Elastic wave device, method for manufacturing elastic wave device, splitter, and communication device

Abstract

This elastic wave device comprises a substrate including an end surface and having a piezoelectric body, and a plurality of strip electrodes located above the substrate and each extending in parallel to each other, wherein: at least a portion of the plurality of strip electrodes is an excitation part capable of exciting an elastic wave; the end surface is parallel to the extending direction of the strip electrodes in plan view and is located in an elastic wave propagation direction with respect to the excitation part; the plurality of strip electrodes includes a first strip electrode located closest to the end surface side in the elastic wave propagation direction and a second strip electrode farther from the end surface than the first strip electrode in the elastic wave propagation direction; the second strip electrode is the excitation part; and the average thickness of the first strip electrode in a cross section cut in the elastic wave propagation direction is less than the average thickness of the second strip electrode.

Description

Elastic Wave Device, Method for Manufacturing Elastic Wave Device, Demultiplexer, and Communication Device

[0001] The present disclosure relates to an elastic wave device that uses elastic waves, a method for manufacturing the elastic wave device, a demultiplexer including the elastic wave device, and a communication device including the demultiplexer.

[0002] Elastic wave devices that use elastic waves are known. An elastic wave device is, for example, a SAW (Surface Acoustic Wave) device. An elastic wave device has a structure that reflects the propagating elastic wave. The elastic surface wave device disclosed in Patent Document 1 is an end face reflection type elastic surface wave device having an end face as a reflection structure.

[0003] International Publication No. WO2018 / 096783 A1

[0004] The elastic wave device according to the present disclosure includes a substrate having a piezoelectric body and including an end face, and a plurality of strip electrodes located above the substrate and each extending in parallel. Among the plurality of strip electrodes, at least some of the strip electrodes are excitation portions capable of exciting elastic waves. The end face is parallel to the extending direction of the strip electrodes in a plan view from above and is located in the elastic wave propagation direction with respect to the excitation portion. The plurality of strip electrodes includes a first strip electrode located closest to the end face in the elastic wave propagation direction and a second strip electrode farther from the end face than the first strip electrode in the elastic wave propagation direction. The second strip electrode is an excitation portion. In a cross section cut in the elastic wave propagation direction, the average thickness of the first strip electrode is smaller than the average thickness of the second strip electrode.

[0005] The method for manufacturing an elastic wave device according to the present disclosure includes a first step of forming a plurality of strip electrodes above a substrate. After the first step, it includes a second step of forming a mask above the strip electrodes. After the second step, it includes a third step of forming an end face on the substrate by etching and removing a part of the first strip electrode located closest to the end face in the elastic wave propagation direction among the plurality of strip electrodes by etching.

[0006] This is a schematic plan view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic cross-sectional view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic cross-sectional view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic cross-sectional view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic plan view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic plan view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic plan view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic cross-sectional view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a diagram illustrating a manufacturing method using a schematic cross-sectional view of an elastic wave apparatus according to an embodiment of the present disclosure. This is a schematic circuit diagram of a demultiplexer according to an embodiment of the present disclosure. This is a schematic circuit diagram of a communication device according to an embodiment of the present disclosure.

[0007] The embodiments and comparative examples related to this disclosure will be described below with reference to the drawings. The figures used in the following description are schematic, and the dimensional ratios shown in the drawings do not necessarily correspond to those of reality. Furthermore, the dimensional ratios do not necessarily match between drawings.

[0008] In this disclosure, a Cartesian coordinate system indicated by the D1, D2, and D3 axes is shown in the drawings. The D2 axis is parallel to the direction in which the excitation unit 311, described later, extends from the second busbar 351b, described later. The D1 axis is perpendicular to the D2 axis in the plane of the substrate 2. The D3 axis is perpendicular to the upper surface of the piezoelectric element 21. In other words, the D3 axis is the stacking direction of the substrate 2. In this disclosure, the positive direction of the D1 axis is the direction from the excitation unit 311, described later, toward one end face 41, described later. In this disclosure, the positive direction of the D1 axis is also referred to as the elastic wave propagation direction. In this disclosure, the negative direction of the D1 axis is also referred to as the direction opposite to the elastic wave propagation direction. The end face 41 may be located in both directions along the D1 axis with respect to the excitation unit 311, but in this disclosure, for the sake of explanation, the direction from the excitation unit 311 toward one end face 41 is conveniently referred to as the elastic wave propagation direction. Here, the elastic wave excited by the excitation unit 311 may be an acoustic surface wave or a plate wave. The positive direction of the D2 axis is the direction in which the second excitation unit 311b, described later, extends from the second busbar 351b, described later. The positive direction of the D3 axis is the direction from the substrate 2, described later, toward the electrode layer 3, described later. Also, when referring to a plan view or plan view, unless otherwise specified, it refers to the view in the direction of the D3 axis. For example, a plan view from above refers to the view from above with respect to the D3 axis.

