Bimetallic oxide thin film preparation method and bimetallic oxide thin film

Abstract

The invention discloses a preparation method of a bimetallic oxide thin film and the bimetallic oxide thin film, relates to the technical field of atomic layer deposition, and aims to solve the problem that conductivity and interface stability cannot be considered under the condition that a battery positive electrode is coated with a single metal oxide. The method comprises the following steps: providing a substrate; forming a first metal oxide layer on the surface of the substrate; sequentially forming a second metal oxide layer and a third metal oxide layer which are alternately stacked on the first metal oxide layer; the first metal oxide layer and the second metal oxide layer are made of the same material, and the structural density of the second metal oxide layer is smaller than that of the first metal oxide layer; forming a fourth metal oxide layer on the third metal oxide layer; the third metal oxide layer and the fourth metal oxide layer are made of the same material, and the structural density of the third metal oxide layer is smaller than that of the fourth metal oxide layer; and carrying out heating, annealing and cooling treatment to obtain the bimetallic oxide thin film on the substrate.

Description

Technical Field

[0001] This invention relates to the field of atomic layer deposition technology, and in particular to a method for preparing bimetallic oxide thin films and the bimetallic oxide thin films themselves. Background Technology

[0002] Atomic layer deposition (ALD) is a technique that grows atomic layers of materials by alternately introducing reactive gases and purging them.

[0003] Ternary materials (LiNi) x CoyMnzO2 (NCM) has become the mainstream cathode for power batteries due to its high energy density, but side reactions such as electrolyte decomposition occur at its interface, leading to microcracks or even failure in the structure. Currently, atomic layer deposition technology is used to protect the battery by coating the battery surface with a metal oxide, but a single oxide cannot simultaneously resolve the contradiction between conductivity and interface stability. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing bimetallic oxide thin films and a bimetallic oxide thin film, which solves the problem that the conductivity and interface stability cannot be simultaneously achieved when using atomic layer deposition technology to coat a single metal oxide on the positive electrode of a battery.

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

[0006] In a first aspect, the present invention provides a method for preparing a bimetallic oxide thin film, comprising:

[0007] Provide a base;

[0008] A first metal oxide layer is formed on the substrate surface;

[0009] Alternating layers of second and third metal oxide layers are sequentially formed on a first metal oxide layer; wherein the first and second metal oxide layers are made of the same material, and the structural density of the second metal oxide layer is less than that of the first metal oxide layer.

[0010] A fourth metal oxide layer is formed on the third metal oxide layer; wherein the third metal oxide layer and the fourth metal oxide layer are made of the same material, and the structural density of the third metal oxide layer is less than that of the fourth metal oxide layer.

[0011] The bimetallic oxide film on the substrate is obtained by heating, annealing and cooling.

[0012] Optionally, in the above-described method for preparing a bimetallic oxide thin film, forming a first metal oxide layer on the substrate surface includes:

[0013] The substrate is placed in the atomic layer deposition reaction chamber and heated to the preset temperature;

[0014] A first metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a first metal oxide layer on the substrate. The duration of each introduction of the first metal precursor is a first preset time.

[0015] Optionally, in the above-described method for preparing bimetallic oxide thin films, the alternating formation of a second metal oxide layer and a third metal oxide layer on the first metal oxide layer includes:

[0016] A second metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a second metal oxide layer on the first metal oxide layer. The first metal precursor and the second metal precursor are made of the same material. The duration of each introduction of the second metal precursor is a second preset time, which is less than the first preset time.

[0017] A third metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a third metal oxide layer on the second metal oxide layer. The duration of each introduction of the third metal precursor is a third preset time.

[0018] A second metal oxide layer and a third metal oxide layer are cyclically grown on the first metal oxide layer.

[0019] Optionally, in the above-described method for preparing a bimetallic oxide thin film, forming a fourth metal oxide layer on the third metal oxide layer includes:

[0020] A fourth metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a fourth metal oxide layer on the third metal oxide layer. The third metal precursor and the fourth metal precursor are made of the same material, and the fourth metal precursor is introduced for a fourth preset time each time, which is longer than the third preset time.

[0021] Optionally, in the above-described method for preparing bimetallic oxide thin films, the ratio of the second preset time to the third preset time is 2 / 1 to 4 / 1.

