Induction method of central topological domain and self-supporting ferroelectric film

Abstract

The invention relates to an induction method of a central topological domain. The induction method comprises the following steps: depositing a Sr3Al2O6 film on a SrTiO3 single crystal substrate in a (001) direction as a sacrificial layer; a rhombohedral-phase ferroelectric film, a bottom electrode and a rhombohedral-phase ferroelectric film are sequentially deposited on the sacrificial layer to form a three-layer heterostructure, and the two layers of ferroelectric films are made of the same material; and after the sacrificial layer is dissolved, transferring a film sample, namely inducing a central topological domain which is in the shape of columnar bubbles along the vertical direction. Compared with the prior art, the method has the advantages that the self-supporting ferroelectric film with the bubble-shaped wrinkle structure is prepared through the substrate stripping technology, the central topological domain is induced without the action of an external electric field, and a new method is provided for constructing and designing the topological domain for the ferroelectric film.

Description

Technical Field

[0001] The invention relates to the technical field of nano ferroelectric materials, in particular to a method for inducing a central topological domain and a self-supporting ferroelectric film. Background Art

[0002] At present, metal oxide thin film materials are widely studied, developed and used due to many novel light, electricity, force, heat and other response effects found in them. Among them, ferroelectric thin film materials have aroused the research interests of scientific research enthusiasts due to their excellent piezoelectricity, pyroelectricity, ferroelectricity, dielectricity and photoelectric effects, and have shown great application prospects in the field of nanoelectronic devices.

[0003] In the past few years, polar topological domains in ferroelectric materials have attracted increasing attention due to their rich novel physical properties and functions, such as strong conductivity, negative capacitance, magnetism, strong photoelectricity, strong piezoelectric properties, etc. So far, a large number of interesting discoveries have been reported, such as flux closure domains, vortex domains, center-type domains, polar skyrmions, bubble domains, and melanosomes. These exotic topological domains can be precisely controlled by external fields, making them ideal building blocks for advanced nanoelectronic devices.

[0004] At present, although there have been some studies that use external electric fields to induce the formation of polar topological domains and reversibly regulate them, the external field induction has no memory, and for ferroelectric topological domains such as vortices, skyrmions, and central types, current technology still finds it difficult to achieve single stable regulation. In addition, research on the preparation of ferroelectric topological domains is mainly focused on lead-based ferroelectric materials, which have problems such as a single material system, complex topological domain induction methods, and difficulty in regulation. At the same time, most of these peculiar topological structures rely on ferroelectric films or superlattices grown on single crystal substrates, and the construction of these topological structures is regulated by electric fields, which limits the range of materials that can be used and the various available operating technologies. Summary of the invention

[0005] Based on this, the purpose of the present invention is to provide a method for inducing a central topological domain and a self-supporting ferroelectric film, which can stably regulate the central topological domain structure by designing the generation of bubble-shaped wrinkles.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for inducing a central topological domain, comprising the following steps:

[0008] SrTiO in the (001) direction 3 Sr deposited on single crystal substrate 3 Al 2 O6 The film acts as a sacrificial layer;

[0009] A rhombohedral ferroelectric film, a bottom electrode and a rhombohedral ferroelectric film are sequentially deposited on the sacrificial layer to form a three-layer heterostructure, wherein the two layers of the ferroelectric film are made of the same material;

[0010] After dissolving the sacrificial layer, the thin film sample is transferred, which induces central topological domains with columnar bubbles along the vertical direction.

[0011] Compared with the prior art, the present invention first epitaxially grows a water-soluble sacrificial layer on the substrate, and then continues to epitaxially grow a heterostructure of alternating ferroelectric layer / conductive layer / ferroelectric layer on the sacrificial layer, and then utilizes the property of the sacrificial layer being soluble in water to peel off the three-layer heterostructure from the original substrate and transfer it to a mica sheet. Due to the difference in lattice constants between different layers in the heterostructure, after the substrate is peeled off and transferred, the residual strain in the heterostructure is released, forming a self-supporting ferroelectric film with a bubble-like wrinkle structure. At the same time, due to the effect of flexoelectricity, a central topological domain with a columnar bubble domain pattern in the vertical direction is induced near the bubble-like wrinkle structure. The present invention prepares a self-supporting ferroelectric film with a bubble-like wrinkle structure by substrate peeling technology, and induces a central topological domain without the action of an external electric field, providing a new method for constructing and designing topological domains in ferroelectric films.

