Multilayer piezoelectric element and electroacoustic transducer

Abstract

To provide a laminated piezoelectric element (10) capable of preventing short circuit in adjacent piezoelectric films (12) and an electroacoustic transducer using the same. A piezoelectric film in which a piezoelectric layer (20) is sandwiched by two thin film electrodes (24, 30) and polarized in the thickness direction is laminated in multiple layers, and the polarization directions of adjacent piezoelectric films are opposite to each other, thereby solving the problem.

Description

TECHNICAL FIELD

[0001] The present application relates to a laminated piezoelectric element for use in an exciter or the like, and an electroacoustic transducer using the laminated piezoelectric element. BACKGROUND

[0002] A so-called exciter (exciter) that vibrates and emits sound by being in contact with and mounted to various articles is used for various purposes.

[0003] For example, if in an office, when giving a presentation or a teleconference or the like, it is possible to emit sound instead of a speaker by mounting an exciter in a conference table, a whiteboard, a screen, or the like. If a vehicle such as an automobile, it is possible to emit a prompt tone, a warning tone, music, or the like by mounting an exciter in a center console, an A-pillar, a ceiling, or the like. Also, in the case of a vehicle that does not emit an engine sound such as a hybrid vehicle and an electric vehicle, it is possible to emit a vehicle approach notification sound from a bumper or the like by mounting an exciter in the bumper or the like.

[0004] As a variable element that generates vibration in these exciters, a combination of a coil and a magnet, a vibration motor such as an eccentric motor and a linear resonance motor, or the like is known.

[0005] These variable elements are difficult to thin. In particular, a vibration motor has difficulties in that in order to increase the vibration force, it is necessary to increase the mass body and it is difficult to perform frequency modulation for adjusting the degree of vibration and the response speed is slow, and the like. SUMMARY

[0006] Technical Problem to be Solved by the Invention

[0007] As a variable element that can solve these problems, it is possible to consider using a piezoelectric film in which a piezoelectric body layer is sandwiched by electrode layers and laminating the piezoelectric film in multiple layers to form a laminated piezoelectric element.

[0008] The rigidity of the piezoelectric film itself is low, but by laminating the piezoelectric film, it is possible to increase the rigidity of the entire element. In addition, in the laminate of the piezoelectric film, it is possible to ensure a high electric field strength even without increasing the driving voltage, and thus is very preferable.

[0009] Among them, in a laminated piezoelectric element in which piezoelectric films are laminated, it is possible to consider adhering the piezoelectric films with an adhesive or the like. On the other hand, in a laminated piezoelectric element in which piezoelectric films are adhered, the thinner the adhesive layer, the higher the performance becomes.

[0010] However, in a laminated piezoelectric element in which piezoelectric films are adhered, if the adhesive layer is made thin, the risk of a short circuit occurring between adjacent piezoelectric films is very high, and thus it is difficult to make the adhesive layer sufficiently thin in order to obtain a high-performance laminated piezoelectric element.

[0011] The present application has an object to solve the problems of the conventional techniques, and to provide a laminated piezoelectric element in which short-circuiting between adjacent piezoelectric films is prevented, for example, even when the adjacent piezoelectric films are bonded to each other, and in which the bonding layer is sufficiently thinned and made high in performance, and an electro-acoustic transducer using the laminated piezoelectric element.

[0012] Means for solving the technical problem

[0013] To achieve these objects, the present application has the following structure.

[0014] [1] A laminated piezoelectric element characterized by laminating a plurality of piezoelectric films each of which is formed by sandwiching a piezoelectric layer with two thin film electrodes,

[0015] The piezoelectric films are polarized in the thickness direction, and the polarization directions of the adjacent piezoelectric films are opposite to each other.

[0016] [2] The laminated piezoelectric element according to [1], wherein the piezoelectric films are laminated by folding the piezoelectric films a plurality of times.

[0017] [3] The laminated piezoelectric element according to [2], wherein the piezoelectric films have a core rod in the folded portion.

[0018] [4] The laminated piezoelectric element according to [2] or [3], wherein the curved portion formed based on the folding of the piezoelectric films is along the long side direction.

[0019] [5] The laminated piezoelectric element according to [2] or [3], wherein the curved portion formed based on the folding of the piezoelectric films is along the short side direction.

[0020] [6] The laminated piezoelectric element according to any one of [1] to [5], wherein at least one of the laminated piezoelectric films has a protective layer laminated to at least one side of the thin film electrode.

[0021] [7] The laminated piezoelectric element according to any one of [1] to [6], having a bonding layer bonding the adjacent piezoelectric films.

[0022] [8] The laminated piezoelectric element according to [7], wherein the thickness of the bonding layer is thinner than the thickness of the piezoelectric layer.

[0023] [9] The laminated piezoelectric element according to [7] or [8], wherein the thickness of the bonding layer is 0.1 to 50 μm.

[0024]

[10] The laminated piezoelectric element according to any one of [7] to [9], wherein the bonding layer is a layer composed of an adhesive.

[0025]

[11] The laminated piezoelectric element as described in any one of [7] to

[10] , wherein the spring constant of the adhesive layer is less than or equal to the spring constant of the piezoelectric film.

[0026]

[12] The laminated piezoelectric element as described in any one of [7] to

[11] , wherein the adhesive layer is conductive.

[0027]

[13] The stacked piezoelectric element as described in any one of [1] to

[12] , wherein the piezoelectric film has a maximum value of loss tangent (Tanδ) at a frequency of 1 Hz obtained based on dynamic viscoelasticity measurement at room temperature.

[0028]

[14] The stacked piezoelectric element as described in any one of [1] to

[13] , wherein the piezoelectric properties of the piezoelectric film are not in-plane anisotropic.

[0029]

[15] The stacked piezoelectric element as described in any one of [1] to

[14] , wherein the piezoelectric layer is a polymer composite piezoelectric layer formed by dispersing piezoelectric particles in a polymer material having cyanoethyl.

[0030]

[16] As described in

[15] , the laminated piezoelectric element is made of cyanoethylated polyvinyl alcohol.

[0031]

[17] The laminated piezoelectric element as described in any one of [1] to

[16] has lead wiring for connection to a thin-film electrode and for connection to an external device.

[0032] The current flowing into the lead-out wiring divided by the width of the lead-out wiring is less than 1A / cm.

[0033]

[18] An electroacoustic transducer having a stacked piezoelectric element as described in any one of [1] to

[17] and a vibrating plate in contact with the stacked piezoelectric element.

[0034] Invention Effects

[0035] According to these inventions, it is possible to provide a stacked piezoelectric element formed by stacking multiple piezoelectric thin films, which can prevent short circuits between adjacent piezoelectric thin films. For example, even when adjacent piezoelectric elements are bonded to each other with an adhesive layer, the adhesive layer can be sufficiently thinned and its performance improved. A high-performance electroacoustic transducer using the stacked piezoelectric element is also provided. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating an example of a stacked piezoelectric element of the present invention.

[0037] Figure 2 It is a schematic representation of the composition. Figure 1 A diagram showing an example of a piezoelectric thin film of a stacked piezoelectric element.

[0038] Figure 3 is a conceptual view for explaining an example of a method of manufacturing a piezoelectric film.

[0039] Figure 4 is a conceptual view for explaining an example of a method of manufacturing a piezoelectric film.

[0040] Figure 5 is a conceptual view for explaining an example of a method of manufacturing a piezoelectric film.

[0041] Figure 6 is a conceptual view for explaining an example of a method of manufacturing a piezoelectric film.

[0042] Figure 7 is a conceptual view for explaining an example of a method of manufacturing a piezoelectric film.

[0043] Figure 8 is a view schematically showing an example of an electro-acoustic transducer of the present application.

[0044] Figure 9 is a view schematically showing another example of a laminated piezoelectric element of the present application.

[0045] Figure 10 is a view schematically showing another example of a laminated piezoelectric element of the present application.

[0046] Figure 11 is a view schematically showing another example of a laminated piezoelectric element of the present application.

[0047] Figure 12 is a conceptual view for explaining a lead wire of a laminated piezoelectric element of the present application.

[0048] Figure 13 is a view schematically showing an example of a conventional laminated piezoelectric element.

[0049] Figure 14 is a conceptual view for explaining an embodiment of the present application.

[0050] Figure 15 is a conceptual view for explaining a sound pressure measuring method in an embodiment.

[0051] Figure 16 is a view schematically showing another example of a laminated piezoelectric element of the present application.

[0052] Figure 17 is a view schematically showing another example of a laminated piezoelectric element of the present application.

[0053] Figure 18 is a view schematically showing another example of a laminated piezoelectric element of the present application. DETAILED DESCRIPTION

[0054] Hereinafter, the laminated piezoelectric element and the electro-acoustic transducer of the present application will be described in detail based on the preferred embodiments shown in the drawings.

[0055] The following description of the constituent elements is sometimes made based on the representative embodiments of the present application, but the present application is not limited to these embodiments.

[0056] In the present specification, the numerical range indicated using "~" means a range including the numerical values before and after the "~" as the lower limit value and the upper limit value.

[0057] Figure 1 In the drawing, an example of the laminated piezoelectric element of the present application is schematically shown.

[0058] Figure 1 The laminated piezoelectric element 10 shown in the drawing has a structure in which three piezoelectric films 12 are laminated and the adjacent piezoelectric films 12 are adhered by an adhesive layer 14. In each piezoelectric film 12, a power source 16 that applies a driving voltage to stretch and contract the piezoelectric film 12 is connected.

[0059] In addition, Figure 1 The laminated piezoelectric element 10 shown in the drawing is composed of three piezoelectric films 12, but the present application is not limited to this. That is, if the laminated piezoelectric element of the present application is composed of a plurality of piezoelectric films 12, the number of laminated piezoelectric films 12 can be two or more than four. With respect to this point, the following Figure 9 The laminated piezoelectric element 56 shown in the drawing is also the same.

[0060] Figure 2 In the drawing, the piezoelectric film 12 is schematically shown by a cross-sectional view.

[0061] As Figure 2 As shown in the drawing, the piezoelectric film 12 has a piezoelectric layer 20 that is a sheet-shaped object having piezoelectricity, a lower film electrode 24 laminated on one surface of the piezoelectric layer 20, a lower protective layer 28 laminated on the lower film electrode 24, an upper film electrode 26 laminated on the other surface of the piezoelectric layer 20, and an upper protective layer 30 laminated on the upper film electrode 26. As will be described later, the piezoelectric film 12 is polarized in the thickness direction.

[0062] In addition, in order to simplify the drawing and clearly show the structure of the laminated piezoelectric element 10, Figure 1 In the drawing, the lower protective layer 28 and the upper protective layer 30 are omitted.

[0063] In the piezoelectric film 12, as a preferred mode, as Figure 2As schematically shown, the piezoelectric layer 20 is composed of a high-molecular composite piezoelectric body in which piezoelectric particles 36 are dispersed in a viscoelastic matrix 34 composed of a high-molecular material having viscoelasticity at ordinary temperature. In the present specification, "ordinary temperature" means a temperature range of about 0 to 50°C.

[0064] The high-molecular composite piezoelectric body (piezoelectric layer 20) preferably has the following requirements.

[0065] (i) Flexibility

[0066] For example, in the case where the portable device is held in a state where it is slowly bent like a file such as a newspaper or a magazine, it is constantly subjected to a relatively slow and large bending deformation of several Hz or less from the outside. At this time, if the high-molecular composite piezoelectric body is too hard, a large bending stress occurs in proportion to the degree, and cracks occur at the interface between the high-molecular matrix and the piezoelectric particles, which can eventually lead to destruction. Therefore, the high-molecular composite piezoelectric body is required to have appropriate flexibility. Furthermore, if the strain energy can be diffused as heat to the outside, the stress can be alleviated. Therefore, the loss tangent of the high-molecular composite piezoelectric body is required to be appropriately large.

[0067] In summary, the flexible high-molecular composite piezoelectric body used as an actuator is required to be hard for vibrations of 20 Hz to 20 kHz and soft for vibrations of several Hz or less. Furthermore, the loss tangent of the high-molecular composite piezoelectric body is required to be appropriately large with respect to vibrations of all frequencies of 20 kHz or less.

[0068] Furthermore, it is preferable to stack by matching the rigidity of the adhered object material, and the spring constant can be easily adjusted. At this time, the thinner the adhesive layer 18, the higher the energy efficiency. As the adhered object material, for example, a vibration plate is exemplified. Furthermore, the rigidity of the adhered object material is, for example, hardness, stiffness, spring constant, and the like.

