Sound wave generating element and sound wave generating device

Abstract

This sound wave generating element is provided with: a base material; a pad and a heat generating layer provided on a surface of the base material; and a spacer. In plan view, the pad is positioned at the perimeter of the heat generating layer, and the pad is electrically connected to the heat generating layer. In an intersection direction that intersects the surface and so as to separate from the base material, the spacer extends from the base material or the pad to a location that is spaced farther apart from the base material or the pad than the heat generating layer.

Description

Sound wave generating element and sound wave generating device

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

[0002] Patent Document 1 discloses a pressure wave generating element. The sound wave generating element in Patent Document 1 includes a silicon substrate, a heating element layer provided on one surface side of the silicon substrate, and a heat insulating layer provided between the silicon substrate and the heating element layer. The heating element layer has a portion (an exposed surface portion) that generates pressure waves. A pair of pads is provided on one surface side of the silicon substrate, each pad contacting both ends of the heating element layer.

[0003] Japanese Patent Application Laid-Open No. 2006-94399

[0004] The sound wave generating element of Patent Document 1 has room for improvement in terms of suppressing damage to the surface of the heat generating layer.

[0005] An object of the present disclosure is to provide an acoustic wave generating element that can suppress damage to the surface of the heat generating layer.

[0006] The sound wave generating element according to the present disclosure comprises a substrate; a heat generating layer provided on the surface of the substrate; a pad provided on the surface of the substrate, positioned around the heat generating layer in a planar view seen from a cross direction intersecting the surface, and electrically connected to the heat generating layer; and a spacer extending from the substrate or the pad in a direction away from the substrate in the cross direction to a position farther from the substrate or the pad than the heat generating layer.

[0007] According to the present disclosure, it is possible to provide an acoustic wave generating element that can suppress damage to the surface of the heat generating layer.

[0008] FIG. 7 is a plan view of a sound wave generating element according to a first embodiment of the present disclosure. FIG. 8 is a cross-sectional view taken along line II-II of the sound wave generating element of FIG. 1. FIG. 9 is a plan view of a sound wave generating element according to a second embodiment of the present disclosure. FIG. 10 is a cross-sectional view taken along line IV-IV of the sound wave generating element of FIG. 3. FIG. 11 is a plan view of a sound wave generating element according to a third embodiment of the present disclosure. FIG. 12 is a cross-sectional view corresponding to FIG. 4, showing a sound wave generating device including the sound wave generating element of FIG. 5. FIG. 13 is a plan view of a sound wave generating element according to a fourth embodiment of the present disclosure. FIG. 14 is a cross-sectional view taken along line VIII-VIII of FIG. 7. FIG. 15 is a plan view showing a modified example of a spacer in the sound wave generating element of FIG. 5.

[0009] <Findings that form the basis of the present disclosure> In a sound wave generating element, a heat generating layer generates heat when a current flows through the heat generating layer. The heat of the heat generating layer is conducted to a medium (e.g., air) near the heat generating layer via the surface that forms the interface between the heat generating layer and the medium. When the medium is heated by the heat of the heat generating layer, it expands. Repeated current flow through the heat generating layer can cause repeated expansion and contraction of the medium. This allows sound waves to be generated in the medium.

[0010] The sound wave generating element is mounted on a circuit board provided in a device in which the element is mounted. The circuit board has electrodes to which a conductive material (e.g., solder paste) is applied. The sound wave generating element is mounted on the circuit board by connecting pads provided on the element to the electrodes on the circuit board via the conductive material. During the mounting process, the sound wave generating element is stored, transported, and mounted in an orientation in which the surface faces downward in the vertical direction.

[0011] The surface may be damaged by contact with other objects (e.g., a mounting base for the sound wave generating element, electronic components on a circuit board, etc.) during storage, transportation, and mounting. Damage to the surface reduces the area of ​​the interface between the heating layer and the medium, reducing the pressure of the sound waves. Furthermore, if damage caused during manufacturing expands as the sound wave generating element is used, the sound wave generating element may suddenly stop generating sound waves during use.

