A preparation method of a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, and products and applications thereof

Abstract

The application discloses a preparation method of a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, which comprises the following steps: conveying a substrate into an MBE growth chamber, and controlling the substrate temperature to be lower than the evaporation temperature of a Bi source; heating the Bi source and a Fe source and adjusting the beam current size; using ozone as an epitaxial growth atmosphere; and performing epitaxial growth of a bismuth ferrite film without oxygen vacancies as a ferroelectric phase by mixing the Bi source and the Fe source in the growth chamber, and then performing epitaxial growth of a bismuth ferrite film with oxygen vacancies as a defect ferroelectric phase after reducing the oxygen pressure; and alternately growing the two epitaxial growths to obtain the bismuth ferrite-based homojunction superlattice. The application controls the oxygen defect content in each bismuth ferrite layer by controlling the ozone partial pressure of the bismuth ferrite in the epitaxial process, provides a depolarization field at the homojunction interface by introducing the bismuth ferrite layer with oxygen vacancies, and prepares the bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice; and the prepared superlattice surface has clear and parallel atomic steps.

Description

Technical Field

[0001] This invention belongs to the field of information storage technology, and in particular relates to ferroelectric superlattice polarized topological storage, especially to a method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, its products, and applications. Background Technology

[0002] Ferroelectric memories are storage devices that achieve rapid writing and reading of information by controlling polarization reversal. Compared to traditional magnetic and semiconductor memories that use current for reading and writing, ferroelectric memories use an applied voltage to achieve short-range displacement of ions in the crystal lattice, effectively reducing Joule heat dissipation during information reading and writing, and have broad development prospects in the field of low-power information storage devices. Ferroelectric memory cells are ferroelectric domain structures with consistent polarization directions. Among various ferroelectric domains, ferroelectric topological domains effectively reduce the size of ferroelectric domains through bending polarization, theoretically increasing their storage density by 100,000 times compared to traditional ferroelectric memories. In 2009, researchers proposed creating track memory by domain flipping in ferroelectric materials, which has important properties such as low heat dissipation and non-volatility (Science, 2009, 320, 190-194). Since then, logic devices (Sci.Rep., 2015, 5, 9400) and neuromorphic devices (Nanotechnology, 2017, 28, 08LT02; Nanotechnology, 2017, 28, 31LT01) developed based on ferroelectric materials have been of milestone significance for the development of artificial intelligence and other fields. Ferroelectric topologies have been extensively studied in perovskite ferroelectric / dielectric superlattice materials, such as lead titanate / strontium titanate (PTO / STO) (Nature, 2016, 530, 198-201), barium titanate / strontium titanate (BTO / STO) (ACS Nano, 2021, 15, 13380-13388), and bismuth ferrite / strontium titanate (BFO / STO) (Nat. Commun., 2023, 14, 4178). Among them, PTO, BTO, and BFO serve as ferroelectric layer materials, providing strong polarization properties, while STO is a commonly used dielectric layer material to confine the charges generated by polarization and provide a strong depolarization field.

[0003] However, most commonly used superlattices are heterostructures, requiring multiple evaporation sources during epitaxial fabrication, which increases the complexity of the process. Furthermore, heteroepitaxialization places higher demands on the epitaxial conditions. Therefore, achieving homoepitaxialization of high-quality ferroelectric superlattices while simplifying the process is a pressing issue. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy. By controlling the ozone partial pressure during the epitaxy process of bismuth ferrite, the oxygen defect content in each layer of bismuth ferrite is regulated. Without changing the material type, a bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice is prepared by introducing a bismuth ferrite layer containing oxygen vacancies and providing a depolarization field at the homojunction interface. Furthermore, the surface of the prepared superlattice has clear and parallel atomic steps.

[0005] This invention provides the following technical solution:

[0006] A method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, the method comprising:

[0007] (1) The substrate is introduced into the MBE growth chamber, and the substrate temperature is lower than the Bi source evaporation temperature;

[0008] (2) Heat the Bi source and Fe source to the evaporation temperature and adjust the beam current of the Bi source and Fe source;

[0009] (3) Ozone is used as the epitaxial growth atmosphere. Bi source and Fe source are mixed in the growth chamber to first grow an oxygen-free bismuth ferrite epitaxial film as the ferroelectric phase. After reducing the oxygen pressure, an oxygen-containing bismuth ferrite film is then grown as the defect ferroelectric phase.

