piezoelectric thin film

Abstract

The present application provides a piezoelectric film, which can achieve high durability and sufficient sound pressure with respect to input operating voltage. The present application solves the problem by having: a polymer composite piezoelectric body containing piezoelectric particle in a matrix containing a polymer material; and an electrode layer arranged on both sides of the polymer composite piezoelectric body. The polymer composite piezoelectric body is divided into 10 regions along the thickness direction by observing the cross section of the thickness direction by a scanning electron microscope, and the area rate of the piezoelectric particle in the two regions farthest apart is measured. When the area rate of the piezoelectric particle with a low area rate is set to 1, the area rate of the piezoelectric particle with a high area rate is 1.2 or more.

Description

Technical Field

[0001] This invention relates to a piezoelectric film for use in electroacoustic conversion films and the like. Background Technology

[0002] In response to the trend towards thinner and lighter displays, such as liquid crystal displays (LCDs) and organic EL (Electro Luminescence) displays, there is also a demand for thinner and lighter speakers used in these thin displays. Furthermore, in response to the development of flexible displays using flexible substrates such as plastics, there is a demand for flexible speakers used in these flexible displays.

[0003] Traditional speakers are typically funnel-shaped, cone-shaped, or dome-shaped. However, incorporating such speakers into the aforementioned thin displays would prevent achieving sufficient thinness and could compromise lightweight design and flexibility. Furthermore, externally mounted speakers present challenges in portability and other aspects.

[0004] Therefore, as a speaker that can be integrated with thin and flexible displays without compromising its thinness and flexibility, a piezoelectric film that is sheet-like, flexible, and has the property of stretching and contracting in response to applied voltage has been proposed.

[0005] For example, the applicant in this case proposed a piezoelectric film (electroacoustic conversion film) as disclosed in Patent Document 1, which is a sheet-like, flexible piezoelectric film capable of stably playing high-quality sound.

[0006] The piezoelectric thin film disclosed in Patent Document 1 comprises a polymer composite piezoelectric material formed by dispersing piezoelectric particles in a viscoelastic matrix composed of a polymer material that is viscoelastic at room temperature, and an electrode layer disposed to sandwich the polymer composite piezoelectric material. Preferably, the piezoelectric thin film described in Patent Document 1 has a protective layer formed on the surface of the thin film electrode.

[0007] Previous technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-212307 Summary of the Invention

[0010] The technical problem to be solved by the invention

[0011] This piezoelectric film functions as a piezoelectric speaker, for example, by maintaining a bent state.

[0012] That is, by maintaining the piezoelectric film in a bent state and applying a driving voltage to the electrode layer, the polymer composite piezoelectric material expands and contracts due to the stretching and contraction of the piezoelectric particles, and in order to absorb this expansion and contraction, the piezoelectric film vibrates in a direction orthogonal to the surface. The piezoelectric film causes the air to vibrate through this vibration and converts electrical signals into sound.

[0013] The vibration of a piezoelectric film in a direction orthogonal to the surface refers to the repeated states of large warping and return to the original state of the polymer composite piezoelectric material constituting the piezoelectric film in a direction orthogonal to the surface.

[0014] When a polymer composite piezoelectric material is warped in a direction orthogonal to its surface, regions exhibit varying degrees of volume change along the thickness direction. Specifically, in the warped state, the volume increases on the convex side and decreases on the concave side.

[0015] This difference in volume change along the thickness direction imposes significant stress on the polymer composite piezoelectric material, resulting in deformation and strain, which in turn causes defects such as cracking and peeling from the electrode layer. Consequently, the acoustic properties of the piezoelectric film deteriorate with use, such as reduced sound pressure.

[0016] However, previous piezoelectric films have not fully considered the degradation of acoustic properties caused by defects resulting from the pressure of such polymer composite piezoelectric materials.

[0017] The purpose of this invention is to address the problems of the prior art and to provide a piezoelectric film with good acoustic properties, namely, good durability to prevent defects caused by pressure from polymer composite piezoelectric materials, and sufficient sound pressure relative to the input operating voltage.

[0018] means for solving technical problems

[0019] To address this issue, the present invention has the following structure.

[0020] [1] A piezoelectric thin film, characterized in that it has:

[0021] A polymer composite piezoelectric material comprises piezoelectric particles within a matrix containing polymer material, and electrode layers disposed on both sides of the polymer composite piezoelectric material.

[0022] The cross-section along the thickness direction was observed using a scanning electron microscope. The polymer composite piezoelectric material was divided into 10 regions along the thickness direction. The area fraction of the piezoelectric particles in the two regions farthest apart was measured. When the area fraction of the piezoelectric particles in the region with the low area fraction was set to 1, the area fraction of the piezoelectric particles in the region with the high area fraction was 1.2 or higher.

[0023] [2] According to the piezoelectric film described in [1], wherein,

[0024] The average area fraction of piezoelectric particles in the two regions furthest apart is over 23%.

[0025] [3] According to the piezoelectric film described in [1] or [2], wherein,

[0026] When the area ratio of the piezoelectric particles in the region with the lowest area ratio among the two farthest regions is set to 1, the area ratio of the piezoelectric particles in the region with the highest area ratio is below 70.

[0027] [4] The piezoelectric thin film according to any one of [1] to [3] is polarized along the thickness direction.

[0028] [5] The piezoelectric film according to any one of [1] to [4], wherein,

[0029] Piezoelectric properties do not exhibit in-plane anisotropy.

[0030] [6] The piezoelectric film according to any one of [1] to [5] has leads for connecting the electrode layer and an external power source.

[0031] [7] The piezoelectric thin film according to any one of [1] to [6] has a protective layer on the surface of an electrode layer stacked on at least one side.

[0032] [8] The piezoelectric film according to any one of [1] to [7], wherein,

[0033] The polymer material contains cyanoethyl groups.

[0034] [9] According to the piezoelectric film described in [8], wherein,

[0035] The polymer material is cyanoethylated polyvinyl alcohol.

[0036]

[10] The piezoelectric film according to any one of [1] to [9], wherein,

[0037] Piezoelectric particles are composed of ceramic particles with perovskite or wurtzite crystal structures.

[0038] Invention Effects

[0039] The piezoelectric film of this invention has the following good acoustic properties: good durability to prevent defects caused by pressure from the polymer composite piezoelectric material, and sufficient sound pressure relative to the input operating voltage. Attached Figure Description

[0040] Figure 1 This is a cross-sectional view that conceptually represents an example of the piezoelectric thin film of the present invention.

[0041] Figure 2 It is used for explanation Figure 1 The diagram shows a conceptual method for manufacturing a piezoelectric thin film.

[0042] Figure 3 It is used for explanation Figure 1 The diagram shows a conceptual method for manufacturing a piezoelectric thin film.

[0043] Figure 4 It is used for explanation Figure 1 The diagram shows a conceptual method for manufacturing a piezoelectric thin film.

[0044] Figure 5 It is used for explanation Figure 1 A conceptual diagram of another example of a method for manufacturing a piezoelectric thin film.

[0045] Figure 6 Conceptual representation of use Figure 1 An example of a piezoelectric loudspeaker with a piezoelectric thin film is shown.

[0046] Figure 7 This is a conceptual diagram used to illustrate the sound pressure measurement method in the embodiments. Detailed Implementation

[0047] Hereinafter, the piezoelectric thin film of the present invention will be described in detail with reference to the preferred embodiments shown in the accompanying drawings.

[0048] The following description of the constituent elements is sometimes based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0049] In addition, in this specification, the numerical range represented by “~” refers to the range including the values ​​recorded before and after “~” as the lower limit and upper limit.

[0050] Furthermore, the figures shown below are conceptual diagrams used to illustrate the present invention, and the thickness of each layer, the size of the piezoelectric particles, and the size of the constituent parts are different from the actual object.

[0051] The piezoelectric thin film of the present invention has electrode layers on both sides of a polymer composite piezoelectric body, and preferably has a protective layer on the surface of at least one electrode layer. The polymer composite piezoelectric body contains piezoelectric particles in a matrix comprising a polymer material. Furthermore, the piezoelectric thin film of the present invention preferably has a protective layer on the surface of both electrode layers.

[0052] In this piezoelectric thin film of the present invention, when the cross-section in the thickness direction is observed by a scanning electron microscope (SEM), and the polymer composite piezoelectric body is divided into 10 regions along the thickness direction, the area fraction of the piezoelectric particles in the two regions furthest apart is measured. When the area fraction of the piezoelectric particles in the region with the low area fraction is set to 1, the area fraction of the piezoelectric particles in the region with the high area fraction is 1.2 or more.

[0053] Additionally, in the following description, unless otherwise stated, "section" refers to a cross-section along the thickness direction of the piezoelectric film. The thickness direction of the piezoelectric film refers to the stacking direction of the layers.

[0054] As an example, the piezoelectric film of the present invention is used as an electroacoustic conversion film. Specifically, the piezoelectric film of the present invention is used as a vibrating plate for electroacoustic converters such as piezoelectric loudspeakers, microphones, and sound sensors.

[0055] In an electroacoustic transducer, when a voltage is applied to a piezoelectric film, causing it to elongate in the planar direction, the film moves upward (in the direction of sound emission) to absorb the elongation. Conversely, when a voltage is applied to a piezoelectric film, causing it to contract in the planar direction, the film moves downward to absorb the contraction.

[0056] An electroacoustic transducer converts vibrations (sound) into electrical signals by means of the repeated vibrations caused by the expansion and contraction of the piezoelectric film. For example, electroacoustic transducers are used for playing sound by inputting an acoustic electrical signal into the piezoelectric film and causing it to vibrate, converting the vibration of the piezoelectric film into an electrical signal by receiving sound waves, imparting tactile sensation through the vibration of the piezoelectric film, and conveying objects through the vibration of the piezoelectric film.

[0057] Furthermore, the piezoelectric film of the present invention can be applied to a variety of uses, such as various sensors, acoustic devices, tactile interfaces, ultrasonic transducers, actuators, damping materials (dampers), and vibration power generation devices.

[0058] Examples of sensors using the piezoelectric thin film of the present invention include acoustic wave sensors, ultrasonic sensors, pressure sensors, tactile sensors, strain sensors, and vibration sensors. Sensors using the piezoelectric thin film of the present invention are particularly useful for infrastructure inspections such as crack detection and foreign matter ingress detection, as well as for on-site inspections in manufacturing facilities.

[0059] Examples of acoustic devices using the piezoelectric film of the present invention include microphones, pickups, loudspeakers, and exciters. Specific applications of acoustic devices using the piezoelectric film of the present invention include noise cancellers for automobiles, trains, airplanes, and robots; artificial vocal cords; buzzers for preventing the intrusion of pests and animals; and furniture, wallpaper, photographs, helmets, goggles, elastic headrests, signs, and robots with audio output functions.

[0060] Examples of suitable tactile interfaces using the piezoelectric film of the present invention include automobiles, smartphones, smartwatches, and game consoles.

[0061] Examples of ultrasonic transducers using the piezoelectric thin film of the present invention include ultrasonic probes and hydrophones.

[0062] Applications of the piezoelectric film of the present invention in actuators include preventing water droplet adhesion, conveying, stirring, dispersing, and grinding.

[0063] Examples of suitable damping materials using the piezoelectric thin film of the present invention include containers, vehicles, buildings, and sports equipment such as skis and rackets.

