A method for constructing ferroelectric topological domain structure induced by three-dimensional structure deformation

Abstract

The application discloses a three-dimensional structure deformation induced ferroelectric topological domain structure construction method, and the method comprises the following steps: providing a self-supporting ferroelectric film, wherein the self-supporting ferroelectric film is composed of an ultrathin oxide material; applying a three-dimensional structure deformation to the self-supporting ferroelectric film; inducing a non-uniform strain field or a strain gradient field in the film through the three-dimensional structure deformation; and reconstructing a ferroelectric polarization distribution based on the non-uniform strain field or the strain gradient field, so as to form a polarity topological domain structure with adjustable lateral size. The application breaks through the dimensional limitation of traditional plane strain regulation and control, supports directional design of novel topological domain structures, and provides a controllable, low-power micro-nano domain engineering platform for novel electronic devices such as integrated photonic devices (such as optical field modulators), optoelectronic coupling devices, flexible electronic devices and high-density nonvolatile memories.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano ferroelectric material preparation and characterization technology, specifically involving a method for controlling the ferroelectric topological domain structure based on three-dimensional structural deformation, which is particularly applicable to the functional micro-nano domain engineering of flexible electronics, integrated photonic devices and high-density non-volatile memories. Background Technology

[0002] Ferroelectric materials, with their spontaneous polarization and controllable electric field reversal properties, have attracted considerable attention in information storage, sensors, and optoelectronic devices. Furthermore, by precisely controlling parameters such as boundary conditions, size, and dimensionality of ferroelectric materials, a series of novel nontrivial polar topological domain structures have been discovered, allowing the elastic energy (strain), electrostatic energy, and gradient energy to compete and balance within minute differences. These include flux-closed domains, vortex domains, polar "bubble" domains, polar skyrmions, and halfons. These nanoscale polar topological structures exhibit novel physical properties significantly different from bulk materials, such as enhanced conductivity, negative capacitance, and enhanced electromechanical response, showing great potential for developing high-density, high-speed, and low-power information storage devices.

[0003] In recent years, with the advancement of micro-nano fabrication technology, the precise control of polarization domain structures (such as polar vortices and skyrmions) in ferroelectric materials through strain engineering has become a research hotspot. Traditional strain control methods (such as epitaxial lattice mismatch and interface stress engineering) change the domain wall energy barrier by introducing in-plane biaxial strain (strain amplitude is usually <3%), thereby optimizing the directional alignment and flipping dynamics of ferroelectric domains. However, these methods are limited by the coupling effect of rigid substrates, making it difficult to overcome the dimensional limitations of two-dimensional planar strain control, which severely restricts the in-depth research and functional development of ferroelectric topological domains for integrated photonic devices, optocouplers, flexible electronic devices, etc. Summary of the Invention

[0004] The purpose of this invention is to provide a method for constructing ferroelectric topological domain structures induced by three-dimensional structural deformation, so as to achieve cross-dimensional ferroelectric polarization reconstruction and controllable construction of polar topological domains.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The first objective of this invention is to provide a method for constructing ferroelectric topological domain structures induced by three-dimensional structural deformation.

[0007] A method for constructing a three-dimensional deformation-induced ferroelectric topological domain structure includes the following steps:

[0008] Step 1: Provide a self-supporting ferroelectric thin film with ultra-flexible properties, wherein the self-supporting ferroelectric thin film is composed of an ultra-thin oxide material;

[0009] Step 2: Apply three-dimensional structural deformation to the self-supporting ferroelectric thin film, wherein the three-dimensional structural deformation includes at least one of bending, bulging or torsion;

[0010] Step 3: Induce a non-uniform strain field or strain gradient field within the thin film through the deformation of the three-dimensional structure;

[0011] Step 4: Based on the non-uniform strain field or strain gradient field, reconstruct the ferroelectric polarization distribution to form a polar topological domain structure with adjustable lateral dimensions. The polar topological domain structure includes at least one of polar vortices, skyrmions, or central polar topological domains.

[0012] Preferably, the self-supporting ferroelectric thin film has ultra-flexible properties.

