Pressure wave generating element

Abstract

Provided is a thermally excited pressure wave generating element capable of generating a higher sound pressure. This pressure wave generating element is a thermally excited pressure wave generating element, and is provided with: a first solid insulating layer having a first main surface; a first metal layer provided on the first main surface of the first solid insulating layer; a second metal layer disposed at a distance from the first metal layer in the thickness direction of the first solid insulating layer; a first electrode electrically connected to one end side of the first metal layer and one end side of the second metal layer; and a second electrode electrically connected to the other end side of the first metal layer and the other end side of the second metal layer, the first solid insulating layer being located between the first metal layer and the second metal layer.

Description

Technical Field

[0001] The present invention relates to a thermally excited pressure wave generating element. Background Art

[0002] There has been proposed a thermally excited pressure wave generating element (also referred to as a “thermal sensitive element”) that heats a medium such as air to generate a pressure wave (for example, Patent Document 1).

[0003] The thermally excited pressure wave generating element has a resistor (typically a metal layer) that generates heat when electricity is applied. When current flows through the resistor, the resistor generates heat, and the air in contact with the resistor expands. If the electricity is then stopped, the expanded air contracts. Pressure waves (also called sound waves) are generated by the expansion and contraction of the air. Unlike a sound source using a piezoelectric body, the thermally excited pressure wave generating element does not utilize a resonance mechanism. Therefore, it is possible to generate wide-band and short-pulse sound waves.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 11-300274

[0005] However, in a thermal excitation type pressure wave generating element, electrical energy is converted into thermal energy and then sound waves are generated. Therefore, the energy conversion efficiency is sometimes low, making it difficult to increase the output sound pressure. Summary of the invention

[0006] An object of the present invention is to solve the above-mentioned problems and to provide a thermally excited pressure wave generating element capable of generating a higher sound pressure.

[0007] In order to achieve the above-mentioned purpose, the pressure wave generating element of the present invention is a thermally excited pressure wave generating element, which comprises: a first solid insulating layer having a first main surface; a first metal layer arranged on the first main surface of the above-mentioned first solid insulating layer; a second metal layer arranged at a distance from the above-mentioned first metal layer in the thickness direction of the above-mentioned first solid insulating layer; a first electrode electrically connected to one end side of the above-mentioned first metal layer and one end side of the above-mentioned second metal layer; and a second electrode electrically connected to the other end side of the above-mentioned first metal layer and the other end side of the above-mentioned second metal layer, and the above-mentioned first solid insulating layer is located between the above-mentioned first metal layer and the above-mentioned second metal layer.

[0008] According to the present invention, there is provided a thermally excited pressure wave generating element capable of generating a higher sound pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic perspective view of a pressure wave generating element according to an embodiment of the present invention.

[0010] Figure 2 yes Figure 1 Schematic top view of a pressure wave generating element.

[0011] Figure 3 yes Figure 1 Schematic cross-sectional view of the pressure wave generating element taken along line A1-A1.

[0012] Figure 4 It is a schematic cross-sectional view showing an example of the first heating element.

[0013] Figure 5 This is a schematic enlarged cross-sectional view illustrating one fiber to which metal coating is applied.

[0014] Figure 6 It is a schematic top view showing another example of the pressure wave generating element.

[0015] Figure 7 This is a schematic cross-sectional view showing a pressure wave generating element according to Modification 1.

[0016] Figure 8 This is a schematic cross-sectional view showing another pressure wave generating element according to Modification 1.

[0017] Fig. 9 This is a schematic cross-sectional view showing a pressure wave generating element according to Modification Example 2.

[0018] Fig.10 This is a schematic cross-sectional view showing another pressure wave generating element according to Modification Example 2.

[0019] Fig.11 This is an electron microscope image showing an example of measuring the thickness of the fiber membrane, the metal layer, and the solid insulating layer. DETAILED DESCRIPTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the embodiments do not limit the present invention. In addition, substantially identical components are marked with the same reference numerals in the accompanying drawings, thereby omitting descriptions. Furthermore, for the purpose of illustration, the sizes of the components in the accompanying drawings are sometimes exaggerated and may not necessarily be in scale.

[0021] In the following, for the sake of convenience, terms such as "up", "down", "right", "left", and "side" are used to indicate directions, but these terms do not limit the manufacturing state and usage state of the pressure wave generating element of the present invention.

[0022] Implementation Method

[0023] The pressure wave generating element of the embodiment of the present invention has a plurality of resistors (metal layers) that generate heat by passing electricity. The plurality of metal layers are stacked at a distance from each other and connected in parallel between a pair of electrodes. In this specification, such a pressure wave generating element is referred to as a "stacked pressure wave generating element" or a "stacked element".

[0024] use Figure 1 to Figure 3 , a pressure wave generating element according to an embodiment of the present invention is described. Figure 1 It is a schematic perspective view of a pressure wave generating element according to an embodiment of the present invention. Figure 2 yes Figure 1 Schematic top view of a pressure wave generating element. Figure 3 yes Figure 2 A schematic cross-sectional view taken along line A1-A1 is shown.

[0025] like Figure 1 to Figure 3 As shown, the pressure wave generating element 100 of the present embodiment includes metal layers 11 , 12 , a solid insulating layer 10 , and a pair of electrodes 31 , 32 .

[0026] exist Figure 1 to Figure 3 In FIG. 1 , the thickness direction of the solid insulating layer 10 is set to the Z direction. Figure 1 as well as Figure 3 In order to facilitate understanding, the dimensions of the components in the Z direction are exaggerated. Figure 2 In the top view shown, the horizontal direction is set as the X direction, and the direction perpendicular to the X direction (the up-down direction) is set as the Y direction. In the example shown in the figure, when viewed from the Z direction, the outer edge of the pressure wave generating element 100 is roughly rectangular, and the directions in which its sides extend are respectively set as the X direction and the Y direction. In addition, the planar shape of the pressure wave generating element 100 is not limited to the shape shown in the figure.

[0027] The metal layers 11 and 12 are arranged at a distance from each other in the thickness direction (Z direction) of the solid insulating layer 10. That is, the metal layers 11 and 12 are stacked in the Z direction. In addition, the metal layers 11 and 12 are connected in parallel between the electrode 31 and the electrode 32.

[0028] The solid insulating layer 10 is located between the metal layer 11 and the metal layer 12 in the Z direction. The solid insulating layer 10 may also have a plurality of through holes penetrating in the thickness direction. For example, the solid insulating layer 10 may also be a layer having a porous structure (eg, a fiber layer).

[0029] The solid insulating layer 10 has a main surface (also referred to as a "first main surface") 10a and a main surface (also referred to as a "second main surface") 10b opposite to the main surface 10a. In this example, the metal layer 11 is provided on the main surface 10a of the solid insulating layer 10, and the metal layer 12 is provided on the main surface 10b of the solid insulating layer 10. The metal layers 11 and 12 may also be in contact with the solid insulating layer 10.

[0030] At least a portion of the surface of each metal layer 11 , 12 opposite to the solid insulating layer 10 is in contact with a medium such as air. In the example shown in the figure, the upper surface 11 a of the metal layer 11 is in contact with the air layer 71 , and the lower surface 12 b of the metal layer 12 is in contact with the air layer 72 .

[0031] In this specification, the structure M1 including the solid insulating layer 10 and the metal layers 11 and 12 provided on both sides of the solid insulating layer 10 is sometimes referred to as the "first heating element". In addition, the metal layer 11 in the first heating element M1 is sometimes referred to as the "first metal layer", and the metal layer 12 is sometimes referred to as the "second metal layer".

[0032] Electrodes 31 and 32 are a pair of electrodes that apply voltage to metal layers 11 and 12 in a specified direction (here, the X direction). When viewed from above, electrode 31 is electrically connected to one end side of metal layer 11 (the left end side in this example) and one end side of metal layer 12 (the left end side in this example). Electrode 32 is electrically connected to the other end side of metal layer 11 (the right end side in this example) and the other end side of metal layer 12 (the right end side in this example). Metal layers 11 and 12 extend continuously from one end side electrically connected to electrode 31 to the other end side electrically connected to electrode 32, respectively. When viewed from above, the width of metal layers 11 and 12 in the direction of current conduction (X direction) and the width in the direction orthogonal to the direction of current conduction (Y direction) are not particularly limited. In this example, the width in the X direction is the same as the width in the Y direction.

[0033] The pressure wave generating element 100 may further include: a pair of connection electrodes 41 , 42 for electrically connecting the metal layer 11 and the electrodes 31 , 32 ; and a pair of connection electrodes 43 , 44 for electrically connecting the metal layer 12 and the electrodes 31 , 32 .