[0010] (4) The two epitaxial growths in step (3) are carried out alternately to obtain a bismuth ferrite-based homojunction superlattice.

[0011] The preparation method provided by this invention regulates the oxygen defect content in each bismuth ferrite layer by controlling the ozone partial pressure during the epitaxial process of bismuth ferrite. Without changing the material type, by introducing a bismuth ferrite layer containing oxygen vacancies, a depolarization field is provided at the homogeneous interface, and an oxygen vacancy layer is introduced between different bismuth ferrite layers to provide a depolarization field, thus constructing a bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice. This avoids the need to change the evaporation source during film growth, and simplifies the superlattice preparation process by only adjusting the ozone partial pressure, thereby improving the superlattice preparation efficiency.

[0012] In step (1), the substrate is a (110) oriented scandium single crystal substrate, which is a substrate with an atomically flat surface after chemical wet treatment and annealing.

[0013] Specifically, the chemical wet processing includes organic solvent cleaning and strong alkaline etching. Adsorbed particles on the substrate surface are removed by alternating cleaning with ketones and alcohols. Then, the substrate surface is etched under ultrasonication with a strong alkaline solution to remove dysprosium oxide, obtaining a surface with a single scandium cutoff. The annealing process involves subjecting the alkaline-treated substrate to high-temperature holding in an oxidizing atmosphere, causing surface atoms to rearrange and obtaining an atomically flat substrate with clear steps.

[0014] Specifically, the substrate is ultrasonically cleaned alternately with organic solvents (acetone and isopropanol), with the solvent volume sufficient to completely submerge the substrate. After each cleaning, the waste liquid is removed, but the substrate surface should remain moist. After organic solvent cleaning, the substrate is ultrasonically cleaned again with pure water to remove the organic solvent. Sodium hydroxide solution is used as an etchant, and the cleaned substrate is ultrasonically etched in NaOH solutions of different concentrations to remove exposed dysprosium oxides, thereby preparing a substrate material with a single scandium cutoff plane. The treated substrate is rinsed with pure water to remove any residual alkaline solution, and then rapidly spun dry at room temperature. To enable the film to grow in a step-flow manner during molecular beam epitaxy, the substrate is annealed at high temperature to rearrange the surface ScO2, creating parallel atomic steps.

[0015] Preferably, the annealing temperature should meet the energy required for atomic migration on the substrate surface but prevent the substrate from deteriorating at high temperatures, and the annealing time should allow for sufficient atomic rearrangement. Therefore, the annealing temperature is usually 1000-1200℃ and the annealing time is 1h.

[0016] The substrate surface can be observed to have parallel atomic steps with a width of about 200 nm, and the overall surface roughness should be less than 0.4 nm, thereby ensuring the quality of the bismuth ferrite homojunction superlattice epitaxy.

[0017] In step (1), the substrate temperature satisfies: 300℃ ≤ substrate temperature < 600℃. The growth temperature should be lower than the evaporation temperature of the evaporation source and provide sufficient energy to promote the migration of epitaxial ions on the substrate surface, and should be 300℃ ≤ substrate temperature < 600℃.

[0018] Specifically, in step (1), the treated substrate is placed on a molybdenum metal support, fixed with tantalum foil by spot welding, and then inverted within the MBE growth chamber. The substrate is then heated to degas, with the temperature rising to 50°C above the predetermined temperature, until the pressure inside the growth chamber is 10... -9 The temperature is on the order of Torr, and after degassing, the temperature is reduced to a predetermined temperature.

[0019] In step (2), the evaporation temperature of the Bi source is 600-700℃, and the evaporation temperature of the Fe source is 1200-1500℃. Preferably, the Bi source is Bi metal particles, and the Fe source is Fe metal particles.

[0020] The beam ratio of the Bi source to the Fe source is greater than or equal to 4:1.

