Self-supporting piezoelectric film and preparation method thereof

Abstract

The invention discloses a self-supporting piezoelectric film and a preparation method thereof. The preparation method of the self-supporting piezoelectric film comprises the following steps: providing an initial layered structure body; the device sequentially comprises a substrate, a conductive electrode layer and a piezoelectric film layer from bottom to top, the substrate contains surface ions, and one side containing the surface ions is in contact with the conductive electrode layer; and a polar solvent is introduced between the substrate and the conductive electrode layer, standing is carried out, the polar solvent and surface ions on the substrate are subjected to solvation, and the substrate is separated from the conductive electrode layer and the piezoelectric film layer. The substrate containing the surface ions is adopted, the polar solvent is introduced to be subjected to solvation with the surface ions, the substrate is separated from the conductive electrode layer and the piezoelectric film layer, the problem that an existing rigid substrate is difficult to peel off is solved, and the obtained film has excellent crystal texture and microstructure integrity; the mechanical clamping effect of the rigid substrate is eliminated, and the piezoelectric and ferroelectric properties are better.

Description

Technical Field

[0001] This invention relates to the field of functional thin film materials technology, and in particular to a self-supporting piezoelectric thin film and its preparation method. Background Technology

[0002] Piezoelectric thin films, as functional materials capable of converting mechanical energy into electrical energy, have broad application prospects in microelectromechanical systems (MEMS), sensors, acoustic devices, and energy harvesting. Traditionally, piezoelectric thin films are typically grown directly on rigid inorganic substrates (such as silicon, sapphire, or zirconium oxide). However, rigid substrates have a high Young's modulus, which can exert a significant mechanical clamping effect on the piezoelectric thin film. This effect suppresses the effective deformation of the film under external stimuli (such as sound waves or mechanical vibrations), thereby limiting the strain generated in the piezoelectric layer, reducing the output amplitude of the piezoelectric signal, and adversely affecting the device's sensitivity, signal-to-noise ratio, and energy conversion efficiency. Furthermore, high-stiffness substrates can cause the device's resonant frequency to shift towards higher frequencies, which is detrimental to the application of acoustic sensors operating in the mid-to-low frequency range, such as human voice.

[0003] To overcome the aforementioned performance bottlenecks, peeling the piezoelectric film from its native growth substrate to prepare a self-supporting film or transferring it to a flexible substrate has become a key technological approach to improve device performance. Currently, the technologies for preparing self-supporting piezoelectric films are mainly divided into physical methods and chemical methods.

[0004] Physical methods primarily utilize external energy or mechanical force to separate the thin film from the substrate. Representative techniques include laser ablation, stress-assisted mechanical ablation, and mechanical thinning. For example, laser ablation uses a high-energy laser beam to irradiate the interface between the transparent substrate and the thin film, achieving separation through interface ablation. While effective, this method typically requires expensive and complex laser equipment, and its application is limited to optically transparent substrates (such as sapphire), lacking universality. Mechanical ablation methods, on the other hand, may introduce uncontrollable mechanical stress during the process, leading to microcracks, curling, or breakage of the thin film, affecting the structural integrity of the film and the yield of the device.

[0005] Chemical methods utilize the selective corrosion properties between materials. A common technique involves pre-growing a sacrificial layer between the substrate and the functional thin film, which can be rapidly corroded by specific chemical reagents. The functional thin film is then released by immersing it in an etching solution to remove the sacrificial layer. While widely used, this method is relatively complex, requiring additional materials and process steps. More importantly, the chemical etching process can damage or contaminate the piezoelectric thin film itself, leading to deterioration of its electrical properties (such as leakage current and piezoelectric coefficient). Furthermore, the surface tension of the liquid during wet etching can cause large-area film rupture.

[0006] Therefore, existing technologies still face challenges in preparing high-quality, large-area self-supporting piezoelectric films, namely, how to achieve efficient and controllable peeling while maximally preserving the film's original excellent crystal structure and electrical properties, and avoiding process damage. There is an urgent need for a universal preparation technique that is based on a clear mechanism, is easy to operate, low in cost, and does not damage the film, in order to promote the development of high-performance flexible piezoelectric devices. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a self-supporting PZT thin film and its preparation method. This invention utilizes a substrate containing surface ions and introduces a polar solvent to solvate the surface ions, achieving separation of the substrate from the conductive electrode layer and the piezoelectric thin film layer, thus obtaining a self-supporting piezoelectric thin film. This solves the problem of difficult peeling from existing rigid substrates. This method ensures that the resulting film possesses excellent crystal texture and microstructure integrity, and exhibits significantly enhanced piezoelectric and ferroelectric properties due to the elimination of the mechanical clamping effect of the rigid substrate.