[0034] In the illustrated example, the electrode 31 has a first portion c1 located above the first heating element M1, a second portion c2 located below the first heating element M1, and a connection portion extending in the Z direction to connect the first portion c1 and the second portion c2, at one end side (here, the left side) of the first heating element M1. Similarly, the electrode 32 has a first portion d1 located above the first heating element M1, a second portion d2 located below the first heating element M1, and a connection portion extending in the Z direction to connect the first portion d1 and the second portion d2, at the other end side (here, the right side) of the first heating element M1. The connecting electrode 41 electrically connects the left end portion 11c of the upper surface 11a of the metal layer 11 to the first portion c1 of the electrode 31. The connecting electrode 42 electrically connects the right end portion 11d of the upper surface 11a of the metal layer 11 to the first portion d1 of the electrode 32. Likewise, the connection electrode 43 electrically connects the left end 12c of the lower surface 12b of the metal layer 12 to the second portion c2 of the electrode 31 , and the connection electrode 44 electrically connects the right end 12d of the lower surface 12b to the second portion d2 of the electrode 32 .

[0035] The pressure wave generating element 100 may further include a supporting structure 50 that supports the first heating element M1 . The supporting structure 50 may be an annular structure that supports the outer periphery of the metal layer 11 (in this example, the outer peripheries of the metal layers 11 and 12 ) and the solid insulating layer 10 .

[0036] The support structure 50 includes, for example, a support body (sometimes referred to as a "first support body") 51 provided on the main surface 10a side of the solid insulating layer 10, and a support body (sometimes referred to as a "second support body") 52 provided on the main surface 10b side of the solid insulating layer 10. The supports 51 and 52 may be configured to hold the peripheral portion of the solid insulating layer 10 therebetween. Alternatively, the peripheral portion of the solid insulating layer 10 and the support body 51 may be bonded by an adhesive layer 61, and the peripheral portion of the solid insulating layer 10 and the support body 52 may be bonded by an adhesive layer 62.

[0037] In the example shown in the figure, the support body 51 is configured to surround the metal layer 11, and the support body 52 is configured to surround the metal layer 12 when viewed from above. The metal layers 11 and 12 may be formed to cover substantially the entire region of the main surfaces 10a and 10b of the solid insulating layer 10 exposed from the support body when viewed from above. The connection electrodes 41 and 42 may extend from a portion of the upper surface 11a of the metal layer 11 to cover a portion of the support body 51. Similarly, the connection electrodes 43 and 44 may extend from a portion of the lower surface 12b of the metal layer 12 to cover a portion of the support body 52.

[0038] In the pressure wave generating element 100, a driving signal is supplied to the metal layers 11 and 12 respectively via a pair of electrodes 31 and 32. The metal layer 11 applies a thermal shock to the air layer 71 by a temperature change corresponding to the waveform of the driving signal, thereby generating a first pressure wave. Similarly, the metal layer 12 generates a second pressure wave in the air layer 72 by a temperature change corresponding to the waveform of the driving signal. The composite wave (acoustic wave) W of the first pressure wave and the second pressure wave can be emitted to the outside of the pressure wave generating element 100, for example, from the Z direction (in the example shown in the figure, from above the metal layer 11).

[0039] The frequency of the synthetic wave W emitted from the pressure wave generating element 100 can be adjusted by the driving signal. For example, if the driving signal is set to an audible frequency, the pressure wave generating element 100 can be used as an audio speaker, and if the driving signal is set to an ultrasonic frequency, the pressure wave generating element 100 can be used as an ultrasonic source.

[0040] The pressure wave generating element 100 may also include a substrate (not shown). The substrate may be arranged at a distance from the first heating element M1 in the Z direction. For example, when the synthetic wave W is emitted from above the metal layer 11, the substrate may be arranged below the metal layer 12 at a distance from the lower surface 12b of the metal layer 12.

[0041] According to the pressure wave generating element 100 of the present embodiment, a plurality of metal layers 11 and 12 are arranged at a distance in the thickness direction (Z direction) of the solid insulating layer 10, and are connected in parallel between the electrodes 31 and 32. The metal layers 11 and 12 are connected in parallel. Thus, the element resistance can be reduced compared to a single-layer type pressure wave generating element (single-layer type element) having a single metal layer. By reducing the element resistance, the input power to the pressure wave generating element 100 can be increased, so the output sound pressure (the sound pressure of the synthetic wave W) of the pressure wave generating element 100 can be increased. In addition, since the metal layers 11 and 12 are stacked and connected in parallel in the Z direction, the increase in the element size when viewed from above can be suppressed, and the sound pressure can be increased.

[0042] In addition, according to the present embodiment, the solid insulating layer 10 is located between the metal layer 11 and the metal layer 12. That is, the metal layers 11 and 12 are arranged with the solid insulating layer 10 sandwiched therebetween. As a result, the synthetic wave W of the pressure wave generated by the air heating of the metal layers 11 and 12 can be efficiently emitted from the thickness direction (Z direction) of the solid insulating layer 10. Specifically, Figure 3As shown, when the composite wave W is emitted from above the metal layer 11, the second pressure wave generated by the heating of the air layer 72 by the metal layer 12 passes through the solid insulating layer 10 and is emitted, but the first pressure wave generated by the heating of the air layer 71 by the metal layer 11 can be emitted without passing through the solid insulating layer 10. On the other hand, when the composite wave is emitted from below the metal layer 12, the first pressure wave passes through the solid insulating layer 10 and is emitted, but the second pressure wave does not pass through the solid insulating layer 10. In this way, the pressure wave generated by the heat of any metal layer can be emitted without passing through the solid insulating layer 10.

[0043] Furthermore, according to the present embodiment, by providing the metal layers 11 and 12 on both surfaces of the solid insulating layer 10, the heat transfer from the metal layers 11 and 12 to the solid insulating layer 10 is suppressed by utilizing the heat insulation effect of the solid insulating layer 10. Therefore, the heat of the metal layers 11 and 12 can be more efficiently transferred to the air layers 71 and 72. Therefore, by energizing the metal layers 11 and 12, a greater temperature change can be generated in the air layers 71 and 72, so that the sound pressure per unit input power can be increased.

[0044] Furthermore, by providing the metal layers 11 and 12 on both surfaces of the solid insulating layer 10, one solid insulating layer 10 can function as a heat insulating layer for the two metal layers 11 and 12. Therefore, compared with the case where separate heat insulating layers are provided on the metal layers 11 and 12, the number of components can be reduced, and the pressure wave generating element 100 can be further miniaturized.

[0045] In the present embodiment, the solid insulating layer 10 may also have a plurality of through holes. For example, the solid insulating layer 10 may also have a porous structure. Each through hole in the solid insulating layer 10 may penetrate the solid insulating layer 10 in the thickness direction, and may be parallel to the Z direction or may not be parallel to the Z direction. When viewed from above, the plurality of through holes may be regularly arranged in the solid insulating layer 10 or may be randomly arranged. Since the solid insulating layer 10 has through holes, the second pressure wave generated on the main surface 10b side of the solid insulating layer 10 by energizing the metal layer 12 can be efficiently emitted to the main surface 10a side of the solid insulating layer 10 through the through holes. Alternatively, the first pressure wave generated in the air layer 71 on the main surface 10a side of the solid insulating layer 10 by energizing the metal layer 11 can be efficiently emitted to the main surface 10b side of the solid insulating layer 10 through the through holes. Therefore, the composite wave W of the first pressure wave and the second pressure wave can be further efficiently emitted from the Z direction of the pressure wave generating element 100.

[0046] The solid insulating layer 10 having a porous structure may also be, for example, an insulating layer including fibers. Since the solid insulating layer 10 includes fibers, the gaps around the fibers can be utilized to allow the first pressure wave or the second pressure wave to pass through the solid insulating layer 10 more efficiently. Alternatively, the solid insulating layer 10 may also be a porous layer that does not include fibers. In this case, too, the plurality of through holes in the porous layer can be utilized to allow the first pressure wave or the second pressure wave to pass through the solid insulating layer 10 more efficiently.

[0047] In this embodiment, an annular support structure 50 may be provided to support the outer periphery of the metal layer 11 (in this example, the outer periphery of the metal layers 11 and 12). Thus, the pressure wave generated by energizing the metal layer 11 is more likely to be emitted from the Z direction than from the side of the pressure wave generating element 100. The support structure 50 may also be configured to block the emission of the pressure wave from the side of the pressure wave generating element 100.

[0048] (First heating element M1)

[0049] The first heating element M1 may be formed of a porous film (eg, a fiber film) having a porous structure. An example of the first heating element M1 in this embodiment will be described below.

[0050] Figure 4 : is a schematic enlarged cross-sectional view showing an example of the first heating element M1 in this embodiment. Figure 4 In the example shown, the first heating element M1 has a fiber membrane 90. The metal layers 11 and 12 are fiber-containing metal layers formed on the surface and back of the fiber membrane 90 by metal coating. The solid insulating layer 10 is an insulating layer located between the metal layers 11 and 12 in the fiber membrane 90, including a portion not coated with metal (referred to as a "non-coating portion").

