Stacked piezoelectric element

Abstract

The present application provides a laminated piezoelectric element capable of maintaining good piezoelectric properties while suppressing heat generation. A laminated piezoelectric element laminating a plurality of piezoelectric thin films, the piezoelectric thin film having: a piezoelectric layer composed of a polymer composite piezoelectric body containing piezoelectric body particles in a base containing a polymer material; and an electrode layer formed on both surfaces of the piezoelectric layer, wherein when a value obtained by dividing a capacitive reactance Xc of the piezoelectric thin film at a frequency of 1 kHz by an equivalent series resistance ESR is set to 1, a value XE obtained by dividing the capacitive reactance Xc at a frequency of 20 kHz by the equivalent series resistance ESR is 0.6 or more and 1.5 or less. 20 in the range of 0.6 to 1.5.

Description

Technical Field

[0001] This invention relates to a laminated piezoelectric element. Background Technology

[0002] To address the trend towards thinner displays such as LCDs and OLEDs, the speakers used in these thin displays also require lightweight and slim designs. Furthermore, in flexible displays, flexibility is also required for integration with the flexible display without compromising lightweightness and flexibility. As such a lightweight, thin, and flexible speaker, a sheet-like piezoelectric film with properties that expand and contract in response to the applied voltage is being considered.

[0003] Furthermore, it is also possible to create a flexible loudspeaker by attaching a flexible exciter to a flexible diaphragm. An exciter is an actuator that vibrates objects to produce sound by contacting them.

[0004] As such flexible sheet-like piezoelectric films or exciters, composite piezoelectric materials containing piezoelectric particles in the matrix have been proposed.

[0005] For example, Patent Document 1 describes a piezoelectric thin film having a polymer composite piezoelectric material formed by dispersing piezoelectric particles in a viscoelastic matrix made of a viscoelastic polymer material at room temperature, thin film electrodes formed on both sides of the polymer composite piezoelectric material, and a protective layer formed on the surface of the thin film electrodes.

[0006] Previous technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2014-014063 Summary of the Invention

[0009] The technical problem to be solved by the invention

[0010] In such piezoelectric films, if the electrode layer is too thick, the deformation (vibration) of the piezoelectric layer is hindered, thus reducing the output. Therefore, the electrode layer is formed very thin. However, according to the present inventors' investigation, if the electrode layer is thin, there is a problem of increased heat generation.

[0011] The objective of this invention is to provide a stacked piezoelectric element that can maintain good piezoelectric properties while suppressing heat generation by solving the problems of such prior art.

[0012] means for solving technical problems

[0013] To address this issue, the present invention has the following structure.

[0014] [1] A stacked piezoelectric element, comprising stacked multiple piezoelectric thin films, wherein the piezoelectric thin films have: a piezoelectric body layer composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix comprising a polymer material; and electrode layers formed on both sides of the piezoelectric body layer, wherein...

[0015] When the value obtained by dividing the capacitive reactance Xc of the piezoelectric film at 1 kHz by the equivalent series resistance ESR is set to 1, the value obtained by dividing the capacitive reactance Xc by the equivalent series resistance ESR at 20 kHz is XE. 20 It is in the range of 0.6 to 1.5.

[0016] [2] According to the laminated piezoelectric element described in [1], wherein,

[0017] Polymer materials exhibit viscoelasticity at room temperature.

[0018] [3] According to the laminated piezoelectric element described in [1] or [2], wherein,

[0019] XE 20 It is in the range of 0.8 to 1.3.

[0020] [4] A multilayer piezoelectric element according to any one of [1] to [3], wherein,

[0021] The thickness of the electrode layer is less than 1 μm.

[0022] [5] The laminated piezoelectric element according to any one of [1] to [4], wherein,

[0023] At least the piezoelectric film stacked on the outermost layer of the stacked piezoelectric element has a protective layer stacked on the side of the electrode layer opposite to the piezoelectric layer on the outermost side.

[0024] The protective layer has pores that extend from the surface to the electrode layer.

[0025] The stacked piezoelectric element has:

[0026] A conductive component is disposed within the hole;

[0027] A wire is disposed on the surface of the hole in the protective layer and is electrically connected to the electrode layer via a conductive component.

[0028] [6] According to the laminated piezoelectric element described in [5], wherein,

[0029] If we define the opening area of ​​the hole as A, the thickness of the electrode layer as t, and the electrostatic capacitance of the stacked piezoelectric element as F, then F / (A×t) is 260 μF / mm. 3 the following.

[0030] Invention Effects

[0031] According to this invention, a stacked piezoelectric element that can maintain good piezoelectric properties while suppressing heat generation can be provided. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating an example of a stacked piezoelectric element according to the present invention.

[0033] Figure 2 This is a schematic diagram illustrating an example of a piezoelectric thin film.

[0034] Figure 3 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0035] Figure 4 This is a schematic diagram illustrating an example of a method for fabricating a piezoelectric thin film.

[0036] Figure 5 This is a schematic diagram illustrating an example of a method for fabricating a piezoelectric thin film.

[0037] Figure 6 This is a schematic diagram illustrating an example of a method for fabricating a piezoelectric thin film.

[0038] Figure 7 This is a schematic diagram illustrating another example of the stacked piezoelectric element of the present invention.

[0039] Figure 8 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0040] Figure 9 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0041] Figure 10 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0042] Figure 11 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0043] Figure 12 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0044] Figure 13 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0045] Figure 14 It is a graph showing the relationship between frequency, capacitive reactance Xc, and equivalent series resistance ESR.

[0046] Figure 15 This is a top view schematically illustrating another example of the stacked piezoelectric element of the present invention.

[0047] Figure 16 yes Figure 15 Side view.

[0048] Figure 17 yes Figure 16 A partially enlarged view of the BB line cross section.

[0049] Figure 18 This is a partially enlarged view of another example of the stacked piezoelectric element of the present invention.

[0050] Figure 19 This is a partially enlarged view of another example of the piezoelectric thin film used in the stacked piezoelectric element of the present invention.

[0051] Figure 20 yes Figure 19 CC-line sectional view. Detailed Implementation

[0052] Hereinafter, the laminated piezoelectric element of the present invention will be described in detail with reference to the preferred embodiment shown in the figures.

[0053] The following description of the structural elements is based on a representative embodiment of the present invention, but the present invention is not limited to this embodiment.

[0054] In addition, in this specification, the numerical range indicated by “~” refers to the range including the values ​​recorded before and after “~” as the lower limit and upper limit values.

[0055] [Laminated piezoelectric elements]

[0056] The stacked piezoelectric element of the present invention is formed by stacking multiple piezoelectric thin films, wherein the piezoelectric thin films have: a piezoelectric body layer composed of a polymer composite piezoelectric body containing piezoelectric particles in a matrix comprising a polymer material; and electrode layers formed on both sides of the piezoelectric body layer, wherein...

[0057] When the value obtained by dividing the capacitive reactance Xc of the piezoelectric film at 1 kHz by the equivalent series resistance ESR is set to 1, the value obtained by dividing the capacitive reactance Xc by the equivalent series resistance ESR at 20 kHz is XE. 20 It is in the range of 0.6 to 1.5.

[0058] Figure 1 The image below schematically illustrates an example of a stacked piezoelectric element of the present invention.

[0059] Figure 1The stacked piezoelectric element 50 shown has the following structure: a first electrode layer 24 is provided on one side of the piezoelectric body layer 20, and three piezoelectric thin films 10, each having a second electrode layer 26, are stacked on the other side. Adjacent piezoelectric thin films are attached via an adhesive layer (attachment layer) 19. The structure of the piezoelectric thin films 10 will be described in detail later. Each piezoelectric thin film 10 is connected in parallel to a power source. That is, the first electrode layer 24 of each piezoelectric thin film 10 is electrically connected to one electrode of the power source via wiring, and the second electrode layer 26 of each piezoelectric thin film 10 is electrically connected to the other electrode of the power source via wiring.

[0060] in addition, Figure 1 Although the illustrations of the first protective layer 28 and the second protective layer 30 of each piezoelectric film 10 are omitted, each piezoelectric film 10 may have the first protective layer 28 and the second protective layer 30.

[0061] in addition, Figure 1 The piezoelectric element 50 shown is formed by stacking three piezoelectric thin films 10, but the present invention is not limited thereto. That is, if the piezoelectric element of the present invention is formed by stacking multiple piezoelectric thin films, the number of piezoelectric thin films can be two or more. The same applies to the piezoelectric elements described later.

[0062] and, Figure 1 The stacked piezoelectric elements 50 shown are preferably stacked as indicated by the arrows labeled on the piezoelectric layer 20, so that the polarization directions in adjacent piezoelectric films 10 are opposite to each other. However, the stacked piezoelectric elements 50 of the present invention are not limited to this, and the polarization directions in adjacent piezoelectric films 10 may be the same.

[0063] like Figure 1 As shown, the laminated piezoelectric element 50 can be used as an exciter for emitting sound from the diaphragm 12 by being bonded to it via the adhesive layer 16. In other words, the diaphragm 12 and the piezoelectric film 10 are fixed together by contact via the adhesive layer 16, and the piezoelectric film 10 functions as an exciter for emitting sound from the diaphragm 12.

[0064] The stacked piezoelectric element 50 consists of multiple stacked piezoelectric films 10. Therefore, even if each individual piezoelectric film 10 has low rigidity and small stretching force, the rigidity increases due to the stacking of the piezoelectric films 10, and the stretching force of the stacked piezoelectric element 50 also increases. As a result, even if the vibrating plate 12 has a certain degree of rigidity, the stacked piezoelectric element 50 can be fully flexed with a large force and vibrate fully along the thickness direction, thereby generating sound from the vibrating plate 12.

[0065] Furthermore, the thicker the piezoelectric layer 20, the greater the stretching force of the piezoelectric film, but correspondingly, the driving voltage required for the same amount of stretching also becomes larger. Here, as will be described later, in the piezoelectric film 10, the thickness of the piezoelectric layer 20 is preferably around 300 μm, even at its maximum, so that even if the voltage applied to each piezoelectric film is reduced, the piezoelectric film can be stretched sufficiently.

[0066] Each piezoelectric film 10 has a power source connected to its first electrode layer 24 and second electrode layer 26, which applies a driving voltage to cause the piezoelectric film 10 to stretch or contract.

[0067] There are no restrictions on the power supply; it can be either DC or AC. Furthermore, the driving voltage can be appropriately set according to the thickness of the piezoelectric layer 20 of each piezoelectric film and the forming material, so as to drive each piezoelectric film appropriately.