[0064] Furthermore, examples of suitable devices for vibration power generation using the piezoelectric film of the present invention include roads, floors, mattresses, chairs, shoes, tires, wheels, and personal computer keyboards.

[0065] Furthermore, the same applies to the piezoelectric film stack (stacked piezoelectric element) formed by stacking multiple piezoelectric films of the present invention, as described later.

[0066] Figure 1 The cross-sectional view in the middle shows a conceptual example of the piezoelectric thin film of the present invention.

[0067] Figure 1 The piezoelectric thin film 10 shown has a piezoelectric layer 12, an upper thin film electrode 14 stacked on one side of the piezoelectric layer 12, an upper protective layer 18 stacked on the upper thin film electrode 14, a lower thin film electrode 16 stacked on the other side of the piezoelectric layer 12, and a lower protective layer 20 stacked on the lower thin film electrode 16. The upper thin film electrode 14 and the lower thin film electrode 16 are the electrode layers in this invention.

[0068] In the piezoelectric thin film 10, such as Figure 1 As conceptually shown, the piezoelectric layer 12 contains piezoelectric particles 26 within a polymer matrix 24 comprising polymeric material. That is, the piezoelectric layer 12 is a polymeric composite piezoelectric in the piezoelectric film of the present invention.

[0069] Here, the polymer composite piezoelectric (piezoelectric layer 12) preferably possesses the following characteristics. Furthermore, in this invention, the ambient temperature is 0–50°C.

[0070] (i) flexibility

[0071] For example, when held in a slightly bent state for carrying purposes, such as with documents like newspapers or magazines, it is subjected to relatively slow and large bending deformations of a few Hz or less from the outside. If the polymer composite piezoelectric is stiff, a correspondingly large bending pressure will be generated, causing cracking at the interface between the polymer matrix and the piezoelectric particles, potentially leading to damage. Therefore, the polymer composite piezoelectric requires appropriate flexibility. Furthermore, if the strain energy can be diffused outwards as heat, the pressure can be relieved. Therefore, the loss tangent of the polymer composite piezoelectric requires a suitable large value.

[0072] (ii) Sound quality

[0073] In a loudspeaker, piezoelectric particles vibrate at frequencies within the 20Hz–20kHz audio band. Through this vibrational energy, the entire resonating plate (polymer composite piezoelectric material) vibrates as a single unit, thus producing sound. Therefore, to improve the efficiency of vibrational energy transmission, the polymer composite piezoelectric material must possess appropriate rigidity. Furthermore, if the loudspeaker's frequency response is smooth, the change in sound quality when the lowest resonant frequency f0 changes with curvature is also smaller. Therefore, the polymer composite piezoelectric material must have a sufficiently large loss tangent.

[0074] As is well known, the lowest resonant frequency f0 of a loudspeaker's diaphragm is given by the following formula. Here, s is the rigidity of the vibrating system, and m is the mass.

[0075] [Formula 1]

[0076] Lowest resonant frequency

[0077] At this point, the greater the curvature radius of the piezoelectric film, the smaller the mechanical stiffness s, and therefore the lower the minimum resonant frequency f0. In other words, the sound quality (volume, frequency response) of the loudspeaker varies according to the curvature radius of the piezoelectric film.

[0078] In summary, the polymer composite piezoelectric material is required to exhibit rigidity relative to vibrations in the 20Hz–20kHz range, while exhibiting flexibility relative to vibrations below a few Hz. Furthermore, the loss tangent of the polymer composite piezoelectric material is required to be appropriately large relative to vibrations at all frequencies below 20kHz.

[0079] Typically, polymeric solids possess viscoelastic relaxation mechanisms. With increasing temperature or decreasing frequency, large-scale molecular motion is observed as a decrease in storage modulus (Young's modulus) (relaxation) or a maximum loss of elastic modulus (absorption). Among these, relaxation caused by the micro-Brownian motion of molecular chains through amorphous regions is called principal dispersion, exhibiting very large relaxation phenomena. The temperature at which this principal dispersion occurs is the glass transition temperature (Tg), where the viscoelastic relaxation mechanism is most pronounced.

[0080] In the polymer composite piezoelectric (piezoelectric layer 12), by using a polymer material with a glass transition temperature at room temperature—in other words, a polymer material that is viscoelastic at room temperature—as the matrix, a polymer composite piezoelectric material exhibiting rigidity relative to vibrations of 20 Hz to 20 kHz and flexibility relative to slow vibrations below a few Hz is achieved. In particular, from the viewpoint of appropriately exhibiting this behavior, it is preferable to use a polymer material with a glass transition temperature at room temperature at a frequency of 1 Hz as the matrix of the polymer composite piezoelectric.

[0081] The polymer material is preferably obtained by dynamic viscoelasticity test at room temperature, with a maximum loss tangent Tanδ of 0.5 or higher at a frequency of 1 Hz.

[0082] Therefore, when the polymer composite piezoelectric is slowly bent by an external force, the pressure concentration at the polymer matrix / piezoelectric particle interface in the part of maximum bending torque is relaxed, and high flexibility can be expected.

[0083] Furthermore, the polymer material preferably has a storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement that is 100 MPa or more at 0 °C and 10 MPa or less at 50 °C.

[0084] Therefore, it is possible to reduce the bending torque generated when the polymer composite piezoelectric is slowly bent by external force, while exhibiting rigidity relative to acoustic vibrations of 20Hz to 20kHz.

[0085] Furthermore, the polymer material is more preferably provided that its relative permittivity is 10 or higher at 25°C. Therefore, when a voltage is applied to the polymer composite piezoelectric, a higher electric field is applied to the piezoelectric particles in the polymer matrix, thus allowing for a larger deformation.

[0086] However, on the other hand, considering the need to ensure good moisture resistance, the polymer material is preferably 10 or less relative permittivity at 25°C.

[0087] Examples of polymeric materials that meet these conditions include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride copolyacrylonitrile, polystyrene-polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate.

[0088] As the polymer material constituting the polymer matrix 24, a polymer material having a cyanoethyl component is preferred, and cyanoethylated PVA is particularly preferred. That is, in the piezoelectric film 10 of the present invention, the piezoelectric layer 12 preferably uses a polymer material having a cyanoethyl component as the polymer matrix 24, and cyanoethylated PVA is particularly preferred.

[0089] In the following description, for convenience, the aforementioned polymeric materials, represented by cyanoethylated PVA, will also be collectively referred to as "polymeric materials with viscoelasticity at room temperature".

[0090] In addition, these viscoelastic polymers at room temperature can be used in combination (mixed use) or only one type can be used.

[0091] In the piezoelectric thin film 10 of the present invention, various polymer materials may be used in combination in the polymer matrix 24 of the piezoelectric layer 12 as needed.

[0092] That is, in the polymer matrix 24 constituting the polymer composite piezoelectric body, in order to adjust the dielectric and mechanical properties, in addition to the above-mentioned viscoelastic polymer materials at room temperature, other dielectric polymer materials may be added as needed.

[0093] Examples of polymers that can be added as dielectric polymers include fluorinated polymers such as polyvinylidene fluoride, polyvinylidene fluoride-tetrafluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, polyvinylidene fluoride-trifluoroethylene copolymer, and polyvinylidene fluoride-tetrafluoroethylene copolymer; vinylidene dicyanoacetic acid copolymer; cyanoethyl cellulose; cyanoethyl hydroxysucrose; cyanoethyl hydroxycellulose; cyanoethyl hydroxy amylopectin; cyanoethyl methacrylate; cyanoethyl cyanoethyl acrylate; cyanoethyl hydroxyethyl cellulose; cyanoethyl linear starch; cyanoethyl hydroxypropyl cellulose; cyanoethyl dihydroxypropyl cellulose; cyanoethyl hydroxypropyl linear starch; cyanoethyl polyacrylamide; cyanoethyl polyacrylate; cyanoethyl amylopectin; cyanoethyl polyhydroxymethylene; cyanoethyl glycidyl amylopectin; cyanoethyl sucrose; and cyanoethyl sorbitol; as well as synthetic rubbers such as nitrile rubber and chloroprene rubber.

[0094] Among them, polymeric materials containing cyanoethyl groups are preferred.

[0095] Furthermore, commercially available products such as HYBRAR5127 (manufactured by KURARAY CO.,LTD) can also be appropriately used as these polymer materials.

[0096] Furthermore, in the polymer matrix 24 of the piezoelectric layer 12, these dielectric polymer materials are not limited to one type, but can be added in multiple ways.

[0097] Furthermore, in addition to dielectric polymer materials, thermoplastic resins such as vinyl chloride resin, polyethylene, polystyrene, methacrylic resin, polybutene and isobutene, as well as thermosetting resins such as phenolic resin, urea resin, melamine resin, alkyd resin and mica can be added to adjust the glass transition temperature of the polymer matrix 24.

[0098] In addition, tackifiers such as rosin esters, rosin, terpenes, terpene phenols, and petroleum resins can be added to improve adhesion.

[0099] In the polymer matrix 24 of the piezoelectric layer 12, there is no limitation on the amount of polymer material other than viscoelastic polymer material at room temperature added, but it is preferred to be 30% by mass or less based on the proportion of polymer matrix 24.

[0100] Therefore, the properties of the added polymer material can be exhibited without damaging the viscoelastic relaxation mechanism in the polymer matrix 24, thus achieving preferred results in terms of high dielectric constant, improved heat resistance, and improved adhesion of piezoelectric particles 26 or electrode layers.

[0101] The piezoelectric layer 12 (polymer composite piezoelectric) is formed by containing piezoelectric particles 26 in this polymer matrix.

[0102] The piezoelectric particles 26 are preferably composed of ceramic particles having a perovskite or wurtzite crystal structure.

[0103] Examples of ceramic particles constituting the piezoelectric particle 26 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). Among these, PZT is preferred.

[0104] The particle size of the piezoelectric particles 26 can be appropriately selected according to the size or application of the piezoelectric film 10. The particle size of the piezoelectric particles 26 is preferably 1 to 10 μm.

[0105] By setting the particle size of the piezoelectric particles 26 within the aforementioned range, optimal results can be obtained that balance high voltage characteristics and flexibility.

[0106] In the piezoelectric film 10, the ratio of the polymer matrix 24 to the piezoelectric particles 26 in the piezoelectric layer 12 can be appropriately set according to the size or thickness of the piezoelectric film 10 in the planar direction, the application of the piezoelectric film 10, and the required characteristics of the piezoelectric film 10.

[0107] The volume fraction of piezoelectric particles 26 in the piezoelectric layer 12 is preferably 30 to 70%, especially preferably 50% or more, and more preferably 50 to 70%.

[0108] By setting the ratio of polymer matrix 24 to piezoelectric particles 26 within the above range, an optimal result can be obtained that balances high voltage characteristics and flexibility.

[0109] Furthermore, the thickness of the piezoelectric layer 12 in the piezoelectric film 10 is not limited and can be appropriately set according to the size of the piezoelectric film 10, the application of the piezoelectric film 10, and the required characteristics of the piezoelectric film 10.

[0110] The thickness of the piezoelectric layer 12 is preferably 8 to 300 μm, more preferably 8 to 150 μm, even more preferably 15 to 100 μm, and especially preferably 25 to 75 μm.

[0111] The piezoelectric layer 12 is preferably polarized in the thickness direction. The polarization process will be described in detail later.