[0022] Optionally, in the above-mentioned method for preparing bimetallic oxide thin films, the materials of the first metal precursor and the second metal precursor are trimethylaluminum, the materials of the third metal precursor and the fourth metal precursor are diethylzinc, and the oxygen plasma is ozone.

[0023] Optionally, in the above-described method for preparing bimetallic oxide thin films, after providing a substrate and before forming a first metal oxide layer on the substrate surface, the preparation method further includes:

[0024] The substrate is heated and dehydrated.

[0025] Nitrogen gas was used to remove impurities from the surface of the treated substrate at a power of 200W to 400W.

[0026] Optionally, in the above-described method for preparing bimetallic oxide thin films, the heating, annealing, and cooling processes are performed to obtain the bimetallic oxide thin film located on the substrate, including:

[0027] Under a nitrogen atmosphere, the substrate is heated to 120℃~180℃;

[0028] Annealing was performed in a nitrogen atmosphere and then cooled to room temperature to obtain a bimetallic oxide film on the substrate.

[0029] Optionally, in the above-mentioned method for preparing bimetallic oxide thin films, the temperature of the atomic layer deposition reaction chamber is 100℃~200℃ before performing heating, annealing and cooling treatments to obtain the bimetallic oxide thin film on the substrate.

[0030] Compared with the prior art, the present invention provides a method for preparing a bimetallic oxide thin film, comprising: providing a substrate; forming a first metal oxide layer on the surface of the substrate; sequentially forming an alternating layer of a second metal oxide layer and a third metal oxide layer on the first metal oxide layer; wherein the first metal oxide layer and the second metal oxide layer are made of the same material, and the structural density of the second metal oxide layer is less than that of the first metal oxide layer; forming a fourth metal oxide layer on the third metal oxide layer; wherein the third metal oxide layer and the fourth metal oxide layer are made of the same material, and the structural density of the third metal oxide layer is less than that of the fourth metal oxide layer; and performing heating, annealing and cooling treatments to obtain a bimetallic oxide thin film located on the substrate.

[0031] This application constructs a first metal oxide layer, a second metal oxide layer, a third metal oxide layer, and a fourth metal oxide layer sequentially on the surface of a substrate. The first and second metal oxide layers are made of the same material, a first metal oxide; the third and fourth metal oxide layers are made of the same material, a second metal oxide. The first metal oxide layer is directly chemically bonded to the substrate; its high density and chemical inertness inhibit electrolyte corrosion and ensure interface stability. The second and third metal oxide layers are formed by alternating deposition of low-density first and second metal oxides, resulting in a structure that combines the chemical stability of the first metal oxide with the ionic conductivity of the second metal oxide. This structure is adaptable to different structural interfaces, buffering thermal expansion stress differences and avoiding interlayer stress concentration, while also providing channels for charge transport. The outer fourth metal oxide layer provides a rapid diffusion path for charge, improving conductivity.

[0032] Secondly, the present invention also provides a bimetallic oxide thin film, which is prepared by the bimetallic oxide thin film preparation method according to any one of claims 1-9.

[0033] Compared with the prior art, the bimetallic oxide thin film provided by the present invention can simultaneously achieve both conductivity and interface stability. Attached Figure Description

[0034] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 This is a flowchart of a method for preparing a bimetallic oxide thin film according to an embodiment of the present invention. Detailed Implementation

[0036] To facilitate a clear description of the technical solutions in the embodiments of the present invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. For example, the first threshold and the second threshold are merely used to distinguish different thresholds and do not limit their order. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that the terms "first" and "second" are not necessarily different.

[0037] It should be noted that in this invention, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0038] In this invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple.

[0039] The positive electrode of a power battery typically uses ternary materials (LiNi). x CoyMnzO2 (NCM) is used for coating power batteries, but it has the following drawbacks: the positive electrode is prone to interfacial side reactions; the electrolyte decomposes under high voltage, leading to a thickening of the CEI layer; transition metal dissolution and Mn / Co ion dissolution cause capacity decay; and the volume change during charge and discharge leads to mechanical stress cracks, resulting in structural failure. Currently, atomic layer deposition (ALD) technology is used to coat the positive electrode of the power battery with a layer of metal oxide to optimize it. However, if a metal oxide that can effectively reduce electrolyte decomposition is used for coating, the high insulation of these materials leads to a decrease in battery conductivity; if a metal oxide material with high conductivity is used for coating, the chemical stability is insufficient, and it cannot effectively suppress electrolyte decomposition. It is precisely because of the aforementioned conflicting properties of single metal oxide materials that the requirements for high stability and high conductivity cannot be met simultaneously.

