CN113394337B - Method for preparing multilayer piezoelectric film, piezoelectric module and electronic equipment - Google Patents

Method for preparing multilayer piezoelectric film, piezoelectric module and electronic equipment Download PDF

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CN113394337B
CN113394337B CN202110579110.8A CN202110579110A CN113394337B CN 113394337 B CN113394337 B CN 113394337B CN 202110579110 A CN202110579110 A CN 202110579110A CN 113394337 B CN113394337 B CN 113394337B
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piezoelectric film
piezoelectric
film layer
film
layer
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CN113394337A (en
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李宋楚
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Jiangxi OMS Microelectronics Co Ltd
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Jiangxi OMS Microelectronics Co Ltd
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/05—Manufacture of multilayered piezoelectric or electrostrictive devices, or parts thereof, e.g. by stacking piezoelectric bodies and electrodes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R17/00—Piezoelectric transducers; Electrostrictive transducers
    • H04R17/005—Piezoelectric transducers; Electrostrictive transducers using a piezoelectric polymer
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R31/00—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor
    • H04R31/003—Apparatus or processes specially adapted for the manufacture of transducers or diaphragms therefor for diaphragms or their outer suspension
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • H04R7/04—Plane diaphragms
    • H04R7/06—Plane diaphragms comprising a plurality of sections or layers
    • H04R7/10—Plane diaphragms comprising a plurality of sections or layers comprising superposed layers in contact
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/01—Manufacture or treatment
    • H10N30/04—Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
    • H10N30/045—Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning by polarising
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N30/00—Piezoelectric or electrostrictive devices
    • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2307/00—Details of diaphragms or cones for electromechanical transducers, their suspension or their manufacture covered by H04R7/00 or H04R31/003, not provided for in any of its subgroups
    • H04R2307/025—Diaphragms comprising polymeric materials

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  • Manufacturing & Machinery (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
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Abstract

The invention discloses a method for preparing a multilayer piezoelectric film, a piezoelectric module and electronic equipment, wherein the method for preparing the multilayer piezoelectric film comprises the steps of sequentially preparing alternately arranged electrode layers and piezoelectric film layers on a substrate to obtain the multilayer piezoelectric film; wherein the step of preparing the n-th laminated film layer includes: crystallizing the n-th laminated film layer by heat treatment in a crystallization auxiliary solvent atmosphere so that the crystalline particle-penetrating portion of the n-th laminated film layer is connected to the n-1-th laminated film layer, n being 2 or more. According to the method for preparing the multilayer piezoelectric film, the piezoelectric module and the electronic equipment, glue is not needed to be attached to the piezoelectric film layer when the multilayer piezoelectric film is prepared, so that the overall thickness of the piezoelectric module can be reduced, and the performance of the piezoelectric module is improved.

Description

Method for preparing multilayer piezoelectric film, piezoelectric module and electronic equipment
Technical Field
The present invention relates to the field of piezoelectric technology, and in particular, to a method for preparing a multilayer piezoelectric film, a piezoelectric module, and an electronic device.
Background
Currently the dominant under-screen sounding devices are typically of the electromagnetic and piezoceramic type. For the electromagnetic drive sound generating device, the volume of the electromagnetic drive sound generating device is larger, the piezoelectric ceramic plate is high in cost and opaque, and the electromagnetic drive sound generating device is not easy to place between the display screen and the glass cover plate, so that a large amount of assembly space can be occupied, the sound conducting layer is thicker, and the energy consumption is increased. And for piezoelectric film materials such as vinylidene fluoride trifluoroethylene copolymer or polyvinylidene fluoride, the piezoelectric film material has the advantages of high transparency, on-screen sounding, assembly space saving, low power consumption, more user functions realization and the like, and is widely favored.
Because the sounding strength of the piezoelectric thin films connected in parallel in multiple layers is stronger than that of a single layer, the piezoelectric thin film sounding scheme generally adopts a mode of connecting multiple layers of piezoelectric thin films in parallel. In the related art, after the electrode is printed on the polarized piezoelectric film, the electrode is cut into a required shape, and all layers are bonded in a glue bonding mode, but the thickness of the single layer of glue is more than 10 mu m, and the thickness of the film and the thickness of the electrode are added, so that the overall thickness of the module is greatly increased along with the increase of the stacking layers, the load of vibration of the module is greatly increased, and the increased thickness can offset the performance improvement caused by the increase of the layers. Although the thickness of the piezoelectric film can be controlled below 10um along with the perfection of the preparation process of the piezoelectric film, the thickness of the interlayer adhesive and the electrode can be larger than that of the functional layer, and the performance can reach the bottleneck after the lamination of 2-3 layers. In addition, the reliability of the glue is low, the risk of aging failure exists, and the problem of glue cracking also exists in the vibration of the film due to the difference between the modulus and the mechanical property of the glue and the vibrating diaphragm.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems existing in the prior art. Therefore, an object of the present invention is to provide a method for preparing a multilayer piezoelectric film, by which the piezoelectric film layer is not bonded by glue, so that the overall thickness of the piezoelectric module can be reduced, and the performance of the piezoelectric module can be improved.