[0069] Generally, a high-molecular solid has a viscoelastic relaxation mechanism, and as the temperature rises or the frequency decreases, a large-scale molecular motion is observed as a decrease (relaxation) in the storage elastic modulus (Young's modulus) or a maximization (absorption) of the loss elastic modulus. Among them, the relaxation caused by the microscopic Brown motion of the molecular chain in the amorphous region is called primary dispersion, and a very large relaxation phenomenon can be observed. The temperature at which this primary dispersion occurs is the glass transition point (Tg), and the viscoelastic relaxation mechanism is most apparent.

[0070] In the polymer composite piezoelectric body (piezoelectric layer 20), by using a high molecular material having a glass transition point at normal temperature, in other words, a high molecular material having viscoelasticity at normal temperature in the matrix, a polymer composite piezoelectric body having a hard action for vibrations of 20 Hz to 20 kHz and a soft action for slow vibrations of several Hz or less is realized. In particular, in terms of preferably finding this action and the like, it is preferable to use a high molecular material having a glass transition point at normal temperature, that is, 0 to 50°C, in the matrix of the polymer composite piezoelectric body at a frequency of 1 Hz.

[0071] As the high molecular material having viscoelasticity at normal temperature, various known high molecular materials can be used. It is preferable to use a high molecular material having a maximum value of a loss tangent Tan δ at a frequency of 1 Hz of 0.5 or more based on a dynamic viscoelasticity test at normal temperature, that is, 0 to 50°C.

[0072] Thus, when the polymer composite piezoelectric body is slowly bent by an external force, stress concentration at the interface between the high molecular matrix and the piezoelectric particle in the maximum bending moment portion is mitigated, and high flexibility can be expected.

[0073] Further, it is preferable that the high molecular material having viscoelasticity at normal temperature is as follows, that is, a storage elastic modulus (E') at a frequency of 1 Hz based on a dynamic viscoelasticity measurement is 100 MPa or more at 0°C and 10 MPa or less at 50°C.

[0074] Thus, while the bending moment generated when the polymer composite piezoelectric body is slowly bent by an external force can be reduced, a hard action for acoustic vibrations of 20 Hz to 20 kHz can be expected.

[0075] Further, if the relative dielectric constant of the high molecular material having viscoelasticity at normal temperature is 10 or more at 25°C, it is more preferable. Thus, a higher electric field is required for the piezoelectric particle in the high molecular matrix when a voltage is applied to the polymer composite piezoelectric body, and thus a larger deformation amount can be expected.

[0076] However, on the other hand, if good moisture resistance and the like are ensured, it is also preferable that the relative dielectric constant of the high molecular material is 10 or less at 25°C.

[0077] As the high molecular material having viscoelasticity at normal temperature satisfying these conditions, cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-ethylene-vinyl isoprene block copolymer, polyvinyl methyl ketone, and polymethyl butyl acrylate, and the like are exemplified. Further, as these high molecular materials, commercially available products such as Hibler 5127 (manufactured by KURARAY CO., LTD.) and the like can also be preferably used. Among them, as the high molecular material, it is preferable to use a material having a cyanoethyl group, and in particular, it is preferable to use cyanoethylated PVA.

[0078] In addition, one kind of these high molecular materials can be used, or a plurality of kinds can be used (mixed) at the same time.

[0079] A plurality of kinds of high molecular materials can be used at the same time as necessary using the viscoelastic matrix 34 using these high molecular materials having viscoelasticity at normal temperature.

[0080] That is, a viscoelastic material such as cyanoethylated PVA is added to the viscoelastic matrix 34 for the purpose of adjusting dielectric properties or mechanical properties, and other dielectric high molecular materials can also be added as necessary.

[0081] As dielectric high molecular materials that can be added, as an example, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-tetrafluoroethylene copolymer, and other fluorine-based polymers, vinylidene cyanide-ethylene copolymer, cyanoethyl cellulose, cyanoethyl hydroxysucrose, cyanoethyl hydroxycellulose, cyanoethyl hydroxypolylactose, cyanoethyl methacrylate, cyanoethyl acrylate, cyanoethyl hydroxyethyl cellulose, cyanoethyl amylose, cyanoethyl hydroxypropyl cellulose, cyanoethyl dihydroxypropyl cellulose, cyanoethyl hydroxypropyl amylose, cyanoethyl polyacrylamide, cyanoethyl polyacrylate, cyanoethyl polylactose, cyanoethyl polyhydroxymethylene, cyanoethyl glycidyl polylactose, cyanoethyl sucrose, cyanoethyl sorbitol, and other polymers having a cyano group or cyanoethyl group, and synthetic rubbers such as nitrile rubber or chloroprene rubber, and the like are exemplified.

[0082] Among these, a high molecular material having a cyanoethyl group is preferable.

[0083] Further, in the viscoelastic matrix 34 of the piezoelectric layer 20, the dielectric polymer added in addition to the material having viscoelasticity at normal temperature such as cyanoethylated PVA is not limited to one kind, and a plurality of kinds can be added.

[0084] Further, for the purpose of adjusting the glass transition point Tg, in addition to the dielectric polymer, a chlorovinyl resin, polyethylene, polystyrene, methacrylic acid resin, polybutylene, isobutylene, and other thermoplastic resins, and a phenol resin, urea resin, melamine resin, alkyd resin, and mica, and other thermosetting resins can also be added to the viscoelastic matrix 34.

[0085] Furthermore, for the purpose of improving adhesion, a tackifier such as rosin ester, rosin, terpene, terpene phenol, and petroleum resin can also be added.

[0086] There is no particular limitation on the amount of materials other than viscoelastic polymers such as cyanoethylated PVA added to the viscoelastic matrix 34 of the piezoelectric layer 20, but it is preferred to be 30% by mass or less based on the proportion of the materials in the viscoelastic matrix 34.

[0087] Thus, the properties of the added polymer material can be discovered without damaging the viscoelastic mitigation mechanism in the viscoelastic matrix 34, thereby achieving preferred results in terms of high dielectric constant, improved heat resistance, and improved adhesion to the piezoelectric particles 36 and the electrode layer.

[0088] The piezoelectric particles 36 are composed of ceramic particles with perovskite or wurtzite crystal structures.

[0089] Examples of ceramic particles constituting piezoelectric particles 36 include lead zirconate titanate (PZT), lanthanum lead zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and a solid solution of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0090] The particle size of these piezoelectric particles 36 is not limited, and can be appropriately selected according to the size of the piezoelectric film 12 and the application of the stacked piezoelectric element 10. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm.

[0091] By setting the particle size of the piezoelectric particles 36 within this range, optimal results can be obtained in terms of both high voltage characteristics and flexibility in the piezoelectric film 12.

[0092] In addition, Figure 2 In the piezoelectric layer 20, the piezoelectric particles 36 are uniformly and regularly dispersed in the viscoelastic matrix 34, but the present invention is not limited thereto.

[0093] That is, the piezoelectric particles 36 in the piezoelectric layer 20 are preferably, if uniformly dispersed, irregularly dispersed in the viscoelastic matrix 34.

[0094] In the piezoelectric film 12, the ratio of viscoelastic matrix 34 to piezoelectric particles 36 in the piezoelectric layer 20 is not limited and can be appropriately set according to the size and thickness of the piezoelectric film 12 in the planar direction, the application of the stacked piezoelectric element 10, and the required characteristics of the piezoelectric film 12.

[0095] The volume fraction of piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30 to 80%, more preferably 50% or more, and even more preferably 50 to 80%.

[0096] By setting the ratio of viscoelastic matrix 34 to piezoelectric particles 36 within the above-mentioned range, an optimal result can be obtained that balances high voltage characteristics and flexibility.

[0097] In the piezoelectric thin film 12 described above, preferably, the piezoelectric layer 20 is a polymer composite piezoelectric layer formed by dispersing piezoelectric particles in a viscoelastic matrix, wherein the viscoelastic matrix contains a polymer material that is viscoelastic at room temperature. However, the present invention is not limited thereto, and various known piezoelectric layers used in known piezoelectric elements can be used as the piezoelectric layer of the piezoelectric thin film.

[0098] As an example, piezoelectric layers composed of the aforementioned dielectric polymer materials such as polyvinylidene fluoride (PVDF) and vinylidene fluoride-tetrafluoroethylene copolymer, and piezoelectric layers composed of the aforementioned piezoelectric materials such as PZT, PLZT, barium titanate, zinc oxide, and BFBT can be exemplified.

[0099] In the piezoelectric film 12, the thickness of the piezoelectric layer 20 is not particularly limited, and can be appropriately set according to the application of the stacked piezoelectric element 10, the number of piezoelectric film layers in the stacked piezoelectric element 10, and the required characteristics of the piezoelectric film 12.

[0100] The thicker the piezoelectric layer 20, the more advantageous it is in terms of rigidity, such as the stiffness of the sheet. However, the voltage (potential difference) required to make the piezoelectric film 12 expand and contract by the same amount increases.

[0101] The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm.

[0102] By setting the thickness of the piezoelectric layer 20 within the aforementioned range, a preferred result can be obtained while ensuring rigidity and appropriate flexibility.

[0103] like Figure 2 As shown, the piezoelectric thin film 12 in the example has the following structure: a lower thin film electrode 24 is provided on one surface of the piezoelectric layers 20, and a lower protective layer 28 is provided thereon; an upper thin film electrode 26 is provided on the other surface of the piezoelectric layers 20, and an upper protective layer 30 is provided thereon. The upper thin film electrode 26 and the lower thin film electrode 24 form an electrode pair.

[0104] In addition to these layers, the piezoelectric film 12 may have, for example, electrode leads from the upper film electrode 26 and the lower film electrode 24, which are connected to the power supply 16. Furthermore, the piezoelectric film 12 may have an insulating layer covering the exposed area of ​​the piezoelectric layer 20 to prevent short circuits, etc.

[0105] That is, the piezoelectric film 12 has a structure in which both surfaces of the piezoelectric layer 20 are sandwiched by the pair of electrodes, i.e., the upper thin film electrode 26 and the lower thin film electrode 24, and the layer stack is sandwiched by the lower protective layer 28 and the upper protective layer 30.

[0106] Thus, in the piezoelectric film 12, the region sandwiched by the upper thin film electrode 26 and the lower thin film electrode 24 expands and contracts in accordance with the applied voltage.

[0107] In addition, in the present application, the upper and lower portions of the lower thin film electrode 24 and the lower protective layer 28 and the upper thin film electrode 26 and the upper protective layer 30 are labeled with names in conjunction with the illustration for the sake of facilitating the explanation of the piezoelectric film 12. Therefore, the upper and lower portions in the piezoelectric film 12 do not have technical meanings and are irrelevant to the actual use state.

[0108] In the layer stack piezoelectric element 10 of the present application, the lower protective layer 28 and the upper protective layer 30 of the piezoelectric film 12 are not essential constituent elements but are provided as a preferred mode.

[0109] In the piezoelectric film 12, the lower protective layer 28 and the upper protective layer 30 cover the upper thin film electrode 26 and the lower thin film electrode 24 while serving to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 12, the piezoelectric layer 20 composed of the viscoelastic matrix 34 and the piezoelectric particles 36 exhibits very excellent flexibility for slow bending deformation, but there are cases where the rigidity or the mechanical strength is insufficient depending on the use. The piezoelectric film 12 provides the lower protective layer 28 and the upper protective layer 30 to compensate for such cases.

[0110] In addition, with respect to Figure 1 In the layer stack piezoelectric element 10 shown in FIG. 1, as a preferred mode, all of the piezoelectric films 12 have both the lower protective layer 28 and the upper protective layer 30. However, the present application is not limited thereto, and piezoelectric films having protective layers and piezoelectric films not having protective layers can be mixed. Furthermore, in the case where the piezoelectric film has a protective layer, the piezoelectric film can have only the lower protective layer 28 or can have only the upper protective layer 30. As an example, if it is a layer stack piezoelectric element 10 having a 3-layer structure as shown in FIG. 2, it can be a structure in which the piezoelectric film on the uppermost layer has only the upper protective layer 30, the piezoelectric film in the middle has no protective layer, and the piezoelectric film on the lowermost layer has only the lower protective layer 28. Figure 1

[0111] The lower protective layer 28 and the upper protective layer 30 are not limited and can be formed using various sheet-like materials, and as an example, various resin films are preferably exemplified.

[0112] ​Among them, a resin film composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyether imide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and a cyclic olefin resin, and the like, which have excellent mechanical properties and heat resistance, and the like, are preferably used.

