Piezoelectric film preparation method and piezoelectric film

Abstract

The invention relates to the technical field of piezoelectric films, and discloses a preparation method of a piezoelectric film and the piezoelectric film, and the preparation method comprises the following steps: mixing a piezoelectric material and a solvent to form slurry, coating the slurry on a substrate, and drying to obtain a piezoelectric wet film; and performing crystallization treatment and polarization treatment on the piezoelectric wet film to prepare the piezoelectric film, wherein the boiling point of the solvent is greater than 200 DEG C. By adopting the preparation method, the effect of reducing the crystallization temperature of the piezoelectric material can be realized, the decomposition or phase change of the material with poor heat resistance in the piezoelectric film can be avoided, and the adhesion stability of the substrate and the piezoelectric layer can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric films, and in particular to a preparation method of a piezoelectric film and a piezoelectric film. Background Art

[0002] In the preparation process of piezoelectric film, the crystallization process will cause the piezoelectric material in the piezoelectric film to change from a paraelectric phase to a ferroelectric phase, thereby giving the piezoelectric film piezoelectric properties.

[0003] However, the crystallization temperature of the piezoelectric material in the current piezoelectric film is between its melting temperature and the Curie temperature, which makes the material with poor heat resistance in the piezoelectric film easy to decompose or phase change, and leads to poor adhesion between the substrate and the piezoelectric layer, which reduces the piezoelectric performance of the piezoelectric film. Summary of the invention

[0004] The embodiments of the present invention disclose a method for preparing a piezoelectric film and a piezoelectric film. The piezoelectric film can reduce the crystallization temperature of the piezoelectric material, avoid the decomposition or phase change of the material with poor heat resistance in the piezoelectric film, and improve the stability of the adhesion between the substrate and the piezoelectric layer.

[0005] In a first aspect, an embodiment of the present application discloses a method for preparing a piezoelectric film, the method comprising the following steps:

[0006] Mixing a piezoelectric material and a solvent to form a slurry, coating the slurry on a substrate, and drying to obtain a piezoelectric wet film;

[0007] Performing crystallization and polarization treatment on the piezoelectric wet film to obtain the piezoelectric thin film;

[0008] Wherein, the boiling point of the solvent is greater than 200°C.

[0009] Furthermore, the solid content of the slurry is 5% to 15%.

[0010] Furthermore, the crystallization temperature of the piezoelectric material of the piezoelectric film is lower than the Curie temperature of the piezoelectric material.

[0011] Further, the solvent includes at least one of triacetin, isophorone, propylene carbonate, and triethyl phosphate; and / or,

[0012] The monomers used to form the piezoelectric material include vinylidene fluoride and trifluoroethylene, and the molar ratio of the vinylidene fluoride to the trifluoroethylene is (76-86):(14-24); and / or,

[0013] The depolarization temperature of the piezoelectric wet film is 120° C. to 150° C.; and / or,

[0014] In the step of crystallization treatment, the crystallization temperature of the piezoelectric material is 100° C. to 144° C., and the crystallization time is 4 hours to 10 hours.

[0015] In a second aspect, an embodiment of the present application discloses a method for preparing a piezoelectric film, the method comprising the following steps:

[0016] Prepare N layers of piezoelectric layers and electrode layers between adjacent piezoelectric layers layer by layer on the surface of the substrate;

[0017] The step of preparing any of the piezoelectric layers from the second piezoelectric layer to the Nth piezoelectric layer comprises: coating and drying a slurry formed by mixing a piezoelectric material and a solvent to obtain a piezoelectric wet film, and performing a crystallization treatment and a polarization treatment on the piezoelectric wet film to obtain the piezoelectric layer; wherein the boiling point of the solvent is greater than 200° C.;

[0018] The crystallization temperature of the piezoelectric material in the piezoelectric layer prepared later is equal to or lower than the lowest depolarization temperature of the piezoelectric material in each of the piezoelectric layers prepared earlier;

[0019] N is an integer greater than or equal to 2.

[0020] Furthermore, the piezoelectric layers of each layer are prepared from the same slurry, and the crystallization temperatures of the piezoelectric materials of the second piezoelectric layer to the Nth piezoelectric layer are equal to or lower than the depolarization temperature of the piezoelectric material.

[0021] Furthermore, the crystallization temperature of the piezoelectric material of the first piezoelectric layer is lower than the Curie temperature of the first piezoelectric layer.

[0022] Furthermore, the piezoelectric material of the piezoelectric layer includes a copolymer formed by copolymerization of vinylidene fluoride and trifluoroethylene in a molar ratio of (76 to 86): (14 to 24), and the number of layers of the piezoelectric layer is 2, wherein the crystallization temperature of the piezoelectric material of the first piezoelectric layer is 136°C to 144°C; the crystallization temperature of the piezoelectric material of the second piezoelectric layer is 100°C to 120°C.

[0023] In a third aspect, an embodiment of the present application discloses a method for preparing a piezoelectric film, the method comprising the following steps:

[0024] Prepare N layers of piezoelectric layers and electrode layers and isolation layers between adjacent piezoelectric layers layer by layer on the surface of the substrate;

[0025] The step of preparing any of the piezoelectric layers from the second piezoelectric layer to the Nth piezoelectric layer comprises: coating and drying a slurry formed by mixing a piezoelectric material and a solvent to obtain a piezoelectric wet film, and performing a crystallization treatment and a polarization treatment on the piezoelectric wet film to obtain the piezoelectric layer; wherein the boiling point of the solvent is greater than 200° C.;

[0026] Among them, the crystallization temperature of the piezoelectric material in the piezoelectric layer prepared later is equal to or lower than the lowest depolarization temperature of the piezoelectric material in each layer of the piezoelectric layer prepared earlier; the surface of any layer of the piezoelectric layer has the electrode layer, and the electrode layers between two adjacent piezoelectric layers are separated by the isolation layer; N is an integer greater than or equal to 2.

[0027] Furthermore, the piezoelectric layers of each layer are prepared from the same slurry, and the crystallization temperatures of the piezoelectric materials of the second piezoelectric layer to the Nth piezoelectric layer are equal to or lower than the depolarization temperature of the piezoelectric material.

[0028] In a fourth aspect, an embodiment of the present application discloses a piezoelectric film, wherein the piezoelectric film is prepared by the preparation method described in any one of the first aspect, or by the preparation method described in any one of the second aspect, or by the preparation method described in any one of the third aspect.