The second objective of the present invention is to provide a piezoelectric module.
Another object of the present invention is to provide an electronic device.
In order to solve the above problems, a method for preparing a multilayer piezoelectric film according to an embodiment of the first aspect of the present invention includes sequentially preparing electrode layers and piezoelectric film layers alternately arranged on a substrate to obtain a multilayer piezoelectric film; wherein the step of preparing the n-th laminated film layer includes: crystallizing the n-th laminated film layer by heat treatment in a crystallization auxiliary solvent atmosphere so that the crystalline particle-penetrating portion of the n-th laminated film layer is connected to the n-1-th laminated film layer, n being 2 or more.
According to the method for preparing the multilayer piezoelectric film, when the n-th laminated film layer is prepared, the crystallization auxiliary solvent atmosphere is added during crystallization treatment, the mobility of molecules in the second piezoelectric film material can be enhanced by utilizing the characteristic that a crystallization auxiliary agent is compatible with the piezoelectric film material, the crystallinity of the second piezoelectric film layer is improved, the crystalline particles of the second piezoelectric film layer partially penetrate through the electrode layer to be bonded with the adjacent piezoelectric film layer, the interaction between the adjacent piezoelectric film layers can be increased, and the firm bonding effect is formed between the adjacent piezoelectric film layers, so that the multilayer piezoelectric film can be prepared in a mode without gluing, the problems of aging failure and cracking caused by glue bonding can be avoided, the thickness of a glue layer can be eliminated, the overall thickness of the piezoelectric module is reduced, and the performance of the piezoelectric module is improved.
In some embodiments, preparing the n-th laminate film layer comprises: coating a film-forming precursor solution containing a first preset solid content piezoelectric film material on the electrode layer to form an n-th laminated film wet film; and carrying out first heat treatment on the wet film of the piezoelectric film layer in the crystallization auxiliary solvent atmosphere to form the n-th laminated film layer, wherein the value of the first heat treatment time T1 is more than or equal to 4h and less than or equal to T1 and less than or equal to 10h, and the value of the first heat treatment temperature T1 is more than 130 ℃ and less than or equal to T1 and less than 145 ℃. Therefore, through adding the crystallization auxiliary solvent atmosphere in the crystallization treatment step and utilizing the compatibility of the crystallization auxiliary solvent and the piezoelectric film, the crystallinity of the n-th laminated film layer can be improved, the effect between adjacent piezoelectric film layers is enhanced, an adhesive layer is not required to be arranged, and the overall thickness of the piezoelectric module is reduced.
In some embodiments, the first heat treatment time has a value of 4 h.ltoreq.t1.ltoreq.6h.
In some embodiments, the first predetermined solid content piezoelectric film material comprises polyvinylidene fluoride or vinylidene fluoride trifluoroethylene copolymer with a solid content value of 10% -20%.
In some embodiments, the solvent of the film forming precursor solution includes at least one of propylene glycol methyl ether acetate, methyl ethyl ketone, and N, N-dimethylformamide. The conditions are convenient for preparing and forming the piezoelectric module with flexibility.
In some embodiments, subjecting the piezoelectric film layer wet film to a first heat treatment in the crystallization auxiliary solvent atmosphere to form the n-th laminated film layer includes: placing the wet film of the piezoelectric film layer and the crystallization auxiliary solvent into a closed container; and heating the closed container at the first heat treatment temperature and maintaining the first heat treatment time, wherein the atmosphere concentration p of the crystallization auxiliary solvent in the closed container takes a value of 3g/m 3<p<10g/m3. Therefore, the volatilization amount of the wet film solvent of the piezoelectric film layer in the heat treatment process is slowed down in the crystallization auxiliary solvent atmosphere, the crystallinity is improved, the bonding effect between the piezoelectric layers is increased, and the electrode layer is not broken.
In some embodiments, the crystallization aid solvent comprises N, N-dimethylformamide or propylene glycol methyl ether acetate.
In some embodiments, the crystallization auxiliary solvent has an atmospheric concentration p of 4g/m 3<p<6g/m3 in the closed vessel.
An embodiment of the second aspect of the present invention provides a piezoelectric module, which includes the multilayer piezoelectric film manufactured by the method for manufacturing a multilayer piezoelectric film according to the above embodiment.
According to the piezoelectric module provided by the embodiment of the invention, the multilayer piezoelectric film is prepared by adopting the method for preparing the multilayer piezoelectric film provided by the embodiment of the invention, and glue is not needed to be used for bonding, so that the problems of aging failure and cracking caused by glue bonding can be avoided, the overall thickness of the piezoelectric module can be reduced, the performance of the piezoelectric module can be improved, and the stability can be improved.