[0008] The technical solution of the present invention is as follows: The first aspect of this invention provides a method for preparing a self-supporting piezoelectric thin film, comprising the following steps: S1: Provides the initial layered structure; The initial layered structure comprises, from bottom to top, a substrate, a conductive electrode layer, and a piezoelectric thin film layer; The substrate is a substrate containing surface ions, and the side containing surface ions is in contact with the conductive electrode layer; S2: A polar solvent is introduced into the interface between the substrate and the conductive electrode layer, and the mixture is left to stand, so that the polar solvent reacts with the surface ions on the substrate to reduce the binding energy of the interface; thus, the substrate is separated from the conductive electrode layer and the piezoelectric thin film layer to obtain a self-supporting piezoelectric thin film.

[0009] Understandably, this invention is the first to propose and verify the "ion-unlocking" interface stripping mechanism. By utilizing the solvation effect of polar solvents on the surface of van der Waals substrates, the interfacial binding energy is weakened, allowing the film stripping process to proceed spontaneously and rapidly at room temperature. This method eliminates the need for a pre-set sacrificial layer, expensive laser equipment, or complex chemical etching steps, significantly simplifying the process, reducing costs considerably, and exhibiting good scalability. Furthermore, the gentle "ion-unlocking" process avoids damage to the film caused by high-energy particle bombardment or strong chemical etching. The self-supporting film obtained using this method retains its excellent crystal structure, chemical composition, dense microstructure, and surface smoothness grown on the native substrate. The leakage current density of the transferred film increases only slightly, indicating that the process does not introduce a large number of conductive defects, laying a material foundation for realizing high-performance devices.

[0010] The DFT calculation model and result diagram of the "ion unlocking" mechanism mentioned in this invention are shown below. Figure 2 As shown in the figure: (a) is the calculation model of ion-locked state and ion-unlocked state; (b) is the differential charge density map of the two states; (c) is the differential charge density distribution curve averaged along the interface normal direction. It can be seen from the figure that the intervention of water molecules significantly reduces the charge density overlap at the interface, which confirms the effective weakening of the interfacial binding energy by solvation.

[0011] This invention further provides AIMD simulation snapshots of the ion unlocking process. For example... Figure 4 As shown, the simulation results dynamically reproduce the microscopic dynamics of water molecules surrounding and carrying away surface potassium ions. This further illustrates the feasibility of the ion unlocking method of this invention.

[0012] Preferably, in S1, the substrate is a van der Waals substrate containing surface ions; In this invention, the van der Waals substrate used, in addition to mica, can also be other materials with a layered structure and containing solvable ions on the surface or between layers, such as certain transition metal sulfides (TMDs) or clay minerals, which can also be used as the van der Waals substrate of this invention.

[0013] Preferably, the substrate is a mica substrate containing surface ions; Preferably, the mica substrate includes at least one of muscovite and phlogopite; More preferably, the mica is artificial fluorophlogopite with the structural formula KMg3(AlSi3O) 10 F2, purchased from Changchun Taiyuan Fluoropyramic Co., Ltd.

[0014] More preferably, the thickness of the substrate is 0.01~0.1 mm.

[0015] Preferably, in S1, the surface ions are alkali metal ions; Preferably, the alkali metal ion includes potassium ion.

[0016] It should be noted that the surface ions are those naturally present in the mica used in this invention.

[0017] Preferably, in S1, the conductive electrode layer includes at least one of platinum, molybdenum, and gold; The piezoelectric thin film is a perovskite structure ferroelectric thin film, preferably a PZT (lead zirconate titanate (Pb(Zr,Ti)O3, abbreviated as PZT)) thin film; the present invention does not limit the PZT thin film, and any solution that can achieve the purpose of the present invention is within the protection scope of the present invention.

[0018] The thickness of the piezoelectric film is 0.5~2μm.

[0019] In one embodiment, the microstructure of the PZT film comprises coexisting trigonal and tetragonal phases, wherein the volume fraction of the trigonal phase is greater than 75%. The coexistence of the two phases is primarily achieved through compositional modulation. Within this compositional range, the thermodynamic free energies of the trigonal and tetragonal phases are extremely small and similar, thereby achieving stable coexistence of the two phases at room temperature.

[0020] It should be noted that the method of this invention is also applicable to the preparation of other perovskite piezoelectric thin films, such as lead magnesium niobate-lead titanate (PMN-PT) and potassium sodium niobate (KNN), as long as they can achieve high-quality textured growth on van der Waals substrates. All of the above methods are within the scope of protection of this invention.