[0029] Compared with the prior art, the beneficial effects of this application are:

[0030] An embodiment of the present application provides a method for preparing a piezoelectric film, which allows the piezoelectric material to crystallize under conditions below its Curie temperature, rather than only being able to crystallize under temperature conditions between the melting temperature and the Curie temperature of the piezoelectric material. This achieves the effect of lowering the crystallization temperature of the piezoelectric material, avoids decomposition or phase change of materials with poor heat resistance in the piezoelectric film, and improves the adhesion stability between the substrate and the piezoelectric layer.

[0031] In this preparation method, since the boiling point of the solvent in the slurry is greater than 200°C, the piezoelectric material crystallizes at a temperature lower than the Curie temperature, which slows down the rate of solvent volatilization, and the solvent has a longer retention time, which can interact with the polymer in the piezoelectric material for a long time, and can effectively drive the migration of the polymer in the piezoelectric material, so that the polymer changes from a disordered state to an ordered state, which is conducive to the formation of the β phase. In addition, the presence of a high-boiling-point solvent will not only reduce the interaction between polymers, making the molecular chain more free, but also make the molecular chain prone to conformational changes, further increasing the degree of freedom of the molecular chain. This higher degree of freedom promotes the formation of the β phase, thereby achieving a better crystallization effect. That is, using a solvent with a boiling point greater than 200°C can make the piezoelectric material crystallize at a temperature lower than the Curie temperature of the piezoelectric material. By adopting a lower crystallization temperature, it not only helps to avoid the decomposition or phase change of materials with poor heat resistance in the piezoelectric film, but also reduces the thermal stress between the piezoelectric film and the substrate, so that the adhesion between the substrate and the piezoelectric layer is higher, thereby helping to improve the piezoelectric performance of the piezoelectric film. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 It is a multilayer piezoelectric film connected in series according to an embodiment of the present application;

[0034] Figure 2 It is a parallel multilayer piezoelectric film according to an embodiment of the present application.

[0035] Icon: 1. Substrate; 2. Piezoelectric layer; 21. First piezoelectric layer; 22. Second piezoelectric layer; 23. Third piezoelectric layer; 3. Electrode layer; 31. First electrode layer; 32. Second electrode layer; 33. Third electrode layer; 31a. First electrode layer; 32a. Second electrode layer; 33a. Third electrode layer; 31b. First electrode layer; 32b. Second electrode layer; 41. First isolation layer; 42. Second isolation layer. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In the present invention, the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like are based on the directions or positional relationships shown in the drawings. These terms are mainly used to better describe the present invention and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific direction, or to be constructed and operated in a specific direction.

[0038] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those skilled in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0039] In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise specified, "plurality" means two or more.

[0040] The technical solution provided by the present invention will be further described below in conjunction with embodiments and drawings.

[0041] Crystallization is the process of keeping the piezoelectric film at a certain temperature for a certain period of time to ensure the growth and full crystallization of the crystals in the material, and transforming the material from the paraelectric phase to the ferroelectric phase through a certain cooling rate. Strengthening the ferroelectric phase is an extremely important part of the film preparation process, so choosing a suitable crystallization temperature is crucial to improving the performance of the piezoelectric film. Among them, the Curie temperature refers to the phase transition temperature when the piezoelectric material transforms from the ferroelectric phase to the paraelectric phase. Therefore, the crystallization temperature of the piezoelectric material is higher than the Curie temperature and lower than the melting temperature, so that the piezoelectric film will have higher piezoelectric performance.

[0042] Among them, since the Curie temperature of the piezoelectric material is relatively high, the material with poor heat resistance in the piezoelectric film is prone to decomposition or phase change during the crystallization process of the piezoelectric material, thereby affecting the piezoelectric properties of the piezoelectric film. It also causes more thermal stress between the substrate and the piezoelectric film, resulting in poor adhesion between the substrate and the piezoelectric film, which reduces the piezoelectric performance of the piezoelectric film.

[0043] Based on the above problems, the embodiments of the present application provide a method for preparing a piezoelectric film and a piezoelectric film. By adopting this preparation method, the crystallization temperature of the piezoelectric material can be reduced, the decomposition or phase change of materials with poor heat resistance in the piezoelectric film can be avoided, and the adhesion stability between the substrate and the piezoelectric layer can be improved.

[0044] In a first aspect, an embodiment of the present application discloses a method for preparing a piezoelectric film, the method comprising the following steps:

[0045] Mixing a piezoelectric material and a solvent to form a slurry, coating the slurry on a substrate, and drying to obtain a piezoelectric wet film;

[0046] Performing crystallization and polarization treatment on the piezoelectric wet film to obtain a piezoelectric thin film;

[0047] Wherein, the boiling point of the solvent is greater than 200°C.

[0048] It can be understood that the piezoelectric film of the embodiment of the present application can include a substrate and a piezoelectric layer located on the substrate (i.e., the piezoelectric layer formed after the piezoelectric wet film is crystallized and polarized), and on this basis, an electrode layer can be arranged on the side of the piezoelectric layer facing away from the substrate.

[0049] The preparation method provided by the present application, since the boiling point of the solvent in the slurry is greater than 200°C, when the piezoelectric material is crystallized at a temperature lower than the Curie temperature of the piezoelectric material, the rate of solvent volatilization can be effectively reduced, so that the solvent can be retained in the piezoelectric wet film for a longer time, so it can effectively drive the migration of polymers, so that the polymers change from a disordered state to an ordered state. In addition, the presence of a high-boiling-point solvent also helps to reduce the interaction between polymers, thereby making the molecular chain have a higher degree of freedom, and also helps to promote conformational changes in the molecular chain, further increasing the degree of freedom of the molecular chain, and this high degree of freedom promotes the formation of the ferroelectric phase β phase, thereby making the piezoelectric material have a higher crystallization effect and improving the piezoelectric properties of the piezoelectric film. In other words, the use of a high-boiling-point solvent allows the piezoelectric material to have a higher crystallization effect when it is crystallized at a temperature lower than the Curie temperature, and the piezoelectric properties of the obtained single-layer piezoelectric film are higher.

[0050] In addition, since the piezoelectric material of the present application can crystallize at a temperature lower than the Curie temperature, it can effectively avoid the decomposition or phase change of materials with poor heat resistance in the piezoelectric film, thereby ensuring that the piezoelectric film has high stability. In addition, it helps to reduce the thermal stress between the substrate and the piezoelectric film and improve the adhesion between the substrate and the piezoelectric film, thereby helping to improve the piezoelectric properties of the piezoelectric film.