An embodiment of a third aspect of the present invention provides an electronic device, including: an equipment body; a display screen and a driving voltage source arranged on the equipment body; the piezoelectric module of the above embodiment is disposed on the display screen, and the driving voltage source is connected with the electrode layer of the piezoelectric module.
According to the electronic equipment provided by the embodiment of the invention, the piezoelectric module provided by the embodiment is beneficial to improving the performance of the electronic equipment and improving the use stability.
Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is a flow chart of a method of preparing a multilayer piezoelectric film according to one embodiment of the invention;
FIG. 2 is a schematic illustration of a polarization process performed in preparing a multilayer piezoelectric film according to one embodiment of the present invention;
FIG. 3 is a schematic view of a multilayer piezoelectric film prepared by a method of preparing a multilayer piezoelectric film according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a piezoelectric module according to one embodiment of the invention;
Fig. 5 is a schematic structural view of an electronic device according to an embodiment of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below, by way of example with reference to the accompanying drawings.
In order to solve the above-mentioned problems, an embodiment of the present invention provides a method for preparing a multilayer piezoelectric film, by which the piezoelectric film layer is not required to be attached by glue, so that the overall thickness of the piezoelectric module can be reduced, and the performance of the piezoelectric module can be improved.
In the embodiment of the invention, electrode layers and piezoelectric film layers which are alternately arranged are sequentially prepared on a substrate to obtain a multilayer piezoelectric film. Wherein the step of preparing the n-th laminated film layer includes: crystallizing the n-th laminated film layer by heat treatment in a crystallization auxiliary solvent atmosphere so that the crystalline particles of the n-th laminated film layer penetrate part of the electrode layer to be connected with the n-1-th laminated film layer, n being 2 or more. That is, when each laminated film layer is prepared from the second laminated film layer, the crystallization auxiliary solvent atmosphere is provided during the crystallization process, so that the crystallization particles of the laminated film layer can partially penetrate through the electrode layer to act with the adjacent piezoelectric film layers in the crystallization process, that is, the adjacent piezoelectric film layers form bonding, therefore, the bonding effect of firm bonding can be formed between the adjacent piezoelectric film layers without using glue bonding, thereby not only avoiding the problems of aging failure and cracking caused by glue bonding, but also eliminating the thickness of the adhesive layer, reducing the overall thickness,
The method for preparing a multilayer piezoelectric film according to an embodiment of the present invention is described below with reference to fig. 1 to 3, and specifically includes the following step S1.
S1, providing a substrate. In the embodiment, a material excellent in transparency, heat resistance, and mechanical characteristics may be used as the substrate, and for example, an ITO (Indium-Tin Oxide) glass substrate may be used. The first piezoelectric film layer may be formed of a polymer piezoelectric thin film material that is easy to process, such as a material containing a fluororesin, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), or the like.
S2, preparing a first laminated film layer on the substrate. In an embodiment, in preparing the first laminate film layer, a film-forming precursor solution containing a piezoelectric thin film material may be coated on a substrate using a slit coating apparatus and baked to form the first laminate film layer.
And S3, alternately preparing an electrode layer and a piezoelectric film layer on the first laminated film layer until the last piezoelectric film layer is prepared, and preparing the electrode layer on the last piezoelectric film layer. Wherein the piezoelectric film layer is subjected to crystallization treatment in a crystallization auxiliary solvent atmosphere.
Specifically, a first electrode layer and a second laminate film layer are prepared on the first laminate film layer. Wherein preparing the second laminated film layer includes subjecting the second laminated film layer to crystallization treatment in a crystallization auxiliary solvent atmosphere, the crystallization auxiliary solvent being compatible with the piezoelectric film material of the second laminated film layer so that crystal particles of the second laminated film layer can partially penetrate the first electrode layer to be bonded with the adjacent first laminated film layer.
Among them, the second laminate film layer may be formed of a polymer piezoelectric film material which is easy to process, such as a fluororesin-containing material such as polyvinylidene fluoride, vinylidene fluoride-trifluoroethylene copolymer, or the like.
Due to the fact that the plurality of piezoelectric film layers are bonded in the glue bonding mode, the problems of increased module thickness, increased load and reduced performance exist, the reliability of the glue is low, and the risks of aging failure and cracking exist during use. Therefore, in the embodiment of the invention, through introducing the crystallization auxiliary solvent atmosphere in the crystallization treatment process of the second laminated film layer, the crystallization auxiliary solvent is compatible with the second laminated film material, and the polymer chains in the second laminated film material have higher degree of freedom in the crystallization auxiliary solvent atmosphere, so that the mobility of molecules can be enhanced, and the thickness of the first electrode layer is in the nanometer level, so that the crystallization particle part of the second laminated film layer can penetrate through the first electrode layer to interact with the adjacent first laminated film layer, that is, through introducing the crystallization auxiliary solvent atmosphere in the crystallization treatment process of the second laminated film layer, molecules between the second laminated film layer and the adjacent first laminated film layer are interacted, and crystal grains are grown in a cross-layer manner, thereby increasing the adhesive force between the adjacent piezoelectric film layer and the piezoelectric film layer, playing a firm bonding effect, avoiding the problem of ageing and cracking caused by adhesive bonding, reducing the overall thickness of the piezoelectric film, reducing the load, and improving the performance and reliability of the multilayer product adopting the piezoelectric film.