[0113] The thickness of the lower protective layer 28 and the upper protective layer 30 is also not limited. Also, the thickness of the lower protective layer 28 and the upper protective layer 30 is substantially the same, but can also be different.

[0114] Among them, if the rigidity of the lower protective layer 28 and the upper protective layer 30 is too high, not only the expansion and contraction of the piezoelectric layer 20 is limited, but also the flexibility is impaired. Therefore, in the case where mechanical strength or good handling properties as a sheet are not required, the thinner the lower protective layer 28 and the upper protective layer 30 are, the more advantageous it is.

[0115] In the piezoelectric film 12, if the thickness of the lower protective layer 28 and the upper protective layer 30 is 2 times or less the thickness of the piezoelectric layer 20, a preferable result can be obtained in terms of ensuring rigidity and appropriate flexibility, and the like.

[0116] For example, in the case where the thickness of the piezoelectric layer 20 is 50 μm and the lower protective layer 28 and the upper protective layer 30 are composed of PET, the thickness of the lower protective layer 28 and the upper protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 25 μm or less.

[0117] In the piezoelectric film 12, a lower thin film electrode 24 is formed between the piezoelectric layer 20 and the lower protective layer 28, and an upper thin film electrode 26 is formed between the piezoelectric layer 20 and the upper protective layer 30. In the following description, the lower thin film electrode 24 will be referred to as a lower electrode 24, and the upper thin film electrode 26 will also be referred to as an upper electrode 26.

[0118] The lower electrode 24 and the upper electrode 26 are provided in order to apply a voltage to the piezoelectric layer 20 (piezoelectric film 12).

[0119] In the present application, the material forming the lower electrode 24 and the upper electrode 26 is not limited, and various conductors can be used. Specifically, metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, alloys of these, laminates and composites of these metals and alloys, and indium tin oxide, and the like are exemplified. Among them, copper, aluminum, gold, silver, platinum, and indium tin oxide are preferably exemplified as the lower electrode 24 and the upper electrode 26.

[0120] Further, the method of forming the lower electrode 24 and the upper electrode 26 is not limited, and a known method such as a film formed by vacuum evaporation, sputtering, or the like, or a method of adhering a foil formed of the above-described material can be used.

[0121] Among others, a thin film of copper or aluminum formed by vacuum evaporation is preferably used as the lower electrode 24 and the upper electrode 26 for the reason that the flexibility of the piezoelectric thin film 12 can be ensured. Among others, a thin film of copper formed by vacuum evaporation is particularly preferably used.

[0122] The thickness of the lower electrode 24 and the upper electrode 26 is not limited. Further, the thickness of the lower electrode 24 and the upper electrode 26 is substantially the same, but can be different.

[0123] Among others, as with the lower protective layer 28 and the upper protective layer 30, if the rigidity of the lower electrode 24 and the upper electrode 26 is too high, not only the expansion and contraction of the piezoelectric layer 20 is limited, but also the flexibility is impaired. Therefore, if the resistance does not become too high, the thinner the lower electrode 24 and the upper electrode 26 are, the more advantageous it is.

[0124] In the piezoelectric thin film 12, if the product of the thickness and the Young's modulus of the lower electrode 24 and the upper electrode 26 is lower than the product of the thickness and the Young's modulus of the lower protective layer 28 and the upper protective layer 30, the flexibility is not significantly impaired, and thus is preferable.

[0125] For example, in the case where the lower protective layer 28 and the upper protective layer 30 are composed of PET (Young's modulus: about 6.2 GPa) and the lower electrode 24 and the upper electrode 26 are composed of copper (Young's modulus: about 130 GPa), if the thickness of the lower protective layer 28 and the upper protective layer 30 is set to 25 μm, the thickness of the lower electrode 24 and the upper electrode 26 is preferably 1.2 μm or less, more preferably 0.3 μm or less, and is preferably 0.1 μm or less.

[0126] As described above, the piezoelectric thin film 12 has a structure in which the piezoelectric layer 20 in which the piezoelectric particles 36 are dispersed in the viscoelastic matrix 34 composed of a high-molecular material having viscoelasticity at ordinary temperature is sandwiched by the lower electrode 24 and the upper electrode 26, and further, the laminate is sandwiched by the lower protective layer 28 and the upper protective layer 30.

[0127] The piezoelectric thin film 12 preferably has a maximum value of the tangent of the loss (Tan δ) at a frequency of 1 Hz based on dynamic viscoelasticity measurement at ordinary temperature, and more preferably has a maximum value of 0.1 or more at ordinary temperature.

[0128] Thus, even if the piezoelectric film 12 is continuously subjected to a relatively slow and large bending deformation of several Hz or less from the outside, the strain energy can be effectively diffused as heat to the outside, and thus cracking at the interface between the polymer matrix and the piezoelectric particles can be prevented.

[0129] The piezoelectric film 12 is preferably such that the storage elastic modulus (E') at 0°C is 10 to 30 GPa and the storage elastic modulus (E') at 50°C is 1 to 10 GPa in a frequency of 1 Hz based on dynamic viscoelasticity measurement.

[0130] Thus, the piezoelectric film 12 can have a large frequency dispersion in the storage elastic modulus (E') at normal temperature. That is, the piezoelectric film 12 can have a hard action for vibrations of 20 Hz to 20 kHz and a soft action for vibrations of several Hz or less.

[0131] Further, the piezoelectric film 12 is preferably such that the product of the thickness and the storage elastic modulus (E') at 0°C is 1.0 x 10 6 to 2.0 x 10 6 N / m and the product of the thickness and the storage elastic modulus (E') at 50°C is 1.0 x 10 5 to 1.0 x 10 6 N / m based on dynamic viscoelasticity measurement.

[0132] Thus, the piezoelectric film 12 can have appropriate rigidity and mechanical strength without impairing flexibility and acoustic characteristics.

[0133] Further, the piezoelectric film 12 is preferably such that the loss tangent (Tan δ) at 25°C in a frequency of 1 kHz in a master curve obtained based on dynamic viscoelasticity measurement is 0.05 or more.

[0134] Thus, the frequency characteristics of a speaker using the piezoelectric film 12 become smooth, and the amount of change in sound quality when the lowest resonance frequency f0 changes in accordance with a change in the curvature of the speaker can be reduced.

[0135] Hereinafter, an example of a manufacturing method of the piezoelectric film 12 will be described with reference to Figures 3-7

[0136] First, as shown in FIG. 1, a sheet 12a in which the lower electrode 24 is formed on the lower protective layer 28 is prepared. The sheet 12a can be produced by forming a copper thin film or the like as the lower electrode 24 on the surface of the lower protective layer 28 by vacuum evaporation, sputtering, plating, or the like. Figure 3

[0137] ​​The lower protective layer 28 is very thin, and a lower protective layer 28 with a spacer (temporary support) can be used as needed when the workability is poor, and the like. In addition, as the spacer, PET or the like having a thickness of 25 to 100 μm can be used. The spacer is removed after the upper electrode 26 and the upper protective layer 30 are thermocompression-bonded, and before the lower protective layer 28 is laminated with any member.

[0138] On the other hand, a coating material is prepared by dissolving a high-molecular material having viscoelasticity at normal temperature such as cyanoethylated PVA in an organic solvent, and further adding piezoelectric body particles 36 such as PZT particles, stirring and dispersing. In the following description, the high-molecular material having viscoelasticity at normal temperature such as cyanoethylated PVA is also referred to as "viscoelastic material".

[0139] The organic solvent is not limited, and various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used.

[0140] When the sheet 12a is prepared and the coating material is prepared, the coating material is cast (applied) on the sheet 12a, and the organic solvent is evaporated and dried. Thus, as shown in FIG. 2, a laminate 12b having the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 formed on the lower electrode 24 is produced. In addition, the lower electrode 24 refers to the electrode on the substrate side at the time of applying the piezoelectric layer 20, and is not the electrode indicating the positional relationship of the upper and lower layers in the laminate. Figure 4

[0141] The casting method of the coating material is not particularly limited, and all of the known coating methods (coating apparatuses) such as a slide coater and a doctor knife can be used.

[0142] In addition, if the viscoelastic material is a substance that can be heat-melted such as cyanoethylated PVA, a melt material in which the viscoelastic material is heat-melted and the piezoelectric body particles 36 are added and dispersed is produced, and is extrusion-molded or the like on the sheet 12a shown in FIG. 1, and is extruded into a thin sheet and cooled. Thus, as shown in FIG. 2, a laminate 12b having the lower electrode 24 on the lower protective layer 28 and the piezoelectric layer 20 formed on the lower electrode 24 can be produced. Figure 3 Figure 4

[0143] As described above, in the piezoelectric thin film 12, a high-molecular piezoelectric material such as PVDF can be added to the viscoelastic matrix 34 in addition to the viscoelastic material such as cyanoethylated PVA.

[0144] ​​​When adding these polymeric piezoelectric materials to the viscoelastic matrix 34, the polymeric piezoelectric materials added to the coating can be dissolved. Alternatively, the desired polymeric piezoelectric material can be added to the heated and melted viscoelastic material and then heated and melted.

[0145] When a laminate 12b is fabricated having a lower electrode 24 on the lower protective layer 28 and a piezoelectric layer 20 formed on the lower electrode 24, a polarization treatment is performed on the piezoelectric layer 20.

[0146] There are no limitations on the method for polarizing the piezoelectric layer 20, and known methods can be used. As a preferred polarization treatment method, an example is shown... Figure 5 and Figure 6 The method shown.

[0147] In this method, such as Figure 5 and Figure 6 As shown, rod-shaped or wire-shaped corona electrodes 40 are provided on the upper surface 20a of the piezoelectric layer 20 of the laminate 12b at intervals g, for example 1 mm, and are movable along the upper surface 20a. Furthermore, the corona electrodes 40 and the lower electrode 24 are connected to a DC power supply 42.

[0148] Furthermore, a heating element for heating and holding the laminate 12b is prepared, for example, a heating plate.

[0149] Then, while the piezoelectric layer 20 is heated and maintained at a temperature of 100°C by a heating element, a DC voltage of several kV, for example 6 kV, is applied from the DC power supply 42 between the lower electrode 24 and the corona electrode 40 to generate corona discharge. Furthermore, while maintaining the interval g, the corona electrode 40 is moved (scanned) along the upper surface 20a of the piezoelectric layer 20 to perform polarization processing of the piezoelectric layer 20.

[0150] As a result, the piezoelectric layer 20 is polarized in the thickness direction.

[0151] In the polarization process utilizing these corona discharges, the movement of the corona electrode 40 can be achieved using a known rod-shaped moving part. For convenience, the polarization process utilizing corona discharge will also be referred to as corona polarization process in the following description.

[0152] Furthermore, there are no limitations on the method of moving the corona electrode 40 during the corona polarization process. That is, a moving mechanism that fixes the corona electrode 40 and moves the laminate 12b can be provided to move the laminate 12b and perform the polarization process. The movement of the laminate 12b can also use a known sheet-like moving component.

[0153] Furthermore, the number of corona electrodes 40 is not limited to one; multiple corona electrodes 40 can also be used for corona polarization treatment.

[0154] Also, the polarization treatment is not limited to the corona polarization treatment, and a general electric field polarization that directly applies a direct current electric field to a polarization treatment target can be used. However, in the case of the general electric field polarization, the upper electrode 26 needs to be formed before the polarization treatment.

[0155] In addition, before the polarization treatment, a calendering treatment that smoothes the surface of the piezoelectric layer 20 using a heating roller or the like can be performed. By performing the calendering treatment, the heat pressure bonding step described later can be smoothly performed.

[0156] Therefore, the piezoelectric layer 20 of the laminate 12b is subjected to the polarization treatment, and at the same time, a sheet 12c in which the upper electrode 26 is formed on the upper protective layer 30 is prepared. The sheet 12c can be produced by forming a copper thin film or the like as the upper electrode 26 on the surface of the upper protective layer 30 by vacuum evaporation, sputtering, plating, or the like.

[0157] Next, as shown in FIG. 6, the upper electrode 26 is directed toward the piezoelectric layer 20, and the sheet 12c is laminated on the laminate 12b in which the piezoelectric layer 20 has been subjected to the polarization treatment. Figure 7

[0158] Further, the laminate 12b and the laminate of the sheet 12c are arranged so as to sandwich the upper protective layer 30 and the lower protective layer 28, and heat pressure bonding is performed by a heat pressure device or a heating roller or the like to produce the piezoelectric film 12.