[0040] To address the above problems, this invention provides a method for preparing bimetallic oxide thin films and a bimetallic oxide thin film, which will be described below with reference to the accompanying drawings.

[0041] See Figure 1 The present invention provides a method for preparing a bimetallic oxide, comprising the following steps:

[0042] Step 100: Provide a substrate;

[0043] The above-mentioned substrate is a pretreated substrate. The substrate material is NCM811 powder, and the median particle size of the powder can be 7.5μm to 8.5μm. For example, the median particle size can be 7.5μm, 8μm, 8.5μm or any value between them. An appropriate particle size can satisfy the sufficient adsorption of the precursor without causing the coating layer to be too thin due to excessive surface area, resulting in coating defects. The pretreatment process of the substrate is as follows: before deposition, the NCM811 powder is placed in a vacuum oven at 100℃ to 140℃ for dehydration. For example, the dehydration time can be 10h, 12h, 13h, etc. After that, nitrogen plasma with a power of 200W to 400W is introduced for treatment for 8min to 12min to remove the surface adsorbed carbon.

[0044] Step 200: Form a first metal oxide layer on the substrate surface;

[0045] Step 300: Sequentially form alternating layers of second and third metal oxide layers on the first metal oxide layer; wherein the first and second metal oxide layers are made of the same material, and the structural density of the second metal oxide layer is less than that of the first metal oxide layer.

[0046] Step 400: Form a fourth metal oxide layer on the third metal oxide layer; wherein the third metal oxide layer and the fourth metal oxide layer are made of the same material, and the structural density of the third metal oxide layer is less than that of the fourth metal oxide layer.

[0047] Step 500: Perform heating, annealing and cooling treatments to obtain a bimetallic oxide film on the substrate.

[0048] Specifically, the heating, annealing, and cooling process is as follows: the sample obtained in the above steps is heated and annealed under nitrogen atmosphere; and the annealed sample is cooled to room temperature to obtain a bimetallic oxide film on the substrate.

[0049] For example, the preparation method will be described below using trimethylaluminum as the first metal precursor and diethylzinc as the second metal precursor. It can be understood that the materials of the first and second metal oxide layers can be aluminum oxide or titanium oxide, and the materials of the third and fourth metal oxide layers can be zinc oxide or lanthanum oxide. Therefore, the corresponding metal precursors can be selectively used to obtain the corresponding metal oxide layers.

[0050] As one possible implementation, step 200 can be based on the following steps:

[0051] Step 210: Place the substrate in the atomic layer deposition reaction chamber and heat it to the preset temperature;

[0052] The pretreated substrate is placed in the heating pan of the atomic layer deposition equipment and heated to 120°C to 180°C.

[0053] Step 220: Alternately introduce a first metal precursor and oxygen plasma into the atomic layer deposition reaction chamber to form a first metal oxide layer on the substrate using the first metal precursor and oxygen plasma. The duration of each introduction of the first metal precursor is a first preset time.

[0054] For example, a trimethylaluminum (TMA) precursor can be introduced into an atomic layer deposition (ALD) apparatus as the first metal precursor for a duration of 0.08 s to 0.12 s as the first preset time. The introduction duration can be any value between 0.08 s, 0.1 s, and 0.12 s to ensure surface saturation adsorption while avoiding gaseous residue. After introduction, nitrogen purging is performed for 12 s to 18 s. For example, the purging duration can be any value between 12 s, 15 s, and 18 s to remove unreacted precursors and byproducts. Then, an ozone oxidation source is introduced as oxygen plasma for a duration of 0.15 s to 0.25 s. For example, the introduction duration can be any value between 0.15 s, 0.2 s, and 0.25 s to ensure sufficient oxidation to form dense alumina. Nitrogen purging is performed again for 12 s to 18 s. For example, the purging time can be 12s, 15s, 18s or any value in between, to purify the reaction interface; repeat the above steps 18 to 22 times. The number of cycles can be 18, 20, 22 or any integer value in between. The thickness of the alumina layer is controlled by the number of cycles to ensure corrosion barrier effect while avoiding excessive thickness that could lead to ion blockage.