The above steps of preparing the first electrode layer and the second laminate film layer are repeated to prepare more electrode layers and piezoelectric film layers. For example, a first electrode layer is prepared on a side of the first laminated film layer away from the substrate, a second laminated film layer is prepared on the first electrode layer, a second electrode layer is prepared on a side of the second laminated film layer away from the first electrode layer, a third piezoelectric film layer is prepared on a side of the second laminated film layer away from the second electrode layer, and so on until the final laminated film layer and electrode layer are prepared.
When preparing the piezoelectric film layers of each layer from the second laminated film layer, a slit coating device can be adopted to coat a film-making precursor solution containing the piezoelectric film material on the electrode layer, after the coating is finished, drying treatment is not carried out, but crystallization auxiliary solvent atmosphere is introduced, drying and crystallization are carried out under the crystallization auxiliary solvent atmosphere, thereby slowing down the volatilization amount of the film-making precursor solution in the heat treatment process through the crystallization auxiliary solvent atmosphere, and enabling the piezoelectric film material to still contain the crystallization auxiliary solvent in the heat treatment process, thereby improving the degree of freedom and migration distance of molecules in the piezoelectric film material through the crystallization auxiliary solvent, enabling crystal grains of the piezoelectric film layer in the crystallization treatment to grow in a cross-layer mode, enhancing interaction between adjacent piezoelectric film layers, avoiding adhesion and reducing the integral thickness of the multilayer piezoelectric film.
In addition, the crystallization auxiliary solvent atmosphere is introduced in the process of crystallizing the piezoelectric film layer, so that the effect of firm adhesion can be realized, the setting of an adhesive layer can be canceled, and compared with the mode of adopting glue adhesion, the multilayer piezoelectric film prepared by the method disclosed by the embodiment of the invention also has higher transparency, and meanwhile, the haze can be reduced, so that the purpose of sounding on a screen can be realized more conveniently.
And S4, carrying out polarization treatment on the piezoelectric film layer.
In an embodiment, the piezoelectric film layer may be subjected to polarization treatment under a high-voltage electric field, so that the piezoelectric film layer has a certain piezoelectric performance.
Specifically, after the piezoelectric film layers are attached, a corona or direct polarization mode can be adopted to obtain a plurality of piezoelectric film layers with opposite polarization directions between adjacent piezoelectric film layers, so that the effect of parallel connection of the plurality of piezoelectric film layers is realized, and the sounding strength of the piezoelectric module is improved.
The multilayer piezoelectric film prepared by the above preparation method is shown in fig. 2, in which the first laminated film layer is denoted by 1, the nth laminated film layer is denoted by 4, the electrode layer is denoted by 3, and the substrate is denoted by 30.
S5, separating the substrate after the polarization treatment, and preparing an electrode layer on the side of the first laminated film layer away from the second laminated film layer.
Wherein the electrode layer is formed of a conductive paste having conductive properties, such as a polymer silver conductive paste. Specifically, after the substrate is separated, a conductive paste may be coated, for example, by bar coating or spin coating, on the side of the first laminate film layer separated from the substrate, i.e., the side of the first laminate film layer remote from the second laminate film layer, and after the coating is completed, an electrode layer may be formed by thermal curing or photo curing, whereby the preparation of the multilayer piezoelectric film is achieved through the above steps. The finally prepared multilayer piezoelectric film is shown in fig. 3, wherein the first laminated film layer is marked with 1, the n-th laminated film layer is marked with 4, the electrode layer is marked with 3, the substrate is marked with 30, and the electrode layer prepared on the side of the first laminated film layer separated from the substrate after the substrate is separated is marked with 2.
According to the method for preparing the multilayer piezoelectric film, from the preparation of the second laminated film layer, each piezoelectric film layer is crystallized in the crystallization auxiliary solvent atmosphere, the mobility of molecules in the piezoelectric film material can be enhanced by utilizing the characteristic that a crystallization auxiliary agent is compatible with the piezoelectric film material, the crystallinity of the piezoelectric film layer is improved, the interaction between adjacent piezoelectric film layers is increased, and a firm bonding effect is formed between the adjacent piezoelectric film layers, so that the multilayer piezoelectric film can be prepared without a bonding mode, the problems of aging failure and cracking caused by glue bonding can be avoided, the thickness of a glue layer can be eliminated, the overall thickness of the piezoelectric module is reduced, and the performance of the piezoelectric module is improved.