[0068] And, as Figure 1 As shown, it is preferable to connect to a power source so that the polarization direction of each piezoelectric film is the same as the polarity of the electrode layer in all piezoelectric films. This allows for the application of in-phase voltages to each piezoelectric film. That is, when a voltage is applied to the piezoelectric film, the stretching and contracting behaviors of all piezoelectric films are in phase. Therefore, the stretching and contraction of each piezoelectric film can be enhanced, and the deformation (output) of the piezoelectric film as a whole can be improved. In other words, high piezoelectric characteristics can be obtained.

[0069] In addition, in this invention, the polarization direction of the piezoelectric thin film can be detected by means of a d33 meter or the like.

[0070] Alternatively, the polarization direction of the piezoelectric layer 20 can be determined from the corona polarization treatment conditions described above.

[0071] [Piezoelectric film]

[0072] Figure 2 An example of a piezoelectric thin film is schematically shown in cross-sectional view.

[0073] like Figure 2 As shown, the piezoelectric thin film 10 has: a piezoelectric layer 20, a sheet having piezoelectric properties; a first electrode layer 24, stacked on one surface of the piezoelectric layer 20; a first protective layer 28, stacked on the first electrode layer 24; a second electrode layer 26, stacked on the other surface of the piezoelectric layer 20; and a second protective layer 30, stacked on the second electrode layer 26.

[0074] The piezoelectric layer 20 is composed of a polymer composite piezoelectric material containing piezoelectric particles 36 in a matrix 34 containing polymer material. Furthermore, the first electrode layer 24 and the second electrode layer 26 are the electrode layers of this invention.

[0075] Although described later, as a preferred embodiment, the piezoelectric thin film 10 (piezoelectric layer 20) is polarized in the thickness direction.

[0076] As an example, such a piezoelectric film 10 can be used in various audio devices (audio equipment) such as pickups used in loudspeakers, microphones and musical instruments such as guitars, to generate (reproduce) sound based on vibrations corresponding to electrical signals or to convert sound-based vibrations into electrical signals.

[0077] In addition, piezoelectric films can also be used in pressure sensors and power generation components.

[0078] Alternatively, piezoelectric films can also be used as exciters (energizers) to make objects vibrate and produce sound by being mounted on various object bases.

[0079] In the piezoelectric thin film 10, the second electrode layer 26 and the first electrode layer 24 form an electrode pair. That is, the piezoelectric thin film 10 has the following structure: the two sides of the piezoelectric body layer 20 are sandwiched by the electrode pair, namely the first electrode layer 24 and the second electrode layer 26, and the laminate is sandwiched by the first protective layer 28 and the second protective layer 30.

[0080] Thus, in the piezoelectric film 10, the area sandwiched between the first electrode layer 24 and the second electrode layer 26 expands and contracts according to the applied voltage.

[0081] Furthermore, the first electrode layer 24, the first protective layer 28, the second electrode layer 26, and the second protective layer 30 are named according to the polarization direction of the piezoelectric layer 20. Therefore, the first electrode layer 24 and the second electrode layer 26, as well as the first protective layer 28 and the second protective layer 30, have substantially the same structure.

[0082] In addition to these layers, the piezoelectric film 10 may have, for example, an insulating layer or the like that has an exposed area of ​​the piezoelectric layer 20 covering the sides to prevent short circuits.

[0083] If a voltage is applied to the first electrode layer 24 and the second electrode layer 26 having these piezoelectric thin films 10, the piezoelectric particles 36 expand and contract in the polarization direction according to the applied voltage. As a result, the piezoelectric thin film 10 (piezoelectric layer 20) contracts in the thickness direction. At the same time, due to Pascal's ratio, the piezoelectric thin film 10 also expands and contracts in the in-plane direction. This expansion and contraction is about 0.01 to 0.1%. In addition, in the in-plane direction, it expands and contracts isotropically in all directions.

[0084] The thickness of the piezoelectric layer 20 is preferably about 10 to 300 μm. Therefore, the maximum stretching in the thickness direction is only about 0.3 μm, which is very small.

[0085] In contrast, the piezoelectric film 10, i.e., the piezoelectric layer 20, has a dimension slightly larger than its thickness in the planar direction. Therefore, for example, if the length of the piezoelectric film 10 is 20 cm, the piezoelectric film 10 can only stretch or contract by a maximum of about 0.2 mm when a voltage is applied.

[0086] Furthermore, if pressure is applied to the piezoelectric film 10, electricity is generated through the action of the piezoelectric particles 36.

[0087] By utilizing this point, the piezoelectric film 10 can be used for various applications such as loudspeakers, microphones, and pressure sensors, as described above.

[0088] In this invention, when the value obtained by dividing the capacitive reactance Xc of the piezoelectric film 10 at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value XE obtained by dividing Xc by the equivalent series resistance ESR at a frequency of 20 kHz is... 20 It is in the range of 0.6 to 1.5.

[0089] Regarding this aspect, use Figure 3 Please provide an explanation.

[0090] Figure 3 This is a graph schematically representing the frequency characteristics of the capacitive reactance Xc and equivalent series resistance ESR of the piezoelectric film 10.

[0091] The structure of a piezoelectric layer sandwiched between electrodes, which serves as the dielectric, is represented by an equivalent circuit, similar to that of a condenser, by a series connection of an electrostatic capacitor, an equivalent series inductance, and an equivalent series resistance. Here, in the audible range (20Hz to 20kHz) utilized by the piezoelectric film of the present invention, there is no contribution to the equivalent series inductance; therefore, the piezoelectric film 10 can be represented by an equivalent circuit of a series connection of an electrostatic capacitor C and an equivalent series resistance ESR.

[0092] In such an equivalent circuit, the capacitive reactance Xc = 1 / (2π×f×C) of the electrostatic capacitor C is inversely proportional to the frequency f of the power supply. Therefore, as Figure 3 As shown, if the frequency increases, the capacitive reactance Xc decreases. This capacitive reactance Xc is the ratio of voltage to current when driving the piezoelectric layer.

[0093] On the other hand, the equivalent series resistance (ESR) corresponds to the heat generated by the resistive component. The ESR is caused by the resistive components of the piezoelectric layer and the electrode layer, among others. It is believed that the heat generated from the piezoelectric layer manifests as frictional heat when the piezoelectric particles within the layer induce domain action. It is also believed that in such a piezoelectric layer, if the frequency of the power supply increases, the frequency associated with domain action disappears, thus reducing the frictional heat generated by domain action.

[0094] Furthermore, the resistance component of the electrode layer is almost constant and independent of frequency. Therefore, as... Figure 3 As shown, the equivalent series resistance ESR decreases as the frequency increases, and becomes almost constant after a certain frequency.

[0095] From the perspective of suppressing the heating of the piezoelectric layer, reducing the equivalent series resistance (ESR) is sufficient.

[0096] Here, in piezoelectric materials, the more active the domain action, the higher the piezoelectric performance. That is, piezoelectric materials with high piezoelectric performance tend to generate more heat. Therefore, it is difficult to suppress the heat generated from the piezoelectric layer without sacrificing piezoelectric performance. Consequently, it is difficult to reduce the equivalent series resistance (ESR) in the low-frequency region where the contribution of the piezoelectric layer is significant.

[0097] On the other hand, in the high-frequency region (10kHz to 20kHz), the contribution of the piezoelectric layer becomes relatively smaller, while the contribution of resistive components such as the electrode layer becomes larger.

[0098] Therefore, the equivalent series resistance (ESR) changes due to factors such as the size of the piezoelectric film. On the other hand, the capacitive reactance (Xc) also depends on factors such as the size of the piezoelectric film. Therefore, by evaluating the ratio of the equivalent series resistance (ESR) to the capacitive reactance (Xc), the resistive component that excludes the influence of size can be evaluated.

[0099] In this invention, when the value XE1 obtained by dividing the capacitive reactance Xc of the piezoelectric film at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value XE1 obtained by dividing Xc by ESR at a frequency of 20 kHz is... 20 It is in the range of 0.6 to 1.5. That is, by using the value XE at a frequency of 20kHz. 20 By setting XE1 to a value close to that at 1 kHz, the ratio of the energy generated at 20 kHz to the energy utilized by the piezoelectric effect in the input energy is set to a value close to that at 1 kHz. This allows for the maintenance of good piezoelectric characteristics while suppressing heat generation.

[0100] The current flowing at 20kHz is the greatest within the audio band, therefore in XE 20 When the value is less than 0.6, the heat generation becomes larger and the situation is the worst, and there is a risk of thermal runaway.

[0101] On the other hand, in the value XE 20 In cases exceeding 1.5, for example, if the electrode layer is very thick, the ESR at 30kHz decreases, but the ESR at 20kHz remains almost unchanged, thus it is considered that there is no real benefit to the audio band below 20kHz.

[0102] Considering the above viewpoints, XE 20 Preferably, it is in the range of 0.6 to 1.5, more preferably in the range of 0.8 to 1.3, and even more preferably in the range of 1.0 to 1.1.

[0103] The capacitive reactance Xc and equivalent series resistance ESR can be measured, for example, with frequency variations using an Agilent 4294A impedance analyzer.

[0104] In order to make XE 20 Within the aforementioned range, reducing the resistance of the electrode layer is preferable. Methods for suppressing the resistance of the electrode layer include, for example, increasing the thickness of the electrode layer, shortening the path of current flow, using a material with low volume resistivity as the electrode layer material, and controlling the film quality of the electrode layer. Furthermore, as with the stacked piezoelectric element of the present invention, when multiple piezoelectric films are stacked, connecting multiple piezoelectric films in parallel can also reduce the overall resistance of the piezoelectric element. Moreover, combining multiple of these methods can also improve the resistance of XE. 20 Assume it falls within the aforementioned range.

[0105] Here, as mentioned, if the electrode layer is too thick, the deformation (vibration) of the piezoelectric layer is hindered, thus reducing the output (piezoelectric characteristics). Therefore, the electrode layer is preferably thickened to a degree that does not reduce the piezoelectric characteristics, but it is difficult to improve XE simply by adjusting the thickness. 20 The above range is set. Furthermore, the path length through which the current flows can be adjusted by designing the connection positions of the electrodes and the wiring from the power source; however, depending on the size of the piezoelectric film, it is difficult to shorten it sufficiently, and it is difficult to achieve XE by simply adjusting the path length. 20 Assume it falls within the aforementioned range.

