Elastic wave device, and communication device

Abstract

The present invention improves the strength of a piezoelectric body. This elastic wave device comprises a support substrate having a first surface, and a piezoelectric body having a second surface. The piezoelectric body has a bonded region in which the second surface is directly or indirectly bonded to the first surface, and a non-bonded region in which the second surface is not bonded to the first surface. The entirety of the second surface in the bonded region protrudes further toward the support substrate side in comparison to all of the second surface in the non-bonded region.

Description

Acoustic wave device and communication device

[0001] The present disclosure relates to an acoustic wave device and a communication device including the acoustic wave device.

[0002] Patent Document 1 discloses an example of the configuration of an acoustic wave device.

[0003] WO2016 / 098526

[0004] An elastic wave device according to one aspect of the present disclosure comprises a support substrate having a first surface, and a piezoelectric body having a thickness of 3 μm or less and a second surface opposite the first surface, wherein the piezoelectric body has a bonded region in which the second surface is directly or indirectly bonded to the first surface, and at least one non-bonded region in which the second surface is not bonded to the first surface and is surrounded by the bonded region, and the entire second surface in the bonded region protrudes toward the support substrate more than the second surface in the non-bonded region.

[0005] 1 is a cross-sectional view illustrating the configuration of an elastic wave device according to a first embodiment; FIG. 2 is a plan view illustrating the configuration of an elastic wave device according to a first embodiment; FIG. 3 is a cross-sectional view illustrating the configuration of an elastic wave device according to a second embodiment; FIG. 4 is a cross-sectional view illustrating the configuration of an elastic wave device according to a third embodiment; FIG. 5 is a cross-sectional view illustrating the configuration of an elastic wave device according to a fourth embodiment; and FIG. 6 is a diagram illustrating a schematic configuration of a communication device according to a fifth embodiment.

[0006] [Embodiment 1] An elastic wave device according to embodiment 1 will be described below. For ease 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 description will not be repeated. For simplicity, descriptions of well-known technical matters will also be omitted as appropriate. Unless otherwise specified, the components, materials, and numerical values ​​described in this specification are merely examples. Therefore, for example, unless otherwise specified, the positional relationship of each component is not limited to the example shown in each figure. Furthermore, the illustrations of each component are not necessarily to scale.

[0007] 1 is a cross-sectional view illustrating the configuration of an elastic wave device 1 according to embodiment 1. As shown in FIG. 1 , the elastic wave device 1 includes a support substrate 10 and a piezoelectric body 20. The elastic wave device 1 further includes an excitation electrode 30.

[0008] The support substrate 10 supports other components included in the elastic wave device 1. The support substrate 10 has a first surface 11. The support substrate 10 has a recess 11a on the first surface 11. The portion of the first surface 11 other than the recess 11a is a support portion 12 to which the piezoelectric body 20 is bonded and supported. The depth of the recess 11a may be 0.1 μm or more and 100 μm or less. The recess 11a may penetrate to the back surface opposite the first surface 11, and may not have a bottom surface. If the recess 11a penetrates to the back surface, it will have the same depth as the support substrate 10.

[0009] FIG. 2 is a plan view illustrating an example of the configuration of the elastic wave device 1. In FIG. 2, reference numerals 201 and 202 indicate different examples of the configuration of the elastic wave device 1. In either example, the elastic wave device 1 may include a plurality of excitation electrodes 30 and two bus bars 35a, 35b to which the excitation electrodes 30 are connected. The excitation electrodes 30 will be described later. Furthermore, the support portion 12 has a frame-like shape in a plan view and supports the piezoelectric body 20.

[0010] In the example indicated by reference numeral 201, the entire excitation electrode 30 overlaps with the recess 11a in a plan view. In the example indicated by reference numeral 201, the excitation electrode 30 has electrode fingers 31 and dummy electrode fingers 32. The electrode fingers 31 are connected to either the bus bar 35a or the bus bar 35b, and are located in intersection regions where the electrode fingers 31 intersect with the electrode fingers 31 connected to the bus bar 35a or the bus bar 35b to which the electrode fingers 31 are not connected. The dummy electrode fingers 32 are connected to either the bus bar 35a or the bus bar 35b, are shorter than the electrode fingers 31, and are not located in the intersection regions. The excitation electrode 30 does not necessarily have to have dummy electrode fingers 32.