For each electrode layer, a bar coating or a spin coating method may be used to coat, and after the coating is completed, the electrode layer may be formed by a heat curing or photo curing method, and the electrode layer may be formed of a conductive paste having conductive properties, such as a polymer silver conductive paste.
In some embodiments of the invention, the preparation of the n-th laminate film layer comprises: coating a film-forming precursor solution containing a piezoelectric film material with a first preset solid content on the electrode layer to form an n-th laminated film layer wet film, and performing first heat treatment on the laminated film layer wet film in a crystallization auxiliary solvent atmosphere to form an n-th laminated film layer, so that the laminated film layer wet film can be formed into a laminated film layer after the crystallization treatment.
Wherein, the piezoelectric film material can be dissolved in the film-making precursor solution. The film-forming precursor solution cannot contain a large amount of aqueous solution, so that the problem of precipitation caused by low solubility of the aqueous solution to the piezoelectric film material is avoided.
In an embodiment, a film-forming precursor solution may be coated on the first electrode layer using bar coating or spin coating to form a piezoelectric film layer wet film. After the wet film preparation step is completed, the preparation of a plurality of n-th piezoelectric film layers is completed by performing a heat treatment step without performing a drying treatment.
Wherein, when the wet film of the nth layer of piezoelectric film is subjected to the first heat treatment, the first heat treatment temperature is greater than the curie temperature and less than the melting temperature, in some embodiments, the value of the first heat treatment temperature T1 may be 130 ℃ < T1<145 ℃, wherein the difference between the maximum temperature value and the minimum temperature value is within 5%, for example, the value may be 132 ℃, 135 ℃, 138 ℃, 140 ℃, 143 ℃; the first heat treatment time t1 may have a value of 4 h.ltoreq.t1.ltoreq.10h, for example, 4h, 5h, 6h, 8h or 10h. Along with the extension of the heat treatment time, the crystallinity adhesion does not change significantly, preferably, the value of the first heat treatment time is 4h less than or equal to t1 less than or equal to 6h, for example, the value of the first heat treatment time is 4h, 4.5h, 5h or 6h, so that the final interlayer adhesion can be ensured, and the time can be saved. Under the condition of a reasonable range, the atmosphere is formed by the crystallization auxiliary solvent to participate in the crystallization process, so that the degree of freedom of a molecular chain is effectively improved. Through the crystallization treatment step, the degree of freedom and migration distance of molecules in the wet film of the piezoelectric film layer can be improved, the degree of crystallization is improved, crystal grains can grow beyond the electrode layer, the adhesive force between adjacent piezoelectric film layers is improved, the bonding effect is achieved, and the electrode layer cannot be influenced.
Further, a process of subjecting the piezoelectric film layer to polarization treatment is described by way of example with reference to fig. 2. As shown in fig. 2, in the polarization treatment, the electrode layer located at the top end is not grounded in the thickness direction of the piezoelectric film layer with the first laminated film layer located at the bottom end. Therefore, the electrode layers of the even layers and the odd layers are respectively led out in a summarizing way, the electrode layers of the even layers are grounded, the electrode layers of the odd layers are not grounded, and the multilayer piezoelectric film layers with opposite polarization directions of the adjacent piezoelectric film layers are obtained by adopting a corona polarization mode. The voltage value can be determined according to the thickness of the film layer when corona polarization is performed.
In some embodiments, the piezoelectric film material is polyvinylidene fluoride or vinylidene fluoride trifluoroethylene copolymer. In the wet film preparation step of the n-th laminated film layer, a film-forming precursor solution containing polyvinylidene fluoride or vinylidene fluoride trifluoroethylene copolymer having a solid content of 10% to 20% is coated on the electrode layer to form a laminated film layer wet film. For example, a solid content of 10%, 15%, 20% or the like can be selected; the solvent of the film-forming precursor solution may be at least one of Propylene Glycol Methyl Ether Acetate (PGMEA), methyl Ethyl Ketone (MEK) and N, N-Dimethylformamide (DMF), that is, the solvent of the film-forming precursor solution may be a single solvent such as propylene glycol methyl ether acetate solvent or methyl ethyl ketone solvent or N, N-dimethylformamide solvent, or a mixed solvent such as propylene glycol methyl ether acetate and methyl ethyl ketone, or a mixed solvent of propylene glycol methyl ether acetate and N, N-dimethylformamide, or a mixed solvent of propylene glycol methyl ether acetate, methyl ethyl ketone and N, N-dimethylformamide. The conditions are convenient for preparing and forming the flexible multilayer piezoelectric film, and the performance of the piezoelectric module is improved by adopting the piezoelectric film material with higher transparency and lower power consumption.
