Pressure wave generating element

Abstract

Provided is a thermal-excitation-type pressure-wave-generating element with which it is possible to generate higher sound pressure. A pressure-wave-generating element according to the present invention is a thermal-excitation-type element and comprises a first solid insulating layer that has a first principal surface, a first metal layer that is provided to the first principal surface of the first solid insulating layer, a second metal layer that is disposed so as to be spaced apart from the first metal layer by a distance in the thickness direction of the first solid insulating layer, a first electrode that is electrically connected to one end of the first metal layer and to one end of the second metal layer, and a second electrode that is electrically connected to the other end of the first metal layer and to the other end of the second metal layer, the first solid insulating layer being positioned between the first and second metal layers.

Description

[Technical field]

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

[0002] A thermally excited pressure wave generating element (also called a "thermophone") has been proposed that generates pressure waves by heating a medium such as air (for example, Patent Document 1).

[0003] A thermally excited pressure wave generating element is equipped with a resistor (typically a metal layer) that generates heat when electricity is passed through it. When current flows through this resistor, it heats up, and the air in contact with the resistor expands due to heat. When the current is then stopped, the expanded air contracts. This expansion and contraction of the air generates pressure waves (also called sound waves). Unlike sound sources that use piezoelectric bodies, thermally excited pressure wave generating elements do not use a resonance mechanism. This makes it possible to generate wideband and short-pulse sound waves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-300274 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in a thermal excitation type pressure wave generating element, since electrical energy is converted into thermal energy before generating sound waves, the energy conversion efficiency is low and it may be difficult to increase the output sound pressure.

[0006] SUMMARY OF THE PRESENT EMBODIMENT In order to solve the above problems, an object of the present invention is to provide a thermally excited pressure wave generating element capable of generating higher sound pressure. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the pressure wave generating element of the present invention is a thermally excited pressure wave generating element comprising 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 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. Effect of the Invention

[0008] According to the present invention, there is provided a thermally excited pressure wave generating element capable of generating higher sound pressure. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic perspective view of a pressure wave generating element according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic top view of the pressure wave generating element of FIG. [Diagram 3] 2 is a schematic cross-sectional view of the pressure wave generating element of FIG. 1 taken along line A1-A1. [Figure 4] FIG. 2 is a schematic cross-sectional view showing an example of a first heating element. [Diagram 5] FIG. 2 is a schematic enlarged cross-sectional view illustrating one fiber having a metal coating. [Figure 6] 13 is a schematic top view showing another example of a pressure wave generating element. FIG. [Figure 7] 1 is a schematic cross-sectional view showing a pressure wave generating element of a first modified example. FIG. [Figure 8] 13 is a schematic cross-sectional view showing another pressure wave generating element of the first modified example. FIG. [Figure 9] 11 is a schematic cross-sectional view showing a pressure wave generating element of a second modified example. FIG. [Figure 10] 13 is a schematic cross-sectional view showing another pressure wave generating element of the second modified example. FIG. [Figure 11] Electron microscope images showing examples of thickness measurements of a fiber membrane, a metal layer, and a solid insulation layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, substantially the same components in the drawings are given the same reference numerals and the description thereof will be omitted. Furthermore, for the purpose of illustration, the dimensions of each component in the drawings may be exaggerated and are not necessarily drawn to scale.

[0011] In the following, for ease of explanation, terms indicating directions such as "up," "down," "right," "left," and "side" are used, but these terms do not limit the manufacturing state and usage state of the pressure wave generating element of the present invention.

[0012] <<Embodiment>>

[0013] The pressure wave generating element according to the embodiment of the present invention comprises a plurality of resistors (metal layers) that generate heat when electricity is passed through them. 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 called a "stacked pressure wave generating element" or a "stacked element."

[0014] A pressure wave generating element according to an embodiment of the present invention will be described with reference to Fig. 1 to Fig. 3. Fig. 1 is a schematic perspective view of a pressure wave generating element according to an embodiment of the present invention. Fig. 2 is a schematic top view of the pressure wave generating element of Fig. 1. Fig. 3 is a schematic cross-sectional view taken along line A1-A1 shown in Fig. 2.

[0015] As shown in FIGS. 1 to 3, the pressure wave generation element 100 according to this embodiment includes metal layers 11 and 12, a solid insulating layer 10, and a pair of electrodes 31 and 32.

[0016] 1 to 3, the thickness direction of the solid insulating layer 10 is the Z direction. In Figs. 1 and 3, the dimensions of each component in the Z direction are exaggerated for ease of understanding. In the top view shown in Fig. 2, the horizontal direction is the X direction, and the direction perpendicular to the X direction (up and down direction) is the Y direction. In the illustrated example, the outer edge of the pressure wave generation element 100 is roughly rectangular when viewed from the Z direction, and the directions in which the sides extend are the X direction and the Y direction, respectively. The planar shape of the pressure wave generation element 100 is not limited to the shape shown in the figures.

[0017] The metal layers 11 and 12 are disposed 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. The metal layers 11 and 12 are connected in parallel between the electrodes 31 and 32.

[0018] Solid insulating layer 10 is located between metal layer 11 and metal layer 12 in the Z direction. Solid insulating layer 10 may have a plurality of through holes penetrating in the thickness direction. For example, solid insulating layer 10 may be a layer having a porous structure (e.g., a fiber layer).

[0019] Solid insulating layer 10 has a principal surface (also referred to as a "first principal surface") 10a and a principal surface (also referred to as a "second principal surface") 10b opposite principal surface 10a. In this example, metal layer 11 is provided on principal surface 10a of solid insulating layer 10, and metal layer 12 is provided on principal surface 10b of solid insulating layer 10. Metal layers 11 and 12 may be in contact with solid insulating layer 10.

[0020] At least a portion of the surface of each of the metal layers 11 and 12 opposite to the solid insulating layer 10 is in contact with a medium such as air. In the illustrated example, the upper surface 11a of the metal layer 11 is in contact with an air layer 71. The lower surface 12b of the metal layer 12 is in contact with an air layer 72.

[0021] In this specification, the structure M1 including the solid insulating layer 10 and the metal layers 11, 12 provided on both sides of the solid insulating layer 10 may be referred to as the "first heating element." Furthermore, the metal layer 11 in the first heating element M1 may be referred to as the "first metal layer," and the metal layer 12 may be referred to as the "second metal layer."

[0022] The electrodes 31 and 32 are a pair of electrodes that apply a voltage to each of the metal layers 11 and 12 in a predetermined direction (here, the X direction). In a plan view, the electrode 31 is electrically connected to one end side (the left end side in this example) of the metal layer 11 and one end side (the left end side in this example) of the metal layer 12. The electrode 32 is electrically connected to the other end side (the right end side in this example) of the metal layer 11 and the other end side (the right end side in this example) of the metal layer 12. Each of the metal layers 11 and 12 extends continuously from one end side electrically connected to the electrode 31 to the other end side electrically connected to the electrode 32. In a plan view, the width of the metal layers 11 and 12 in the current-carrying direction (X direction) and the width in the direction perpendicular to the current-carrying direction (Y direction) are not particularly limited. In this example, the width in the X direction and the width in the Y direction are approximately the same.

[0023] The pressure wave generating element 100 may further include a pair of connection electrodes 41, 42 for electrically connecting the metal layer 11 to the electrodes 31, 32, and a pair of connection electrodes 43, 44 for electrically connecting the metal layer 12 to the electrodes 31, 32.