[0159] As described later, the laminated piezoelectric element 10 of the present application has a structure in which the piezoelectric films 12 are laminated and are preferably adhered by the adhesive layer 14. In this case, as shown by the arrows indicated on the piezoelectric layer 20 in FIG. 7, the polarization directions in the adjacent piezoelectric films 12 of the laminated piezoelectric element 10 of the present application are opposite to each other. Figure 1

[0160] A general laminated ceramic piezoelectric element in which piezoelectric ceramics are laminated is subjected to a polarization treatment after a laminate of the piezoelectric ceramics is produced. Only a common electrode exists on the interface of each piezoelectric layer, and thus the polarization directions of each piezoelectric layer are alternated in the laminating direction.

[0161] In contrast, the piezoelectric film 12 that constitutes the laminated piezoelectric element 10 of the present application can be subjected to the polarization treatment in the state of the piezoelectric film 12 before lamination. As shown in FIG. 8, it is preferable that the piezoelectric film 12 that constitutes the laminated piezoelectric element 10 of the present application be subjected to the polarization treatment of the piezoelectric layer 20 by a corona polarization treatment before the upper electrode 26 and the upper protective layer 30 are laminated. Figure 5 Figure 6

[0162] ​​​​Therefore, the laminated piezoelectric element 10 of the present application can be produced by laminating the piezoelectric thin films 12 which have been subjected to the polarization treatment. It is preferable that a long piezoelectric thin film (a large-area piezoelectric thin film) subjected to the polarization treatment be produced, cut and provided as each piezoelectric thin film 12, and then the piezoelectric thin films 12 be laminated as the laminated piezoelectric element 10 of the present application.

[0163] Therefore, the laminated piezoelectric element 10 of the present application can also arrange the polarization directions of the adjacent piezoelectric thin films 12 in the laminating direction, and can also alternate as shown in Figure 1

[0164] As shown in Figure 1 the laminated piezoelectric element 10 of the present application has a structure in which the polarization directions of the adjacent piezoelectric thin films 12 are set to be opposite to each other, the piezoelectric thin films 12 are laminated in multiple layers (three layers in the illustrated example), and the adjacent piezoelectric thin films 12 are adhered by the adhesive layer 14.

[0165] In the present application, if the adjacent piezoelectric thin films 12 can be adhered, various publicly known adhesive layers 14 can be used.

[0166] Therefore, the adhesive layer 14 can be a layer composed of an adhesive which has fluidity at the time of adhesion and then becomes a solid state, can be a layer composed of an adhesive which is a soft solid in a gel (rubber) state at the time of adhesion and then also maintains the state in a gel state, and can also be a layer composed of a material which has both the characteristics of the adhesive and the adhesive.

[0167] In the laminated piezoelectric element 10 of the present application, the multiple piezoelectric thin films 12 which are laminated are stretched and contracted, for example, a diaphragm 50 is vibrated as described later to emit sound. Therefore, it is preferable that the laminated piezoelectric element 10 of the present application directly transmit the stretching and contraction of each piezoelectric thin film 12. If a substance having viscosity such as a vibration-damping substance exists between the piezoelectric thin films 12, the transmission efficiency of the stretching and contraction energy of the piezoelectric thin films 12 can be lowered to cause a decrease in the driving efficiency of the laminated piezoelectric element 10.

[0168] If this is taken into consideration, the adhesive layer 14 is preferably an adhesive layer composed of an adhesive which can obtain a solid and relatively hard adhesive layer 14, as compared with an adhesive layer composed of an adhesive. As a more preferable adhesive layer 14, specifically, an adhesive layer composed of a thermoplastic type adhesive such as a polyester-based adhesive and a styrene-butadiene rubber (SBR)-based adhesive can be preferably exemplified.

[0169] Adhesion is different from bonding, and is useful when a high adhesion temperature is required. Also, a thermoplastic type adhesive has "relatively low temperature, short time and strong adhesion", and is therefore preferable.

[0170] ​In the laminated piezoelectric element 10 of the present application, the thickness of the adhesive layer 14 is not limited, and can be appropriately set to a thickness capable of exhibiting sufficient adhesive force (adhesion, cohesion) depending on the material forming the adhesive layer 14.

[0171] In the laminated piezoelectric element 10 of the present application, the thinner the adhesive layer 14, the higher the transmission effect of the expansion energy (vibration energy) of the piezoelectric layer 20, and the energy efficiency can be improved. Also, if the adhesive layer 14 is thick and has high rigidity, it can limit the expansion of the piezoelectric film 12. Furthermore, as described later, the adjacent piezoelectric films 12 of the laminated piezoelectric element 10 of the present application do not short-circuit each other, and thus the adhesive layer 14 can be made thin.

[0172] In view of this, the adhesive layer 14 is preferably thinner than the piezoelectric layer 20. That is, in the laminated piezoelectric element 10 of the present application, the adhesive layer 14 is preferably hard and thin.

[0173] Specifically, the thickness of the adhesive layer 14 after bonding is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and further preferably 0.1 to 10 μm.

[0174] In the laminated piezoelectric element 10 of the present application, if the spring constant of the adhesive layer 14 is high, it can limit the expansion of the piezoelectric film 12. Therefore, it is preferable that the spring constant of the adhesive layer 14 is the same as or lower than that of the piezoelectric film 12. Note that the spring constant is "thickness x Young's modulus".

[0175] Specifically, the product of the thickness of the adhesive layer 14 and the storage elastic modulus (E') at a frequency of 1 Hz based on dynamic viscoelasticity measurement is preferably 2.0 x 10 6 N / m or less at 50°C, and 1.0 x 10 6 N / m or less at 50°C.

[0176] Also, the internal loss of the adhesive layer based on dynamic viscoelasticity measurement at a frequency of 1 Hz is preferably 1.0 or less at 25°C in the case of the adhesive layer 14 composed of an adhesive, and 0.1 or less at 25°C in the case of the adhesive layer 14 composed of an adhesive.

[0177] Note that, in the laminated piezoelectric element of the present application, the adhesive layer 14 is provided as a preferable mode, and is not an essential component.

[0178] Therefore, the laminated piezoelectric element of the present application does not have the adhesive layer 14, and can use a known crimping member, a fastening member, a fixing member, or the like to laminate the piezoelectric films 12 to constitute the laminated piezoelectric element. For example, in the case where the piezoelectric film 12 is rectangular, the laminated piezoelectric element can be constituted by fastening the four corners with members such as bolts and nuts, or can be further constituted by fastening the center portion in the same manner. Alternatively, after the piezoelectric films 12 are laminated, the laminated piezoelectric films 12 can be fixed by adhering an adhesive tape to the peripheral portion (end surface) to constitute the laminated piezoelectric element.

[0179] However, in this case, when a driving voltage is applied from the power source 16, each piezoelectric film 12 is caused to independently stretch and contract, and depending on the situation, each layer of each piezoelectric film 12 is caused to bend in opposite directions to form a gap. In this way, in the case where each piezoelectric film 12 is caused to independently stretch and contract, the driving efficiency of the laminated piezoelectric element is reduced, and the stretching and contracting of the laminated piezoelectric element as a whole is reduced, so that it can become impossible to sufficiently vibrate the abutted vibration plate or the like. In particular, in the case where each layer of each piezoelectric film 12 is caused to bend in opposite directions to form a gap, the driving efficiency of the laminated piezoelectric element is greatly reduced.

[0180] In view of this, the laminated piezoelectric element of the present application is preferably provided with the adhesive layer 14 that adheres the adjacent piezoelectric films 12 to each other, as in the illustrated example of the laminated piezoelectric element 10.

[0181] As shown in FIG. 1, the laminated piezoelectric element 10 of the present application is provided with a plurality of piezoelectric films 12 that are laminated to each other. The piezoelectric film 12 is a thin film that is formed by applying a piezoelectric body layer 20 to a substrate 22. The piezoelectric body layer 20 is formed of a piezoelectric material such as lead zirconate titanate (PZT) or lead magnesium niobate (PMN). The piezoelectric body layer 20 is formed in a rectangular shape, for example, and has a thickness of 0.1 to 0.5 mm, for example. The substrate 22 is formed of a material such as aluminum or stainless steel, and has a thickness of 0.1 to 0.5 mm, for example. The piezoelectric film 12 is provided with a lower electrode 24 and an upper electrode 26. The lower electrode 24 is formed of a material such as aluminum or copper, and has a thickness of 0.01 to 0.1 mm, for example. The upper electrode 26 is formed of a material such as aluminum or copper, and has a thickness of 0.01 to 0.1 mm, for example. The lower electrode 24 and the upper electrode 26 are formed in a rectangular shape, for example, and are arranged to face each other with the piezoelectric body layer 20 interposed therebetween. The piezoelectric film 12 is provided with a plurality of piezoelectric films 12 that are laminated to each other. The piezoelectric film 12 is a thin film that is formed by applying a piezoelectric body layer 20 to a substrate 22. The piezoelectric body layer 20 is formed of a piezoelectric material such as lead zirconate titanate (PZT) or lead magnesium niobate (PMN). The piezoelectric body layer 20 is formed in a rectangular shape, for example, and has a thickness of 0.1 to 0.5 mm, for example. The substrate 22 is formed of a material such as aluminum or stainless steel, and has a thickness of 0.1 to 0.5 mm, for example. The piezoelectric film 12 is provided with a lower electrode 24 and an upper electrode 26. The lower electrode 24 is formed of a material such as aluminum or copper, and has a thickness of 0.01 to 0.1 mm, for example. The upper electrode 26 is formed of a material such as aluminum or copper, and has a thickness of 0.01 to 0.1 mm, for example. The lower electrode 24 and the upper electrode 26 are formed in a rectangular shape, for example, and are arranged to face each other with the piezoelectric body layer 20 interposed therebetween. Figure 1 As shown in FIG. 1, the laminated piezoelectric element 10 of the present application is provided with a plurality of piezoelectric films 12 that are laminated to each other. The piezoelectric film 12 is a thin film that is formed by applying a piezoelectric body layer 20 to a substrate 22. The piezoelectric body layer 20 is formed of a piezoelectric material such as lead zirconate titanate (PZT) or lead magnesium niobate (PMN). The piezoelectric body layer 20 is formed in a rectangular shape, for example, and has a thickness of 0.1 to 0.5 mm, for example. The substrate 22 is formed of a material such as aluminum or stainless steel, and has a thickness of 0.1 to 0.5 mm, for example. The piezoelectric film 12 is provided with a lower electrode 24 and an upper electrode 26. The lower electrode 24 is formed of a material such as aluminum or copper, and has a thickness of 0.01 to 0.1 mm, for example. The upper electrode 26 is formed of a material such as aluminum or copper, and has a thickness of 0.01 to 0.1 mm, for example. The lower electrode 24 and the upper electrode 26 are formed in a rectangular shape, for example, and are arranged to face each other with the piezoelectric body layer 20 interposed therebetween.

[0182] The power source 16 is not limited to a direct current power source, and can be an alternating current power source. Also, as for the driving voltage, the driving voltage that can correctly drive each piezoelectric film 12 can be appropriately set according to the thickness and the formed material of the piezoelectric body layer 20 of each piezoelectric film 12.

[0183] As described later, the polarization directions of the adjacent piezoelectric films 12 of the laminated piezoelectric element 10 of the present application are opposite to each other. Therefore, in the adjacent piezoelectric films 12, the lower electrodes 24 face each other and the upper electrodes 26 face each other. Therefore, regardless of whether the power source 16 is an alternating current power source or a direct current power source, the power source 16 generally supplies power of the same polarity to the facing electrodes. For example, Figure 1 In the laminated piezoelectric element 10 shown in FIG. 1, power of the same polarity is generally supplied to the upper electrodes 26 of the piezoelectric film 12 of the lowermost layer in the drawing and the piezoelectric film 12 of the second layer (the layer in the middle), and power of the same polarity is generally supplied to the lower electrodes 24 of the piezoelectric film 12 of the second layer and the lower electrodes 24 of the piezoelectric film 12 of the uppermost layer in the drawing.

[0184] The method of leading out the electrodes from the lower electrode 24 and the upper electrode 26 is not limited, and various known methods can be used.

[0185] As an example, a method of connecting a conductive body such as a copper foil to the lower electrode 24 and the upper electrode 26 to lead out the electrodes to the outside, and a method of forming a through-hole in the lower protective layer 28 and the upper protective layer 30 by laser or the like and filling the through-hole with a conductive material to lead out the electrodes to the outside, and the like are exemplified.