[0012] Therefore, the inventors conducted extensive research to find a way to prevent damage to the surface of the heat generating layer, and discovered a configuration of a sound wave generating element that includes a spacer positioned farther from the substrate than the heat generating layer in a direction intersecting the surface of the substrate. With this configuration, for example, when the surface is mounted facing downward in the vertical direction, an object positioned below the sound wave generating element in the vertical direction will come into contact with the spacer before the heat generating layer, thereby preventing contact between the object and the heat generating layer, thereby preventing damage to the surface of the heat generating layer. Based on this novel finding, the inventors have come to the following disclosure.

[0013] According to a first aspect of the present disclosure, there is provided an acoustic wave generating element comprising: a substrate; a heat generating layer provided on a surface of the substrate; a pad provided on the surface of the substrate, positioned around the heat generating layer in a planar view seen from a cross direction that crosses the surface, and electrically connected to the heat generating layer; and a spacer extending from the substrate or the pad in a direction away from the substrate in the cross direction to a position farther from the substrate or the pad than the heat generating layer.

[0014] According to a second aspect of the present disclosure, there is provided an acoustic wave generating element as described in the first aspect, wherein the heating layer has a first surface facing the substrate in the intersecting direction and a second surface located on the opposite side of the first surface in the intersecting direction, the second surface having an uncovered area not covered by the pad in the planar view, the pad being adjacent to the heating layer in the planar view, and the spacer extending from the pad in a direction away from the substrate in the intersecting direction and extending along the boundary between the pad and the uncovered area in the planar view.

[0015] According to a third aspect of the present disclosure, there is provided an acoustic wave generating element as described in the first aspect, wherein the heating layer has a first surface facing the substrate in the intersecting direction and a second surface located on the opposite side of the first surface in the intersecting direction, the second surface having an uncovered area that is not covered by the pad in the planar view, and the spacer extends from the pad in a direction away from the substrate in the intersecting direction and is located between the pad and the uncovered area in the planar view.

[0016] According to a fourth aspect of the present disclosure, there is provided an acoustic wave generating element described in any one of the first to third aspects, wherein the heat generating layer has a first surface facing the substrate in the intersecting direction and a second surface located on the opposite side of the first surface in the intersecting direction, the second surface having an uncovered area that is not covered by the pad in the planar view, and the spacer surrounds the uncovered area in the planar view.

[0017] According to a fifth aspect of the present disclosure, there is provided the acoustic wave generating element according to any one of the first to fourth aspects, wherein the spacer has a thickness of 5 μm or more in the intersecting direction.

[0018] According to a sixth aspect of the present disclosure, there is provided an acoustic wave generating element described in any one of the first to fifth aspects, wherein the spacer includes a film layer and a bonding material that bonds the substrate or the pad to the film layer.

[0019] According to a seventh aspect of the present disclosure, there is provided a sound wave generating device comprising: a sound wave generating element according to any one of the first to sixth aspects; a circuit board having a mounting surface on which the sound wave generating element is mounted; and a conductive member that electrically connects the heat generating layer and the circuit board, wherein the circuit board has an electrode provided on the mounting surface and connected to the pad via the conductive member.

[0020] According to an eighth aspect of the present disclosure, there is provided the sound wave generating device described in the seventh aspect, wherein the heat generating layer has a first surface facing the substrate in the intersecting direction and a second surface located on the opposite side of the first surface in the intersecting direction, the second surface having an uncovered area that is not covered by the pad in the planar view, and the conductive member is located farther from the uncovered area than the spacer in the planar view.

[0021] An example of the present disclosure will be described below with reference to the accompanying drawings. The following description is merely exemplary in nature and does not limit the present disclosure, its applications, or uses. The accompanying drawings are schematic drawings, and the illustrated configuration and actual products may differ in dimensional proportions, etc.