[0051] In summary, the preparation method provided in the embodiments of the present application enables the piezoelectric material to crystallize under conditions lower than its Curie temperature, rather than only being able to crystallize under temperature conditions between the melting temperature and the Curie temperature of the piezoelectric material, thereby achieving the effect of lowering the crystallization temperature of the piezoelectric material, avoiding the decomposition or phase change of materials with poor heat resistance in the piezoelectric film, and improving the adhesion stability between the substrate and the piezoelectric layer.

[0052] Among them, in addition to being able to crystallize below the Curie temperature, the preparation method of the present application can also crystallize between the Curie temperature and the melting temperature, making it applicable to various process production processes and improving applicability.

[0053] The present application has no particular restrictions on the material of the substrate, as long as the purpose of the present application can be achieved. For example, the material of the substrate includes at least one of a thin film transistor (TFT), indium tin oxide (ITO), and a complementary metal oxide semiconductor (CMOS); the coating method can be a doctor blade coating, a light roller coating, a mesh roller coating, a slit coating, etc. The present application has no particular restrictions on the coating method, as long as the purpose of the present application can be achieved.

[0054] Preferably, when the boiling point of the solvent is greater than 250°C, it is more helpful to improve the effect of crystallization below the Curie temperature. This is because the boiling point of the solvent affects the volatilization rate of the solvent. A higher boiling point will make the solvent retain time longer, and it can interact with the polymer of the piezoelectric material for a long time, thereby driving the migration of the polymer and improving its crystallization polarization effect. It is also more helpful to increase the degree of freedom of the molecular chain, thereby achieving a better crystallization effect. That is to say, when the boiling point of the solvent is higher than 250°C, it is more helpful to improve the crystallization and polarization effects of the solvent.

[0055] Furthermore, since the crystallization temperature of the piezoelectric material in the piezoelectric film is lower than the Curie temperature of the piezoelectric material, it helps to further reduce the decomposition of the heat-resistant material in the piezoelectric film, reduce the adverse effects such as thermal stress and thermal expansion caused by high-temperature crystallization, thereby improving the compactness and stability of the piezoelectric film and improving the piezoelectric performance of the piezoelectric film. In addition, it also helps to reduce energy consumption, reduce production costs and efficiency.

[0056] Furthermore, the solvent includes at least one of triacetin, isophorone, propylene carbonate, and triethyl phosphate. The boiling points of the above solvents are higher than 200°C, and they are all high-boiling-point solvents, which can help promote the crystallization of the piezoelectric film at low temperatures, increase the freedom of the molecular chain, ensure the effect of the piezoelectric film at low temperature crystallization, and improve the piezoelectric properties of the piezoelectric film.

[0057] Furthermore, the solid content of the slurry is 5% to 15%. When the solid content of the slurry is within the above range, the size of the crystal is appropriate, the interaction force between the crystals is moderate, which helps to promote its transformation into a ferroelectric phase, and the internal defects of the crystal are small, the film layer of the piezoelectric film is denser, which helps to improve the piezoelectric performance and yield of the piezoelectric film.

[0058] The solid content of the slurry refers to the proportion of the piezoelectric material in the slurry, that is, the ratio of the mass of the piezoelectric material to the total mass of the slurry, wherein the total mass of the slurry includes the mass of the piezoelectric material and the mass of the solvent.

[0059] The monomers used to form the piezoelectric material include vinylidene fluoride and trifluoroethylene, and the molar ratio of vinylidene fluoride to trifluoroethylene is (76-86): (14-24). When the mass ratio of vinylidene fluoride to trichloroethylene is within the above range, the molecular steric hindrance increases, promoting the formation of the ferroelectric phase β phase, and making the β phase a stable phase at room temperature, thereby helping to improve the piezoelectric properties of the piezoelectric film.

[0060] Furthermore, the depolarization temperature of the piezoelectric wet film is 120°C to 150°C. The depolarization temperature refers to the temperature at which the polarized piezoelectric layer undergoes depolarization. After depolarization, the polarization of the piezoelectric film fails. Moreover, the depolarization temperature of the material is usually lower than its Curie temperature. Therefore, when preparing a multilayer piezoelectric film, the crystallization temperature of the unprepared piezoelectric layer can be controlled to be lower than or equal to the depolarization temperature of the prepared piezoelectric layer, thereby avoiding adverse effects on the polarized piezoelectric layer when polarizing the later prepared piezoelectric layer, achieving the effect of layer-by-layer crystallization polarization, and improving the piezoelectric properties of the multilayer piezoelectric film.

[0061] Furthermore, in the crystallization step, by controlling the crystallization temperature of the piezoelectric material to be 100° C. to 144° C. and the crystallization time to be 4 h to 10 h, it helps to further improve the crystallinity of the piezoelectric film and improve the piezoelectric performance of the piezoelectric film.

[0062] In a second aspect, the present application discloses a method for preparing a piezoelectric film, the method comprising the following steps:

[0063] Prepare N layers of piezoelectric layers and electrode layers between adjacent piezoelectric layers layer by layer on the surface of the substrate;

[0064] The steps of preparing any piezoelectric layer from the second piezoelectric layer to the Nth piezoelectric layer include: coating and drying a slurry formed by mixing a piezoelectric material and a solvent to obtain a piezoelectric wet film, and performing a crystallization treatment and a polarization treatment on the piezoelectric wet film to obtain a piezoelectric layer; wherein the boiling point of the solvent is greater than 200° C.;

[0065] The crystallization temperature of the piezoelectric material in the piezoelectric layer prepared later is equal to or lower than the lowest depolarization temperature of the piezoelectric material in each of the piezoelectric layers prepared earlier;

[0066] N is an integer greater than or equal to 2.

[0067] The preparation method of the piezoelectric film provided by the present application is that the prepared multilayer piezoelectric layers are connected in series with each other, and the crystallization temperature of the piezoelectric material of the piezoelectric layer prepared later is controlled to be equal to or lower than the minimum depolarization temperature of the piezoelectric material in the piezoelectric layer prepared earlier, thereby achieving the effect of layer-by-layer crystallization and polarization, improving the success rate of polarization of the multilayer piezoelectric film, and improving the receiving and transmitting performance of the multilayer piezoelectric film for signals. In addition, the multilayer piezoelectric film prepared by the coating process in the present application has a simple preparation process, good adhesion between the film layers, and no glue bonding process is used, so that the problems of aging failure and cracking due to glue bonding can be avoided, so that the flatness between different film layers is high, there are fewer bubbles, the adhesion effect of different film layers is improved, the yield of the multilayer piezoelectric film is improved, and the conductive glue layer can be eliminated, the overall thickness of the multilayer piezoelectric film is reduced, and the performance of the multilayer piezoelectric film is improved.