[0012] In a preferred embodiment, the thickness of the sacrificial layer is 20-50 nm, which not only provides a sufficient film thickness, but also facilitates the subsequent dissolution step.

[0013] In a preferred embodiment, the sacrificial layer is deposited by pulse laser deposition technology, and the experimental conditions are: pulse energy of 62-66 mJ, pulse frequency of 1-8 Hz, epitaxial temperature of 750-780° C., and oxygen pressure of 4-10 Pa. Under the above experimental conditions, a sacrificial layer with uniform thickness, smooth surface and easy dissolution can be deposited.

[0014] In a preferred embodiment, the sacrificial layer is dissolved by immersion in deionized water. 3 Al 2 O 6 ) is soluble in water, and the sacrificial layer can be easily dissolved by immersing the sample in deionized water, thereby peeling the ferroelectric film from the original substrate.

[0015] In a preferred embodiment, the sacrificial layer is dissolved after being soaked in deionized water for 10 to 24 hours, and then the floating film is picked up with a mica sheet, so as to obtain a self-supporting ferroelectric film with a bubble-like convex wrinkle structure, and a central topological domain with columnar bubbles along the vertical direction is induced. Since the thickness of the sacrificial layer is controlled within a suitable size range, the dissolution time is short, and it can be completely dissolved after 10 to 24 hours. After dissolution, the film floating on the surface of deionized water is picked up with a mica sheet. Due to the difference in lattice constants between different layers in the heterogeneous structure, the residual strain in the heterogeneous film is released after the substrate is peeled off and transferred, forming a self-supporting ferroelectric film with a bubble-like wrinkle structure. At the same time, due to the effect of flexoelectricity, a central topological domain with a columnar bubble domain pattern along the vertical direction is induced near the bubble-like wrinkle structure.

[0016] In a preferred embodiment, the ferroelectric thin film is BiFeO 3 Thin film, PbTiO 3 Thin film or SrTiO 3 Any of the films.

[0017] In a preferred embodiment, the ferroelectric thin film is BiFeO 3 Thin film, first layer BiFeO 3 The film thickness is 40nm, and it is epitaxially grown on the sacrificial layer by pulse laser deposition technology. The experimental conditions are: pulse energy of 62-66mJ, pulse frequency of 4-8Hz, temperature of 660-730℃, oxygen pressure of 15-20Pa; the second layer BiFeO 3 The film thickness is 70nm, and it is epitaxially grown on the bottom electrode by pulse laser deposition technology. The experimental conditions are: pulse energy of 62-66mJ, pulse frequency of 4-8Hz, temperature of 660-730℃, and oxygen pressure of 15-20Pa. The BFO film grown by the above method has good epitaxy, clean and flat surface, uniform thickness, and good ferroelectricity.

[0018] In a preferred embodiment, the bottom electrode is SrRuO 3 Conductive layer.

[0019] In a preferred embodiment, SrRuO 3 The thickness of the conductive layer is 40 nm, which is formed by pulsed laser deposition of SrTiO in the (001) direction. 3 The electrode is epitaxially grown on a single crystal substrate under the following experimental conditions: pulse energy of 75-90 mJ, pulse frequency of 8 Hz, temperature of 660-720°C, and oxygen pressure of 15-20 Pa. Under these experimental conditions, a uniform and flat bottom electrode can be obtained.

[0020] In the second aspect, the present invention also provides a self-supporting ferroelectric film, which is a three-layer heterogeneous structure formed by stacking ferroelectric film / conductive layer / ferroelectric film in sequence, and the materials of the two layers of ferroelectric film are the same; its surface has a bubble-like convex wrinkle structure, and around the bubble-like convex wrinkle structure, there are central topological domains in the form of columnar bubbles in the vertical direction. The central topological domain presents a columnar bubble domain outside the surface, which is different from the morphology of ordinary central topological domains. It is a new type of topological domain and is expected to be used in advanced nanoelectronic devices.