[0055] As one possible implementation, step 300 can be implemented based on the following steps:

[0056] Step 310: Alternately introduce a second metal precursor and oxygen plasma into the atomic layer deposition reaction chamber to form a second metal oxide layer on the first metal oxide layer using the second metal precursor and oxygen plasma; wherein, the first metal precursor and the second metal precursor are made of the same material; the time for each introduction of the second metal precursor is a second preset time, which is less than the first preset time.

[0057] For example, a trimethylaluminum precursor can be introduced into the atomic layer deposition apparatus as a second metal precursor for a duration of 0.05 s to 0.07 s (the second preset time), where the introduction duration can be any value between 0.05 s, 0.06 s, and 0.07 s. Following the introduction, nitrogen purging is performed for a duration of 6 s to 10 s. For example, the purging duration can be any value between 6 s, 8 s, and 10 s to quickly remove residues and maintain atomic-level deposition precision. An ozone (O3) oxidation source is then introduced as an oxygen plasma for a duration of 0.15 s to 0.25 s. For example, the introduction duration can be any value between 0.15 s, 0.2 s, and 0.25 s to ensure sufficient oxidation reaction. Nitrogen purging is then performed again for a duration of 6 s to 10 s. The purging time can be 6s, 8s, 10s, or any value between them, to suppress the formation of gaseous byproducts and obtain a second metal oxide layer made of alumina. The second preset time is shorter than the first preset time, the purpose of which is to obtain an alumina layer with a lower density than the inner alumina layer, allowing the alumina on the second metal oxide layer to form an undersaturated deposition, creating zinc atom migration channels and improving conductivity; furthermore, the low-density alumina layer can effectively bond with the zinc oxide layer, relieving interfacial stress and suppressing crack formation.

[0058] Step 320: The third metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form the third metal oxide layer on the second metal oxide layer; the time for each introduction of the third metal precursor is the third preset time.

[0059] Diethylzinc (DEZ) precursor is introduced as a third metal precursor for a duration of 0.015 s to 0.025 s, which is a third preset time. For example, the introduction duration can be 0.015 s, 0.02 s, 0.025 s, or any value between them, and the doping concentration is controlled by short pulses. After introduction, nitrogen is purged for 6 s to 10 s. For example, the purging duration can be 6 s, 8 s, 10 s, or any value between them to remove reaction byproducts and avoid carbon residue. Ozone (O3) oxidation source is then introduced as oxygen plasma for a duration of 0.15 s to 0.25 s. For example, the introduction duration can be 0.15 s, 0.2 s, 0.25 s, or any value between them to ensure sufficient oxidation and bonding of zinc atoms. Nitrogen is then purged again for 6 s to 10 s. For example, the purging duration can be 6s, 8s, 10s or any value in between.

[0060] Step 330: Cyclicly grow a second metal oxide layer and a third metal oxide layer on the first metal oxide layer.

[0061] For example, the above steps are repeated 4 to 6 times. For example, the number of cycles can be 4, 5, 6 or any integer value in between, to control the film growth.

[0062] As one possible implementation, step 400 can be implemented in the following way:

[0063] A fourth metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a fourth metal oxide layer on the third metal oxide layer. The third metal precursor and the fourth metal precursor are made of the same material, and the fourth metal precursor is introduced for a fourth preset time each time, which is longer than the third preset time.

[0064] For example, a diethylzinc (DEZ) precursor is introduced into the atomic layer deposition equipment as a fourth metal precursor for a duration of 0.04 s to 0.06 s as a fourth preset time. For example, the fourth preset time can be any value between 0.04 s, 0.05 s, and 0.06 s, and by extending the deposition time, zinc atom saturation coverage is achieved, constructing a highly conductive substrate. After introduction, nitrogen is used for purging for a duration of 8 s to 12 s. For example, the purging duration can be any value between 8 s, 10 s, and 12 s to fully remove organic byproducts and ensure film purity. An ozone (O3) oxidation source is introduced as an oxygen plasma for a duration of 0.12 s to 0.18 s. For example, the purging time can be 0.12s, 0.15s, 0.18s, or any value between them, to optimize the oxidation reaction efficiency and avoid over-oxidation damage to the structure; then, nitrogen is used for purging again, with a purging time of 8s to 12s. For example, the purging time can be 8s, 10s, 12s, or any value between them, to maintain atomic-level surface cleanliness; the above steps are repeated 9 to 11 times. For example, the number of cycles can be 9, 10, 11, or any integer value between them, to precisely control the thickness of the zinc oxide layer, ensuring high conductivity while avoiding excessive thickness that could block ion diffusion. The fourth preset time is longer than the third preset time. The fourth preset time is 0.04s to 0.06s, and the third preset time is 0.015s to 0.025s. The outermost DEZ layer needs a longer time to achieve saturation deposition and form a dense zinc oxide layer, while the third metal oxide layer only needs a short time of undersaturation deposition to create lattice vacancies for zinc atoms to diffuse toward the first metal oxide layer. This ensures conductivity and also allows for good bonding with the second metal oxide layer, relieving interfacial stress.