[0022] 1 and 2, an acoustic wave generating element according to a first embodiment of the present disclosure will be described. While an X-Y-Z Cartesian coordinate system is shown in the drawings, this coordinate system is provided to facilitate understanding of the present disclosure and does not limit the present disclosure. The Z direction in this coordinate system is an example of a direction intersecting the surface of the substrate.

[0023] As shown in Figures 1 and 2, the sound wave generating element 1 of the first embodiment comprises a substrate 2, a heat generating layer 3 provided on the surface of the substrate 2, a pad 4 electrically connected to the heat generating layer 3, and a spacer 5 extending from the substrate 2 or the pad 4.

[0024] In this specification and claims, the term "surface" is not limited to a flat surface but may include a curved surface and an uneven surface. Furthermore, "provided on a surface" is not limited to a case where a certain member is directly provided on a target member, but may also include a case where a certain member is provided on a target member via another member.

[0025] As shown in Figure 2, the substrate 2 has a lower surface 2a facing downward in the Z direction and an upper surface 2b facing upward in the Z direction. The lower surface 2a and the upper surface 2b extend in a plane direction intersecting the Z direction. In this embodiment, the lower surface 2a and the upper surface 2b extend in the XY plane. The upper surface 2b is an example of the "surface of the substrate" in this disclosure. In the following description, the orientation of the sound wave generating element 1 in which the lower surface 2a of the substrate 2 faces downward in the vertical direction is referred to as the "normal orientation," and the orientation of the sound wave generating element 1 in which the lower surface 2a faces upward in the vertical direction is referred to as the "reverse orientation."

[0026] 1 , the substrate 2 has a rectangular shape in plan view from the Z direction, for example. In this embodiment, the substrate 2 has two first edges 23 extending along the X direction in plan view and two second edges 24 extending along the Y direction and connecting the first edges 23 to each other.

[0027] As shown in Figure 2, the base material 2 includes a support substrate 21 and a heat insulating layer 22 laminated in the Z direction on the support substrate 21. The support substrate 21 has a lower surface 21a that constitutes the lower surface 2a of the base material 2, and an upper surface 21b on the opposite side. In this embodiment, the heat insulating layer 22 is provided on the entire upper surface 21b of the support substrate 21. The heat insulating layer 22 has a lower surface 22a bonded to the upper surface 21b of the support substrate 21, and an upper surface 22b on the opposite side. The upper surface 22b of the heat insulating layer 22 constitutes the upper surface 2b of the base material 2.

[0028] For example, the substrate 2 is made of a semiconductor such as silicon, or an insulating material such as glass, ceramic, or polymer. In this embodiment, the substrate 2 is a silicon substrate. For example, the heat insulating layer 22 is made of a material with low thermal conductivity such as porous silicon, silicon oxide, or polymer. In this embodiment, the heat insulating layer 22 is made of polyimide and has a thickness of 7 μm.

[0029] The heat insulating layer 22 is formed by spin-coating polyimide varnish on the surface of the silicon wafer and curing it at 350° C. for 1 hour in a nitrogen atmosphere.

[0030] A heat generating layer 3 that generates heat when a current flows therethrough is provided on the upper surface 2b of the substrate 2. As shown in Fig. 1, in this embodiment, the heat generating layer 3 is rectangular in plan view and has two edges 31 extending along the Y direction. The heat generating layer 3 is located in the center of the upper surface 2b of the substrate 2 in plan view.

[0031] The heating layer 3 is made of a metal such as gold, silver, copper, platinum, rhodium, palladium, ruthenium, nickel, iridium, chromium, molybdenum, tungsten, titanium, aluminum, or tin, or an alloy containing two or more of these metals. The heating layer 3 may also be made of a conductive material such as carbon nanotubes or metal-coated fibers. In this embodiment, the heating layer 3 has a multilayer structure including a gold layer in contact with the upper surface 2b of the substrate 2 and a chromium layer laminated on the gold layer. The gold layer has a thickness of 20 nm in the Z direction, and the chromium layer has a thickness of 2 nm in the Z direction.