[0021] Preferably, in S1, the preparation step of the initial layered structure includes: S11: Prepare a substrate containing surface ions; S12: A conductive electrode layer is obtained by magnetron sputtering metal ions on the side of the substrate containing surface ions; S13: A piezoelectric thin film layer is grown on the surface of the conductive electrode layer by means of a sol-gel method.

[0022] Preferably, in S1, the initial layered structure further includes a mechanical support layer; The mechanical support layer is disposed on the side of the piezoelectric thin film layer away from the conductive electrode layer; the mechanical support layer is used to maintain the structural integrity of the piezoelectric thin film during separation and transfer. Preferably, the mechanical support layer is a hydrophobic polymer layer; for example, a polydimethylsiloxane (PDMS) layer.

[0023] The contact angle between the mechanical support layer and the polar solvent in S2 is >90°, and the contact angle between the surface of the substrate and the polar solvent in S2 is <20°, thereby forming a wettability gradient at the edge of the initial layered structure to provide capillary driving force to promote the penetration of the polar solvent.

[0024] Figure 3 The figures show the water contact angle measurements of different material surfaces involved in this invention. In the figure: (a) is the Mica substrate, (b) is the Pt layer, (c) is the PZT film, and (d) is the PDMS protective layer. The data in the figure show that the hydrophobicity (>90°) of the PDMS layer is significantly different from that of the Mica substrate (<20°), confirming the successful construction of the wettability gradient used to drive solvent penetration.

[0025] Preferably, in S1, the initial layered structure further includes a seed layer; The seed layer is disposed between the piezoelectric thin film layer and the conductive electrode layer, and is used to induce the preferred orientation growth of the piezoelectric thin film; The thickness of the seed layer is 1~10 nm; Preferably, the seed layer is formed by mixing seed sols via a sol-gel method; More preferably, the mixed seed crystal is obtained by mixing PbO sol and TiO2 sol; The molar ratio of the PbO sol to the TiO2 sol is (75~25):(90~10), preferably 85:15, to obtain a (100) preferentially oriented PZT film.

[0026] Preferably, in S2, the polar solvent includes at least one of water and alcohol solvents.

[0027] Preferably, the alcohol solvent includes at least one of ethanol and ethylene glycol.

[0028] It is understood that in S2, introducing the polar solvent between the substrate and the conductive electrode layer can be done by immersing the entire initial layered structure in the polar solvent and allowing it to stand and separate, or by immersing the substrate and the conductive electrode layer of the initial structure in the polar solvent to achieve substrate separation.

[0029] The reduction of interfacial binding energy mentioned in S2 of this invention is achieved through the following mechanism: the polar solvent molecules form a solvation shell around the surface ions, shielding the electrostatic interaction and / or van der Waals interaction between the surface ions and the conductive electrode layer.

[0030] Preferably, in step S2, after separating the substrate from the conductive electrode layer and the piezoelectric thin film layer, the step further includes setting a flexible substrate on the side of the piezoelectric thin film away from the conductive electrode layer. The flexible substrate includes at least one of polyethylene terephthalate (PET), polyimide (PI), polyethylene naphthalate (PEN), or ultrathin metal foil.

[0031] The thickness of the flexible substrate is 10~100μm.

[0032] A second aspect of the present invention provides a self-supporting piezoelectric thin film prepared by the preparation method described in the first aspect above.

[0033] A third aspect of the present invention provides a piezoelectric device comprising a self-supporting piezoelectric thin film prepared by the preparation method described in the first aspect above, or a self-supporting piezoelectric thin film described in the second aspect above.

[0034] In some embodiments, the piezoelectric device includes a piezoacoustic sensor, an energy harvester, an actuator, or an ultrasonic transducer.

[0035] In one embodiment, the piezoelectric device has an open-circuit output voltage greater than 0.6 V under a dynamic load of 110 mN.

[0036] The beneficial technical effects of this invention are as follows: This invention proposes and verifies for the first time an "ion-unlocking" interface stripping mechanism. By utilizing the solvation effect of polar solvents on the surface of van der Waals substrates, the interfacial binding energy is weakened, allowing the film stripping process to proceed spontaneously and rapidly at room temperature. This method eliminates the need for a pre-set sacrificial layer, expensive laser equipment, or complex chemical etching steps, significantly simplifying the process, reducing costs considerably, and exhibiting good scalability. Furthermore, the gentle "ion-unlocking" process avoids damage to the film caused by high-energy particle bombardment or strong chemical etching. The self-supporting film obtained using this method retains its excellent crystal structure, chemical composition, dense microstructure, and surface smoothness grown on the native substrate. The leakage current density of the transferred film increases only slightly, indicating that the process does not introduce a large number of conductive defects, laying a material foundation for realizing high-performance devices.