[0068] like Figure 1 As shown, taking the case where the number of piezoelectric layers 2 is three as an example, the surface of the substrate 1 is sequentially provided with the first piezoelectric layer 21, the first electrode layer 31, the second piezoelectric layer 22, the second electrode layer 32, the third piezoelectric layer 23, and the third electrode layer 33, and an electrode layer 3 is provided on any piezoelectric layer 2, and the charge carried by the substrate 1 is opposite to the charge type carried by the third electrode layer 33. That is, when the substrate 1 is negatively charged, the third electrode layer 33 is positively charged, thereby realizing the series structure of the three piezoelectric layers 2.

[0069] The preparation process of the first piezoelectric layer includes: coating a slurry containing the first piezoelectric layer on a substrate and drying it to obtain a piezoelectric wet film; performing crystallization and polarization treatment on the piezoelectric wet film to obtain the first piezoelectric layer; the boiling point of the solvent for preparing the first piezoelectric layer may be higher than 200°C or less than or equal to 200°C.

[0070] In an optional embodiment, in the preparation process of the first piezoelectric layer, the boiling point of the solvent in the slurry for preparing the first piezoelectric layer is less than or equal to 200°C. Since the boiling point of the solvent is low, its volatilization rate is fast, which helps to shorten the film forming time of the piezoelectric layer and improve production efficiency. In another optional embodiment, in the preparation process of the first piezoelectric layer, the boiling point of the solvent in the slurry for preparing the first piezoelectric layer is greater than 200°C. Since the boiling point of the solvent for preparing the first piezoelectric layer is greater than 200°C, the first piezoelectric layer can also be crystallized at a Curie temperature lower than the Curie temperature of the piezoelectric material of the first piezoelectric layer, thereby helping to further reduce the energy consumption of the multilayer piezoelectric film, improve production efficiency, and help to further reduce thermal stress and thermal expansion in the preparation process, thereby ensuring that the piezoelectric layer has a high adhesion to the substrate, which helps to further improve the piezoelectric properties of the piezoelectric film.

[0071] In addition, in the step of preparing any piezoelectric layer from the second piezoelectric layer to the Nth piezoelectric layer, the piezoelectric layer and the electrode layer are prepared alternately, that is, the piezoelectric layer is prepared first and then the electrode layer is prepared on the surface of the piezoelectric layer facing away from the substrate, and the preparation is performed alternately in this order, thereby obtaining a multi-layer piezoelectric film connected in series.

[0072] Among them, the solvent with a boiling point higher than 200°C includes at least one of triacetin, isophorone, propylene carbonate, and triethyl phosphate; the coating method can be blade coating, smooth roller coating, mesh roller coating, slit coating, etc. This application does not specifically limit the coating method as long as the purpose of this application can be achieved.

[0073] The present application has no particular restrictions on the material of the substrate and the material of the electrode layer, as long as the purpose of the present application can be achieved. For example, the material of the substrate includes at least one of a thin film transistor (TFT), indium tin oxide (ITO), and a complementary metal oxide semiconductor (CMOS). The material of the electrode layer includes but is not limited to silver, gold, platinum, tungsten, conductive ink and other materials. When silver or conductive ink is selected as the material of the electrode layer, the electrode layer has a high adhesion to the piezoelectric layer and a good degree of adhesion, which helps to reduce interface defects and is conducive to further improving the performance of the multilayer piezoelectric film.

[0074] In the preparation process of the multilayer piezoelectric film, each piezoelectric layer can be prepared using different piezoelectric materials or the same piezoelectric material. In an optional embodiment, each piezoelectric layer can be prepared using different piezoelectric materials. Therefore, in the preparation process, due to the different depolarization temperatures of different piezoelectric materials, the crystallization temperature of the piezoelectric layer prepared later needs to be equal to or lower than the lowest depolarization temperature of the prepared piezoelectric layer. Specifically, the depolarization temperature of the piezoelectric material of the first piezoelectric layer is 100°C, so the crystallization temperature of the second piezoelectric layer is lower than or equal to the depolarization temperature of the first piezoelectric material. Since the depolarization temperature of the piezoelectric material of the second piezoelectric layer is 120°C, the crystallization temperature of the third piezoelectric layer needs to be lower than or equal to the depolarization temperature of the first layer. In this way, it can be ensured that in the process of crystallization polarization of the third piezoelectric layer, it will not have an adverse effect on the already polarized second piezoelectric layer and the first piezoelectric layer, ensuring that the polarization effect of each piezoelectric layer is high, thereby helping to improve the piezoelectric performance of the multilayer piezoelectric film.

[0075] In another optional embodiment, each piezoelectric layer is prepared from the same slurry. In this case, the depolarization temperature of any piezoelectric layer is the same. Therefore, when the crystallization temperatures of the piezoelectric materials from the second piezoelectric layer to the Nth piezoelectric layer are equal to or lower than the depolarization temperature of the piezoelectric material, the effect of layer-by-layer crystallization polarization can be achieved. In addition, the preparation process of this method is simple, which helps to improve the efficiency of production and processing.

[0076] Specifically, when the piezoelectric material of the piezoelectric layer includes a copolymer formed by copolymerization of vinylidene fluoride and trifluoroethylene in a molar ratio of (76 to 86): (14 to 24), and the number of piezoelectric layers is 2, the crystallization temperature of the piezoelectric material of the first piezoelectric layer is 136°C to 144°C, and the crystallization temperature of the piezoelectric material of the second piezoelectric layer is 100°C to 120°C.

[0077] Furthermore, the solid content of the slurry of any piezoelectric layer is 5% to 15%. When the solid content of the slurry is within the above range, the size of the crystal is appropriate and the interaction force between the crystals is moderate, which helps to promote its transformation into a ferroelectric phase with a larger solid content and smaller internal defects of the crystal. The film layer density of the piezoelectric film is higher, which helps to improve the piezoelectric properties of the piezoelectric film.

[0078] In a third aspect, an embodiment of the present application discloses a method for preparing a piezoelectric film, the method comprising the following steps:

[0079] Prepare N layers of piezoelectric layers and electrode layers and isolation layers between adjacent piezoelectric layers layer by layer on the surface of the substrate;

[0080] The steps of preparing any piezoelectric layer from the second piezoelectric layer to the Nth piezoelectric layer include: coating and drying a slurry formed by mixing a piezoelectric material and a solvent to obtain a piezoelectric wet film, and performing a crystallization treatment and a polarization treatment on the piezoelectric wet film to obtain a piezoelectric layer; wherein the boiling point of the solvent is greater than 200° C.;

[0081] Among them, the crystallization temperature of the piezoelectric material in the piezoelectric layer prepared later is equal to or lower than the lowest depolarization temperature of the piezoelectric material in each of the piezoelectric layers prepared earlier; the surface of any piezoelectric layer has an electrode layer, and the electrode layers between two adjacent piezoelectric layers are separated by an isolation layer; N is an integer greater than or equal to 2.