[0186] As a preferable method of leading out the electrodes, a method described in Japanese Patent Application Publication No. 2014-209724 and a method described in Japanese Patent Application Publication No. 2016-015354, and the like are exemplified.

[0187] As described above, the laminated piezoelectric element 10 of the present application has a structure in which a plurality of piezoelectric thin films 12 are laminated and adjacent piezoelectric thin films 12 are adhered to each other with an adhesive layer 14.

[0188] Further, the polarization directions of the adjacent piezoelectric thin films 12 of the laminated piezoelectric element 10 of the present application are opposite to each other. Specifically, the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric thin films 12 of the laminated piezoelectric element 10 of the present application are opposite to each other.

[0189] That is, the laminated piezoelectric element 10 of the present application laminates the piezoelectric thin films 12 in such a manner that the polarization directions are alternately oriented in the laminating direction of the piezoelectric thin films 12. The laminating direction of the piezoelectric thin films 12 is the thickness direction of each layer.

[0190] As an example, as Figure 8 schematically shown in FIG. 1, these laminated piezoelectric elements 10 of the present application can be used as an exciter for emitting sound from a diaphragm 50 by adhering to the diaphragm 50 with an adhesive layer 52. That is, Figure 8 An example of the electro-acoustic transducer of the present application is shown in FIG. 2.

[0191] In addition, in FIG. 1, Figure 8 in order to simplify the illustration, the lower protective layer 28 and the upper protective layer 30 are omitted.

[0192] As described above, in the laminated piezoelectric element 10 of the present application, the piezoelectric layer 20 constituting the piezoelectric thin film 12 laminated with a plurality of layers is formed by dispersing piezoelectric particles 36 in a viscoelastic matrix 34. Further, the lower electrode 24 and the upper electrode 26 are provided in such a manner as to sandwich the piezoelectric layer 20 in the thickness direction.

[0193] If a voltage is applied to the lower electrode 24 and the upper electrode 26 of the piezoelectric film 12 having the piezoelectric layer 20, the piezoelectric particles 36 are stretched and contracted in the polarization direction according to the applied voltage. As a result, the piezoelectric film 12 (piezoelectric layer 20) is contracted in the thickness direction. At the same time, the piezoelectric film 12 is also stretched and contracted in the plane direction due to the Poisson's ratio.

[0194] The stretching and contraction is about 0.01 to 0.1%.

[0195] As described above, the thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum stretching and contraction in the thickness direction is only about 0.3 μm, which is very small.

[0196] On the other hand, the piezoelectric film 12, i.e., the piezoelectric layer 20, has a dimension in the plane direction that is significantly larger than the thickness. Therefore, for example, if the length of the piezoelectric film 12 is 20 cm, the piezoelectric film 12 is stretched and contracted by about 0.2 mm at the maximum by the application of a voltage.

[0197] As described above, the diaphragm 50 is attached to the laminated piezoelectric element 10 by the adhesive layer 52. Therefore, the diaphragm 50 is bent by the stretching and contraction of the piezoelectric film 12, and as a result, the diaphragm 50 vibrates in the thickness direction.

[0198] By the vibration in the thickness direction, the diaphragm 50 emits sound. That is, the diaphragm 50 vibrates according to the magnitude of the voltage (driving voltage) applied to the piezoelectric film 12, and emits sound according to the driving voltage applied to the piezoelectric film 12.

[0199] It is known that a conventional piezoelectric film composed of a high molecular material such as PVDF is stretched in a uniaxial direction after polarization treatment to align the molecular chains in the stretching direction, and as a result, a large piezoelectric property can be obtained in the stretching direction. Therefore, the piezoelectric property of the conventional piezoelectric film has in-plane anisotropy, and the amount of stretching and contraction in the plane direction when a voltage is applied has anisotropy.

[0200] On the other hand, in the laminated piezoelectric element 10 of the present application, the piezoelectric film 12 composed of a high molecular composite piezoelectric material in which piezoelectric particles are dispersed in a viscoelastic matrix can obtain a large piezoelectric property even without stretching treatment after polarization treatment. Therefore, the piezoelectric property of the piezoelectric film 12 has no in-plane anisotropy and is isotropic in all directions in the plane direction. That is, in the laminated piezoelectric element 10 of the present application, the piezoelectric film 12 is isotropically stretched and contracted in two dimensions. According to the laminated piezoelectric element 10 of the present application in which these piezoelectric films 12 that are isotropically stretched and contracted in two dimensions are laminated, the diaphragm 50 can be vibrated with a larger force, and a louder and more beautiful sound can be emitted, compared to the case where conventional piezoelectric films such as PVDF that are greatly stretched and contracted only in one direction are laminated.

[0201] As described above, the laminated piezoelectric element of the present application is laminated with a plurality of the piezoelectric thin films 12. As a preferable mode, the laminated piezoelectric element 10 of the illustrated example further adheres the adjacent piezoelectric thin films 12 to each other with the adhesive layer 14.

[0202] Therefore, even if the rigidity of each 1 piece of the piezoelectric thin film 12 is low and the expansion and contraction force is small, by laminating the piezoelectric thin films 12, the rigidity becomes high and the expansion and contraction force as the laminated piezoelectric element 10 becomes large. As a result, the laminated piezoelectric element 10 of the present application can sufficiently bend the diaphragm 50 and vibrate the diaphragm 50 in the thickness direction with a large force even if the diaphragm 50 has a certain degree of rigidity, and can make the diaphragm 50 emit sound.

[0203] Further, the thicker the piezoelectric layer 20, the larger the expansion and contraction force of the piezoelectric thin film 12 becomes, but the driving voltage required to make it expand and contract by the same amount becomes large accordingly. Among them, as described above, in the laminated piezoelectric element 10 of the present application, the thickness of the piezoelectric layer 20 is preferably at most about 300 μm, and therefore the voltage applied to each piezoelectric thin film 12 is small and can sufficiently expand and contract the piezoelectric thin film 12.

[0204] Among them, as described above, the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric thin films 12 of the laminated piezoelectric element 10 of the present application are opposite to each other.

[0205] In the piezoelectric thin film 12, the polarity of the voltage applied to the piezoelectric layer 20 becomes the polarity according to the polarization direction. Therefore, in the laminated piezoelectric element 10 of the present application, the polarity of the voltage applied to the piezoelectric layer 20 of each piezoelectric thin film 12 is opposite to the polarity of the voltage applied to the piezoelectric layer 20 of the adjacent piezoelectric thin film 12. Figure 1 and Figure 8 In the polarization directions indicated by the arrows in the laminated piezoelectric element 10 of the present application, the polarity of the voltage applied makes the polarity of the electrode on the side toward which the arrow points, i.e., the downstream side of the arrow, and the polarity of the electrode on the opposite side, i.e., the upstream side of the arrow, consistent in all the piezoelectric thin films 12.

[0206] In the illustrated example, the electrode on the side toward which the arrow indicating the polarization direction points is provided as the lower electrode 24, and the electrode on the opposite side is provided as the upper electrode 26, and the polarities of the upper electrode 26 and the lower electrode 24 are provided as the same polarity in all the piezoelectric thin films 12.

[0207] Therefore, in the laminated piezoelectric element 10 of the present application in which the polarization directions of the piezoelectric layers 20 of the adjacent piezoelectric thin films 12 are opposite to each other, the upper electrodes 26 on one surface of the adjacent piezoelectric thin films 12 face each other, and the lower electrodes on the other surface face each other. Therefore, in the laminated piezoelectric element 10 of the present application, even if the electrodes of the adjacent piezoelectric thin films 12 contact each other, short circuit does not occur.

[0208] As described above, in order to stretch and stack the piezoelectric element 10 with good energy efficiency, it is preferable to form the adhesive layer 14 relatively thin so that the adhesive layer 14 does not hinder the stretching and shrinking of the piezoelectric layer 20.

[0209] Furthermore, as described above, conventional laminated ceramic piezoelectric elements, which are composed of stacked piezoelectric ceramics, undergo polarization treatment after the piezoelectric ceramic stack is fabricated. Only a common electrode exists at the interfaces of each piezoelectric layer; therefore, the polarization directions of each piezoelectric layer alternate in the stacking direction.

[0210] like Figure 13 As shown, in a stacked piezoelectric element where the polarization directions of the stacked piezoelectric films 100 are all in the same direction, the lower electrode 104 of adjacent piezoelectric films 100 faces the upper electrode 106. Therefore, if the adhesive layer 108 is not formed to a sufficiently thick thickness, the lower electrode 104 of adjacent piezoelectric films 100 may come into contact with the upper electrode 106 at the outer end of the adhesive layer 108 in the planar direction, potentially causing a short circuit. That is, as... Figure 13 As shown, in conventional stacked piezoelectric elements where the polarization directions of the piezoelectric body layers 102 of the stacked piezoelectric thin film 100 are all in the same direction, it is impossible to thin the adhesive layer 108, thus making it impossible to stretch the stacked piezoelectric element with good energy efficiency.

[0211] In contrast, the laminated piezoelectric element of the present invention, which does not short-circuit even when the electrodes of adjacent piezoelectric films 12 come into contact with each other, may be without the adhesive layer 14. Furthermore, since the laminated piezoelectric element of the present invention does not short-circuit, even when the adhesive layer 14 is present as a preferred embodiment, the adhesive layer 14 can be made extremely thin if the required adhesive force can be obtained.

[0212] Therefore, according to the present invention, it is possible to stretch and stack piezoelectric elements 10 with high energy efficiency.

[0213] Furthermore, as described above, in the piezoelectric film 12, the absolute amount of stretching and contraction of the piezoelectric layer 20 in the thickness direction is very small, and the stretching and contraction of the piezoelectric film 12 actually only occurs in the planar direction.

[0214] Therefore, even if the polarization directions of the stacked piezoelectric films 12 are opposite, as long as the polarity of the voltage applied to the lower electrode 24 and the upper electrode 26 is correct, all the piezoelectric films 12 will stretch and contract in the same direction.

[0215] In addition, in the stacked piezoelectric element 10 of the present invention, the polarization direction of the piezoelectric thin film 12 can be detected by using a d33 tester (Meter) or the like.

[0216] Alternatively, based on the corona polarization treatment conditions described above, the polarization direction of the piezoelectric layer 20 can be determined.

[0217] In the electro-acoustic transducer of the present application using the laminated piezoelectric element of the present application, the adhesive layer between the laminated piezoelectric element 10 and the vibrating plate 50 is not limited, and various adhesives and cements known in the art can be used. As an example, the same adhesive layer as the above-described adhesive layer 14 is exemplified.

[0218] In the electro-acoustic transducer of the present application using the laminated piezoelectric element of the present application, the vibrating plate 50 is also not limited, and various materials can be used.

[0219] As the vibrating plate 50, as an example, a plate material such as a resin-made plate and a glass plate, an advertising and notification medium such as a signboard, office equipment and furniture such as a desk, a whiteboard, and a projection screen, a display element such as an organic light emitting diode (OLED) display and a liquid crystal display, a part of a vehicle such as an instrument panel, a pillar, a roof, and a bumper of an automobile, and a building material such as a wall of a house is exemplified.

[0220] In the exemplified laminated piezoelectric element 10, it is preferable that, as described above, a long (large area) piezoelectric film is produced, and the long piezoelectric film is cut to be used as each piezoelectric film 12. Therefore, in this case, the plurality of piezoelectric films 12 constituting the laminated piezoelectric element 10 are all the same piezoelectric film.

[0221] However, the present application is not limited thereto. That is, the laminated piezoelectric element of the present application can use various structures, for example, a structure in which a piezoelectric film having a lower protective layer 28 and an upper protective layer 30 and a piezoelectric film not having a piezoelectric film are laminated, a structure in which piezoelectric films having different layer structures are laminated, and a structure in which piezoelectric films having different thicknesses of piezoelectric body layers 20 are laminated.

[0222] Figure 1 The laminated piezoelectric element 10 shown in FIG. 1 is a structure in which a plurality of piezoelectric films 12 are laminated with the polarization directions of the adjacent piezoelectric films being opposite to each other, and the adjacent piezoelectric films 12 are adhered by the adhesive layer 14 as a preferable mode.

[0223] The present application is not limited thereto, and as long as the piezoelectric films are laminated in multiple layers and the polarization directions of the adjacent piezoelectric films are opposite to each other, various structures can be used.

