A method for preparing cobalt ferrite epitaxial film by using plasma field activation assistance
The method of preparing cobalt ferrite epitaxial thin films by plasma field activation-assisted preparation solves the problems of long preparation cycle, size limitation and low crystallinity in the existing technology, and realizes the efficient preparation of high-performance cobalt ferrite epitaxial thin films with preferred epitaxial orientation and high crystallinity.
Patent Information
- Application Number
- CN202211273241.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-10-18
- Publication Date
- 2026-01-20
- Estimated Expiration
- 2042-10-18
AI Technical Summary
Existing technologies for preparing cobalt ferrite epitaxial thin films suffer from problems such as long preparation cycles, size limitations, low crystallinity, and residual oxygen vacancies, making it difficult to meet the demands of modern society for high-performance information storage devices.
A plasma field activation-assisted preparation method was adopted, combining magnetron sputtering technology and PECVD vacuum annealing furnace. By depositing a CFO precursor film at room temperature, activating it with a plasma field and annealing it in a vacuum, and finally annealing it in an oxygen atmosphere, a high-quality CFO epitaxial film was prepared.
This method enables the preparation of high-quality, large-area epitaxial thin films, shortens the preparation cycle, improves the crystallinity and surface activity of the films, reduces oxygen vacancies, enables preferred epitaxial orientation, and enhances film performance.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of ferroic functional materials, and particularly relates to a method for preparing a cobalt ferrite epitaxial film by means of plasma field activation. BACKGROUND
[0002] Since the 21st century, the advent of the information age has led to an explosive growth in the total amount of data generated globally, especially in recent years, the development of artificial intelligence big data is in full swing, which has put forward higher requirements for information storage technology. Information storage technology not only needs to develop towards high speed, large capacity and low loss, but also needs to be miniaturized, integrated and multifunctional. However, the development of semiconductor devices based on traditional single ferroic functional materials and microelectronic integrated processes has reached its limit, which cannot meet the urgent needs of modern society for high-performance information storage devices in the field of semiconductors. As is known to all, in addition to the traditional ferroelectric and ferromagnetic properties, multi-ferroic materials also have a coupling effect between the two properties, i.e. magnetoelectric coupling effect. Based on the characteristics of the magnetoelectric coupling effect, scientists have found through theoretical calculations that integrating the magnetoelectric coupling effect into integrated devices can develop multi-ferroelectric random storage devices to four resistance states or even eight resistance states, which can exponentially increase the storage space. Moreover, based on the special working mode of "electric writing and magnetic reading", the read and storage rates of the storage device can be further improved, which greatly expands the development space of key devices in the field of semiconductors and shows great development potential.
[0003] Nowadays, it is generally recognized that the magnetoelectric coupling effect mainly originates from the mechanical action of magnetostriction and piezoelectric effect in each phase of the magnetoelectric composite film. In order to obtain an integrated composite film with more significant magnetoelectric coupling effect, it is the key to select a ferromagnetic phase with greater magnetostriction effect and a ferroelectric phase with greater piezoelectric effect. Among them, cobalt ferrite (CoFe2O4, CFO) is a spinel-type iron-cobalt oxide, which has attracted a large number of researches in the industry due to its significant magnetostriction performance, magnetic anisotropy, high saturation magnetization and good chemical stability.