[0037] This invention further eliminates the "mechanical clamping effect" by peeling and transferring the piezoelectric thin film structure from a rigid substrate to a flexible substrate. This allows the film to generate greater macroscopic strain under external loads, thereby greatly releasing its inherent piezoelectric potential. Compared to films grown on mica substrates, the self-supporting PZT film prepared by this invention exhibits [significant advantages]. d 33,d From 217 pC N -1 Upgraded to 528 pC N -1 (An increase of approximately 143%) d 33,c An increase of approximately 90%.

[0038] Furthermore, this invention optimizes the seed layer, resulting in a self-supporting piezoelectric thin film that not only possesses ultra-high piezoelectric response but also exhibits high (100) texture and high... P r It features a phase composition with low surface roughness and near-isomorphic phase boundaries. This combination of excellent properties makes it a promising candidate for cutting-edge applications such as high-performance flexible sensors, wearable devices, and energy harvesters. Attached Figure Description

[0039] Figure 1 This is an optical photograph of the water-assisted van der Waals stripping process in Embodiment 1 of the present invention.

[0040] In the figure: (a) is a schematic diagram of the peeling process, (b) is the initial layered structure of PDMS / PZT / Pt / Mica, (c) is water seeping into the interface from the edge, and (d) is the completely peeled film floating on the water surface.

[0041] Figure 2 This is a schematic diagram of the DFT calculation model and results of the "ion unlocking" mechanism in one embodiment of the present invention.

[0042] In the figure: (a) is the calculation model of ion locked state and ion unlocked state, (b) is the differential charge density map of the two states, and (c) is the differential charge density distribution curve averaged along the interface normal direction.

[0043] Figure 3 The results show the water contact angle measurements of different material surfaces involved in an embodiment of the present invention.

[0044] In the figure: (a) is the Mica substrate, (b) is the Pt layer, (c) is the PZT thin film, and (d) is the PDMS protective layer.

[0045] Figure 4 This is an AIMD simulation snapshot of the ion unlocking process in one embodiment of the present invention.

[0046] In the figure: (a) is an AIMD simulation snapshot with a simulation time of 0 ps; (b) is an AIMD simulation snapshot with a simulation time of 0.12 ps; (c) is an AIMD simulation snapshot with a simulation time of 0.2 ps.

[0047] Figure 5 This is a comparison diagram of the structural characterization of the initial layered structure of PDMS / PZT / Pt / Mica before transfer and the self-supporting PZT film after transfer in Embodiment 1 of the present invention.

[0048] In the figure, (a) is the XRD pattern of the film before and after transfer, (b) is the XPS energy spectrum of the film before and after transfer, (c) is the SEM cross-sectional morphology before transfer, (d) is the SEM cross-sectional morphology after transfer, (e) is the AFM surface morphology of the film after transfer, and (f) is the AFM surface morphology of the film before transfer.

[0049] Figure 6 The results are obtained by scanning transmission electron microscopy (STEM) characterization of the self-supporting PZT thin film in Example 1 of this invention. In the figure: (a) is the atomic resolution HAADF image, (b) and (c) are polarization vector distribution maps, and (d) and (e) are polarization intensity distribution maps and statistical histograms.

[0050] Figure 7 These are comparison images of the piezoelectric microscopy (PFM) characterization of the PZT thin film before and after transfer in Example 1 of the present invention. (a) is the PFM phase image of the PZT thin film before transfer, (b) is the PFM phase image of local polarization behavior, (c) is the spot scan phase amplitude curve; (d) is the PFM phase image of the PZT thin film after transfer, (e) is the PFM phase image of local polarization behavior, and (f) is the spot scan phase amplitude curve.

[0051] Figure 8 This is a comparison diagram of the macroscopic ferroelectric and leakage current properties of the PZT thin film before and after transfer in one embodiment of the present invention.

[0052] In the figure: (a) is the PE hysteresis loop, and (b) is the JE leakage current curve.

[0053] Figure 9 This is a linear fit of the output charge and applied stress of the PZT film before and after transfer in one embodiment of the present invention.

[0054] Figure 10 The piezoelectric response voltages of the PZT film before and after transfer in Example 1 of this invention are characterized. The results show that the self-supporting film of this invention exhibits high sensitivity and good linear output characteristics under dynamic mechanical loads.

[0055] In the figure: (a) is the output voltage before the transfer, and (b) is the output voltage after the transfer. Detailed Implementation

[0056] The present invention will now be described in detail with reference to the embodiments.