[0112] Figure 1 The piezoelectric thin film 10 shown has the following structure: an upper thin film electrode 14 is provided on one side of the piezoelectric layer 12, and preferably an upper protective layer 18 is provided on the upper thin film electrode 14; a lower thin film electrode 16 is provided on the other side of the piezoelectric layer 12, and preferably a lower protective layer 20 is provided on the lower thin film electrode 16. In the piezoelectric thin film 10, the upper thin film electrode 14 and the lower thin film electrode 16 form an electrode pair.

[0113] In other words, the piezoelectric thin film 10 of the present invention has the following structure: the two sides of the piezoelectric layer 12 are sandwiched by an electrode pair, namely an upper thin film electrode 14 and a lower thin film electrode 16, preferably further sandwiched by an upper protective layer 18 and a lower protective layer 20.

[0114] Thus, the region held between the upper thin-film electrode 14 and the lower thin-film electrode 16 is driven according to the applied voltage.

[0115] In addition, in this invention, the upper and lower parts of the upper thin film electrode 14 and the upper protective layer 18, and the lower thin film electrode 16 and the lower protective layer 20 are labeled with names for convenience when describing the piezoelectric thin film 10 of this invention, referring to the accompanying drawings.

[0116] Therefore, the upper and lower portions of the piezoelectric film 10 of the present invention have no positional or technical significance, and are irrelevant to the actual use.

[0117] In addition to these layers, the piezoelectric thin film 10 of the present invention may also have, for example, an adhesive layer for attaching the thin film electrode and the piezoelectric body layer 12, and an adhesive layer for attaching the thin film electrode and the protective layer.

[0118] The adhesive can be either a binder or an adhesive. Furthermore, the adhesive can preferably be a polymer material from which the piezoelectric particles 26 are removed from the piezoelectric layer 12, i.e., the same material as the polymer matrix 24. Additionally, the adhesive layer can be provided on both the upper thin-film electrode 14 side and the lower thin-film electrode 16 side, or it can be provided on only one of the upper thin-film electrode 14 side and the lower thin-film electrode 16 side.

[0119] In addition to these layers, the piezoelectric film 10 preferably also has electrode leads (leads) for contacting the upper film electrode 14, the lower film electrode 16, and an external power source. Furthermore, the piezoelectric film 10 may also have an insulating layer covering the exposed area of ​​the piezoelectric body layer 12 to prevent short circuits, etc.

[0120] As an electrode lead-out portion, a portion protruding outward in the direction of the piezoelectric layer from the thin film electrode and the protective layer can be provided as an electrode lead-out portion. Alternatively, a portion of the protective layer can be removed to form a hole, and a conductive material such as silver paste can be inserted into the hole to make the conductive material electrically connected to the thin film electrode, thus serving as an electrode lead-out portion.

[0121] Furthermore, in each thin-film electrode, the electrode lead is not limited to one; there may be two or more electrode leads. In particular, in the case where a portion of the protective layer is removed and a conductive material is inserted into the hole to serve as the electrode lead, it is preferable to have three or more electrode leads to ensure more reliable energization.

[0122] In the piezoelectric film 10, the upper protective layer 18 and the lower protective layer 20 cover the upper thin-film electrode 14 and the lower thin-film electrode 16, and serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 12. That is, in the piezoelectric film 10 of the present invention, the piezoelectric layer 12, which contains the polymer matrix 24 and piezoelectric particles 26, exhibits excellent flexibility relative to slow bending deformation; on the other hand, depending on the application, there may be cases where the rigidity or mechanical strength is insufficient. The piezoelectric film 10 is provided with the upper protective layer 18 and the lower protective layer 20 to compensate for this deficiency.

[0123] The lower protective layer 20 and the upper protective layer 18 differ only in their placement; their structures are identical. Therefore, in the following description, without needing to distinguish between the lower protective layer 20 and the upper protective layer 18, both components will be collectively referred to as protective layers.

[0124] Furthermore, the piezoelectric thin film 10 in the example figure is more preferably stacked on two thin film electrodes and has a lower protective layer 20 and an upper protective layer 18. However, the present invention is not limited thereto, and may also have a structure having only one of the lower protective layer 20 and the upper protective layer 18.

[0125] Furthermore, in the piezoelectric thin film of the present invention, the protective layer is provided as a preferred embodiment, but is not an essential component. That is, the piezoelectric thin film of the present invention can be composed of a piezoelectric body layer 12, an upper thin film electrode 14, and a lower thin film electrode 16.

[0126] There are no limitations on the protective layer; various sheet-like materials can be used. Various resin films are appropriately exemplified, for instance. Among these, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyamide (PA), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferred due to their excellent mechanical properties and heat resistance.

[0127] There is no limit to the thickness of the protective layer. Furthermore, the upper protective layer 18 and the lower protective layer 20 have essentially the same thickness, but they can also be different.

[0128] If the rigidity of the protective layer is too high, it will not only restrict the expansion and contraction of the piezoelectric layer 12, but also impair its flexibility. Therefore, except in cases where mechanical strength or good operability as a sheet is required, a thinner protective layer is more advantageous.

[0129] According to the research of the inventors, if the thicknesses of the upper protective layer 18 and the lower protective layer 20 are each less than twice the thickness of the piezoelectric layer 12, then a preferred result can be obtained in terms of balancing rigidity and appropriate flexibility.

[0130] For example, when the thickness of the piezoelectric layer 12 is 50 μm and the lower protective layer 20 and the upper protective layer 18 are composed of PET, the thickness of the lower protective layer 20 and the upper protective layer 18 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0131] In the piezoelectric thin film 10, an upper thin film electrode 14 is formed between the piezoelectric body layer 12 and the upper protective layer 18, and a lower thin film electrode 16 is formed between the piezoelectric body layer 12 and the lower protective layer 20. In the following description, the upper thin film electrode 14 is also referred to as the upper electrode 14, and the lower thin film electrode 16 is also referred to as the lower electrode 16.

[0132] The upper electrode 14 and the lower electrode 16 are provided to apply an electric field to the piezoelectric thin film 10 (piezoelectric layer 12).

[0133] Furthermore, the lower electrode 16 and the upper electrode 14 are essentially the same except for their positions. Therefore, in the following description, without needing to distinguish between the lower electrode 16 and the upper electrode 14, both components will be collectively referred to as thin-film electrodes.

[0134] In the piezoelectric thin film of the present invention, there are no limitations on the material used to form the thin film electrode, and various conductors can be used. Specifically, examples include carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, chromium, molybdenum, alloys of these, indium tin oxide, and conductive polymers such as PEDOT / PPS (polyvinyl dioxythiophene-polystyrene sulfonic acid).

[0135] Examples of preferred materials include copper, aluminum, gold, silver, platinum, and indium tin oxide. Among these, copper is preferred from the viewpoints of conductivity, cost, and flexibility.

[0136] Furthermore, there are no restrictions on the method of forming the thin film electrode. Various known methods can be used, such as vapor deposition (vacuum film formation) based on vacuum evaporation or sputtering, or methods for forming films based on coating, bonding foils formed from the above materials, and coating methods.

[0137] In particular, for reasons such as ensuring the flexibility of the piezoelectric film 10, a copper or aluminum film deposited by vacuum evaporation is preferably used as the film electrode. Among them, a copper film formed by vacuum evaporation is particularly preferred.

[0138] There is no limitation on the thickness of the upper electrode 14 and the lower electrode 16. Furthermore, the thickness of the upper electrode 14 and the lower electrode 16 can be basically the same, but they can also be different.

[0139] Similar to the aforementioned protective layer, if the rigidity of the thin-film electrode is too high, it will not only restrict the expansion and contraction of the piezoelectric layer 12, but also impair its flexibility. Therefore, as long as the resistance does not become excessively high, a thinner thin-film electrode is more advantageous.

[0140] In the piezoelectric thin film 10 of the present invention, if the product of the thickness of the thin film electrode and Young's modulus is lower than the product of the thickness of the protective layer and Young's modulus, the flexibility will not be severely damaged, and therefore it is preferred.

[0141] For example, in the case of a combination in which the protective layer is made of PET (Young's modulus: about 6.2 GPa) and the thin film electrode is made of copper (Young's modulus: about 130 GPa), if the thickness of the protective layer is 25 μm, then the thickness of the thin film electrode is preferably 1.2 μm or less, more preferably 0.3 μm or less, and even more preferably 0.1 μm or less.

[0142] As described above, the piezoelectric thin film 10 has the following structure: a piezoelectric layer 12 containing piezoelectric particles 26 is sandwiched in a polymer matrix 24 containing polymer material by an upper electrode 14 and a lower electrode 16, and an upper protective layer 18 and a lower protective layer 20 are further sandwiched.

[0143] This piezoelectric film 10 preferably has a maximum value of 0.1 or more at room temperature and a loss tangent (Tanδ) at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement.

[0144] Therefore, even if the piezoelectric film 10 is subjected to relatively slow large bending deformation of less than a few Hz from the outside, it can effectively diffuse the strain energy to the outside as heat, thus preventing cracking at the interface between the polymer matrix and the piezoelectric particles.

[0145] The storage modulus (E') of the piezoelectric film 10 at a frequency of 1 Hz, obtained by dynamic viscoelasticity measurement, is preferably 10–30 GPa at 0 °C and 1–10 GPa at 50 °C.

[0146] Therefore, the piezoelectric film 10 can have a large frequency dispersion in its storage modulus (E') at room temperature. That is, it can exhibit rigidity relative to vibrations of 20 Hz to 20 kHz and flexibility relative to vibrations below a few Hz.

[0147] Furthermore, the product of the thickness of the piezoelectric film 10 and the storage modulus (E') at a frequency of 1 Hz obtained by dynamic viscoelasticity measurement is preferably 1.0 × 10⁻⁶ at 0 °C. 6 ~2.0×10 6 N / m, 1.0×10 at 50℃ 5 ~1.0×10 6 N / m.

[0148] Thus, the piezoelectric film 10 can possess appropriate rigidity and mechanical strength without compromising flexibility and acoustic properties.

[0149] Furthermore, in the master curve obtained by dynamic viscoelasticity measurement, the loss tangent (Tanδ) of the piezoelectric film 10 at 25°C and 1kHz is preferably 0.05 or higher.

[0150] As a result, the frequency response of the loudspeaker using the piezoelectric film 10 becomes smooth, and the amount of change in sound quality when the lowest resonant frequency f0 changes with the curvature of the loudspeaker (piezoelectric film 10) is reduced.

[0151] As described above, in the cross-section observed by SEM, the piezoelectric thin film 10 of the present invention divides the piezoelectric layer 12 into 10 regions along the thickness direction and calculates the area ratio of the piezoelectric particles 26 in the two regions that are furthest apart. When the area ratio of the piezoelectric particles 26 in the region with the lower area ratio is set to 1, the area ratio of the piezoelectric particles 26 in the region with the higher area ratio is 1.2 or more.

[0152] Specifically, as an example, an SEM image of a cross-section obtained by cutting the piezoelectric thin film 10 along its thickness direction at an arbitrary location is obtained. In this cross-sectional SEM image, the interface between the upper electrode 14 and the piezoelectric layer 12 and the interface between the lower electrode and the piezoelectric layer 12 are taken as the upper and lower surfaces in the thickness direction of the piezoelectric layer 12, as shown below. Figure 1 As shown by the dashed lines, the piezoelectric layer 12 is divided into 10 parts in the thickness direction.