[0021] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the process flow of a self-supporting three-layer heterostructure ferroelectric thin film with a bubble-like corrugated structure in Example 1 of the present invention

[0023] Figure 2 The surface morphology of the three-layer heterostructure film after transfer in Example 1 of the present invention

[0024] Figure 3 The morphology of the bubble-shaped wrinkle protrusions in Example 1 of the present invention is shown in FIG.

[0025] Figure 4 for Figure 3 Out-of-plane phase image corresponding to the bubble-shaped wrinkle bulge

[0026] Figure 5 The RSM diagram of the epitaxial film after peeling and transfer in Example 1 of the present invention near the (103) peak is shown in FIG.

[0027] Figure 6 In the figure, Figure (a) is the out-of-plane phase image of the bubble-shaped wrinkle protrusion of Example 1 of the present invention, Figure (d) is the corresponding out-of-plane amplitude image, Figure (b) is the in-plane phase image of the bubble-shaped wrinkle protrusion when the sample rotation angle is 0°, Figure (e) is the corresponding in-plane amplitude image of the bubble-shaped wrinkle protrusion when the sample rotation angle is 0°, Figure (c) is the in-plane phase image of the bubble-shaped wrinkle protrusion when the sample rotation angle is 90°, and Figure (f) is the corresponding in-plane amplitude image of the bubble-shaped wrinkle protrusion when the sample rotation angle is 90°.

[0028] Figure 7 The two-dimensional vector contour map of the PFM combination conversion in the plane of the sample rotated 0° and 90° obtained in Example 1 of the invention

[0029] Figure 8 The three-dimensional domain structure of the sample obtained in Example 1 of the invention DETAILED DESCRIPTION

[0030] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0031] The method for inducing a central topological domain and the self-supporting ferroelectric film provided by the present invention are described in detail below.

[0032] The present invention provides a method for inducing a central topological domain, comprising the following steps:

[0033] SrTiO in the (001) direction 3 Sr deposited on single crystal substrate 3 Al 2 O 6 The film acts as a sacrificial layer;

[0034] A rhombohedral ferroelectric film, a bottom electrode and a rhombohedral ferroelectric film are sequentially deposited on the sacrificial layer to form a three-layer heterostructure, wherein the two layers of the ferroelectric film are made of the same material;

[0035] After dissolving the sacrificial layer, the thin film sample is transferred, which induces central topological domains with columnar bubbles along the vertical direction.

[0036] Further, the thickness of the sacrificial layer is 20-50 nm. Exemplarily, the thickness of the sacrificial layer can be 20 nm, 30 nm, 40 nm or 50 nm, or any other value within the range of 20-50 nm. A suitable thickness of the sacrificial layer is conducive to the subsequent dissolution step.

[0037] For reference, the sacrificial layer is deposited by pulsed laser deposition technology. Pulsed laser deposition is a method of using high-energy laser pulses generated by a laser to evaporate the target material and deposit a film on the substrate. The experimental conditions are: pulse energy of 62-66mJ, pulse frequency of 1-8Hz, epitaxial temperature of 750-780°C, and oxygen pressure of 4-10Pa. Exemplarily, the pulse energy can be 62mJ, 63mJ, 64mJ, 65mJ or 66mJ, or any other value in the range of 62-66mJ. The pulse frequency can be 1Hz, 2Hz, 3Hz, 4Hz, 5Hz, 6Hz, 7Hz or 8Hz, or any other value in the range of 1-8Hz. The epitaxial temperature can be 750°C, 760°C, 770°C or 780°C, or any other value in the range of 750-780°C. The oxygen pressure may be 4Pa, 5Pa, 6Pa, 7Pa, 8Pa, 9Pa or 10Pa, or any other value within the range of 4 to 10Pa.

[0038] As a reference, the sacrificial layer is dissolved by soaking in deionized water. The sacrificial layer is dissolved after soaking in deionized water for 10 to 24 hours, and then the floating film is picked up with a mica sheet, so as to obtain a self-supporting ferroelectric film with a bubble-like convex wrinkle structure, and a central topological domain with columnar bubbles along the vertical direction is induced. Exemplarily, the soaking time can be 10h, 12h, 15h, 18h, 20h or 24h, or any other value within the range of 10 to 24h, as long as the sacrificial layer is completely dissolved in deionized water. After dissolution, the film floating on the surface of deionized water is picked up with a mica sheet. Due to the difference in lattice constants between different layers in the heterostructure, after the substrate is peeled off and transferred, the residual strain in the heterogeneous film is released, forming a self-supporting ferroelectric film with a bubble-like wrinkle structure. At the same time, due to the effect of flexoelectricity, a central topological domain with a columnar bubble domain pattern along the vertical direction is induced near the bubble-like wrinkle structure.