[0024] In the illustrated example, the electrode 31 has, at one end side (here, the left side) of the first heating element M1, 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. Similarly, at the other end side (here, the right side) of the first heating element M1, 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. The connection electrode 41 electrically connects the left end portion 11c on the upper surface 11a of the metal layer 11 to the first portion c1 of the electrode 31. The connection electrode 42 electrically connects the right end portion 11d on the upper surface 11a of the metal layer 11 to the first portion d1 of the electrode 32. Similarly, connection electrode 43 electrically connects left end portion 12c on lower surface 12b of metal layer 12 to second portion c2 of electrode 31, and connection electrode 44 electrically connects right end portion 12d on lower surface 12b to second portion d2 of electrode 32.

[0025] The pressure wave generating element 100 may further include a support structure 50 that supports the first heating element M1. The support structure 50 may be an annular structure that supports the outer periphery of the metal layer 11 (in this example, the outer periphery of the metal layers 11 and 12) and the solid insulating layer 10.

[0026] The support structure 50 includes, for example, a support (sometimes referred to as a "first support") 51 provided on the main surface 10a side of the solid insulating layer 10, and a support (sometimes referred to as a "second support") 52 provided on the main surface 10b side of the solid insulating layer 10. The supports 51, 52 may be arranged so as to hold the peripheral portion of the solid insulating layer 10 between them. The peripheral portion of the solid insulating layer 10 and the support 51 may be bonded by an adhesive layer 61, and the peripheral portion of the solid insulating layer 10 and the support 52 may be bonded by an adhesive layer 62.

[0027] In the illustrated example, in a plan view, the support 51 is disposed so as to surround the metal layer 11, and the support 52 is disposed so as to surround the metal layer 12. In a plan view, the metal layers 11 and 12 may be formed over substantially the entire regions of the main surfaces 10a and 10b of the solid insulating layer 10 that are exposed from the support. Each of 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 51. Similarly, each of 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 52.

[0028] In the pressure wave generating element 100, a drive signal is supplied to each of the metal layers 11, 12 via a pair of electrodes 31, 32. The metal layer 11 generates a first pressure wave by applying a thermal shock to the air layer 71 due to a temperature change corresponding to the waveform of the drive signal. Similarly, the metal layer 12 generates a second pressure wave in the air layer 72 due to a temperature change corresponding to the waveform of the drive signal. A composite wave (sound wave) W of the first and second pressure waves can be emitted to the outside of the pressure wave generating element 100, for example, from the Z direction (in the illustrated example, from above the metal layer 11).

[0029] The frequency of the composite wave W emitted from the pressure wave generating element 100 can be adjusted by the driving signal. For example, when the driving signal is set to an audio frequency, the pressure wave generating element 100 can be used as an acoustic speaker, and when the driving signal is set to an ultrasonic frequency, the pressure wave generating element 100 can be used as an ultrasonic source.

[0030] The pressure wave generating element 100 may further include a substrate (not shown). The substrate may be disposed at a distance from the first heating element M1 in the Z direction. For example, when the composite wave W is emitted from above the metal layer 11, the substrate may be disposed below the metal layer 12 at a distance from the lower surface 12b of the metal layer 12.

[0031] According to the pressure wave generating element 100 of this embodiment, a plurality of metal layers 11, 12 are arranged at a distance from each other in the thickness direction (Z direction) of the solid insulating layer 10, and are connected in parallel between the electrodes 31, 32. The metal layers 11, 12 are connected in parallel. This allows the element resistance to be reduced more than that of a single-layer pressure wave generating element (single-layer element) having a single metal layer. By reducing the element resistance, the input power to the pressure wave generating element 100 can be increased, and therefore the output sound pressure of the pressure wave generating element 100 (sound pressure of the composite wave W) can be improved. In addition, since the parallel-connected metal layers 11, 12 are stacked in the Z direction, the sound pressure can be increased while suppressing an increase in the element size in a planar view.

[0032] According to this 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. This allows the composite wave W of pressure waves generated by air heating by the metal layers 11 and 12 to be efficiently emitted from the thickness direction (Z direction) of the solid insulating layer 10. Specifically, as shown in FIG. 3, when the composite wave W is emitted from above the metal layer 11, the second pressure wave generated by heating 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 heating 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 is emitted without passing through the solid insulating layer 10. In this way, the pressure wave generated by heat generation of either one of the metal layers can be emitted without passing through the solid insulating layer 10.

[0033] Furthermore, according to this embodiment, by providing metal layers 11 and 12 on both sides of solid insulation layer 10, the heat insulating effect of solid insulation layer 10 suppresses heat transfer from metal layers 11 and 12 to solid insulation layer 10. This allows heat from metal layers 11 and 12 to be transferred more efficiently to air layers 71 and 72. Therefore, by passing current through metal layers 11 and 12, a large temperature change can be caused in air layers 71 and 72, making it possible to increase sound pressure per unit input power.

[0034] Furthermore, by providing the metal layers 11 and 12 on both sides of the solid insulating layer 10, the single solid insulating layer 10 can function as a heat insulating layer for the two metal layers 11 and 12. Therefore, compared to the case where separate heat insulating layers are provided for the metal layers 11 and 12, the number of parts can be reduced, and the pressure wave generating element 100 can be further miniaturized.

[0035] In this embodiment, the solid insulating layer 10 may have a plurality of through holes. For example, the solid insulating layer 10 may 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 or may not be parallel to the Z direction. The plurality of through holes may be regularly arranged in the solid insulating layer 10 in a plan view, or may be randomly arranged. By having the through holes in the solid insulating layer 10, the second pressure wave generated on the main surface 10b side of the solid insulating layer 10 by the current passing through 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 the current passing through 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 emitted more efficiently from the Z direction of the pressure wave generation element 100.

[0036] The solid insulation layer 10 having a porous structure may be, for example, an insulation layer containing fibers. When the solid insulation layer 10 contains fibers, the first pressure wave or the second pressure wave can be passed through the solid insulation layer 10 more efficiently by utilizing the voids around the fibers. Alternatively, the solid insulation layer 10 may be a porous layer that does not contain fibers. Even in this case, the first pressure wave or the second pressure wave can be passed through the solid insulation layer 10 more efficiently by utilizing the multiple pores in the porous layer.

[0037] In this embodiment, a ring-shaped 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). This makes it easier to emit pressure waves generated by passing electricity through the metal layer 11 from the Z direction rather than from the side of the pressure wave generation element 100. The support structure 50 may be arranged to block the emission of pressure waves from the side of the pressure wave generation element 100.

[0038] (First heating element M1) The first heating element M1 may be formed of a porous film (for example, a fiber film) having a porous structure. An example of the first heating element M1 in this embodiment will be described below.

[0039] Fig. 4 is a schematic enlarged cross-sectional view showing an example of the first heating element M1 in this embodiment. In the example shown in Fig. 4, the first heating element M1 has a fiber membrane 90. The metal layers 11 and 12 are fiber-containing metal layers formed by metal coating on the front and back surfaces of the fiber membrane 90. The solid insulating layer 10 is an insulating layer located between the metal layers 11 and 12 of the fiber membrane 90 and including a portion not coated with metal (referred to as an "uncoated portion").

[0040] 4, it is possible to increase the sound pressure per unit input power while reducing the element resistance by the parallel connection of the metal layers 11, 12. The reasons why the sound pressure per unit input power can be increased include, for example, the following (1) to (3). (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. (2) The metal layers 11 and 12 are formed by coating a fiber membrane with metal, and therefore may have surface irregularities and / or may contain voids (through holes) due to the fiber structure. This increases the contact area between the metal and air. In addition, an uncoated portion of the fiber membrane is provided as the solid insulation layer 10 between the metal layers 11 and 12. This enhances the heat insulating effect of the solid insulation layer 10. Therefore, the air layers 71 and 72 can be heated more efficiently by passing electricity through the metal layers 11 and 12. (3) The pressure wave generated by passing a current through the metal layer 11 or the metal layer 12 passes through the voids in the porous fiber membrane 90 and is easily emitted to the opposite side of the fiber membrane 90. Since the decrease in sound pressure caused by the pressure wave passing through the solid insulating layer 10 can be suppressed, the composite wave W can be efficiently emitted.