[0009] The elastic wave apparatus 1 according to this disclosure may have either an upward or downward orientation, but for convenience, terms such as upper surface or lower surface may be used with the positive direction of the D3 axis as the upward orientation.

[0010] Furthermore, while the thickness of a layer may be mentioned in this disclosure, unless otherwise specified, it may be considered at the thickest part or the thinnest part in any cross-section.

[0011] Embodiments of this disclosure are shown below. Furthermore, the configurations described in the embodiments shown below may be freely combined with several other embodiments.

[0012] [First Embodiment] A first embodiment of the elastic wave apparatus 1 according to the present disclosure will be described. Figure 1 is a schematic diagram of the elastic wave apparatus 1 in plan view. The elastic wave apparatus 1 comprises a substrate 2, an electrode layer 3 located above the substrate 2, and an end face 41 included in the substrate 2. Figure 2 is a schematic diagram of the elastic wave apparatus 1 in cross-sectional view.

[0013] (Substrate) The substrate 2 has a piezoelectric element 21. The substrate 2 may also have a first layer 22 and / or a support substrate 23 located below the piezoelectric element 21, as shown in Figure 2.

[0014] Piezoelectric material 21 is lithium niobate (LiNbO ３ (Hereinafter referred to as LN) or lithium tantalate (LiTaO) ３ It is composed of a piezoelectric single crystal containing (hereinafter referred to as LT). For example, the piezoelectric body 21 may be composed of an LT layer with 36-54° Y-cut X propagation.

[0015] The first layer 22 is silicon dioxide (SiO ２ Examples include the following. The first layer 22 reduces surface waves leaking below the piezoelectric body 21, thereby reducing the insertion loss of the elastic wave device 1.

[0016] The support substrate 23 supports the electrode layer 3 and the piezoelectric element 21, improving the strength of the substrate 2. When the support substrate 23 is present, the first layer 22 improves the bonding strength between the piezoelectric element 21 and the support substrate 23.

[0017] (End Face) As shown in Figure 1, the substrate 2 includes an end face 41. One end face 41 is positioned in the direction of elastic wave propagation relative to the excitation section 311, which will be described later. The end face 41 may be positioned in both directions along the D1 axis relative to the excitation section 311. The end face 41 reflects the elastic wave as a reflected wave in the negative direction of the D1 axis. In other words, the end face 41 is a reflective structure.

[0018] The end face 41 may be part of the groove 4. Specifically, as shown in Figure 1, the end face 41 may be part of the side surface of the groove 4. In this case, both sides of the groove 4 can be used as the end face 41.

[0019] In a plan view, the end face 41 is positioned parallel to the direction in which the strip electrode 31 extends. Here, "parallel" may include errors within a range that does not significantly affect the specific characteristics of the elastic wave apparatus 1.

[0020] In this disclosure, “end face” is defined as a surface that reflects elastic waves. For example, the end face may be the edge surface of the substrate or the inner wall surface of a groove in the substrate.

[0021] (Electrode Layer) The electrode layer 3 is formed to be in direct or indirect contact with the upper surface of the piezoelectric body 21. Although not specifically shown, a base layer may be located between the electrode layer 3 and the piezoelectric body 21. The base layer can improve the adhesive strength between the electrode layer 3 and the piezoelectric body 21. Examples of base layer materials include titanium (Ti), chromium (Cr), or various dielectric materials.

[0022] The electrode layer 3 is made of a conductive material. Various conductive materials can be used for the electrode layer 3, such as aluminum (Al), copper (Cu), platinum (Pt), molybdenum (Mo), gold (Au), titanium (Ti), or alloys thereof. Furthermore, multiple layers of these materials may be laminated. Although not shown in the figures, the electrode layer 3 may also be a laminated structure combining the above materials. For example, Al and CuAl. ２ A laminated structure may be formed by LT, or a laminated structure of Al and Ti. The etching selectivity ratio of LT to Al is lower than that of LT to Pt, Mo, Au, or Ti. Therefore, when an electrode layer 3 containing Al as the main component is used, it is easy to thin by etching, making it easy to form the first strip electrode 315 described later. In this disclosure, the main component may be the substance that accounts for the largest proportion by weight or molar ratio, or the substance that accounts for more than half. Also, in a cross section cut in the direction of elastic wave propagation, the main component may be the substance that accounts for the largest proportion of the total thickness along the D3 axis, or the substance that accounts for more than half.

[0023] As shown in Figure 1, the electrode layer 3 has a plurality of strip electrodes 31. In this disclosure, a strip electrode 31 refers to one of a group of thin electrodes extending parallel to the D2 axis. The plurality of strip electrodes 31 each extend parallel to one another. The number of strip electrodes 31 may be set appropriately according to the electrical characteristics required of the elastic wave apparatus 1. It may be more or less than the number shown in the schematic cross-sectional and plan views in this disclosure.

