Method for regenerating single-crystal strontium titanate substrates

Abstract

The disclosure provides a method for regenerating a single-crystal strontium titanate substrate, comprising: depositing a strontium aluminate film on a single-crystal strontium titanate substrate, then epitaxially growing a perovskite film; dissolving the strontium aluminate film and transferring the perovskite film by placing the sample after epitaxial growth in water to obtain a strontium titanate substrate; after cleaning the strontium titanate substrate, etching the strontium titanate substrate with an ammonium fluoride-hydrofluoric acid buffer solution, and then annealing to regenerate the single-crystal strontium titanate substrate. The regeneration method provided by the disclosure can obtain a single-crystal strontium titanate substrate with a single titanium-oxygen termination surface, and can realize the reuse of the single-crystal strontium titanate substrate.

Description

Technical Field

[0001] This disclosure relates to the technical field of semiconductor materials, and more specifically, to a method for regenerating a single-crystal strontium titanate substrate. Background Technology

[0002] Single-crystal perovskite oxide (ABO3 type) thin films possess rich functionalities, such as ferroelectricity, ferromagnetism, and metal-insulator phase transition properties, making them suitable for advanced logic devices, high-speed non-volatile memories, and special sensors. Currently, their structure, properties, and control methods have been comprehensively studied. However, a key bottleneck limiting the practical application of single-crystal oxide thin films stems from the challenge of material integration: the incompatibility between oxide devices and complementary metal-oxide-semiconductor (CMOS) processes. These complex oxides typically require high temperatures to crystallize, usually above 600°C. If directly epitaxially grown on semiconductor wafers, they react with the semiconductor substrate, degrading the quality of both and their interface, thus affecting performance.

[0003] With the development of self-supporting oxide thin film technology, oxides can be directly transferred onto semiconductor substrates at room temperature, enabling the integration of high-quality heterogeneous materials. Self-supporting oxide thin films have already been applied to microelectronic devices such as ferroelectric tunnel junctions and transistors. However, the fabrication of self-supporting oxides requires the use of semiconductor substrates, resulting in a significant waste of semiconductor substrates. Summary of the Invention

[0004] In view of this, the present disclosure provides a method for regenerating single-crystal strontium titanate substrates to at least partially solve the above-mentioned technical problems.

[0005] To solve the above-mentioned technical problems, the technical solution provided in this disclosure is as follows:

[0006] According to embodiments of this disclosure, a method for regenerating a single-crystal strontium titanate substrate is provided, comprising:

[0007] First, a strontium aluminate thin film is deposited on a single-crystal strontium titanate substrate, and then the perovskite thin film is epitaxially grown.

[0008] The epitaxial sample was placed in water to dissolve the strontium aluminate film, and then the perovskite film was transferred to obtain a strontium titanate substrate.

[0009] After cleaning the strontium titanate substrate, it is etched with ammonium fluoride-hydrofluoric acid buffer solution and then annealed to regenerate the single-crystal strontium titanate substrate.

[0010] According to embodiments of this disclosure, when cleaning a strontium titanate substrate, it is cleaned sequentially with acetone solution, ethanol solution, and deionized water.

[0011] According to embodiments of this disclosure, the ammonium fluoride-hydrofluoric acid buffer solution is prepared by mixing ammonium fluoride and hydrofluoric acid.

[0012] According to embodiments of this disclosure, the molar ratio of ammonium fluoride to hydrofluoric acid in the ammonium fluoride-hydrofluoric acid buffer solution is 7:1.

[0013] According to embodiments of this disclosure, the etching process is performed at room temperature for 40 to 55 seconds.

[0014] According to embodiments of this disclosure, the above regeneration method further includes: cleaning the etched strontium titanate substrate with deionized water, drying it with nitrogen gas, and then annealing it.

[0015] According to embodiments of this disclosure, the annealing process is carried out in an oxygen environment at a temperature of 950–1100°C for a processing time of not less than 30 minutes to obtain a single-crystal strontium titanate substrate with an atomic-level step structure.

[0016] According to embodiments of this disclosure, pulsed laser deposition technology is used to deposit strontium aluminate thin films and perovskite-type thin films on a single-crystal strontium titanate substrate.

[0017] According to embodiments of this disclosure, the temperature for depositing strontium aluminate thin films is 700–750°C;

[0018] The temperature for epitaxial perovskite thin films is 600–1000℃.

[0019] According to embodiments of this disclosure, polydimethylsiloxane is used as a support layer to transfer perovskite-type thin films.

