An elastic wave device according to a second aspect of the present disclosure is an elastic wave device including a piezoelectric substrate having a first surface including a single-crystal piezoelectric body, and a plurality of IDT electrodes located on the first surface, wherein the piezoelectric substrate has a first region and a second region thicker than the first region, and the surface roughness of the second region on the first surface side is smaller than the surface roughness of the first region, and the plurality of IDT electrodes include a first IDT electrode located on the first region and a second IDT electrode located on the second region, and the elastic wave device has series resonators and parallel resonators that form a ladder-type filter, and the series resonators have the first IDT electrode, and the parallel resonators have the second IDT electrode.

[0086] In the elastic wave device according to aspect 3 of the present disclosure, in aspect 1 or 2, when the arithmetic mean roughness of the surface of the first region on the first surface side is denoted as Ra1 and the arithmetic mean roughness of the surface of the second region on the first surface side is denoted as Ra2, Ra2 may be smaller than 0.2 times Ra1.

[0087] In the elastic wave device according to Aspect 4 of the present disclosure, in any one of Aspects 1 to 3, the material of the piezoelectric body may be LN.

[0088] In an elastic wave device according to a fifth aspect of the present disclosure, in the fourth aspect, the cut angle of the LN may be 100° to 120°.

[0089] In the elastic wave device according to a sixth aspect of the present disclosure, in any one of the first to fifth aspects, the IDT electrode may contain Al as a main component.

[0090] In an elastic wave device according to aspect 7 of the present disclosure, in the sixth aspect, the IDT electrode may have an Al layer, and the Al of the Al layer located on the first region may be oriented in the

[111] direction.

[0091] In an elastic wave device according to aspect 8 of the present disclosure, in the seventh aspect, the IDT electrode may have a base layer located between the Al layer and the first surface, and the material of the base layer may be Ti.

[0092] In an elastic wave device according to aspect 9 of the present disclosure, in any one of aspects 1 to 8, the first region may be a dry-etched region, and the second region may be a CMP-finished region.

[0093] In an elastic wave device according to aspect 10 of the present disclosure, in any one of aspects 1 to 9, the first region may have a heterogeneous layer, and the crystallinity of the heterogeneous layer may be different from the crystallinity of the remaining region, which is the region other than the heterogeneous layer in the first region.

[0094] In an elastic wave device according to aspect 11 of the present disclosure, in aspect 10, the heterogeneous layer may be an amorphous layer, and the heterogeneous layer may contain the same type of element as the element contained in the piezoelectric body.

[0095] In the elastic wave device according to Aspect 12 of the present disclosure, in Aspects 10 or 11, the oxygen content of the heterogeneous layer may be lower than the oxygen content of the remaining region.

[0096] In an elastic wave device according to a thirteenth aspect of the present disclosure, in any one of the tenth to twelfth aspects, the heterogeneous layer may contain Ar.

[0097] In an elastic wave device according to a fourteenth aspect of the present disclosure, in any one of the first to thirteenth aspects, the first region may surround the second region.

[0098] In an elastic wave device according to a fifteenth aspect of the present disclosure, in any one of the first to fourteenth aspects, the IDT electrode may be configured to excite a plate wave or a bulk wave.

[0099] An elastic wave device according to aspect 16 of the present disclosure may be any one of aspects 1 to 15, further comprising a support substrate and an acoustic reflection film positioned between the support substrate and the piezoelectric substrate.

[0100] An elastic wave device according to aspect 17 of the present disclosure may have a support substrate in any one of aspects 1 to 15, and the elastic wave device may include a membrane structure having a hollow portion surrounded by the support substrate and the piezoelectric substrate.

[0101] A communication device according to an eighteenth aspect of the present disclosure may include the acoustic wave device according to any one of the first to seventeenth aspects.

[0102] A piezoelectric substrate according to aspect 19 of the present disclosure is a piezoelectric substrate including a single-crystal piezoelectric material and having a first surface, wherein the piezoelectric substrate has a first region and a second region that is thicker than the first region, and on the first surface side, the crystallinity of the second region is higher than the crystallinity of the first region.

[0103] A piezoelectric substrate according to aspect 20 of the present disclosure is a piezoelectric substrate including a single crystal piezoelectric material and having a first surface, wherein the piezoelectric substrate has a first region and a second region that is thicker than the first region, and on the first surface side, the surface roughness of the second region is smaller than the surface roughness of the first region.

[0104] A method for manufacturing a piezoelectric substrate according to aspect 21 of the present disclosure is a method for manufacturing a piezoelectric substrate including a single-crystal piezoelectric body, and includes the steps of forming a first region by dry etching and forming a second region thicker than the first region by CMP finishing.