In some embodiments, the first heat treatment temperature is applied to the closed vessel by placing the piezoelectric film layer wet film and the crystallization auxiliary solvent into the closed vessel, wherein the atmosphere concentration p of the crystallization auxiliary solvent in the closed vessel has a value of 3g/m 3<p<10g/m3, for example, 4g/m 3、5g/m3、6g/m3、8g/m3. Preferably, the atmosphere concentration p of the crystallization auxiliary solvent in the closed vessel has a value of 4g/m 3<p<6g/m3, for example a value of 5g/m 3. Therefore, the crystallization treatment of the n-th laminated film layer is realized, the volatilization amount of the wet film solvent of the laminated film layer in the heat treatment process is slowed down in the crystallization auxiliary solvent atmosphere, and the crystallinity of the n-th laminated film layer is improved.
For example, in the crystallization process step, the mass of the crystallization auxiliary solvent is calculated according to the volume and the concentration of the desired crystallization auxiliary solvent atmosphere, the wet film of the piezoelectric film layer and the calculated mass of the crystallization auxiliary solvent are placed in a closed container having a small volume, for example, 30x30x30 cubic centimeters, and the closed container is subjected to heat treatment, for example, in an oven, to complete the crystallization process at a specified heat treatment temperature and heat treatment time. Therefore, in the crystallization process, the crystallization auxiliary solvent atmosphere is introduced, so that the crystal grains can grow in a cross-layer manner through the mobility of molecules, the adhesion between layers is improved, and the effect of firmly bonding is achieved by replacing glue.
In some embodiments, the crystallization aid solvent includes N, N-dimethylformamide or propylene glycol methyl ether acetate to increase the crystallinity of the piezoelectric film material upon heat treatment.
In some embodiments, the preparation of the electrode layer is achieved by disposing the nanoscale electrode material on the piezoelectric film layer and performing a second heat treatment, so as to facilitate the sound-producing vibration performance of the piezoelectric module. The electrode material adopts indium tin oxide or poly 3, 4-ethylenedioxythiophene, the value of the second heat treatment temperature T2 can be 130 ℃ < T2<145 ℃, for example, 135 ℃, 140 ℃ and 143 ℃; the second heat treatment time t2 can be 4h less than or equal to t2 less than or equal to 10h, for example, 4h, 5h, 6h and 10h. The first electrode layer and the second electrode layer are prepared by adopting nanoscale ITO or 3, 4-ethylenedioxythiophene monomer (PEDOT) so as to better reflect the sounding vibration performance of the piezoelectric module, and the piezoelectric module which is also more convenient to prepare is used as a transparent sounding layer to be embedded into electronic equipment, so that the effect of sounding on a screen is realized.
For example, after the first laminated film layer is prepared on the substrate, a layer of PEDOT may be coated on a side of the first laminated film layer remote from the substrate by bar coating or spin coating, or a thin layer of ITO may be evaporated at a low temperature, and an electrode layer may be formed after heat treatment, thereby sequentially preparing the second laminated film layer after annealing. And, after preparing the second laminated film layer, preparing an electrode layer on a side of the piezoelectric film layer remote from the first laminated film layer in the same manner as described above for each laminated film layer. And, after separating the substrates, preparing an electrode layer on a side of the first laminated film layer remote from the second laminated film layer in the same manner as described above, thereby obtaining a film stack in which the laminated film layers are connected in parallel.
In some embodiments, the first laminate film layer is prepared by coating a film-forming precursor solution comprising polyvinylidene fluoride or vinylidene fluoride-trifluoroethylene copolymer having a solids content of 10% to 20% on a substrate, and drying the film-forming precursor solution in a vacuum environment for a second predetermined time, such as at least 30 minutes, followed by a third heat treatment of the dried film-forming precursor solution.
In some embodiments, for example, the solids content value may be 10%, 16%, 20%, etc.; the third heat treatment temperature T3 may have a value of 130 ℃ < T3<145 ℃, for example 132 ℃, 135 ℃, 140 ℃; the third heat treatment time t3 has a value of 4 h.ltoreq.t3.ltoreq.10h, and may be, for example, 4h, 7h or 10h. Thus, the first laminated film layer is prepared by the above reasonable range.
The multilayer piezoelectric film produced by the method of the example of the present invention is described below with reference to table 1. Wherein table 1 is a comparison table of crystallinity and adhesion of the multilayer piezoelectric thin film prepared under different conditions under the crystallization auxiliary solvent atmosphere and the multilayer piezoelectric thin film not prepared under the crystallization auxiliary solvent atmosphere, respectively.
TABLE 1
As shown in table 1, the piezoelectric film layers prepared under different crystallization auxiliary solvent atmospheres, different crystallization temperatures and heat treatment times were example 1 to example 10, respectively, and the piezoelectric modules not prepared under the crystallization auxiliary solvent atmospheres were comparative example 1 and comparative example 2, respectively.