[0013] Preferably, in step 1, the thickness of the self-supporting ferroelectric thin film is from 1 nm to 100 μm.

[0014] Preferably, in step 1, the material of the self-supporting ferroelectric thin film is a ferroelectric oxide, more preferably a perovskite ferroelectric oxide, including but not limited to one or more of barium titanate (BaTiO), lead titanate (PbTiO), bismuth ferrite (BiFeO), lithium niobate (LiNbO), lead zirconate titanate (PZT), potassium niobate (KNbO), or perovskite ferroelectric thin films doped with rare earth elements.

[0015] In some preferred embodiments, in step 1, the method for preparing the self-supporting ferroelectric thin film is as follows:

[0016] (1) Epitaxial growth of a sacrificial layer on a single-crystal substrate;

[0017] (2) Deposit a ferroelectric layer on the sacrificial layer;

[0018] (3) The sacrificial layer is removed by chemical or mechanical stripping to obtain a self-supporting ferroelectric thin film.

[0019] In some preferred embodiments, the ferroelectric layer is grown by one or more of molecular beam epitaxy, pulsed laser deposition, atomic layer deposition, metal oxide chemical vapor deposition, or sol-gel method.

[0020] In some preferred embodiments, the sacrificial layer is one or more of an acid-corroding sacrificial layer, an alkali-corroding sacrificial layer, a water-soluble sacrificial layer, or graphene.

[0021] In some preferred embodiments, the chemical stripping method is one of acid etching of the sacrificial layer, alkali etching of the sacrificial layer, or water-soluble sacrificial layer.

[0022] In some preferred embodiments, the mechanical stripping method is a remote epitaxy method.

[0023] Preferably, in step 2, the three-dimensional structural deformation is achieved in one of the following ways:

[0024] (a) A bilayer homogeneous or heterogeneous structure is constructed in the self-supporting ferroelectric thin film. There is a strain mismatch between the lattice parameters of the bilayer structure. The lattice mismatch degree is 0.1%-8%. When the bilayer structure is freed from the substrate, it spontaneously forms a dome-shaped three-dimensional morphology due to strain relaxation. Its size is controlled from submicron to hundreds of micrometers by adjusting the thickness of the bilayer structure and the lattice mismatch degree.

[0025] (b) Alternatively, the self-supporting ferroelectric thin film may be transferred to a pre-formed three-dimensional curved substrate with a curvature radius of 1 nm-10 mm, and the curvature of the three-dimensional curved substrate may be used to drive the thin film to produce bending or bulging deformation, wherein the substrate material is a flexible polymer material or a hard oxide. In some preferred embodiments, the flexible polymer material is PDMS, and the hard oxide is Al2O3.

[0026] In some preferred embodiments, in step 2, the three-dimensional structural deformation is achieved by applying bending, bulging, or torsion deformation using a fixture or a nanoindenter.

[0027] In some preferred embodiments, the radius of curvature of the bend is 1 nm-10 mm.

[0028] In some preferred embodiments, the height of the bulge is 1 nm-10 mm.

[0029] In some preferred embodiments, the angle of twist is 5°-30°.

[0030] Preferably, in step 3, the strain gradient field generates a corresponding flexural electric field through the flexural electric effect.

[0031] Preferably, in step 4, the three-dimensional deformation-induced non-uniform strain field or strain gradient field modulates the topological domains in the following manner:

[0032] The flexoelectric effect lowers the nucleation energy barrier of topological domains, while competing with the wall energy, elastic energy, and electrostatic energy of ferroelectric domains, thus determining the size and topological number of topological domains.

[0033] Preferably, in step 4, the lateral dimension of the polar topological domain structure is adjustable from 1 nm to 10 mm, and submicron-level precision domain structure adjustment is achieved by adjusting the radius of curvature or torsion angle of the three-dimensional deformation.

[0034] Preferably, the method further includes characterizing the ferroelectric topological domain structure.

[0035] In some preferred embodiments, the characterization method is one or more of atomic force microscopy (AFM), scanning probe microscopy (SPM), and transmission electron microscopy (TEM).

[0036] The second objective of the invention is to provide a micro / nano ferroelectric device.