[0024] Of the multiple strip electrodes 31, at least some of the strip electrodes 31 are excitation units 311 capable of exciting elastic waves. For example, as shown in Figure 1, the excitation unit 311 may be included in the IDT electrode 35. Elastic waves can be excited by the IDT electrode 35, which is composed of the excitation unit 311 and the busbar 351.

[0025] When the elastic wave apparatus 1 has an IDT electrode 35, the IDT electrode 35 includes an excitation section 311 and a busbar 351. Here, the busbar 351 refers to the portion that electrically connects to the strip electrode 31, which is the excitation section 311. The IDT electrode 35 has two opposing busbars, a first busbar 351a and a second busbar 351b, which are not electrically connected to each other, as the busbar 351. The excitation section 311 has a first excitation section 311a extending from the first busbar 351a toward the second busbar 351b, and a second excitation section 311b extending from the second busbar 351b toward the first busbar 351a.

[0026] The lengths of the excitation sections 311 are, for example, equal. The IDT electrodes 35 may be apodized, in which the length of the excitation section 311 changes according to the position in the propagation direction. Apodization makes the elastic wave propagating as the main resonance more dominant.

[0027] Although not specifically shown in the figures, the IDT electrode 35 may have dummy electrode fingers extending from one busbar 351 toward the opposite busbar 351. The dummy electrode fingers may be shorter in the D2 axis compared to the excitation section 311. The width of the IDT electrode 35 between the excitation sections 311 may vary, or it may be inclined with respect to the D1 axis.

[0028] The multiple strip electrodes 31 include a first strip electrode 315 located closest to the end face 41 in the elastic wave propagation direction, and a second strip electrode 3117 located further from the end face than the first strip electrode 315. Here, the second strip electrode 3117 is an excitation unit 311. The second strip electrode 3117 may be any of the excitation units 311 that excite the main resonance of the elastic wave device 1.

[0029] In the elastic wave apparatus 1, the average thickness of the excitation section 311 in a cross-section cut in the direction of elastic wave propagation is adjusted as appropriate to contribute to the propagation of elastic waves in the positive direction of the D1 axis. In other words, the average thickness of the excitation section 311 may be determined for the propagation of elastic waves. In this disclosure, unless otherwise specified, the term "average thickness" refers to the thickness in a cross-section cut in the direction of elastic wave propagation. In this disclosure, the average thickness of each strip electrode 31 may be determined by dividing the cross-sectional area of ​​the strip electrode 31 by the lower edge of the strip electrode 31 in a cross-section cut along the D1 axis of the elastic wave apparatus 1, or by various other methods.

[0030] In the elastic wave apparatus 1 according to the first embodiment, the average thickness of the first strip electrode 315 is smaller than the average thickness of the second strip electrode 3117. As a result, the behavior of the propagating elastic waves changes between the second strip electrode 3117, which is the excitation section 311, and the first strip electrode 315. A portion of the elastic wave energy that becomes spurious near the first strip electrode 315 can be leaked downward. Furthermore, the elastic wave apparatus 1 utilizes reflected waves reflected at the end face 41. By leaking a portion of the elastic wave energy that becomes spurious from the reflected waves downward near the end face 41 where the reflected waves are generated, the spurious emissions of the elastic wave apparatus 1 can be reduced.

[0031] The average thickness of the first strip electrode 315 may be set to an appropriate size to adjust specific characteristics. As described above, the first strip electrode 315, by having a small average thickness, can leak some of the elastic waves that become spurious downwards, thereby reducing the spurious emissions of the elastic wave device 1. On the other hand, the first strip electrode 315 leaks some of the elastic waves that become the main resonance, increasing the loss of the elastic wave device 1. For example, the average thickness of the first strip electrode 315 may be adjusted to balance the loss and spurious emissions of the elastic wave device 1. For example, it may be adjusted to reduce both loss and spurious emissions.

[0032] The average thickness of the majority of the strip electrodes 31 that constitute the excitation section 311 is the same as that of the second strip electrode 3117. This allows the elastic wave excited as the main resonance of the elastic wave device 1 to be more dominant. In this disclosure, "same" average thickness may include errors within a range that does not significantly affect specific characteristics of the elastic wave device 1. In this disclosure, "majority of the strip electrodes 31 that constitute the excitation section 311" means the majority of the strip electrodes 31 that constitute the excitation section 311, including the second strip electrode 3117. For example, this can be determined by finding the average thickness of the strip electrodes 31 that constitute the excitation section 311 and counting the number of strip electrodes 31 that have the same average thickness as the second strip electrode 3117.

[0033] The first strip electrode 315 may have a reduced thickness in some areas. For example, if the first strip electrode 315 has the shape shown in Figures 3A to C, spurious emissions can be further reduced. In this case, for example, it becomes easier to adjust the balance between loss and spurious emissions.