[0051] according to Figure 4 The first heating element M1 of the structure shown can reduce the element resistance and further improve the sound pressure per unit input power by connecting the metal layers 11 and 12 in parallel. The following (1) to (3) are cited as reasons for improving the sound pressure per unit input power.

[0052] (1) By using a metal-coated fiber membrane as the first heating element M1, the heat capacity per unit volume of the first heating element M1 can be reduced.

[0053] (2) The metal layers 11 and 12 are formed by coating the fiber membrane with metal, so that the surface can be uneven and / or can include gaps (through holes) inside due to the fiber structure. Therefore, the contact area between the metal and the air can be increased. In addition, a non-coated portion of the fiber membrane is provided between the metal layers 11 and 12 as a solid insulating layer 10. Thus, the heat insulation effect of the solid insulating layer 10 can be improved. Therefore, the air layers 71 and 72 can be further efficiently heated by energizing the metal layers 11 and 12.

[0054] (3) The pressure wave generated by energizing the metal layer 11 or the metal layer 12 easily passes through the gaps in the fiber membrane 90 having a porous structure and is emitted to the opposite side of the fiber membrane 90. The reduction in sound pressure caused by the pressure wave passing through the solid insulating layer 10 can be suppressed, so the synthetic wave W can be efficiently emitted.

[0055] The fiber membrane 90 including the solid insulating layer 10 and the metal layers 11 and 12 may have a plurality of through holes that interconnect the air layers 71 and 72 on the front and back surfaces of the fiber membrane 90 . This makes it easier for the pressure wave to pass through the fiber membrane 90 .

[0056] The porosity of the non-coated portion of the fiber membrane 90, i.e., the solid insulating layer 10, is, for example, the same as the porosity of the fiber membrane before metal coating is applied. The porosity of the solid insulating layer 10 may also be greater than 80% and less than 95%. If the porosity is greater than 80%, the pressure wave can pass through the solid insulating layer 10 more efficiently. In addition, the heat capacity per unit volume of the first heating element M1 can be further reduced. Furthermore, by forming the metal layers 11 and 12 on the fiber membrane with a high porosity (greater than 80%), the contact area between the metal layers 11 and 12 and the air can be further increased. On the other hand, if the porosity of the solid insulating layer 10 is less than 95%, the metal layers 11 and 12 can be more reliably supported on the surface of the solid insulating layer 10. The porosity of the solid insulating layer 10 can be appropriately adjusted according to the fiber structure, material, fiber diameter, etc.

[0057] The thickness of the non-coated portion, i.e., the solid insulating layer 10, may be, for example, 1 μm or more. From the viewpoint of ensuring the heat insulation effect, the thickness of the solid insulating layer 10 is preferably 10 μm or more. In the case where the metal layers 11 and 12 are formed by metal coating of a fiber membrane having a porosity of 80% or more and 95% or less, the thickness of each metal layer 11 and 12 may be, for example, 1 μm or more.

[0058] When the fiber membrane 90 is coated with a metal, the thickness of the metal covering the surface of each fiber constituting the fiber membrane 90 may be uniform or non-uniform in the circumferential direction of the fiber. Figure 51 is a schematic enlarged cross-sectional view showing a fiber 91 located in the metal layers 11 and 12 and coated with metal. Figure 5 As shown in the example, the thickness of the metal 92 covering each fiber 91 increases as it is farther from the main surface 10a of the solid insulating layer 10. On the peripheral surface of the fiber 91, the thickness of the metal 92 at the position closest to the solid insulating layer 10 may be smaller than the thickness of the metal 92 at the position farthest from the solid insulating layer 10. In addition, a portion 93 not covered by the metal may exist on the solid insulating layer 10 side of the peripheral surface of the fiber 91. In this way, the heat generation inside the solid insulating layer 10 can be suppressed, and the heat generation of the metal layers (fiber-containing metal layers) 11 and 12 can be enhanced.

[0059] In addition, the coating state (cross-sectional image) of the metal-coated fiber can be analyzed, for example, by processing the sample using a focused ion beam (FIB), observing the cross section under a transmission electron microscope (JEM-F200 manufactured by JEOL), and performing elemental mapping analysis based on energy dispersive X-ray spectroscopy.

[0060] (Method of Manufacturing Pressure Wave Generating Element 100)

[0061] An example of a method for manufacturing the pressure wave generating element 100 will be described.

[0062] First, a porous membrane to be the metal layers 11, 12 and the solid insulating layer 10 is prepared. Here, a fiber membrane is prepared as the porous membrane. The fiber membrane may also have the following form (non-woven fabric form): when viewed from above, randomly oriented fibers are bonded or entangled by heat, mechanical or chemical action to form a sheet. Alternatively, the fiber membrane may be in the form of a fabric in which warp yarns and weft yarns are combined, or in the form of a woven fabric formed by weaving fibers. Alternatively, the fiber membrane may be in the form of a mixture of two or more of a non-woven fabric, a fabric and a woven fabric. In the fiber membrane, the cavities around the fibers are interconnected to form a plurality of tiny through holes to ensure air permeability.

[0063] The fiber can be selected from the group consisting of polymer fiber, glass fiber, carbon fiber, carbon nanotube, metal fiber and ceramic fiber. As the fiber, for example, low thermal conductivity materials such as polymer, glass and ceramic can also be used.

[0064] Specific examples of polymer materials include polyimide (PI), polyamide, polyamide-imide, polyethylene, polypropylene, acrylic resin, polyvinyl chloride, polystyrene, polyvinyl acetate, polytetrafluoroethylene, liquid crystal polymer, polyphenylene sulfide, polyetheretherketone, polyarylate, polysulfone, polyethersulfone, polyetherimide, polycarbonate, modified polyphenylene ether, polybutylene terephthalate, polyethylene terephthalate (PET), polyacetal, polylactic acid, polyvinyl alcohol, ABS resin, polyvinylidene fluoride, cellulose, polyethylene oxide, polyethylene glycol, and polyurethane. From the viewpoint of heat resistance, as a material of the fiber membrane, for example, polyimide can be used.

[0065] As the porous membrane, a porous membrane not including fibers such as a porous polytetrafluoroethylene membrane or a porous polyimide membrane may be used instead of the fiber membrane.

[0066] Next, the support 51 is bonded to a part of the surface of the fiber membrane via, for example, the adhesive layer 61. Similarly, the support 52 is bonded to a part of the back surface of the fiber membrane via, for example, the adhesive layer 62. As the support 51, 52, for example, a ceramic substrate such as glass, silicon, aluminum oxide, zirconium oxide, magnesium oxide, aluminum nitride, boron nitride, silicon nitride, or a flexible substrate such as a PI film or a PET film can be used. As the material of the adhesive layers 61, 62, a thermosetting resin or the like can be used.

[0067] Next, a metal layer 11 is formed by applying a metal coating to the area of ​​the surface of the fiber membrane exposed from the support 51. Similarly, a metal layer 12 is formed in the area of ​​the back side of the fiber membrane exposed from the support 52. As a coating method, a vapor deposition method, an ion plating method, an atomic layer deposition method, an electroless plating method, etc. can be used. Examples of materials for the metal layers 11 and 12 include metal materials such as Au, Ag, Cu, Pt, Rh, Pd, Ru, Ni, Ir, Cr, Mo, W, Ti, Al, or alloys containing two or more of these metals. The metal layer may be a single-layer structure, or may be a stacked structure consisting of a plurality of materials.

[0068] Next, connection electrodes 41 to 44 are formed. As a method for forming the connection electrodes 41 to 44, evaporation, sputtering, ion plating, atomic layer deposition, electroless plating, spraying, printing, dipping, etc. can be adopted. Examples of connection electrode materials include metals such as Au, Ag, Cu, Pt, Rh, Pd, Ru, Ni, Ir, Cr, Mo, W, Ti, Al, or alloys containing two or more of these metals.

[0069] Then, the pressure wave generating element 100 is obtained by forming the electrodes 31 and 32. As the method for forming the electrodes, evaporation, sputtering, ion plating, atomic layer deposition, electroplating, electroless plating, spraying, dipping, printing, etc. can be used. Examples of the materials of the electrodes 31 and 32 include metals such as Au, Ag, Cu, Pt, Rh, Pd, Ru, Ni, Ir, Cr, Mo, W, Ti, and Al. The electrodes 31 and 32 may each have a single-layer structure or a multilayer structure composed of a plurality of materials.

[0070] The structure of the pressure wave generating element 100, the materials of each component, the manufacturing method, etc. are not limited to the above examples. The solid insulating layer 10 may also be solid (i.e., non-porous). The solid insulating layer 10 may also be a polymer film containing the above-mentioned polymer material. In this case, through holes for passing sound waves may also be formed by patterning the polymer film, for example.

[0071] In addition, the metal layers 11 and 12 may not be formed by metal coating. For example, metal foils containing the above-mentioned metal materials or alloy materials may be used as the metal layers 11 and 12. The metal foils may be bonded to the surface and back of the solid insulating layer 10 by a known method.