[0153] In this invention, the focus is on the two regions that are furthest apart from each of the 10 regions equally divided along the thickness direction. That is, in this invention, among the 10 regions equally divided along the thickness direction, the focus is on the region adjacent to the upper electrode 14 and the region adjacent to the lower electrode 16.

[0154] In the following description, for convenience, the piezoelectric layer 12, which is divided into 10 equal regions along the thickness direction, is designated as the first region 12a, which is adjacent to the upper electrode 14, and the tenth region 12b, which is on the side of the lower electrode 16. Similar to the upper and lower regions described above, the first and tenth regions have no technical significance.

[0155] The area fraction of the piezoelectric particles 26 was measured in the first region 12a and the tenth region 12b, which were set as described above.

[0156] The area ratio of piezoelectric particles 26 refers to the total area ratio of piezoelectric particles 26 in region 12a and region 102b of the cross-sectional SEM image. For example, if it is the area ratio of piezoelectric particles 26 in region 12a, then image analysis is performed on the cross-sectional SEM image, and the area of ​​region 12a and the total area of ​​piezoelectric particles 26 obtained by summing the areas of all piezoelectric particles 26 in region 12a are calculated. Then, the area ratio of piezoelectric particles 26 in region 12a can be calculated.

[0157] Typically, in a cross-sectional SEM image (monochrome image) of the piezoelectric thin film 10, the density (brightness) in the image is ranked as follows: "piezoelectric particles and thin film electrodes > polymer matrix (adhesive) and protective layer". Furthermore, when voids exist within the piezoelectric layer 12, the voids exhibit the highest density.

[0158] Therefore, for example, in the cross-sectional SEM image of the piezoelectric thin film 10, the piezoelectric layer 12 is divided into 10 regions along the thickness direction as described above, with the first region 12a on the side of the upper electrode 14 and the tenth region 12b on the side of the lower electrode 16 being the regions furthest apart from each other. Then, using an appropriately selected concentration as a threshold, the cross-sectional SEM image is binarized into black (high concentration) and white (low concentration). By analyzing this binarized image, the area of ​​the first region 12a and the area of ​​the tenth region 12b, as well as the total area of ​​the piezoelectric particles 26 in each region, are calculated, and the area ratio of each region is determined.

[0159] In this invention, as an example, the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b is measured in 10 cross sections arbitrarily set in the piezoelectric film 10.

[0160] The average area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b of the ten cross sections is taken as the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b of the piezoelectric film 10. That is, in this invention, as an example, the average value of the ten cross sections is taken as the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b, which are the furthest apart in the piezoelectric layer 12 formed by dividing the piezoelectric film 10 into ten regions along the thickness direction.

[0161] In the piezoelectric thin film 10 of the present invention, when the area fraction of piezoelectric particles 26 in the first region 12a and the tenth region 12b is measured in this manner, the area fraction of piezoelectric particles 26 in the region with low area fraction is set to 1, and the area fraction of piezoelectric particles 26 in the region with high area fraction is 1.2 or more.

[0162] In other words, in the piezoelectric thin film 10 of the present invention, when the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b as measured above is normalized to 1, the area ratio of the piezoelectric particles 26 in the region with low area ratio is 1.2 or higher.

[0163] That is, in the piezoelectric thin film 10 of the present invention, the ratio of the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b to the area ratio of the piezoelectric particles 26 in the region with the higher area ratio to the area ratio in the region with the lower area ratio is 1.2 or more.

[0164] For example, when the area ratio of piezoelectric particles 26 in region 12a is higher than that in region 10b, the ratio of the area ratios obtained by dividing the area ratio of piezoelectric particles 26 in region 12a by the area ratio of piezoelectric particles 26 in region 10b is 1.2 or higher. That is, in this case, "the ratio of the area ratios of piezoelectric particles 26 = [the area ratio of piezoelectric particles 26 in region 12a] / [the area ratio of piezoelectric particles 26 in region 10b] ≥ 1.2".

[0165] The piezoelectric film 10 of the present invention, by having such a structure, has high durability to prevent damage to the piezoelectric layer 12 due to warping, and can obtain sufficient sound pressure relative to the input operating voltage.

[0166] As described above, when a piezoelectric film is used as an electroacoustic conversion film in a piezoelectric loudspeaker, the piezoelectric film is kept in a bent state and a driving voltage is applied to the electrode layer, causing the piezoelectric film to stretch and contract along the surface direction. The piezoelectric loudspeaker outputs sound by causing the piezoelectric film to vibrate in a direction orthogonal to the surface through this stretching and contraction.

[0167] Vibration of the piezoelectric film causes it to warp significantly. In this warped state, regions within the piezoelectric layer constituting the film exhibit varying degrees of volume change along the thickness direction. This difference in volume change along the thickness direction exerts significant stress on the piezoelectric layer, leading to defects such as cracking and peeling from the electrode layer.

[0168] Therefore, conventional piezoelectric films have experienced degradation in acoustic properties, such as reduced sound pressure, with use.

[0169] In contrast, in the piezoelectric thin film 10 of the present invention, when the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b, which are the furthest regions divided into 10 regions along the thickness direction, is set to 1 in the region with the low area ratio, the area ratio of the piezoelectric particles 26 in the region with the high area ratio is 1.2 or more.

[0170] In other words, in the piezoelectric thin film 10 of the present invention, the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b, which are the furthest regions divided into 10 regions along the thickness direction, is 1.2 or more.

[0171] That is, the piezoelectric layer 12 has regions with relatively more polymer matrix 24 and regions with relatively less polymer matrix 24 in the thickness direction.

[0172] The piezoelectric particles 26 have high rigidity, but the polymer matrix 24 has a certain degree of flexibility and elasticity. Therefore, in this piezoelectric film 10 of the present invention, when warping occurs, the polymer matrix 24 in the region with more polymer matrix 24 absorbs the volume change in the thickness direction of the piezoelectric layer 12 caused by warping.

[0173] As a result, the piezoelectric film 10 of the present invention reduces the pressure applied to the piezoelectric layer 12 due to the warping of the piezoelectric film 10, and can prevent defects such as cracking of the piezoelectric layer 12 and peeling of the piezoelectric layer 12 from the thin film electrode over a long period of time. Therefore, the piezoelectric film 10 of the present invention has good durability, suppressing the deterioration of acoustic properties such as sound pressure reduction caused by use.

[0174] From a durability point of view, it is preferable that the area fraction of the piezoelectric particles 26 throughout the piezoelectric film is uniformly low. However, if the area fraction of the piezoelectric particles 26 is uniformly low throughout the piezoelectric film, sufficient acoustic characteristics, such as low sound pressure relative to the input operating voltage, cannot be obtained.

[0175] In contrast, in the piezoelectric film 10 of the present invention, among the farthest regions, namely the first region 12a and the tenth region 12b, which are equally divided into 10 regions along the thickness direction, one region has an area ratio of piezoelectric particles 26 that is more than 1.2 times that of the other region. That is, the piezoelectric film 10 of the present invention has a region in the thickness direction with a relatively high area ratio of piezoelectric particles 26 compared to other regions.

[0176] Therefore, in the piezoelectric film 10 of the present invention, the region with a high area ratio of piezoelectric particles 26 can ensure acoustic properties, thus having high durability by having a region with a low area ratio of piezoelectric particles 26, and obtaining sufficient sound pressure relative to the input operating voltage.

[0177] That is, according to the present invention, a piezoelectric film 10 that combines durability and acoustic properties can be realized: it can obtain sufficient sound pressure relative to the input operating voltage and does not suffer from acoustic property degradation such as a decrease in sound pressure due to use, and has good durability that can maintain its initial performance over a long period of time.

[0178] In the piezoelectric thin film 10 of the present invention, when the area ratio of the piezoelectric particles 26 in the low area ratio region is set to 1 in the first region 12a and the tenth region 12b, the area ratio of the piezoelectric particles 26 in the high area ratio region is 1.2 or more.

[0179] That is, in the first region 12a and the tenth region 12b, the ratio of the area ratio of the piezoelectric particles 26 in the region with the high area ratio to the area ratio of the piezoelectric particles 26 in the region with the low area ratio is 1.2 or more.

[0180] In the following description, the ratio of the area ratios of the piezoelectric particles 26 in the first region 12a and the tenth region 12b, that is, "the ratio of the area ratios obtained by dividing the area ratio of the piezoelectric particles 26 in the region with the area ratio of the region with the area ratio of the region with the area ratio", is also simply referred to as "the ratio of the area ratios of the piezoelectric particles 26".

[0181] When the area ratio of piezoelectric particles 26 is less than 1.2, adverse conditions such as a decrease in sound pressure and degradation of acoustic properties will occur with use.

[0182] The area ratio of the piezoelectric particles 26 is preferably 1.3 or more, more preferably 1.4 or more, and even more preferably 1.5 or more.

[0183] In the piezoelectric thin film 10 of the present invention, from the viewpoint of preventing the deterioration of acoustic properties, it is preferable that the area ratio of the piezoelectric particles 26 is substantially large. However, if the area ratio of the piezoelectric particles 26 is too large, there may be regions in the thickness direction of the piezoelectric layer 12 where the proportion of piezoelectric particles 26 is too low, and these regions may not contribute to the acoustic properties.

[0184] In view of this, the area ratio of the piezoelectric particles 26 is preferably 70 or less, more preferably 50 or less, and even more preferably 12 or less.

[0185] Furthermore, in the piezoelectric film 10 of the present invention, even if the area ratio of the piezoelectric particles 26 is higher in either the first region 12a or the tenth region 12b compared to the other region, the performance of the piezoelectric film 10 will not be affected. Moreover, as described above, in the piezoelectric film 10 of the present invention, the terms "first" and "second" have no technical significance and are irrelevant to usage in the vertical direction, etc.

[0186] Therefore, in the piezoelectric thin film 10 of the present invention, the area ratio of the piezoelectric particles 26 can be high in either the first region 12a or the tenth region 12b.

[0187] In the piezoelectric thin film 10 of the present invention, there is no limitation on the area ratio of the piezoelectric particles 26 in the first region 12a and the tenth region 12b. Basically, the higher the area ratio of the piezoelectric particles 26 in the piezoelectric layer 12, the higher the acoustic properties of the piezoelectric thin film 10.

[0188] In the piezoelectric thin film 10, the average area ratio of the piezoelectric particles 26 in the first region 12a and the area ratio of the piezoelectric particles 26 in the tenth region 12b is preferably 23% or more.

[0189] In the following description, the average of the area ratio of the piezoelectric particles 26 in the first region 12a and the area ratio of the piezoelectric particles 26 in the tenth region 12b is also referred to as the "average area ratio of the piezoelectric particles 26".

[0190] By setting the average area fraction of the piezoelectric particles 26 to 23% or more, the piezoelectric film 10 can exhibit good acoustic properties.

[0191] The average area fraction of the piezoelectric particles 26 is more preferably 40% or more, and even more preferably 60% or more.

[0192] There is no upper limit to the average surface fraction of the piezoelectric particles 26.

[0193] Considering that the area ratio of the piezoelectric particles 26 is stably set to 1.2 or higher, the average area ratio of the piezoelectric particles 26 is preferably 80% or less.