[0037] A micro / nano ferroelectric device is fabricated using the three-dimensional structural deformation-induced ferroelectric topological domain structure construction method, wherein the micro / nano ferroelectric device belongs to any of the following categories:

[0038] (a) Integrated photonic devices: including optical field modulators or optical vortex generators, which achieve dynamic modulation of beam phase and polarization state through electric field control of polar vortex domains;

[0039] (b) Optocoupler: The coupling effect between the strain gradient field and photogenerated carriers is used to improve the efficiency of photoelectric signal conversion;

[0040] (c) Flexible electronic devices: Based on the ultra-flexible properties of self-supporting thin films, they maintain topological domain stability even when the bending radius is ≥1mm, and are suitable for wearable sensors or flexible memory.

[0041] (d) High-density non-volatile memory: using periodic conductive domain wall arrays as memory cells.

[0042] Beneficial effects: Compared with existing technologies, the innovative method of three-dimensional structural deformation control of ferroelectric topological domain structures in this invention has significant advantages: By combining three-dimensional structural deformation with ultra-flexible thin films, it solves the core problems of traditional ferroelectric topological domain control technology, such as limited dimensions, insufficient precision, and complex processes, and realizes full-chain innovation from basic materials to functional devices, providing a brand-new material design paradigm for new electronic devices such as optoelectronics, flexible electronics, and quantum information technology.

[0043] The main innovations of this invention are:

[0044] Cross-dimensional control capability: Breaking through the limitations of two-dimensional plane, it achieves for the first time the leap from two-dimensional plane strain to three-dimensional strain gradient, solving the problem that traditional methods are difficult to construct out-of-plane strain fields;

[0045] Control range and efficiency: By adjusting the three-dimensional deformation parameters (radius of curvature 1nm-10mm), a wide range of control over the lateral size of the topological domains (1nm-10mm) can be achieved.

[0046] Process compatibility and scalability: Combining epitaxial growth with chemical exfoliation (such as a water-soluble Sr3Al2O6 sacrificial layer), the process is simple and substrate-free; traditional topological domains are mainly used in non-volatile memories (such as FeRAM), with limited functionality and performance. This invention can extend the application of ferroelectric topological domains to integrated photonic devices: utilizing the chiral polarization of vortex domains to control the phase of the optical field; flexible electronic devices: maintaining domain stability when the bending radius is ≥10mm, suitable for wearable sensors; high-density memories: using periodic conductive domain wall arrays to store data. Attached Figure Description

[0047] Figure 1 A schematic diagram of lattice deformation and induced flexural electric field in a three-dimensional dome-shaped microstructure;

[0048] Figure 2 A schematic diagram of the experimental design for the double-layer structure (including layer 1: relaxation layer and layer 2: strain layer) required for the dome-shaped microstructure;

[0049] Figure 3 This is a schematic diagram of the growth, water dissolution, and transfer of ferroelectric thin films.

[0050] Figure 4 LPFM characterization of the rotation angle of the centrally convergent ferroelectric domain structure;

[0051] Figure 5 Thickness dependence of centrally convergent ferroelectric topological domain structures;

[0052] Figure 6 This is a ferroelectric topological domain structure induced by other bilayer structures;

[0053] Figure 7 A schematic diagram of the process for constructing ferroelectric topological domain structures induced by three-dimensional structural deformation. Detailed Implementation

[0054] This invention discloses a method for constructing ferroelectric topological domain structures induced by three-dimensional structural deformation. By utilizing the ultra-flexible properties of self-supporting thin films, it breaks through the physical limitations of traditional two-dimensional strain engineering. Through three-dimensional structural deformation (bending, bulging, or torsion), it directly induces non-uniform strain fields and flexural electric fields, realizing cross-dimensional ferroelectric polarization reconstruction and controllable construction of polar topological domains, providing a brand-new solution for the development of multifunctional devices.

[0055] The present invention provides a method for constructing a three-dimensional deformation-induced ferroelectric topological domain structure, comprising the following steps:

[0056] Step 1: Provide a self-supporting ferroelectric thin film, which is composed of an ultrathin oxide material;

[0057] Among them, self-supporting ferroelectric thin films have ultra-flexible properties.