[0039] As a reference, the ferroelectric film is BFO (BiFeO 3 ) thin film, PTO(PbTiO 3 ) film or STO(SrTiO 3 ) films. For example, BFO (BiFeO 3 ) / SRO(SrRuO 3 ) / BFO(BiFeO 3 )、PTO(PbTiO 3 ) / SRO(SrRuO 3 ) / PTO(PbTiO 3 )、STO(SrTiO 3 ) / SRO(SrRuO 3 ) / STO(SrTiO 3 ) and other different three-layer heterostructures.

[0040] Preferably, the ferroelectric thin film is BiFeO 3 Thin film, first layer BiFeO 3 The film thickness is 40nm, and it is epitaxially grown on the sacrificial layer by pulse laser deposition technology. The experimental conditions are: pulse energy of 62-66mJ, pulse frequency of 4-8Hz, epitaxial temperature of 660-730℃, oxygen pressure of 15-20Pa; the second layer BiFeO 3The film thickness is 70nm, and it is epitaxially grown on the bottom electrode by pulse laser deposition technology. The experimental conditions are: pulse energy is 62-66mJ, pulse frequency is 4-8Hz, epitaxial temperature is 660-730℃, and oxygen pressure is 15-20Pa. The BFO film grown by the above method has good epitaxy, a clean and flat surface, uniform thickness, and good ferroelectricity. Exemplarily, the pulse energy can be 62mJ, 63mJ, 64mJ, 65mJ or 66mJ, or any other value within the range of 62-66mJ. The pulse frequency can be 4Hz, 5Hz, 6Hz, 7Hz or 8Hz, or any other value within the range of 4-8Hz. The epitaxial temperature can be 660℃, 680℃, 700℃ or 730℃, or any other value within the range of 660-730℃. The oxygen pressure may be 15Pa, 16Pa, 17Pa, 18Pa, 19Pa or 20Pa, or any other value within the range of 15 to 20Pa.

[0041] Preferably, the bottom electrode is SrRuO 3 Conductive layer.

[0042] Preferably, SrRuO 3 The thickness of the conductive layer is 40 nm, which is formed by pulsed laser deposition of SrTiO in the (001) direction. 3 The epitaxial growth is performed on a single crystal substrate under the following experimental conditions: the pulse energy is 75-90 mJ, the pulse frequency is 8 Hz, the epitaxial temperature is 660-720°C, and the oxygen pressure is 15-20 Pa. For example, the pulse energy can be 75 mJ, 80 mJ, 85 mJ or 90 mJ, or any other value in the range of 75-90 mJ. The epitaxial temperature can be 660°C, 680°C, 700°C or 720°C, or any other value in the range of 660-720°C. The oxygen pressure can be 15 Pa, 16 Pa, 17 Pa, 18 Pa, 19 Pa or 20 Pa, or any other value in the range of 15-20 Pa.

[0043] Correspondingly, the present invention also provides a self-supporting ferroelectric film, which is a three-layer heterogeneous structure, formed by stacking ferroelectric film / conductive layer / ferroelectric film in sequence, and the two layers of ferroelectric film use the same ferroelectric material. The surface of the self-supporting ferroelectric film has a bubble-like convex wrinkle structure, and around the bubble-like convex wrinkle structure are distributed central topological domains in the form of columnar bubbles in the vertical direction. The central topological domain presents a columnar bubble domain outside the plane, which is different from the ordinary central topological domain morphology. It is a new type of topological domain and is expected to be used in advanced nanoelectronic devices.

[0044] The following is the best embodiment of the present invention. It should be noted that the various parameter values ​​used in the embodiments are all preferred parameter values ​​within the parameter range limited by the claims. In other embodiments, as long as the adopted parameter values ​​are within the scope of the claims, the purpose of the present invention can be achieved.