[0004] As is well known, epitaxial films have attracted much attention compared to polycrystalline films due to their unique epitaxial preferred orientation characteristics, and can achieve controllable modulation of various dimensions such as strain and size effects. High-quality CFO epitaxial films are an important foundation for the fabrication of high-performance, large-area multiferroic integrated semiconductor devices. Currently, pulsed laser deposition technology is mostly used to prepare CFO epitaxial films. Although this technology can directly generate high-quality CFO epitaxial films in situ, the substrate often requires a long preheating time (usually 3 to 5 hours), and the deposition size of the film is easily limited (typically 5×5 to 10×10 mm). In industrial applications, magnetron sputtering deposition is commonly used to prepare large-area epitaxial thin films. While this method offers a simple process and stable products, and compared to existing sol-gel techniques, it can deposit high-quality large-area thin film materials with preferred epitaxial orientation, magnetron sputtering requires a substrate preheating time similar to pulsed laser deposition. This undoubtedly complicates the industrial epitaxial thin film deposition process and prolongs the product preparation cycle. Furthermore, conventional magnetron sputtering equipment has limited heating temperatures (typically <600℃), while the crystallization temperature of CFO thin films needs to be above 700℃, necessitating subsequent annealing. Annealing is generally used in sol-gel methods for CFO thin film preparation, involving prolonged high-temperature heat treatment in a muffle furnace and air atmosphere. During high-temperature annealing, the film exhibits no preferred epitaxial orientation and instead displays a polycrystalline state. Additionally, high-temperature annealing in air atmosphere reduces oxygen vacancy defects and improves the overall performance of the film. However, conventional annealing processes require a long cycle (usually >6 hours), which wastes energy to some extent. Furthermore, the air flow inside the muffle furnace is poor, the oxygen content is limited, the degree of crystallization after annealing is not high, and some oxygen vacancies remain in the product, which inhibits the improvement of performance to some extent. Summary of the Invention
[0005] The present invention aims to provide a method for preparing cobalt ferrite epitaxial thin films using plasma field activation assistance, so as to solve the drawbacks of the prior art.
[0006] To achieve the above objectives, the present invention will adopt the following technical solution:
[0007] The method for preparing cobalt ferrite epitaxial thin films provided by the present invention comprises the following steps:
[0008] (1) Using cobalt ferrite ceramic as the deposition target and strontium titanate single crystal substrate as the deposition substrate, CFO precursor film was deposited at room temperature by magnetron sputtering technology;
[0009] (2) Place the CFO precursor membrane into a PECVD vacuum annealing furnace and evacuate it. Introduce an Ar atmosphere, turn on the high voltage power supply, and activate the plasma field.
[0010] (3) After the plasma field activation is completed, Ar atmosphere is kept flowing, and the heating power is turned on to perform vacuum annealing treatment;
[0011] (4) After the vacuum annealing treatment is completed, Ar atmosphere is closed, O2 atmosphere is connected, and annealing treatment under O2 atmosphere is continuously performed;
[0012] (5) After the annealing is completed, the product is taken out, and a CFO epitaxial film is obtained.
[0013] In the above method, the CFO epitaxial film prepared has a chemical composition of CoFe2O4.
[0014] In the preparation method of the CFO epitaxial film in step (1), the size of the CFO precursor film ranges from 5*5 mm to 50*50 mm.
[0015] In the preparation method of the CFO epitaxial film in step (2), the vacuum degree of the vacuum annealing furnace ranges from 20 Pa to 40 Pa.
[0016] In the preparation method of the CFO epitaxial film in step (2), the activation time using the plasma field ranges from 20 s to 120 s.
[0017] In the preparation method of the CFO epitaxial film in step (3), the annealing parameters of the vacuum annealing treatment are as follows: the annealing temperature ranges from 400 ℃ to 500 ℃, and the annealing time ranges from 30 min to 60 min.
[0018] In the preparation method of the CFO epitaxial film in step (4), the annealing parameters of the oxygen atmosphere annealing treatment are as follows: the annealing temperature ranges from 650 ℃ to 700 ℃, and the annealing time ranges from 30 min to 60 min.
[0019] Compared with the prior art, the present application has the following beneficial effects:
[0020] 1. The cobalt ferrite epitaxial film is prepared by using the plasma field activation assistance, which not only retains the advantages of high quality, large area, and product with epitaxial preferred orientation prepared by traditional magnetron sputtering technology, but also effectively avoids the disadvantages of complex film deposition process, long product preparation period, and polycrystalline product; and the plasma field activation assistance also plays the advantages of improving the deposition quality of the epitaxial film, has the characteristics of improving the surface activity of the film, shortening the preparation period, improving the crystallization degree of the film, and reducing the oxygen vacancy, and achieves the effect of further improving the film performance.
[0021] 2. As an effective epitaxial thin film preparation method, the preparation of CFO epitaxial thin film in the application utilizes plasma field activation assistance, overcomes the problem of limited thin film deposition size existing in the current pulse laser deposition technology, has the advantages of stable preparation of high-quality large-area epitaxial thin film; also overcomes the problems of complex process, long product preparation period and the like existing in the current magnetron sputtering technology, has the characteristics of simple process and rapid preparation; and also overcomes the problems of long period, low crystallization degree, residual oxygen vacancy and no epitaxial preferred orientation of the product in the thin film annealing by the current sol-gel method, and can rapidly prepare high-quality CFO epitaxial thin film.