[0034] As shown in Figures 3A to 3C, the first strip electrode 315 may have a portion on the end face 41 side that is thinner. In other words, the first strip electrode 315 includes a first portion 315a and a second portion 315b which is thinner than the first portion 315a in a cross-section cut in the direction of elastic wave propagation, and in the direction of elastic wave propagation, the second portion 315b is located on the end face 41 side than the first portion 315a.

[0035] As shown in Figure 3A, the first strip electrode 315 may be stepped toward the negative direction of the D2 axis. In other words, the first strip electrode 315 has a lower surface R, a first upper surface T1, a second upper surface T2 located on the end surface 41 side of the first upper surface T1 in the elastic wave propagation direction, and a riser surface K connecting the first upper surface T1 and the second upper surface T2, and the first upper surface T1 may be located above the second upper surface T2. In this case, a portion of the elastic wave that becomes spurious propagates on the second upper surface T2 located below and is more likely to leak downward. As a result, the spurious emissions of the elastic wave device 1 can be further reduced.

[0036] As shown in Figure 3B, the strip electrode has a trapezoidal shape, and its upper surface may be inclined. In other words, the first strip electrode 315 has a lower surface R, a first surface S located on the end surface 41 side of the side surface in contact with the lower surface R in the elastic wave propagation direction, and an upper surface T in contact with the first surface S, and the upper surface T may be inclined with respect to the lower surface R. In this case, a portion of the elastic waves that would become spurious leaks downward along the inclined upper surface T. As a result, the spurious emissions of the elastic wave device 1 can be further reduced.

[0037] As shown in Figure 3C, the vertex portion on the end face 41 side may be curved. In other words, the first strip electrode 315 has a lower surface R, a first surface S located on the end face 41 side of the side surface in contact with the lower surface R in the elastic wave propagation direction, an upper surface T in contact with the first surface S, and a second surface U connecting the first surface S and the upper surface T, and the second surface U may be curved. In this case, a portion of the elastic waves that become spurious leaks downward along the curved second surface U. As a result, the spurious emissions of the elastic wave device 1 can be reduced.

[0038] As shown in Figure 4A, the first strip electrode 315 may be a floating electrode 313 that is not electrically connected to the excitation unit 311. The influence of the first strip electrode 315, which has a small average thickness, on the excitation of the elastic waves of the excitation unit 311 can be reduced. In addition, the floating electrode 313 can be used to adjust the sound velocity of the excited elastic waves and / or reflected waves.

[0039] As shown in FIG. 4B, the electrode layer 3 may have a reflector 37. In this case, the first strip electrode 315 refers to the strip electrode 31 of the reflector 37 that is located closest to the end face 41 side in the elastic wave propagation direction.

[0040] The side surface of the first strip electrode 315 and the end face 41 do not necessarily have to be continuous, but as shown in FIG. 1, the side surface of the first strip electrode 315 may be continuous with the end face 41. In this case, the first strip electrode 315 and the end face 41 can be formed by etching in one step.

[0041] The width of the first strip electrode 315 in the D1 axis direction may be changed as compared with other strip electrodes 31. In this case, the mode of the reflected wave can be adjusted so as to reduce the spurious of the elastic wave device 1. For example, as shown in FIG. 5, the width of the first strip electrode 315 in the elastic wave propagation direction may be made larger as compared with the second strip electrode 3117. In this case, in the manufacturing method described later, the possibility that the second strip electrode 3117 is etched is reduced.

[0042] [Second Embodiment] A second embodiment according to the present disclosure will be described. Hereinafter, the description of the parts common to the first embodiment will be omitted, and only the different parts will be described.

[0043] (End face) In the elastic wave device 1 according to the second embodiment, as shown in FIG. 2, the end face 41 is inclined. In other words, the angle α formed by the extension line of the upper surface of the piezoelectric body 21 and the tangent line at any point on the end face 41 is smaller than 90°. By the end face 41 being inclined, a part of the elastic wave that becomes spurious downward can be leaked, and the spurious of the elastic wave device 1 can be reduced.

[0044] In the present disclosure, when obtaining the angle formed by the "tangent line", for any point on the straight line, the straight line is regarded as the "tangent line" for obtaining. The description "tangent line at any point on the end face" does not limit that the end face is a curved surface or a curve.

[0045] The angle α may be set to an appropriate magnitude to adjust specific characteristics. As described above, since the end face 41 is inclined, a part of the spurious elastic wave that becomes spurious downward can be leaked, and the spurious of the elastic wave device 1 can be reduced. On the other hand, the end face 41 leaks a part of the elastic wave that becomes the main resonance, increasing the loss of the elastic wave device 1. For example, the angle α may be adjusted to balance the loss and spurious of the elastic wave device 1. For example, it may be adjusted so that the loss and spurious are reduced. Since the elastic wave device 1 according to the second embodiment has the first strip electrode 315 and the end face 41 as a structure for reducing spurious, it becomes easy to adjust the balance between loss and spurious.