[0021] In step (2), the Bi / Fe beam ratio should be greater than 4:1 to compensate for the Bi... x O y The volatilization at high temperatures improves the crystallinity and purity of bismuth ferrite epitaxial films.

[0022] Preferably, the beam ratio of the Bi source to the Fe source is 4-16:1.

[0023] Specifically, in step (2), the temperature of the evaporation source is raised to a predetermined temperature to provide a predetermined beam, and the beam magnitude is measured by a quartz microbalance (QCM).

[0024] In step (3), the oxygen pressure of the epitaxial growth is 10. -6 -10 -5 Torr, the oxygen pressure reduction of the epitaxially grown bismuth ferrite epitaxial film with oxygen vacancies does not exceed 1×10 -6 Following the Torr process, bismuth ferrite films containing oxygen vacancies are epitaxially grown. The growth oxygen pressure should be controlled at 10. -6 -10 -5 Torr provides sufficient oxidizing power and ensures a long atomic free path. To guarantee the oxidizing power of ozone, the growth oxygen pressure of bismuth ferrite layers with oxygen vacancies should be reduced by no more than 1 × 10⁻⁶ compared to those with oxygen-vacancy-free sites. -6 Torr.

[0025] Preferably, the oxygen pressure control accuracy should be 10. -8 Torr.

[0026] In step (3), the oxygen pressure is the ozone pressure. Ozone is obtained by high-voltage ionization of pure oxygen and by fractional distillation of liquid nitrogen. The partial pressure should be less than 10. -5 Torr ensures that the molecular beam has a long mean free path.

[0027] The specific operation process is as follows: open the micro-leak valve, adjust the ozone pressure in the growth chamber to the predetermined value, and simultaneously open the baffles of the Bi source and Fe source. After stabilization, open the baffle of the growth chamber to carry out epitaxial growth of the thin film. The thickness of the thin film is controlled by controlling the growth time and the beam current. After the growth is completed, close the baffle of the growth chamber to stop the film growth and obtain the bismuth ferrite epitaxial thin film.

[0028] Preferably, in step (4), the thickness of the bismuth ferrite epitaxial film without oxygen vacancies is 0.8-20 nm.

[0029] Preferably, the thin film surface should have atomic steps similar to the substrate, and the surface roughness should be less than 0.4 nm.

[0030] In step (4), the growth is repeated 2-16 times each.

[0031] It should be understood that the epitaxial sequence should first grow a bismuth ferrite epitaxial film, then grow a bismuth ferrite film containing oxygen vacancies, alternating between the two growths 2-16 times. Each time the growth is alternating, the evaporation source should be turned off first, and the oxygen pressure should be adjusted to a stable level before proceeding with the growth of the next layer.

[0032] Specific explanation of steps (3)-(4): A bismuth ferrite film of a certain thickness without oxygen vacancies is grown on the substrate. After the growth of the bismuth ferrite film without oxygen vacancies is completed, the baffle of the growth chamber is turned off, and the oxygen pressure is reduced to the required growth conditions. After the oxygen pressure stabilizes, the baffle of the growth chamber is turned off to perform homoepitaxial growth of bismuth ferrite with oxygen vacancies. After the epitaxy is completed, the baffle is turned off, and the growth of the bismuth ferrite film without oxygen vacancies is repeated. After 2-16 cycles of growth, the molybdenum support is removed to obtain BFO(V o )-SL homojunction superlattice.

[0033] In this invention, the ferroelectric phase is prepared by controlling the substrate temperature, growth oxygen pressure, and Bi / Fe beam current ratio through oxide molecular beam epitaxy; the defect ferroelectric phase is prepared by adjusting the growth oxygen pressure to reduce the lattice oxygen content of bismuth ferrite while maintaining the original phase: specifically, by calculating the element content and ratio of the thin film, the linear region of element ratio change with oxygen pressure is found, thereby achieving the adjustability of oxygen vacancy concentration in the bismuth ferrite thin film.

[0034] The present invention also provides a bismuth ferrite-based homojunction superlattice obtained according to the above preparation method.

[0035] The bismuth ferrite-based homojunction superlattice is a (001) oriented bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice, comprising a substrate, a ferroelectric phase, and a defect ferroelectric phase.