[0041] The fiber membrane 90 including the solid insulating layer 10 and the metal layers 11, 12 may have a plurality of through holes that connect the air layers 71, 72 located on the front and back sides of the fiber membrane 90 to each other, which makes it easier for pressure waves to pass through the fiber membrane 90.

[0042] The porosity of the solid insulation layer 10, which is the uncoated portion of the fiber membrane 90, is, for example, approximately the same as the porosity of the fiber membrane before metal coating is applied. The porosity of the solid insulation layer 10 may be 80% or more and 95% or less. If the porosity is 80% or more, pressure waves can be passed through the solid insulation layer 10 more efficiently. In addition, the heat capacity per volume of the first heating element M1 can be further reduced. Furthermore, by forming the metal layers 11, 12 on a fiber membrane with a high porosity (80% or more), the contact area between the metal layers 11, 12 and the air can be further increased. On the other hand, if the porosity of the solid insulation layer 10 is 95% or less, the metal layers 11, 12 can be more reliably supported on the surface of the solid insulation layer 10. The porosity of the solid insulation layer 10 can be appropriately adjusted depending on the fiber structure, material, fiber diameter, etc.

[0043] The thickness of the solid insulation layer 10, which is the uncoated portion, may be, for example, 1 μm or more. From the viewpoint of ensuring the heat insulating effect, the thickness of the solid insulation layer 10 is preferably 10 μm or more. When the metal layers 11, 12 are formed by metal coating on a fiber membrane having a porosity of 80% or more and 95% or less, the thickness of each of the metal layers 11, 12 may be, for example, 1 μm or more.

[0044] 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. FIG. 5 is a schematic enlarged cross-sectional view illustrating one fiber 91 located in the metal layers 11 and 12 and coated with a metal. As illustrated in FIG. 5, the thickness of the metal 92 covering each fiber 91 may increase as it moves away from the main surface 10a of the solid insulation layer 10. On the circumferential surface of the fiber 91, the thickness of the metal 92 at the position closest to the solid insulation layer 10 may be smaller than the thickness of the metal 92 at the position farthest from the solid insulation layer 10. In addition, a portion 93 not covered with metal may be present on the solid insulation layer 10 side of the circumferential surface of the fiber 91. This makes it possible to suppress heat generation inside the solid insulation layer 10 while enhancing heat generation in the metal layers (fiber-containing metal layers) 11 and 12.

[0045] The coating state (cross-sectional image) of metal-coated fibers can be analyzed, for example, by processing the sample with a focused ion beam (FIB), observing the cross-section with a transmission electron microscope (JEOL JEM-F200), and performing element mapping analysis using energy dispersive X-ray spectroscopy.

[0046] (Manufacturing method of pressure wave generating element 100) An example of a method for manufacturing the pressure wave generating element 100 will be described.

[0047] First, a porous film that will become the metal layers 11, 12 and the solid insulating layer 10 is prepared. Here, a fiber film is prepared as the porous film. The fiber film may have a form in which fibers randomly oriented in a plan view are bonded or entangled by thermal, mechanical, or chemical action to form a sheet (nonwoven fabric form). Alternatively, the fiber film may be in the form of a woven fabric in which warp threads and weft threads are combined, or in the form of a knitted fabric in which fibers are knitted. Alternatively, the fiber film may be in the form of a mixture of two or more of nonwoven fabric, woven fabric, and knitted fabric. In the fiber film, the cavities around the fibers communicate with each other to form a plurality of minute through holes, ensuring breathability.

[0048] The fibers may be selected from the group consisting of polymer fibers, glass fibers, carbon fibers, carbon nanotubes, metal fibers and ceramic fibers. Materials with low thermal conductivity, such as polymers, glasses, ceramics, etc. may be used as the fibers.

[0049] Specific examples of polymer materials include polyimide (PI), polyamide, polyamideimide, polyethylene, polypropylene, acrylic resin, polyvinyl chloride, polystyrene, polyvinyl acetate, polytetrafluoroethylene, liquid crystal polymer, polyphenylene sulfide, polyether ether ketone, polyarylate, polysulfone, polyether sulfone, 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, for example, polyimide can be used as the material of the fiber membrane.

[0050] As the porous membrane, a porous membrane that does not contain fibers, such as a porous polytetrafluoroethylene membrane or a porous polyimide membrane, may be used instead of a fibrous membrane.

[0051] Next, a support 51 is adhered to a part of the front surface of the fiber membrane, for example, via an adhesive layer 61. Similarly, a support 52 is adhered to a part of the back surface of the fiber membrane, for example, via an adhesive layer 62. As the supports 51 and 52, for example, ceramic substrates such as glass, silicon, alumina, zirconia, magnesium oxide, aluminum nitride, boron nitride, silicon nitride, etc., and flexible substrates such as PI film and PET film can be used. As the material of the adhesive layers 61 and 62, a thermosetting resin or the like can be used.

[0052] Next, a metal layer 11 is formed by applying a metal coating to the area of ​​the surface of the fiber membrane that is exposed from the support 51. Similarly, a metal layer 12 is formed on the area of ​​the back surface of the fiber membrane that is exposed from the support 52. As a coating method, a deposition method, an ion plating method, an atomic layer deposition method, an electroless plating method, or the like can be adopted. 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, and Al, or alloys containing two or more of these metals. The metal layer may have a single layer structure or a laminate structure made of multiple materials.

[0053] Next, the connection electrodes 41 to 44 are formed. The connection electrodes 41 to 44 can be formed by vapor deposition, sputtering, ion plating, atomic layer deposition, electroless plating, spraying, printing, dipping, etc. Examples of connection electrode materials include metals such as Au, Ag, Cu, Pt, Rh, Pd, Ru, Ni, Ir, Cr, Mo, W, Ti, and Al, or alloys containing two or more of these metals.

[0054] Thereafter, the electrodes 31 and 32 are formed to obtain the pressure wave generating element 100. Methods for forming the electrodes include vapor deposition, sputtering, ion plating, atomic layer deposition, electrolytic plating, electroless plating, spray coating, dip coating, and printing. Examples of materials for the electrodes 31 and 32 include metals such as Au, Ag, Cu, Pt, Rh, Pd, Ru, Ni, Ir, Cr, Mo, W, Ti, and Al. Each of the electrodes 31 and 32 may have a single-layer structure or a multi-layer structure made of multiple materials.

[0055] The structure of the pressure wave generating element 100, the materials of each component, the manufacturing method, etc. are not limited to the above-mentioned examples. The solid insulating layer 10 may be solid (i.e., non-porous). The solid insulating layer 10 may be a polymer film containing the above-mentioned polymer material. In this case, through holes for passing sound waves may be formed in the polymer film by, for example, patterning.

[0056] Furthermore, the metal layers 11 and 12 do not have to be layers 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 front and back surfaces of the solid insulating layer 10 by a known method.

[0057] Furthermore, the structures of the connection electrodes 41 to 44 and the electrodes 31 and 32 are not limited to the examples shown in the drawings. For example, a pair of connection electrodes (e.g., the connection electrodes 41 and 42) may have a comb-like structure arranged to face each other when viewed in a plan view from the Z direction, as illustrated in FIG.

[0058] Furthermore, depending on the structure, process, etc. of the pressure wave generating element, components such as connecting electrodes, support structures, adhesive layers, etc. may be omitted as appropriate.

[0059] <Variation 1> Fig. 7 is a schematic cross-sectional view showing a pressure wave generation element 101 of modified example 1. The pressure wave generation element 101 differs from the pressure wave generation element 100 shown in Figs. 1 to 3 in that it further includes another metal layer 21 arranged at a distance from the metal layers 11 and 12 in the Z direction.