[0046] Further, when the end face 41 is inclined, the distance of the D1 axis from the IDT electrode 35 to the end face 41 varies depending on the coordinates of the D2 axis. As a result, since spurious is likely to occur due to the reflection of the elastic wave by the end face 41, the spurious can be further reduced by the first strip electrode 315 that leaks the elastic wave energy near the end face 41. For example, when the angle α is smaller than 82°, spurious is particularly likely to occur near the end face 41, so the spurious can be further reduced by the first strip electrode 315.

[0047] [Third Embodiment] The third embodiment according to the present disclosure will be described. Hereinafter, the description of the parts common to the first embodiment will be omitted, and only the different parts will be described.

[0048] (End Face) As shown in FIG. 6, the end face 41 includes a first end face 41a and a second end face 41b. The first end face 41a is located on the upper surface side of the piezoelectric body 21, and the second end face 41b is located on the lower surface side of the piezoelectric body 21. As shown in FIG. 6, the first end face 41a is steeper than the second end face 41b. In other words, the angle α formed by the extension line of the upper surface of the piezoelectric body 21 and the tangent line at any point of the first end face 41a is larger than the angle β formed by the extension line of the upper surface of the piezoelectric body 21 and the tangent line at any point of the second end face 41b.

[0049] In the elastic wave device 1 according to the second embodiment, the upper surface side of the piezoelectric body 21 through which the elastic wave that becomes the main resonance propagates becomes steep, and the first end face 41a reflects the elastic wave to be used more, contributing to reduction of loss.

[0050] Furthermore, since the end face 41 has a first end face 41a and a second end face 41b with different inclination angles, it becomes easy to adjust specific characteristics of the end face 41 by adjusting the respective inclination angles. For example, it becomes easier to balance losses and spurious emissions.

[0051] [Manufacturing Method] The manufacturing method for the elastic wave apparatus 1 according to this disclosure will be described. Figure 7 shows the manufacturing process, in which the process proceeds in the order of A, B, C, and D.

[0052] The elastic wave apparatus 1 is manufactured by stacking a substrate 2 and an electrode layer 3 in that order. Subsequently, multiple strip electrodes 31 are formed on top of the substrate 2.

[0053] The elastic wave apparatus 1 forms a mask 5 above the strip electrode 31 as shown in Figure 7A and etches it. By etching, an end face 41 can be formed on the piezoelectric body 21.

[0054] The elastic wave apparatus 1 forms a mask 5 above the strip electrode 31 as shown in Figure 7A and etches it. By etching, the strip electrode 31 is thinned, and the first strip electrode 315 can be formed.

[0055] The end face 41 and the first strip electrode 315 may be formed separately by multiple etching processes, or they may be formed simultaneously or continuously by a single etching process.

[0056] When both the end face 41 and the first strip electrode 315 are formed by etching, by appropriately adjusting the material and thickness of the mask 5, the plasma generation conditions in dry etching, or various other conditions, when the end face 41 is formed, the mask 5 will gradually recede from the positive direction to the negative direction of the D1 axis by etching, as shown in Figure 7B, and the end face 41 side of the first strip electrode 315 will be exposed. Since it is naturally exposed from the end face 41 side, the mask 5 can be formed such that the average thickness of only the first strip electrode 315 is smaller. For example, the mask 5 can be formed such that the second portion 315b is located in the elastic wave propagation direction more than the first portion 315a.

[0057] Compared to etching the end face 41 and the first strip electrode 315 separately, this method avoids the difficulty of accurately forming the mask 5, making it easier to manufacture the elastic wave apparatus 1. The retracted mask 5 forms the first strip electrode 315, as shown in Figure 7C. Finally, the elastic wave apparatus 1 can be manufactured by removing the mask 5, as shown in Figure 7D.

[0058] When etching both the end face 41 and the first strip electrode 315, etching may be performed after removing a portion of the mask 5 located above the first strip electrode 315. This makes it easier to expose a portion of the first strip electrode 315.

[0059] Furthermore, after a portion of the first strip electrode 315 is exposed, the first strip electrode 315 becomes a metal mask, as shown in Figure 7B. Since a metal mask is less susceptible to etching than a resin mask, the end face 41 can be formed more steeply. In other words, the first end face 41a formed after a portion of the first strip electrode 315 is exposed is steeper than the second end face 41b formed before exposure. The elastic wave apparatus 1 according to the third embodiment can be manufactured. For example, when an electrode layer 3 containing Ti as the main component is used, the etching selectivity ratio of LT and Ti is higher than that of LT and Al, making it easier to function as a metal mask. As a result, the first end face 41a can be made even steeper.

[0060] Etching may be performed by dry etching.

[0061] For mask 5, for example, a resist for i-lines may be used. A positive resist type resist may be used. A novolac resin may be used.

[0062] [First Example of Use: Demultiplexer] Figure 8 is a schematic circuit diagram showing the configuration of a demultiplexer 8 as an example of use of the elastic wave device 1.