[0065] As one possible implementation, the ratio of the second preset time to the third preset time is 2 / 1 to 4 / 1.

[0066] For example, the ratio of the second preset time (the introduction time of the second metal precursor, i.e., the introduction time of trimethylaluminum each time) to the third preset time (the introduction time of the third metal precursor, i.e., the introduction time of diethylzinc each time) is 2 / 1 to 4 / 1. For example, the ratio can be 2 / 1, 3 / 1, 4 / 1, or any value in between. By adjusting the introduction time ratio of the second metal precursor and the third metal precursor, a film layer with good uniformity can be formed. If the ratio is too low, such as 1:1, island-like aggregation will form, resulting in an uneven film layer. If the ratio is too high, such as 5:1, the thickness of the second metal oxide layer will be too large, and the conductivity will be poor. Therefore, the introduction time ratio of the two is selected as 2 / 1 to 4 / 1.

[0067] As one possible implementation, the first and second metal precursors are made of trimethylaluminum, the third and fourth metal precursors are made of diethylzinc, and the oxygen plasma is ozone.

[0068] The first and second metal precursors are made of the same material. When the material is trimethylaluminum, it is oxidized by oxygen plasma to obtain alumina, which is used as the material for both the first and second metal precursors. Alumina has good chemical inertness and does not easily react with the electrolyte of the battery electrode, thus exhibiting good stability. The third and fourth metal precursors are made of the same material. When the material is diethylzinc, it is oxidized by oxygen plasma to obtain zinc oxide, which is used as the material for both the third and fourth metal precursors. Zinc oxide and alumina can form a good bond, and no large stress is formed in the bonding layer. At the same time, zinc oxide has good electrical conductivity, ensuring conductivity.

[0069] In some embodiments, the materials of the first metal precursor and the third metal precursor can be titanium tetraisopropoxide and tricyclopentadienyl lanthanum, respectively, so that after oxidation, titanium oxide and lanthanum oxide are obtained as the materials of the first metal oxide layer and the third metal oxide layer.

[0070] As one possible implementation, step 500 can be implemented in the following way:

[0071] Under a nitrogen atmosphere, the substrate is heated to 200℃~300℃;

[0072] Annealing was performed in a nitrogen atmosphere and then cooled to room temperature to obtain a bimetallic oxide film on the substrate.

[0073] Under a nitrogen atmosphere, the deposited sample is heated to 200°C–300°C. For example, the heating temperature can be 0°C, 250°C, 300°C, or any value between them. During the heating process, by controlling the heating rate, for example, keeping it below 5°C per minute, thermal shock-induced film cracking can be effectively avoided. Annealing is then performed at the above temperature, specifically, holding for 1–3 hours, with the holding time being 1 hour, 2 hours, 3 hours, or any duration between them, to promote interdiffusion of aluminum and zinc atoms and complete the spinel phase (ZnAl2O4) lattice reconstruction. After annealing, the sample is cooled to room temperature under nitrogen protection to obtain a bimetallic oxide film on the substrate. For example, the cooling rate can be controlled below 0.5°C per minute; slow cooling eliminates internal stress and effectively ensures the integrity of the film structure.

[0074] For example, before performing heating, annealing, and cooling processes to obtain a bimetallic oxide film on the substrate, the temperature of the atomic layer deposition reaction chamber is 120°C to 180°C. By controlling the relatively low temperature environment during the process, keeping the temperature between 120°C and 180°C, the loss of lattice oxygen in the cathode material can be effectively avoided.