[0082] The preparation method of the piezoelectric film provided by the present application has an electrode layer on the surface of any piezoelectric layer, and the electrode layer between two adjacent piezoelectric layers is separated by an isolation layer, so that multiple piezoelectric layers are connected in parallel. And by controlling the crystallization temperature of the piezoelectric material of the piezoelectric layer prepared later to be lower than the minimum depolarization temperature of the piezoelectric material in the piezoelectric layer prepared earlier, the effect of layer-by-layer crystallization and polarization is achieved, the success rate of polarization of the multilayer piezoelectric film is improved, and the receiving and transmitting performance of the multilayer piezoelectric film for signals is improved. In addition, the multilayer piezoelectric film prepared by the coating process in the present application has a simple preparation process, good adhesion between the film layers, and no glue bonding process is used, so that the problems of aging failure and cracking due to glue bonding can be avoided, so that the flatness between different film layers is high, there are fewer bubbles, the adhesion effect of different film layers is improved, the yield of the multilayer piezoelectric film is improved, and the conductive glue layer can be eliminated, the overall thickness of the multilayer piezoelectric film is reduced, and the performance of the multilayer piezoelectric film is improved.

[0083] like Figure 2 As shown, the surface of the substrate 1 is provided with a first piezoelectric layer 21, a first first electrode layer 31a, a first isolation layer 41, a first second electrode layer 31b, a second piezoelectric layer 22, a second first electrode layer 32a, a second isolation layer 42, a second second electrode layer 32b, a third piezoelectric layer 23, and a third first electrode layer 33a in sequence, and the first electrode layer and the second electrode layer have opposite charges. Among them, the first first electrode layer 31a and the first second electrode layer 31b are separated by the first isolation layer 41, and the second first electrode layer 32a and the second second electrode layer 32b are separated by the second isolation layer 42. The first first electrode layer 31a, the second first electrode layer 32a, and the third first electrode layer 33a are all arranged on the surface of the piezoelectric layer facing away from the substrate 1, and the first second electrode layer 31b and the second second electrode layer 32b are all arranged on the surface of the piezoelectric layer close to the substrate 1. When the substrate 1 is positively charged, multiple first electrode layers are interconnected to form a positive electrode, multiple second electrode layers are interconnected with the substrate 1 to form a negative electrode, and the isolation layer separates adjacent piezoelectric layers, thereby realizing a parallel structure of three piezoelectric layers.

[0084] The preparation process of the first piezoelectric layer includes: coating a slurry containing the first piezoelectric layer on a substrate and drying it to obtain a piezoelectric wet film; performing crystallization and polarization treatment on the piezoelectric wet film to obtain the first piezoelectric layer; the boiling point of the solvent for preparing the first piezoelectric layer may be higher than 200°C or less than or equal to 200°C.

[0085] In an optional embodiment, in the preparation process of the first piezoelectric layer, the boiling point of the solvent in the slurry for preparing the first piezoelectric layer is less than or equal to 200°C. The boiling point of the solvent is low, so its volatilization rate is fast, which helps to shorten the film forming time of the piezoelectric layer and improve production efficiency. In another optional embodiment, in the preparation process of the first piezoelectric layer, the boiling point of the solvent in the slurry for preparing the first piezoelectric layer is greater than 200°C. Since the boiling point of the solvent for preparing the first piezoelectric layer is greater than 200°C, the first piezoelectric layer can also be crystallized at a Curie temperature lower than the piezoelectric material of the first piezoelectric layer, thereby helping to further reduce the energy consumption of the multilayer piezoelectric film, improve production efficiency, and help to further reduce thermal stress and thermal expansion in the preparation process, thereby ensuring that the piezoelectric layer has a high adhesion to the substrate, which helps to further improve the piezoelectric properties of the piezoelectric film.

[0086] Among them, the solvent can be selected from at least one of triacetin, isophorone, propylene carbonate, and triethyl phosphate. The coating method can be blade coating, smooth roller coating, mesh roller coating, slit coating, etc. The present application does not specifically limit the coating method as long as the purpose of the present application can be achieved.

[0087] The present application has no particular restrictions on the material of the substrate and the material of the electrode layer, as long as the purpose of the present application can be achieved. For example, the material of the substrate includes conductive thin film transistors (TFT), indium tin oxide (ITO), complementary metal oxide semiconductors (CMOS), etc. The material of the electrode layer includes but is not limited to one of silver, gold, platinum, tungsten, and conductive ink. When silver or conductive ink is selected as the material of the electrode layer, the electrode layer has a high adhesion to the piezoelectric layer and a good degree of adhesion, which helps to reduce interface defects and is conducive to further improving the performance of the multilayer piezoelectric film.

[0088] In the process of preparing a multilayer piezoelectric film, any piezoelectric layer can be prepared using different piezoelectric materials or the same piezoelectric material. In one optional embodiment, different piezoelectric layers can be prepared using different piezoelectric materials. Therefore, in the preparation process, due to the different depolarization temperatures of different piezoelectric materials, the crystallization temperature of the piezoelectric layer prepared later needs to be equal to or lower than the lowest temperature of the prepared piezoelectric layer. Specifically, the depolarization temperature of the piezoelectric material of the first piezoelectric layer is 100°C, so the crystallization temperature of the second piezoelectric layer is lower than or equal to the depolarization temperature of the first piezoelectric material. Since the depolarization temperature of the piezoelectric material of the second piezoelectric layer is 120°C, the crystallization temperature of the third piezoelectric layer needs to be lower than or equal to the depolarization temperature of the first layer. In this way, it can be ensured that in the process of crystallization polarization of the third piezoelectric layer, it will not have an adverse effect on the already polarized second piezoelectric layer and the first piezoelectric layer, ensuring that the polarization effect of each piezoelectric layer is high, thereby helping to improve the piezoelectric performance of the multilayer piezoelectric film.