[0194] Furthermore, the average area ratio of the piezoelectric particles 26 is the average of the area ratios of the piezoelectric particles 26 in the farthest first region 12a and the tenth region 12b when the piezoelectric layer 12 is divided into 10 regions along the thickness direction. It is not necessarily consistent with the area ratio of the piezoelectric particles 26 in the entire region of the piezoelectric layer 12.

[0195] However, according to the inventors' research, the area ratio of piezoelectric particles 26 in the first region 12a and the tenth region 12b, which are the farthest regions among the 10 regions divided along the thickness direction, is mostly related to the area ratio of piezoelectric particles 26 in the entire region along the thickness direction of the piezoelectric layer 12.

[0196] Therefore, by using the average of the area ratio of the piezoelectric particles 26 in the first region 12a and the area ratio of the piezoelectric particles 26 in the tenth region 12b, i.e. the average area ratio of the piezoelectric particles 26, the area ratio of the piezoelectric particles 26 in the entire region of the piezoelectric layer 12 can be known.

[0197] Figures 2-4 The diagram illustrates an example of a method for manufacturing a piezoelectric thin film 10.

[0198] First, such as Figure 2 As shown conceptually, a sheet 34 on which a lower electrode 16 is prepared to be formed on the surface of the lower protective layer 20 is prepared.

[0199] The sheet 34 can be fabricated by forming a copper thin film on the surface of the lower protective layer 20 using vacuum evaporation, sputtering, or plating, and thus serving as the lower electrode 16. Similarly, the sheet 38 can be fabricated by forming a copper thin film on the surface of the upper protective layer 18 using vacuum evaporation, sputtering, or plating, and thus serving as the upper thin film electrode 14.

[0200] Alternatively, a sheet of commercially available material with a copper film or the like formed on the protective layer can be used as sheet 34 (sheet 38 described later).

[0201] Additionally, when the protective layer is very thin and has poor operability, a protective layer with a separator (pseudo-support) can be used as needed. Furthermore, PET or similar materials with a thickness of 25–100 μm can be used as the separator. The separator can be removed after the thin-film electrode and the protective layer are thermally bonded.

[0202] Next, as Figure 3 As conceptually shown, after coating a piezoelectric layer 12 onto the lower electrode 16 of the sheet 34, a lower-side piezoelectric layer 12L, approximately half the thickness in the thickness direction on the lower electrode 16 side of the piezoelectric layer 12, is formed by heating and drying to cure it, thereby creating a lower-side laminate 36L in which the sheet 34 and the lower-side piezoelectric layer 12L are stacked. That is, in this example, a lower-side piezoelectric layer 12L with a thickness of approximately half the thickness of the originally formed piezoelectric layer 12 is formed on the lower electrode 16 of the sheet 34.

[0203] In the formation of the lower half of the piezoelectric layer 12L on the lower electrode side of the piezoelectric layer 12, firstly, the polymer material that forms the polymer matrix 24 is dissolved in an organic solvent, and then piezoelectric particles 26 such as PZT particles are added and stirred to prepare a coating that forms a piezoelectric layer.

[0204] There are no restrictions on the organic solvents used; various organic solvents such as dimethylformamide (DMF), methyl ethyl ketone, and cyclohexanone can be used. Multiple organic solvents can be mixed.

[0205] After preparing the sheet 34 and the coating, the coating is cast (coated) onto the sheet 34 (lower electrode 16), and dried by heating to evaporate the organic solvent. Thus, as... Figure 3 As shown, a lower side laminate 36L is formed by fabricating a lower side piezoelectric layer 12L on the lower protective layer 20, which has a lower electrode 16 and a piezoelectric layer 12 is stacked on the lower electrode 16, about half of the lower electrode 16 side.

[0206] There are no restrictions on the coating application method; all known methods (coating devices) such as rod coaters, sliding coaters, and doctor blades can be used.

[0207] Alternatively, if the polymer material is a heat-melting substance, the polymer material is heated and melted to prepare a melt in which piezoelectric particles 26 are added, and then processed by extrusion molding, etc. Figure 2 The sheet 34 shown is extruded into a sheet shape and then cooled, thereby producing a product such as... Figure 3 The lower side laminate 36L is shown.

[0208] In addition, as mentioned above, in the piezoelectric film 10, in addition to a viscoelastic polymer material at room temperature, a polymeric piezoelectric material such as PVDF can also be added to the polymer matrix 24.

[0209] When adding these polymeric piezoelectric materials to the polymer matrix 24, the polymeric piezoelectric materials added to the coating above can be dissolved. Alternatively, the desired polymeric piezoelectric material can be added to a viscoelastic polymer material that is heated and melted at room temperature, and then heated and melted.

[0210] Next, the lower piezoelectric layer 12L formed on the lower side stack 36L is subjected to polarization treatment.

[0211] There are no limitations on the method for polarizing the piezoelectric layer, and known methods can be used. For example, electric field polarization by directly applying a DC electric field to the object to be polarized can be exemplified. Alternatively, when polarizing by electric field polarization, instead of separately polarizing the lower piezoelectric layer 12L of the lower side stack 36L and the upper piezoelectric layer 12U of the upper side stack 36U (described later), the upper side piezoelectric layer 12U can be stacked on the lower side piezoelectric layer 12L before polarization, as described later, and electric field polarization can be performed using the upper electrode 14 and the lower electrode 16.

[0212] Furthermore, when manufacturing the piezoelectric thin film 10 of the present invention, the polarization treatment is preferably performed in the thickness direction rather than in the surface direction of the piezoelectric layer 12 (polymer composite piezoelectric).

[0213] Furthermore, prior to this polarization treatment, a calendering process can be performed to smooth the surface of the lower piezoelectric layer 12L using heated rollers or the like. By performing this calendering process, the hot pressing process described later can be carried out smoothly.

[0214] On the other hand, a sheet 38, similar to the sheet 34 described above, having an upper electrode 14 formed on the surface of the upper protective layer 18, is prepared (see reference). Figure 2 ).

[0215] On the sheet 38, an upper side piezoelectric layer 12U, half of the upper electrode 14 side of the piezoelectric layer 12, is formed in the same manner as the lower side piezoelectric layer 12L of the lower side laminate 36L, thereby fabricating the upper side laminate 36U. Furthermore, the upper side piezoelectric layer 12U of the upper side laminate 36U is polarized in the thickness direction.

[0216] Furthermore, in the polarization treatment of the upper piezoelectric layer 12U, the polarization direction is opposite to that of the lower piezoelectric layer 12L. For example, in the case of electric field polarization, when the negative terminal of the DC power supply is connected to the lower electrode 16 side in the polarization treatment of the lower piezoelectric layer 12L, the positive terminal of the DC power supply 32 is connected to the upper electrode 14 side in the polarization treatment of the upper piezoelectric layer 12U.

[0217] When forming the upper side piezoelectric layer 12U, the amount of piezoelectric particles 26 in the coating used to form the upper side piezoelectric layer 12U relative to the polymer matrix 24 (which becomes the polymer material of the polymer matrix 24) is set to a different amount than that in the coating used to form the lower side piezoelectric layer 12L.

[0218] As an example, in the coating used to form the upper piezoelectric layer 12U, the amount of piezoelectric particles 26 relative to the polymer matrix 24 is set to be lower than that in the coating used to form the lower piezoelectric layer 12L. For example, in the coating used to form the lower piezoelectric layer 12L, the polymer matrix 24 is set to 100 parts by mass and the piezoelectric particles 26 is set to 100 parts by mass; in the coating used to form the upper piezoelectric layer 12U, the polymer matrix 24 is set to 100 parts by mass and the piezoelectric particles 26 is set to 30 parts by mass.

[0219] Conversely, in the coating used to form the upper piezoelectric layer 12U, the amount of piezoelectric particles 26 relative to the polymer matrix 24 can be set higher than that in the coating used to form the lower piezoelectric layer 12L. For example, in the coating used to form the lower piezoelectric layer 12L, the polymer matrix 24 can be set to 200 parts by mass and the piezoelectric particles 26 to 100 parts by mass; in the coating used to form the upper piezoelectric layer 12U, the polymer matrix 24 can be set to 200 parts by mass and the piezoelectric particles 26 to 200 parts by mass.

[0220] As a result, the piezoelectric particle content in the first region 12a and the tenth region 12b are different from each other, thereby forming a piezoelectric layer 12 in which the area ratio of the piezoelectric particles 26 in the first region 12a is different from that in the tenth region 12b.

[0221] Furthermore, by appropriately adjusting the amount of piezoelectric particles 26 relative to the polymer matrix 24 in the coating forming the upper side piezoelectric layer 12U and the amount of piezoelectric particles 26 relative to the polymer matrix 24 in the coating forming the lower side piezoelectric layer 12L, the ratio of the area ratio of piezoelectric particles 26 in the piezoelectric layer 12 of the piezoelectric film 10 can be set to 1.2 or more.

[0222] In addition, as mentioned above, the area fraction of the piezoelectric particle 26 can be high in either the 10th region 12b or the 1st region 12a.

[0223] Thus, after fabricating the lower side laminate 36L, which has undergone polarization treatment of the lower side piezoelectric layer 12L, and the upper side laminate 36U, which has undergone polarization treatment of the upper side piezoelectric layer 12U, as follows: Figure 4 As shown, the lower piezoelectric layer 12L and the upper piezoelectric layer 12U are stacked opposite each other, and the lower side laminate 36L and the upper side laminate 36U are stacked.

[0224] Next, the laminate is hot-pressed using a hot press and heating rollers, holding the lower protective layer 20 and the upper protective layer 18 together, and the lower side piezoelectric layer 12L and the upper side piezoelectric layer 12U are bonded together to create a laminate as shown in the figure. Figure 1 The piezoelectric thin film 10 of the present invention is shown.

[0225] In the above example, a lower piezoelectric layer 12L of the piezoelectric layer 12 is formed on sheet 34, and an upper piezoelectric layer 12U of the piezoelectric layer 12 is formed on sheet 38, and the layers are stacked. That is, in this example, piezoelectric layers corresponding to about half the thickness of the final obtained piezoelectric layer are formed on two sheets and then stacked to produce the piezoelectric thin film 10 of the present invention.

[0226] However, the piezoelectric film 10 of the present invention is not limited to being manufactured by this method; piezoelectric layers can be formed on two sheets at various thickness ratios and then laminated. For example, the piezoelectric film 10 can be manufactured by forming approximately 9 / 10 of the piezoelectric layer 12 on the sheet 34 on the lower electrode 16 side and forming 1 / 10 of the piezoelectric layer 12 on the sheet 38 on the upper electrode 14 side, and then laminating and thermally bonding the two together. Alternatively, the piezoelectric layer 12 can be formed by laminating three or more layers.

[0227] In this manufacturing method, by appropriately setting the amount of piezoelectric particles 26 in the coating forming each layer relative to the polymer matrix 24, it is possible to preferably manufacture the piezoelectric film 10 of the present invention, which is divided into 10 regions along the thickness direction, and the ratio of the area ratio of the piezoelectric particles 26 of the farthest first region 12a to the tenth region 12b is 1.2 or more.

[0228] Furthermore, the piezoelectric thin film 10 of the present invention is not limited to being made by stacking two piezoelectric layers with different contents of piezoelectric particles 26.