[0060] The metal layer 21 is disposed at a distance from the metal layer 12 on the opposite side of the metal layer 12 from the solid insulating layer 10 in the Z direction. The metal layer 12 and the metal layer 21 face each other with an air layer 72 therebetween. An upper surface 21a of the metal layer 21 may 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 the 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 be electrically connected via connection electrodes 45 and 46.

[0061] The pressure wave generating element 101 may further include a solid insulating layer (sometimes referred to as a "second solid insulating layer") 20. In the illustrated example, the metal layer 21 is provided on a main surface (sometimes referred to as a "third main surface") 20a of the solid insulating layer 20 on the metal layer 12 side. The metal layer 21 is a fiber-containing metal layer formed by metal coating on the surface of the fiber membrane, and the solid insulating layer 20 may be an insulating layer including an uncoated portion of the fiber membrane.

[0062] 7, the metal layer 21 is disposed between the solid insulating layer 10 and the solid insulating layer 20 at a distance from the solid insulating layer 10. With this arrangement, when the composite wave W is emitted from above the metal layer 11, the pressure wave (third pressure wave) generated in the air layer 72 by the passage of electricity through the metal layer 21 passes only through the solid insulating layer 10 before being emitted without passing through the solid insulating layer 20. Therefore, the composite wave W can be emitted more efficiently.

[0063] In this specification, a structure M2 in which a resistor (metal layer) that generates a pressure wave when current is applied is provided only on one main surface of a 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 the metal layer may be in contact with a heat dissipation layer such as a substrate, or may be in contact with air.

[0064] A substrate 80 may be provided on the main surface 20b of the solid insulating layer 20 opposite to the metal layer 21. The solid insulating layer 20 and the substrate 80 may be bonded via an adhesive layer 64. The substrate 80 may function as, for example, a heat dissipation layer. Examples of the substrate 80 include a glass substrate, a ceramic substrate such as silicon, alumina, zirconia, magnesium oxide, aluminum nitride, boron nitride, or silicon nitride, and a flexible substrate such as PI or PET film.

[0065] The support structure 50 may further include a support 53 disposed on a peripheral portion of the main surface 20a of the solid insulating layer 20. The solid insulating layer 20 and the support 53 may be adhered to each other by an adhesive layer 63. The support 53 and the substrate 80 may be configured to sandwich and hold the peripheral portion of the solid insulating layer 20 therebetween.

[0066] In the pressure wave generating element 101, the support structure 50 is, for example, a ring-shaped structure that supports the outer periphery of the metal layers 11, 12, and 21 and the solid insulating layers 10 and 20. The support structure 50 and the substrate 80 may be arranged so as to block the emission of sound waves from the sides and below of the pressure wave generating element 101. This allows the composite wave W of pressure waves generated by driving the metal layers 11, 12, and 21 to be emitted mainly from above the pressure wave generating element 101 (above the metal layer 11).

[0067] The pressure wave generating element 101 can be manufactured by preparing a laminate L1 including the first heating element M1, supports 51, 52, and connecting electrodes 41 to 44, and a lower laminate LB including the second heating element M2, support 53, connecting electrodes 45, 46, and substrate 80, and stacking the lower laminate LB and laminate L1 in the Z direction, for example, via an adhesive layer 65. The materials, structures, and formation methods of the metal layer 21, connecting electrodes 45, 46, and solid insulating layer 20 may be similar to those of the metal layers 11, 12, connecting electrodes 45, 46, and solid insulating layer 10, respectively.

[0068] 8 is a schematic cross-sectional view showing another pressure wave generating element 102 of the first modified example. The pressure wave generating element 102 includes a plurality of (here, two) first heating elements M1 stacked at intervals above the metal layer 21. One end side of the metal layers 11, 12 of each first heating element M1 is electrically connected to the electrode 31, and the other end side of the metal layers 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, first heating elements M1) including a solid insulating layer and a metal layer are stacked, each heating element may be referred to as a "unit heating element."

[0069] In the illustrated example, a plurality of (here, two) laminates L1 are stacked in the Z direction above the lower laminate LB via an adhesive layer 66. The pressure wave generating element of this modified example does not need to have a lower laminate LB. The pressure wave generating element may have a structure in which a plurality of first heating elements M1 are stacked above a substrate (a substrate on which no metal layer is provided), for example.

[0070] According to this modification, the number of metal layers can be further increased, which further reduces the element resistance, thereby further increasing the input power and further increasing the sound pressure.

[0071] <Variation 2> The pressure wave generating element of the second modification has a structure in which two or more second heating elements M2 are stacked at intervals.

[0072] Fig. 9 is a schematic cross-sectional view showing a pressure wave generation element 103 of modification 2. The pressure wave generation element 103 differs from the pressure wave generation element 101 shown in Fig. 7 in that the metal layer 12 and the support 52 are not provided on the main surface 10b of the solid insulating layer 10.

[0073] In the pressure wave generating element 103, the metal layer 11 is provided only on the main 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 main surface 10b of the solid insulating layer 10 opposite to the metal layer 11 is in contact with, for example, an air layer 72.

[0074] A second heating element M2 including a solid insulating layer 20 and a metal layer 21 is located below the solid insulating layer 10. An upper surface 21a of the metal layer 21 may be in contact with the air layer 72. The metal layer 21 is disposed between the solid insulating layer 10 and the solid insulating layer 20 at a distance from the solid insulating layer 10. As a result, when a composite wave W is emitted from above the element, a pressure wave (third pressure wave) generated by energization of the metal layer 21 passes only through the solid insulating layer 10 without passing through the solid insulating layer 20 and is emitted. Therefore, the third pressure wave can be efficiently emitted from above the metal layer 11.

[0075] The pressure wave generating element 103 can be manufactured, for example, by stacking a laminate L2 including the second heating element M2, the support 51, and the connection electrodes 41, 42, and a lower laminate LB in the Z direction via an adhesive layer 65.

[0076] 10 is a schematic cross-sectional view showing another pressure wave generating element 104 of the second modification. The pressure wave generating element 104 includes a plurality (two in this case) of second heating elements (unit heating elements) M2 stacked at intervals above a metal layer 21. One end side of the metal layer 11 of each second heating element M2 is electrically connected to an electrode 31, and the other end side of the metal layer 11 of each second heating element M2 is electrically connected to an electrode 32. In the example shown in the figure, a plurality (two in this case) of laminates L2 are stacked in the Z direction above the lower laminate LB via an adhesive layer 66.

[0077] According to this modification, the number of metal layers can be further increased, which further reduces the element resistance, thereby further increasing the input power and further increasing the sound pressure.

[0078] Furthermore, 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 that emits the composite wave W (here, the upper side of the solid insulating layer). In this way, by stacking the second heating elements M2 so that the metal layer is on the emission side (here, the upper side) of 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 more efficiently emitted in the Z direction (here, above the element).

[0079] <Examples and Comparative Examples> Example 1 In Example 1, laminated pressure wave generating elements having a fiber membrane (first heating element M1) with metal coating on both sides were fabricated as Samples 1 to 3 (see Figs. 1 to 3). In addition, a single-layer pressure wave generating element having a single metal layer was fabricated as a comparative sample.

[0080] Samples 1-3 The methods for producing Samples 1 to 3 will be described with reference to Figures 1 to 3. In the following description, the "size" of each member refers to the size in plan view from the Z direction.

[0081] First, a polyimide (PI) fiber membrane was prepared by electrospinning as follows.