[0089] In another optional embodiment, each piezoelectric layer is prepared from the same slurry, and the crystallization temperature of the piezoelectric materials from the second piezoelectric layer to the Nth piezoelectric layer is equal to or lower than the depolarization temperature of the piezoelectric material. When each piezoelectric layer is prepared from the same slurry, the depolarization temperature of any piezoelectric layer is the same. Therefore, when the crystallization temperature of the piezoelectric materials from the second piezoelectric layer to the Nth piezoelectric layer is equal to or lower than the depolarization temperature of the piezoelectric material, the effect of layer-by-layer crystallization polarization can be achieved. In addition, the preparation process of this method is simple, which helps to improve the efficiency of production and processing.

[0090] Specifically, when the piezoelectric material of the piezoelectric layer includes a copolymer formed by copolymerization of vinylidene fluoride and trifluoroethylene in a molar ratio of (76 to 86): (14 to 24), and the number of piezoelectric layers is 2, the crystallization temperature of the piezoelectric material of the first piezoelectric layer is 136°C to 144°C; the crystallization temperature of the piezoelectric material of the second piezoelectric layer is 100°C to 120°C.

[0091] Furthermore, the solid content of the slurry of any piezoelectric layer is 5% to 15%. When the solid content of the slurry is within the above range, the size of the crystal is appropriate and the interaction force between the crystals is moderate, which helps to promote its transformation into a ferroelectric phase with a larger solid content and smaller internal defects of the crystal. The film layer density of the piezoelectric film is higher, which helps to improve the piezoelectric properties of the piezoelectric film.

[0092] In a fourth aspect, the embodiments of the present application disclose a piezoelectric film produced by the production method of the first aspect, or produced by the production method of the second aspect, or produced by the production method of the third aspect.

[0093] The preparation method of the piezoelectric film and the piezoelectric film of the embodiment of the present application are further described below in conjunction with more specific embodiments.

[0094] 1. The embodiments of the present application provide specific embodiments of single-layer piezoelectric films.

[0095] Embodiment 1:

[0096] A single-layer piezoelectric film, the preparation method of which comprises the following steps:

[0097] Coating a piezoelectric layer slurry on the surface of a thin film transistor substrate to form a piezoelectric layer wet film, wherein the molar ratio of vinylidene fluoride to trifluoroethylene in the piezoelectric material of the piezoelectric layer slurry is 80:20, the solid content of the slurry is 10%, the solvent is triacetin, and the thickness of the thin film transistor substrate is 500 μm;

[0098] The piezoelectric layer wet film is subjected to crystallization treatment and polarization treatment, wherein the crystallization treatment temperature is 120° C. and the time is 4 hours, to obtain a piezoelectric layer with a thickness of 10 μm;

[0099] A silver electrode layer is prepared on the surface of the piezoelectric layer, wherein the thickness of the silver electrode layer is 3 μm.

[0100] Embodiment 2:

[0101] The only difference between this embodiment and the first embodiment is that the crystallization temperature is 144°C.

[0102] Embodiment three:

[0103] The only difference between this embodiment and the first embodiment is that the solvent type is isophorone.

[0104] Embodiment 4:

[0105] The only difference between this embodiment and the first embodiment is that the solvent type is triethyl phosphate.

[0106] Embodiment five:

[0107] The only difference between this embodiment and the first embodiment is that the solid content of the slurry is 5%.

[0108] Embodiment six:

[0109] The only difference between this embodiment and the first embodiment is that the solid content of the slurry is 15%.

[0110] Comparative Example 1:

[0111] The only difference between this comparative example and Example 1 is that the solvent is propylene glycol methyl ether acetate.

[0112] Test result 1:

[0113] The single-layer piezoelectric film obtained in Examples 1 to 6 and Comparative Example 1 was tested with an oscilloscope to collect trigger voltage signals, and voltage data of each example and comparative example was obtained. The measured voltage data can directly reflect the signal receiving capability of the single-layer piezoelectric film. The greater the voltage, the stronger the signal receiving capability of the single-layer piezoelectric film. The test results are shown in Table 1 below.

[0114] Table 1 Voltage data of the embodiments and comparative examples

[0115] Serial number Voltage (mV) Serial number Voltage (mV) Embodiment 1 759 Embodiment 5 743 Embodiment 2 833 Embodiment 6 749 Embodiment 3 623 Comparative Example 1 54 Embodiment 4 654

[0116] By analyzing the data of Example 1, Example 3 to Example 6 and Comparative Example 1, it can be seen that the performance of the examples is better than that of Comparative Example 1. This is because the solvent used in the examples is triacetin, which has a relatively high boiling point. Therefore, the piezoelectric material can be crystallized and polarized at a temperature lower than its Curie temperature, avoiding the decomposition of materials with poor heat resistance, and improving the adhesion stability between the piezoelectric layer and the substrate, thereby helping to improve the piezoelectric properties of the piezoelectric film.

[0117] Analysis of the data of Example 1 and Example 2 shows that the performance of Example 2 is better than that of Example 1, wherein the crystallization temperature of Example 1 is lower than the Curie temperature, and the crystallization temperature of Example 2 is higher than the Curie temperature, indicating that the preparation method of the present application can not only perform crystallization polarization between the Curie temperature and the melting temperature, but also perform crystallization polarization below the Curie temperature, which broadens the crystallization temperature range of the piezoelectric material and is helpful for preparing multilayer piezoelectric films. Moreover, when crystallization polarization is performed above the Curie temperature, it is more helpful to improve the piezoelectric properties of the piezoelectric film.

[0118] Analysis of the data of Example 1, Example 3 and Example 4 shows that the performance of Example 1 is better than that of Example 3 and Example 4. This is because the solvent used in Example 1 is triacetin, which has a boiling point of about 260°C, the solvent used in Example 3 is isophorone, which has a boiling point of about 210°C, and the solvent used in Example 4 is triethyl phosphate, which has a boiling point of about 210°C. That is, the boiling point of the solvent in Example 1 is higher than that of Example 3 and Example 4, so it can effectively reduce the rate of solvent volatilization, so that the solvent retention time is longer, and can effectively drive the migration of polymers in the piezoelectric material, thereby ensuring that its crystallization and polarization effects are higher, which helps to improve the piezoelectric properties of the piezoelectric film.

[0119] Analysis of the data of Example 1, Example 5 and Example 6 shows that the performance of Example 1 is better than that of Example 5. This is because the solid content of the slurry of Example 1 is higher than that of Example 5. Therefore, the film density of the piezoelectric layer prepared in Example 1 is higher, which helps to further improve the piezoelectric properties of the piezoelectric film; the performance of Example 1 is better than that of Example 6. This is because the solid content of the slurry of Example 1 is lower than that of Example 6. Therefore, the fluidity of the slurry during the preparation process is appropriate, which is more conducive to forming a film layer of uniform thickness, ensuring that the prepared piezoelectric layer has a higher quality, thereby helping to improve the piezoelectric properties of the piezoelectric film.