[0058] The thickness of the self-supporting ferroelectric thin film ranges from 1 nm to 100 μm.

[0059] The material of the self-supporting ferroelectric thin film is a ferroelectric oxide, preferably a perovskite ferroelectric oxide, including but not limited to one or more of barium titanate (BaTiO), lead titanate (PbTiO), bismuth ferrite (BiFeO), lithium niobate (LiNbO), lead zirconate titanate (PZT), potassium niobate (KNbO), or perovskite ferroelectric thin films doped with rare earth elements.

[0060] The method for preparing self-supporting ferroelectric thin films is as follows:

[0061] (1) Epitaxial growth of a sacrificial layer on a single-crystal substrate;

[0062] (2) Deposit a ferroelectric layer on the sacrificial layer;

[0063] (3) The sacrificial layer is removed by chemical or mechanical stripping to obtain a self-supporting ferroelectric thin film;

[0064] The ferroelectric layer can be grown using one or more of the following methods: molecular beam epitaxy, pulsed laser deposition, atomic layer deposition, metal oxide chemical vapor deposition, or sol-gel method.

[0065] The sacrificial layer is one or more of the following: acid-corrosion sacrificial layer, alkali-corrosion sacrificial layer, water-soluble sacrificial layer, or graphene.

[0066] The chemical stripping method involves one of the following: acid etching of the sacrificial layer, alkali etching of the sacrificial layer, or water-soluble sacrificial layer.

[0067] The mechanical stripping method is the long-range epitaxy method.

[0068] Step 2: Apply three-dimensional structural deformation to the self-supporting ferroelectric thin film, the three-dimensional structural deformation including at least one of bending, bulging or torsion;

[0069] The deformation of a three-dimensional structure can be achieved in one of the following ways:

[0070] (a) A bilayer homogeneous or heterogeneous structure is constructed in a self-supporting ferroelectric thin film. There is a strain mismatch between the lattice parameters of the bilayer structure. The lattice mismatch degree is 0.1%-8%. When the bilayer structure is freed from the substrate, a dome-shaped three-dimensional morphology is spontaneously formed due to strain relaxation. Its size is controlled from submicron to hundreds of micrometers by adjusting the thickness of the bilayer structure and the lattice mismatch degree.

[0071] (b) Alternatively, the self-supporting ferroelectric thin film can be transferred to a pre-formed three-dimensional curved substrate with a curvature radius of 1 nm-10 mm, and the curvature of the three-dimensional curved substrate can be used to drive the thin film to produce bending or bulging deformation, wherein the substrate material is a flexible polymer material or a hard oxide. The flexible polymer material is preferably PDMS, and the hard oxide is preferably Al2O3.

[0072] In three-dimensional structural deformation, bending, bulging, or torsion deformations are applied using a fixture or nanoindenter. Specifically: the radius of curvature for bending is 1 nm-10 mm, the height of the bulge is 1 nm-10 mm, and the angle of torsion is 5°-30°.

[0073] Step 3: Inducing a non-uniform strain field or strain gradient field within the thin film through the deformation of the three-dimensional structure, wherein the strain gradient field generates a corresponding flexural electric field through the flexural electric effect.

[0074] Step 4: Based on the non-uniform strain field or strain gradient field, reconstruct the ferroelectric polarization distribution to form a polar topological domain structure with adjustable lateral dimensions. The polar topological domain structure includes at least one of polar vortices, skyrmions, or central polar topological domains.

[0075] Among them, the non-uniform strain field or strain gradient field induced by three-dimensional deformation modulates the topological domains in the following ways:

[0076] The flexoelectric effect lowers the nucleation energy barrier of topological domains, while competing with the wall energy, elastic energy, and electrostatic energy of ferroelectric domains, thus determining the size and topological number of topological domains.

[0077] Among them, the lateral size of the polar topological domain structure can be adjusted from 1 nm to 10 mm, and the domain structure can be controlled with sub-micron precision by adjusting the curvature radius or torsion angle of the three-dimensional deformation.