[0057] Example 1 This embodiment provides a self-supporting PZT thin film, the preparation method of which includes the following steps: S1. (100) Preparation of initial layered structures of textured PDMS / PZT / Pt / Mica (1) Substrate and electrode fabrication: Mica sheets were selected as van der Waals substrates. Atomically flat surfaces were obtained through mechanical cleavage along the (001) crystal plane, and then thinned to approximately 100 µm. Subsequently, a (111) oriented platinum (Pt) layer with a thickness of approximately 100 nm was deposited on the mica substrate as a conductive bottom electrode layer using magnetron sputtering at a substrate temperature of 450°C. The mica sheets were artificial fluorophlogopite with the structural formula KMg3(AlSi3O4). 10 F2, purchased from Changchun Taiyuan Fluoropyramic Co., Ltd.

[0058] (2) Preparation of mixed seed layer: To induce the (100) preferred orientation of the subsequent PZT thin film, a mixed seed layer was spin-coated onto the surface of the Pt electrode layer using a sol-gel method. Specifically, the steps included are as follows: (2-1) Preparation of PbO sol: 2.08 g of lead acetate trihydrate was dissolved in a mixture of 15 mL of acetic acid and 7.5 mL of ethylene glycol methyl ether. 3 mL of acetylacetone was added as a stabilizer. The mixture was heated and stirred at 130 °C for 18 min until a clear solution was formed. After cooling, filtration, sealing, and aging, PbO sol was obtained.

[0059] (2-2) Preparation of TiO2 sol: 5.0 mL of acetic acid and 3.0 mL of acetylacetone were added to 15.0 mL of ethylene glycol methyl ether and stirred for 10 minutes to obtain a mixed solution. 1.5 mL of tetraisopropoxide was added to the mixed solution, and the mixture was stirred at room temperature for 22 minutes. Then, 5.0 mL of acetic acid and 15.0 mL of ethylene glycol methyl ether were added sequentially, and the mixture was stirred for 12 minutes and sonicated for 5 minutes. Finally, 5.5 mL of ethylene glycol methyl ether was added, and the mixture was stirred for another 30 minutes. The resulting solution was filtered, sealed, and allowed to stand for 48 hours to age, yielding TiO2 sol.

[0060] (2-3) Preparation of composite seed sol: The PbO sol obtained in step (2-1) and the TiO2 sol obtained in step (2-2) were mixed at a molar ratio of PbO:TiO2=85:15. After ultrasonic treatment for 5 minutes, the mixture was sealed and aged for 48 hours to obtain a composite seed sol for later use.

[0061] (2-4) Preparation of mixed seed layer: Take the composite seed sol from step (2-3) and spin-coat it onto the surface of the conductive electrode layer (5000 r / min, 30 s). Then, perform heat treatment in a rapid annealing furnace: first, dry at 150 °C for 5 min, then pyrolyze at 400 °C for 5 min, and finally anneal at 700 °C for 1 min.

[0062] Repeat this step once to form a mixed seed layer of a predetermined thickness of 10 nm on the surface of the conductive electrode layer.

[0063] (3) Growth of PZT thin films: PZT films were prepared on seed layers using the sol-gel method.

[0064] (3-1) Preparation of PZT sol: Prepare a 0.4 M, 20 mL PZT sol with a 10% Pb excess. Weigh 1.36 g of zirconium propoxide, 1.09 g of isopropyl titanate, and 3.34 g of lead acetate trihydrate according to stoichiometry. First, place 3.34 g of lead acetate trihydrate and 15 mL of ethylene glycol methyl ether in a three-necked flask and stir at 80 °C for 30 min to remove water of crystallization, obtaining a semi-dry powder. Next, mix 1.09 g of isopropyl titanate and 1.36 g of zirconium propoxide with 3 mL of acetylacetone and 10 mL of ethylene glycol methyl ether in another three-necked flask until homogeneous. Then, add this mixture to the aforementioned semi-dry powder and reflux at 80 °C for 120 min. After cooling to room temperature, add n-butanol and stir until homogeneous, then filter to obtain the PZT sol.

[0065] (3-2) Growth of PZT thin film layer: The PZT sol prepared in step (3-1) was drop-coated onto the mixed seed layer and spin-coated at 5000 rpm for 30 s. Subsequently, the sample was dried sequentially on a hot plate at 150°C for 5 min, pyrolyzed in a tube furnace at 400°C for 10 min, and finally rapidly annealed at 700°C for 1 min. The above spin-coating-annealing process was repeated 10-20 times until a PZT film with a thickness of approximately 1.6 µm was obtained, resulting in the initial layered structure of PZT / Pt / Mica.