[0036] Preferably, the bismuth ferrite-based homojunction superlattice is (001) oriented (BiFeO3)x / (BiFeO3-V) o ) y (x and y represent the number of alternating growth cycles, ranging from 2 to 16) Epitaxial superlattice (BFO(V) o )-SL),

[0037] This invention prepares BFO(V) by oxide molecular beam epitaxy. o)-SL has high single-crystal quality (FWHM of diffraction peak < 0.02°), smooth surface and clear atomic steps (RMS of roughness < 200 pm).

[0038] The present invention also provides an application of the above-mentioned bismuth ferrite-based homojunction superlattice in ferroelectric memory.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] The preparation method provided by this invention prepares BFO(V) at a relatively low temperature (<600℃). o )-SL can effectively reduce Bi x O y The volatilization of oxygen allows for precise control of oxygen vacancy defects.

[0041] The preparation method provided by this invention allows for precise control of temperature, oxygen partial pressure, and beam current ratio during the growth of bismuth ferrite (BFO) via oxide molecular beam epitaxy (O-MBE) (wherein the oxygen pressure accuracy for bismuth ferrite growth reaches 1×10⁻⁶). -8 Torr) can further improve BFO(V) o The phase purity and crystal quality of )-SL (high-resolution thin film XRD and XPS were also used to detect the film quality during the preparation process). Attached Figure Description

[0042] Figure 1 The molecular beam epitaxy method for preparing BFO (V) provided in this embodiment of the invention o )Schematic diagram of SL principle;

[0043] Figure 2 BFO(V) provided for embodiments of the present invention o Schematic diagram of a homojunction superlattice structure;

[0044] Figure 3 BFO(V) provided for embodiments of the present invention o High-resolution XRD pattern of SL:

[0045] Figure 4 XPS diagrams and phase diagrams showing the effect of oxygen pressure on elemental content in BFO provided in embodiments of the present invention;

[0046] Figure 5 AFM and TEM images of BFO surfaces grown under different oxygen pressures are provided in this embodiment of the invention.

[0047] Figure 6 AFM images of the substrate and superlattice surface provided in the embodiments of the present invention. Detailed Implementation

[0048] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments.

[0049] Specifically, the method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy provided in this invention includes:

[0050] (1) Surface treatment process for dysprosium scandium substrate, specifically including:

[0051] The dysprosium scandate substrate was immersed in 30 mL of acetone and ultrasonically cleaned for 20 min. The substrate was then removed and placed in 30 mL of isopropanol for another 20 min of ultrasonic cleaning, and this process was repeated. After the final isopropanol cleaning, the substrate was placed in pure water and ultrasonically cleaned to remove residual organic solvent. 10 mol / L and 1 mol / L NaOH etching solutions were prepared, and the substrate was ultrasonically etched sequentially in both solutions for 30 min each, followed by three rinses with pure water to remove any remaining alkaline solution. The cleaned substrate was then spin-coated at 5000 rpm at room temperature to remove surface moisture. The dried substrate was placed in a tube furnace and heated to 1100 °C at a rate of 5 °C / min under an oxygen atmosphere, held for 1 h, then cooled to 800 °C at a rate of 5 °C / min, and finally cooled to room temperature with the furnace to obtain a dysprosium scandate substrate with parallel atomic steps and a roughness of less than 0.2 nm.

[0052] (2) Bismuth ferrite epitaxial films prepared by molecular beam epitaxy specifically include:

[0053] First, the prepared substrate is placed on a molybdenum metal support, fixed with tantalum foil by spot welding, and then inverted within the MBE growth chamber. The substrate is then slowly heated to degas, with the final degassing temperature reaching 400℃, until the pressure inside the growth chamber reaches 10... -9 Degassing was completed at the Torr level, and the substrate temperature was lowered to 350°C in preparation for film growth. The Bi source was heated to 650°C, and the Fe source to 1350°C. At this point, the beam current ratio J measured by QCM was... Bi / J Fe The ratio is approximately 8:1. Ozone is prepared by high-pressure ionization of pure oxygen, and fractionation is performed using liquid nitrogen at a controlled temperature of -170℃ to improve ozone purity. The micro-leak valve is opened, and the ozone pressure in the growth chamber is adjusted to 4 × 10⁻⁶. -6 Torr was used, and the baffles of both the Bi and Fe sources were opened simultaneously. After stabilization, the baffle of the growth chamber was opened to allow for epitaxial growth of the thin film. After 5 minutes of growth, the epitaxial thickness was 4 nm. The growth chamber baffle was then closed to stop film growth, yielding a bismuth ferrite epitaxial film (ferroelectric phase).