[0032] 2, the heat generating layer 3 has a lower surface 3a facing the substrate 2 in the Z direction and an upper surface 3b opposite the lower surface 3a. The lower surface 3a is an example of a first surface in the present disclosure, and the upper surface 3b is an example of a second surface in the present disclosure.

[0033] 1, two pads 4 are provided on the upper surface 2b of the substrate 2, positioned around the heat generating layer 3 in a plan view. Each pad 4 is adjacent to the heat generating layer 3 in a plan view. The two pads 4 are provided in positions facing each other across the heat generating layer 3 in a direction intersecting the Z direction.

[0034] In this embodiment, two pads 4 are adjacent to two edge portions 31. As shown in Figures 1 and 2, each pad 4 covers the adjacent edge portion 31 and is connected to the heating layer 3 at the edge portion 31. As shown in Figure 1, the pad 4 has, for example, a rectangular shape extending in the Y direction in a plan view.

[0035] The upper surface 3b of the heat generating layer 3 includes an uncovered area 32 that is not covered by the two pads 4 in plan view. The uncovered area 32 forms the interface between the heat generating layer 3 and the medium (e.g., air) that generates sound waves when the sound wave generating element 1 is in use. In other words, when a current flows through the heat generating layer 3, heat from the heat generating layer 3 is conducted to the medium via the uncovered area 32.

[0036] The pad 4 has two first edges 41 extending along the X direction in a plan view and two second edges 42 extending along the Y direction and connecting the first edges 41. The two second edges 42 include a second edge 421 that is closer to the uncovered region 32 in the X direction and a second edge 422 that is farther from the uncovered region 32 in the X direction.

[0037] 2 , the pad 4 has an upper surface 4 a facing upward in the Z direction. The pad 4 is made of a metal such as gold, silver, copper, platinum, rhodium, palladium, ruthenium, nickel, iridium, chromium, molybdenum, tungsten, titanium, aluminum, or tin, or an alloy containing two or more of these metals. In this embodiment, the pad 4 has a multi-layer structure including a silver layer in contact with the upper surface 2 b of the substrate 2, a copper-nickel alloy layer located on the silver layer, and a nickel-chromium alloy layer located on the copper-nickel alloy layer and having the upper surface 4 a of the pad 4.

[0038] For example, the heat generating layer 3 and the pad 4 can be formed by stacking the layers included in the multi-layer structure by vapor deposition, sputtering, electrolytic plating, electroless plating, ion plating, or the like.

[0039] 1, four spacers 5 are provided on the upper surface 2b of the substrate 2, extending in the Z direction from the upper surface 2b away from the substrate 2. In this embodiment, the four spacers 5 are located at four corners of the substrate 2 in a plan view.

[0040] 2, the spacer 5 includes a film layer 51 and a bonding material 52 that bonds the film layer 51 to the substrate 2. The spacer 5 is made of an insulating material such as glass, ceramic, or polymer. In this embodiment, the film layer 51 is a polyimide film, and the bonding material 52 is a bonding sheet.

[0041] The spacer 5 has a base end 53 joined to the upper surface 2b of the substrate 2 in the Z direction, and a tip end 54 opposite the base end 53. The spacer 5 extends from the substrate 2 or the pad 4 in a direction away from the substrate 2 in the Z direction to a position farther from the substrate 2 or the pad 4 than the heat generating layer 3. The tip end 54 is located farther from the substrate 2 in the Z direction than the uncovered region 32. For example, the thickness T1 of the spacer 5 in the Z direction is 5 μm or more.

[0042] For example, the spacers 5 can be formed by thermocompression bonding a polyimide film with a bonding sheet to the upper surface 2b of the base material 2. The spacers 5 may also be formed by photolithography, coating with a dispenser, or the like.