[0066] (4) Mechanical support layer encapsulation: A layer of liquid polydimethylsiloxane (PDMS) prepolymer (Sylgard 184, base adhesive to curing agent mass ratio 10:1) was spin-coated onto the surface of the prepared PZT / Pt / Mica sample and cured in an oven at 60°C for 24 hours to form a PDMS mechanical support layer with a thickness of about 1-2 mm, thus obtaining the (100) textured PDMS / PZT / Pt / Mica initial layered structure.

[0067] S2. Water-assisted "ion unlocking" stripping and transfer (1) Peeling process: The edges of the encapsulated sample are carefully brought into contact with the surface of deionized water. Due to the significant wettability difference between the hydrophobic PDMS support layer (contact angle > 90°) and the hydrophilic Mica substrate (contact angle < 20°), a large surface energy gradient is constructed at the gas-liquid-solid three-phase interface. The directional capillary driving force generated by this gradient forces water molecules to spontaneously penetrate from the sample edges into the Pt / Mica interface. A peeling crack starts from the contact point and rapidly propagates along the interface until the entire PDMS / PZT / Pt composite layer is completely separated from the Mica substrate and floats on the water surface. The entire process is usually completed within a few minutes and is easy to operate.

[0068] (2) Transfer Process: The film floating on the water surface was carefully lifted with a clean glass slide and dried at 60°C for 30 min to remove residual moisture. Then, the film was transferred to a flexible polyethylene terephthalate (PET) substrate coated with UV-curable adhesive (model NOA.89, coating thickness 10 μm). The adhesive was cured by UV light (365 nm) for 60 min, firmly fixing the film onto the PET substrate. Finally, the PDMS protective layer was carefully mechanically peeled off from one corner to obtain the final self-supporting PZT film composite structure.

[0069] Figure 1 An optical photograph of the water-assisted van der Waals stripping process in Example 1 is provided, which visually demonstrates that the method of the present invention can achieve large-area, complete, non-destructive film stripping.

[0070] Examples 2-5 Examples 2-5 are basically the same as Example 1, except that the ratio of the composite seed sol in step (4) is changed. In Examples 2-5, two sols with the following molar ratios are used in sequence: Example 2, PbO:TiO2 = 50:50 (molar ratio). Example 3, PbO:TiO2 = 75:25 (molar ratio). Example 4, PbO:TiO2 = 25:75 (molar ratio). Example 5, PbO:TiO2 = 15:85 (molar ratio). Comparative examples 1-5 show that when the composite seed gel is prepared by mixing according to the molar ratio of PbO:TiO2 = 85:15, the resulting film has the best orientation, and Example 1 has a better (100) orientation.

[0071] Example 6 Example 6 is basically the same as Example 1, except that the polar solvent is changed. In this example, ethanol is used instead of water as the polar solvent.

[0072] Example 7 Example 7 is basically the same as Example 1, except that the polar solvent is changed. In this example, ethylene glycol is used instead of water as the polar solvent.

[0073] Example 8 Example 8 is basically the same as Example 1, except that the material of the flexible substrate is changed. In this example, polyimide (PI) is used as the flexible substrate.

[0074] Comparative Example 1 This comparative example aims to verify the necessity of hydrophobicity on the surface of the mechanical support layer.

[0075] This comparative example is basically the same as that of Example 1, except that in step S1 (4) mechanical support layer encapsulation, epoxy resin is used instead of PDMS as the mechanical support layer. The water contact angle of the epoxy resin support layer surface was measured to be about 65°; the water contact angle of the mica substrate surface was still 15.5°. When the sample edge is brought into contact with the water surface, since both the support layer and the substrate are hydrophilic surfaces, water molecules tend to spread on both surfaces simultaneously, and cannot form an effective asymmetric meniscus and directional capillary driving force at the interface. The experiment observed that the peeling process was extremely slow, and due to the lack of sufficient wedging stress, multiple macroscopic cracks and local detachment occurred in the PZT film during the forced separation process, making it impossible to obtain a complete self-supporting film.

[0076] Test example: A series of structural and performance characterizations were performed on the initial layered structure of PDMS / PZT / Pt / Mica before transfer and the self-supporting PZT film after transfer to evaluate the effectiveness of the method of the present invention.

[0077] (1) Structural integrity The initial layered structure of PDMS / PZT / Pt / Mica before transfer and the self-supporting PZT film after transfer in Example 1 were analyzed using XRD, XPS, SEM, and AFM. The results are as follows: Figure 5 As shown in Figures (a) and (b), Freestanding PZT represents the self-supporting PZT film after transfer, and PZT on Mica represents the initial layered structure of PDMS / PZT / Pt / Mica before transfer.