[0063] The demultiplexer 8 includes, for example, a transmit filter 83 that filters the transmit signal from the transmit terminal 81 and outputs it to the antenna terminal 82, and a receive filter 85 that filters the receive signal from the antenna terminal 82 and outputs it to a pair of receive terminals 84.

[0064] The transmitting filter 83 is configured, for example, by having multiple elastic wave devices 1 arranged in a ladder-type filter. That is, the transmitting filter 83 has multiple (or even just one) elastic wave devices 1 connected in series between the transmitting terminal 81 and the antenna terminal 82, and multiple (or even just one) elastic wave devices 1 (parallel arms) connecting the series line (series arm) to the reference potential.

[0065] The receiving filter 85 is configured to include, for example, an elastic wave device 1 and a multimode filter (including a double-mode filter) 87. The multimode filter 87 has a plurality of (three in the illustrated example) IDT electrodes 35 arranged in the direction of the arrangement of a plurality of strip electrodes 31.

[0066] The example described above includes a transmit filter 83 and a receive filter 85 as the decoupler 8, but it is not limited to this. The decoupler 8 may be, for example, a diplexer, or a multiplexer including three or more filters.

[0067] [Second Example of Use: Communication Device] Figure 9 is a block diagram showing the main parts of a communication device 9 as an example of the use of the demultiplexer 8. The communication device 9 performs wireless communication using radio waves and includes the demultiplexer 8.

[0068] In the communication device 9, the transmission information signal TIS, which contains the information to be transmitted, is modulated and its frequency is increased (converted to a high-frequency signal of the carrier frequency) by the RF-IC (Radio Frequency Integrated Circuit) 91 to become the transmission signal TS. The transmission signal TS has unwanted components other than the transmission passband removed by the bandpass filter 92a, is amplified by the amplifier 93a, and input to the demultiplexer 8 (transmission terminal 81). The demultiplexer 8 (transmission filter 83) then removes unwanted components other than the transmission passband from the input transmission signal TS and outputs the transmission signal TS after removal to the antenna terminal 82 or the antenna 95. The antenna 95 converts the input electrical signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

[0069] Furthermore, in the communication device 9, the radio signal (radio wave) received by the antenna 95 is converted into an electrical signal (received signal RS) by the antenna 95 and input to the demultiplexer 8 (antenna terminal 82). The demultiplexer 8 (receive filter 85) removes unwanted components other than the passband for reception from the input received signal RS, amplifies it by the amplifier 93b from the receiving terminal 84, and removes unwanted components other than the passband for reception by the bandpass filter 92b. The received signal RS is then frequency-downgraded and demodulated by the RF-IC 901 to become the received information signal RIS.

[0070] The transmitted information signal TIS and the received information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, such as analog or digitized audio signals. Wireless signal passbands (e.g., 5 GHz or higher) are also possible. The modulation scheme may be phase modulation, amplitude modulation, frequency modulation, or a combination of two or more of these. While Figure 9 illustrates a direct conversion circuit, other appropriate circuit schemes may be used, such as a double superheterodyne circuit. Furthermore, Figure 9 schematically shows only the essential components; low-pass filters or isolators may be added at appropriate positions, and the positions of amplifiers may be changed.

[0071] (Summary) (1) An elastic wave apparatus according to a first aspect of the present disclosure comprises a substrate having a piezoelectric material and including an end face, and a plurality of strip electrodes located above the substrate and extending in parallel to each other. At least some of the plurality of strip electrodes are excitation units capable of exciting elastic waves. The end face is parallel to the direction in which the strip electrodes extend when viewed from above and is located in the direction of elastic wave propagation relative to the excitation units. The plurality of strip electrodes include a first strip electrode located closest to the end face in the direction of elastic wave propagation, and a second strip electrode located further from the end face than the first strip electrode in the direction of elastic wave propagation. The second strip electrode is an excitation unit. In a cross section cut in the direction of elastic wave propagation, the average thickness of the first strip electrode is smaller than the average thickness of the second strip electrode.

[0072] (2) In an elastic wave apparatus according to a second aspect of the present disclosure, in the first aspect, the first strip electrode may include a first portion and a second portion which is less thick than the first portion in a cross-section cut in the direction of elastic wave propagation. In the direction of elastic wave propagation, the second portion may be located on the end face side of the first portion.

[0073] (3) In an elastic wave apparatus according to a third aspect of the present disclosure, in the first or second aspect, the first strip electrode may have a lower surface, a first upper surface, a second upper surface located on the end face side of the first upper surface in the elastic wave propagation direction, and a riser surface connecting the first upper surface and the second upper surface, wherein the first upper surface may be located above the second upper surface.

[0074] (4) In the elastic wave apparatus according to the fourth aspect of the present disclosure, in the first to third aspects described above, the first strip electrode may have a lower surface, a first surface located on the end face side of the side surface in contact with the lower surface in the elastic wave propagation direction, and an upper surface in contact with the first surface. The upper surface may be inclined downward with respect to the lower surface.