[0011] In the example indicated by the reference numeral 202, the intersection region of the electrode fingers 31 of the excitation electrode 30 overlaps with the recess 11a in a plan view. The edge of the recess 11a, i.e., the boundary line between the region where the support substrate 10 supports the piezoelectric element 20 and the region where it does not support the piezoelectric element 20, is located in the gap portion of the excitation electrode 30. The gap portion is the region between the tip of the electrode finger 31 and the tip of the dummy electrode finger 32 facing the tip.

[0012] However, as described above, the excitation electrode 30 does not necessarily have to have the dummy electrode fingers 32. When the excitation electrode 30 does not have the dummy electrode fingers 32, the gap portion is the region between the tip of the electrode finger 31 and the bus bars 35 a, 35 b facing the tip. Furthermore, the support substrate 10 does not necessarily have to have the recess 11 a and the support portion 12 on the first surface 11. In other words, the first surface 11 may be a flat surface.

[0013] The material of the support substrate 10 may be, for example, silicon (Si) or another material. The support substrate 10 may be integrally formed from a single material, or may be formed by combining multiple materials. When the support substrate 10 is integrally formed from a single material, the support substrate 10 having the recess 11a may be formed, for example, by etching the surface of a flat, plate-shaped substrate. When the support substrate 10 is formed from a combination of multiple materials, the support substrate 10 may be formed, for example, by arranging the support portion 12 on a flat, plate-shaped substrate. In this case, the region of the support substrate 10 where the support portion 12 is not arranged becomes the recess 11a.

[0014] The piezoelectric body 20 is a substantially flat member having a second surface 22 facing the first surface 11 of the support substrate 10. Specifically, the second surface 22 may be bonded to the support portion 12 of the first surface 11. Therefore, the piezoelectric body 20 overlaps the recess 11a in a planar view. Here, the planar view refers to a planar view from a direction perpendicular to the first surface 11. In other words, the piezoelectric body 20 covers the recess 11a with a space 13 therebetween. That is, the acoustic wave device 1 has a cavity. The material of the piezoelectric body 20 may be, for example, lithium tantalate (LT) or lithium niobate (LN). The thickness of the piezoelectric body 20 may be 3 μm or less. Alternatively, the thickness of the piezoelectric body 20 may be 1 μm or less.

[0015] The piezoelectric body 20 has a bonded region 211 and a non-bonded region 212. The bonded region 211 is defined as a region where the piezoelectric body 20 is directly or indirectly bonded to the support substrate 10. The non-bonded region 212 is defined as a region where the piezoelectric body 20 is not bonded to the support substrate 10. For example, the bonded region 211 may be located at the outer edge of the piezoelectric body 20, and the non-bonded region 212 may be located inside the bonded region 211. In other words, the non-bonded region 212 may be surrounded by the bonded region 211. However, the positional relationship between the bonded region 211 and the non-bonded region 212 is not limited to this.

[0016] In the piezoelectric body 20, the entire second surface 22 in the bonding region 211 protrudes toward the support substrate 10 further than the second surface 22 in the non-bonding region 212. In other words, the maximum value of the distance between the second surface 22 and the first surface 11 in the bonding region 211 is smaller than the minimum value of the distance between the second surface 22 and the first surface 11 in the non-bonding region 212.

[0017] Specifically, the second surface 22 in the bonding region 211 may have a bonding portion 24 formed thereon that protrudes toward the support substrate 10 further than the second surface 22 in the non-bonding region 212. The height by which the bonding portion 24 protrudes may be 1 nm or more and 100 μm or less. Alternatively, the height by which the bonding portion 24 protrudes may be 0.1 μm or more and 100 μm or less. The bonding portion 24 has a frame-like shape that overlaps with the support portion 12 in a plan view. The bonding portion 24 is bonded to the support portion 12, thereby bonding the piezoelectric body 20 to the support substrate 10.

[0018] In the elastic wave device 1, the piezoelectric body 20 has the above-described configuration, which distributes the stress acting on the piezoelectric body 20 more effectively than when the piezoelectric body 20 does not have this configuration. This improves the strength of the piezoelectric body 20 in the elastic wave device 1.

[0019] The excitation electrode 30 is an electrode that excites an elastic wave in the piezoelectric body 20. The excitation electrode 30 may be, for example, an IDT (Inter-Digital Transducer) electrode. In FIG. 1 , the excitation electrode 30 extends in a direction perpendicular to the paper surface. For example, when an alternating current is applied to such an excitation electrode 30, an elastic wave is excited in the piezoelectric body 20.