[0120] 2. The embodiments of the present application provide specific embodiments of multi-layer piezoelectric films.

[0121] Embodiment seven:

[0122] The present application provides a multilayer piezoelectric film connected in series, and the preparation method thereof comprises the following steps:

[0123] Step 1: coating a first piezoelectric layer slurry on the surface of a thin film transistor substrate to form a first piezoelectric layer wet film, wherein the molar ratio of vinylidene fluoride to trifluoroethylene in the piezoelectric material of the first piezoelectric layer slurry is 80:20, the solid content of the slurry is 10%, the solvent is propylene glycol methyl ether acetate, and the thickness of the thin film transistor substrate is 500 μm;

[0124] The first piezoelectric layer wet film is subjected to crystallization treatment and polarization treatment, wherein the crystallization treatment temperature is 144° C. and the time is 4 hours, to obtain a first piezoelectric layer with a thickness of 10 μm;

[0125] Step 2: sequentially preparing a silver electrode layer on the surface of the first piezoelectric layer, wherein the thickness of the silver electrode layer is 3 μm;

[0126] Step 3: coating a second piezoelectric layer slurry on the surface of the silver electrode layer to form a second piezoelectric layer wet film, wherein the molar ratio of vinylidene fluoride to trifluoroethylene in the piezoelectric material of the first piezoelectric layer slurry is 80:20, the solid content of the slurry is 10%, and the solvent is triacetin;

[0127] The second piezoelectric layer wet film is subjected to crystallization treatment and polarization treatment, wherein the crystallization treatment temperature is 120° C. and the time is 4 hours, to obtain a second piezoelectric layer with a thickness of 10 μm;

[0128] Step 4: sequentially preparing a silver electrode layer on the surface of the second piezoelectric layer, wherein the thickness of the silver electrode layer is the same as the thickness of the silver electrode layer in step 2.

[0129] Embodiment eight:

[0130] The only difference between this embodiment and embodiment seven is that the molar percentage of vinylidene fluoride and trifluoroethylene in the piezoelectric material of the first piezoelectric layer slurry is 75:25, the molar percentage of vinylidene fluoride and trifluoroethylene in the piezoelectric material of the second piezoelectric layer slurry is 80:20, and the crystallization temperature of the second piezoelectric wet film is 110°C.

[0131] Embodiment nine:

[0132] The only difference between this embodiment and the seventh embodiment is that N is three layers, wherein the second piezoelectric layer and the third piezoelectric layer are both prepared by using the same slurry and the crystallization treatment conditions are the same.

[0133] Embodiment ten:

[0134] The present application embodiment provides a multi-layer piezoelectric film connected in parallel, and the preparation method thereof comprises the following steps:

[0135] Step 1: coating a first piezoelectric layer slurry on the surface of a thin film transistor substrate to form a first piezoelectric layer wet film, wherein the molar ratio of vinylidene fluoride to trifluoroethylene in the piezoelectric material of the first piezoelectric layer slurry is 80:20, the solid content of the slurry is 10%, the solvent is propylene glycol methyl ether acetate, and the thickness of the thin film transistor substrate is 500 μm;

[0136] The first piezoelectric layer wet film is subjected to crystallization treatment and polarization treatment, wherein the crystallization treatment temperature is 144° C. and the time is 4 hours, to obtain a first piezoelectric layer with a thickness of 10 μm;

[0137] Step 2: sequentially preparing a first silver electrode layer, an ink layer, and a second silver electrode layer on the surface of the first piezoelectric layer, wherein the thickness of the first silver electrode layer is 3 μm, the thickness of the ink layer is 5 μm, and the thickness of the second silver electrode layer is 3 μm;

[0138] Step 3: coating a second piezoelectric layer slurry on the surface of the silver electrode layer to form a second piezoelectric layer wet film, wherein the molar ratio of vinylidene fluoride to trifluoroethylene in the piezoelectric material of the first piezoelectric layer slurry is 80:20, the solid content of the slurry is 10%, and the solvent is triacetin;

[0139] The second piezoelectric layer wet film is subjected to crystallization treatment and polarization treatment, wherein the crystallization treatment temperature is 124° C. and the time is 4 hours, to obtain a second piezoelectric layer with a thickness of 10 μm;

[0140] Step 4: sequentially preparing a first silver electrode layer, an ink layer, and a second silver electrode layer on the surface of the second piezoelectric layer, wherein the thicknesses of the first silver electrode layer, the ink layer, and the second silver electrode layer are the same as those of the first silver electrode layer, the ink layer, and the second silver electrode layer in step 2.

[0141] Comparative Example 2:

[0142] The only difference between this comparative example and the first embodiment is that the solvent in the slurry of the second piezoelectric layer is propylene glycol methyl ether acetate.

[0143] Comparative Example 3:

[0144] The only difference between this comparative example and the second embodiment is that the crystallization temperature of the second piezoelectric wet film is 130°C.

[0145] Test result 1:

[0146] The multilayer piezoelectric films obtained in Examples 7 to 10 and Comparative Examples 2 to 3 were tested with an oscilloscope to collect trigger voltage signals, and voltage data of each embodiment and comparative example was obtained. Among them, the measured voltage data can directly reflect the signal receiving ability of the multilayer piezoelectric film. The greater the voltage, the stronger the signal receiving ability of the multilayer piezoelectric film. The test results are shown in Table 2 below.

[0147] Table 2 Voltage data of the embodiments and comparative examples

[0148]

[0149]

[0150] Analysis of the data of Examples 7 to 9 and Comparative Example 2 shows that the performance of Examples 7 to 9 is better than that of Comparative Example 2. This is because the solvent used in the slurry of the second piezoelectric layer of Examples 7 to 9 is triacetin, and the solvent in the slurry of the second piezoelectric layer of Comparative Example 2 is propylene glycol methyl ether acetate. Among them, the boiling point of the triacetin solvent is relatively high, so it can achieve the effect of crystallization at a temperature lower than the Curie temperature of the piezoelectric material, which helps to improve the piezoelectric properties of the multilayer piezoelectric film. The boiling point of propylene glycol methyl ether acetate is relatively low, so it is difficult to perform crystallization polarization at 120°C, which makes the load of Comparative Example 2 relatively high, and it is difficult to effectively improve its piezoelectric performance.