[0106] Therefore, it is preferable to combine multiple of the above methods to achieve XE 20 Set to the range mentioned above.

[0107] <Piezoelectric layer>

[0108] The piezoelectric layer is a layer composed of a polymer composite piezoelectric material containing piezoelectric particles in a matrix containing polymer materials, and is a layer that exhibits a piezoelectric effect of stretching and contracting by applying a voltage.

[0109] In the piezoelectric film 10, preferably, the piezoelectric layer 20 is composed of a polymer composite piezoelectric material in which piezoelectric particles 36 are dispersed in a matrix 34 made of a viscoelastic polymer material at room temperature. Furthermore, in this specification, "room temperature" refers to a temperature range of approximately 0 to 50°C.

[0110] The polymer composite piezoelectric (piezoelectric layer 20) preferably has the following components.

[0111] (i) flexibility

[0112] For example, when documents like newspapers or magazines are held in a slightly bent state for carrying purposes, they are subjected to relatively slow but large bending deformations of a few Hz or less from the outside. If the polymer composite piezoelectric material is stiff, it will generate a correspondingly large bending stress, causing cracks at the interface between the polymer matrix and the piezoelectric particles, potentially leading to damage. Therefore, the polymer composite piezoelectric material is required to have appropriate flexibility. Furthermore, if the strain energy can be diffused outwards as heat, the stress can be relieved. Therefore, the polymer composite piezoelectric material is required to have a moderately large loss tangent.

[0113] In summary, the flexible polymer composite piezoelectric element used as an exciter is required to exhibit rigidity relative to vibrations in the 20Hz–20kHz range and flexibility relative to vibrations below a few Hz. Furthermore, the loss tangent of the polymer composite piezoelectric element is required to be moderately large relative to vibrations at all frequencies below 20kHz.

[0114] Furthermore, it is preferable to stack the layers according to the rigidity (hardness, stiffness, elastic constant) of the material to which the adhesive is applied (vibrating plate), so that the spring constant can be easily adjusted. In this case, the thinner the adhesive layer, the higher the energy efficiency.

[0115] Typically, polymeric solids exhibit a viscoelastic relaxation mechanism. With increasing temperature or decreasing frequency, large-scale molecular motion is observed as a decrease in the storage elastic modulus (Young's modulus) (relaxation) or a maxima in the loss elastic modulus (absorption). Among these, the relaxation caused by the micro-Brownian motion of molecular chains through amorphous regions is called principal dispersion, where very large relaxation phenomena can be observed. The temperature at which this principal dispersion occurs is the glass transition point (Tg), where the viscoelastic relaxation mechanism is most clearly manifested.

[0116] In the polymer composite piezoelectric (piezoelectric layer 20), by using a polymer material with a glass transition point at room temperature—in other words, a polymer material that is viscoelastic at room temperature—in 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, considering factors such as the preferred realization of this operation, it is preferable to use a polymer material with a glass transition point at room temperature (0–50°C) at a frequency of 1 Hz in the matrix of the polymer composite piezoelectric material.

[0117] As a viscoelastic polymer material at room temperature, various known materials can be used. Preferably, a polymer material with a maximum loss tangent Tanδ of 0.5 or higher at a frequency of 1 Hz, obtained based on dynamic viscoelasticity tests, is used at room temperature, i.e., 0–50°C.

[0118] Therefore, when a polymer composite piezoelectric is slowly bent by an external force, the pressure concentration at the interface between the polymer matrix and the piezoelectric particles in the part of maximum bending torque is relaxed, and high flexibility can be expected.

[0119] Furthermore, the preferred polymeric material exhibiting viscoelasticity at room temperature is one with a storage elastic coefficient (E') at a frequency of 1 Hz, obtained based on dynamic viscoelasticity measurements, that is 100 MPa or higher at 0°C and 10 MPa or lower at 50°C.

[0120] 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.

[0121] Furthermore, in viscoelastic polymer materials at room temperature, a relative permittivity of 10 or higher at 25°C is preferred. 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.

[0122] However, on the other hand, considering the need to ensure good moisture resistance, the relative permittivity of the polymer material at 25°C is preferably 10 or less.

[0123] Examples of viscoelastic polymers that meet these conditions at room temperature include cyanoethylated polyvinyl alcohol (cyanoethylated PVA), polyvinyl acetate, polyvinylidene chloride acrylonitrile, polystyrene-vinyl polyisoprene block copolymer, polyvinyl methyl ketone, and polybutyl methacrylate. Furthermore, commercially available products such as HYBRAR5127 (manufactured by KURARAY CO.,LTD) can also be appropriately used as these polymers. Among these, materials containing cyanoethyl groups are preferred, and cyanoethylated PVA is particularly preferred.

[0124] In addition, these polymer materials can be used in single or multiple ways.

[0125] The matrix 34, which uses these viscoelastic polymers at room temperature, can be combined with a variety of polymers as needed.

[0126] That is, in the matrix 34, in order to adjust dielectric or mechanical properties, other dielectric polymer materials may be added as needed, in addition to viscoelastic materials such as cyanoethylated PVA.

[0127] 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 hydroxyamylopectin; cyanoethyl cyanoacrylate; 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.

[0128] Among them, polymeric materials containing cyanoethyl groups are preferably utilized.

[0129] Furthermore, in the matrix 34 of the piezoelectric layer 20, the dielectric polymer added is not limited to one type, except for materials such as cyanoethylated PVA that have viscoelasticity at room temperature; multiple types can also be added.

[0130] In addition to dielectric polymers, 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 also be added to the matrix 34 for the purpose of adjusting the glass transition point Tg.

[0131] In addition, tackifiers such as rosin esters, rosin, terpenes, terpene phenols, and petroleum resins can be added to improve adhesion.

[0132] There is no particular limitation on the amount of materials other than viscoelastic polymers such as cyanoethylated PVA added to the matrix 34 of the piezoelectric layer 20, but it is preferred to set the proportion in the matrix 34 to 30% by mass or less.

[0133] Therefore, the properties of the added polymer material can be manifested without damaging the viscoelastic relief mechanism in the matrix 34, thus achieving preferred results in terms of high dielectric constant, improved heat resistance, and improved adhesion to the piezoelectric particles 36 and the electrode layer.

[0134] The piezoelectric particles 36 are composed of ceramic particles with perovskite or wurtzite crystalline structures.

[0135] Examples of ceramic particles constituting piezoelectric particles 36 include lead zirconate titanate (PZT), lanthanum lead zirconate titanate (PLZT), barium titanate (BaTiO3), zinc oxide (ZnO), and solid solutions of barium titanate and bismuth ferrite (BiFe3) (BFBT).

[0136] The particle size of these piezoelectric particles 36 is not limited, and can be appropriately selected according to the size of the piezoelectric film 10 and its application. The particle size of the piezoelectric particles 36 is preferably 1 to 10 μm.

[0137] By setting the particle size of the piezoelectric particles 36 within this range, optimal results can be obtained in the piezoelectric film 10, which can take into account both high voltage characteristics and flexibility.

[0138] In addition, Figure 2 In the piezoelectric layer 20, the piezoelectric particles 36 are uniformly and regularly dispersed in the substrate 34, but the present invention is not limited thereto.

[0139] That is, the piezoelectric particles 36 in the piezoelectric layer 20 are preferably uniformly dispersed, but they can also be irregularly dispersed in the substrate 34.

[0140] In the piezoelectric thin film 10, the ratio of the substrate 34 to the piezoelectric particles 36 in the piezoelectric layer 20 is not limited and can be appropriately set according to the size and thickness of the piezoelectric thin film 10 in the surface direction, the application of the piezoelectric thin film 10, and the required characteristics of the piezoelectric thin film 10.

[0141] The volume fraction of piezoelectric particles 36 in the piezoelectric layer 20 is preferably 30-80%, more preferably 50% or more, and even more preferably 50-80%.

[0142] By setting the ratio of the substrate 34 to the piezoelectric particles 36 within the above-mentioned range, an optimal result can be obtained that balances high voltage characteristics and flexibility.

[0143] In the piezoelectric thin film 10 described above, preferably, the piezoelectric layer 20 is a viscoelastic composite piezoelectric layer formed by dispersing piezoelectric particles in a polymer matrix, wherein the polymer matrix contains a viscoelastic polymer material at room temperature. However, the present invention is not limited thereto; as the piezoelectric layer, a polymer composite piezoelectric layer formed by dispersing piezoelectric particles in a matrix containing a polymer material, as used in known piezoelectric elements, can be utilized.

[0144] In the piezoelectric film 10, the thickness of the piezoelectric body layer 20 is not particularly limited, and can be appropriately set according to the application of the piezoelectric film 10, the number of layers of the piezoelectric film 10 in the piezoelectric element described later, and the required characteristics of the piezoelectric film 10.

[0145] The thicker the piezoelectric layer 20, the more advantageous it is in terms of rigidity, such as the stiffness of the sheet. However, the voltage (potential difference) required to make the piezoelectric film 10 expand and contract by the same amount increases.

[0146] The thickness of the piezoelectric layer 20 is preferably 10 to 300 μm, more preferably 20 to 200 μm, and even more preferably 30 to 150 μm.

[0147] By setting the thickness of the piezoelectric layer 20 within the aforementioned range, a preferred result can be obtained while ensuring rigidity and appropriate flexibility.

[0148] <Protective Layer>

[0149] In the piezoelectric film 10, the first protective layer 28 and the second protective layer 30 cover the second electrode layer 26 and the first electrode layer 24, respectively, and serve to impart appropriate rigidity and mechanical strength to the piezoelectric layer 20. That is, in the piezoelectric film 10, the piezoelectric layer 20, composed of the substrate 34 and piezoelectric particles 36, exhibits excellent flexibility to slow bending deformation, but its rigidity or mechanical strength may be insufficient depending on the application. The piezoelectric film 10 provides the first protective layer 28 and the second protective layer 30 to compensate for these deficiencies.

[0150] The first protective layer 28 and the second protective layer 30 are not limited and can be made of various sheet materials. For example, various resin films are preferably exemplified.

[0151] Among them, resin films composed of polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polycarbonate (PC), polyphenylene sulfide (PPS), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyimide (PI), polyethylene naphthalate (PEN), triacetyl cellulose (TAC), and cyclic olefin resins are preferred due to their excellent mechanical properties and heat resistance.

[0152] There is no limitation on the thickness of the first protective layer 28 and the second protective layer 30. Furthermore, the thickness of the first protective layer 28 and the second protective layer 30 can be basically the same, but they can also be different.