[0020] The excitation electrodes 30 may be disposed on the piezoelectric body 20. In the example shown in FIG. 1 , the piezoelectric body 20 further has a third surface 23 located on the opposite side to the second surface 22. The excitation electrodes 30 may be disposed on the third surface 23. Specifically, the excitation electrodes 30 may be disposed along a certain arrangement direction on the third surface 23. However, the excitation electrodes 30 may also be disposed on the second surface 22. Furthermore, the excitation electrodes 30 are disposed in the non-bonded region 212. That is, the excitation electrodes 30 overlap the recesses 11a when viewed from a direction perpendicular to the first surface 11.

[0021] 1 , the third surface 23 of the piezoelectric body 20 is flat. That is, the thickness of the piezoelectric body 20 in the bonded region 211 is greater than the thickness of the piezoelectric body 20 in the non-bonded region 212. This particularly improves the strength of the portion of the piezoelectric body 20 in the elastic wave device 1 that is bonded to the support substrate 10.

[0022] 1 , both the second surface 22 and the third surface 23 are flat in the non-bonding region 212. However, both the second surface 22 and the third surface 23 may be curved with the same curvature in the non-bonding region 212. That is, the piezoelectric body 20 may have a constant thickness in the non-bonding region 212 and may be curved toward the third surface 23.

[0023] The thickness of the piezoelectric body 20 may be constant directly below the excitation electrode 30. This makes it easier for the elastic waves excited by the piezoelectric body 20 and the excitation electrode 30 to be reflected in a constant direction. Furthermore, the shape of the piezoelectric body 20 becomes simple, making it easier to manufacture the piezoelectric body 20.

[0024] The distance between adjacent excitation electrodes 30 is defined as pitch PT, and the ratio of the width of excitation electrode 30 to pitch PT is defined as duty D. In this case, D may be less than 0.3 in elastic wave device 1. Furthermore, the thickness of the thickest portion of piezoelectric body 20 in non-bonded region 212 is defined as thickest-portion thickness T. In this case, T / (PT×D) may be less than 0.3 in elastic wave device 1.

[0025] Specifically, the pitch PT may be 3 μm or more and 5 μm or less, for example, 4 μm. The duty D may be 0.2 or more and less than 0.3. The thickness T of the thickest part of the piezoelectric body 20 may be 3 μm or less or 1 μm or less, as described above, for example, 0.4 μm.

[0026] When the pitch PT, duty D, and thickness T of the thickest part satisfy the above conditions, the elastic wave excited by the excitation electrode 30 may be a bulk wave. The bulk wave may be, for example, a thickness-shear mode wave. In this case, the elastic wave propagates in the thickness direction of the piezoelectric body 20. In addition, in this case, the resonant frequency of the elastic wave depends on the thickness of the piezoelectric body 20.

[0027] The pitch PT, duty D, and thickness T of the thickest portion do not necessarily have to satisfy the above conditions. If the pitch PT, duty D, and thickness T of the thickest portion do not satisfy the above conditions, the elastic wave excited by the excitation electrode 30 may be a plate wave. The plate wave may be, for example, an A1 mode Lamb wave. In this case, the elastic wave propagates in the thickness direction of the piezoelectric body and in the arrangement direction of the excitation electrodes 30. Furthermore, in this case, the resonant frequency of the elastic wave depends on the thickness of the piezoelectric body 20 and the pitch PT of the excitation electrodes.

[0028] The excitation electrode 30 is not limited to an IDT electrode. Furthermore, the material of the piezoelectric body 20 is not limited to LT or LN. When the excitation electrode 30 is not an IDT electrode and the material of the piezoelectric body 20 is not LT or LN, the acoustic wave excited by the excitation electrode 30 is not limited to a bulk wave or a plate wave.

[0029] (Manufacturing Method) An example of a method for manufacturing the elastic wave device 1 is shown below. For example, the bonding portion 24 is formed on the second surface 22 of the piezoelectric body 20 by dry etching. Next, a sacrificial layer is formed on the recess 11a of the support substrate 10, and the support substrate 10 and the piezoelectric body 20 are bonded together. The sacrificial layer between the piezoelectric body 20 and the recess 11a is then removed by wet etching, thereby manufacturing the elastic wave device 1 in which the bonding portion 24 is bonded to the support portion 12. Alternatively, the elastic wave device 1 may be manufactured by bonding the bonding portion 24 of the piezoelectric body 20, which is separately manufactured, to the support portion 12 of the support substrate 10 by ultrasonic bonding or the like.