[0072] Furthermore, the structure of the connecting electrodes 41 to 44 and the electrodes 31 and 32 is not limited to the example shown in the figure. For example, a pair of connecting electrodes (such as the connecting electrodes 41 and 42) may also have a structure such as Figure 6 As shown in the example in FIG. 1 , the comb-teeth-shaped structures are arranged to face each other when viewed from above in the Z direction.

[0073] Furthermore, by adjusting the structure and process of the pressure wave generating element, constituent elements such as the connecting electrodes, the supporting structure, and the adhesive layer can be appropriately omitted.

[0074] <Variation 1>

[0075] Figure 7 FIG. 1 is a schematic cross-sectional view showing a pressure wave generating element 101 according to a first modification. The pressure wave generating element 101 is different from the first modification in the following aspects. Figure 1 to Figure 3 The pressure wave generating element 100 shown is different in that it further includes another metal layer 21 that is arranged at a distance from the metal layers 11 and 12 in the Z direction.

[0076] The metal layer 21 is arranged on the side of the metal layer 12 opposite to the solid insulating layer 10 at a distance from the metal layer 12 in the Z direction. The metal layer 12 and the metal layer 21 are opposed to each other with the air layer 72 interposed therebetween. The upper surface 21a of the metal layer 21 may also be in contact with the air layer 72. The metal layers 11, 12, and 21 are connected in parallel between a pair of electrodes 31 and 32. One end side of these metal layers 11, 12, and 21 is electrically connected to the electrode 31, and the other end side is electrically connected to the electrode 32. The metal layer 21 and the electrodes 31 and 32 may also be electrically connected via the connecting electrodes 45 and 46.

[0077] The pressure wave generating element 101 may also include a solid insulating layer (sometimes referred to as a "second solid insulating layer") 20. In the example shown in the figure, the metal layer 21 is provided on the main surface (sometimes referred to as a "third main surface") 20a on the metal layer 12 side of the solid insulating layer 20. Alternatively, the metal layer 21 may be a fiber-containing metal layer formed on the surface of the fiber membrane by metal coating, and the solid insulating layer 20 may be an insulating layer including a non-coated portion of the fiber membrane.

[0078] exist Figure 7 In the example shown, the metal layer 21 is arranged between the solid insulating layer 10 and the solid insulating layer 20 at a distance from the solid insulating layer 10. With such an arrangement, when the synthetic wave W is emitted from above the metal layer 11, the pressure wave (third pressure wave) generated in the air layer 72 by the energization of the metal layer 21 does not pass through the solid insulating layer 20, but is emitted only through the solid insulating layer 10. Therefore, the synthetic wave W can be emitted more efficiently.

[0079] In this specification, a structure M2 including a resistor (metal layer) that generates pressure waves by energizing only one main surface of the solid insulating layer, such as a structure including a metal layer 21 and a solid insulating layer 20, is referred to as a "second heating element". In the second heating element M2, the main surface of the solid insulating layer opposite to the metal layer may be in contact with a heat dissipation layer such as a substrate, or may be in contact with air.

[0080] A substrate 80 may be provided on the main surface 20b of the solid insulating layer 20 on the opposite side to the metal layer 21. The solid insulating layer 20 and the substrate 80 may also be bonded via the adhesive layer 64. The substrate 80 may function as a heat dissipation layer, for example. Examples of the substrate 80 include glass substrates, ceramic substrates such as silicon, aluminum oxide, zirconium oxide, magnesium oxide, aluminum nitride, boron nitride, and silicon nitride, and flexible substrates such as PI and PET films.

[0081] The support structure 50 may further include a support body 53 disposed on the peripheral portion of the main surface 20a of the solid insulating layer 20. The solid insulating layer 20 and the support body 53 may be bonded by an adhesive layer 63. The support body 53 and the substrate 80 may be configured to sandwich and hold the peripheral portion of the solid insulating layer 20 therebetween.

[0082] In the pressure wave generating element 101, the support structure 50 is, for example, an annular structure that supports the outer periphery of the metal layers 11, 12, 21 and the solid insulating layers 10, 20. The support structure 50 and the substrate 80 may also be configured to block the emission of sound waves from the side and bottom of the pressure wave generating element 101. Thus, the synthetic wave W of the pressure wave generated by driving the metal layers 11, 12, 21 can be emitted mainly from the top of the pressure wave generating element 101 (top of the metal layer 11).

[0083] The pressure wave generating element 101 can be manufactured as follows: a stacked body L1 including a first heating element M1, support bodies 51, 52 and connecting electrodes 41 to 44 and a lower stacked body LB including a second heating element M2, support body 53, connecting electrodes 45, 46 and substrate 80 are separately manufactured, and the lower stacked body LB and the stacked body L1 are stacked in the Z direction, for example, via an adhesive layer 65. The material, structure and formation method of the metal layer 21, the connecting electrodes 45, 46 and the solid insulating layer 20 may be the same as those of the metal layers 11, 12, the connecting electrodes 45, 46 and the solid insulating layer 10, respectively.

[0084] Figure 8 1 is a schematic cross-sectional view of another pressure wave generating element 102 of variant example 1. In the pressure wave generating element 102, a plurality of (here, two) first heating elements M1 are stacked at intervals above the metal layer 21. One end side of the metal layer 11, 12 of each first heating element M1 is electrically connected to the electrode 31, and the other end side of the metal layer 11, 12 of each first heating element M1 is electrically connected to the electrode 32. In this specification, when a plurality of heating elements (here, the first heating element M1) including a solid insulating layer and a metal layer are stacked, each heating element is sometimes referred to as a "unit heating element".

[0085] In the example shown in the figure, a plurality of (here, two) stacks L1 are stacked in the Z direction via an adhesive layer 66 above the lower stack LB. In addition, the pressure wave generating element of this modified example may not have a lower stack LB. The pressure wave generating element may also have a structure in which a plurality of first heating elements M1 are stacked above a substrate (a substrate without a metal layer).

[0086] According to this modification, the number of metal layers can be further increased, so the element resistance can be further reduced. Therefore, the input power can be further increased, and the sound pressure can be further improved.

[0087] <Variation 2>

[0088] The pressure wave generating element of Modification 2 has a structure in which two or more second heating elements M2 are stacked at a distance.

[0089] Fig. 9 FIG. 1 is a schematic cross-sectional view showing a pressure wave generating element 103 of Modification 2. The pressure wave generating element 103 is different from the pressure wave generating element 103 in the following aspects. Figure 7 The pressure wave generating element 101 shown is different in that the metal layer 12 and the support body 52 are not provided on the main surface 10 b of the solid insulating layer 10 .

[0090] In the pressure wave generating element 103, the metal layer 11 is provided only on the principal surface 10a of the solid insulating layer 10. The solid insulating layer 10 and the metal layer 11 constitute the second heating element M2. The principal surface 10b of the solid insulating layer 10 opposite to the metal layer 11 is in contact with the air layer 72, for example.

[0091] The second heating element M2 including the solid insulating layer 20 and the metal layer 21 is located below the solid insulating layer 10. The upper surface 21a of the metal layer 21 may also be in contact with the air layer 72. The metal layer 21 is arranged between the solid insulating layer 10 and the solid insulating layer 20 at a distance from the solid insulating layer 10. Thus, when the synthetic wave W is emitted from above the element, the pressure wave (third pressure wave) generated by the energization of the metal layer 21 does not pass through the solid insulating layer 20, but is emitted only through the solid insulating layer 10. Therefore, the third pressure wave can be efficiently emitted from above the metal layer 11.

[0092] The pressure wave generating element 10 can be manufactured, for example, by stacking the stacked body L2 including the second heat generating body M2 , the support body 51 , and the connecting electrodes 41 , 42 and the lower stacked body LB in the Z direction via the adhesive layer 65 .

[0093] Fig.10 2 is a schematic cross-sectional view of another pressure wave generating element 104 of variant example 2. The pressure wave generating element 104 includes a plurality of (here two) second heating elements (unit heating elements) M2 stacked at intervals above the metal layer 21. One end side of the metal layer 11 of each second heating element M2 is electrically connected to the electrode 31, and the other end side of the metal layer 11 of each second heating element M2 is electrically connected to the electrode 32. In the example shown in the figure, a plurality of (here two) stacked bodies L2 are stacked in the Z direction via an adhesive layer 66 above the lower stacked body LB.

[0094] According to this modification, the number of metal layers can be further increased, so the element resistance can be further reduced. Therefore, the input power can be further increased, and the sound pressure can be further improved.

[0095] In addition, according to this modification, in each of the stacked second heating elements M2, the metal layer is located on the side of the solid insulating layer (here, the upper side of the solid insulating layer) on which the synthetic wave W is emitted. In this way, by stacking the second heating elements M2 so that the metal layer is closer to the emission side (here, the upper side) than the solid insulating layer, the pressure wave generated in the air layer near the surface of the metal layer of each second heating element M2 can be emitted more efficiently from the Z direction (here, above the element).