[0043] The provision of the spacer 5 increases the surface area of ​​the sound wave generating element 1. This improves the heat dissipation of the sound wave generating element 1 compared to a configuration without the spacer 5, allowing a larger voltage to be applied to the heat generating layer 3. This allows the pressure of the sound waves generated by the sound wave generating element 1 to be increased.

[0044] According to this embodiment, the spacer 5 is positioned farther from the substrate 2 in the Z direction than the heat generating layer 3. Therefore, in the sound wave generating element 1 in the inverted position, the upper surface 3b of the heat generating layer 3 is positioned vertically above the tip 54 of the spacer 5. In this case, an object positioned vertically below the sound wave generating element 1 (for example, an electronic component on a mounting table or circuit board) may come into contact with the spacer 5 before the upper surface 3b. This reduces the possibility that the upper surface 3b of the sound wave generating element 1 in the inverted position will come into contact with another object and be damaged. Therefore, malfunctions of the sound wave generating element 1 can be suppressed.

[0045] <Second embodiment> A pressure wave generating element according to a second embodiment of the present disclosure will be described with reference to Figures 3 and 4. Figure 3 is a plan view of the sound wave generating element according to the second embodiment of the present disclosure. Figure 4 is a cross-sectional view of the sound wave generating element of Figure 3 taken along line IV-IV.

[0046] The sound wave generating element 1A according to the second embodiment differs from the sound wave generating element 1 according to the first embodiment in that a spacer 5A is also provided on the upper surface 4a of the pad 4. In the following description of the second embodiment, the same components as those of the sound wave generating element 1 will be given the same reference numerals and their description may be omitted.

[0047] As shown in Fig. 3, the spacer 5A is provided across the upper surface 2b of the substrate 2 and the upper surface 4a of the pad 4 in a plan view. That is, as shown in Fig. 4, a portion of the spacer 5A extends from the upper surface 4a of the pad 4 in a direction away from the substrate 2 in the Z direction. In this embodiment, as shown in Fig. 3, the spacer 5A extends linearly in the Y direction from one first edge portion 23 of the substrate 2 to the other first edge portion 23. In a plan view, the portion of the spacer 5A that overlaps with the pad 4 extends along the boundary portion 33 between the pad 4 and the uncovered region 32.

[0048] In a plan view, the distance D1 between the second edge portion 421 and the spacer 5A is shorter than the distance between the second edge portion 422 and the spacer 5A. For example, the minimum distance D1 between the second edge portion 421 and the spacer 5A is shorter than the minimum distance D2 between the second edge portion 422 and the spacer 5A.

[0049] When the sound wave generating element 1A is mounted on a circuit board, the two pads 4 are connected to two electrodes on the circuit board via conductive materials such as solder or conductive paste. The conductive materials are heated and melted during mounting, and spread over the surfaces of the pads. If the melted conductive material reaches the uncovered area 32, there is a risk that the conductive material will be disposed on the uncovered area 32 as well.

[0050] Typically, the thermal conductivity of the conductive member is lower than that of the heat generating layer 3. Therefore, the area of ​​the uncovered region 32 that is covered with the conductive member loses its original function of conducting heat from the heat generating layer 3 to a medium (e.g., air). This reduces the pressure of the sound waves generated by the sound wave generating element 1A.

[0051] On the other hand, the conductive material located above the uncovered region 32 functions as part of the pad 4. Therefore, if the conductive material flows into the uncovered region 32, the distance between the two pads 4 in a plan view becomes shorter than the desired distance. This causes the magnitude of the electrical resistance in the sound wave generating element 1A to deviate from the desired range, increasing the failure rate of the sound wave generating element 1A.

[0052] According to this embodiment, the spacer 5 extending along the boundary 33 between the pad 4 and the uncovered region 32 can prevent the molten conductive material from flowing from the upper surface 4a of the pad 4 into the uncovered region 32. This makes it difficult for the conductive material to be disposed in the uncovered region 32, thereby preventing a decrease in the pressure of the sound waves generated by the sound wave generating element 1A.