[0229] That is, in the same manner as in the example above, a piezoelectric layer 12 is formed on a sheet 34 having a lower electrode 16 and a lower protective layer 20 by using a coating containing a polymer material forming a polymer matrix 24 and piezoelectric particles 26, and then polarization treatment is performed. Then, as in... Figure 5 As shown conceptually, the piezoelectric film 10 of the present invention can be manufactured by stacking and hot-pressing a sheet 38 having an upper electrode 14 and an upper protective layer 18.

[0230] Here, in this manufacturing method, when the piezoelectric layer 12 is formed by conventional methods, it is not possible to manufacture the piezoelectric thin film 10 of the present invention in which the area ratio of the piezoelectric particles 26 of the first region 12a to the 10th region 12b in the piezoelectric layer 12 is 1.2 or more.

[0231] However, by adjusting the ratio of piezoelectric particles 26 in the thickness direction in the piezoelectric layer 12 using the method shown below, the ratio of the area fraction of the piezoelectric particles 26 can be set to 1.2 or higher.

[0232] As an example, a method can be illustrated by making the drying time of the coating, which forms the piezoelectric layer 12, longer than usual after coating the lower electrode 16 (upper electrode 14).

[0233] As described above, the piezoelectric layer 12 is formed using a coating prepared by dissolving the polymer material that forms the polymer matrix 24 in an organic solvent, adding piezoelectric particles 26 such as PZT particles, and stirring.

[0234] When this coating is used to form the piezoelectric layer 12, in order to promote the evaporation of the organic solvent and maintain the uniform dispersion of the piezoelectric particles, the coating is usually dried and cured by heating after application.

[0235] In contrast, by drying and curing the coating at room temperature, preferably below room temperature, and applying the coating at a low temperature of 5°C or below, the drying time of the coating forming the piezoelectric layer 12 is longer than usual.

[0236] The specific gravity of the piezoelectric particles 26 is higher than that of the polymer material that forms the polymer matrix 24. Therefore, by allowing the coating to dry for a long time, sufficient time can be ensured for the piezoelectric particles 26 to settle in the coating that forms the piezoelectric layer 12, thereby setting the area ratio of the piezoelectric particles 26 in the piezoelectric layer 12 to be 1.2 or higher.

[0237] In addition, regarding the length of the drying time at this time, the time that allows the piezoelectric particles 26 to fully precipitate in the coating that becomes the piezoelectric layer 12 can be appropriately set according to the particle size of the piezoelectric particles 26, the ratio of the polymer matrix 24 to the piezoelectric particles 26 in the coating, the film thickness of the piezoelectric layer 12, and the boiling point of the organic solvent.

[0238] As another method, an example can be illustrated by using a larger amount of organic solvent than usual in the coating used to form the piezoelectric layer 12, in order to set the viscosity of the coating to a low viscosity.

[0239] If the viscosity of the coating is low, the piezoelectric particles 26 will easily precipitate in the coating applied to the lower electrode 16 (upper electrode 14). Therefore, in the coating used to form the piezoelectric layer 12, the amount of organic solvent is increased more than usual, and the viscosity of the coating is set to low, so that the area ratio of the piezoelectric particles 26 in the piezoelectric layer 12 can be set to 1.2 or more.

[0240] In addition, regarding the viscosity of the coating at this time, the viscosity can be appropriately set to allow the piezoelectric particles 26 to fully precipitate in the coating that forms the piezoelectric matrix 24, based on the particle size of the piezoelectric particles 26, the ratio of the polymer material that forms the polymer matrix 24 in the coating to the piezoelectric particles 26, the film thickness of the piezoelectric layer 12, and the boiling point of the organic solvent.

[0241] The piezoelectric thin film 10 of the present invention, thus manufactured, is polarized in the thickness direction rather than in the planar direction, and large piezoelectric properties can be obtained even without stretching after polarization. Therefore, the piezoelectric thin film 10 of the present invention does not exhibit in-plane anisotropy in its piezoelectric properties, and when a driving voltage is applied, it isotropically stretches and contracts in all directions in the planar direction.

[0242] The piezoelectric thin film 10 of this invention can be manufactured using sliced ​​sheets 34 or the like, preferably using roll-to-roll. In the following description, roll-to-roll is also referred to as "RtoR".

[0243] As is well known, RtoR is a manufacturing method in which raw materials are pulled out from a roller formed by winding long strips of raw materials, conveyed along the length direction while undergoing various treatments such as film formation or surface treatment, and then the processed raw materials are wound back into a roller shape.

[0244] When the piezoelectric film 10 is manufactured by RtoR using the above manufacturing method, a first roller formed by winding a long strip of sheet 34 having a lower electrode 16, etc., and a second roller formed by winding a long strip of sheet 38 having an upper electrode 14, etc.

[0245] The first and second rollers can be exactly the same.

[0246] A sheet 34 is pulled out from the first roller and conveyed along its length. Meanwhile, a coating containing polymer material and piezoelectric particles 26 is applied to the lower electrode 16 of the sheet 34 and dried by heating, thereby creating a lower side piezoelectric layer 12L on the lower electrode 16, forming a piezoelectric layer 12. The sheet 34 and the lower side piezoelectric layer 12L are then stacked to form a lower laminate 36L.

[0247] Next, the lower side piezoelectric layer 12L is polarized. Here, when the piezoelectric thin film 10 is manufactured by RtoR, the lower side laminate 36L is transported while the lower side laminate 36L is polarized by a rod-shaped electrode that extends in a direction orthogonal to the transport direction of the lower side laminate 36L.

[0248] On the other hand, the sheet 38 is pulled out from the second roller that winds the long sheet 38. While conveying the sheet 38, the upper side piezoelectric layer 12U of the piezoelectric layer 12 is formed in the same way as the lower side piezoelectric layer 12L to form an upper side laminate 36U. Then, the upper side piezoelectric layer 12U of the upper side laminate 36U is subjected to polarization treatment.

[0249] At this time, in order to set the area ratio of the piezoelectric particles 26 in the first region 12a to be different from that in the tenth region 12b, as described above, the coating forming the upper side piezoelectric layer 12U is changed to a different ratio of polymer material of the polymer matrix 24 to piezoelectric particles 26 compared to the coating forming the lower side piezoelectric layer 12L. Furthermore, as described above, the polarization direction in the polarization treatment is set to the opposite direction to that of the lower side piezoelectric layer 12L.

[0250] Then, the lower side laminate 36L and the upper side laminate 36U, which have undergone polarization treatment, are conveyed along the length direction with the lower side piezoelectric layer 12L and the upper side piezoelectric layer 12U facing each other, and the two are laminated simultaneously. Furthermore, the laminate, which holds the lower side laminate 36L and the upper side laminate 36U, is heat-pressed by conveying it with a heated roller, thereby completing the piezoelectric film 10 of the present invention, and the piezoelectric film 10 is wound into a roller shape.

[0251] Furthermore, in the above example, the piezoelectric film 10 of the present invention is produced by conveying the sheet (laminated body) only once along the length direction via RtoR, but it is not limited to this. That is, after completing any one or more processes, the long sheet can be wound into a roller, and the next process can pull the sheet out of the roller for the next process.

[0252] For example, the lower side laminate 36L, which has undergone polarization treatment in region 10 12b, is first wound into a roll shape. On the other hand, the upper side laminate 36U, which has undergone polarization treatment in region 1 12a, is also first wound into a roll shape. Then, the lower side laminate 36L is pulled out from one roll, and the upper side laminate 36U is pulled out from another roll. Similarly, the lower side piezoelectric layer 12L and the upper side piezoelectric layer 12U are stacked and heat-pressed while being transported along the length direction, thereby completing the piezoelectric film 10 of the present invention and allowing it to be wound into a roll shape.

[0253] Figure 6 The diagram shows a conceptual illustration of an example of a planar piezoelectric loudspeaker utilizing the piezoelectric film 10 of the present invention.

[0254] The piezoelectric speaker 40 is a flat-plate piezoelectric speaker in which the piezoelectric film 10 of the present invention is used as a vibrating plate to convert electrical signals into vibrational energy. In addition, the piezoelectric speaker 40 can also be used as a microphone and sensor, etc.

[0255] The piezoelectric loudspeaker 40 is composed of a piezoelectric diaphragm 10, a housing 42, a viscoelastic support 46, and a frame 48.

[0256] The outer shell 42 is a thin frame made of plastic or the like, with one side open. Examples of the frame shape include a cuboid, a cube, and a cylinder.

[0257] Furthermore, the frame 48 is a frame material that has a through hole in the center with the same shape as the open surface of the outer shell 42 and engages with the open surface side of the outer shell 42.

[0258] The viscoelastic support 46 has suitable viscosity and elasticity to support the piezoelectric film 10, and converts the stretching motion of the piezoelectric film 10 into forward and backward motion without waste by applying a certain mechanical bias to any part of the piezoelectric film 10. Examples include nonwoven fabrics such as wool felt and wool felt containing PET, as well as glass wool. Furthermore, as described above, the forward and backward motion of the piezoelectric film 10 is a motion in a direction orthogonal to the film surface of the piezoelectric film 10 (perpendicular direction).

[0259] The piezoelectric loudspeaker 40 is configured such that a viscoelastic support 46 is housed in a housing 42, and the housing 42 and the viscoelastic support 46 are covered by a piezoelectric film 10. The frame 48 is fixed to the housing 42 while the periphery of the piezoelectric film 10 is pressed to the upper surface of the housing 42 by the frame 48.

[0260] Here, in the piezoelectric loudspeaker 40, the height (thickness) of the viscoelastic support 46 is greater than the height of the inner surface of the housing 42.

[0261] Therefore, in the piezoelectric loudspeaker 40, the viscoelastic support 46 is held at its periphery while being pressed downwards by the piezoelectric film 10, causing it to become thinner. Furthermore, also at the periphery of the viscoelastic support 46, the curvature of the piezoelectric film 10 changes abruptly, forming a rising portion on the piezoelectric film 10 that decreases in size towards the periphery of the viscoelastic support 46. Additionally, the central region of the piezoelectric film 10 is pressed against the prism-shaped viscoelastic support 46, becoming (approximately) planar.

[0262] Regarding the piezoelectric speaker 40, when the piezoelectric film 10 is elongated in the planar direction by applying a driving voltage to the lower electrode 16 and the upper electrode 14, in order to absorb this elongation, the rising portion of the piezoelectric film 10 changes its angle in the rising direction due to the action of the viscoelastic support 46. As a result, the piezoelectric film 10, which has a planar portion, moves upward.

[0263] Conversely, when the piezoelectric film 10 contracts along the planar direction by applying a driving voltage to the lower electrode 16 and the upper electrode 14, the rising portion of the piezoelectric film 10 changes its angle in the inclined direction (approaching the planar direction) to absorb the amount of contraction. As a result, the piezoelectric film 10, which has a planar portion, moves downward.

[0264] The piezoelectric loudspeaker 40 produces sound through the vibration of the piezoelectric diaphragm 10.

[0265] Furthermore, in the piezoelectric film 10 of the present invention, the conversion from stretching motion to vibration can also be achieved by maintaining the piezoelectric film 10 in a bent state.

[0266] Therefore, the piezoelectric thin film 10 of the present invention is not as... Figure 6 The piezoelectric loudspeaker 40 shown has a rigid, flat plate shape, but it can also function as a flexible piezoelectric loudspeaker simply by being held in a bent state.