[0022] 3. By adopting the method, the preparation period of CFO epitaxial thin film can be shortened to 1-2h, which is shortened by about 1-2h of product preparation period compared with the pulse laser deposition technology or the magnetron sputtering technology, and is shortened by about 5h of product preparation period compared with the sol-gel technology, greatly saving the production cost; and can effectively increase the thin film deposition size, improve the CFO thin film surface activity, improve the thin film crystallization degree, reduce the oxygen vacancy, and show epitaxial preferred orientation, achieving the effect of further improving the thin film performance.
[0023] In summary, the application overcomes the problems of long preparation period, size limitation, long annealing time, low crystallization degree, residual oxygen vacancy and the like existing in the current CFO epitaxial thin film preparation method, has the advantages of shortened preparation period and improved thin film surface activity, and the product has the advantages of large size, epitaxial preferred orientation, high crystallization degree and elimination of oxygen vacancy, and can further improve the performance of CFO epitaxial thin film. BRIEF DESCRIPTION OF DRAWINGS
[0024] Figure 1 It is a process flow chart of the application.
[0025] Figure 2 It is the X-ray diffraction phase analysis result of the CFO epitaxial thin film obtained in Examples 1-5 of the application.
[0026] Figure 3 It is the scanning electron microscope morphology diagram of the CFO epitaxial thin film obtained in Example 1 of the application.
[0027] Figure 4 It is the scanning electron microscope morphology diagram of the CFO epitaxial thin film obtained in Example 2 of the application.
[0028] Figure 5 It is the scanning electron microscope morphology diagram of the CFO epitaxial thin film obtained in Example 3 of the application.
[0029] Figure 6 It is the scanning electron microscope morphology diagram of the CFO epitaxial thin film obtained in Example 4 of the application.
[0030] Figure 7A scanning electron microscope morphology diagram of the CFO epitaxial thin film obtained in Embodiment 5 of the present application.
[0031] Figure 8 In-plane and out-of-plane M-H hysteresis loop diagrams of the CFO epitaxial thin film obtained in Embodiment 1 of the present application.
[0032] Figure 9 In-plane and out-of-plane M-H hysteresis loop diagrams of the CFO epitaxial thin film obtained in Embodiment 2 of the present application.
[0033] Figure 10 In-plane and out-of-plane M-H hysteresis loop diagrams of the CFO epitaxial thin film obtained in Embodiment 3 of the present application.
[0034] Figure 11 In-plane and out-of-plane M-H hysteresis loop diagrams of the CFO epitaxial thin film obtained in Embodiment 4 of the present application.
[0035] Figure 12 In-plane and out-of-plane M-H hysteresis loop diagrams of the CFO epitaxial thin film obtained in Embodiment 5 of the present application. DETAILED DESCRIPTION
[0036] For better understanding of the present application, the content of the present application is further illustrated in combination with the embodiments below, but the content of the present application is not limited to the embodiments below.
[0037] Embodiment 1:
[0038] (1) A CFO precursor film (size 5x5mm) is deposited on a strontium titanate single crystal substrate at room temperature by a magnetron sputtering technique with a cobalt ferrite ceramic as a deposition target;
[0039] (2) The CFO precursor film is placed in a PECVD vacuum annealing furnace and vacuumized (vacuum degree 20Pa), Ar atmosphere is introduced, a high-voltage power supply is turned on to excite a plasma field to activate (activation time 20s);
[0040] (3) After the plasma field activation is completed, Ar atmosphere is kept flowing and a heating power supply is turned on to perform vacuum annealing treatment (annealing parameters: annealing temperature 400℃, annealing time 30min);
[0041] (4) After the vacuum annealing treatment is completed, Ar atmosphere is closed and O2 atmosphere is connected to continue the annealing treatment under O2 atmosphere (annealing parameters: annealing temperature 650℃, annealing time 30min);
[0042] (5) After the annealing is completed, the product is taken out to obtain a CFO epitaxial thin film.