[0224] Figure 9 An example thereof is shown. In addition, Figure 9 The laminated piezoelectric element 56 shown in FIG. 6 uses a plurality of the same components as the above-described laminated piezoelectric element 10, and therefore the same components are denoted by the same symbols, and mainly the different parts are described.

[0225] Figure 9The laminated piezoelectric element 56 shown is a more preferable form of the laminated piezoelectric element of the present application, and is formed by folding the piezoelectric film 12L multiple times to laminate the piezoelectric film 12L in multiple layers. Also, the laminated piezoelectric element 56 shown in Figure 1 is the same as the laminated piezoelectric element 10 shown in Figure 9 , and is also a preferable form in which the piezoelectric film 12L laminated by folding is adhered using the adhesive layer 14.

[0226] By folding and laminating one piezoelectric film 12L polarized in the thickness direction, the polarization directions of the piezoelectric films 12L adjacent (opposite) in the laminating direction become opposite directions.

[0227] According to the laminated piezoelectric element 56 shown in Figure 9 , it is possible to configure the laminated piezoelectric element 56 using only one piezoelectric film 12L. Also, according to the laminated piezoelectric element 56 shown in Figure 9 , it is possible to use only one power source 16 for applying a driving voltage, and furthermore, it is possible to use only one place for leading out from the electrodes of the piezoelectric film 12L.

[0228] Therefore, according to the laminated piezoelectric element 56 shown in Figure 9 , it is possible to improve the reliability as a piezoelectric element (module) by reducing the number of components and simplifying the structure, and furthermore, it is possible to achieve cost reduction.

[0229] As shown in Figure 9 , in the laminated piezoelectric element 56 formed by folding the piezoelectric film 12L, it is preferable to insert the mandrel 58 into the folded portion of the piezoelectric film 12L in contact with the piezoelectric film 12L.

[0230] As described above, the lower electrode 24 and the upper electrode 26 of the piezoelectric film 12L are formed of a metal evaporation film or the like. If the metal evaporation film is bent at an acute angle, cracks (crazing) or the like are likely to occur, which can cause the electrodes to break. That is, Figure 9 In the laminated piezoelectric element 56 shown, cracks or the like are likely to occur in the electrodes on the inside of the bent portion.

[0231] In contrast, in the laminated piezoelectric element 56 in which one piezoelectric film 12L is folded, by inserting the mandrel 58 into the folded portion of the piezoelectric film 12L, it is possible to prevent the lower electrode 24 and the upper electrode 26 from being bent, and thus it is preferable to prevent breakage from occurring.

[0232] The shape of the mandrel 58 is not limited, and various rod shapes such as a cylindrical shape and a polygonal shape can be used. In terms of easily folding the piezoelectric film 12L or the like, the mandrel 58 is preferably cylindrical (cylindrical).

[0233] The size of the core rod 58 is not limited. For example, if the core rod 58 is cylindrical, the diameter is also not limited. It can be appropriately set according to the size of the stacked piezoelectric element 56, the thickness of the piezoelectric film 12L, and the rigidity of the piezoelectric film 12L. In the case of a cylindrical core rod 58, the diameter is preferably 0.1 to 50 μm, more preferably 0.1 to 5 μm. The size of the core rod 58 is preferably equal to the thickness of the adhesive layer 14 after bonding.

[0234] There are no restrictions on the material used to form the mandrel 58; various materials can be used if they have sufficient strength.

[0235] In this invention, the laminated piezoelectric element can utilize a conductive adhesive layer 14. In particular, as... Figure 2 In the stacked piezoelectric element 56 shown, which is formed by folding and stacking a piezoelectric film 12L, a conductive adhesive layer 14 is preferably used.

[0236] In the stacked piezoelectric thin film 12 of the stacked piezoelectric element of the present invention, the opposite electrodes are supplied with electricity of the same polarity. Therefore, short circuits will not occur between the opposite electrodes.

[0237] On the other hand, as described above, the stacked piezoelectric element 56 formed by folding and stacking the piezoelectric film 12L is prone to electrode breakage on the inside of the bend portion folded into an acute angle.

[0238] Therefore, by using a conductive adhesive layer 14 to adhere the stacked piezoelectric film 12L, even if an electrode breaks in the inner side of the bend, the adhesive layer 14 can be used to ensure continuity, thus preventing wire breakage and significantly improving the reliability of the stacked piezoelectric element 56.

[0239] Among them, such as Figure 9 As shown, the piezoelectric thin film 12L constituting the stacked piezoelectric element of the present invention preferably has a lower protective layer 28 and an upper protective layer 30 such that it is opposite to the lower electrode 24 and the upper electrode 26 and sandwiches the stack.

[0240] In this case, even using a conductive adhesive layer 14 cannot ensure conductivity. Therefore, when the piezoelectric film 12L has a protective layer, in the region where the lower electrodes 24 and the upper electrodes 26 of the stacked piezoelectric films 12L are opposite to each other, through holes are provided in the lower protective layer 28 and the upper protective layer 30 to allow the lower electrodes 24 and the upper electrodes 26 to contact the conductive adhesive layer 14.

[0241] At this point, the through holes in the lower protective layer 28 and the upper protective layer 30 can be formed by laser processing and removal of the protective layers based on solvent etching and mechanical polishing. Furthermore, if possible, the piezoelectric thin film 12L can be fabricated using the pre-formed through holes in the lower protective layer 28 and the upper protective layer 30.

[0242] The through holes in the lower protective layer 28 and the upper protective layer 30 can be provided in one or more locations in the regions where the lower electrodes 24 and the upper electrodes 26 of the stacked piezoelectric film 12L are opposite to each other. Alternatively, the through holes in the lower protective layer 28 and the upper protective layer 30 can be formed regularly or irregularly over the entire surface of the lower protective layer 28 and the upper protective layer 30.

[0243] Preferably, the through holes formed in the lower protective layer 28 and the upper protective layer 30 are sealed with silver paste or a conductive adhesive, and then the adjacent piezoelectric films 12L are adhered with a conductive adhesive layer 14 such as conductive tape.

[0244] When using a conductive adhesive layer 14, as long as there is one or more through holes in the lower protective layer 28 and the upper protective layer 30 in the area where the lower electrode 24 and the upper electrode 26 of the stacked piezoelectric film 12L are opposite to each other, except for the bending portion, preferably one or more including the central portion of the stacked piezoelectric film 12L, the reliability of the stacked piezoelectric element 56 can be greatly improved.

[0245] Furthermore, there are no limitations on the conductive adhesive layer 14, and various known adhesive layers can be used.

[0246] Therefore, the conductive adhesive layer 14 can be an adhesive layer in which the adhesive and bonding agent constituting the adhesive layer 14 are themselves conductive. Alternatively, the conductive adhesive layer 14 can be obtained by dispersing metal particles, conductive fillers, and metal fibers in a non-conductive adhesive and bonding agent. Furthermore, it is also possible to use, for example, silver paste such as Dotite manufactured by FUJIKURA KASEI CO.,LTD., which is cured by drying.

[0247] Among them, such as Figure 10 As shown, there are two possible structures for a stacked piezoelectric element formed by folding a single piezoelectric film to stack multiple piezoelectric films. In the following description, for convenience, the stacked piezoelectric element formed by folding a single piezoelectric film to stack multiple piezoelectric films will also be referred to as a "stacked piezoelectric element formed by folding and stacking piezoelectric films".

[0248] The first structure is a structure in which the curved portions formed based on the folding of the piezoelectric film are aligned in the long side direction of the laminated piezoelectric element. That is, the first structure is a structure in which the ridgelines formed by folding the piezoelectric film are aligned in the long side direction of the laminated piezoelectric element.

[0249] The second structure is a structure in which the curved portions formed based on the folding of the piezoelectric film are aligned in the short side direction of the laminated piezoelectric element. That is, the second structure is a structure in which the ridgelines formed by folding the piezoelectric film are aligned in the short side direction of the laminated piezoelectric element.

[0250] In other words, the laminated piezoelectric element in which the piezoelectric film is folded and laminated can be considered to have a structure in which the ridgelines formed by folding the piezoelectric film are aligned in the long side direction of the laminated piezoelectric element and a structure in which the ridgelines are aligned in the short side direction of the laminated piezoelectric element.

[0251] Specifically, in a case where a laminated piezoelectric element of 20 x 5 cm is produced by folding one piezoelectric film to laminate five piezoelectric films, the following two structures can be considered.

[0252] As schematically shown in FIG. 6A, the first structure is a laminated piezoelectric element 56A in which five piezoelectric films 12La of a rectangular shape of 20 x 25 cm are laminated by folding the piezoelectric films 12La four times at every 5 cm in the direction of 25 cm. In the laminated piezoelectric element 56A, the curved portions formed based on the folding of the piezoelectric films 12La are aligned in the direction of 20 cm which is the long side direction of the laminated piezoelectric element 56A. That is, in the laminated piezoelectric element 56A, the ridgelines formed by folding the piezoelectric films 12La are aligned in the long side direction of the laminated piezoelectric element 56A. Figure 11 As schematically shown in FIG. 6B, the second structure is a laminated piezoelectric element 56B in which five piezoelectric films 12Lb of a rectangular shape of 100 x 5 cm are laminated by folding the piezoelectric films 12Lb four times at every 20 cm in the direction of 100 cm. In the laminated piezoelectric element 56B, the curved portions formed based on the folding of the piezoelectric films 12Lb are aligned in the direction of 5 cm which is the short side direction of the laminated piezoelectric element 56B. That is, in the laminated piezoelectric element 56B, the ridgelines formed by folding the piezoelectric films 12Lb are aligned in the short side direction of the laminated piezoelectric element 56B.

[0253] Figure 12 In the present application, the laminated piezoelectric element in which the piezoelectric film is folded and laminated can preferably use any one of a structure in which the curved portions formed based on the folding of the piezoelectric film are aligned in the long side direction of the laminated piezoelectric element and a structure in which the curved portions are aligned in the short side direction of the laminated piezoelectric element.

[0254] In the present application, the laminated piezoelectric element in which the piezoelectric film is folded and laminated can preferably use any one of a structure in which the curved portions formed based on the folding of the piezoelectric film are aligned in the long side direction of the laminated piezoelectric element and a structure in which the curved portions are aligned in the short side direction of the laminated piezoelectric element.

[0255] ​That is, the structure in which the curved portion formed based on the folding of the piezoelectric thin film is along the long side direction of the laminated piezoelectric element and the structure in which the curved portion is along the short side direction each have advantages. Therefore, it is sufficient to appropriately set which structure to use depending on the use or the like of the laminated piezoelectric element.

[0256] For example, in the structure in which the curved portion formed based on the folding of the piezoelectric thin film 12La is along the long side direction, such as the laminated piezoelectric element 56A, it is preferable to prevent disconnection of the lower electrode 24 and the upper electrode 26, and thus a highly reliable laminated piezoelectric element can be obtained.

[0257] As described above, the lower electrode 24 and the upper electrode 26 of the piezoelectric thin film 12La are formed of an evaporation film of metal or the like. If the evaporation film of metal is bent, a crack (crazing) or the like is easily generated. If a crack is generated in the electrode (electrode layer), the resistance of the position where the crack is generated increases. Therefore, if current flows at this position, heat is generated due to the resistance, and thus becomes a cause of failure such as disconnection.

[0258] These inconveniences can be improved by reducing the current density.

[0259] In contrast to this, in the laminated piezoelectric element in which the piezoelectric thin film is folded and laminated, by the curved portion being along the long side direction, the width of the curved portion is increased with respect to the flow of current, and thus the current density of the current flowing through the curved portion is reduced. As a result, it is possible to suppress heat generation due to the generation of a crack in the electrode and prevent disconnection. Therefore, in the structure in which the curved portion formed based on the folding of the piezoelectric thin film 12La is along the long side direction, such as the laminated piezoelectric element 56A, a highly reliable laminated piezoelectric element can be obtained.

[0260] Further, in order to be connected to an external device such as a power supply device, a lead wire connected to the lower electrode 24 and the upper electrode 26 and connected to the outside of the laminated piezoelectric element can be provided on the laminated piezoelectric element. In addition, the lead wire refers to a wire that does not necessarily have to be physically protruded to the outside and is electrically led from the electrode.