Wherein, in the embodiment of the invention, when the wet film of the n-th laminated film layer is subjected to crystallization treatment, the boundary auxiliary solvent atmosphere is increased, so that the crystallization degree of freedom of the wet film can be improved, thereby enabling the wet film molecules to partially penetrate the adjacent electrode layer to interact with the adjacent laminated film layer. The degree of freedom of molecular chains of the piezoelectric film layer is increased, so that the resistance of regular arrangement of the polymers is reduced, more polymers participate in the crystallization process, and the free range of molecular motion is increased, so that interlayer molecules have interaction, and the adhesive force is improved; i.e. the root cause of the improved adhesion is the interaction of the interlayer molecules. In the embodiment, the crystallinity can be regarded as a measure of the piezoelectric performance of the piezoelectric film layer; since in general the greater the crystallinity, the stronger the piezoelectric properties after polarization. It is clear that the crystallinity and the adhesion are not obviously related under other conditions, such as a mode of not increasing interlayer interaction, for example, the crystallinity is improved by adding a nucleating agent and the like, or the heat treatment time is improved to improve the crystallinity, and the interlayer adhesion of the PVDF/PVDF-Trfe film cannot be effectively improved
In the embodiment of the invention, the test data are referred to for analysis, and whether the multilayer piezoelectric film is qualified or not can be judged by taking crystallinity of more than 70% and interlayer adhesion of more than 4B as standards.
Specifically, as shown in table 1, it can be seen from the comparison of parameters that the difference of the atmosphere concentration of the crystallization auxiliary solvent can have a certain influence on the performance of the piezoelectric film layer, if the atmosphere concentration of the crystallization auxiliary solvent is too low during the crystallization treatment of the piezoelectric film layer, for example, the atmosphere concentration of example 4 is 3g/m3, the interlayer adhesion force is 4B, the labeling requirement cannot be met, for example, the wet film of the piezoelectric film layer is subjected to the crystallization treatment in the air atmosphere in comparative example 1 and comparative example 2, the interlayer interaction is weak, for example, the interlayer adhesion force is 0, and the degree of freedom and the adhesion force of molecules cannot be effectively improved; if the atmosphere concentration is too high as in example 5, the atmosphere concentration is 10g/m3, serious interpenetration of interlayer molecules occurs, and the crystallized portion is dissolved, the interlayer electrode is destroyed, and even the boundary between layers disappears. Therefore, the appropriate concentration of the atmosphere of the crystallization auxiliary solution is selected, so that the interlayer adhesion can be improved, for example, in the embodiment of the invention, the concentration p of the atmosphere of the crystallization auxiliary solvent is 3g/m 3<p<10g/m3, for example, examples 1, 2, 3 and 8 in table 1, the concentration of the atmosphere is 5g/m 3, and in examples 9 and 10, 4g/m 3 and 6g/m 3 are respectively selected, the interlayer adhesion is more than 4B, the crystallinity is more than 70%, and the standard requirement is met.
Further, as shown in table 1, the difference of the heat treatment time also has a certain influence on the performance of the piezoelectric film, and if the heat treatment time is too short, the crystallinity is low, the adhesive force is poor, and the standard requirement cannot be met; if the heat treatment time is too long, the crystallinity and the adhesion can reach the limit, and no obvious change exists, for example, the heat treatment time is different from that of example 8 and example 9 or example 10 in table 1 by 1 hour, the adhesion is 5B, and the crystallinity is only changed by 1.36% or 0.61%; for example, example 1 and example 7, the heat treatment time was increased by 4 hours, but the crystallinity and interlayer adhesion were not significantly changed. In some embodiments of the present invention, the first heat treatment time is preferably 4 h.ltoreq.t1.ltoreq.6h, for example, examples 1 to 3, 9 and 10 use 6h, example 6 uses 4h, example 8 uses 5h, and when the atmosphere concentration is appropriate, the appropriate heat treatment time is selected, so that the crystallinity and interlayer adhesion of the piezoelectric film layer can reach the standards, and time can be saved.
In addition, in the case of subjecting the n-th laminated film layer to crystallization treatment, the temperature of the heat treatment has little influence on the crystallinity, and the maximum temperature value and the minimum temperature value may differ by within 5%, for example, 135 ℃ and 140 ℃ in table 1.
Therefore, when the crystallization auxiliary solvent atmosphere is introduced to participate in the crystallization process, the embodiment of the invention can effectively improve the adhesion between layers by reasonably controlling the concentration of the crystallization auxiliary solvent atmosphere and reasonably setting the heat treatment time, thereby effectively improving the crystallinity and the piezoelectric performance of the piezoelectric module.
An embodiment of the second aspect of the present invention provides a piezoelectric module, as shown in fig. 4, the piezoelectric module 10 including a multilayer piezoelectric film 11 prepared by the method for preparing a multilayer piezoelectric film according to the above embodiment, the multilayer piezoelectric film 11 being stacked, wherein electrode layers and piezoelectric film layers are alternately arranged. The preparation process of the multilayer piezoelectric film 11 may be described with reference to the above embodiments, and will not be described herein.