[0054] (3) Bismuth ferrite-based homojunction superlattice prepared by molecular beam epitaxy, with [(BiFeO3)] 4nm / (BiFeO3-V o ) 4nm Taking 8 as an example, it specifically includes:

[0055] After the 4nm bismuth ferrite film growth was completed, the growth chamber baffle was closed, and the ozone end microleak valve was slowly adjusted to reduce the oxygen pressure to 3.5×10⁻⁶. -6 After the pressure stabilizes, the growth chamber baffle is opened to begin the growth of the oxygen vacancy layer (defect ferroelectric phase). After 5 minutes of growth, the growth chamber baffle is closed, resulting in one cycle of bismuth ferrite homojunction. The above process is repeated for eight cycles. Then, the growth chamber baffle and the two evaporation source baffles are closed, and the substrate is cooled to room temperature with the furnace before being removed, resulting in eight cycles of bismuth ferrite-based homojunction superlattices, each 8 nm in length.

[0056] The above embodiments employ oxide molecular beam epitaxy (O-MBE) to regulate the ambient ozone partial pressure and growth time of bismuth ferrite (BiFeO3) growth, in the case of dysprosium scandate (DyScO3-(110)). pc (001) oriented (BiFeO3 / BiFeO3-V) was prepared on a single crystal substrate. o )8 Epitaxial Superlattice (BFO(V) o )-SL).

[0057] Figure 1 The molecular beam epitaxy method for preparing BFO (V) provided in this embodiment of the invention o )Schematic diagram of SL principle: Figure 1 (a) in the diagram is a flowchart of molecular beam epitaxy. Figure 1 (b) in the diagram is a schematic of the molecular beam epitaxy growth mechanism; from Figure 1 It can be seen that the growth mechanism of BFO is an oxidation-adsorption-diffusion mechanism. Since Bi oxides have strong volatility, they need to be adsorbed and deposited based on Fe oxides. Therefore, within a certain range, increasing the beam current of Bi will be beneficial to the purity of the BFO phase.

[0058] Figure 2 BFO(V) provided for embodiments of the present invention o Schematic diagram of a homojunction superlattice structure: Figure 2 (a) in the text represents BFO(V) o )SL devices, Figure 2 (b) in the text represents BFO(V) o SL atomic model; Figure 2 BFO(V) is given o The application of homojunction superlattices can be achieved by using voltage and needle tip force to write and erase the topological structure in the superlattice, thus realizing information storage.

[0059] Figure 3 BFO(V) provided for embodiments of the present invention o )SL high-resolution XRD pattern; where, Figure 3 In the figure (a), BFO(V) is in linear coordinates. o The XRD diffraction peaks of the (001) crystal plane of SL show that the thin film has strong diffraction peaks and good crystal quality. Figure 3 In (b), BFO(V) is defined in logarithmic coordinates. o The XRD diffraction peaks of the (001) crystal plane of SL show that only the substrate and superlattice have diffraction peaks in this range, with no other impurity peaks, indicating high phase purity of the device. Therefore, from Figure 3 It can be seen from this that BFO has good epitaxiality and crystallinity.

[0060] Figure 4 XPS plots and phase diagrams illustrating the effect of oxygen pressure on elemental content in BFO, provided in embodiments of the present invention: Figure 4 (a)-(c) in the figure are X-ray photoelectron spectra of Fe, Bi, and O in BFO grown under 4e-6T, respectively. Figure 4 (d) The content of each element and the corresponding phase diagram under different oxygen pressures. Figure 4 (e) Phase diagram of O / Bi ratio under different oxygen pressures. Figure 4 (f) in the diagram is an enlarged phase diagram of region I in (d) and (e); from Figure 4 As can be seen, by finely controlling the ozone pressure, the phase composition and oxygen vacancy content in BFO can be precisely controlled.