[0030] (Modification) As described above, when the elastic wave excited by the excitation electrode 30 is a bulk wave or a plate wave, the resonant frequency of the elastic wave is affected by the thickness of the piezoelectric body 20 directly below the excitation electrode 30. In the example shown in Fig. 1 , the thickness of the piezoelectric body 20 is constant directly below the excitation electrode 30. However, the thickness of the piezoelectric body 20 does not have to be constant directly below the excitation electrode 30. For example, the thickness of the piezoelectric body 20 may be different between a region of the non-bonded region 212 that is close to the bonded region 211 and a region that is distant from the bonded region 211.

[0031] In general, when an elastic wave device is applied to a frequency filter, the frequency characteristics become steeper as the difference between the resonant frequency and anti-resonant frequency of the elastic waves excited in the piezoelectric body becomes smaller. When a thin portion of piezoelectric body 20 exists directly below excitation electrode 30, the difference between the resonant frequency and anti-resonant frequency of the elastic waves excited in piezoelectric body 20 becomes smaller. Therefore, when elastic wave device 1 is applied to a frequency filter, the attenuation characteristics of the frequency filter can be made steeper.

[0032] For example, the piezoelectric body 20 may be thinner in a region of the non-bonded region 212 that is separated from the bonded region 211 than in a region that is separated from the bonded region 211. Such an example will be described later as a third embodiment.

[0033] 3 is a cross-sectional view illustrating the configuration of an elastic wave device 2 according to embodiment 2. As shown in Fig. 3 , elastic wave device 2 differs from elastic wave device 1 in that it includes a piezoelectric body 40 instead of piezoelectric body 20. Piezoelectric body 40 differs from piezoelectric body 20 in that it includes a second surface 42 instead of second surface 22.

[0034] The second surface 42 may have an inclined surface 45 at the outer edge of the non-bonded region 212, which gradually moves away from the support substrate 10 as it moves away from the boundary between the bonded region 211 and the non-bonded region 212. By having the inclined surface 45 on the second surface 42, stress due to an external force is dispersed more effectively in the piezoelectric body 40 than in the piezoelectric body 20. As a result, the strength of the piezoelectric body 40 is further improved.

[0035] The second surface 42 may further include a flat surface 46 on the inner side of the slope 45 in the non-bonded region 212. The angle formed between the slope 45 and the flat surface 46 at the boundary between the slope 45 and the flat surface 46 may be an obtuse angle. This allows the stress in the piezoelectric body 40 in the elastic wave device 2 to be dispersed more than the stress in the piezoelectric body 20, further improving the strength of the piezoelectric body 40.

[0036] 3, the inclined surface 45 is a flat surface. However, the inclined surface 45 may be a curved surface whose degree of inclination changes with increasing distance from the boundary between the bonded region 211 and the non-bonded region 212. Even when the inclined surface 45 is a curved surface, the strength of the piezoelectric body 40 is improved, just as when the inclined surface 45 is a flat surface.

[0037] 4 is a cross-sectional view illustrating the configuration of an elastic wave device 3 according to embodiment 3. As shown in FIG. 4 , elastic wave device 3 differs from elastic wave device 1 in that it includes a piezoelectric body 50 instead of piezoelectric body 20. Piezoelectric body 50 differs from piezoelectric body 20 in that it includes a second surface 52 instead of second surface 22.

[0038] In the elastic wave device 3, the third surface 23 is flat. In Fig. 4, reference numeral 401 denotes a cross-sectional view perpendicular to the third surface 23 and along the arrangement direction of the excitation electrodes 30. Reference numeral 402 denotes a cross-sectional view perpendicular to the third surface 23 and orthogonal to the arrangement direction of the excitation electrodes 30. That is, the arrangement direction of the excitation electrodes 30 is parallel to the paper surface in the view indicated by reference numeral 401, and perpendicular to the paper surface in the view indicated by reference numeral 402.