According to the piezoelectric module 10 provided by the embodiment of the invention, the piezoelectric film is prepared by adopting the method for preparing the multilayer piezoelectric film provided by the embodiment, and glue is not needed to be used for bonding, so that the problems of aging failure and cracking caused by glue bonding can be avoided, the overall thickness of the piezoelectric module can be reduced, the performance of the piezoelectric module can be improved, and the stability can be improved.
An embodiment of the third aspect of the present invention provides an electronic device, as shown in fig. 5, where the electronic device 20 includes a device body 5, a display screen 6 disposed on the device body 5, a driving voltage source 7, and the piezoelectric module 10 provided in the foregoing embodiment, and the piezoelectric module 10 is disposed on the display screen 6.
In the embodiment, the driving voltage source 7 is connected to the electrode layer of the piezoelectric module 10, and the driving voltage source 7 outputs the modulated ac voltage to drive the piezoelectric module 10 to vibrate or generate sound.
In the embodiment, the piezoelectric module 10 is formed by laminating a plurality of laminated film layers in a mode of not needing to be glued, so that the glue layer is reduced, the overall thickness of the module is reduced, the performance is improved, meanwhile, the piezoelectric module 10 has higher transparency and lower haze due to the cancellation of the glue layer, and therefore the performance of the electronic equipment 20 can be improved, the use stability is improved, and the on-screen sounding is also facilitated by adopting the piezoelectric module 10 provided by the embodiment.
According to the electronic device 20 of the embodiment of the present invention, by adopting the piezoelectric module 10 provided in the above embodiment, performance of the electronic device 20 is improved, and use stability is improved.
In the description of the present specification, reference to the terms "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the spirit and principles of the invention, the scope of which is defined by the claims and their equivalents.

Claims (9)

1. A method of making a multilayer piezoelectric film comprising:
Sequentially preparing electrode layers and piezoelectric film layers which are alternately arranged on a substrate to obtain a multilayer piezoelectric film;
Wherein the step of preparing the n-th laminated film layer includes: coating a film-forming precursor solution containing a first preset solid content piezoelectric film material on the electrode layer to form an n-th laminated film wet film;
The method for producing a piezoelectric film layer wet film includes the steps of, after completion of the piezoelectric film layer wet film producing step, performing a first heat treatment of the n-th laminated film layer wet film in a crystallization auxiliary solvent atmosphere to form the n-th laminated film layer, including:
placing the wet film of the piezoelectric film layer and the crystallization auxiliary solvent into a closed container;
Heating the closed container at a first heat treatment temperature and maintaining the first heat treatment time, wherein the atmosphere concentration p of the crystallization auxiliary solvent in the closed container is 3g/m 3<p<8g/m3, the value of the first heat treatment time t1 is 4h less than or equal to t1 less than or equal to 10h, and the first heat treatment temperature is higher than the Curie temperature and lower than the melting temperature; crystallizing the n-th laminated film layer by the first heat treatment so that the electrode layer of the crystal particle penetrating portion of the n-th laminated film layer is connected to the n-1-th laminated film layer, n being 2 or more;
The first preset solid content piezoelectric film material is a fluorine-containing resin material, and the crystallization auxiliary solvent is compatible with the first preset solid content piezoelectric film material;
The film-forming precursor solution cannot contain a large amount of aqueous solution, so that the problem of precipitation caused by low solubility of the aqueous solution to the piezoelectric film material with the first preset solid content is avoided.
2. The method of producing a multilayer piezoelectric film according to claim 1, wherein the first heat treatment temperature T1 has a value of 130 ℃ < T1<145 ℃.
3. The method of producing a multilayer piezoelectric film according to claim 1, wherein the first heat treatment time has a value of 4 h.ltoreq.t1.ltoreq.6h.
4. The method of claim 1, wherein the first predetermined solid content piezoelectric film material comprises polyvinylidene fluoride or vinylidene fluoride trifluoroethylene copolymer having a solid content value of 10% to 20%.
5. The method of producing a multilayer piezoelectric film according to claim 4, wherein the film-forming precursor solution includes at least one of propylene glycol methyl ether acetate, methyl ethyl ketone, and N, N-dimethylformamide.
6. The method for producing a multilayer piezoelectric film according to claim 1 or 2, wherein the crystallization auxiliary solvent comprises N, N-dimethylformamide or propylene glycol methyl ether acetate.
7. The method for producing a multilayer piezoelectric film according to claim 1, wherein the atmosphere concentration p of the crystallization auxiliary solvent in the closed container has a value of 4g/m 3<p<6g/m3.
8. A piezoelectric module comprising a multilayer piezoelectric film produced by the method of producing a multilayer piezoelectric film according to any one of claims 1 to 7.
9. An electronic device, comprising:
An equipment body;
A display screen and a driving voltage source arranged on the equipment body;
the piezoelectric module of claim 8, wherein the piezoelectric module is disposed on the display screen, and the driving voltage source is connected to an electrode layer of the piezoelectric module.
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