[0053] Furthermore, since the conductive member remains on each connection pad, the distance between the two connection pads is made uniform between individual sound wave generating elements, which makes the electrical resistance of the sound wave generating elements uniform to a desired level, thereby keeping the failure rate of the sound wave generating elements low.

[0054] Third Embodiment A sound wave generating element 1B according to a third embodiment of the present disclosure will be described with reference to Fig. 5. Fig. 5 is a plan view of the sound wave generating element according to the third embodiment of the present disclosure.

[0055] The sound wave generating element 1B according to the third embodiment differs from the sound wave generating element 1A according to the second embodiment in that, in plan view, a spacer 5B surrounds the uncovered region 32. In the following description of the third embodiment, the same reference numerals will be used to designate components similar to those of the sound wave generating element 1B, and their description may be omitted.

[0056] As shown in FIG. 5 , the spacer 5B is rectangular in plan view and surrounds the uncovered region 32. The spacer 5B has two linear first portions 55 extending along the Y direction and two linear second portions 56 extending along the X direction and connecting the first portions 55 to each other. The two first portions 55 correspond to the spacer 5A in the second embodiment. The second portions 56 connect the ends of the two first portions 55 to each other. In this embodiment, the second portions 56 extend along the X direction from the end of one first portion 55 to the end of the other first portion 55 along the first edge 23 of the substrate 2.

[0057] A sound wave generating device including a sound wave generating element 1B will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view corresponding to Fig. 4, showing a sound wave generating device including the sound wave generating element of Fig. 5.

[0058] The sound wave generating device 10 shown in FIG. 6 includes a sound wave generating element 1B and a circuit board 6 on which the sound wave generating element 1B is mounted.

[0059] For example, the circuit board 6 is a motherboard of a device on which the sound wave generating element 1B is mounted. One main surface of the circuit board 6 constitutes a mounting surface 6a on which the sound wave generating element 1B is mounted. The sound wave generating element 1B is mounted on the circuit board 6 with the upper surface 3b of the heat generating layer 3 facing the mounting surface 6a.

[0060] The circuit board 6 has a hole 61 formed in a position facing the uncovered area 32 to allow the generated sound waves to pass through. Two electrodes 62 are provided on the mounting surface 6a. The two electrodes 62 are connected to the two pads 4 via the conductive members 7, respectively. This allows current to flow from the circuit board 6 to the heating layer 3 via the electrodes 62, the conductive members 7, and the pads 4.

[0061] For example, the conductive member 7 is a conductive member such as solder or conductive paste.

[0062] The electrode 62 and the conductive member 7 are positioned farther from the uncovered region 32 than the spacer 5 is in a direction intersecting the Z direction.

[0063] In the mounting process of the sound wave generating element 1B, a conductive member 7 is placed on the electrode 62. For example, solder paste is applied to the electrode 62. At this time, the thickness of the applied solder paste is set to be greater than the distance between the pad 4 and the electrode 62 when the tip end 54 of the spacer 5B is in contact with the mounting surface 6a. This allows the electrode 62 and the pad 4 to be more reliably connected by the conductive member 7 even when the tip end 54 of the spacer 5B is in contact with the mounting surface 6a.

[0064] The sound wave generating element 1B is transported by a chip mounter with the upper surface 3b of the heat generating layer 3 facing vertically downward, and is placed on the circuit board 6 with the pads 4 in contact with the conductive members 7. The conductive members 7 are melted by reflow, thereby connecting the electrodes 62 and the pads 4. The spacers 5B surrounding the uncovered areas 32 prevent the melted conductive members 7 from reaching the uncovered areas 32 along the upper surfaces 4a of the pads 4.