[0153] If the rigidity of the first protective layer 28 and the second protective layer 30 is too high, it will not only restrict the expansion and contraction of the piezoelectric layer 20, but also impair its flexibility. Therefore, unless mechanical strength or good operability as a sheet is required, it is more advantageous for the first protective layer 28 and the second protective layer 30 to be as thin as possible.

[0154] In the piezoelectric film 10, if the thickness of the first protective layer 28 and the second protective layer 30 is less than twice the thickness of the piezoelectric layer 20, then a preferred result can be obtained in terms of balancing rigidity and appropriate flexibility.

[0155] For example, when the thickness of the electrode layer 20 is 50 μm and the first protective layer 28 and the second protective layer 30 are made of PET, the thickness of the first protective layer 28 and the second protective layer 30 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0156] <Electrode layer>

[0157] In the piezoelectric film 10, a first electrode layer 24 is formed between the piezoelectric body layer 20 and the first protective layer 28, and a second electrode layer 26 is formed between the piezoelectric body layer 20 and the second protective layer 30. The first electrode layer 24 and the second electrode layer 26 are provided for applying a voltage to the piezoelectric body layer 20 (piezoelectric film 10).

[0158] In this invention, the materials used to form the first electrode layer 24 and the second electrode layer 26 are not limited, and various conductors can be used. Specifically, examples include metals such as carbon, palladium, iron, tin, aluminum, nickel, platinum, gold, silver, copper, titanium, chromium, and molybdenum, alloys of these metals, laminates and composites of these metals and alloys, and indium tin oxide. Among these, the aforementioned XE... 20 From the perspective of the above-mentioned range, copper, aluminum, gold, silver, platinum and indium tin oxide are preferably examples of materials used as the first electrode layer 24 and the second electrode layer 26.

[0159] Furthermore, there are no restrictions on the method of forming the first electrode layer 24 and the second electrode layer 26. Various known methods can be used, such as vapor deposition (vacuum film formation) based on vacuum evaporation, ion-assisted evaporation and sputtering, or methods of depositing films or attaching foils formed from the above materials.

[0160] Here, even when the same material is used as the electrode layer, the resistance varies depending on the quality of the electrode layer (metal film). For example, if there are many grain boundaries and pores in the film, the resistance increases. Therefore, it is preferable to adjust the quality of the electrode layer by controlling the electrode layer formation method and formation conditions.

[0161] For the sake of forming films with good quality and low resistivity, ion-assisted evaporation and sputtering are preferred methods for film formation. Thin films grown by vapor-phase deposition methods such as sputtering and evaporation typically form columnar structures, but their resistivity depends on the grain boundary density per unit area; therefore, it is ideal to have columnar structures composed of coarse grains. For example, in the case of sputtering, increasing the substrate temperature as much as possible promotes surface diffusion, and decreasing the gas pressure as much as possible to extend the mean free motion process suppresses projective effects, thereby producing a dense columnar structure with few voids and large grain diameters. Furthermore, injecting high-speed charged particles, such as ion-assisted particles, into the substrate is also effective in promoting surface diffusion.

[0162] There is no limitation on the thickness of the first electrode layer 24 and the second electrode layer 26. Furthermore, the thickness of the first electrode layer 24 and the second electrode layer 26 can be substantially the same, but they can also be different.

[0163] Similar to the first protective layer 28 and the second protective layer 30, if the rigidity of the first electrode layer 24 and the second electrode layer 26 is too high, it will not only restrict the expansion and contraction of the piezoelectric layer 20, but also impair its flexibility. Therefore, from the viewpoint of flexibility and piezoelectric properties, it is more advantageous for the first electrode layer 24 and the second electrode layer 26 to be thinner. On the other hand, if the first electrode layer 24 and the second electrode layer 26 are too thin, the resistance will be high, making it difficult to meet the aforementioned XE. 20 The range.

[0164] From the above perspectives, the thickness of the first electrode layer 24 and the second electrode layer 26 is preferably 3 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. Furthermore, the thickness of the first electrode layer 24 and the second electrode layer 26 is 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more.

[0165] Furthermore, the wiring from the power source is connected to the first electrode layer 24 and the second electrode layer 26. However, from the viewpoint of shortening the path length of the current flow, for example, when the planar shape of the piezoelectric film is rectangular, it is preferable to place the connection points between the first electrode layer 24 and the wiring, and the connection points between the second electrode layer 26 and the wiring, on the long side. It is also preferable to connect each electrode layer and the wiring at multiple points.

[0166] As described above, the piezoelectric film 10 preferably has the following structure: a piezoelectric layer 20 formed by dispersing piezoelectric particles 36 in a matrix 34 containing a viscoelastic polymer material at room temperature, sandwiched by a first electrode layer 24 and a second electrode layer 26, and further sandwiched by a first protective layer 28 and a second protective layer 30.

[0167] These piezoelectric films 10 preferably have a maximum value of loss tangent (Tanδ) at a frequency of 1 Hz, obtained based on dynamic viscoelasticity measurements, at room temperature, and more preferably have a maximum value of 0.1 or higher at room temperature.

[0168] Therefore, even if the piezoelectric film 10 is subjected to relatively slow and large bending deformation of less than a few Hz from the outside, the strain energy can be effectively diffused to the outside as heat, thus preventing cracking at the interface between the polymer matrix and the piezoelectric particles.

[0169] Regarding the piezoelectric film 10, the storage elastic coefficient (E') at a frequency of 1 Hz, obtained based on dynamic viscoelasticity measurements, is preferably 10–30 GPa at 0 °C and 1–10 GPa at 50 °C.

[0170] Therefore, the piezoelectric thin film 10 at room temperature can have a large frequency dispersion in its storage elastic modulus (E'). That is, it can exhibit rigidity relative to vibrations of 20 Hz to 20 kHz and flexibility relative to vibrations below a few Hz.

[0171] Furthermore, regarding the piezoelectric film 10, the product of its thickness and the storage elastic coefficient (E') at a frequency of 1 Hz, obtained based on dynamic viscoelasticity measurements, 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.

[0172] Thus, the piezoelectric film 10 can possess appropriate rigidity and mechanical strength without compromising flexibility and acoustic properties.

[0173] Furthermore, regarding the piezoelectric film 10, in the master curve obtained by dynamic viscoelastic measurement, the loss tangent (Tanδ) at 25°C and 1kHz is preferably 0.05 or higher.

[0174] As a result, the frequency response of the loudspeaker using the piezoelectric film 10 becomes smooth, and the change in sound quality when the lowest resonant frequency f0 changes with the curvature of the loudspeaker is also reduced.

[0175] The following is for reference. Figures 4-6 An example of a method for manufacturing the piezoelectric thin film 10 will be described.

[0176] First, such as Figure 4 As shown, a sheet 10a is prepared to have a first electrode layer 24 formed on the first protective layer 28. The sheet 10a can be fabricated by forming a copper thin film or the like on the surface of the first protective layer 28 through vacuum evaporation, sputtering, or plating, thus serving as the first electrode layer 24.

[0177] When the first protective layer 28 is very thin and has poor operability, a first protective layer 28 with a partition (temporary support) can be used as needed. Alternatively, a partition made of PET or similar material with a thickness of 25 μm to 100 μm can be used. The partition can be removed after hot-pressing the second electrode layer 26 and the second protective layer 30 and before any components are stacked on the first protective layer 28.

[0178] On the other hand, a polymer material that is dissolved in an organic solvent to become a matrix is ​​then added with piezoelectric particles such as PZT particles 36 and stirred to prepare a dispersed coating.

[0179] There are no restrictions on the use of organic solvents other than those mentioned above; a variety of organic solvents can be used.

[0180] When sheet 10a is prepared and coating is prepared, the coating is cast onto sheet 10a, and the organic solvent is evaporated and dried. Thus, as... Figure 5 As shown, a laminate 10b is fabricated having a first electrode layer 24 on a first protective layer 28 and a piezoelectric layer 20 formed on the first electrode layer 24. Note that the first electrode layer 24 refers to the electrode on the substrate side when the piezoelectric layer 20 is coated, and does not indicate the vertical positional relationship within the laminate.

[0181] There are no restrictions on the casting method of this coating; all known methods (coating devices) such as sliding coating machines and doctor blades can be used.

[0182] As mentioned above, in the piezoelectric film 10, in addition to viscoelastic materials such as cyanoethylated PVA, dielectric polymer materials can also be added to the substrate 34.

[0183] When adding these polymer materials to the matrix 34, the polymer materials added to the coating described above can be dissolved.

[0184] After fabricating a laminate 10b having a first electrode layer 24 on the first protective layer 28 and a piezoelectric layer 20 formed on the first electrode layer 24, it is preferable to perform a polarization treatment (polling) on ​​the piezoelectric layer 20.

[0185] There are no restrictions on the method of polarization treatment of the piezoelectric layer 20, and known methods can be used.

[0186] Alternatively, prior to this polarization treatment, a calendering process can be performed to smooth the surface of the piezoelectric layer 20 using a heated roller or similar material. This calendering process allows for the smooth execution of the hot pressing process described later.

[0187] While performing the polarization treatment of the piezoelectric layer 20 of the laminate 10b, a sheet 10c on which the second electrode layer 26 is formed is prepared. The sheet 10c can be fabricated by forming a copper thin film or the like on the surface of the second protective layer 30 through vacuum evaporation, sputtering, or plating to serve as the second electrode layer 26.

[0188] Next, as Figure 6 As shown, the sheet 10c is stacked on the laminate 10b after the polarization treatment of the piezoelectric layer 20 by aligning the second electrode layer 26 with the piezoelectric layer 20.

[0189] Furthermore, by clamping the second protective layer 30 and the first protective layer 28, the laminate of the laminate 10b and the sheet 10c is hot-pressed together by a hot press or a heating roller, and then cut into the desired shape to produce the piezoelectric film 10.

[0190] Alternatively, the current process can also be carried out without sheets, using components wound in a mesh-like, or sheet-like, state for an extended period, while being transported. Both the laminate 10b and the sheet 10c are mesh-like, and can be heat-pressed as described above. In this case, the piezoelectric film 10 is formed into a mesh at this point.

[0191] Furthermore, a special paste layer can be provided when bonding the laminate 10b and the sheet 10c. For example, a paste layer can be provided on the surface of the second electrode layer 26 of the sheet 10c. The most preferred paste layer is made of the same material as the substrate 34. Bonding can also be performed by coating the same material on the surface of the second electrode layer 26.