[0082] A PI solution prepared using N,N-dimethylformamide (DMF) as a solvent was used as the spinning solution. The solution concentrations were adjusted to 5.5wt% and 12wt%, and lithium chloride was added to the solution at 0.2wt% and 0.1wt%, respectively. Other additives that can be used include tetrabutylammonium chloride and potassium trifluoromethanesulfonate. Next, PI fibers were simultaneously spun onto an aluminum (Al) foil using a multi-nozzle electrospinning method using the 5.5wt% PI solution and the 12wt% PI solution. The discharge rate of the 5.5wt% PI solution and the 12wt% PI solution was set to 1:1. The discharge rate can be adjusted by the discharge speed, the number of nozzles, etc. A 200mmφ drum collector was used as the collector on which the fiber membrane was deposited, and spinning was performed while rotating at 100 rpm. In electrospinning, the applied voltage was 30 kV, the distance between the nozzle and the collector was 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 produced with the 5.5 wt% PI solution was 41 nm, and the average fiber diameter of the fibers produced with the 12 wt% PI solution was 176 nm. As a result, a fiber membrane was obtained in which fibers with an average fiber diameter of 41 nm and fibers with an average fiber diameter of 176 nm were combined. The porosity of the fiber membrane was 90.1%.

[0083] Next, the supports 51 and 52 were bonded to the obtained fiber membrane. First, the surface of the fiber membrane was bonded to a PI film (support 51) having an opening of 4 mm x 4 mm size. Here, a PI film with an adhesive layer 61 formed on one side in advance was used, and the fiber membrane and the PI film were thermally pressed together via the adhesive layer 61 to bond the fiber membrane to the PI film. Next, the Al foil was peeled off from the fiber membrane, so that the fiber membrane was transferred to the support 51. After this, the back side of the fiber membrane (the side opposite to the PI film, i.e., the side from which the Al foil was peeled off) was bonded to a PI film (support 52) ​​having an opening of 4 mm x 4 mm size (size: 4 mm x 4 mm) in the same manner as above.

[0084] Next, an Au film (size: 4 mm x 4 mm) having a thickness distributed in the range of 1 to 40 nm was formed as the metal layer 11 by sputtering on the area of ​​the surface of the fiber membrane exposed by the opening of the support 51. Similarly, an Au film (size: 4 mm x 4 mm) having a thickness distributed in the range of 1 to 40 nm was formed as the metal layer 12 by sputtering on the area of ​​the back surface of the fiber membrane exposed by the opening of the support 52. The non-coated part of the fiber membrane located between the metal layers 11 and 12 was designated as the "solid insulating layer 10" (see FIG. 4). The thickness of the metal coated on the surface of each fiber may have a distribution as described above with reference to FIG. 5, for example.

[0085] Next, a pair of connection electrodes 41, 42 were formed on both ends of the metal layer 11 and both ends of the support 51 by, for example, a sputtering method. Similarly, a pair of connection electrodes 43, 44 were formed on both ends of the metal layer 12 and both ends of the support 52. Here, electrodes having a laminated structure containing Ti (thickness: 10 nm), Cu (thickness: 500 nm), and Au (thickness: 100 nm) from the solid insulating layer side were formed as the connection electrodes 41 to 44. In a plan view, the size of each of the connection electrodes 41 to 44 was 1.4 mm x 4 mm, and the distance between the pair of connection electrodes (electrode distance) was 3.2 mm. In this way, a laminate including the solid insulating layer 10, the metal layers 11 and 12, the supports 51 and 52, and the connection electrodes 41 to 44 was obtained.

[0086] The obtained laminate was cut into individual pieces measuring 6 mm x 6 mm, and then the electrodes 31 and 32 were formed. Here, Ag electrode paste was applied so as to bond to each of the connection electrodes 41 to 44. The Ag electrode paste was then dried and hardened by heat treatment to form the electrodes 31 and 32. Note that, in addition to Ag, other metal materials such as Cu may also be used as the electrode material. Through this process, pressure wave generating elements of samples 1 to 3 were obtained.

[0087] Comparison sample 1 A single-layer element was fabricated using a PI film as a solid insulating layer. Here, an Au film (thickness: 20 nm, size: 4 mm x 4 mm) was formed as a metal layer on only one side of the PI film (thickness: 25 μm, size: 6 mm x 6 mm) by sputtering. After that, a pair of electrodes was 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.

[0088] Comparison sample 2 A single-layer element was produced that had a fiber membrane with a metal coating on only one side. Here, the pressure wave generating element of Comparative Sample 2 was produced using the same materials and in the same manner as Samples 1 to 3, except that a support and an Au film (metal layer) were formed on only one side of the fiber membrane. The part of the fiber membrane where the Au film was not formed (uncoated part) was used as a solid insulating layer.

[0089] Evaluation method The methods for evaluating the fiber membrane and element characteristics carried out in this example will be described.

[0090] 1) Average fiber diameter The fiber diameter of the fiber membrane (PI fiber) was measured as follows. The fiber membrane was observed with a scanning electron microscope (Hitachi S-4800, accelerating voltage 5 kV, 3k to 120k magnification) and an SEM image was obtained. The average fiber diameter was calculated by measuring the fiber diameter from the obtained image. Specifically, 10 fibers were randomly extracted from each field of view from the obtained image, and this was repeated for five fields of view to measure the fiber diameters of a total of 50 fibers, and the average fiber diameter was calculated.

[0091] 2) Porosity of the fiber membrane The porosity of the fiber membrane (here, the polyimide fiber membrane) was calculated by the following formula. Porosity (%) = {1-(bulk density ÷ true density)} x 100

[0092] As another method for calculating the porosity, it is also possible to calculate the porosity by repeating cross-sectional processing with FIB and SEM observation to obtain a 3D stereoscopic image. Specifically, FIB processing is performed with FEI's HELIOS NANORAB 660i, the SEM image is observed, and then the FIB is used to process again 10 nm in the depth direction, and the SEM image is observed. By repeating FIB processing and SEM observation in this way, SEM images with a depth of 400 nm (41 images in total) are obtained. A 3D stereoscopic image of the fiber membrane can be constructed from these 41 SEM images, and the porosity can be calculated.

[0093] 3) Thickness of the fiber membrane and solid insulation layer The cross section of each sample was observed with a scanning electron microscope (Hitachi S-4800, accelerating voltage 5 to 15 kV, 1 k to 20 k magnification), and the thickness of the fiber membrane, the thickness of the metal layer, and the thickness of the solid insulation layer were determined from the obtained images.

[0094] FIG. 11 is a diagram illustrating a scanning electron microscope image of a fiber membrane 90 coated with a metal. Here, the distance t1 between the front and back surfaces of the metal-coated fiber membrane was measured as the thickness of the fiber membrane 90. In addition, the penetration depths m1 and m2 of the metal into the fiber membrane were measured. Furthermore, the thickness t2 of the solid insulation layer 10 was calculated by subtracting the penetration depths m1 and m2 of the metal from the thickness t1 of the fiber membrane. Note that an image may be obtained by elemental mapping analysis using a backscattered electron image or energy dispersive X-ray spectroscopy, and the thicknesses t1, t2, m1, and m2 may be measured from the obtained image.

[0095] Before observing the cross-section with a scanning electron microscope, each sample may be pre-processed. In this example, as the pre-processing, each sample was solidified with resin, and then the cross-section of the sample was polished so that the fiber membrane was exposed. By such pre-processing, a cross-sectional image including the metal-coated portion of the fiber membrane can be obtained. In this example, the depth of the region where the contrast between the metal and the resin can be visually recognized in the cross-sectional image is defined as the penetration depth m1, m2.

[0096] The fiber membrane has a porous structure and has an uneven surface. Therefore, the thickness t1 of the fiber membrane and the thickness t2 of the solid insulation layer may vary depending on the measurement position. In this example, the maximum thickness of the fiber membrane in the cross-sectional image is defined as thickness t1, and the minimum thickness of the solid insulation layer in the cross-sectional image is defined as thickness t2.