[0039] As shown in Fig. 4, the second surface 52 may be arch-shaped in a cross section perpendicular to the third surface 23. Here, the term "arch-shaped" refers to a curved shape that is convex in a direction away from the support substrate 10. However, the term "arch-shaped" does not refer to a shape that is line-symmetric with respect to a predetermined axis of symmetry. Therefore, when the second surface 52 is arch-shaped in a certain cross section, the second surface 52 does not need to have a shape that is line-symmetric with respect to the axis of symmetry included in the cross section.

[0040] The cross section perpendicular to the third surface 23 can be defined arbitrarily, and the second surface 52 does not need to be arched in all cross sections perpendicular to the third surface 23. In the elastic wave device 3, the second surface 52 is arched in at least one cross section perpendicular to the third surface 23, which improves the strength of the piezoelectric body 50 compared to a case in which the second surface 52 is not arched in all cross sections perpendicular to the third surface 23.

[0041] In particular, as indicated by reference numeral 401 in FIG. 4 , the second surface 52 may be arch-shaped in a cross section perpendicular to the third surface 23 and along the arrangement direction of the excitation electrodes 30. The excitation electrodes 30 function like beams reinforcing the piezoelectric bodies 50 in a direction perpendicular to the arrangement direction of the excitation electrodes 30, as indicated by reference numeral 402. On the other hand, the excitation electrodes 30 do not function like beams reinforcing the piezoelectric bodies 50 in a direction along the arrangement direction of the excitation electrodes 30, as indicated by reference numeral 401. For this reason, the strength of the piezoelectric bodies 50 is likely to be lower in the direction along the arrangement direction of the excitation electrodes 30 compared to the direction perpendicular to the arrangement direction. By making the second surface 52 arch-shaped at least in a cross section along the arrangement direction of the excitation electrodes 30, the strength of the piezoelectric bodies 50 in the direction along the arrangement direction of the excitation electrodes 30 can be compensated for.

[0042] The second surface 52 may further be arched in any cross section perpendicular to the third surface 23. For example, as indicated by reference numeral 402 in Fig. 4 , the second surface 52 may also be arched in a cross section perpendicular to the third surface 23 and perpendicular to the arrangement direction of the excitation electrodes 30. This can further improve the strength of the piezoelectric body 50.

[0043] 4 , the third surface 23 of the piezoelectric body 50 is flat. Therefore, the thickness of the piezoelectric body 50 in the non-bonded region 212 is thinner in a region away from the bonded region 211 than in a region away from the bonded region 211. The thickness of the piezoelectric body 50 in the non-bonded region 212 may be 0.5 μm or less at its thinnest point. Even when the piezoelectric body 50 has such a thin portion, the strength of the piezoelectric body 50 can be supplemented by the arch-shaped second surface 52 in a cross section perpendicular to the third surface 23. Furthermore, the presence of a thin portion in the piezoelectric body 50 can provide steeper attenuation characteristics when the acoustic wave device 3 is applied to a frequency filter, as described in the modification of the first embodiment.

[0044] 5 is a cross-sectional view illustrating the configuration of an elastic wave device 4 according to embodiment 4. As shown in FIG. 5 , elastic wave device 4 differs from elastic wave device 1 in that it includes a support substrate 60 and a piezoelectric body 70 instead of support substrate 10 and piezoelectric body 20.

[0045] The support substrate 60 differs from the support substrate 10 in that it includes a first surface 61 instead of the first surface 11, and a support portion 62 instead of the support portion 12. The support portion 62 differs from the support portion 12 in that it includes a chamfered portion 64. The chamfered portion 64 is a portion of the support portion 62 that is inclined so as to move away from the piezoelectric body 70 as it approaches the recess 11a. The chamfered portion 64 is located on the edge of the support portion 62 on the recess 11a side. The first surface 61 differs from the first surface 11 in that it includes an area corresponding to the chamfered portion 64.

[0046] Piezoelectric body 70 differs from piezoelectric body 20 in that it includes a second surface 72 instead of second surface 22 and a bonding portion 74 instead of bonding portion 24. Bonding portion 74 differs from bonding portion 24 in that it includes a chamfered portion 75. Chamfered portion 75 is a portion of bonding portion 74 that is inclined so as to move away from support substrate 60 as it approaches non-bonding region 212. Chamfered portion 75 is located on the edge of bonding portion 74 on the non-bonding region 212 side. Second surface 72 differs from second surface 22 in that it includes a region corresponding to chamfered portion 75.