[0096] <Examples and Comparative Examples>

[0097] (Example 1)

[0098] In Example 1, as samples 1 to 3, a laminated pressure wave generating element having a fiber membrane (first heating element M1) with metal coating applied on both surfaces was prepared (see Figure 1 to Figure 3 ). In addition, as a comparative sample, a single-layer type pressure wave generating element having a single metal layer was produced.

[0099] Samples 1 to 3

[0100] Reference Figure 1 to Figure 3 , the method of preparing samples 1 to 3 is described. In the following description, the "dimensions" of each component refer to the dimensions when viewed from above in the Z direction.

[0101] First, a polyimide (PI) fiber membrane was produced by electrospinning as follows.

[0102] A PI solution prepared using N,N-dimethylformamide (DMF) as a solvent is used as a spinning solution. The solution concentration is adjusted to 5.5wt% and 12wt%, and 0.2wt% and 0.1wt% of lithium chloride are added to the solution, respectively. In addition, tetrabutylammonium chloride, potassium trifluoromethanesulfonate, etc. can be used as additives. Next, using 5.5wt% PI solution and 12wt% PI solution, PI fibers are simultaneously spun onto aluminum (Al) foil using a multi-nozzle-based electrospinning method. The discharge amount of 5.5wt% PI solution and 12wt% PI solution is set to 1:1. The discharge amount can be adjusted according to the discharge speed, the number of nozzles, etc. As a collector for the accumulation of fiber membranes, use The drum collector was placed in an electrospinning machine and spinning was performed while rotating at 100 rpm. In electrospinning, the applied voltage was set to 30 kV, the distance between the nozzle and the collector was set to 13 cm, and the film formation time was adjusted so that the thickness of the fiber membrane was about 2 to 60 μm. The average fiber diameter of the fibers made with 5.5 wt% PI solution was 41 nm, and the average fiber diameter of the fibers made with 12 wt% PI solution was 176 nm. Thus, a fiber membrane was obtained by combining fibers with an average fiber diameter of 41 nm and fibers with an average fiber diameter of 176 nm. The porosity of the fiber membrane was 90.1%.

[0103] Next, the support bodies 51 and 52 are bonded to the obtained fiber membrane. First, the surface of the fiber membrane is bonded to the PI film (support body 51) having an opening of 4 mm×4 mm in size. Here, a PI film having an adhesive layer 61 formed on one side in advance is used, and the fiber membrane and the PI film are heat-pressed via the adhesive layer 61, thereby bonding the fiber membrane to the PI film. Next, the fiber membrane is transferred to the support body 51 by peeling off the Al foil from the fiber membrane. Then, the back side of the fiber membrane (the side opposite to the PI film, that is, the side from which the Al foil is peeled off) is bonded to the PI film (support body 52) having an opening of 4 mm×4 mm in size (size: 4 mm×4 mm) using the same method as described above.

[0104] Next, in the area exposed through the opening of the support 51 on the surface of the fiber membrane, an Au film (size: 4 mm×4 mm) with a thickness ranging from 1 to 40 nm was formed by sputtering as the metal layer 11. Similarly, in the area exposed through the opening of the support 52 on the back side of the fiber membrane, an Au film (size: 4 mm×4 mm) with a thickness ranging from 1 to 40 nm was formed by sputtering as the metal layer 12. The non-coated portion of the fiber membrane between the metal layers 11 and 12 was set as the "solid insulating layer 10" (see Figure 4 ). The thickness of the metal coated on the surface of each fiber may also have a reference Figure 5 The distribution described.

[0105] Next, a pair of connecting electrodes 41 and 42 are formed at both ends of the metal layer 11 and both ends of the support body 51, for example, by sputtering. Similarly, a pair of connecting electrodes 43 and 44 are also formed at both ends of the metal layer 12 and both ends of the support body 52. ​​Here, as connecting electrodes 41 to 44, electrodes having a stacked structure including Ti (thickness: 10nm), Cu (thickness: 500nm) and Au (thickness: 100nm) from the solid insulating layer side are formed. When viewed from above, the size of each connecting electrode 41 to 44 is set to 1.4mm×4mm, and the distance between a pair of connecting electrodes (distance between electrodes) is set to 3.2mm. In this way, a stacked body including a solid insulating layer 10, metal layers 11, 12, support bodies 51, 52 and connecting electrodes 41 to 44 is obtained.

[0106] After the obtained laminated body is singulated to a size of 6 mm×6 mm, electrodes 31 and 32 are formed. Here, Ag electrode paste is applied to be bonded to the connection electrodes 41 to 44, respectively. Then, the Ag electrode paste is dried and solidified by heat treatment, thereby forming electrodes 31 and 32. In addition, as an electrode material, other metal materials such as Cu can also be used in addition to Ag. Through such a process, pressure wave generating elements of samples 1 to 3 are obtained.

[0107] Comparison sample 1

[0108] A single-layer element using a PI film as a solid insulating layer was produced. Here, an Au film (thickness: 20 nm, size: 4 mm × 4 mm) was formed by sputtering only on one side of the PI film (thickness: 25 μm, size: 6 mm × 6 mm) as a metal layer. Then, a pair of electrodes were formed on the Au film to obtain a pressure wave generating element of comparative sample 1. The structure and formation method of the electrodes were the same as those of samples 1 to 3.

[0109] Comparison sample 2

[0110] A single-layer element having a fiber membrane with a metal coating applied only on one side was produced. Here, the pressure wave generating element of Comparative Sample 2 was produced using the same materials and the same method as Samples 1 to 3, except that the support and the Au film (metal layer) were formed only on one side of the fiber membrane. The portion of the fiber membrane where the Au film was not formed (non-coated portion) was set as a solid insulating layer.

[0111] Evaluation method

[0112] The fiber membrane and device characteristics evaluation method implemented in this example are described.

[0113] 1) Average fiber diameter

[0114] The fiber diameter of the fiber membrane (PI fiber) is measured as follows. The fiber membrane is observed using a scanning electron microscope (S-4800 manufactured by Hitachi, acceleration voltage 5kV, 3k to 120k times) to obtain a SEM image. The average fiber diameter is calculated by measuring the fiber diameter from the obtained image. Specifically, 10 fibers are randomly extracted from each field of view from the obtained image, and this is performed for 5 fields of view, thereby measuring the fiber diameters of a total of 50 fibers and calculating the average fiber diameter.

[0115] 2)Porosity of fiber membrane

[0116] The porosity of the fiber membrane (here, the polyimide fiber membrane) is calculated by the following formula.

[0117] Void ratio (%) = {1-(bulk density ÷ true density)} × 100

[0118] As another method for calculating the porosity, the porosity can also be calculated by repeatedly performing cross-section processing and SEM observation under FIB and obtaining a three-dimensional stereoscopic image. Specifically, FIB processing is performed using HELIOS NANORAB 660i manufactured by FEI, and the SEM image is observed. Then, after processing 10nm in the depth direction again using FIB, the SEM image is observed. By repeatedly performing FIB processing and SEM observation in this way, SEM images of a depth of 400nm (41 in total) are obtained. A 3D stereoscopic image of the fiber membrane can be constructed based on these 41 SEM images to calculate the porosity.

[0119] 3) Thickness of fiber membrane and solid insulation layer

[0120] The cross section of each sample was observed using a scanning electron microscope (S-4800 manufactured by Hitachi, accelerating voltage 5-15 kV, 1k-20k times), and the thickness of the fiber membrane, the thickness of the metal layer, and the thickness of the solid insulating layer were determined from the obtained images.

[0121] Fig.11 1 is a diagram illustrating a scanning electron microscope image of a fiber membrane 90 coated with a metal. Here, as the thickness of the fiber membrane 90, the distance t1 between the surface and the back of the fiber membrane coated with a metal is measured. In addition, the penetration depths m1 and m2 of the metal into the fiber membrane are measured. And, by subtracting the penetration depths m1 and m2 of the metal from the thickness t1 of the fiber membrane, the thickness t2 of the solid insulating layer 10 is calculated. In addition, it is also possible to obtain an image by element mapping analysis based on reflected electron imaging or energy dispersive X-ray spectroscopy, and measure the above-mentioned thicknesses t1, t2, m1, and m2 based on the obtained image.

[0122] Before the cross-sectional observation based on the scanning electron microscope, each sample may be pre-processed. In the present embodiment, as the pre-processing, after the resin of each sample is cured, the cross-sectional grinding of the sample may be performed to expose the fiber membrane. Through such pre-processing, a cross-sectional image including the metal-coated part of the fiber membrane may be obtained. In the present embodiment, in the cross-sectional image, the depth of the area where the contrast between the metal and the resin can be visually confirmed is set as the penetration depth m1, m2.

[0123] The fiber membrane has a porous structure and has concavoconvexities on the surface. Therefore, the thickness t1 of the fiber membrane and the thickness t2 of the solid insulating layer can be different depending on the measurement position. In this embodiment, the maximum thickness of the fiber membrane in the cross-sectional image is defined as thickness t1, and the minimum thickness of the solid insulating layer in the cross-sectional image is defined as thickness t2.