[0192] [Another way to stack piezoelectric elements]

[0193] Here, in Figure 1 In the example shown, the stacked piezoelectric element 50 is a structure formed by stacking multiple piezoelectric thin films 10 (hereinafter also referred to as a monolithic stacked piezoelectric element), but the stacked piezoelectric element of the present invention is not limited to this and various structures can be used.

[0194] Figure 7 One example is shown below. Additionally, Figure 7 The stacked piezoelectric element 56 shown uses multiple components that are the same as those in the stacked piezoelectric element 50 described above. Therefore, the same symbols are marked on the same components to indicate that the main differences are in the parts.

[0195] Figure 7 The stacked piezoelectric element 56 shown is constructed by stacking multiple piezoelectric films in a layered manner, using strips of piezoelectric film 10L that are folded back more than once (preferably multiple times) along their length. Furthermore, compared with the above-described... Figure 1 Similarly, the stacked piezoelectric element 50 shown also Figure 7 The piezoelectric element 56 shown is also preferably attached to the piezoelectric film stacked by folding through the adhesive layer 19.

[0196] A single piezoelectric film 10L, which is a strip with polarization in the thickness direction, is stacked by folding it back. The polarization direction of the piezoelectric film in the portion adjacent (opposite) to the stacking direction is as follows: Figure 7 The direction indicated by the arrow is the opposite direction.

[0197] in addition, Figure 7 Although the illustrations of the first protective layer 28 and the second protective layer 30 of the piezoelectric film 10L are omitted, the piezoelectric film 10L may have the first protective layer 28 and the second protective layer 30.

[0198] According to this structure, a stacked piezoelectric element 56 can be formed by a single long strip of piezoelectric film 10L, and only one power supply PS is needed for applying the driving voltage, and the electrode lead-out from the piezoelectric film 10L can also be at one point.

[0199] Therefore, according to Figure 7 The stacked piezoelectric element 56 shown can reduce the number of parts and simplify the structure, improve the reliability as a piezoelectric element (module), and thus reduce costs.

[0200] However, folding back such a long strip of piezoelectric film 10L (hereinafter also referred to as a basal piezoelectric element) easily leads to a longer path length for current flow, and, like a monolithic stacked piezoelectric element, it is impossible to connect multiple piezoelectric films in parallel. Therefore, from satisfying the above-mentioned XE 20 From the perspective of the range, monolithic stacked piezoelectric elements are preferred.

[0201] like Figure 7 In the piezoelectric element 56 shown, in the piezoelectric element 56 of the folded-back elongated piezoelectric film 10L, it is preferable that the core rod 58 is incorporated into the folded-back portion of the piezoelectric film 10L where it abuts against the piezoelectric film 10L.

[0202] As described above, the first electrode layer 24 and the second electrode layer 26 of the piezoelectric thin film 10L are formed from a metal vapor-deposited film or the like. If the metal vapor-deposited film is bent at an acute angle, cracks (fissures) are likely to occur, and this may lead to electrode breakage. That is, in Figure 7 In the piezoelectric element 56 shown, cracks are prone to appear on the electrode on the inner side of the bent portion.

[0203] In contrast, in the piezoelectric element 56 of the folded-back piezoelectric film 10L, by inserting the core rod 58 into the folded portion of the piezoelectric film 10L, it is possible to prevent the first electrode layer 24 and the second electrode layer 26 from being bent, and to properly prevent wire breakage.

[0204] <Adhesive Layer>

[0205] There are no limitations on the adhesive layers 19 for attaching the piezoelectric films 10 to each other and the adhesive layers 16 for attaching the laminated piezoelectric elements 50 to the vibrating plate 12; various known adhesives and bonding agents can be used.

[0206] As long as the adhesive layer can adhere the components to each other, various known adhesive layers can be used.

[0207] Therefore, the adhesive layer can be a layer composed of an adhesive that is fluid when bonded and then becomes solid, or a layer composed of a soft, solid adhesive that is gel-like (rubber-like) when bonded and then remains gel-like, or a layer composed of a material that has the characteristics of both an adhesive and a bonding agent.

[0208] Here, regarding the stacked piezoelectric element 50 of the present invention, sound is generated by stretching and contracting the stacked piezoelectric films 10, for example, by vibrating the vibrating plate 12. Therefore, it is preferable to directly transmit the stretching and contraction of each piezoelectric film 10. If there is a viscous substance, such as a relaxation vibration, between the piezoelectric films 10, the energy transmission efficiency of the stretching and contraction of the piezoelectric films 10 will decrease, thereby reducing the driving efficiency of the piezoelectric films 10.

[0209] With this in mind, the adhesive layer is preferably an adhesive layer composed of an adhesive that provides a solid and relatively hard adhesive layer, rather than an adhesive layer composed of a binder. As a more preferred adhesive layer, specifically, an adhesion layer composed of thermoplastic adhesives such as polyester adhesives and styrene-butadiene rubber (SBR) adhesives is preferably exemplified.

[0210] Adhesion differs from bonding and is useful when high bonding temperatures are required. Furthermore, thermoplastic adhesives combine "relatively low temperature, short time, and strong adhesion," making them a preferred choice.

[0211] There is no limit to the thickness of the adhesive layer. Depending on the material used to form the adhesive layer, the thickness can be appropriately set to ensure sufficient adhesion (bonding force, adhesive strength).

[0212] Regarding the laminated piezoelectric element 50 of the present invention, a thinner adhesive layer improves the transmission effect of the stretching energy (vibrational energy) of the piezoelectric layer 20, thereby increasing energy efficiency. However, if the adhesive layer is thick and has high rigidity, it may restrict the stretching of the piezoelectric film. Furthermore, as... Figure 1 As shown, when adjacent piezoelectric films 10 are stacked with opposite polarization directions, adjacent piezoelectric films 10 will not short-circuit with each other, thus making the adhesive layer thinner.

[0213] With this in mind, the adhesive layer is preferably thinner than the piezoelectric layer 20. That is, in the laminated piezoelectric element 50 of the present invention, the adhesive layer is preferably rigid and thin.

[0214] Specifically, regarding the thickness of the adhesive layer, the thickness after attachment is preferably 0.1 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 0.1 to 10 μm.

[0215] In the laminated piezoelectric element 50 of the present invention, if the elastic constant of the adhesive layer is high, it may restrict the expansion and contraction of the piezoelectric film 10. Therefore, the elastic constant of the adhesive layer is preferably equal to or less than the elastic constant of the piezoelectric film 10. Furthermore, the elastic constant is defined as "thickness × Young's modulus".

[0216] Specifically, the product of the adhesive layer thickness and the storage elastic coefficient (E') at 1 Hz, obtained based on dynamic viscoelasticity measurements, is 2.0 × 10⁻⁶ at 0°C. 6 For values ​​below N / m, 1.0 × 10⁻⁶ is preferred at 50°C. 6 Below N / m.

[0217] Furthermore, regarding the frequency loss within 1 Hz of the adhesive layer obtained based on dynamic viscoelasticity measurements, in the case of an adhesive layer composed of an adhesive, it is 1.0 or less at 25°C, and in the case of an adhesive layer composed of an adhesive agent, it is preferably 0.1 or less at 25°C.

[0218] <Vibrating Plate>

[0219] There are no limitations on the vibrating plate 12; various items can be used.

[0220] As an example of the vibrating plate 12, examples include resin boards and glass boards, advertising and notification media such as billboards, office equipment and furniture such as tables, whiteboards and projection screens, display elements such as organic light-emitting diode (OLED) displays and liquid crystal displays, vehicle parts such as consoles, A-pillars, canopies and bumpers, and building materials such as walls of houses.

[0221] The vibrating plate 12 to which the stacked piezoelectric element 50 of the present invention is attached is preferably flexible, and more preferably can be rolled up.

[0222] The flexible vibrating plate 12 is preferably exemplified by a flexible display panel or similar panel-shaped display device. Furthermore, the display device is more preferably rollable.

[0223] Here, when the vibrating plate 12 is wound, it is preferable that the stacked piezoelectric element 50 also bends along with the vibrating plate 12 according to the curvature of the winding of the vibrating plate 12, so as to prevent the stacked piezoelectric element 50 from peeling off from the vibrating plate 12. In addition, the piezoelectric film 10 has suitable flexibility, so the stacked piezoelectric element 50 of the present invention also exhibits good flexibility.

[0224] At this point, the curvature of the winding of the vibrating plate 12 is basically a fixed curvature, but the curvature of the winding of the vibrating plate 12 can also be variable.

[0225] In this invention, when the display device is configured as a vibrating plate 12, the stacked piezoelectric element 50 is preferably attached to the back side of the display device, that is, the non-image display side of the display device.

[0226] At this time, the dimensions of the adhesive layer 16 in the planar direction are preferably the same as or less than the dimensions of the planar shape of the stacked piezoelectric element 50.

[0227] In addition, when using a display device as the vibrating plate 12, the display device itself, such as a flexible display panel, can be used as the vibrating plate 12, or a plate-shaped component that is attached to the display device or the display device can be used as the vibrating plate 12.

[0228] When the vibrating plate 12 can be wound, it is preferable to energize the piezoelectric film 10 with a driving current when the vibrating plate 12 is not wound, and when the vibrating plate 12 is wound, it is preferable to keep the piezoelectric film 10 unenergized.

[0229] Furthermore, when the vibrating plate 12 is electrically driven as in a display device, it is preferable to energize the piezoelectric film 10 and / or the vibrating plate 12 without winding the vibrating plate 12, and when winding the vibrating plate 12, it is preferable to keep the piezoelectric film 10 and / or the vibrating plate 12 unenergized.

[0230] These methods for switching between energized and de-energized states can utilize various well-known techniques.

[0231] From the viewpoint of improving sound quality over a wide frequency band, the planar shape of the stacked piezoelectric element is preferably rectangular (see reference). Figure 15 Furthermore, by setting the planar shape of the stacked piezoelectric element to rectangular, and by making the length of the long side W2 longer without changing the length of the short side W1, the sound pressure level can be increased further under the same applied voltage. Therefore, the voltage required to obtain the same sound pressure level can be further reduced, and heat generation can be suppressed.

[0232] Figure 15 The image shows a top view of an example of a rectangular stacked piezoelectric element. Figure 16 The image shows the view from the short side. Figure 15 Side view. Figure 16 The diagram of the adhesive layer and the electrode lead-out portion is omitted. Figure 15 and Figure 16 The example shown is an example of a laminate made by repeatedly folding back a long strip of piezoelectric film 10L. Figure 15 and Figure 16 In the example shown, the directions of multiple folds back become the short side directions.