[0075] (5) In the elastic wave apparatus according to the fifth aspect of the present disclosure, in the first to fourth aspects described above, the first strip electrode may have a lower surface, a first surface located on the end face side of the side surface in contact with the lower surface in the elastic wave propagation direction, an upper surface in contact with the first surface, and a second surface connecting the first surface and the upper surface. The second surface may be curved.

[0076] (6) In the elastic wave apparatus according to the sixth aspect of the present disclosure, in the first to fifth aspects described above, the average thickness of the majority of the strip electrodes which are the excitation section is the same as that of the second strip electrode.

[0077] (7) In the elastic wave apparatus according to the seventh aspect of the present disclosure, in the first to sixth aspects described above, the angle α formed by the extension of the upper surface of the piezoelectric body and the tangent at any point on the end face in a cross section cut in the direction of elastic wave propagation may be less than 90°.

[0078] (8) In the elastic wave apparatus according to the eighth aspect of the present disclosure, the angle α may be less than 82° in the first to seventh aspects described above.

[0079] (9) In the elastic wave apparatus according to the ninth aspect of the present disclosure, in the first to eighth aspects described above, the end face may have a first end face located on the upper side of the piezoelectric body and a second end face located on the lower side of the piezoelectric body. In a cross section cut in the direction of elastic wave propagation, the angle formed by the extension of the upper surface of the piezoelectric body and the tangent at any point on the first end face may be greater than the angle formed by the extension of the upper surface of the piezoelectric body and the tangent at any point on the second end face.

[0080] (10) In the elastic wave apparatus according to the tenth aspect of the present disclosure, the first strip electrode may be an excitation section, as in the first to ninth aspects described above.

[0081] (11) In the elastic wave apparatus according to the eleventh aspect of the present disclosure, the first strip electrode may be a floating electrode that is not electrically connected to the excitation unit, in the first to tenth aspects described above.

[0082] (12) In the elastic wave apparatus according to the twelfth aspect of the present disclosure, in the first to eleventh aspects, the first strip electrode may have a larger width in the elastic wave propagation direction than the second strip electrode.

[0083] (13) In the elastic wave apparatus according to the thirteenth aspect of the present disclosure, the first strip electrode may contain Al as a main component, as in the first to twelfth aspects described above.

[0084] (14) In the elastic wave apparatus according to the 14th aspect of the present disclosure, in the first to 13th aspects, the substrate may have a groove on its upper surface, and the end face may be a side surface of the groove.

[0085] (15) In the elastic wave apparatus according to the fifteenth aspect of the present disclosure, the substrate may have a support substrate and a first layer located between the support substrate and the piezoelectric element, as in the first to fourteenth aspects described above.

[0086] (16) A method for manufacturing an elastic wave apparatus according to the 16th aspect of the present disclosure, according to the 1st to 15th aspects, comprises a first step of forming a plurality of strip electrodes on a substrate; a second step of forming a mask on the strip electrodes after the first step; and a third step of forming an end face on the substrate by etching and removing a portion of the first strip electrode, which is located furthest to the end face in the elastic wave propagation direction, from among the plurality of strip electrodes by etching.

[0087] (17) In the method for manufacturing an elastic wave apparatus according to the 17th aspect of the present disclosure, the second step may be performed after removing a portion of the mask located above the first strip electrode, as in the 16th aspect.

[0088] (18) In the method for manufacturing an elastic wave apparatus according to the eighteenth aspect of the present disclosure, in the seventeenth aspect, the third step may be that the mask is gradually retracted in the direction opposite to the direction of elastic wave propagation.

[0089] (19) A demultiplexer according to a 19th aspect of the present disclosure may include an antenna terminal, a transmit filter configured to filter a transmit signal and output it to the antenna terminal, and a receive filter configured to filter a receive signal from the antenna terminal. At least one of the transmit filter and the receive filter may include an acoustic wave apparatus according to the first to fifteenth aspects.

[0090] (20) A communication device according to the 20th aspect of the present disclosure may include an antenna, a demultiplexer according to the 19th aspect, with an antenna terminal connected to the antenna, and an IC connected to a transmit filter and a receive filter.

[0091] (Additional Notes) The inventions described in this disclosure have been explained above based on the drawings and embodiments. However, the inventions described in this disclosure are not limited to the embodiments described above. That is, the inventions described in this disclosure can be modified in various ways within the scope shown in this disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the inventions described in this disclosure. In other words, it should be noted that it is easy for those skilled in the art to make various modifications or alterations based on this disclosure. Furthermore, it should be noted that these modifications or alterations are included in the scope of this disclosure.