[0124] 4) Acoustic characteristics (sound pressure ratio)

[0125] The acoustic characteristics of the pressure wave generating element of each sample were measured using a MEMS microphone (Knowles: SPU0410LR5H).

[0126] First, the pressure wave generating element of each sample is mounted on a circuit substrate so that the metal layer is located above the solid insulating layer (in the case where there are metal layers on both sides of the solid insulating layer, one metal layer is located above). Next, a microphone is arranged above the pressure wave generating element mounted on the circuit substrate. The distance between the pressure wave generating element and the microphone (the distance in the thickness direction of the solid insulating layer from the metal layer located at the top in each sample to the microphone) is set to 6 cm. Next, a driving signal is input to the pressure wave generating element. In this embodiment, the output voltage of the microphone is measured when the frequency of the driving signal is 60 kHz. The input voltage to the pressure wave generating element is set to 6 to 18 V.

[0127] If the input power to the pressure wave generating element is increased, the output of the microphone can be increased linearly. The higher the sound conversion efficiency of the pressure wave generating element, the greater the slope of the microphone output relative to the input power, that is, the ratio of the increase dV of the microphone output to the increase dW of the input power. In this embodiment, in order to evaluate the sound conversion efficiency of the pressure wave generating element, the slope dV / dW in each sample is obtained as an index of sound pressure, and the ratio to the dV / dW of the comparison sample 1 (the comparison object of the index) is calculated (hereinafter referred to as the "sound pressure ratio").

[0128] 5) Component resistance

[0129] The device resistance of each sample was measured by a four-terminal method using a digital multimeter (Agilent 34410A).

[0130] Evaluation results

[0131] Table 1 shows the evaluation results of the thickness t1 of the fiber membrane, the thickness t2 of the solid insulating layer (non-coating portion), the sound pressure ratio, and the element resistance of each sample.

[0132] [Table 1]

[0133]

[0134] According to the results shown in Table 1, it is confirmed that by forming a fiber membrane with a metal coating applied on the surface (samples 1 to 3 and comparative sample 2), the sound pressure per unit input power can be greatly improved (for example, sound pressure ratio: 5 or more) compared with a single-layer element having a metal layer on one side of a PI membrane (comparative sample 1). The reason for this is considered to be as follows: in samples 1 to 3 and comparative sample 2, the metal layer is formed by metal coating the fiber membrane, which can increase the contact area between the metal layer and the air, and the non-coated part of the PI fiber membrane can have a higher heat insulation effect than the PI membrane, so the air can be efficiently heated by the metal layer.

[0135] In addition, it can be seen that by providing metal layers on both sides of the fiber membrane and connecting these metal layers in parallel (samples 1 to 3), a higher sound pressure ratio can be ensured and the element resistance can be reduced. In samples 1 to 3, by making the total thickness of the two metal layers greater than the thickness of the metal layer of comparative sample 2, the element resistance is significantly reduced compared with comparative sample 2.

[0136] The sound pressure ratio of samples 1 to 3 is the same as or greater than that of comparative sample 2. This is considered to be because, in comparative sample 2, pressure waves based on air heating are generated only on one side of the fiber membrane, while in samples 1 to 3, pressure waves based on air heating can be generated on both sides of the fiber membrane. In addition, this is considered to be because, in samples 1 to 3, the pressure waves generated on the lower surface side of the fiber membrane pass through the fiber membrane and are efficiently emitted from above the element, thereby suppressing the decrease in the sound pressure ratio caused by the pressure waves on the lower surface side passing through the fiber membrane.

[0137] If the sound pressure ratios of samples 1 to 3 are compared, it can be seen that the sound pressure ratio can be further improved by making the solid insulation layer (non-coated part of the fiber membrane) thicker (for example, 10 μm or more). This is considered to be because the heat insulation effect of the solid insulation layer can be further increased by making the solid insulation layer thicker. In addition, it can be seen that if the thickness of the solid insulation layer is, for example, 10 μm or more, it can have a sufficient heat insulation effect.

[0138] Furthermore, according to the structures of samples 1 to 3, since metal layers are provided on both sides of the fiber membrane, the increase in element size due to the addition of metal layers can be suppressed. Therefore, the pressure wave generating element capable of achieving high efficiency and high sound pressure can be miniaturized.

[0139] (Example 2)

[0140] In Example 2, as Sample 4, a laminated element was prepared as follows: having a structure in which a fiber film (second heating element M2) coated with a metal only on one side was laminated (see Fig. 9 ) In addition, as a comparative sample 3, a single-layer element was prepared: it had only one fiber membrane with a metal coating applied only on one side.

[0141] Sample 4

[0142] Reference Fig. 9 , the method for manufacturing the element of sample 4 is described.

[0143] First, a PI fiber membrane was produced by electrospinning as follows.

[0144] A PI solution prepared using N,N-dimethylformamide (DMF) as a solvent was used as a spinning solution. The solution concentration was adjusted to 5.5wt%, and 0.2wt% of lithium chloride was added to the solution. Next, this solution (5.5wt% PI solution) was used to spin PI fibers on Al foil by electrospinning. As a collector for the fiber membrane to accumulate, a The drum collector was rotated at 100 rpm while spinning. In electrospinning, the applied voltage was set to 30 kV, the distance between the nozzle and the collector was set to 13 cm, and the film formation time was adjusted so that the thickness of the fiber film was about 1 to 60 μm. The average fiber diameter of the produced fiber was 41 nm, the porosity was 87.3%, and the thickness of the fiber film was 17.2 μm.

[0145] Next, the obtained fiber membrane is used to produce a lower laminate LB.

[0146] First, the surface of the fiber membrane is bonded to a PI membrane (support 53) having an opening of 4 mm×4 mm in size. Here, an adhesive layer 63 is pre-formed on one side of the PI membrane, and the fiber membrane and the PI membrane are thermally pressed via the adhesive layer 63, thereby bonding the fiber membrane to the PI membrane. Then, the Al foil is peeled off from the fiber membrane, thereby transferring the fiber membrane to the support 53.

[0147] Next, a Si substrate (substrate 80) is bonded to the surface of the fiber membrane opposite to the PI membrane (i.e., the side from which the Al foil is peeled off). Here, a Si substrate having an adhesive layer 64 pre-formed on one side is used, and the fiber membrane and the Si substrate are thermally pressed via the adhesive layer 64, thereby bonding the fiber membrane to the Si substrate.

[0148] Next, an Au film (size: 4 mm×4 mm) with a thickness ranging from 1 to 40 nm is formed by sputtering in the area exposed through the opening of the support body 53 on the surface of the fiber film as the metal layer 21. The portion of the fiber film that is located between the Au film and the Si substrate and is not coated with Au (non-coated portion) is set as the "solid insulating layer 20". The thickness of the metal coated on the surface of each fiber can also have a reference thickness of 20, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 160, 170, 180, 190, 200, 210, 220, 230, 240, 260, 270, 280, 360, 370, 380, 390, 400, 500, 510, 520, 610, 610, 700, 800, 900, 110, 120, 210, 220, 230, 240, 360, 380, 390, 400, 510, 610, 700, 800, 900, 110 Figure 5 The distribution described.

[0149] Next, a pair of connection electrodes 45 and 46 are formed by sputtering at both ends of the metal layer 21 and both ends of the support body 53. The structure (thickness, material, size, distance between electrodes, etc.) of the connection electrodes 45 and 46 is the same as that of the connection electrodes 41 and 42 in samples 1 to 3 of Example 1. In this way, a lower laminate LB including the substrate 80, the solid insulating layer 20, the metal layer 21 and the support body 53 is obtained.

[0150] Next, the above-mentioned fiber membrane is used to produce a laminate L2.

[0151] First, the surface of the fiber membrane is bonded to a PI film (support body 51) having an opening of 4 mm × 4 mm in size, and the Al foil is peeled off from the fiber membrane, thereby transferring the fiber membrane to the support body 51. Here, a PI film having an adhesive layer 61 formed on one side in advance is used, and the fiber membrane and the PI film are heat-pressed via the adhesive layer 61, thereby bonding the fiber membrane to the PI film. Next, a PET release film is bonded to the back side of the fiber membrane (the side from which the Al foil is peeled off). Here, an adhesive layer 65 (adhesive layer with a PET release film) having a PET release film formed on the surface is arranged on the back side of the fiber membrane, and the PET release film is heat-pressed to the fiber membrane via the adhesive layer 65.

[0152] Next, an Au film (size: 4 mm×4 mm) with a thickness ranging from 1 to 40 nm is formed by sputtering in the area exposed through the opening of the support body 51 on the surface of the fiber membrane as the metal layer 11. The non-coated portion of the fiber membrane not coated with Au is set as the "solid insulating layer 10". The thickness of the metal coated on the surface of each fiber can also have a reference thickness of, for example, Figure 5 The distribution described.