[0105] [Additional Notes] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. In other words, it should be noted that a person skilled in the art could easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure.

[0106] REFERENCE SIGNS LIST 1 Acoustic wave resonator 1S Series resonator 1P Parallel resonator 3 IDT electrode 4 Piezoelectric substrate 4q Heterogeneous layer 4r Remaining region 5 Acoustic reflection film 6 Support substrate 32 Electrode fingers 36 Underlayer REG1 First region REG2 Second region FIL Frequency filter (ladder type filter) MA Hollow portion 100, 100V Acoustic wave device 151 Communication device

Claims

1. An elastic wave device comprising: a piezoelectric substrate including a single-crystal piezoelectric material and having a first surface; and a plurality of IDT electrodes located on the first surface, wherein the piezoelectric substrate has a first region and a second region thicker than the first region, and on the first surface side, the crystallinity of the second region is higher than that of the first region, and the plurality of IDT electrodes include a first IDT electrode located on the first region and a second IDT electrode located on the second region, and the elastic wave device has series resonators and parallel resonators that form a ladder-type filter, and the series resonators have the first IDT electrodes, and the parallel resonators have the second IDT electrodes.

2. An elastic wave device comprising: a piezoelectric substrate including a single-crystal piezoelectric material and having a first surface; and a plurality of IDT electrodes located on the first surface, wherein the piezoelectric substrate has a first region and a second region thicker than the first region, the surface roughness of the second region on the first surface side is smaller than the surface roughness of the first region, and the plurality of IDT electrodes include a first IDT electrode located on the first region and a second IDT electrode located on the second region, and the elastic wave device has series resonators and parallel resonators that form a ladder-type filter, wherein the series resonators have the first IDT electrodes, and the parallel resonators have the second IDT electrodes.

3. The elastic wave device according to claim 1 or 2, wherein, when the arithmetic mean roughness of the surface of the first region on the first surface side is denoted as Ra1 and the arithmetic mean roughness of the surface of the second region on the first surface side is denoted as Ra2, Ra2 is smaller than 0.2 times Ra1.

4. The acoustic wave device according to claim 1, wherein the piezoelectric material is LN.

5. The acoustic wave device according to claim 4, wherein the cut angle of the LN is 100° to 120°.

6. The acoustic wave device according to claim 1, wherein the IDT electrode contains Al as a main component.

7. The acoustic wave device according to claim 6, wherein the IDT electrode has an Al layer, and the Al of the Al layer located on the first region is oriented in the [111] direction.

8. The acoustic wave device according to claim 7, wherein the IDT electrode has an underlayer located between the Al layer and the first surface, and the material of the underlayer is Ti.

9. The acoustic wave device according to claim 1, wherein the first region is a region that has been dry-etched, and the second region is a region that has been finished by CMP.

10. An elastic wave device according to any one of claims 1 to 9, wherein the first region has a heterogeneous layer, and the crystallinity of the heterogeneous layer is different from the crystallinity of the remaining region of the first region other than the heterogeneous layer.

11. The acoustic wave device according to claim 10, wherein the heterogeneous layer is an amorphous layer, and the heterogeneous layer contains the same type of element as the element contained in the piezoelectric body.

12. The acoustic wave device according to claim 10, wherein the oxygen content of the heterogeneous layer is lower than the oxygen content of the remaining region.

13. The acoustic wave device according to claim 10, wherein the heterogeneous layer contains Ar.

14. The acoustic wave device according to claim 1, wherein the first region surrounds the second region.

15. The acoustic wave device according to claim 1, wherein the IDT electrode is configured to excite a plate wave or a bulk wave.

16. The acoustic wave device according to any one of claims 1 to 15, comprising: a support substrate; and an acoustic reflection film located between the support substrate and the piezoelectric substrate.

17. The elastic wave device according to any one of claims 1 to 15, wherein the elastic wave device has a support substrate, and the elastic wave device includes a membrane structure having a hollow portion surrounded by the support substrate and the piezoelectric substrate.

18. A communication device comprising the acoustic wave device according to any one of claims 1 to 17.

19. A piezoelectric substrate including a single-crystal piezoelectric material and having a first surface, the piezoelectric substrate having a first region and a second region that is thicker than the first region, and on the first surface side, the crystallinity of the second region is higher than the crystallinity of the first region.

20. A piezoelectric substrate including a single crystal piezoelectric material and having a first surface, the piezoelectric substrate having a first region and a second region that is thicker than the first region, and on the first surface side, the surface roughness of the second region is smaller than the surface roughness of the first region.

21. A method for manufacturing a piezoelectric substrate including a single-crystal piezoelectric material, comprising: forming a first region by dry etching; and forming a second region thicker than the first region by CMP finishing.

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