[0267] The piezoelectric speaker utilizing this piezoelectric film 10 of the present invention exhibits good flexibility, and can be housed in a bag or the like, for example, by rolling or folding it. Therefore, according to the piezoelectric film 10 of the present invention, a portable piezoelectric speaker can be realized even at a certain size.

[0268] Furthermore, as described above, the piezoelectric film 10 of the present invention exhibits excellent flexibility and suppleness, and does not possess anisotropy of piezoelectric properties in-plane. Therefore, the sound quality of the piezoelectric film 10 of the present invention changes little regardless of which direction it is bent, and the sound quality change is also minimal with changes in curvature. Thus, the piezoelectric speaker utilizing the piezoelectric film 10 of the present invention offers a high degree of freedom in its placement, and, as described above, can be mounted on various items. For example, by mounting the piezoelectric film 10 of the present invention in a bent state onto clothing such as suits and carrying items such as bags, a so-called wearable speaker can be realized.

[0269] Furthermore, as described above, by attaching the piezoelectric film of the present invention to flexible display devices such as flexible organic EL display devices and flexible liquid crystal display devices, it can also be used as a speaker for display devices.

[0270] As described above, the piezoelectric thin film 10 of the present invention stretches and expands along the surface direction by the application of voltage, and vibrates appropriately along the thickness direction by the stretching and expansion in the surface direction. Therefore, when used, for example, in a piezoelectric loudspeaker, it exhibits good acoustic characteristics that enable it to output high sound pressure.

[0271] The piezoelectric film 10 of the present invention, which exhibits excellent acoustic properties—namely, high stretchability due to piezoelectricity—by stacking multiple layers, also functions well as a piezoelectric oscillator for vibrating vibrating bodies such as diaphragms. Because of its high durability, the piezoelectric film 10 of the present invention also exhibits high durability when stacked as a piezoelectric oscillator.

[0272] Additionally, when stacking the piezoelectric film 10, if there is no possibility of a short circuit, the piezoelectric film may not have an upper protective layer 18 and / or a lower protective layer 20. Alternatively, a piezoelectric film without an upper protective layer 18 and / or a lower protective layer 20 may be stacked via an insulating layer.

[0273] As an example, the laminate of the piezoelectric film 10 can be adhered to a diaphragm, thereby serving as a loudspeaker that outputs sound by vibrating the diaphragm through the laminate of the piezoelectric film 10. That is, in this case, the laminate of the piezoelectric film 10 is used as a so-called exciter that outputs sound by vibrating the diaphragm.

[0274] By applying a driving voltage to the stacked piezoelectric films 10, each piezoelectric film 10 stretches and contracts along its surface direction. Through the stretching and contraction of each piezoelectric film 10, the entire stack of piezoelectric films 10 stretches and contracts along its surface direction. Due to the stretching and contraction of the stack of piezoelectric films 10 in the surface direction, a vibrating plate to which the stack is attached flexes, resulting in vibration of the vibrating plate along its thickness direction. This vibration in the thickness direction generates sound. The vibrating plate vibrates according to the magnitude of the driving voltage applied to the piezoelectric films 10, producing sound corresponding to the applied driving voltage.

[0275] Therefore, at this time, the piezoelectric film 10 itself does not output sound.

[0276] Even if each individual piezoelectric film 10 has low rigidity and small stretching force, the rigidity is increased by stacking the piezoelectric films 10, and the stretching force is also increased as a whole. As a result, in the stack of piezoelectric films 10, even if the vibrating plate has a certain degree of rigidity, it can be fully flexed with a large force and vibrate fully along the thickness direction, thereby generating sound on the vibrating plate.

[0277] In the stack of piezoelectric films 10, there is no limit to the number of layers of piezoelectric films 10. For example, the number of layers can be appropriately set according to the rigidity of the vibrating plate to obtain a sufficient amount of vibration.

[0278] In addition, as long as there is sufficient stretching force, a single piezoelectric film 10 of the present invention can also be used as an exciter (piezoelectric vibrator).

[0279] The vibrating plate that vibrates from the stack of the piezoelectric thin film 10 of the present invention is not limited, and various sheet-like materials (plate-like materials, thin films) can be used.

[0280] Examples include resin films made of polyethylene terephthalate (PET), foamed plastics made of expanded polystyrene, paper materials such as corrugated cardboard, glass plates, and wood. Furthermore, as long as it can be sufficiently flexible, it can also be used as a vibrating plate in machines such as display devices.

[0281] The piezoelectric film 10 laminate is preferably bonded to adjacent piezoelectric films via an adhesive layer (adhesive). Furthermore, the piezoelectric film 10 laminate and the vibrating plate are also preferably bonded via an adhesive layer.

[0282] There are no limitations on the adhesive layer; any adhesive layer capable of bonding objects to each other can be used. Therefore, the adhesive layer can be made of either an adhesive or an adhesive agent. Preferably, it is an adhesive layer made of an adhesive agent that provides a solid and hard adhesive layer after bonding.

[0283] The same applies to the laminate formed by folding the strip of piezoelectric film 10 described later.

[0284] In the stack of piezoelectric thin films 10, there is no limitation on the polarization direction of each stacked piezoelectric thin film 10. Furthermore, as described above, the polarization direction of the piezoelectric thin film 10 of the present invention is the polarization direction in the thickness direction.

[0285] Therefore, in the stack of piezoelectric thin films 10, the polarization direction can be the same in all piezoelectric thin films 10, or there can be piezoelectric thin films with different polarization directions.

[0286] Here, in the stack of piezoelectric thin films 10, it is preferable that the piezoelectric thin films 10 are stacked in such a way that the polarization directions of adjacent piezoelectric thin films 10 are opposite to each other.

[0287] In the piezoelectric thin film 10, the polarity of the voltage applied to the piezoelectric layer 12 corresponds to the polarization direction. Therefore, regardless of whether the polarization direction is from the upper electrode 14 to the lower electrode 16 or from the lower electrode 16 to the upper electrode 14, the polarity of the upper electrode 14 and the polarity of the lower electrode 16 are set to be the same in all the stacked piezoelectric thin films 10.

[0288] Therefore, by making the polarization directions of adjacent piezoelectric films 10 opposite to each other, even if the thin film electrodes of adjacent piezoelectric films 10 are in contact with each other, the contacting thin film electrodes have the same polarity, so there is no need to worry about short circuits.

[0289] The stack of piezoelectric films 10 can also be configured as a structure in which multiple piezoelectric films 10 are stacked by folding the long strip of piezoelectric film 10 once or more, preferably multiple times.

[0290] The structure of stacking long strip piezoelectric films by folding 10 has the following advantages.

[0291] That is, in a laminate formed by stacking multiple slices of piezoelectric film 10, the upper electrode 14 and the lower electrode 16 of each piezoelectric film need to be connected to a driving power source. In contrast, in a structure where a long strip of piezoelectric film 10 is folded and stacked, the laminate can be formed by only one long strip of piezoelectric film 10. Furthermore, in a structure where a long strip of piezoelectric film 10 is folded and stacked, only one power source is needed to apply the driving voltage, and the electrode can be pulled out from the piezoelectric film 10 at a single point.

[0292] Furthermore, in the structure of folding and stacking long strip piezoelectric films 10, it is necessary to ensure that the polarization directions of adjacent piezoelectric films 10 are opposite to each other.

[0293] The piezoelectric thin film of the present invention has been described in detail above. However, the present invention is not limited to the above examples. Various improvements and modifications can be made without departing from the spirit of the present invention.

[0294] Example

[0295] The following are specific embodiments of the present invention to provide a more detailed description. Furthermore, the present invention is not limited to these embodiments; the materials, amounts, proportions, processing content, and processing steps shown in the following embodiments can be appropriately modified as long as they do not depart from the spirit of the present invention.

[0296] [Example 1]

[0297] pass Figures 2-4 The method shown was used to fabricate a piezoelectric thin film.

[0298] First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in dimethylformamide (DMF) in the following composition ratio. Then, PZT particles were added to the solution as piezoelectric particles in the following composition ratio, and the mixture was stirred using a propeller mixer (2000 rpm) to prepare coatings (coating A and coating B) for forming piezoelectric layers.

[0299] Paint A

[0300] ·PZT particles··········300 parts by mass

[0301] • Cyanoethylated PVA • 30 parts by weight

[0302] ·DMF············70 parts by weight

[0303] Paint B

[0304] ·PZT particles··········10 parts by mass

[0305] • Cyanoethylated PVA • 30 parts by weight

[0306] ·DMF············70 parts by weight

[0307] In addition, the PZT particles were made by wet mixing of powders of Pb oxide, Zr oxide and Ti oxide, which will become the main components, in a ball mill such that Zr = 0.52 moles and Ti = 0.48 moles relative to Pb = 1 mole. The mixed powder was then calcined at 800°C for 5 hours and then crushed.

[0308] On the other hand, a sheet-like material was prepared by vacuum evaporating a copper film with a thickness of 0.1 μm onto a PET film with a thickness of 4 μm. That is, in this example, the upper electrode and the lower electrode are copper vapor-deposited films with a thickness of 0.1 μm, and the upper protective layer and the lower protective layer are PET films with a thickness of 4 μm.

[0309] A pre-prepared coating material A for forming a piezoelectric layer was applied to the lower electrode (copper vapor-deposited thin film) of a sheet having a lower electrode and a lower protective layer using a sliding coating machine.

[0310] Next, the coating was dried and cured by heating and drying the object obtained by coating the sheet on a hot plate at 120°C to evaporate the DMF. Thus, a lower-side laminate was fabricated, consisting of a lower protective layer made of PET, a lower thin-film electrode made of copper, and a piezoelectric layer formed thereon.

[0311] Next, the lower piezoelectric layer was polarized along the thickness direction.

[0312] Thus, a lower-side laminate consisting of a lower protective layer, a lower electrode, and a lower-side piezoelectric layer, and having undergone polarization treatment of the lower-side piezoelectric layer, is formed.

[0313] On the other hand, except for using coating B, an upper-side piezoelectric layer is formed on the upper electrode (copper vapor-deposited thin film) of the sheet having an upper electrode and an upper protective layer in the same manner, and polarization treatment is performed. Thus, an upper-side laminate with an upper protective layer, an upper electrode, and an upper-side piezoelectric layer stacked together, and polarization treatment of the upper-side piezoelectric layer is formed.

[0314] The lower side stack, which has undergone piezoelectric layer polarization treatment, is stacked with the upper side stack in such a way that the lower side piezoelectric layer and the upper side piezoelectric layer are opposite each other.

[0315] The lower and upper piezoelectric layers were heat-pressed using a laminating apparatus at 120°C and 0.01 MPa to bond and adhere regions 10 and 1, thus creating the product described above. Figure 1 The piezoelectric thin film shown.

[0316] The thickness of the piezoelectric layer of the fabricated piezoelectric thin film is 96 μm.

[0317] Samples were cut from the fabricated piezoelectric thin film, and the area fraction of piezoelectric particles in regions 1 and 10 of the piezoelectric thin film was determined by the following method.

[0318] First, to observe the cross-section of the piezoelectric film, it was cut along the thickness direction. For the cutting, a Drukker Histo cutter with an 8mm blade width was mounted on a Leica Biosystems RM2265. The speed was set to controller scale 1, and the engagement distance was set to 0.25–1 μm to obtain the cross-section.

[0319] The cross section was observed using a SEM (Shipped Microscope, Hitachi High-Tech Corporation, SU8220).