[0097] 4) Acoustic characteristics (sound pressure ratio) The acoustic characteristics of the pressure wave generating element of each sample were measured using a MEMS microphone (Knowles: SPU0410LR5H).

[0098] First, the pressure wave generating element of each sample was mounted on a circuit board so that the metal layer was located above the solid insulating layer (if there were metal layers on both sides of the solid insulating layer, one of the metal layers was placed on top). Next, a microphone was placed above the pressure wave generating element mounted on the circuit board. The distance between the pressure wave generating element and the microphone (the distance in the thickness direction of the solid insulating layer from the uppermost metal layer in each sample to the microphone) was 6 cm. Next, a drive signal was input to the pressure wave generating element. In this example, the output voltage of the microphone was measured when the frequency of the drive signal was 60 kHz. The input voltage to the pressure wave generating element was 6 to 18 V.

[0099] When the input power to the pressure wave generating element is increased, the microphone output can increase linearly. The higher the acoustic conversion efficiency of a pressure wave generating element, the greater the slope of the microphone output relative to the input power, i.e., the ratio of the increase dV in the microphone output to the increment dW of the input power. In this embodiment, in order to evaluate the acoustic conversion efficiency of the pressure wave generating element, the slope dV / dW of each sample was obtained as an index of sound pressure, and the ratio to the dV / dW of the comparative sample 1 (the index to be compared) (hereinafter referred to as the "sound pressure ratio") was calculated.

[0100] 5) Element Resistance The element resistance of each sample was measured by the four-terminal method using a digital multimeter (Agilent 34410A).

[0101] Evaluation results Table 1 shows the evaluation results of the fiber membrane thickness t1, solid insulation layer (uncoated portion) thickness t2, sound pressure ratio, and element resistance for each sample. [Table 1]

[0102] From the results shown in Table 1, it is confirmed that by forming a fiber membrane with a metal coating on the surface (Samples 1 to 3 and Comparative Sample 2), the sound pressure per unit input power can be significantly increased (for example, sound pressure ratio: 5 or more) compared to a single-layer element having a metal layer on one side of a PI film (Comparative Sample 1). The reason for this is thought to be that in Samples 1 to 3 and Comparative Sample 2, the contact area between the metal layer and the air can be increased by forming a metal layer by metal coating the fiber membrane, and the uncoated part of the PI fiber membrane can have a higher heat insulating effect than the PI film, so that the air can be efficiently heated by the metal layer.

[0103] In addition, by providing metal layers on both sides of the fiber membrane and connecting these metal layers in parallel (Samples 1 to 3), it is possible to reduce the element resistance while maintaining a high sound pressure ratio. In Samples 1 to 3, the total thickness of the two metal layers is made larger than that of the metal layer in Comparative Sample 2, and thus the element resistance is significantly reduced compared to Comparative Sample 2.

[0104] The sound pressure ratios of Samples 1 to 3 are equal to or greater than that of Comparative Sample 2. This is believed to be because, in Comparative Sample 2, pressure waves due to air heating are generated only on one side of the fiber membrane, whereas in Samples 1 to 3, pressure waves due to air heating can be generated on both sides of the fiber membrane. Also, in Samples 1 to 3, pressure waves generated on the lower side of the fiber membrane pass through the fiber membrane and are efficiently emitted from above the element, suppressing a decrease in the sound pressure ratio caused by the pressure waves on the lower side passing through the fiber membrane.

[0105] When comparing the sound pressure ratios of Samples 1 to 3, it can be seen that the sound pressure ratio can be further improved by thickening the solid insulation layer (the uncoated portion of the fiber membrane) (for example, 10 μm or more). This is thought to be because the heat insulating effect of the solid insulation layer can be further increased by thickening the solid insulation layer. It can also be seen that if the thickness of the solid insulation layer is, for example, 10 μm or more, it can have a sufficient heat insulating effect.

[0106] Furthermore, in the structures of Samples 1 to 3, metal layers are provided on both sides of the fiber membrane, so that the increase in element size due to the increase in the metal layers can be suppressed, and therefore it is possible to miniaturize the pressure wave generating element that can achieve high efficiency and high sound pressure.

[0107] Example 2 In Example 2, a laminated element having a structure in which fiber membranes (second heating element M2) each having a metal coating on only one side were stacked was prepared as Sample 4 (see FIG. 9). Also, a single-layered element having only one fiber membrane each having a metal coating on only one side was prepared as Comparative Sample 3.

[0108] Sample 4 A method for fabricating the element of Sample 4 will be described with reference to FIG.

[0109] First, a PI fiber membrane was prepared by electrospinning as follows.

[0110] A PI solution prepared using N,N-dimethylformamide (DMF) as a solvent was used as the spinning solution. The solution concentration was adjusted to 5.5 wt%, and 0.2 wt% lithium chloride was added to the solution. Next, this solution (5.5 wt% PI solution) was used to spin PI fibers onto an Al foil by electrospinning. A 200 mmφ drum collector was used as a collector on which the fiber film was deposited, and spinning was performed while rotating at 100 rpm. In electrospinning, the applied voltage was 30 kV, the distance between the nozzle and the collector was 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 prepared fibers was 41 nm, the porosity was 87.3%, and the thickness of the fiber film was 17.2 μm.

[0111] Next, the resulting fiber membrane was used to prepare a lower laminate LB.

[0112] First, the surface of the fiber membrane was adhered to a PI film (support 53) having an opening of 4 mm x 4 mm. Here, an adhesive layer 63 was formed in advance on one side of the PI film, and the fiber membrane and the PI film were thermocompressed together via the adhesive layer 63, thereby adhering the fiber membrane to the PI film. After this, the Al foil was peeled off from the fiber membrane, thereby transferring the fiber membrane to the support 53.

[0113] Next, a Si substrate (substrate 80) was attached to the surface of the fiber membrane opposite to the PI film (i.e., the side from which the Al foil was peeled off). Here, a Si substrate with an adhesive layer 64 formed on one side was used, and the fiber membrane and the Si substrate were bonded by thermocompression bonding via the adhesive layer 64, thereby bonding the fiber membrane to the Si substrate.

[0114] Next, an Au film (size: 4 mm×4 mm) having a thickness distributed in the range of 1 to 40 nm was formed as a metal layer 21 by sputtering on the area of ​​the surface of the fiber membrane exposed by the opening of the support 53. The portion of the fiber membrane that was located between the Au film and the Si substrate and was not coated with Au (uncoated portion) was designated as a "solid insulating layer 20." The thickness of the metal coated on the surface of each fiber may have a distribution as described above with reference to FIG. 5, for example.

[0115] Next, a pair of connection electrodes 45, 46 were formed by sputtering on both ends of the metal layer 21 and both ends of the support 53. The structures (thickness, material, size, distance between electrodes, etc.) of the connection electrodes 45, 46 were similar to the structures of the connection electrodes 41, 42 in Samples 1 to 3 of Example 1. In this manner, a lower laminate LB including the substrate 80, the solid insulating layer 20, the metal layer 21, and the support 53 was obtained.

[0116] Next, the above fiber membrane was used to prepare a laminate L2.

[0117] First, the surface of the fiber membrane was adhered to a PI film (support 51) having an opening of 4 mm x 4 mm in size, and the Al foil was peeled off from the fiber membrane to transfer the fiber membrane to the support 51. Here, a PI film with an adhesive layer 61 formed on one side was used, and the fiber membrane and the PI film were thermocompressed together via the adhesive layer 61 to adhere the fiber membrane to the PI film. Next, a PET release film was adhered to the back side of the fiber membrane (the side from which the Al foil was peeled off). Here, an adhesive layer 65 (adhesive layer with PET release film) with a PET release film formed on its surface was placed on the back side of the fiber membrane, and the PET release film was thermocompressed to the fiber membrane via the adhesive layer 65.