[0043] The phase structure, micro-morphology and in-plane and out-of-plane hysteresis loops are respectively as shown in Figure 2 , Figure 3 andFigure 8 As shown. According to Figure 2 , Figure 3 and Figure 8 As can be seen from the content, the CFO epitaxial film obtained in Example 1 has a single phase, no impurity phase, strong epitaxial preferred orientation, good crystallinity, no oxygen vacancy characteristics, and excellent ferromagnetic properties and significant anisotropy.
[0044] Example 2:
[0045] (1) Using cobalt ferrite ceramic as the deposition target and strontium titanate single crystal substrate as the deposition substrate, a CFO precursor film (size 10×10mm) was deposited at room temperature by magnetron sputtering.
[0046] (2) Place the CFO precursor membrane into a PECVD vacuum annealing furnace and evacuate it (vacuum degree 25 Pa). Introduce an Ar atmosphere, turn on the high voltage power supply, and activate the plasma field (activation time 40 s).
[0047] (3) After the plasma field activation is complete, keep the Ar atmosphere flowing and turn on the heating power supply to perform vacuum annealing (annealing parameters: annealing temperature 420℃, annealing time 40min).
[0048] (4) After vacuum annealing is completed, turn off the Ar atmosphere and introduce the O2 atmosphere to continue annealing under the O2 atmosphere (annealing parameters are: annealing temperature 670℃, annealing time 40min).
[0049] (5) After annealing, the product is removed to obtain CFO epitaxial film.
[0050] The phase structure, microstructure, and in-plane and out-of-plane hysteresis loops are respectively as follows: Figure 2 , Figure 4 and Figure 9 As shown. According to Figure 2 , Figure 4 and Figure 9 As can be seen from the content, the CFO epitaxial film obtained in Example 2 has a single phase, no impurity phase, strong epitaxial preferred orientation, good crystallinity, no oxygen vacancy characteristics, excellent ferromagnetic properties, and significant anisotropy.
[0051] Example 3:
[0052] (1) Using cobalt ferrite ceramic as the deposition target and strontium titanate single crystal substrate as the deposition substrate, a CFO precursor film (size 20×20mm) was deposited at room temperature by magnetron sputtering.
[0053] (2) Place the CFO precursor membrane into a PECVD vacuum annealing furnace and evacuate it (vacuum degree 30Pa). Introduce an Ar atmosphere, turn on the high voltage power supply, and activate the plasma field (activation time 60s).
[0054] (3) After the plasma field activation is complete, keep the Ar atmosphere flowing and turn on the heating power supply to perform vacuum annealing (annealing parameters: annealing temperature 450℃, annealing time 45min).
[0055] (4) After the vacuum annealing is completed, turn off the Ar atmosphere and introduce the O2 atmosphere to continue the annealing process under the O2 atmosphere (annealing parameters are: annealing temperature 680℃, annealing time 45min).
[0056] (5) After annealing, the product is removed to obtain CFO epitaxial film.
[0057] The phase structure, microstructure, and in-plane and out-of-plane hysteresis loops are respectively as follows: Figure 2 , Figure 5 and Figure 10 As shown. According to Figure 2 , Figure 5 and Figure 10 As can be seen from the content, the CFO epitaxial film obtained in Example 3 has a single phase, no impurity phase, strong epitaxial preferred orientation, good crystallinity, no oxygen vacancy characteristics, excellent ferromagnetic properties, and significant anisotropy.
[0058] Example 4:
[0059] (1) Using cobalt ferrite ceramic as the deposition target and strontium titanate single crystal substrate as the deposition substrate, a CFO precursor film (size 30×30mm) was deposited at room temperature by magnetron sputtering.
[0060] (2) Place the CFO precursor membrane into a PECVD vacuum annealing furnace and evacuate it (vacuum degree 35Pa). Introduce an Ar atmosphere, turn on the high voltage power supply, and activate the plasma field (activation time 90s).
[0061] (3) After the plasma field activation is complete, keep the Ar atmosphere flowing and turn on the heating power supply to perform vacuum annealing (annealing parameters: annealing temperature 480℃, annealing time 50min).