[0261] The lead wire can be formed by the above-described method. For example, the lead wire is provided such that, in the end portion of the piezoelectric thin film or the region protruded to the outside, the piezoelectric layer 20 is not provided and the lower electrode 24 and the upper electrode 26 are exposed and connected thereto. As another example, the lead wire is provided such that, in the end portion of the piezoelectric thin film or the region protruded to the outside, the protective film and the electrode layer are peeled off and a copper foil tape or the like is inserted between the piezoelectric layer 20 and the electrode layer. As still another example, the lead wire is provided such that, in the end portion of the piezoelectric thin film or the region protruded to the outside, a through hole is provided in the protective layer of the piezoelectric thin film, a conductive paste such as silver paste is used for the through hole to form a conductive member, and a copper foil tape or the like is connected to the conductive member.

[0262] AsFigure 10 The lead-out wiring is typically provided on the end portion of the piezoelectric film 12La in the folding direction in the laminated piezoelectric element in which the piezoelectric film is folded and laminated.

[0263] That is, in the case of the laminated piezoelectric element 56A shown in FIG. 6A, the lead-out wiring is provided on the end portion of the piezoelectric film 12La of 20 cm in width on the long side. Figure 11 On the other hand, in the case of the laminated piezoelectric element 56B shown in FIG. 6B, the lead-out wiring is provided on the end portion of the piezoelectric film 12Lb of 5 cm in width on the short side. Figure 12

[0264] Further, as shown in FIG. 6A, the lead-out wiring is provided with the lead-out wiring 62 connected to the lower electrode 24 and the lead-out wiring 64 connected to the upper electrode 26. Figure 12

[0265] Among the methods of providing the lead-out wiring, there are various methods, but in a mode in which the piezoelectric layer 20 is not provided in the end portion of the piezoelectric film or the region protruding to the outside and the lower electrode 24 and the upper electrode 26 are exposed to protrude directly to the outside and function as the lead-out wiring, in particular, the connection portion of the lead-out wiring to the lower electrode 24 and the upper electrode 26 of the piezoelectric film is a portion in which the current density sharply rises and easily generates heat. Therefore, the lead-out wiring is preferably wide in width. That is, if it is the laminated piezoelectric element 56A, the width a of the lead-out wiring 62 and the lead-out wiring 64 shown in FIG. 6A is preferably wide. Figure 10

[0266] In addition, in the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the width (width direction) indicates the length of the direction in which the lead-out wiring exists. That is, if it is the laminated piezoelectric element 56A and the piezoelectric film 12La shown in FIG. 6A, the width is 20 cm. Further, if it is the laminated piezoelectric element 56B and the piezoelectric film 12Lb shown in FIG. 6B, the width is 5 cm. Figure 11 Figure 12

[0267] Further, the piezoelectric layer 20 of the piezoelectric film is preferably 10 to 300 μm in thickness and is very thin. Therefore, in order to prevent short circuit, the lead-out wiring is preferably provided at different positions in the surface direction of the piezoelectric film. That is, the lead-out wiring is preferably provided staggered in the surface direction of the piezoelectric film.

[0268] Further, in the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the lead-out wiring which becomes the heat generating portion is preferably separated as much as possible in the width direction from each other. That is, if it is the laminated piezoelectric element 56A, the lead-out wiring 62 and the lead-out wiring 64 shown in FIG. 6A are preferably separated by a wide interval b in the width direction. Figure 10 ​​​​​​

[0269] In contrast, in the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the width of the piezoelectric film in the connecting portion of the lead-out wiring can be increased by the bending portion along the long side direction.

[0270] Therefore, in the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the laminated piezoelectric element in which the bending portion is along the long side direction can preferably prevent short circuit while also preferably suppressing heat generation.

[0271] In the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the width of the lead-out wiring is not limited, but is preferably as wide as described above.

[0272] In the laminated piezoelectric element in which the piezoelectric film is folded and laminated, in order to suppress heat generation in the lead-out wiring, it is preferable to set the current line density of the lead-out wiring to 1 A / cm or less. The current line density of the lead-out wiring refers to the value of the current value [A] of the current flowing into the lead-out wiring divided by the width [cm] of the lead-out wiring.

[0273] In the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the width (length in the direction in which the lead-out wiring exists) of the lead-out wiring is preferably 10% or more (1 / 10 or more) of the width of the piezoelectric film, more preferably 20% or more, and further preferably 30% or more. That is, if it is the laminated piezoelectric element 56A in which the bending portion is along the long side direction as shown in FIG. 6, the width of the piezoelectric film 12La is 20 cm, and therefore it is preferable to set the width a of the lead-out wiring 62 and the lead-out wiring 64 to 2 cm or more. Figure 12 and Figure 10 If it is the laminated piezoelectric element 56A in which the bending portion is along the long side direction as shown in FIG. 6, the width of the piezoelectric film 12La is 20 cm, and therefore it is preferable to set the width a of the lead-out wiring 62 and the lead-out wiring 64 to 2 cm or more.

[0274] The wider the width of the piezoelectric film becomes, the greater the electrostatic capacity of the piezoelectric film becomes (the impedance value becomes smaller), and therefore the amount of current flowing into the piezoelectric film becomes greater with respect to the same applied voltage. However, by setting the width of the lead-out wiring to 10% or more of the width of the piezoelectric film, the current line density of the lead-out wiring can be stably set to 1 A / cm or less.

[0275] Further, by setting the thickness of the electrode layer to 0.1 μm or more, the current density obtained by dividing the amount of current flowing through the lead-out wiring by the cross-sectional area of the lead-out wiring can be set to 1 x 10 5 A / cm 2 Therefore, it is preferable.

[0276] In the laminated piezoelectric element in which the piezoelectric film is folded and laminated, the width of the lead-out wiring is not limited, but is preferably as wide as described above.

[0277] The width direction interval of the lead-out wiring is preferably 25% or more (1 / 4 or more) of the width of the piezoelectric film, more preferably 30% or more, and further preferably 40% or more.

[0278] That is, if the piezoelectric laminate 56A in which the curved portion shown in FIG. 6A is along the long side direction, the width of the piezoelectric film 12La is 20 cm, and thus it is preferable to set the width direction interval b of the lead-out wiring 62 and the lead-out wiring 64 to 5 cm or more. Figure 12 Figure 11 In addition, the current line density of the lead-out wiring, the width of the lead-out wiring, and the interval are the same not only for the piezoelectric laminate 56A in which the curved portion is along the long side direction, but also for the piezoelectric laminate 56B in which the curved portion is along the short side direction.

[0279] In addition, the current line density of the lead-out wiring, the width of the lead-out wiring, and the interval are the same not only for the piezoelectric laminate 56A in which the curved portion is along the long side direction, but also for the piezoelectric laminate 56B in which the curved portion is along the short side direction.

[0280] On the other hand, in the piezoelectric laminate in which the piezoelectric film is folded and laminated, as in the piezoelectric laminate 56B shown in FIG. 6B, it is preferable that the piezoelectric laminate in which the curved portion formed based on the folding of the piezoelectric film 12Lb is along the short side direction be maximized in terms of vibration efficiency. Figure 12

[0281] That is, the curved portion formed based on the folding itself also strictly expands and contracts, and thus generates a vibration mode different from the expansion and contraction mode of the piezoelectric laminate. Thus, compared with the piezoelectric laminate in which the curved portion is along the long side direction, the piezoelectric laminate in which the curved portion is along the short side direction does not need to consume energy in unnecessary vibration modes.

[0282] In addition, in the piezoelectric laminate of the present application, in addition to the structure shown in FIG. 6A, the formation method of the lead-out wiring 62 and the lead-out wiring 64 can also utilize various structures. Figure 16 For example, if the piezoelectric laminate 56A in which the curved portion formed based on the folding of the piezoelectric film 12La is along the long side direction, as schematically shown in FIG. 6A, a protruding portion in the form of an island can be provided on the one end portion in the folding direction, and the lead-out wiring 62 and the lead-out wiring 64 can be connected at this portion.

[0283] Figure 17 In addition, if the piezoelectric laminate 56B in which the curved portion formed based on the folding of the piezoelectric film 12Lb is along the short side direction, as schematically shown in FIG. 6B, the one end portion in the folding direction can be elongated, and the lead-out wiring 62 and the lead-out wiring 64 can be connected at the elongated end portion.

[0284] Figure 18

[0285] ​​​​​Furthermore, if the piezoelectric element 56B is a stacked piezoelectric element with a curved portion formed by folding the piezoelectric thin film 12Lb along the short side direction, then as Figures 3-7 The diagram schematically shows that an island-shaped protrusion can be provided at the end in the direction orthogonal to the folding direction, that is, at the end in the long side direction of the piezoelectric film 12Lb, and the lead wire 62 and lead wire 64 can be connected here.

[0286] The stacked piezoelectric element and electroacoustic converter of the present invention have been described in detail above. However, the present invention is not limited to the above examples. Various improvements or modifications can be made without departing from the spirit of the present invention, which is to be expected.

[0287] Example

[0288] The present invention will be further described in detail below with specific embodiments.

[0289] [Fabrication of piezoelectric thin films]

[0290] Through the above Figure 2 The method shown was used to create, as follows: Figure 3 The piezoelectric thin film shown.

[0291] First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) according to the following composition ratio. Then, PZT particles were added to the solution according to the following composition ratio, and dispersed using a propeller mixer (2000 rpm) to prepare a coating for forming a piezoelectric layer.

[0292] PZT particles... 1000 parts by mass

[0293] • Cyanoethylated PVA……100 parts by weight

[0294] MEK……600 parts by weight

[0295] In addition, the PZT particles were decomposed and graded after sintering commercially available PZT raw material powder at 1000-1200℃, with an average particle size of 3.5μm.

[0296] On the other hand, a copper film with a thickness of 0.1 μm is prepared by vacuum evaporation onto a long strip of PET film with a width of 23 cm and a thickness of 4 μm. Figure 14 The sheet-like structure shown. That is, in this example, the upper and lower electrodes are copper vapor-deposited thin films with a thickness of 0.1 μm, and the upper and lower protective layers are PET films with a thickness of 4 μm.

[0297] In addition, in order to achieve good operation, the PET film uses a film with a 50μm thick separator (temporary support PET). After the film electrode and protective layer are heat-pressed together, the separators of each protective layer are removed.

[0298] Using a slant-plate coater, a coating material for forming a pre-prepared piezoelectric layer is applied to the lower electrode of the sheet. The coating is applied such that the dried film thickness is 40 μm. As described above, the lower electrode is a copper vapor-deposited thin film.

[0299] Furthermore, the coating is applied by leaving 1 cm wide uncoated portions at both ends of the long strip of PET film along its width (short side direction). That is, the 1 cm uncoated portions at both ends of the width direction are formed to expose the lower electrode (copper film) (see reference). Figure 4 ).

[0300] Next, the material coated with the paint was dried in an oven at 120°C, thereby causing the MEK to evaporate. This produced a product such as... Figure 5 The laminate shown is a PET-made lower protective layer with a copper lower electrode and a 40μm thick piezoelectric layer formed thereon.

[0301] Through the above Figure 6 and Figure 7 The corona polarization shown involves polarizing the piezoelectric layer of the laminate in the thickness direction. Furthermore, the temperature of the piezoelectric layer is set to 100°C, and a 6kV DC voltage is applied between the lower electrode and the corona electrode to generate corona discharge for polarization.

[0302] like Figure 14 As shown, a similar sheet-like material, formed by vacuum evaporating a copper thin film onto a PET film, is stacked on a polarized laminate. This sheet-like material is also stacked with upper electrodes protruding 1 cm wide from the piezoelectric layer at both ends in the width direction (see reference). Figure 2 ).

[0303] Next, the piezoelectric layer is bonded to the upper and lower electrodes by hot-pressing the laminate and the sheet at 120°C using a laminating device. The piezoelectric layer is sandwiched between the upper and lower electrodes, and the laminate is sandwiched between the upper and lower protective layers, thereby fabricating a product as shown. Figure 1 The piezoelectric thin film shown.

[0304] [Example 1]

[0305] The fabricated piezoelectric film is cut into a 5×8cm rectangle. The cut piezoelectric film is designed with a 1cm section at one end along its long side that exposes the aforementioned upper and lower electrodes.

[0306] That is, the cut piezoelectric film has an area at one end along its long side where the upper and lower electrodes are exposed, each measuring 5 × 1 cm. Therefore, in this example, the thickness of the piezoelectric layer is 40 μm and its surface dimension is 5 × 7 cm.

[0307] Three cut piezoelectric films are stacked with adjacent piezoelectric films having opposite polarization directions and then bonded together using an adhesive layer, thereby fabricating a material such as... Figure 1 The stacked piezoelectric element shown.