[0151] Analysis of the data of Example 7, Example 9 and Comparative Example 3 shows that the performance of Examples 7 to 9 are all better than that of Comparative Example 3. This is because the depolarization temperature of the piezoelectric material in the examples is 120°C, and the crystallization temperature of the second layer of piezoelectric wet film in the examples is lower than the depolarization temperature of the first layer of piezoelectric wet film. Therefore, the phenomenon of depolarization of the first layer of piezoelectric layer when the second layer of piezoelectric layer is crystallized is avoided, thereby achieving the effect of layer-by-layer crystallization polarization and improving the piezoelectric properties of the multilayer piezoelectric film to a greater extent.

[0152] Analysis of the data of Example 8 shows that the piezoelectric material of the first piezoelectric layer of Example 8 is different from the piezoelectric material of the second piezoelectric layer, and the depolarization temperature of the first piezoelectric layer is 110°C, and the depolarization temperature of the second piezoelectric layer is 120°C. Therefore, when the second piezoelectric layer is crystallized and polarized, its crystallization temperature is set to 110°C, thereby effectively ensuring that the second piezoelectric layer will not cause the first piezoelectric layer to produce depolarization during the crystallization and polarization process, so that the multi-layer piezoelectric layers can be crystallized and polarized layer by layer, improving the polarization effect of the multi-layer piezoelectric film, which helps to improve the piezoelectric properties of the piezoelectric film.

[0153] Analysis of the data of Example 7 and Example 9 shows that the data of Example 9 is better than that of Example 7. This is because the number of piezoelectric layers in Example 9 is more than that in Example 7. Therefore, the multilayer piezoelectric film prepared in Example 9 is more sensitive to signals and is more helpful in improving its piezoelectric performance.

[0154] Analysis of the data of Example 10 shows that Example 10 is a parallel multilayer piezoelectric film, which means that when the preparation method of the present application is used to prepare a parallel multilayer piezoelectric film, the effect of layer-by-layer crystallization and polarization can be achieved, and the parallel structure enables the piezoelectric film to have higher driving performance.

[0155] The above is a detailed introduction to the preparation method and piezoelectric film disclosed in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the preparation method and piezoelectric film of the piezoelectric film: At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for preparing a piezoelectric film, characterized in that: The preparation method comprises the following steps: Mixing a piezoelectric material and a solvent to form a slurry, coating the slurry on a substrate, and drying to obtain a piezoelectric wet film; Performing crystallization and polarization treatment on the piezoelectric wet film to obtain the piezoelectric thin film; Wherein, the boiling point of the solvent is greater than 200°C.

2. The preparation method according to claim 1, characterized in that: The solid content of the slurry is 5% to 15%.

3. The preparation method according to claim 1, characterized in that: The piezoelectric material of the piezoelectric film has a crystallization temperature lower than a Curie temperature of the piezoelectric material.

4. The preparation method according to claim 1, characterized in that: The solvent comprises at least one of triacetin, isophorone, propylene carbonate and triethyl phosphate; and / or, The monomers used to form the piezoelectric material include vinylidene fluoride and trifluoroethylene, and the molar ratio of the vinylidene fluoride to the trifluoroethylene is (76-86):(14-24); and / or, The depolarization temperature of the piezoelectric wet film is 120° C. to 150° C.; and / or, In the step of crystallization treatment, the crystallization temperature of the piezoelectric material is 100° C. to 144° C., and the crystallization time is 4 hours to 10 hours.

5. A method for preparing a piezoelectric film, characterized in that: The preparation method comprises the following steps: Prepare N layers of piezoelectric layers and electrode layers between adjacent piezoelectric layers layer by layer on the surface of the substrate; The step of preparing any of the piezoelectric layers from the second piezoelectric layer to the Nth piezoelectric layer comprises: coating and drying a slurry formed by mixing a piezoelectric material and a solvent to obtain a piezoelectric wet film, and performing a crystallization treatment and a polarization treatment on the piezoelectric wet film to obtain the piezoelectric layer; wherein the boiling point of the solvent is greater than 200° C.; The crystallization temperature of the piezoelectric material in the piezoelectric layer prepared later is equal to or lower than the lowest depolarization temperature of the piezoelectric material in each of the piezoelectric layers prepared earlier; N is an integer greater than or equal to 2.

6. The preparation method according to claim 5, characterized in that: The piezoelectric layers of each layer are prepared from the same slurry, and the crystallization temperatures of the piezoelectric materials of the second piezoelectric layer to the Nth piezoelectric layer are all equal to or lower than the depolarization temperature of the piezoelectric material.

7. The preparation method according to claim 5, characterized in that: The crystallization temperature of the piezoelectric material of the first piezoelectric layer is lower than the Curie temperature of the first piezoelectric layer.

8. The preparation method according to claim 5, characterized in that: The piezoelectric material of the piezoelectric layer includes a copolymer formed by copolymerization of vinylidene fluoride and trifluoroethylene in a molar ratio of (76-86):(14-24), and the piezoelectric layer has two layers, wherein the crystallization temperature of the piezoelectric material of the first piezoelectric layer is 136°C-144°C; the crystallization temperature of the piezoelectric material of the second piezoelectric layer is 100°C-120°C.

9. A method for preparing a piezoelectric film, characterized in that: The preparation method comprises the following steps: Prepare N layers of piezoelectric layers and electrode layers and isolation layers between adjacent piezoelectric layers layer by layer on the surface of the substrate; The step of preparing any of the piezoelectric layers from the second piezoelectric layer to the Nth piezoelectric layer comprises: coating and drying a slurry formed by mixing a piezoelectric material and a solvent to obtain a piezoelectric wet film, and performing a crystallization treatment and a polarization treatment on the piezoelectric wet film to obtain the piezoelectric layer; wherein the boiling point of the solvent is greater than 200° C.; Among them, the crystallization temperature of the piezoelectric material in the piezoelectric layer prepared later is equal to or lower than the lowest depolarization temperature of the piezoelectric material in each layer of the piezoelectric layer prepared earlier; the surface of any layer of the piezoelectric layer has the electrode layer, and the electrode layers between two adjacent piezoelectric layers are separated by the isolation layer; N is an integer greater than or equal to 2.

10. The preparation method according to claim 9, characterized in that: The piezoelectric layers of each layer are prepared from the same slurry, and the crystallization temperatures of the piezoelectric materials of the second piezoelectric layer to the Nth piezoelectric layer are all equal to or lower than the depolarization temperature of the piezoelectric material.

11. A piezoelectric film, characterized in that: The piezoelectric film is prepared by the preparation method described in any one of claims 1 to 4, or prepared by the preparation method described in any one of claims 5 to 8, or prepared by the preparation method described in any one of claims 9 to 10.

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