[0045] Example 1

[0046] This embodiment provides a method for inducing a central topological domain, such as Figure 1 As shown, the following steps are included:

[0047] S1: Preparation of sacrificial layer: (001) oriented STO (SrTiO 3 ) as the substrate, a 30nm thick SAO (Sr) layer was grown by pulsed laser deposition technology under the experimental conditions of pulse energy of 63mJ, pulse frequency of 5Hz, epitaxial temperature of 780℃, and oxygen pressure of 4Pa. 3 Al 2 O 6 ) film as a sacrificial layer.

[0048] S2: A rhombohedral ferroelectric film, a bottom electrode and a rhombohedral ferroelectric film are sequentially deposited on the sacrificial layer to form a three-layer heterostructure. Specifically, a 40 nm thick BFO (BiFeO) layer is epitaxially grown under the experimental conditions of pulse energy of 66 mJ, pulse frequency of 5 Hz, temperature of 680°C and oxygen pressure of 20 Pa. 3 ) film; a 40nm thick SRO (SrRuO) film was grown under the experimental conditions of pulse energy of 78mJ, pulse frequency of 8Hz, temperature of 680℃ and oxygen pressure of 20Pa. 3 ) conductive layer as the bottom electrode; then a 70nm thick BFO (BiFeO) layer was epitaxially grown under the experimental conditions of pulse energy of 66mJ, pulse frequency of 5Hz, temperature of 680℃, and oxygen pressure of 20Pa. 3 )film.

[0049] S3: Substrate transfer treatment: Place the sample in a beaker filled with deionized water and soak it for 10 to 24 hours until the sacrificial layer is completely dissolved. Peel off the BFO / SRO / BFO three-layer heterostructure film, and then use a clean and flat mica sheet to pick up the floating film. You can get a self-supporting ferroelectric film with a bubble-like raised wrinkle structure, and induce a central topological domain of columnar bubbles along the vertical direction on its surface.

[0050] S4: Atomic force microscopy characterization

[0051] The atomic force microscopy test system mainly includes: cantilever and probe system, laser system, feedback system and data processing system. The atomic force microscope maps the surface morphology of the object based on the interaction force between the sample surface and the probe, which causes the tiny bending changes of the probe cantilever. A probe (nanoscale) is installed below the end of the elastic cantilever of the instrument. During the test, the probe will move on the surface of the sample. Due to the fluctuation of the morphology, the interaction force between the needle tip and the sample surface will cause the elastic cantilever to bend slightly. This tiny bending causes the change of the reflected light, which is further amplified by the optical lever. The signal is finally read by the sensitive optical detector and then processed by the data processing system to obtain the morphology of the sample. Here, an atomic force microscope is used to characterize the morphology of the three-layer heterostructure film after peeling and transfer. As observed by an optical microscope Figure 2 And atomic force microscopy observations Figure 3 As shown, a large area of ​​bubble-like shapes appeared on the film surface, with contrast differences of different sizes and different from the substrate background contrast. The results show that the residual strain between different layers of heterogeneous structures on the film surface after transfer was released, thus forming a large area of ​​bubble-like raised wrinkled structure.

[0052] S5: Piezoelectric response force microscopy characterization

[0053] Piezoelectric response force microscopy is a microscope developed on the basis of contact mode atomic force microscopy that detects the amount of electroinduced deformation on the sample surface at a microscopic scale. This mode is mainly used to characterize the domain structure of ferroelectric materials and detect the mechanical deformation of the sample caused by the inverse piezoelectric effect under an external electric field. By applying an AC voltage to the conductive needle tip, the local tested sample under the needle tip undergoes periodic deformation. This deformation causes the cantilever connected to the needle tip to twist, thereby affecting the optical signal reflected by it. This signal is collected by a photodiode and subsequently analyzed by a phase-locked amplifier to achieve detection. At the same time, the needle tip can also apply a DC bias during contact scanning with the sample to reverse the polarization of the ferroelectric material. Here, a piezoelectric response force microscope is used to characterize the domain structure of the three-layer heterostructure film after peeling and transfer. As Figure 4 The out-of-plane phase image of the bubble-shaped wrinkle convexity is shown, which corresponds to Figure 3 From the atomic force topography, it can be clearly observed that each bubble-like convex out-of-plane phase corresponds to a ring-shaped anti-domain, and the center presents a dot-shaped single domain. Figure 6As shown in the in-plane 0° phase image of (b) and the in-plane 90° phase image of (c), the in-plane phase of the bubble-like protrusions shows a pair of domain structures with opposite contrasts, half at 0° and half at 90°, that is, the bubble-like protrusions show the characteristics of a central domain structure in the plane. The results show that the central topological domain of columnar bubbles along the vertical direction can be stably induced around the bubble-like protrusion wrinkle structure on the surface of the transferred film due to the flexoelectric effect.