[0078] Step 5: Characterize the ferroelectric topological domain structure using one or more of atomic force microscopy (AFM), scanning probe microscopy (SPM), and transmission electron microscopy (TEM).

[0079] Using the above-described method for constructing ferroelectric topological domain structures induced by three-dimensional structural deformation, a micro / nano ferroelectric device can be obtained, belonging to any of the following categories:

[0080] (a) Integrated photonic devices: including optical field modulators or optical vortex generators, which achieve dynamic modulation of beam phase and polarization state through electric field control of polar vortex domains;

[0081] (b) Optocoupler: The coupling effect between the strain gradient field and photogenerated carriers is used to improve the efficiency of photoelectric signal conversion;

[0082] (c) Flexible electronic devices: Based on the ultra-flexible properties of self-supporting thin films, they maintain topological domain stability even when the bending radius is ≥1mm, and are suitable for wearable sensors or flexible memory.

[0083] (d) High-density non-volatile memory: using periodic conductive domain wall arrays as memory cells.

[0084] To more clearly illustrate this application, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the application. It should be noted that these embodiments are merely illustrative of the technical solutions of the present invention. Those skilled in the art can adjust material selection, process parameters, or structural design according to actual needs, and all such modifications should be considered to fall within the protection scope of the present invention.

[0085] Example

[0086] In this embodiment, one method of generating three-dimensional structural deformation and the lattice distortion generated by the structure are as follows: Figure 1 As shown. Utilizing the strain mismatch in the double-layer structure, a dome-shaped microstructure (bulge) spontaneously forms under free strain relaxation, as... Figure 1 As shown in Figure A, the three-dimensional strain distribution induced by this structure includes: radially distributed tensile strain and perpendicularly radially distributed compressive strain. Figure 1 B). Combining Figure 1 The microscopic lattice distortion in C and the resulting flexural electric field indicate that the introduction of the dome-shaped microstructure leads to anisotropic lattice distortion, generating a radially distributed flexural electric field, which in turn drives the dipoles to align and form centrally converging polar topological microdomains. It should be noted that the dome-shaped morphology represents one form of three-dimensional deformation; any geometric configuration capable of generating an equivalent deformation gradient field (such as helical deformation or folded structures) falls within the scope of this invention.

[0087] In this embodiment, a growth and transfer process for a self-supporting ferroelectric thin film is as follows: Figure 2 As shown. In this embodiment, the ferroelectric oxide thin film is grown using molecular beam epitaxy (MBE) technology. The MBE growth process is only an example; alternative processes such as pulsed laser deposition, metal oxide vapor deposition, or sol-gel method can also be used, provided that the crystal quality of the thin film is guaranteed. The epitaxial substrate material is SrTiO3 (STO), and the water-soluble sacrificial layer is Sr3Al2O6 (SAO). The growth sequence is SAO followed by BTO. In the preferred embodiment, the SAO film thickness is 10 nm, and the BTO film thickness is 16 nm. The transfer method involves flipping this three-layer structure onto functional substrates such as sapphire, ITO, and Si wafers, as described in Chinese Invention Patent (application number CN202110830705.6), using external pressure to achieve the transfer of a flat, self-supporting thin film. Those skilled in the art will understand that the BTO film used in this embodiment can be replaced with other perovskite oxides with similar ferroelectric properties.

[0088] In this embodiment, the lattice mismatch (~2.3%) between the strontium titanate substrate and the epitaxial BTO film is utilized to induce strain relaxation during growth, resulting in a bilayer structure. Figure 3After water-soluble stripping of the substrate, the bilayer structure spontaneously forms a dome-shaped microstructure due to strain relaxation. Its radius of curvature (R) can be estimated using the formula: R≈T / x%, where T is the total film thickness and x% is the lattice mismatch rate of the bilayer structure. For example, when T = 20 nm and x% = 1%, R≈2 μm. Furthermore, by controlling the thickness of the bilayer structure (1 nm-100 μm) and the lattice mismatch rate (0.1%-8%), a wide range of control over the dome diameter can be achieved, thereby controlling the size of the ferroelectric topological domains (1 nm-100 mm).