[0118] Next, an Au film (size: 4 mm×4 mm) having a thickness distributed in the range of 1 to 40 nm was formed as a metal layer 11 by sputtering on the area of ​​the surface of the fiber membrane exposed by the opening of the support 51. The uncoated portion of the fiber membrane that was not coated with Au was designated as a "solid insulating layer 10." The thickness of the metal coated on the surface of each fiber may have a distribution such as that described above with reference to FIG. 5, for example.

[0119] Next, a pair of connection electrodes 41, 42 were formed by sputtering on both ends of the metal layer 21 and both ends of the support 51. The structures (thickness, material, size, interelectrode distance, etc.) of the connection electrodes 41, 42 were similar to the structures of the connection electrodes 41, 42 in Samples 1 to 3 of Example 1. In this manner, a laminate L2 including the solid insulating layer 10, the metal layer 21, and the support 51 was obtained.

[0120] The laminate L2 produced by the above method was stacked on the lower laminate LB. Here, after the PET release film was peeled off from the laminate L2, the laminate L2 and the lower laminate LB were thermocompressed via the adhesive layer 65. The distance between the solid insulation layer 10 and the solid insulation layer 20 (the distance in the Z direction between the fiber membranes) can be arbitrarily selected within the range of more than 0 μm and 2000 μm or less. After stacking the laminate L2 and the lower laminate LB, they were cut into individual pieces with a size of 6 mm × 6 mm.

[0121] Next, Ag electrode paste was applied so as to bond to the connection electrodes 41, 42, 45, 46, and dried and hardened by heat treatment to form the electrodes 31, 32. Note that, before forming the electrodes, the support, adhesive layer, fiber membrane, etc. may be pre-processed by laser, punching, etc. to expose parts of the connection electrodes 45, 46 of the lower laminate LB (areas to be connected to the electrodes). By bonding an electrode material to the exposed parts of the connection electrodes 45, 46, good conduction between the metal layer 21 of the lower laminate LB and the electrodes 31, 32 can be ensured. Through such a process, the pressure wave generating element of sample 4 was obtained.

[0122] Comparison sample 3 As Comparative Sample 3, a single-layer element having the same structure as Sample 4 except that it does not have the laminate L2 was produced. First, a laminate including a Si substrate, a solid insulating layer, a metal layer, a support, and a connection electrode was formed in the same manner as for the lower laminate LB in Sample 4. Next, a pair of electrodes was formed on the laminate in the same manner as for Sample 4, to obtain the pressure wave generating element of Comparative Sample 3.

[0123] Evaluation results The element characteristics of Sample 4 and Comparative Sample 3 were evaluated in the same manner as in Example 1. The results are shown in Table 2. [Table 2]

[0124] From the results in Table 2, it can be seen that by stacking fiber membranes (second heating elements) having a metal layer on one side and connecting the metal layers in parallel (Sample 4), it is possible to ensure a high sound pressure ratio (e.g., 5 or more) while reducing the element resistance more than that of the single-layer element, Comparative Sample 3. The reason why the decrease in sound pressure ratio was suppressed is thought to be that the pressure wave generated by air heating of the metal layer located below can pass through the fiber membrane and be efficiently emitted from above the element.

[0125] Example 3 In Example 3, as Samples 5 to 7, stacked elements were produced having a structure in which a fiber membrane (first heating element) with metal coating on both sides was stacked above a lower stack LB (see Figures 7 and 8).

[0126] Sample 5 A method for fabricating the element of Sample 5 will be described with reference to FIG.

[0127] First, in the same manner as in Example 1, a fibrous membrane (porosity: 90.1%) was prepared in which fibers having an average fiber diameter of 41 nm and fibers having an average fiber diameter of 176 nm were combined.

[0128] Next, the above-mentioned fiber membrane was used to obtain a lower laminate LB. The structure and manufacturing 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 above-mentioned fiber membrane was used.

[0129] Further, the laminate L1 was obtained using the above fiber membrane. The structure and manufacturing method of the laminate L1 were the same as those of the laminates in Samples 1 to 3 of Example 1, except that the above fiber membrane was used. However, in this example, the thickness t1 of the fiber membrane was 18.1 μm, and the thickness t2 of the solid insulation layer (uncoated portion of the fiber membrane) 10 was 12.7 μm.

[0130] Next, an adhesive layer 65 was introduced between the laminate L1 and the lower laminate LB, and they were laminated by pressing. The gap between the fiber membrane including the solid insulating layer 10 and the fiber membrane including the solid insulating layer 20 (the thickness of the air layer 72 in this example) can be arbitrarily selected within a range of more than 0 μm and 2000 μm or less. After the laminate L1 and the lower laminate LB were laminated, they were cut into individual pieces having a size of 6 mm×6 mm.

[0131] Next, Ag electrode paste was applied so as to bond to each of the connection electrodes 41-46, and dried and hardened by heat treatment to form the electrodes 31 and 32. Note that, before forming the electrodes, the support, adhesive layer, fiber membrane, etc. may be processed by laser, punching, etc., so that the connection electrodes 41-46 of the lower laminate LB and the laminate L1 are exposed in advance. By bonding an electrode material to the exposed parts of the connection electrodes 41-46, good conduction between the metal layers 11, 12, and 21 of the lower laminate LB and the laminate L1 and the electrodes 31 and 32 can be ensured. Through such a process, the pressure wave generating element of sample 5 was obtained.

[0132] Sample 6 The pressure wave generating element of Sample 6 was produced in the same manner as Sample 5, except that two laminates L1 were laminated above the lower laminate LB (see FIG. 8). The two laminates L1 were bonded by thermocompression via an adhesive layer. The distance between the fiber membranes in the two laminates L1 can be selected arbitrarily within the range of more than 0 μm and not more than 2000 μm.

[0133] Sample 7 The pressure wave generating element of sample 7 was produced in the same manner as samples 5 and 6, except that three laminates L1 were laminated above the lower laminate LB.

[0134] Evaluation results The element characteristics of Samples 5 to 7 were evaluated in the same manner 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 element produced using the same fiber membrane as in this example. [Table 3] From the results in Table 3, it can be seen that by stacking fiber membranes with metal layers formed on both sides and connecting the metal layers in parallel (Samples 5 to 7), it is possible to reduce the element resistance more than that of the single-layer element, Comparative Sample 2, while maintaining a high sound pressure ratio (for example, 4 or more). The reason why the decrease in the sound pressure ratio is suppressed is thought to be that, as explained in Example 2, the pressure wave generated by air heating of the metal layer located below passes through the fiber membrane and is efficiently emitted from above the element.

[0135] Moreover, a comparison of the element characteristics of Samples 5 to 7 shows that the element resistance can be further reduced with an increase in the number of metal layers. When the number of fiber membranes on which metal layers are formed increases, the pressure wave generated by the current passing through the metal layers located below must pass through more fiber membranes, making it difficult for it to be emitted from above the element. For this reason, there is a tendency for the sound pressure ratio to decrease (sound pressure per unit input power to decrease) with an increase in the number of metal layers. Even in such cases, the element resistance can be significantly reduced, so sufficient sound pressure can be generated by increasing the input power.

[0136] Example 4 In Example 4, a laminated element having a structure in which PI films (second heating element) having a metal layer formed on one side were laminated was prepared as Sample 8. Also, a laminated element having a structure in which PI films (first heating element) having metal layers formed on both sides were laminated was prepared as Sample 9.