[0062] (4) After the vacuum annealing is completed, turn off the Ar atmosphere and introduce the O2 atmosphere to continue the annealing process under the O2 atmosphere (annealing parameters are: annealing temperature 690℃, annealing time 50min).
[0063] (5) After annealing, the product is removed to obtain CFO epitaxial film.
[0064] The phase structure, microstructure, and in-plane and out-of-plane hysteresis loops are respectively as follows: Figure 2 , Figure 6 and Figure 11 As shown. According to Figure 2 , Figure 6 and Figure 11As can be seen from the content, the CFO epitaxial film obtained in Example 4 has a single phase, no impurity phase, strong epitaxial preferred orientation, good crystallinity, no oxygen vacancy characteristics, excellent ferromagnetic properties, and significant anisotropy.
[0065] Example 5:
[0066] (1) Using cobalt ferrite ceramic as the deposition target and strontium titanate single crystal substrate as the deposition substrate, a CFO precursor film (size 50×50mm) was deposited at room temperature by magnetron sputtering.
[0067] (2) Place the CFO precursor membrane into a PECVD vacuum annealing furnace and evacuate it (vacuum degree 40Pa). Introduce an Ar atmosphere, turn on the high voltage power supply, and activate the plasma field (activation time 120s).
[0068] (3) After the plasma field activation is complete, keep the Ar atmosphere flowing and turn on the heating power supply to perform vacuum annealing (annealing parameters: annealing temperature 500℃, annealing time 60min).
[0069] (4) After vacuum annealing is completed, turn off the Ar atmosphere and introduce the O2 atmosphere to continue annealing under the O2 atmosphere (annealing parameters are: annealing temperature 700℃, annealing time 60min).
[0070] (5) After annealing, the product is removed to obtain CFO epitaxial film.
[0071] The phase structure, microstructure, and in-plane and out-of-plane hysteresis loops are respectively as follows: Figure 2 , Figure 7 and Figure 12 As shown. According to Figure 2 , Figure 7 and Figure 12 As can be seen from the content, the CFO epitaxial film obtained in Example 5 has a single phase, no impurity phase, strong epitaxial preferred orientation, good crystallinity, no oxygen vacancy characteristics, excellent ferromagnetic properties, and significant anisotropy.
[0072] The specific embodiments of the present invention have been described in detail above, but they are merely examples, and the present invention is not equivalent to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.
Claims
1. A method for preparing cobalt ferrite epitaxial thin films using plasma field activation-assisted preparation, characterized in that, Includes the following steps: (1) Using cobalt ferrite ceramic as the deposition target and strontium titanate single crystal substrate as the deposition substrate, CFO precursor film was deposited at room temperature by magnetron sputtering. (2) The CFO precursor film was placed in an Ar atmosphere and activated by plasma field treatment; (3) After the plasma field activation is completed, maintain the Ar atmosphere and perform vacuum annealing treatment at a temperature of 400-500℃. (4) After vacuum annealing, turn off the Ar atmosphere and perform annealing under O2 atmosphere; annealing temperature 650~700℃; (5) After annealing, the product is taken out to obtain CFO epitaxial film. The chemical composition of the prepared CFO epitaxial film is: CoFe2O4.
2. The method for preparing cobalt ferrite epitaxial thin films using plasma field activation-assisted preparation according to claim 1, characterized in that, The specific implementation steps of step (2) are as follows: place the CFO precursor membrane into a PECVD vacuum annealing furnace and evacuate it, introduce an Ar atmosphere, turn on the high voltage power supply, and activate the plasma field.
3. The method for preparing cobalt ferrite epitaxial thin films using plasma field activation-assisted preparation according to claim 1, characterized in that, The ion field activation time in step (2) is 20-120 s.
4. The method for preparing cobalt ferrite epitaxial thin films using plasma field activation-assisted preparation according to claim 1, characterized in that, The vacuum degree of vacuum annealing in step (3) is 20-40 Pa.
5. The method for preparing cobalt ferrite epitaxial thin films using plasma field activation-assisted preparation according to claim 1, characterized in that, The annealing time in step (3) is 10 to 60 minutes.
6. The method for preparing cobalt ferrite epitaxial thin films using plasma field activation-assisted preparation according to claim 1, characterized in that, The annealing time in step (4) is 10 to 60 minutes.