[0078] XRD results showed that the characteristic diffraction peaks of the Mica substrate completely disappeared in the transferred film, indicating that the peeling was thorough. The positions and intensities of the (100) and (200) diffraction peaks of the PZT film remained basically unchanged, confirming that its highly (100) textured crystal structure was maintained during the transfer process.

[0079] XPS results showed that the peak positions and shapes of the core energy levels such as Pb 4f, Zr 3d, Ti 2p, and O 1s did not change significantly before and after the transfer, indicating that the surface chemical composition and elemental valence states of the film remained stable.

[0080] SEM images show that the transferred film still exhibits a dense columnar crystalline structure with a uniform thickness (approximately 1.6 µm) and no obvious cracks or pores, indicating that the transfer process did not introduce significant mesoscopic damage.

[0081] As can be seen from the AFM image, the film surface maintained a high degree of flatness after transfer. R q The nm increased only slightly from 1.35 nm to 1.49 nm, with no obvious scratches or defects.

[0082] The self-supporting PZT film after transfer in Example 1 was tested using STEM, and the results are as follows: Figure 6 As shown in the figure, the coexistence of trigonal and tetragonal nanodomains in the transferred film of this embodiment provides a microstructural basis for its excellent piezoelectric properties. By calculating the relative displacement of the cations, the average polarization displacement was found to be approximately 19.1 pm, which is consistent with the typical value of PZT materials with MPB composition.

[0083] (2) Ferroelectric and piezoelectric properties: PFM was used to analyze the initial layered structure of PDMS / PZT / Pt / Mica before transfer and the self-supporting PZT film after transfer in Example 1. The results are as follows: Figure 7 As shown in the figure. The results indicate that both the film before and after the transfer exhibit good ferroelectric domain flipping characteristics. Importantly, the self-supporting PZT film... d 33,c From the pre-transfer Mica base of 128.56 pm V -1 Significantly improved to 244.33 pm V -1 This represents an improvement of approximately 90%. This directly demonstrates that the self-supporting film of the present invention can eliminate the inhibitory effect of substrate clamping on the piezoelectric response. The self-supporting film prepared by the present invention exhibits more significant phase reversal and amplitude response, effectively improving local piezoelectric activity by eliminating the substrate clamping effect.

[0084] The macroscopic ferroelectric properties of the initial layered structure of PDMS / PZT / Pt / Mica before transfer and the self-supporting PZT thin film after transfer in Example 1 were tested, and the results are as follows: Figure 8 As shown in the figure, Freestanding PZT represents the self-supporting PZT film after transfer, and PZT on Mica represents the initial layered structure of PDMS / PZT / Pt / Mica before transfer. The results show that the PE hysteresis loop of the self-supporting film is more saturated. P r From 31.61 µC cm -2 Increased to 34.81 µC cm -2 Meanwhile, its leakage current density is only slightly higher than that of Mica-based films, remaining at 10. -5 A cm -2 The magnitude indicates that the film has good insulation properties and that the transfer process did not introduce a large number of conductive defects. In other words, the self-supporting film of this invention has a higher P value. r It also maintained a low leakage current level.

[0085] Using a customized dynamic mechanical testing platform, the piezoelectric properties of the initial layered structure of PDMS / PZT / Pt / Mica before transfer and the self-supporting PZT film after transfer in Example 1 were tested under sinusoidal dynamic loads ranging from 10 mN to 110 mN at a frequency of 1 Hz. The results are as follows: Figure 9 As shown in the figure, Freestanding PZT represents the self-supporting PZT film after transfer, and PZT on Mica represents the initial layered structure of PDMS / PZT / Pt / Mica before transfer. The results show that under a maximum load of 110 mN, the output current density of the self-supporting film prepared in Example 1 of this invention reaches 16.17 nA cm⁻¹. -2 The output voltage reached 0.67 V, which is 5.75 nA cm⁻¹ for the Mica-based thin film (PDMS / PZT / Pt / Mica initial layered structure) before transfer. -2 The piezoelectricity is approximately 2.8 times and 3.2 times that of the self-supported PZT film (0.21 V). Fitting calculations show that the effective piezoelectric coefficient of the self-supported PZT film is as high as approximately 528 pC N. - ¹, approaching the level of high-performance bulk PZT ceramics.

[0086] The high-performance self-supporting piezoelectric thin film composite structure prepared based on the present invention can be used to construct various high-performance piezoelectric devices, including but not limited to: flexible microphones and acoustic sensors with high signal-to-noise ratio, wearable health sensors for monitoring human physiological signals (such as pulse and respiration), efficient vibration energy harvesters, and flexible actuators for tactile feedback or microfluidics.