[0233] In addition, Figure 15 and Figure 16 In the example shown, the layers are folded back in such a way that the lengths of the short sides of the overlapping areas become the same, but only the ends of the outermost layers are formed with protrusions 60 that protrude from the overlapping portions. Figure 15 As shown, electrode protrusions (62, 64) are respectively provided near both ends of the protrusion 60 in the length direction.

[0234] By setting the planar shape of the stacked piezoelectric element to a rectangular shape, the length of the long side W2 is made longer without changing the length of the short side W1, thereby combining the heat-suppressing structure with the stacked piezoelectric element of the present invention described above.

[0235] From the viewpoint of maintaining sound pressure while suppressing heat generation, the ratio of the length of the long side W2 to the length of the short side W1 is preferably 3 to 30, more preferably 3 to 20, and even more preferably 3 to 10.

[0236] Here, in rectangular laminated piezoelectric elements, where the short sides are of the same length but the long sides are of different lengths, the manufacturing process can be simplified by fabricating a laminate of piezoelectric films with longer long sides, followed by cutting as needed. For example, by fabricating a laminate of piezoelectric films with a long side of 46cm × a short side of 3cm and cutting it 20cm from one of the short sides, it is possible to fabricate laminated piezoelectric elements with a long side of 20cm × a short side of 3cm and laminated piezoelectric elements with a long side of 26cm × a short side of 3cm.

[0237] like Figure 16 The image shows a partial enlarged cross-section of the BB line when a piezoelectric film 10L, folded back multiple times, is cut parallel to the paper as a laminate. Figure 17 middle.

[0238] If the 10L piezoelectric film is cut after lamination, such as Figure 17 As shown, the ends of the short sides of each layer of the piezoelectric film 10L are deformed in the same direction. In the example shown, the ends of each layer are deformed in the downward direction. Thus, the cut ends of each layer are deformed in the same direction, thereby preventing short circuits caused by contact between the electrode layers. Furthermore, an adhesive layer 19 is provided between each layer, thus the adhesive layer acts as an insulator, further preventing short circuits caused by contact between the electrode layers.

[0239] Furthermore, in this invention, after cutting the long strip of piezoelectric film 10L, the repeatedly cut piezoelectric film 10L can also be folded back and stacked. In this case, as... Figure 18 As shown, the ends of the short sides of each layer of the piezoelectric film 10L are deformed in the opposite direction to the adjacent layers. In the structure of stacking piezoelectric films 10L by folding back and forth multiple times, the electrode layers opposite each other of the adjacent layers are connected, so there is no problem even if they come into contact. It is difficult to come into contact with electrode layers of different polarities, thus preventing short circuits.

[0240] In this invention, the connection method between the electrode layer, which is a piezoelectric thin film, and the wiring is not particularly limited, and various known methods can be used. For example, if the electrode layer and the protective layer have convex protrusions on the outside of the piezoelectric layer in the surface direction, the wiring can be connected to the electrode layer at these protrusions. Alternatively, as... Figure 19 and Figure 20 The example shown removes the protective layer (in) Figure 20 A hole 70 is formed in a portion of the second protective layer 30, and a conductive component 72, such as silver paste, is disposed on the hole 70 to conduct electricity between the conductive component 72 and the electrode layer (in Figure 20 The middle part is the second electrode layer 26), and the wiring (wire 74a) can also be connected to the electrode layer (second electrode layer 26) via the conductive component 72.

[0241] When the stacked piezoelectric element is a monolithic type, it is preferable to provide a protective layer on the electrode layer disposed on the outermost side of the piezoelectric film of at least the outermost layer of the stacked piezoelectric element. Alternatively, all piezoelectric films of a monolithic stacked piezoelectric element may also have a protective layer.

[0242] In the stacked piezoelectric element of the present invention, in at least one piezoelectric film, the protective layer has a hole extending from the surface to the electrode layer, and a conductive member is disposed (filled) within the hole. In the case where the wire (wiring) is electrically connected to the electrode layer via the conductive member, if the opening area of ​​the hole is set to A, the thickness of the electrode layer is set to t, and the electrostatic capacitance of the stacked piezoelectric element is set to C, then C / (A×t) is preferably 260 μF / mm². 3 the following.

[0243] In a structure where a hole is provided in the protective layer, a conductive component is disposed in the hole, and a wire is connected to the electrode layer via the conductive component, all the current applied to the laminated piezoelectric element flows through the conductive component. Therefore, due to the current concentration, heat is more easily generated at the contact point between the conductive component and the conductive component of the electrode layer (hereinafter also referred to as the electrode contact). As a result, when the laminated piezoelectric element is continuously driven, the temperature of the laminated piezoelectric element may become too high.

[0244] In contrast, by setting C / (A×t) to 260 μF / mm 3 The following is an explanation of how reducing the electrostatic capacitance of a laminated piezoelectric element and / or increasing the volume of the electrode layer in the electrode contact portion can reduce the current density in the electrode contact portion and suppress local heating in the electrode contact portion.

[0245] From the viewpoint of suppressing heat generation, C / (A×t) is more preferably 260 μF / mm. 3 Hereinafter, 150 μF / mm is further preferred. 3 Below. On the other hand, from a productivity point of view, C / (A×t) is preferably 50 μF / mm. 3 above.

[0246] Here, the electrostatic capacitance C of the stacked piezoelectric element can be measured using an LCR meter (e.g., NF Corporation ZM2372) between the wirings leading from each electrode layer of the piezoelectric film constituting the stacked piezoelectric element. The measurement is performed at a measurement frequency of 1 kHz and a voltage of 5 V.

[0247] In addition, when the stacked piezoelectric element is a single piece, the electrostatic capacitance C of the stacked piezoelectric element can be measured when the two electrode layers of each piezoelectric film are connected to each other with the same polarity, that is, when multiple piezoelectric films are connected in parallel.

[0248] Furthermore, the electrostatic capacitance C of the piezoelectric film is determined based on the thickness of the piezoelectric layer, the area of ​​the piezoelectric layer, and the relative permittivity of the piezoelectric layer. Therefore, by adjusting these factors, the electrostatic capacitance C of the piezoelectric film can be adjusted.

[0249] Furthermore, the opening area A (area in planar view) of the hole can be measured using a CNC image measuring machine (such as the Quick Vision machine manufactured by Mitutoyo Corporation) to measure the area of ​​the protective layer exposed after removing the wire. Conductive components can be removed even when the outline of the hole is not visible. In this case, it is necessary to choose a method that will not damage the protective layer.

[0250] From the perspective of reducing C / (A×t), a larger opening area A is preferable for the hole. On the other hand, if the opening area A is too large, it will be detrimental to productivity.

[0251] Furthermore, the shape of the opening of the hole (its shape in planar view) is not limited, and it can be made into various shapes such as round, oval, rectangular, polygonal, and irregular. From the viewpoint of ease of formation, a round shape is preferred.

[0252] There are no limitations on the method for forming the hole; it can be performed using known methods depending on the material used to form the protective layer. Examples of methods for forming the hole include laser processing, solvent dissolution and removal, and mechanical processing such as mechanical grinding.

[0253] Regarding the thickness of the electrode layer, it can be measured by observing the cross-section using SEM (such as Hitachi High-Tech Corporation SU8220) after cutting the piezoelectric film using an ultrathin slicer (such as Leica UC6).

[0254] As conductive components, conductive pastes such as silver paste, solder, conductive cloth, metal cloth, and conductive polyurethane foam can be used.

[0255] As a conductive paste, materials using silver, copper, gold, carbon, nickel, solder, etc., as fillers can be used. The conductive paste is then filled into the hole using a dispenser or similar device. Preferably, a sufficient amount of conductive paste is filled to completely fill the hole. More preferably, the amount of conductive paste filling the hole or the amount overflowing from the hole is filled.

[0256] Conductive fabric can be, for example, woven or non-woven fabric made of threads coated with a metal film on the surface of threads made of electroplating resin. Various known conductive fabrics can be used as conductive fabrics. Examples of conductive fabrics include those made of PET with Cu or Ni electroplating on the surface. Specifically, SEIREN Co., Ltd.'s Sui-10-511M can be used as a conductive fabric.

[0257] Metallic fabric is either woven or non-woven fabric woven with metallic threads. Various known metallic fabrics can be used as metallic fabrics. For example, Okutani Ltd.'s flat woven wire mesh with a diameter of Φ0.05×200m / s can be used as metallic fabric.

[0258] Conductive polyurethane foam is a flexible polyurethane foam in which conductive particles such as carbon black are loaded. Various known conductive polyurethane foams can be used as conductive polyurethane foams.

[0259] Furthermore, the thickness of the conductive component is preferably greater than the thickness of the protective layer. This ensures a reliable connection between the conductive component and the wire.

[0260] As a conductor, a sheet-like material (metal foil) or a wire-like material (metal wire) formed of a conductive metal can be used. Examples of preferred conductor materials include copper, aluminum, nickel, tin, gold, and silver. Furthermore, FFC cables can be used as conductors.

[0261] There are no particular restrictions on the shape and size of the wire. The shape and size of the wire should be such that it can be electrically connected to the conductive parts and can be used as a protruding electrode.

[0262] Furthermore, the connection between the wire and the conductive component can be performed using known methods. When the conductive component is a conductive paste, the wire can be connected to the conductive component by allowing the paste to cure after contact with the wire. Alternatively, with the wire in contact with the conductive component, at least a portion of the contact area can be covered by attaching an adhesive layer to the protective layer, thereby connecting the wire to the component. Alternatively, with the wire in contact with the conductive component, attaching the wire to the protective layer can also secure the connection between the wire and the conductive component.

[0263] The stacked piezoelectric element of the present invention has been described in detail above. However, the present invention is not limited to the above examples. Various modifications and changes can be made without departing from the spirit of the present invention.

[0264] Example

[0265] The following are specific embodiments of the present invention to provide a more detailed description. However, the present invention is not limited to these embodiments; the materials, amounts, proportions, processing contents, 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.

[0266] [Example 1]

[0267] Sheets 10a and 10c were prepared by sputtering a copper film with a thickness of 100 nm onto a PET film with a thickness of 4 μm. That is, in this example, the first electrode layer 24 and the second electrode layer 26 are copper films with a thickness of 100 nm, and the first protective layer 28 and the second protective layer 30 are PET films with a thickness of 4 μm.