[0089] In this embodiment, to achieve accurate characterization of the ferroelectric domain structure, the present invention employs the following sample preparation process: First, a self-supporting ferroelectric thin film is transferred onto a rigid target substrate such as sapphire (Al2O3) or a silicon substrate. Then, an optimized drying process (including nitrogen purging and vacuum baking at 60-80℃) is used to thoroughly remove residual moisture from the interface. This process ensures that the thin film and substrate form an atomically smooth contact interface (surface roughness <0.5 nm RMS), effectively eliminating the interference of morphological fluctuations on piezoelectric microscopy (PFM) characterization, controlling the proportion of extrinsic signals to below 5%, and significantly improving the accuracy of domain structure characterization.

[0090] The topological domain structure in self-supporting ferroelectric thin films was systematically characterized using piezoelectric electric microscopy (PFM). Experimental results revealed the existence of central-type topological domain structures. Figure 4 Lateral piezoelectric response (LPFM) testing at rotation angles revealed that the BTO film exhibits significant in-plane multi-domain polarization characteristics. Figure 4 A), while out-of-plane polarization is weaker; several domain wall-like regions with reduced piezoelectric response amplitude were detected. These regions remained stable during rotation angle tests, indicating that they are regions with weak polarization. The formation of these domain wall-like regions can be attributed to the reduction of lattice distortion during the transition of the film from a dome-shaped morphology to a flat structure; this lattice relaxation mechanism is a key factor in the preservation of the three-dimensional topological pattern. Further statistical analysis of the polarization orientation of the central-type topological microdomain structure ( Figure 4 C) shows that the polarization orientation in the BTO thin film is mainly distributed along the high symmetry direction, exhibiting a typical Maltese cross contrast. This feature is due to the constraint effect of the tetragonal lattice symmetry of BTO on the anisotropic elastic properties during the formation of topological texture.

[0091] By precisely controlling the thickness parameters of the self-supporting ferroelectric thin film, the size of the ferroelectric topological domain structure can be controlled. Specifically, by adjusting the thickness of the self-supporting ferroelectric thin film, i.e., changing the thickness ratio of the strain layer (layer 1) to the relaxation layer (layer 2), the size of the ferroelectric topological domains can be precisely controlled. Figure 5As shown, by changing the thickness of the BTO thin film from 40 layers to 160 layers, the size of the ferroelectric topological domain structure generated by three-dimensional structural deformation shows a significant increasing trend. Under the condition of keeping the interlayer strain difference (Δx%) constant, the increase of the total film thickness (T) will inevitably lead to an increase in the topological domain size (R).

[0092] Furthermore, by introducing a bilayer structure into the self-supporting ferroelectric thin film, this invention not only allows for the generation of strain differences in homogeneous materials through strain relaxation during growth, but also enables the fabrication of self-supporting thin films using heterogeneous structures with lattice mismatch (such as BTO / STO or other similar structures), thereby achieving similar dome-shaped microstructure deformation. Figure 6 As shown, in this heterostructure, the ferroelectric topological domain structure formed by introducing three-dimensional dome-shaped structural deformation can exhibit a similar modulation effect to that of a single BTO self-supporting thin film.