[0061] Figure 5 AFM and TEM images of BFO surfaces grown under different oxygen pressures provided in embodiments of the present invention: Figure 5 Images (a) and (b) in the figure are atomic force microscopy images. Figure 5 (c) and (d) in the image are cross-sectional views obtained using a transmission electron microscope; from Figure 5 It can be seen that the BFO superlattice surface is flat and has an atomic step at the unit cell level, with different contrasts in layers with different oxygen contents.

[0062] Figure 6 AFM images of the substrate and superlattice surface provided in the embodiments of the present invention: Figure 6 In the image, (a) and (b) represent atomic steps on the surface of the DSO(110) substrate. Figure 6 (c) and (d) in the figure represent BFO(V) o )SL surface atomic steps; from Figure 6It can be seen that the step width of the BFO superlattice is similar to that of the substrate, and it has extremely high flatness: the superlattice surface has clear and parallel atomic steps with a roughness of about 0.2 nm. This homojunction superlattice grows along the (001) orientation and is related to DyScO3-(110). pc The substrate mismatch is approximately -0.2%.

[0063] In summary, this invention provides a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy. A bismuth ferrite / oxygen-vacancy bismuth ferrite homojunction superlattice was constructed on a dysprosium scandate substrate by precisely controlling the ozone pressure using molecular beam epitaxy. The use of oxygen-vacancy bismuth ferrite to provide a depolarization field at the homojunction interface simplifies the fabrication process of the ferroelectric superlattice and improves its fabrication efficiency. Furthermore, precise control of the growth parameters during the superlattice growth process enhances both the crystallinity and epitaxial quality of the superlattice.

[0064] Although preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will recognize that various modifications, additions, and substitutions are possible, and therefore the scope of the invention should not be limited to the embodiments described above.

Claims

1. A method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy, characterized in that, The preparation method includes: (1) The substrate is introduced into the MBE growth chamber, and the substrate temperature is lower than the Bi source evaporation temperature; (2) Heat the Bi source and Fe source to the evaporation temperature and adjust the beam current of the Bi source and Fe source; (3) Ozone is used as the epitaxial growth atmosphere. Bi source and Fe source are mixed in the growth chamber to first grow an oxygen-vacancy-free bismuth ferrite epitaxial film as the ferroelectric phase. After reducing the oxygen pressure, an oxygen-vacancy-containing bismuth ferrite film is then grown as the defect ferroelectric phase. (4) The two epitaxial growths in step (3) are carried out alternately to obtain a bismuth ferrite-based homojunction superlattice; In step (1), the substrate is a (110) oriented scandium single crystal substrate, which is a substrate with an atomically flat surface after chemical wet processing and annealing. In step (1), the substrate temperature satisfies: 300°C o C≤substrate temperature<600 o C; In step (2), the evaporation temperature of the Bi source is 600-700 °C. o C, the evaporation temperature of the Fe source is 1200-1500℃. o C; The beam ratio of the Bi source and the Fe source is greater than or equal to 4:1; In step (3), the oxygen pressure of the epitaxial growth is 10. -6 -10 -5 Torr, the oxygen pressure reduction of the epitaxially grown bismuth ferrite epitaxial film with oxygen vacancies does not exceed 1×10 -6 Following the Torr process, bismuth ferrite films containing oxygen vacancies are epitaxially grown.

2. The method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 1, characterized in that, The beam ratio of the Bi source to the Fe source is 4-16:

1.

3. The method for preparing a bismuth ferrite-based homojunction superlattice based on molecular beam epitaxy according to claim 1, characterized in that, In step (4), the growth is repeated 2-16 times each.

4. A bismuth ferrite-based homojunction superlattice obtained by the preparation method according to any one of claims 1-3.

5. The bismuth ferrite-based homojunction superlattice according to claim 4, characterized in that, The bismuth ferrite-based homojunction superlattice is a (001) oriented bismuth ferrite / oxygen vacancy bismuth ferrite homojunction superlattice.

6. The application of the bismuth ferrite-based homojunction superlattice of claim 4 in ferroelectric memory.

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