[0268] The gas pressure for sputtering the copper thin film onto the PET film was set to 0.4 Pa, and the substrate temperature (the temperature of the PET film) was set to 120°C. In the column of the electrode layer formation method in Table 1 below, the case where sputtering is performed under the same conditions as in Example 1 is indicated as "Sputtering 1".

[0269] In addition, in order to obtain good operability, the PET film uses a film with a thickness of 50μm as a separator (temporary support PET). After the sheet is heat-pressed at 10c, the separators of each protective layer are removed.

[0270] First, cyanoethylated PVA (manufactured by CR-V Shin-Etsu Chemical Co., Ltd.) was dissolved in methyl ethyl ketone (MEK) at the following composition ratio. Then, PZT particles were added to the solution at the following composition ratio, and the mixture was dispersed using a propeller mixer (2000 rpm) to prepare a coating for forming the piezoelectric layer 20.

[0271] ·PZT particles··········300 parts by mass

[0272] • Cyanoethylated PVA • 15 parts by weight

[0273] ·MEK············85 parts by weight

[0274] In addition, the PZT particles were made by sintering commercially available PZT raw material powder at 1000-1200℃, followed by crushing and grading to make them particles with an average particle size of 5μm.

[0275] A pre-prepared coating material for forming the piezoelectric layer 20 was applied to the first electrode layer 24 (copper thin film) of the pre-prepared sheet 10a using a sliding coating machine. Furthermore, the coating was applied such that the dried film thickness was 20 μm.

[0276] Next, the substance coated on the sheet 10a is heated and dried on a heating plate at 120°C, thereby causing MEK to evaporate and forming a laminate 10b.

[0277] On the laminate 10b, a sheet 10c is laminated with the second electrode layer 26 (copper thin film side) facing the piezoelectric layer 20, and then hot-pressed at 120°C.

[0278] Thus, a piezoelectric thin film 10 having a first protective layer 28, a first electrode layer 24, a piezoelectric layer 20, a second electrode layer 26 and a second protective layer 30 in sequence was produced.

[0279] The fabricated piezoelectric film was cut into planar dimensions of 200mm × 190mm, and folded back four times along its length to create a basal piezoelectric element 56. The folded surfaces that came into contact were then bonded together using a thermal bonding sheet (FB-ML4 manufactured by NITTO SHINKO CORPORATION).

[0280] Furthermore, on one end of the long side of the folded-back piezoelectric film, the first electrode layer 24 is connected to the wiring as described below, and on the other end, the second electrode layer 26 is connected to the wiring.

[0281] The first and second protective layers were each processed using a laser processing machine to form holes. The opening shape of the holes was set to be circular, and the opening area was set to 60mm². 2 As conductive components, a conductive paste containing Ni filler is used, and 35μm thick copper foil is used for wiring (wires). After filling the holes with the conductive paste using a dispenser, the wiring is brought into contact, and the conductive paste is dried to cure.

[0282] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 8 In the middle. By Figure 8It can be seen that the capacitive reactance Xc at 1kHz is 148Ω, and the equivalent series resistance ESR is 12.2Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 12.1. On the other hand, the capacitive reactance Xc at 20kHz is 8.29Ω, and the equivalent series resistance ESR is 0.77Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 10.8. Let Xc / ESR at 20kHz, where Xc / ESR is 1 at 1kHz, be XE. 20 It is 0.89.

[0283] Furthermore, the electrostatic capacitance between the wiring connected to the first electrode layer 24 of the fabricated piezoelectric element and the wiring connected to the second electrode layer 26 was measured using an LCR meter (e.g., NF Corporation ZM2372), and the result was 1.2 μF. Therefore, the electrostatic capacitance C divided by the opening area A of the hole and the thickness t of the electrode layer, C / (A×t), is 200.0 μF / mm. 3 .

[0284] [Example 2]

[0285] The thickness of the first electrode layer 24 and the second electrode layer 26 (copper thin film) was set to 150 nm. Otherwise, the piezoelectric thin film was fabricated in the same manner as in Example 1.

[0286] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 9 In the middle. By Figure 9 It can be seen that the capacitive reactance Xc at 1kHz is 149Ω, and the equivalent series resistance ESR is 12.3Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 12.1. On the other hand, the capacitive reactance Xc at 20kHz is 8.32Ω, and the equivalent series resistance ESR is 0.58Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 14.3. Let Xc / ESR at 20kHz, where Xc / ESR is 1 at 1kHz, be XE. 20 It is 1.18.

[0287] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance-to-weight ratio (C / (A×t)) is 133.3 μF / mm². 3 .

[0288] [Example 3]

[0289] The piezoelectric film 10 prepared in Example 1 was cut into 5 pieces with a planar size of 200mm × 38mm. The 5 pieces of piezoelectric film 10 were stacked to make a monolithic piezoelectric element 50. Adjacent piezoelectric films 10 were bonded to each other using a thermal bonding sheet (NITTOSHINKO CORPORATION FB-ML4).

[0290] Furthermore, a first electrode layer 24 and wiring are connected to one side of the 200mm edge of each piezoelectric film 10 in the width direction, and a second electrode layer 26 and wiring are connected to the other side. That is, the first electrode layer 24 and wiring, and the second electrode layer 26 and wiring of each piezoelectric film 10 are connected at two locations respectively. Moreover, the piezoelectric films 10 are connected in parallel.

[0291] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 10 In the middle. By Figure 10 It can be seen that the capacitive reactance Xc at 1kHz is 150Ω, and the equivalent series resistance ESR is 12.1Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 12.1. On the other hand, the capacitive reactance Xc at 20kHz is 8.37Ω, and the equivalent series resistance ESR is 0.70Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 12.0. Let Xc / ESR at 20kHz, where Xc / ESR is 1 at 1kHz, be XE. 20 It is 0.99.

[0292] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 200.0 μF / mm². 3 .

[0293] [Example 4]

[0294] A copper thin film was formed by ion-assisted evaporation with a thickness of 150 nm. Otherwise, a monolithic piezoelectric element 50 was fabricated in the same manner as in Example 3.

[0295] The ion gun used for ion-assisted deposition of copper thin film onto PET film was the ST55 (1500W, 7A, 225eV) manufactured by TELEMARK.

[0296] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 11 In the middle. By Figure 11It can be seen that the capacitive reactance Xc at 1kHz is 148Ω, and the equivalent series resistance ESR is 12.1Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 12.2. On the other hand, the capacitive reactance Xc at 20kHz is 8.28Ω, and the equivalent series resistance ESR is 0.73Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 11.4. Let Xc / ESR at 20kHz, where Xc / ESR is 1 at 1kHz, be XE. 20 It is 0.93.

[0297] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance-to-weight ratio (C / (A×t)) is 133.3 μF / mm². 3 .

[0298] [Example 5]

[0299] The opening area A of the hole is set to 40mm. 2 In addition, a basal piezoelectric element was fabricated in the same manner as in Example 2.

[0300] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. At 1 kHz, the capacitive reactance Xc was 147 Ω, and the equivalent series resistance ESR was 12.9 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 11.4. On the other hand, at 20 kHz, the capacitive reactance Xc was 8.36 Ω, and the equivalent series resistance ESR was 0.68 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 12.3. Let Xc / ESR at 20 kHz, where Xc / ESR is 1 at 1 kHz, be XE. 20 It is 1.08.

[0301] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 200.0 μF / mm². 3 .

[0302] [Example 6]

[0303] The thickness of the first electrode layer 24 and the second electrode layer 26 (copper thin film) is set to 300 nm, and the opening area A of the hole is set to 20 mm. 2 In addition, a piezoelectric thin film was prepared in the same manner as in Example 1.

[0304] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. At 1 kHz, the capacitive reactance Xc was 145 Ω, and the equivalent series resistance ESR was 10.2 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 14.2. On the other hand, at 20 kHz, the capacitive reactance Xc was 8.44 Ω, and the equivalent series resistance ESR was 0.49 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 17.2. Let Xc / ESR at 20 kHz, where Xc / ESR is 1 at 1 kHz, be XE. 20 It is 1.21.

[0305] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 200.0 μF / mm². 3 .

[0306] [Example 7]

[0307] The opening area A of the hole is set to 30mm. 2 In addition, a piezoelectric thin film was prepared in the same manner as in Example 6.

[0308] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. At 1 kHz, the capacitive reactance Xc was 145 Ω, and the equivalent series resistance ESR was 10.0 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 14.5. On the other hand, at 20 kHz, the capacitive reactance Xc was 8.43 Ω, and the equivalent series resistance ESR was 0.44 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 19.2. Let Xc / ESR at 20 kHz, where Xc / ESR is 1 at 1 kHz, be XE. 20 It is 1.33.

[0309] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance-to-weight ratio (C / (A×t)) is 133.3 μF / mm². 3 .

[0310] [Example 8]

[0311] The opening area A of the hole is set to 15mm. 2 In addition, a piezoelectric thin film was prepared in the same manner as in Example 6.

[0312] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. At 1 kHz, the capacitive reactance Xc was 146 Ω, and the equivalent series resistance ESR was 10.4 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 14.0. On the other hand, at 20 kHz, the capacitive reactance Xc was 8.46 Ω, and the equivalent series resistance ESR was 0.54 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 15.7. Let Xc / ESR at 20 kHz, where Xc / ESR is 1 at 1 kHz, be XE. 20 It is 1.12.

[0313] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 266.6 μF / mm². 3 .

[0314] [Comparative Example 1]

[0315] A copper thin film was formed by vacuum evaporation, and a ceviche-type piezoelectric element was fabricated in the same manner as in Example 1.

[0316] When vacuum evaporating copper thin film onto PET film, the evaporation source is set to resistance heating, the substrate temperature is set to 50℃, and the gas pressure is set to 5×10. -3 Pa.

[0317] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 12 In the middle. By Figure 12 It can be seen that the capacitive reactance Xc at 1kHz is 151Ω, and the equivalent series resistance ESR is 11.8Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 12.8. On the other hand, the capacitive reactance Xc at 20kHz is 8.33Ω, and the equivalent series resistance ESR is 1.25Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 6.7. Let Xc / ESR at 20kHz be XE when Xc / ESR is 1 at 1kHz. 20 It is 0.52.

[0318] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 200.0 μF / mm². 3 .

[0319] [Comparative Example 2]

[0320] The gas pressure for sputtering the copper thin film onto the PET film was set to 1.2 Pa, and the substrate temperature (PET film temperature) was set to 60°C. Otherwise, a basal piezoelectric element was fabricated in the same manner as in Example 1. In the column for the method of forming the electrode layer in Table 1 below, the case where sputtering was performed under the same conditions as Comparative Example 2 is indicated as "Sputtering 2".