[0093] In summary, this invention proposes a method for constructing ferroelectric topological domains based on three-dimensional structural deformation. By introducing three-dimensional structural deformation (bending, bulging, or torsion), it directly induces a non-uniform strain field and a flexural electric field, achieving cross-dimensional ferroelectric polarization reconstruction and controllable construction of polar topological domains. This solves the core problems of limited strain dimension and uncontrollable domain structure in traditional ferroelectric materials, and establishes a collaborative design paradigm of "three-dimensional structural deformation - ultra-flexible self-supporting thin film - dynamic domain engineering". This provides an efficient means of controlling functionalized micro-nano domains for next-generation optoelectronics, flexible electronics, and quantum communication technologies.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for constructing a three-dimensional deformation-induced ferroelectric topological domain structure, characterized in that: Includes the following steps: Step 1: Provide a self-supporting ferroelectric thin film, which is composed of an ultrathin oxide material; the thickness of the self-supporting ferroelectric thin film is from 1 nm to 100 μm, and the material is a ferroelectric oxide, which is one or more of barium titanate, lead titanate, bismuth ferrite, lithium niobate, lead zirconate titanate, potassium niobate, or perovskite-type ferroelectric thin films doped with rare earth elements. Step 2: Apply three-dimensional structural deformation to the self-supporting ferroelectric thin film, wherein the three-dimensional structural deformation includes at least one of bending, bulging or torsion; The three-dimensional structural deformation is achieved in one of the following ways: (a) A bilayer homogeneous or heterogeneous structure is constructed in the self-supporting ferroelectric thin film. There is a strain mismatch between the lattice parameters of the bilayer structure. The lattice mismatch degree is 0.1%–8%. When the bilayer structure is freed from the binding of the substrate, a dome-shaped three-dimensional morphology is spontaneously formed due to strain relaxation. Its size is controlled from submicron to hundreds of microns by adjusting the thickness of the bilayer structure and the lattice mismatch degree. (b) Alternatively, the self-supporting ferroelectric thin film may be transferred to a pre-formed three-dimensional curved substrate with a curvature radius of 1 nm-10 mm, and the curvature of the three-dimensional curved substrate may be used to drive the thin film to produce bending or bulging deformation, wherein the substrate material is a flexible polymer or a hard oxide. Step 3: Inducing a non-uniform strain field or strain gradient field within the thin film through the deformation of the three-dimensional structure; the strain gradient field generates a corresponding flexural electric field through the flexural electric effect; Step 4: Based on the non-uniform strain field or strain gradient field, reconstruct the ferroelectric polarization distribution to form a polar topological domain structure with adjustable lateral dimensions. The polar topological domain structure includes at least one of polar vortices, skyrmions, or central polar topological domains. The non-uniform strain field or strain gradient field modulates the topological domains in the following ways: The nucleation energy barrier of topological domains is reduced by the flexoelectric effect, while competing with the wall energy, elastic energy and electrostatic energy of ferroelectric domains, thus determining the size and topological number of topological domains. The lateral dimension of the polar topological domain structure can be adjusted from 1 nm to 10 mm, and submicron-level precision domain structure control can be achieved by adjusting the radius of curvature or torsion angle of the three-dimensional deformation.

2. The method according to claim 1, characterized in that: In step 1, the method for preparing the self-supporting ferroelectric thin film is as follows: (1) Epitaxial growth of a sacrificial layer on a single-crystal substrate; (2) A ferroelectric layer is deposited on the sacrificial layer, wherein the ferroelectric layer is grown by one or more of molecular beam epitaxy, pulsed laser deposition, atomic layer deposition, metal oxide chemical vapor deposition or sol-gel method; (3) The sacrificial layer is removed by chemical or mechanical stripping to obtain a self-supporting ferroelectric thin film; the sacrificial layer is one or more of acid-corroded sacrificial layer, alkali-corroded sacrificial layer, water-soluble sacrificial layer or graphene; the chemical stripping method is one of acid-corroded sacrificial layer, alkali-corroded sacrificial layer or water-soluble sacrificial layer, and the mechanical stripping method is remote epitaxy.

3. The method according to claim 1, characterized in that: It also includes characterizing the ferroelectric topological domain structure, wherein the characterization method is one or more of atomic force microscopy (AFM), scanning probe microscopy (SPM) and transmission electron microscopy (TEM).

4. A micro / nano ferroelectric device prepared according to the method of any one of claims 1-3, characterized in that, The micro / nano ferroelectric device belongs to any of the following categories: (a) Integrated photonic devices: including optical field modulators or optical vortex generators, which achieve dynamic modulation of beam phase and polarization state through electric field control of polar vortex domains; (b) Optocoupler: The coupling effect between the strain gradient field and photogenerated carriers is used to improve the efficiency of photoelectric signal conversion; (c) Flexible electronic devices: Based on the ultra-flexible properties of self-supporting thin films, they maintain topological domain stability even when the bending radius is ≥1 mm, and are suitable for wearable sensors or flexible memory. (d) High-density non-volatile memory: using periodic conductive domain wall arrays as memory cells.

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