[0092] 1: Elastic wave device 2: Substrate 21: Piezoelectric layer 22: First layer 23: Support substrate 3: Electrode layer 31: Strip electrode 311: Excitation section 311a: First excitation section 311b: Second excitation section 3117: Second strip electrode 313: Floating electrode 315: First strip electrode 35: IDT electrode 351: Busbar 351a: First busbar 351b: Second busbar 37: Reflector 4: Groove section 41: End face 41a: First end face 41b: Second end face 5: Mask 8: Demultiplexer 9: Communication device

Claims

1. An elastic wave apparatus comprising: a substrate including an end face and having a piezoelectric material; a plurality of strip electrodes located above the substrate and each extending in parallel, wherein at least some of the plurality of strip electrodes are excitation units capable of exciting elastic waves; the end face, in a plan view from above, is parallel to the direction in which the strip electrodes extend and is located in the elastic wave propagation direction relative to the excitation units; the plurality of strip electrodes include: a first strip electrode located closest to the end face in the elastic wave propagation direction; and a second strip electrode further from the end face than the first strip electrode in the elastic wave propagation direction, wherein the second strip electrode is the excitation unit; and in a cross section cut in the elastic wave propagation direction, the average thickness of the first strip electrode is smaller than the average thickness of the second strip electrode.

2. The elastic wave apparatus according to claim 1, wherein the first strip electrode includes a first portion and a second portion having less thickness than the first portion in the cross-section, and in the elastic wave propagation direction, the second portion is located closer to the end face than the first portion.

3. The elastic wave apparatus according to claim 1 or 2, wherein the first strip electrode has a lower surface, a first upper surface, a second upper surface located on the end face side of the first upper surface in the elastic wave propagation direction, and a riser surface connecting the first upper surface and the second upper surface, and the first upper surface is located above the second upper surface.

4. The elastic wave apparatus according to any one of claims 1 to 3, wherein the first strip electrode has a lower surface, a first surface located on the end face side of the side surface in contact with the lower surface in the direction of elastic wave propagation, and an upper surface in contact with the first surface, the upper surface being inclined downward with respect to the lower surface.

5. The elastic wave apparatus according to any one of claims 1 to 4, wherein the first strip electrode has a lower surface, a first surface located on the end face side of the side surface in contact with the lower surface in the direction of elastic wave propagation, an upper surface in contact with the first surface, and a second surface connecting the first surface and the upper surface, the second surface being curved.

6. The elastic wave apparatus according to any one of claims 1 to 5, wherein the average thickness of the majority of the strip electrodes that constitute the excitation section is the same as that of the second strip electrode.

7. The elastic wave apparatus according to any one of claims 1 to 6, wherein in the cross-section, the angle α formed by the extension line of the upper surface of the piezoelectric body and the tangent line at any point on the end face is less than 90°.

8. The elastic wave apparatus according to claim 7, wherein the angle α is less than 82°.

9. The elastic wave apparatus according to any one of claims 1 to 8, wherein the end face has a first end face located on the upper side of the piezoelectric body and a second end face located on the lower side of the piezoelectric body, and in the cross-section, the angle formed by the extension of the upper surface of the piezoelectric body and the tangent at any point of the first end face is greater than the angle formed by the extension of the upper surface of the piezoelectric body and the tangent at any point of the second end face.

10. The elastic wave apparatus according to any one of claims 1 to 9, wherein the first strip electrode is the excitation unit.

11. The elastic wave apparatus according to any one of claims 1 to 10, wherein the first strip electrode is a floating electrode that is not electrically connected to the excitation unit.

12. The elastic wave apparatus according to any one of claims 1 to 11, wherein the first strip electrode has a greater width in the elastic wave propagation direction than the second strip electrode.

13. The elastic wave apparatus according to any one of claims 1 to 12, wherein the first strip electrode comprises Al as a main component.

14. The elastic wave apparatus according to any one of claims 1 to 13, wherein the substrate has a groove on its upper surface, and the end face is the side surface of the groove.

15. The elastic wave apparatus according to any one of claims 1 to 14, wherein the substrate comprises a support substrate and a first layer located between the support substrate and the piezoelectric body.

16. A method for manufacturing an elastic wave apparatus, comprising: a first step of forming a plurality of strip electrodes on a substrate; a second step of forming a mask on the strip electrodes after the first step; and a third step of forming an end face on the substrate by etching after the second step, and removing a portion of the first strip electrode that is located furthest to the end face in the elastic wave propagation direction among the plurality of strip electrodes by etching.

17. The method for manufacturing an elastic wave apparatus according to claim 16, wherein a portion of the mask located above the first strip electrode is removed, and then the second step is performed.

18. The method for manufacturing an elastic wave apparatus according to claim 16 or 17, wherein the third step is to gradually retract the mask in the direction opposite to the direction of elastic wave propagation.

19. A demultiplexer comprising: an antenna terminal; a transmit filter configured to filter a transmit signal and output it to the antenna terminal; and a receive filter configured to filter a receive signal from the antenna terminal, wherein at least one of the transmit filter and the receive filter is an elastic wave device as described in any one of claims 1 to 15.

20. A communication device comprising: an antenna; a demultiplexer according to claim 19, the antenna terminal of which is connected to the antenna; and an IC connected to the transmitting filter and the receiving filter.

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