[0321] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 13 In the middle. By Figure 13 It can be seen that the capacitive reactance Xc at 1kHz is 152Ω, and the equivalent series resistance ESR is 11.6Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 13.1. On the other hand, the capacitive reactance Xc at 20kHz is 8.34Ω, and the equivalent series resistance ESR is 1.15Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 7.25. Let Xc / ESR at 20kHz, where Xc / ESR is 1 at 1kHz, be XE. 20 It is 0.55.

[0322] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 200.0 μF / mm². 3 .

[0323] [Comparative Example 3]

[0324] The piezoelectric film prepared in Example 1 was cut into planar dimensions of 200mm × 380mm and folded back 9 times along its length to create a basal piezoelectric element 56. The folded surfaces that came into contact were bonded together using a thermal adhesive sheet (NITTO SHINKO CORPORATION FB-ML4).

[0325] Furthermore, the first electrode layer 24 is connected to wiring at one end of the long side of the folded-back piezoelectric film, and the second electrode layer 26 is connected to wiring at the other end.

[0326] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. The measured frequency versus resistance value is plotted in [the graph]. Figure 14 In the middle. By Figure 14It can be seen that the capacitive reactance Xc at 1kHz is 64.1Ω, and the equivalent series resistance ESR is 6.12Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 10.5. On the other hand, the capacitive reactance Xc at 20kHz is 3.66Ω, and the equivalent series resistance ESR is 1.05Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, is 3.49. Let Xc / ESR at 20kHz be XE when Xc / ESR is 1 at 1kHz. 20 It is 0.33.

[0327] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 2.4 μF. The capacitance C / (A×t) is 400.0 μF / mm². 3 .

[0328] [Comparative Example 4]

[0329] The opening area A of the hole is set to 20mm. 2 In addition, a basal piezoelectric element was fabricated in the same manner as in Comparative Example 2.

[0330] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. At 1 kHz, the capacitive reactance Xc was 150 Ω, and the equivalent series resistance ESR was 13.5 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 11.1. On the other hand, at 20 kHz, the capacitive reactance Xc was 8.31 Ω, and the equivalent series resistance ESR was 1.41 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 5.9. Let Xc / ESR at 20 kHz, where Xc / ESR is 1 at 1 kHz, be XE. 20 It is 0.53.

[0331] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 600.0 μF / mm². 3 .

[0332] [Comparative Example 5]

[0333] The thickness of the first electrode layer 24 and the second electrode layer 26 (copper thin film) is set to 300 nm, and the opening area A of the hole is set to 8 mm. 2 In addition, a basal piezoelectric element was fabricated in the same manner as in Comparative Example 2.

[0334] The capacitive reactance Xc and equivalent series resistance ESR of the fabricated piezoelectric element were measured using the method described above. At 1 kHz, the capacitive reactance Xc was 146 Ω, and the equivalent series resistance ESR was 12.2 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 12.0. On the other hand, at 20 kHz, the capacitive reactance Xc was 8.42 Ω, and the equivalent series resistance ESR was 1.22 Ω. Therefore, the ratio of capacitive reactance Xc to equivalent series resistance ESR, Xc / ESR, was 6.90. Let Xc / ESR at 20 kHz, where Xc / ESR is 1 at 1 kHz, be XE. 20 It is 0.58.

[0335] Furthermore, the electrostatic capacitance of the fabricated multilayer piezoelectric element is 1.2 μF. The capacitance C / (A×t) is 500.0 μF / mm². 3 .

[0336] [evaluate]

[0337] The fabricated multilayer piezoelectric element was connected to a continuous drive test (40Vrms). With the multilayer piezoelectric element suspended in the air, the temperature reached after one hour of continuous drive was measured. The input signal was set to SN2. The SN2 signal conforms to the noise signal specifications defined by JEITA and is designed to reduce high-frequency or low-frequency noise components. The applied voltage frequency was within the range of 20Hz to 20kHz. Furthermore, the temperature measurement point of the multilayer piezoelectric element was set to any location displaying the highest reached temperature.

[0338] The results are shown in Table 1.

[0339] [Table 1]

[0340]

[0341] As shown in Table 1, the piezoelectric element of the present invention reaches a lower temperature and suppresses heat generation compared to the comparative example. Furthermore, a comparison between Example 1 and Comparative Example 2 shows that even with the same film formation method, the film quality varies depending on the film formation conditions; a poorer film quality results in greater heat generation. Moreover, a comparison between Example 1 and Comparative Example 3 shows that a longer path length for the current results in greater heat generation.

[0342] Furthermore, based on a comparison of Example 1 and Example 3, it can be seen that when fabricating a piezoelectric element with stacked piezoelectric thin films, it is preferable to connect the piezoelectric thin films in parallel.

[0343] Furthermore, a comparison between Examples 2 and 5, and between Examples 6 to 8, shows that the smaller C / (A×t) is, the lower the temperature reached, preferably 260.0 μF / mm. 3 the following.

[0344] [Reference Example 1]

[0345] Sheets 10a and 10c were prepared by forming a copper thin film with a thickness of 300 nm on a 5 μm thick PET film by vacuum evaporation. The conditions for vacuum evaporation of the copper thin film were set to be the same as those in Comparative Example 1. That is, in this example, the first electrode layer 24 and the second electrode layer 26 are copper thin films with a thickness of 300 nm, and the first protective layer 28 and the second protective layer 30 are PET thin films with a thickness of 5 μm.

[0346] Using the sheets 10a and 10c, a piezoelectric layer 20 with a thickness of 50 μm was formed in the same manner as in Example 1, thereby producing a strip of piezoelectric film 10L.

[0347] The fabricated piezoelectric film was cut into planar dimensions of 150mm × 200mm, and then folded back four times along the 150mm direction to create a basaltic layered piezoelectric element. Specifically, the short side of the layered piezoelectric element was set to 30mm, and the long side to 200mm. The folded surfaces that came into contact were then bonded together using a butadiene-based adhesive. The adhesive layer thickness was set to 30μm.

[0348] Furthermore, the first electrode layer 24 and wiring are connected to one end of the long side of the folded-back piezoelectric element, and the second electrode layer 26 and wiring are connected to the other end.

[0349] [Refer to Examples 2 and 3]

[0350] The length of the long side was set to 260mm and 320mm. Otherwise, the stacked piezoelectric element was fabricated in the same manner as in Reference Example 1.

[0351] [evaluate]

[0352] The fabricated multilayer piezoelectric element was attached to a vibrating plate as an exciter, and the sound pressure was measured.

[0353] A hard aluminum plate with a thickness of 0.8 mm and a length of 450 mm × width of 500 mm was used as the vibrating plate. The transverse direction of the vibrating plate was aligned with the length direction of the stacked piezoelectric element, and the stacked piezoelectric element was attached to approximately the center of the vibrating plate.

[0354] The stacked piezoelectric element was connected to a continuous drive test and driven at an applied voltage of 40 Vrms. The sound pressure was measured using a microphone placed 1 m away from the center of the vibrating plate. The sound pressure measurement results at frequencies from 1 kHz to 20 kHz are shown in Table 2.

[0355] [Table 2]

[0356]

[0357] As shown in Table 2, increasing the length of the longer side can generally increase the sound pressure level from 1 kHz to 15 kHz.

[0358] Furthermore, when the applied voltage is set to 40 Vrms, the temperature of the 200 mm long piezoelectric element is approximately 40°C. By adjusting the applied voltage using a 260 mm long piezoelectric element, the applied voltage that achieves the same sound pressure as the 40 Vrms applied voltage was determined using a 200 mm long piezoelectric element, resulting in 32 Vrms. At this point, the temperature of the piezoelectric element is approximately 33°C. In other words, when achieving the same sound pressure as a 200 mm long piezoelectric element with an applied voltage of 40 Vrms using a 260 mm long piezoelectric element, the temperature of the piezoelectric element decreases to approximately 7°C.

[0359] The results above show that by increasing the length of the long side of the stacked piezoelectric element, the sound pressure can be increased more under the same applied voltage, thus reducing the heat generation required to obtain the same sound pressure.

[0360] Based on the above results, the effects of the present invention are quite obvious.

[0361] Symbol Explanation

[0362] 10-Piezoelectric film, 10a, 10c-Sheet, 10b-Laminated body, 12-Vibrating plate, 16, 19-Adhesive layer, 20-Piezoelectric layer, 24-First electrode layer, 26-Second electrode layer, 28-First protective layer, 30-Second protective layer, 34-Viscoelastic matrix, 36-Piezoelectric particle, 50, 56-Piezoelectric element, 58-Core rod, 60-Protrusion, 62, 64-Electrode protrusion, 70-Hole, 72-Conductive component, 74a, 74b-Wire.

Claims

1. A stacked piezoelectric element, comprising multiple layers of piezoelectric thin films, wherein the piezoelectric thin films have: The piezoelectric layer is composed of a polymer composite piezoelectric material containing piezoelectric particles within a matrix comprising a polymer material; and Electrode layers are formed on both sides of the piezoelectric layer. in, When the value obtained by dividing the capacitive reactance Xc of the piezoelectric film at a frequency of 1 kHz by the equivalent series resistance ESR is set to 1, the value obtained by dividing the capacitive reactance Xc of the piezoelectric film at a frequency of 20 kHz by the equivalent series resistance ESR is XE. 20 It is in the range of 0.6 to 1.

5.

2. The laminated piezoelectric element according to claim 1, wherein, The polymer material exhibits viscoelasticity at room temperature.

3. The laminated piezoelectric element according to claim 1 or 2, wherein, The XE 20 It is in the range of 0.8 to 1.

3.

4. The laminated piezoelectric element according to claim 1 or 2, wherein, The thickness of the electrode layer is less than 1 μm.

5. The laminated piezoelectric element according to claim 1 or 2, wherein, At least the outermost piezoelectric film stacked in the stacked piezoelectric element has a protective layer, which is stacked on the side of the outermost electrode layer opposite to the piezoelectric body layer. The protective layer has holes extending from the surface to the electrode layer. The stacked piezoelectric element has: A conductive component is disposed within the hole. A wire is disposed on the surface of the hole in the protective layer and is electrically connected to the electrode layer via the conductive component.

6. The laminated piezoelectric element according to claim 5, wherein, If we define the opening area of ​​the hole as A, the thickness of the electrode layer as t, and the electrostatic capacitance of the stacked piezoelectric element as C, then C / (A×t) is 260 μF / mm. 3 the following.

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