[0065] According to this embodiment, the spacer 5B surrounds the uncovered region 32 in a plan view. As a result, when the sound wave generating element 1B is mounted on the circuit board 6 in an inverted position, the stability of the sound wave generating element 1B placed on the circuit board 6 is increased compared to a configuration in which the spacer 5B has a different shape. In other words, the sound wave generating element 1B is less likely to fall over during the process of mounting the sound wave generating element 1B on the circuit board 6. Therefore, mounting defects of the sound wave generating element 1B can be suppressed.

[0066] Furthermore, when the spacer 5B extends along the boundary portion 33 on the pad 4, the molten conductive member 7 can be further prevented from flowing from the pad 4 into the uncovered region 32.

[0067] <Fourth embodiment> An acoustic wave generating element according to a fourth embodiment of the present disclosure will be described with reference to Fig. 7 and Fig. 8. Fig. 7 is a plan view of the acoustic wave generating element according to the fourth embodiment of the present disclosure. Fig. 8 is a cross-sectional view taken along line VIII-VIII in Fig. 7.

[0068] The sound wave generating element 1C according to the fourth embodiment differs from the sound wave generating element 1A according to the second embodiment in terms of the position of the spacer 5C in a plan view. In the following description of the fourth embodiment, the same reference numerals will be used to designate the same components as those of the sound wave generating element 1A, and the description thereof may be omitted.

[0069] As shown in Figures 7 and 8, the spacer 5C is located between the uncovered area 32 and the pad 4 in a direction intersecting the Z direction (e.g., the Y direction), and extends from the upper surface 2b of the substrate 2 along the Z direction.

[0070] For example, the pad 4 is connected to the heat generating layer 3 by a wire (not shown).

[0071] The present disclosure is not limited to the above-described embodiment, and can be embodied in various other forms. The number, shape, and positions of the spacers 5, 5A to 5C are not limited to those shown in the above-described embodiment.

[0072] The number of spacers 5, 5A to 5C may be 1 or 3 or more. The shapes of the base material 2, the heat generating layer 3, and the spacers 5, 5A to 5C in plan view are not limited to rectangular, but may also be polygonal, circular, elliptical, etc.

[0073] Fig. 9 is a plan view showing a modified example of the spacer in the sound wave generating element of Fig. 1. In the modified example shown in Fig. 9, two spacers 5D extend along two edges extending in the X direction of the base material 2 in a plan view. The spacers 5D extend from one second edge 24 of the base material 2 to the other second edge 24.

[0074] Fig. 10 is a plan view showing a modified example of the spacer in the sound wave generating element of Fig. 5. In the modified example shown in Fig. 10, the second portion 56 extends in the X direction along the first edge 23 of the base material 2 from one second edge 24 to the other second edge 24.

[0075] The base material 2 does not need to include the heat insulating layer 22. In this case, the heat generating layer 3, the pads 4, and the spacers 5 may be provided directly on the upper surface 21b of the support substrate 21.

[0076] A recess recessed downward from the upper surface 21b may be provided in the support substrate 21. A heat insulating layer 22 may be embedded in the recess.

[0077] The heat generating layer 3 and the pad 4 are not limited to a multi-layer structure, but may have a single-layer structure.

[0078] <Example> The following describes the results of an experiment demonstrating the effect of the spacer 5. In this experiment, an example and a comparative example were prepared, and the variations in electrical resistance and the upper limit power that can be applied in the sound wave generator were evaluated. The example is a sound wave generator in which the sound wave generating element shown in Figure 10 is mounted on a circuit board, and the comparative example is a sound wave generator in which the sound wave generating element shown in Figure 10 without the spacer 5B is mounted on a circuit board.

[0079] Regarding the variation in electrical resistance, the resistance of the sound wave generating elements of the examples and comparative examples was measured by the four-terminal method, and the coefficient of variation of the resistance was calculated and evaluated. Regarding the upper limit power, the power when the circuit is open was calculated and evaluated. The power when the circuit is open was calculated based on the voltage applied to the sound wave generating element and the voltage when the circuit is open, and the resistance of the sound wave generating elements of the examples and comparative examples.