[0047] In the elastic wave device 4, the support portion 62 of the support substrate 60 has a chamfered portion 64, and the joint portion 74 of the piezoelectric body 70 has a chamfered portion 75, which facilitates stress dispersion in the piezoelectric body 70. Therefore, the strength of the piezoelectric body 70 in the elastic wave device 4 is improved compared to the strength of the piezoelectric body 20 in the elastic wave device 1.

[0048] Furthermore, in the elastic wave device 4, the support portion 62 has the chamfered portion 64, and the joint portion 74 has the chamfered portion 75, which facilitates stress dispersion at the joint between the support portion 62 and the joint portion 74. This makes it difficult for the joint between the support portion 62 and the joint portion 74 to come apart, and reduces the possibility of the piezoelectric body 70 or the support substrate 60 cracking.

[0049] Fifth Embodiment FIG. 6 illustrates a schematic configuration of a communication device 151 according to a fifth embodiment. The communication device 151 is an application example of an elastic wave device according to an aspect of the present disclosure and performs wireless communication using radio waves. The communication device 151 may include one duplexer 101 as a transmit filter 109 and another duplexer 101 as a receive filter 111. Each of the two duplexers 101 may include an elastic wave device according to an aspect of the present disclosure (e.g., elastic wave devices 1, 2, 3, and 4). In this manner, the communication device 151 may include an elastic wave device according to an aspect of the present disclosure.

[0050] 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 band-pass 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 input to the transmission filter 109.

[0051] The transmission filter 109 may remove unnecessary components outside the transmission passband from the input transmission signal TS. The transmission filter 109 may output the TS after removing the unnecessary components to the antenna 159. The antenna 159 may convert the TS, which is an electrical signal input thereto, into radio waves as a wireless signal and transmit the radio waves to the outside of the communication device 151.

[0052] Furthermore, the antenna 159 may convert the received external radio waves into a received signal RS, which is an electrical signal, and input the RS to the receiving filter 111 via the antenna terminal. The receiving filter 111 may remove unnecessary components outside the receiving passband from the input RS. The receiving filter 111 may output the received signal RS after the unnecessary components have been removed to the amplifier 161. The output RS may be amplified by the amplifier 161. The bandpass filter 163 may remove unnecessary components outside the receiving passband from the amplified RS. The RS after the unnecessary components have been removed may be frequency-downgraded and demodulated by the RF-IC 153, and converted into a received information signal RIS.

[0053] The TIS and RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the TIS and RIS may be analog audio signals or digitized audio signals. The passband of the wireless signals may be set appropriately and may comply with various known standards.

[0054] [Summary] An elastic wave device according to aspect 1 of the present disclosure comprises a support substrate having a first surface, and a piezoelectric body having a thickness of 3 μm or less and a second surface opposite the first surface, wherein the piezoelectric body has a bonded region where the second surface is directly or indirectly bonded to the first surface, and at least one non-bonded region where the second surface is not bonded to the first surface and is surrounded by the bonded region, and the entire second surface in the bonded region protrudes toward the support substrate further than the second surface in the non-bonded region.

[0055] An elastic wave device according to aspect 2 of the present disclosure is the same as in aspect 1, wherein the second surface has a slope at the outer edge of the non-bonded region that moves away from the support substrate as it moves away from the boundary between the bonded region and the non-bonded region.

[0056] According to a third aspect of the present disclosure, in the elastic wave device of the second aspect, the inclined surface is a curved surface whose degree of inclination changes with increasing distance from the boundary between the bonded region and the non-bonded region.

[0057] The elastic wave device according to aspect 4 of the present disclosure is in any one of aspects 1 to 3, and further includes an excitation electrode disposed on the piezoelectric body and exciting the piezoelectric body, and the thickness of the piezoelectric body is constant directly below the excitation electrode.

[0058] An elastic wave device according to aspect 5 of the present disclosure is any one of aspects 1 to 4, in which the piezoelectric element is excited to vibrate as a bulk wave or a plate wave, and the thickness of the piezoelectric element differs between a region of the non-bonded region that is close to the bonded region and a region that is distant from the bonded region.

[0059] An elastic wave device according to aspect 6 of the present disclosure is any one of aspects 1 to 5, wherein the piezoelectric body has a flat third surface located opposite the second surface, and the second surface is arched in a cross section perpendicular to the third surface.