[0054] Further, such as Figure 5 As shown, the lattice constants of SRO and BFO can be calculated by calculating the corresponding in-plane lattice parameters. Compared with the unpeeled and transferred film, the lattice constant of the film after peeling is significantly increased, indicating that the in-plane compressive strain of BFO and the in-plane tensile strain of SRO are released, thereby driving the formation of surface wrinkles.

[0055] In summary, compared with the prior art, the present invention prepares a self-supporting ferroelectric film with a bubble-like wrinkled structure through substrate peeling technology, and induces a central topological domain in the absence of an external electric field, providing a new method for constructing and designing topological domains in ferroelectric films.

[0056] The above-mentioned embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for inducing a central topological domain, characterized in that: The following steps are involved: A Sr3Al2O6 film was deposited as a sacrificial layer on a (001) oriented SrTiO3 single crystal substrate; Depositing a rhombohedral ferroelectric film, a bottom electrode and a rhombohedral ferroelectric film on the sacrificial layer in sequence to form a three-layer heterostructure, wherein two layers of the ferroelectric film are made of the same material; After dissolving the sacrificial layer, the thin film sample is transferred, thereby inducing a central topological domain of columnar bubbles along the vertical direction.

2. The induction method according to claim 1, characterized in that: The thickness of the sacrificial layer is 20-50 nm.

3. The induction method according to claim 2, characterized in that: The sacrificial layer is deposited by pulse laser deposition technology, and the experimental conditions are: pulse energy is 62-66 mJ, pulse frequency is 1-8 Hz, epitaxial temperature is 750-780° C., and oxygen pressure is 4-10 Pa.

4. The induction method according to claim 1, characterized in that: The sacrificial layer is dissolved by soaking in deionized water.

5. The induction method according to claim 4, characterized in that: The sacrificial layer is dissolved after being immersed in deionized water for 10 to 24 hours, and then the floating film is picked up with a mica sheet to obtain a self-supporting ferroelectric film with a bubble-like raised wrinkle structure, and a central topological domain of columnar bubbles along the vertical direction is induced.

6. The induction method according to claim 1, characterized in that: The ferroelectric film is any one of a BiFeO3 film, a PbTiO3 film or a SrTiO3 film.

7. The induction method according to claim 6, characterized in that: The ferroelectric film is a BiFeO3 film; the first layer of the BiFeO3 film has a thickness of 40nm, and is epitaxially grown on the sacrificial layer by pulse laser deposition technology, and the experimental conditions are: pulse energy of 62-66mJ, pulse frequency of 4-8Hz, temperature of 660-730℃, and oxygen pressure of 15-20Pa; the second layer of the BiFeO3 film has a thickness of 70nm, and is epitaxially grown on the bottom electrode by pulse laser deposition technology, and the experimental conditions are: pulse energy of 62-66mJ, pulse frequency of 4-8Hz, temperature of 660-730℃, and oxygen pressure of 15-20Pa.

8. The induction method according to claim 1, characterized in that: The bottom electrode is a SrRuO3 conductive layer.

9. The induction method according to claim 8, characterized in that: The SrRuO3 conductive layer is 40 nm thick and is epitaxially grown on a SrTiO3 single crystal substrate in the (001) direction by pulse laser deposition technology. The experimental conditions are: pulse energy of 75-90 mJ, pulse frequency of 8 Hz, temperature of 660-720°C, and oxygen pressure of 15-20 Pa.

10. A self-supporting ferroelectric thin film, characterized in that: It is a three-layer heterostructure formed by stacking ferroelectric film / conductive layer / ferroelectric film in sequence, and the materials of the two layers of ferroelectric film are the same; its surface has a bubble-like raised wrinkle structure, and around the bubble-like raised wrinkle structure are distributed central topological domains in the form of columnar bubbles in the vertical direction.

Images