[0080]

[0081] As shown in Table 1, the coefficient of variation of the resistance of the sound wave generating element in the example with the spacer 5B was about 1 / 28 of that in the comparative example without the spacer 5B. The power when the circuit of the sound wave generating element was open in the example with the spacer 5B was about four times that of the comparative example without the spacer 5B. These experimental results show that providing a spacer in the sound wave generating element reduces the variation in the resistance of the sound wave generating element after it is mounted on a circuit board, thereby lowering the failure rate.

[0082] Any of the various embodiments or modifications described above can be combined appropriately to achieve the effects of each. In addition, combinations of embodiments, combinations of examples, or combinations of embodiments and examples are possible, and combinations of features from different embodiments or examples are also possible.

[0083] Although the present disclosure has been fully described in connection with the preferred embodiments with reference to the accompanying drawings, various changes and modifications will be apparent to those skilled in the art, and such changes and modifications are to be understood as being included within the scope of the present disclosure as defined by the appended claims unless they depart therefrom.

[0084] INDUSTRIAL APPLICABILITY The present disclosure is useful for sound wave generating devices and various devices equipped with sound wave generating devices, as it can suppress damage to the surface of the heat generating layer.

[0085] REFERENCE SIGNS LIST 1, 1A to 1C sound wave generating element 2 substrate 2b upper surface 3 heat generating layer 3b upper surface 32 non-coated area 33 boundary portion 4 pad 5, 5A to 5D spacer 51 film layer 52 bonding material 6 circuit board 6a mounting surface 62 electrode 7 conductive member 10 sound wave generating device

Claims

1. An acoustic wave generating element comprising: a substrate; a heat generating layer provided on a surface of the substrate; pads provided on the surface of the substrate, positioned around the heat generating layer in a plan view seen from a cross direction intersecting the surface, and electrically connected to the heat generating layer; and a spacer extending from the substrate or the pad in a direction away from the substrate in the cross direction to a position farther from the substrate or the pad than the heat generating layer.

2. The sound wave generating element of claim 1, wherein the heat generating layer has a first surface facing the substrate in the cross direction and a second surface located on the opposite side of the first surface in the cross direction, the second surface having an uncovered area not covered by the pad in the planar view, the pad being adjacent to the heat generating layer in the planar view, and the spacer extending from the pad in a direction away from the substrate in the cross direction and extending along the boundary between the pad and the uncovered area in the planar view.

3. The sound wave generating element of claim 1, wherein the heat generating layer has a first surface facing the substrate in the cross direction and a second surface located on the opposite side of the first surface in the cross direction, the second surface having an uncovered area that is not covered by the pad in the planar view, and the spacer extends from the pad in a direction away from the substrate in the cross direction and is located between the pad and the uncovered area in the planar view.

4. An acoustic wave generating element according to any one of claims 1 to 3, wherein the heat generating layer has a first surface facing the substrate in the cross direction and a second surface located on the opposite side of the first surface in the cross direction, the second surface having an uncovered area that is not covered by the pad in the planar view, and the spacer surrounds the uncovered area in the planar view.

5. The sound wave generating element according to any one of claims 1 to 4, wherein the spacer has a thickness of 5 μm or more in the cross direction.

6. The sound wave generating element according to any one of claims 1 to 5, wherein the spacer includes a film layer and a bonding material that bonds the base material or the pad to the film layer.

7. A sound wave generating device comprising: a sound wave generating element according to any one of claims 1 to 6; a circuit board having a mounting surface on which said sound wave generating element is mounted; and a conductive member that electrically connects said heat generating layer and said circuit board, wherein said circuit board has electrodes provided on said mounting surface and connected to said pads via said conductive member.

8. The sound wave generating device according to claim 7, wherein the heat generating layer has a first surface facing the substrate in the cross direction and a second surface located on the opposite side of the first surface in the cross direction, the second surface having an uncovered area that is not covered by the pad in the planar view, and the conductive member is located farther from the uncovered area than the spacer in the planar view.

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