[0153] Next, a pair of connection electrodes 41 and 42 are formed by sputtering at both ends of the metal layer 21 and both ends of the support body 51. The structure (thickness, material, size, distance between electrodes, etc.) of the connection electrodes 41 and 42 is the same as that of the connection electrodes 41 and 42 in samples 1 to 3 of Example 1. In this way, a laminate L2 including the solid insulating layer 10, the metal layer 21 and the support body 51 is obtained.

[0154] The laminate L2 produced by the above method is stacked on the lower laminate LB. Here, after the PET release film is peeled off from the laminate L2, the laminate L2 and the lower laminate LB are thermally pressed together via the adhesive layer 65. The interval between the solid insulating layer 10 and the solid insulating layer 20 (the distance between the fiber membranes in the Z direction) can be arbitrarily selected within the range of more than 0 μm and less than 2000 μm. After the laminate L2 and the lower laminate LB are stacked, they are singulated so that the size becomes 6 mm×6 mm.

[0155] Next, Ag electrode paste is applied so as to be bonded to the connection electrodes 41, 42, 45, 46, and dried and solidified by heat treatment, thereby forming electrodes 31, 32. In addition, before forming the electrodes, the support body, adhesive layer, fiber membrane, etc. may be pre-processed by laser, punching, etc. to expose a portion of the connection electrodes 45, 46 of the lower stack LB (the area connected to the electrodes). By bonding the electrode material to the exposed portion of the connection electrodes 45, 46, good conduction between the metal layer 21 of the lower stack LB and the electrodes 31, 32 can be ensured. After such a process, the pressure wave generating element of sample 4 is obtained.

[0156] Comparison sample 3

[0157] As comparative sample 3, a single-layer element having the same structure as sample 4 except that the laminate L2 is not provided was produced. First, a laminate including a Si substrate, a solid insulating layer, a metal layer, a support body, and a connecting electrode was formed by the same method as the lower laminate LB in sample 4. Next, a pair of electrodes was formed on the laminate by the same method as sample 4, thereby obtaining a pressure wave generating element of comparative sample 3.

[0158] Evaluation results

[0159] The device characteristics of Sample 4 and Comparative Sample 3 were evaluated by the same method as in Example 1. Table 2 shows the results.

[0160] [Table 2]

[0161]

[0162] According to the results in Table 2, it can be seen that by laminating a fiber membrane (second heating element) having a metal layer on one side and connecting the metal layers in parallel (sample 4), a higher sound pressure ratio (e.g., 5 or more) can be ensured, and the element resistance can be reduced compared to the single-layer element, that is, comparative sample 3. The reason why the reduction in the sound pressure ratio is considered to be suppressed is that the pressure wave generated by heating the air through the metal layer located below can pass through the fiber membrane and be efficiently emitted from above the element.

[0163] (Example 3)

[0164] In Example 3, as samples 5 to 7, the following stacked elements were prepared: having a structure in which a fiber film (first heating element) coated with metal on both sides was stacked on top of a lower stack LB (see Figure 7 , Figure 8 ).

[0165] Sample 5

[0166] Reference Figure 7 , the method for manufacturing the element of sample 5 is described.

[0167] First, by the same method as in Example 1, a fiber membrane (void ratio: 90.1%) was prepared by combining fibers having an average fiber diameter of 41 nm and fibers having an average fiber diameter of 176 nm.

[0168] Next, the fiber membrane was used to obtain a lower laminate LB. The structure and production method of the lower laminate LB were the same as those of the lower laminate LB in Sample 4 of Example 2 except that the fiber membrane was used.

[0169] In addition, the above-mentioned fiber membrane is used to obtain a laminate L1. The structure and production method of the laminate L1 are the same as those of the laminates in samples 1 to 3 of Example 1, except that the above-mentioned fiber membrane is used. However, in this example, the thickness t1 of the fiber membrane is set to 18.1 μm, and the thickness t2 of the solid insulating layer (non-coated portion of the fiber membrane) 10 is set to 12.7 μm.

[0170] Next, an adhesive layer 65 is introduced between the laminate L1 and the lower laminate LB, and they are laminated by crimping. The interval between the fiber membrane including the solid insulating layer 10 and the fiber membrane including the solid insulating layer 20 (in this example, the thickness of the air layer 72) can be arbitrarily selected within the range of more than 0 μm and less than 2000 μm. After the laminate L1 and the lower laminate LB are laminated, they are singulated to a size of 6 mm×6 mm.

[0171] Next, Ag electrode paste is applied so as to be bonded to the connection electrodes 41 to 46, respectively, and dried and cured by heat treatment, thereby forming electrodes 31 and 32. In addition, before forming the electrodes, the support body, adhesive layer, fiber membrane, etc. may be processed by laser, punching, etc. so as to expose the connection electrodes 41 to 46 of the lower stack LB and the stack L1 in advance. By bonding the electrode material to the exposed portions of the connection electrodes 41 to 46, good conduction between the metal layers 11, 12, 21 of the lower stack LB and the stack L1 and the electrodes 31 and 32 can be ensured. After such a process, the pressure wave generating element of sample 5 is obtained.

[0172] Sample 6

[0173] The pressure wave generating element of sample 6 was manufactured by the same method as sample 5 except that two stacked bodies L1 were stacked on the lower stacked body LB (see Figure 8 The two stacked bodies L1 are bonded by thermocompression bonding via an adhesive layer. The interval between the fiber membranes in the two stacked bodies L1 can be arbitrarily selected within the range of more than 0 μm and 2000 μm or less.

[0174] Sample 7

[0175] The pressure wave generating element of sample 7 was manufactured by the same method as samples 5 and 6 except that three stacked bodies L1 were stacked on the lower stacked body LB.

[0176] Evaluation results

[0177] The device characteristics of samples 5 to 7 were evaluated by the same method as in Example 1. The results are shown in Table 3. For comparison, the results of Comparative Sample 2 of Example 1 are also shown in Table 3. Comparative Sample 2 is a single-layer device produced using the same fiber membrane as in this example.

[0178] [Table 3]

[0179]

[0180] According to the results in Table 3, it can be seen that by stacking fiber membranes having metal layers formed on both sides and connecting the metal layers in parallel (samples 5 to 7), a higher sound pressure ratio (for example, four or more) can be ensured, and the element resistance can be reduced compared to the single-layer type element, that is, comparative sample 2. The reason for suppressing the reduction in the sound pressure ratio is that, as described in Example 2, the pressure wave generated by heating the air of the metal layer located below passes through the fiber membrane and is efficiently emitted from above the element.

[0181] In addition, according to the comparison of the element characteristics of samples 5 to 7, it can be seen that the element resistance can be further reduced as the number of metal layers increases. In addition, if the number of fiber membranes formed with metal layers increases, the pressure wave generated by the energization of the metal layer located below needs to pass through more fiber membranes, and therefore it is not easy to be emitted from the top of the element. Therefore, there is a tendency to lower the sound pressure ratio (lower sound pressure relative to unit input power) by increasing the number of metal layers. In such a case, the element resistance can also be greatly reduced, so sufficient sound pressure can be generated by increasing the input power.

[0182] (Example 4)

[0183] In Example 4, as Sample 8, a laminated element having a structure in which a PI film (second heating element) with a metal layer formed on one side is laminated was prepared. In addition, as Sample 9, a laminated element having a structure in which a PI film (first heating element) with a metal layer formed on both sides is laminated was prepared.

[0184] Sample 8

[0185] As a solid insulating layer, a PI film (thickness: 25 μm, size: 6 mm×6 mm) is prepared. On only one side of the PI film, an Au film (thickness: 20 nm, size: 4 mm×4 mm) is formed by sputtering as a metal layer. Next, a pair of connecting electrodes are formed at both ends of the metal layer by sputtering. In this way, a stack including a PI film formed with an Au film is obtained. Two of the stacks are made, and the two stacks are stacked via an adhesive layer so that the surface formed with the metal layer (Au film) is on top. Then, a pair of electrodes are formed to join with the connecting electrodes of each metal layer. The structure (thickness, material, size, distance between electrodes, etc.) and formation method of the connecting electrode and the electrode are the same as those of samples 1 to 3 described above. After such a process, the pressure wave generating element of sample 8 is obtained.

[0186] Sample 9

[0187] As a solid insulating layer, a PI film (thickness: 25μm, size: 6mm×6mm) is prepared. On the surface and back of the PI film, an Au film (thickness: 20nm, size: 4mm×4mm) is formed by sputtering as a metal layer. Next, a pair of connecting electrodes are formed at both ends of each metal layer by sputtering. Then, a pair of electrodes are formed to join with the connecting electrodes of each metal layer. The structure (thickness, material, size, distance between electrodes, etc.) and formation method of the connecting electrode and the electrode are the same as those of samples 1 to 3 mentioned above. After such a process, the element of sample 9 is obtained.