[0087] This invention discloses and utilizes a novel physicochemical mechanism for interfacial exfoliation: "ion unlocking." Unlike existing technologies that rely on pure physical force (mechanical exfoliation), high energy (laser exfoliation), or chemical etching (sacrificial layer method), this invention achieves non-destructive exfoliation by reducing the interfacial binding energy through a gentle solvation process. Simultaneously, this method eliminates the complex steps of growing and etching the sacrificial layer in traditional chemical methods and avoids the dependence on expensive equipment and specific substrates required by physical methods. This method is simple to operate, environmentally friendly, and theoretically can be extended to any thin film system that can be grown on van der Waals substrates containing surface ions. Furthermore, this invention achieves a significant improvement in the performance of self-supporting piezoelectric thin films. The obtained PZT thin film has a d33 and d value as high as 528 pC N. -1 This not only far surpasses all previously reported flexible piezoelectric films, but also reaches a level comparable to commercial bulk piezoelectric ceramics.

[0088] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for preparing a self-supporting piezoelectric thin film, characterized in that, Includes the following steps: S1: Provides the initial layered structure; The initial layered structure comprises, from bottom to top, a substrate, a conductive electrode layer, and a piezoelectric thin film layer; The substrate is a substrate containing surface ions, and the side containing surface ions is in contact with the conductive electrode layer; S2: A polar solvent is introduced between the substrate and the conductive electrode layer, and the mixture is left to stand, so that the polar solvent reacts with the surface ions on the substrate to achieve separation of the substrate from the conductive electrode layer and the piezoelectric thin film layer, thereby obtaining a self-supporting piezoelectric thin film.

2. The preparation method according to claim 1, characterized in that, In S1, the substrate is a van der Waals substrate containing surface ions; Preferably, the substrate is a mica substrate containing surface ions; Preferably, the mica substrate includes at least one of muscovite and phlogopite; More preferably, the mica is artificial fluorophlogopite, purchased from Changchun Taiyuan Fluorophlogopite Co., Ltd. More preferably, the thickness of the substrate is 0.01~0.1 mm.

3. The preparation method according to any one of claims 1-2, characterized in that, In S1, the surface ions are alkali metal ions; Preferably, the alkali metal ion includes potassium ion.

4. The preparation method according to claim 1, characterized in that, In S1, the conductive electrode layer includes at least one of platinum, molybdenum, and gold; The piezoelectric thin film is a perovskite ferroelectric thin film, preferably a PZT thin film; The thickness of the piezoelectric film is 0.5~2μm.

5. The preparation method according to claim 1, characterized in that, In S1, the preparation steps of the initial layered structure include: S11: Prepare a substrate containing surface ions; S12: A conductive electrode layer is obtained by magnetron sputtering metal ions on the side of the substrate containing surface ions; S13: A piezoelectric thin film layer is grown on the surface of the conductive electrode layer by means of a sol-gel method.

6. The preparation method according to claim 1, characterized in that, In S1, the initial layered structure also includes a mechanical support layer; The mechanical support layer is disposed on the side of the piezoelectric thin film layer away from the conductive electrode layer; Preferably, the mechanical support layer is a hydrophobic polymer layer; The contact angle between the mechanical support layer and the polar solvent in S2 is >90°, and the contact angle between the surface of the substrate and the polar solvent in S2 is <20°.

7. The preparation method according to claim 1 or 6, characterized in that, In S1, the initial layered structure further includes a seed layer; The seed layer is disposed between the piezoelectric thin film layer and the conductive electrode layer; The thickness of the seed layer is 1~10 nm; Preferably, the seed layer is formed by mixing seed sols via a sol-gel method; More preferably, the mixed seed crystal is obtained by mixing PbO sol and TiO2 sol; The molar ratio of the PbO sol to the TiO2 sol is (75~25):(90~10), preferably 85:

15.

8. The preparation method according to claim 1, characterized in that, In S2, the polar solvent includes at least one of water and alcohol solvents; Preferably, in step S2, after separating the substrate from the conductive electrode layer and the piezoelectric thin film layer, the step further includes setting a flexible substrate on the side of the piezoelectric thin film away from the conductive electrode layer. The flexible substrate includes at least one of polyethylene terephthalate, polyimide, polyethylene naphthalate (PEN), and ultrathin metal foil; The thickness of the flexible substrate is 10~100μm.

9. A self-supporting piezoelectric thin film prepared by the preparation method according to any one of claims 1-8.

10. A piezoelectric device, characterized in that, This includes the self-supporting piezoelectric thin film prepared by the preparation method according to any one of claims 1-8, or the self-supporting piezoelectric thin film according to claim 9.

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