[0137] Sample 8 A PI film (thickness: 25 μm, size: 6 mm × 6 mm) was prepared as a solid insulating layer. A Au film (thickness: 20 nm, size: 4 mm × 4 mm) was formed as a metal layer on only one side of the PI film by sputtering. Then, a pair of connection electrodes was formed on both ends of the metal layer by sputtering. In this way, a laminate including a PI film on which an Au film was formed was obtained. Two such laminates were produced, and the two laminates were stacked via an adhesive layer with the surface on which the metal layer (Au film) was formed facing up. After this, a pair of electrodes was formed so as to be joined to the connection electrodes of each metal layer. The connection electrodes and the structure of the electrodes (thickness, material, size, distance between electrodes, etc.) and the formation method were the same as those of Samples 1 to 3 described above. Through such a process, a pressure wave generating element of Sample 8 was obtained.

[0138] Sample 9 A PI film (thickness: 25 μm, size: 6 mm × 6 mm) was prepared as a solid insulating layer. A Au film (thickness: 20 nm, size: 4 mm × 4 mm) was formed as a metal layer on each of the front and back surfaces of the PI film by sputtering. Then, a pair of connection electrodes was formed on both ends of each metal layer by sputtering. After this, a pair of electrodes was formed so as to join to the connection electrodes of each metal layer. The connection electrodes and the structure (thickness, material, size, distance between electrodes, etc.) and the formation method were the same as those of Samples 1 to 3 described above. Through such a process, an element of Sample 9 was obtained.

[0139] Evaluation results The element characteristics of Samples 8 and 9 were evaluated in the same manner 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 element using a PI film as a solid insulating layer. [Table 4]

[0140] From 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 more than that of the single-layer element, Comparative Sample 1. In Samples 8 and 9, the sound pressure ratio is somewhat lower than that of Comparative Sample 1, but the element resistance is significantly reduced. Therefore, it is possible to generate high sound pressure by increasing the input power.

[0141] Any of the various embodiments described above may be appropriately combined to achieve the effects of each of the embodiments.

[0142] Although the present invention has been fully described in connection with the preferred embodiment with reference to the accompanying drawings, various changes and modifications will be apparent to those skilled in the art, and such changes and modifications should be understood to be included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.

[0143] The description of the pressure wave generating element according to the present invention can also be expressed as follows.

[0144] The pressure wave generating element of the first embodiment is A thermally excited pressure wave generating element, a first solid insulating layer having a first major 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 a 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; 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; Equipped with The first solid insulating layer is located between the first metal layer and the second metal layer.

[0145] The pressure wave generating element of the second embodiment is In the pressure wave generating element of the first embodiment, the first solid insulating layer has a second principal surface opposing the first principal surface; The second metal layer is disposed on the second main surface of the first solid insulating layer.

[0146] The pressure wave generating element of the third embodiment is In the pressure wave generating element of the second embodiment, The first metal layer and the second metal layer are fiber-containing metal layers formed on the front and back surfaces of a fiber membrane having a porous structure, respectively; The pressure wave generating element according to claim 2 , wherein the first solid insulating layer includes a portion of the fiber membrane located between the first metal layer and the second metal layer.

[0147] The pressure wave generating element of the fourth aspect is In the pressure wave generating element of the third embodiment, The first solid insulating layer has a thickness of 10 μm or more.

[0148] The pressure wave generating element of the fifth aspect is In the pressure wave generating element according to the second to fourth aspects, a third metal layer disposed at a distance from the second metal layer on a side of the second metal layer opposite the first solid insulating 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.

[0149] The pressure wave generating element of the sixth aspect is In the pressure wave generating element of the first embodiment, a second solid insulating layer having a third major surface; the second metal layer is provided on the third principal surface of the second solid insulating layer; The second metal layer is disposed between the first solid insulating layer and the second solid insulating layer and spaced apart from the first solid insulating layer.

[0150] The seventh aspect of the pressure wave generating element is In the pressure wave generating element according to any one of the first to sixth aspects, The first solid insulating layer has a porous structure having a plurality of through holes.

[0151] The pressure wave generating element of the eighth aspect is In the seventh embodiment of the pressure wave generating element, The first solid insulating layer contains fibers, and the porosity of the first solid insulating layer is 80% or more and 95% or less.

[0152] The pressure wave generating element of the ninth aspect is In the pressure wave generating element according to any one of the first to eighth aspects, The semiconductor device further includes an annular support structure that supports an outer periphery of the first metal layer.

[0153] The pressure wave generating element of the tenth aspect is In the pressure wave generating element of the ninth aspect, The annular support structure supports the periphery of the first metal layer and the second metal layer.

[0154] The pressure wave generating element of the eleventh aspect is In the pressure wave generating element of the sixth aspect, a plurality of unit heating elements, each unit heating element including 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 from the second metal layer side, One end side of the first metal layer of each of the multiple unit heating elements is electrically connected to the first electrode, and the other end side of the first metal layer of each of the multiple unit heating elements is electrically connected to the second electrode.

[0155] The pressure wave generating element of the twelfth aspect is In the pressure wave generating element according to any one of the second to fifth aspects, a plurality of unit heating elements each including the first solid insulating layer, the first metal layer, and the second metal layer; The plurality of unit heating elements are stacked at intervals along the thickness direction, The one end side of the first metal layer and the one end side of the second metal layer in each of the multiple 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 in each of the multiple unit heating elements are electrically connected to the second electrode. [Industrial Applicability]

[0156] The pressure wave generating element according to the present invention is capable of generating higher sound pressure and is therefore industrially useful. [Explanation of symbols]

[0157] 10, 20 Solid insulation layer 10a, 10b, 20a, 20b Main surfaces of solid insulating layer 11, 12, 21 metal layer 11a, 21a Top surface of metal layer 11b Underside of metal layer 31, 32 electrode 41~46 Connection electrodes 50 Support structure 51~53 Support 61~66 Adhesive layer 71, 72 Air layer 80 Substrate 90 Fiber Membrane 101-104 Pressure wave generating element

Claims

1. A thermally excited pressure wave generating element, a first solid insulating layer having a first major surface and a second major surface opposite the first major 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 a thickness direction of the first solid insulating layer and provided on the second main surface 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; 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; Equipped with A pressure wave generating element, wherein the first solid insulating layer is located between the first metal layer and the second metal layer.

2. The first metal layer and the second metal layer are fiber-containing metal layers formed on the front and back surfaces of a fiber membrane having a porous structure, respectively; The pressure wave generating element according to claim 1 , wherein the first solid insulating layer includes a portion of the fiber membrane located between the first metal layer and the second metal layer.

3. The pressure wave generating element according to claim 2 , wherein the first solid insulating layer has a thickness of 10 μm or more.

4. a third metal layer disposed at a distance from the second metal layer on a side of the second metal layer opposite to the first solid insulating layer in the thickness direction; The pressure wave generating element according to any one of claims 1 to 3, wherein 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.

5. The pressure wave generating element according to claim 1 , wherein the first solid insulating layer has a porous structure having a plurality of through holes.

6. The pressure wave generation element according to claim 5 , wherein the first solid insulating layer contains fibers, and the porosity of the first solid insulating layer is 80% or more and 95% or less.

7. The pressure wave generating element according to claim 1 , further comprising an annular support structure supporting an outer periphery of the first metal layer.

8. The pressure wave generating element according to claim 7 , wherein the annular support structure supports an outer periphery of the first metal layer and the second metal layer.

9. a plurality of unit heating elements each including the first solid insulating layer, the first metal layer, and the second metal layer; The plurality of unit heating elements are stacked at intervals along the thickness direction, A pressure wave generating element as described in any one of claims 1 to 3, wherein one end side of the first metal layer and one end side of the second metal layer in each of 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 in each of the plurality of unit heating elements are electrically connected to the second electrode.

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