[0188] Evaluation results

[0189] The device characteristics of samples 8 and 9 were evaluated by the same method as in Example 1. The results are shown in Table 4. For comparison, the results of Comparative Sample 1 of Example 1 are also shown in Table 4. Comparative Sample 1 is a single-layer device using a PI film as a solid insulating layer.

[0190] [Table 4]

[0191]

[0192] According to the results in Table 4, it can be seen that by providing metal layers on both sides of the PI film and connecting the metal layers in parallel (samples 8 and 9), the element resistance can be reduced compared with the single-layer element, that is, comparative sample 1. In samples 8 and 9, the sound pressure ratio is slightly reduced compared with comparative sample 1, but the element resistance is significantly reduced. Therefore, by increasing the input power, a higher sound pressure can be generated.

[0193] In addition, by appropriately combining any of the various embodiments described above, the effects possessed by each can be achieved.

[0194] While the present invention has been fully described in relation to the preferred embodiments with reference to the accompanying drawings, various modifications and variations will be apparent to those skilled in the art, and such modifications and variations should be understood to be included therein as long as they do not depart from the scope of the present invention based on the claims.

[0195] The description of the pressure wave generating element according to the present invention can be expressed as follows.

[0196] The first type of pressure wave generating element is a thermally excited pressure wave generating element, which comprises: a first solid insulating layer having a first main surface; a first metal layer arranged on the first main surface of the first solid insulating layer; a second metal layer arranged at a distance from the first metal layer in the thickness direction of the first solid insulating layer; a first electrode electrically connected to one end side of the first metal layer and one end side of the second metal layer; and a second electrode electrically connected to the other end side of the first metal layer and the other end side of the second metal layer, and the first solid insulating layer is located between the first metal layer and the second metal layer.

[0197] The pressure wave generating element of the second aspect is the pressure wave generating element of the first aspect, wherein the first solid insulating layer has a second main surface opposite to the first main surface, and the second metal layer is provided on the second main surface of the first solid insulating layer.

[0198] The third type of pressure wave generating element is a pressure wave generating element of the second type, wherein the first metal layer and the second metal layer are fiber-containing metal layers respectively formed on the surface and back side of a fiber membrane having a porous structure, and the first solid insulating layer includes a portion of the fiber membrane located between the first metal layer and the second metal layer.

[0199] A pressure wave generating element according to a fourth aspect is the pressure wave generating element according to the third aspect, wherein the thickness of the first solid insulating layer is greater than or equal to 10 μm.

[0200] The fifth type of pressure wave generating element is a pressure wave generating element in the second to fourth types, and further comprises a third metal layer, wherein the third metal layer is arranged on the side of the second metal layer opposite to the first solid insulating layer and is separated from the second metal layer in the thickness direction, the first electrode is electrically connected to one end side of the third metal layer, and the second electrode is electrically connected to the other end side of the third metal layer.

[0201] The sixth type of pressure wave generating element is a pressure wave generating element of the first type, further comprising a second solid insulating layer having a third main surface, the second metal layer being arranged on the third main surface of the second solid insulating layer, and the second metal layer being arranged between the first solid insulating layer and the second solid insulating layer at a distance from the first solid insulating layer.

[0202] A pressure wave generating element according to a seventh aspect is the pressure wave generating element according to any one of the first to sixth aspects, wherein the first solid insulating layer has a porous structure having a plurality of through holes.

[0203] The pressure wave generating element according to an eighth aspect is the pressure wave generating element according to the seventh aspect, wherein the first solid insulating layer includes fibers, and a porosity of the first solid insulating layer is greater than or equal to 80% and less than or equal to 95%.

[0204] A pressure wave generating element according to a ninth aspect is the pressure wave generating element according to any one of the first to eighth aspects, further comprising an annular supporting structure that supports the outer periphery of the first metal layer.

[0205] A pressure wave generating element according to a tenth aspect is the pressure wave generating element according to the ninth aspect, wherein the annular supporting structure supports the outer peripheries of the first metal layer and the second metal layer.

[0206] The eleventh embodiment of the pressure wave generating element is a pressure wave generating element of the sixth embodiment, comprising a plurality of unit heating elements, the unit heating elements including the first solid insulating layer and the first metal layer, the plurality of unit heating elements being stacked at a distance from each other along the thickness direction starting from the second metal layer side, the one end side of the first metal layer of each of the plurality of unit heating elements being electrically connected to the first electrode, and the other end side of the first metal layer of each of the plurality of unit heating elements being electrically connected to the second electrode.

[0207] The pressure wave generating element of the twelfth mode is a pressure wave generating element in any one of the second to fifth modes, and comprises a plurality of unit heating elements, the unit heating elements comprising the first solid insulating layer, the first metal layer and the second metal layer, the plurality of unit heating elements being stacked at a distance from each other along the thickness direction, the one end side of the first metal layer and the one end side of the second metal layer of each of the plurality of unit heating elements being electrically connected to the first electrode, and the other end side of the first metal layer and the other end side of the second metal layer of each of the plurality of unit heating elements being electrically connected to the second electrode.

[0208] Industrial Applicability

[0209] The pressure wave generating element of the present invention can generate higher sound pressure and is therefore industrially useful.

[0210] Explanation of the reference numerals: 10, 20…solid insulating layer; 10a, 10b, 20a, 20b…main surface of the solid insulating layer; 11, 12, 21…metal layer; 11a, 21a…upper surface of the metal layer; 11b…lower surface of the metal layer; 31, 32…electrodes; 41-46…connecting electrodes; 50…supporting structure; 51-53…supporting body; 61-66…adhesive layer; 71, 72…air layer; 80…substrate; 90…fiber membrane; 101-104…pressure wave generating element.

Claims

1. A pressure wave generating element, which is a thermal excitation type pressure wave generating element, wherein: have: A first solid insulating layer having a first main surface; A first metal layer, disposed on the first main surface of the first solid insulating layer; a second metal layer, arranged at a distance from the first metal layer in a thickness direction of the first solid insulating layer; a first electrode electrically connected to one end of the first metal layer and one end of the second metal layer; as well as a second electrode electrically connected to the other end side of the first metal layer and the other end side of the second metal layer, The first solid insulating layer is located between the first metal layer and the second metal layer.

2. The pressure wave generating element according to claim 1, wherein: The first solid insulating layer has a second main surface opposite to the first main surface, The second metal layer is disposed on the second main surface of the first solid insulating layer.

3. The pressure wave generating element according to claim 2, wherein: The first metal layer and the second metal layer are fiber-containing metal layers formed on the surface and back of the fiber membrane having a porous structure, respectively. The first solid insulating layer includes a portion of the fiber membrane located between the first metal layer and the second metal layer.

4. The pressure wave generating element according to claim 3, wherein: The thickness of the first solid insulating layer is greater than 10 μm.

5. The pressure wave generating element according to any one of claims 2 to 4, wherein: further comprising a third metal layer, the third metal layer being arranged at a distance from the second metal layer in the thickness direction and on a side of the second metal layer opposite to the first solid insulating layer, The first electrode is electrically connected to one end of the third metal layer, and the second electrode is electrically connected to the other end of the third metal layer.

6. The pressure wave generating element according to claim 1, wherein: further comprising a second solid insulating layer having a third main surface, The second metal layer is disposed on the third main surface of the second solid insulating layer, The second metal layer is spaced apart from the first solid insulating layer and is disposed between the first solid insulating layer and the second solid insulating layer.

7. The pressure wave generating element according to any one of claims 1 to 6, wherein: The first solid insulating layer has a porous structure having a plurality of through holes.

8. The pressure wave generating element according to claim 7, wherein: The first solid insulating layer includes fibers, and a void ratio of the first solid insulating layer is greater than or equal to 80% and less than or equal to 95%.

9. The pressure wave generating element according to any one of claims 1 to 8, wherein: An annular support structure for supporting the outer periphery of the first metal layer is further provided.

10. The pressure wave generating element according to claim 9, wherein: The annular support structure supports the outer circumferences of the first metal layer and the second metal layer.

11. The pressure wave generating element according to claim 6, wherein: A plurality of unit heating elements are provided, each of which includes the first solid insulating layer and the first metal layer. The plurality of unit heating elements are stacked at intervals from each other along the thickness direction starting from the second metal layer side, The one end side of the first metal layer of each of the plurality of unit heating elements is electrically connected to the first electrode, and the other end side of the first metal layer of each of the plurality of unit heating elements is electrically connected to the second electrode.

12. The pressure wave generating element according to any one of claims 2 to 5, wherein: A plurality of unit heating elements are provided, wherein the unit heating elements include the first solid insulating layer, the first metal layer and the second metal layer. The plurality of unit heating elements are stacked at intervals from each other along the thickness direction. The one end side of the first metal layer and the one end side of the second metal layer of each unit heating element in the plurality of unit heating elements are electrically connected to the first electrode, and the other end side of the first metal layer and the other end side of the second metal layer of each unit heating element in the plurality of unit heating elements are electrically connected to the second electrode.

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