[0308] For the adhesive layer, an adhesive (manufactured by TOYOCHEM CO.,LTD., TSU0041SI) was used. The thickness of the adhesive layer was set to 25 μm.

[0309] Will as Figure 14 An AC power supply, as shown, is connected to the fabricated stacked piezoelectric element. Furthermore, the AC power supply is connected in such a way that it supplies power of the same polarity to the upper electrode and power of the opposite polarity to the lower electrode in all the piezoelectric films. Therefore, in this example, power of the same polarity is supplied to the opposing electrodes of the stacked piezoelectric films. Also, the lower electrode refers to the electrode on the substrate side when the piezoelectric layer is coated, and as described above, it does not refer to the electrode's vertical position within the stack.

[0310] like Figure 9 The diagram illustrates the extraction of electrodes from each piezoelectric film for connection to an AC power source.

[0311] First, on the side of the electrode where the piezoelectric film is exposed, a 12μm thick copper foil tape T1 is attached to the lower electrode. Next, about 2-3mm is peeled off the end on the upper electrode side, and a 20μm thick insulating double-sided tape Z is attached, inserted into the peeled part and covering the copper foil tape T1.

[0312] Then, after attaching a 12μm thick copper foil tape T2 to the upper electrode side, the copper foil tape T2 is brought into contact with the insulating double-sided tape Z.

[0313] Connect the lead L to the copper foil tapes T1 and T2 using solder S, and connect the lead L to the AC power supply.

[0314] [Example 2]

[0315] The adhesive used for the bonding layer was changed to FB-ML4-50S manufactured by Nitto Denko Corporation, and the thickness of the bonding layer was changed to 50 μm. Otherwise, the stacked piezoelectric element was fabricated and connected to a power source in the same manner as in Example 1.

[0316] [Example 3]

[0317] The adhesive layer was changed to a 30μm thick double-sided tape (manufactured by Nitto Denko Corporation, No. 5603), which was changed to an adhesive layer. Otherwise, the stacked piezoelectric element was fabricated and connected to a power source in the same manner as in Example 1.

[0318] [Example 4]

[0319] The adhesive layer was changed to a 50μm thick double-sided tape (manufactured by Nitto Denko Corporation, No. 5919ML), which was changed to an adhesive layer. Otherwise, the stacked piezoelectric element was fabricated and connected to a power source in the same manner as in Example 1.

[0320] [Example 5]

[0321] Instead of using an adhesive layer, tape was used to fix the end faces of the stacked piezoelectric films, except for the electrode leads. This fixed three piezoelectric films. Otherwise, the stacked piezoelectric elements were fabricated in the same manner as in Example 1 and connected to a power source.

[0322] [Example 6]

[0323] The piezoelectric film was cut into strips along its width to form a 5×23cm sheet.

[0324] Next, the piezoelectric film is cut off at one end along its long side, exposing the upper and lower electrodes. Therefore, in this example, the piezoelectric film is 5 × 22 cm, the piezoelectric layer is 40 μm thick, and the surface dimension is 5 × 21 cm.

[0325] The piezoelectric film is folded along its long side to divide the length of the piezoelectric layer into three equal parts of 7 cm. Adjacent piezoelectric films are then bonded together in the areas where the piezoelectric films are stacked using an adhesive layer. This process creates a piezoelectric film as shown in the image. Figure 9 The piezoelectric element shown is a stacked piezoelectric element with three layers of piezoelectric films. Additionally, in this example, no core rod is provided in the folded portion.

[0326] In addition, an adhesive (manufactured by TOYOCHEM CO.,LTD., TSU0041SI) was used for the adhesive layer. The thickness of the adhesive layer was set to 25 μm.

[0327] Similarly, as described above, Figure 13 An AC power supply, as shown, is connected to the stacked piezoelectric element. Therefore, in this example, the power supply connection is at point 1.

[0328] [Comparative Example 1]

[0329] like Figure 15As shown, the polarization direction of the piezoelectric thin film is made to be all the same. Otherwise, the stacked piezoelectric element is fabricated in the same manner as in Example 1 and connected to a power source. Therefore, in this example, the adhesive layer is an adhesive layer with a thickness of 25 μm.

[0330] In this example, the upper and lower electrodes of the stacked piezoelectric films, each supplied with an electric current of different polarities, are opposite each other.

[0331] [Comparative Example 2]

[0332] The thickness of the adhesive layer was set to 70 μm. Otherwise, the stacked piezoelectric element was fabricated in the same manner as in Comparative Example 1 and connected to a power source.

[0333] [evaluate]

[0334] A PET film with a thickness of 300 μm and a diameter of 30 × 70 cm was prepared as the vibrating plate B. The long side direction was aligned with the short side direction, and the fabricated multilayer piezoelectric element was fixed in the center of the vibrating plate B (see reference). Figure 15 ).

[0335] like Figure 10 The diagram schematically shows that the vibrating plate B, measuring 30×70cm, is erected by supporting both ends along its long side. On the PET film (vibrating plate) side, a microphone M is positioned 1m away from the center of the stacked piezoelectric element along the normal direction (perpendicular to the PET film) to drive the stacked piezoelectric element and measure the sound pressure.

[0336] The input signal to the stacked piezoelectric element is set to a 1kHz sine wave (80Vp-p).

[0337] The results are shown in the table below.

[0338] [Table 1]

[0339]

[0340]

[0341] As shown in the table above, the stacked piezoelectric element of the present invention, with adjacent piezoelectric films having opposite polarization directions, can supply the opposite electrodes with the same polarity of electricity. Therefore, even if the thickness of the adhesive layer is set to 50 μm or less, a short circuit will not occur between adjacent piezoelectric films, allowing the vibrating plate (PET film) to vibrate preferably, thereby enabling the generation of high sound pressure levels.

[0342] On the other hand, in Comparative Example 1 in which the polarization directions of the adjacent piezoelectric films are in the same direction, the opposite electrodes are supplied with electric power of opposite polarity, and thus shorting occurs between the adjacent piezoelectric films, so that the measurement of sound pressure cannot be performed. Also, as shown in Comparative Example 2, by setting the thickness of the adhesive layer to 70 μm, shorting can be prevented, but as shown in Table 1, the sound pressure obtainable is lower than that of Example 5 which does not have the adhesive layer.

[0343] Also, as shown in Examples 1 and 2 and Examples 3 and 4, in the present application, by using an adhesive layer having high hardness as the adhesive layer, the vibrating plate is more preferably vibrated, so that a higher sound pressure can be obtained. Also, as shown in Examples 1 and 3 and Examples 2 and 4, in the present application, by making the adhesive layer thinner, the vibrating plate is more preferably vibrated, so that a higher sound pressure can be obtained.

[0344] Example 1 in which three piezoelectric films are stacked and Example 6 in which three piezoelectric films are stacked by folding a long piezoelectric film have the same adhesive layer (an adhesive layer having a thickness of 25 μm), and the sound pressure levels are also the same. However, in Example 1 in which three piezoelectric films are stacked, three power sources are required for driving, and on the other hand, in Example 6 in which a long piezoelectric film is folded, one power source is sufficient for driving.

[0345] [Examples 7 and 8]

[0346] The piezoelectric film produced as described above was cut into 20 x 25 cm. The piezoelectric film was folded four times at intervals of 5 cm in the 25 cm direction. Thus, a stacked piezoelectric element (Example 7) of 5 x 20 cm in which five piezoelectric films were stacked as shown in Fig. 7 was produced. In this case, the curved portions formed based on the folding of the piezoelectric film were in the long side direction of the stacked piezoelectric element. Figure 11

[0347] On the other hand, the piezoelectric film produced as described above was cut into 5 x 100 cm. The piezoelectric film was folded four times at intervals of 20 cm in the 100 cm direction. Thus, a stacked piezoelectric element (Example 8) of 5 x 20 cm in which five piezoelectric films were stacked as shown in Fig. 8 was produced. In this case, the curved portions formed based on the folding of the piezoelectric film were in the short side direction of the stacked piezoelectric element. ​

[0348] In addition, in the stacked piezoelectric element produced, the adjacent piezoelectric films were adhered in the same manner as in Example 6.

[0349] ​​In the end portion of the piezoelectric film on the side of the folding direction, the peeling protective layer and the electrode layer were peeled and an electrode for supplying driving power was inserted and returned to the original state. Then, a pink noise signal was supplied at 30 Vrms for 6 hours to drive the laminated piezoelectric element.

[0350] After 6 hours, the temperature of the laminated piezoelectric element was measured and the temperature of the portion that became the highest temperature was compared. As a result, Example 7 was 35°C and Example 8 was 50°C.

[0351] That is, in the laminated piezoelectric element in which one piezoelectric film is folded to laminate a plurality of piezoelectric films, the structure of the curved portion formed based on the folding of the piezoelectric film along the long direction is more advantageous in terms of suppressing heat generation and the like.

[0352] According to the above results, the effects of the present application are more apparent.

[0353] Industrial applicability

[0354] As an exciter or the like that makes various components abut to make them emit sound, it can be preferably used.

[0355] Explanation of symbols

[0356] 10, 56, 56A, 56B - laminated piezoelectric element, 12, 12L, 12La, 12Lb - piezoelectric film, 12a, 12c - sheet, 12b - laminate, 14, 52 - adhesive layer, 16, 110 - power source, 20, 102 - piezoelectric layer, 24 - lower (film) electrode, 26 - upper (film) electrode, 28 - lower protective layer, 30 - upper protective layer, 34 - viscoelastic matrix, 36 - piezoelectric particle, 40 - corona electrode, 42 - DC power source, 50 - vibration plate, 58 - mandrel, 62, 64 - lead wire, 100 - unit variable element, 104 - lower electrode, 106 - upper electrode, 108 - adhesive layer.

Claims

1. An electroacoustic transducer having a stacked piezoelectric element adapted to vibrate a diaphragm, the diaphragm being adapted to emit sound upon vibration, the diaphragm being in contact with the stacked piezoelectric element. The stacked piezoelectric element is formed by stacking multiple piezoelectric thin films, in which two thin film electrodes sandwich the piezoelectric body layer. The piezoelectric thin film is polarized in the thickness direction, and the polarization directions of adjacent piezoelectric thin films are opposite to each other. The vibrating plate is attached to the laminated piezoelectric element via an adhesive layer. Each of the piezoelectric films is connected to a power source that applies a driving voltage to cause the piezoelectric film to expand and contract. Sound is produced by the vibration of the vibrating plate caused by the expansion and contraction of the multi-layered piezoelectric film induced by the power source. The stacked piezoelectric element has lead wires that connect to the thin-film electrode and are used for connection to external devices. The width of the lead-out wiring is designed such that the linear current density of the current flowing into the lead-out wiring is less than 1A / cm.

2. The electroacoustic converter according to claim 1, wherein, The piezoelectric film has a core rod in its folded portion.

3. The electroacoustic converter according to claim 1 or 2, wherein, The curved portion formed by folding the piezoelectric film runs along the long side.

4. The electroacoustic converter according to claim 1 or 2, wherein, The curved portion formed by folding the piezoelectric film runs along the short side.

5. The electroacoustic converter according to claim 1 or 2, wherein, At least one layer of the stacked piezoelectric film has a protective layer stacked on at least one side of the film electrode.

6. The electroacoustic converter according to claim 1, wherein, The stacked piezoelectric element has an adhesive layer for bonding adjacent piezoelectric films.

7. The electroacoustic converter according to claim 6, wherein, The thickness of the adhesive layer is thinner than the thickness of the piezoelectric layer.

8. The electroacoustic converter according to claim 6, wherein, The thickness of the adhesive layer is 0.1–50 μm.

9. The electroacoustic converter according to claim 6, wherein, The adhesive layer is a layer composed of adhesive.

10. The electroacoustic converter according to claim 6, wherein, The spring constant of the adhesive layer is lower than the spring constant of the piezoelectric film.

11. The electroacoustic transducer according to claim 1 or 2, wherein, The piezoelectric film is composed of a viscoelastic polymer material that exhibits a maximum loss tangent (Tanδ) at a frequency of 1 Hz at room temperature.

12. The electroacoustic converter according to claim 1 or 2, wherein, The piezoelectric thin film exhibits piezoelectric properties without in-plane anisotropy.

13. The electroacoustic converter according to claim 1 or 2, wherein, The piezoelectric layer is a polymer composite piezoelectric layer formed by dispersing piezoelectric particles in a polymer material containing cyanoethyl groups.

14. The electroacoustic converter according to claim 13, wherein, The polymer material is cyanoethylated polyvinyl alcohol.

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