[0320] The samples were made conductive by platinum vapor deposition, with the working distance set at 8 mm.

[0321] The observation conditions were SE (secondary-electron) image (Upper), accelerating voltage: 1.0kV. The clearest image was produced through focus adjustment and astigmatism adjustment. Automatic brightness adjustment (automatic brightness setting: 0, contrast setting: 0) was performed when the piezoelectric film became the entire image.

[0322] The magnification was set so that the upper and lower electrodes were within one frame, and the width between the two electrodes was more than half the frame width. Furthermore, the image was taken with the two electrodes horizontally aligned with the bottom of the image.

[0323] Image binarization was performed using the image analysis software ImageJ. The lower limit of Threshold was set to the maximum value of the uncolored protective layer, and the upper limit of Threshold was set to the maximum value of 255.

[0324] The area between the upper and lower electrodes that is colored is divided into 10 equal parts along the thickness direction.

[0325] In the region on the uppermost electrode side of the 10-divided area, the area ratio of PZT particles in the piezoelectric film was calculated by using the total area of ​​PZT particles as the numerator and the area of ​​the piezoelectric film as the denominator. Thus, the area ratio of PZT particles (piezoelectric particles) in the first region adjacent to the upper electrode was calculated. Furthermore, the area of ​​the piezoelectric film was calculated by setting the longitudinal (thickness direction) width to 1 / 10 of the distance between electrodes and the lateral width to the two ends of the SEM image.

[0326] Furthermore, in the region on the lower electrode side of the 10-divided area, the area ratio of PZT particles in the piezoelectric film was calculated by using the total area of ​​PZT particles as the numerator and the area of ​​the piezoelectric film as the denominator. Thus, the area ratio of PZT particles (piezoelectric particles) in the 10th region adjacent to the lower electrode was calculated. Similarly, the longitudinal (thickness direction) width was set to 1 / 10 of the distance between electrodes, and the lateral width was set to the two ends of the SEM image to calculate the area of ​​the piezoelectric film.

[0327] The area fraction of PZT particles in region 1 and region 10 was calculated at any 10 cross-sections of the fabricated piezoelectric thin film. The average area fraction of PZT particles in region 1 and region 10 of the 10 cross-sections was calculated. This average value was taken as the area fraction of PZT particles in region 1 and region 10 of the piezoelectric layer of the fabricated piezoelectric thin film.

[0328] As a result, the area fraction of PZT particles in region 1 was 2.8%, and the area fraction of PZT particles in region 10 was 75.9%.

[0329] In this example, the area fraction of PZT particles in region 1 (upper electrode side) is low.

[0330] Therefore, the ratio of PZT particle area ratios is calculated by dividing the area ratio of PZT particles in the 10th region (where the PZT particle area ratio is high) by the area ratio of PZT particles in the 1st region (where the PZT particle area ratio is low). The result is a ratio of 27.5. That is, when the area of ​​PZT particles in the 1st region (where the area ratio is low) is set to 1, the area of ​​PZT particles in the 10th region (where the area ratio is high) is 27.5.

[0331] Furthermore, the average surface area of ​​PZT particles is 39.3%.

[0332] [Examples 2-8, Examples 10-15, Examples 17-19, and Comparative Examples 1-5]

[0333] In the formation of the upper and lower side laminates, except for various changes to the coating thickness of the coating that forms the piezoelectric layer and the ratio of PZT particles to cyanoethylated PVA in coatings A and B, the upper and lower side laminates are formed in the same manner as in Example 1, thereby producing a piezoelectric film.

[0334] For the fabricated piezoelectric film, the area ratio of PZT particles in the first region and the area ratio of PZT particles in the tenth region were measured in the same manner as in Example 1, and the ratio of the area ratios of PZT particles and the average area ratio were calculated.

[0335] [Example 9]

[0336] Except for changing the ratio of PZT particles to cyanoethylated PVA in coating A and the coating thickness of coating A forming the piezoelectric layer, a laminate having a lower protective layer, a lower electrode, and a piezoelectric layer subjected to calendering and polarization treatment was produced in the same manner as the formation of the lower side laminate in Example 1. The ratio of PZT particles to cyanoethylated PVA in coating A was set to PZT particles: cyanoethylated PVA = 185:30 (parts by mass).

[0337] However, coating A is dried without using a 120°C heating plate, but rather by being placed at room temperature. That is, in this example, the drying time for the coating forming the piezoelectric layer is set to be longer than usual.

[0338] A sheet-like material with an upper electrode and an upper protective layer, identical to that in Example 1, was stacked on the fabricated laminate in such a manner that the upper electrode was positioned opposite the piezoelectric layer (see reference). Figure 5 ).

[0339] For the fabricated piezoelectric film, the area ratio of PZT particles in the first region and the area ratio of PZT particles in the tenth region were measured in the same manner as in Example 1, and the ratio of the area ratios of PZT particles and the average area ratio were calculated.

[0340] [Example 16]

[0341] The amount of DMF in coating A was changed to 210 parts by mass, thereby changing the coating thickness of coating A that forms the piezoelectric layer. Otherwise, a laminate having a lower protective layer, a lower electrode, and a piezoelectric layer subjected to calendering and polarization treatment was produced in the same manner as the lower side laminate in Example 1.

[0342] A sheet-like material with an upper electrode and an upper protective layer, identical to that in Example 1, was stacked on the fabricated laminate in such a manner that the upper electrode was positioned opposite the piezoelectric layer (see reference). Figure 5 ).

[0343] For the fabricated piezoelectric film, the area ratio of PZT particles in the first region and the area ratio of PZT particles in the tenth region were measured in the same manner as in Example 1, and the ratio of the area ratios of PZT particles and the average area ratio were calculated.

[0344] [Example 20]

[0345] Except that the coating thickness of coating A and coating B was set to 9:1 (9 for coating A), the piezoelectric film was prepared in the same manner as in Example 1.

[0346] For the fabricated piezoelectric film, the area ratio of PZT particles in the first region and the area ratio of PZT particles in the tenth region were measured in the same manner as in Example 1, and the ratio of the area ratios of PZT particles and the average area ratio were calculated.

[0347] [Construction of piezoelectric loudspeakers and measurement of sound pressure levels]

[0348] The piezoelectric film was used to make... Figure 6 The piezoelectric loudspeaker shown.

[0349] First, a rectangular test piece measuring 210 × 300 mm (A4 size) is cut from the fabricated piezoelectric film. For example... Figure 6As shown, after placing the cut piezoelectric film onto a 210×300mm outer shell pre-filled with glass wool as a viscoelastic support, the frame is used to press down the perimeter, applying appropriate tension and curvature to the piezoelectric film, thereby creating a structure as shown. Figure 6 The piezoelectric loudspeaker shown.

[0350] In addition, the depth of the outer shell is set to 9mm, and the density of the glass wool is set to 32kg / m³. 3 The thickness before assembly is set to 25mm. Furthermore, in all piezoelectric loudspeakers, the lower electrode side of the piezoelectric film is fabricated as the viscoelastic support side.

[0351] A 1kHz sine wave is input as the input signal to the fabricated piezoelectric loudspeaker through a power amplifier, such as... Figure 7 As shown, the sound pressure was measured using a microphone 50 placed 50 cm from the center of the speaker.

[0352] The sound pressure was measured twice: 30 seconds after the piezoelectric speaker started outputting (initial) and 36 hours after the piezoelectric speaker started outputting (after durability test). The initial sound pressure, the sound pressure after durability test, and the difference between the initial and durable sound pressures (deterioration) are shown in Table 1.

[0353] [Table 1]

[0354]

[0355] As shown in the table above, the piezoelectric layer is divided into 10 regions along the thickness direction. For the first region adjacent to the upper electrode and the tenth region adjacent to the lower electrode, the area ratio obtained by dividing the area ratio of the region with a high area ratio of PZT particles (piezoelectric particles) by the area ratio of the region with a low area ratio is 1.2 or higher. The piezoelectric film of the present invention exhibits excellent durability, with a small decrease in sound pressure relative to the initial sound pressure after the durability test.

[0356] Furthermore, as shown in Examples 5 and 6, the piezoelectric film of the present invention can achieve the same effect even when the area ratio of PZT particles in either the first or tenth region is low. Moreover, as shown in Table 1, as long as the piezoelectric film of the present invention has the same ratio of PZT particle area ratios, approximately the same effect can be obtained regardless of the thickness of the piezoelectric layer. Furthermore, by setting the average area ratio of PZT particles to 23% or more, a preferred initial sound pressure level exceeding 60 dB can be obtained.

[0357] In contrast, in comparative examples where the area ratio of PZT particles is less than 1.2, the decrease in sound pressure after the durability test relative to the initial sound pressure is greater.

[0358] The effects of the present invention can be clearly seen from the above results.

[0359] Symbol Explanation

[0360] 10-Piezoelectric thin film, 12-Piezoelectric layer, 12a-Region 1, 12b-Region 10, 12U-Upper side piezoelectric layer, 12L-Lower side piezoelectric layer, 14-Upper (thin film) electrode, 16-Lower (thin film) electrode, 18-Upper protective layer, 20-Lower protective layer, 24-Polymer matrix, 26-Piezoelectric particles, 34, 38-Sheets, 36U-Upper side laminate, 36L-Lower side laminate, 40-Piezoelectric speaker, 42-Shell, 46-Viscoelastic support, 48-Frame, 50-Microphone.

Claims

1. An electroacoustic transducer comprising a piezoelectric thin film having: Polymer composite piezoelectrics, wherein piezoelectric particles are contained within a matrix comprising polymer materials; and Electrode layers are disposed on both sides of the polymer composite piezoelectric body. The cross-section along the thickness direction was observed using a scanning electron microscope. The cross-section along the thickness direction of the polymer composite piezoelectric body was divided into 10 equal regions. In the two regions that were furthest apart, the area fraction of the piezoelectric particles in the cross-section along the thickness direction was measured. When the area fraction of the piezoelectric particles in the region with the low area fraction was set to 1, the area fraction of the piezoelectric particles in the region with the high area fraction was 1.2 or higher.

2. The electroacoustic converter according to claim 1, wherein, The average area ratio of the piezoelectric particles in one of the two farthest regions is more than 23% compared to that in the other region.

3. The electroacoustic converter according to claim 1 or 2, wherein, When the area ratio of the piezoelectric particles in the region with the lower area ratio among the two farthest regions is set to 1, the area ratio of the piezoelectric particles in the region with the higher area ratio is 70 or less.

4. The electroacoustic transducer according to claim 1 or 2, wherein it is polarized along the thickness direction.

5. The electroacoustic converter according to claim 1 or 2, wherein, Piezoelectric properties do not exhibit in-plane anisotropy.

6. The electroacoustic transducer according to claim 1 or 2, having leads for connecting the electrode layer and an external power source.

7. The electroacoustic transducer according to claim 1 or 2, having a protective layer stacked on the surface of at least one side of the electrode layer.

8. The electroacoustic converter according to claim 1 or 2, wherein, The polymer material contains cyanoethyl.

9. The electroacoustic converter according to claim 8, wherein, The polymer material is cyanoethylated polyvinyl alcohol.

10. The electroacoustic transducer according to claim 1 or 2, wherein, The piezoelectric particles are composed of ceramic particles with a perovskite or wurtzite crystal structure.

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