[0060] The elastic wave device according to aspect 7 of the present disclosure is the same as in aspect 6, further comprising an excitation electrode arranged along a certain arrangement direction on the third surface and exciting the piezoelectric element, and the second surface is arch-shaped in a cross section perpendicular to the third surface and along the arrangement direction.

[0061] An elastic wave device according to aspect 8 of the present disclosure is any one of aspects 1 to 7, wherein the thickness of the piezoelectric body in the non-bonded region is 0.5 μm or less at its thinnest point.

[0062] An elastic wave device according to aspect 9 of the present disclosure is, in any one of aspects 1 to 8, further comprising an excitation electrode disposed on the piezoelectric body and exciting the piezoelectric body, wherein when the spacing between the excitation electrodes is defined as a pitch and the ratio of the width of the excitation electrode to the pitch is defined as a duty, the duty is less than 0.3.

[0063] The elastic wave device according to aspect 10 of the present disclosure is any one of aspects 1 to 9, further comprising an excitation electrode disposed on the piezoelectric body and exciting the piezoelectric body, wherein when the spacing between the excitation electrodes is defined as a pitch, the ratio of the thickness of the thickest part of the piezoelectric body to the pitch is less than 0.3.

[0064] A communication device according to an eleventh aspect of the present disclosure includes the acoustic wave device according to any one of the first to tenth aspects.

[0065] [Additional Notes] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

[0066] REFERENCE SIGNS LIST 1, 2, 3, 4 Acoustic wave device 10, 60 Support substrate 11, 61 First surface 20, 40, 50, 70 Piezoelectric body 22, 42, 52, 72 Second surface 23 Third surface 30 Excitation electrode 45 Slope 151 Communication device 211 Bonded region 212 Non-bonded region

Claims

1. An elastic wave device comprising: a support substrate having a first surface; and a piezoelectric body having a thickness of 3 μm or less and a second surface opposing the first surface, wherein the piezoelectric body has a bonding region where the second surface is directly or indirectly bonded to the first surface, and at least one non-bonding region where the second surface is not bonded to the first surface and is surrounded by the bonding region, and the entire second surface in the bonding region protrudes toward the support substrate further than the second surface in the non-bonding region.

2. The elastic wave device according to claim 1, wherein the second surface has a slope at the outer edge of the non-bonded region that moves away from the support substrate as it moves away from the boundary between the bonded region and the non-bonded region.

3. The elastic wave device according to claim 2, wherein the inclined surface is a curved surface whose degree of inclination changes with increasing distance from the boundary between the bonded region and the non-bonded region.

4. An elastic wave device according to any one of claims 1 to 3, further comprising an excitation electrode disposed on the piezoelectric body and exciting the piezoelectric body, the thickness of the piezoelectric body being constant directly below the excitation electrode.

5. An elastic wave device as claimed in any one of claims 1 to 4, wherein the piezoelectric body is excited to produce bulk waves or plate waves, and the thickness of the piezoelectric body differs between a region of the non-bonded region close to the bonded region and a region of the non-bonded region separated from the bonded region.

6. An elastic wave device according to any one of claims 1 to 5, wherein the piezoelectric body has a flat third surface located opposite the second surface, and the second surface is arch-shaped in a cross section perpendicular to the third surface.

7. The elastic wave device according to claim 6, further comprising excitation electrodes arranged along a certain arrangement direction on the third surface and exciting the piezoelectric element, and the second surface is arch-shaped in a cross section perpendicular to the third surface and along the arrangement direction.

8. The elastic wave device according to claim 1, wherein the thickness of the piezoelectric body in the non-bonded region is 0.5 μm or less at its thinnest point.

9. An elastic wave device according to any one of claims 1 to 8, further comprising an excitation electrode arranged on the piezoelectric body and exciting the piezoelectric body, wherein the spacing between the excitation electrodes is defined as a pitch and the ratio of the width of the excitation electrode to the pitch is defined as a duty, and the duty is less than 0.

3.

10. An elastic wave device as claimed in any one of claims 1 to 9, further comprising an excitation electrode arranged on the piezoelectric body and exciting the piezoelectric body, wherein when the spacing between the excitation electrodes is defined as a pitch, the ratio of the thickness of the thickest part of the piezoelectric body to the pitch is less than 0.

3.

11. A communication device comprising the acoustic wave device according to any one of claims 1 to 10.

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