[0075] It should be noted that when trimethylaluminum is used as the precursor material, the purity of the trimethylaluminum raw material is greater than or equal to 99.999%, and when diethylzinc is used as the precursor material, the purity of the diethylzinc raw material is greater than or equal to 99.995%. By using high-purity raw materials, impurities in the deposition process are reduced, further improving the conductivity and stability of the deposited film.

[0076] The present invention also provides a bimetallic oxide thin film, which is prepared by a bimetallic oxide thin film preparation method.

[0077] The bimetallic oxide thin films prepared by the above-mentioned method can simultaneously achieve both conductivity and interfacial stability.

[0078] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0079] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A method for preparing a bimetallic oxide thin film, characterized in that, include: Provide a base; A first metal oxide layer is formed on the surface of the substrate; Alternating layers of a second metal oxide layer and a third metal oxide layer are sequentially formed on the first metal oxide layer; wherein the first metal oxide layer and the second metal oxide layer are made of the same material, and the structural density of the second metal oxide layer is less than that of the first metal oxide layer. A fourth metal oxide layer is formed on the third metal oxide layer; wherein the third metal oxide layer and the fourth metal oxide layer are made of the same material, and the structural density of the third metal oxide layer is less than that of the fourth metal oxide layer; The material is subjected to heating, annealing, and cooling processes to obtain a bimetallic oxide film on the substrate.

2. The method for preparing bimetallic oxide thin films according to claim 1, characterized in that, The formation of the first metal oxide layer on the substrate surface includes: The substrate is placed in the atomic layer deposition reaction chamber and heated to a preset temperature; A first metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a first metal oxide layer on the substrate using the first metal precursor and the oxygen plasma. The duration of each introduction of the first metal precursor is a first preset time.

3. The method for preparing bimetallic oxide thin films according to claim 2, characterized in that, The step of sequentially forming alternating layers of a second metal oxide layer and a third metal oxide layer on the first metal oxide layer includes: A second metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a second metal oxide layer on the first metal oxide layer using the second metal precursor and oxygen plasma; wherein the first metal precursor and the second metal precursor are made of the same material; the duration of each introduction of the second metal precursor is a second preset time, which is less than the first preset time. A third metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a third metal oxide layer on the second metal oxide layer using the third metal precursor and oxygen plasma; the duration of each introduction of the third metal precursor is a third preset time. The second metal oxide layer and the third metal oxide layer are cyclically grown on the first metal oxide layer.

4. The method for preparing bimetallic oxide thin films according to claim 3, characterized in that, The formation of the fourth metal oxide layer on the third metal oxide layer includes: A fourth metal precursor and oxygen plasma are alternately introduced into the atomic layer deposition reaction chamber to form a fourth metal oxide layer on the third metal oxide layer. The third metal precursor and the fourth metal precursor are made of the same material. The fourth metal precursor is introduced for a fourth preset time each time, and the fourth preset time is longer than the third preset time.

5. The method for preparing bimetallic oxide thin films according to claim 3, characterized in that, The ratio of the second preset time to the third preset time is 2 / 1 to 4 / 1.

6. The method for preparing bimetallic oxide thin films according to claim 4, characterized in that, The first and second metal precursors are made of trimethylaluminum, the third and fourth metal precursors are made of diethylzinc, and the oxygen plasma is ozone.

7. The method for preparing bimetallic oxide thin films according to claim 1, characterized in that, After providing a substrate and before forming a first metal oxide layer on the substrate surface, the preparation method further includes: The substrate is subjected to heating and dehydration treatment; Nitrogen gas was used to remove impurities from the surface of the treated substrate at a power of 200W to 400W.

8. The method for preparing bimetallic oxide thin films according to claim 1, characterized in that, The process of heating, annealing, and cooling to obtain a bimetallic oxide film on the substrate includes: The substrate was heated to 200°C–300°C under a nitrogen atmosphere. Annealing was performed in a nitrogen atmosphere and then cooled to room temperature to obtain a bimetallic oxide film on the substrate.

9. The method for preparing bimetallic oxide thin films according to claim 1, characterized in that, Before the heating, annealing and cooling processes are performed to obtain the bimetallic oxide film on the substrate, the temperature of the atomic layer deposition reaction chamber is 120°C to 180°C.

10. A bimetallic oxide thin film, characterized in that, The bimetallic oxide thin film is prepared by the bimetallic oxide thin film preparation method according to any one of claims 1-9.

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