[0020] According to embodiments of this disclosure, the regeneration method for single-crystal strontium titanate substrates provided herein involves depositing water-soluble strontium aluminate as a sacrificial layer on the single-crystal strontium titanate substrate. The strontium aluminate film can be dissolved and removed with water, achieving the transfer of a perovskite-type film. The substrate is then cleaned to remove residual organic matter from its surface. Etching is performed using an ammonium fluoride-hydrofluoric acid buffer solution to directionally etch a titanium-oxygen termination surface with a stepped structure. Annealing is then performed to remove adsorbed water vapor and molecular impurities from the strontium titanate substrate surface. Under high-temperature conditions, the strontium oxygen on the surface is desorbed, and the remaining titanium-oxygen layer forms an orderly arrangement of steps at high temperature, regenerating a single-crystal strontium titanate substrate. This substrate is a single-crystal strontium titanate (001) substrate with a single titanium-oxygen termination surface and can be reused. This method is simple, effective, and cost-efficient. Attached Figure Description

[0021] Figure 1 This is an atomic force microscope image of the single-crystal strontium titanate substrate in Embodiment 1 of this disclosure;

[0022] Figure 2This is a high-energy electron diffraction pattern of the single-crystal strontium titanate substrate in Embodiment 1 of this disclosure;

[0023] Figure 3 The image shows the rocking curve of the barium hafnium titanate thin film prepared on the single-crystal strontium titanate substrate in Example 1 of this disclosure.

[0024] Figure 4 An atomic force microscope image of the regenerated single-crystal strontium titanate substrate in Embodiment 1 of this disclosure;

[0025] Figure 5 This is a high-energy electron diffraction pattern of the regenerated single-crystal strontium titanate substrate in Embodiment 1 of this disclosure;

[0026] Figure 6 A rocking curve diagram of a barium hafnium titanate thin film prepared from a regenerated single-crystal strontium titanate substrate in Example 1 of this disclosure;

[0027] Figure 7 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 1 of this disclosure;

[0028] Figure 8 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 2 of this disclosure;

[0029] Figure 9 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 3 of this disclosure;

[0030] Figure 10 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 4 of this disclosure;

[0031] Figure 11 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 5 of this disclosure;

[0032] Figure 12 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 6 of this disclosure;

[0033] Figure 13 An atomic force microscope image of the regenerated strontium titanate substrate in Comparative Example 7 of this disclosure. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0035] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0036] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0037] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0038] When using expressions such as "at least one of A, B, and C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, and C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). Similarly, when using expressions such as "at least one of A, B, or C," the expression should generally be interpreted in accordance with the meaning commonly understood by a person skilled in the art (e.g., "a system having at least one of A, B, or C" should include, but is not limited to, systems having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0039] In the process of developing this disclosure, it was discovered that the current method for preparing self-supporting oxide thin films mainly utilizes the strontium aluminate sacrificial layer etching method. The process involves epitaxially depositing a strontium aluminate sacrificial layer onto a single-crystal strontium titanate substrate, followed by the epitaxy of other perovskite thin films, and finally dissolving the strontium aluminate layer with water to obtain the self-supporting oxide thin film. Therefore, the preparation of self-supporting oxide thin films requires a large quantity of single-crystal strontium titanate substrates, which are expensive, costing approximately 600 yuan / cm², compared to about 1 yuan / cm² for single-crystal silicon. This results in significant substrate waste and high costs during the preparation of self-supporting oxide thin films.

[0040] In view of this, the present disclosure provides a method for regenerating a single-crystal strontium titanate substrate. Specifically, according to embodiments of the present disclosure, the regeneration method includes:

[0041] First, a strontium aluminate thin film is deposited on a single-crystal strontium titanate substrate, followed by epitaxy of a perovskite-type thin film. The epitaxial sample is placed in water to dissolve the strontium aluminate thin film, and the perovskite-type thin film is transferred to obtain a strontium titanate substrate. After cleaning the strontium titanate substrate, it is etched with ammonium fluoride-hydrofluoric acid buffer solution, and then annealed to regenerate the single-crystal strontium titanate substrate.

[0042] According to embodiments of this disclosure, firstly, the polished strontium titanate substrate is sequentially cleaned with acetone, alcohol, and deionized water, then treated with ammonium fluoride-hydrofluoric acid buffer solution. Following this, the strontium titanate substrate is subjected to high-temperature annealing in an oxygen environment to obtain a single-crystal strontium titanate substrate with atomically flat surface and stepped surfaces. After depositing the target thin film according to the above method, the strontium titanate substrate undergoes a regeneration process.

[0043] According to embodiments of this disclosure, in the use of a single-crystal strontium titanate substrate, a water-soluble strontium aluminate film is first deposited on the substrate, followed by an epitaxial perovskite film on the strontium aluminate film. Using the strontium aluminate film as a sacrificial layer, it can be dissolved and removed in water, separating the strontium titanate substrate from the perovskite film. Polydimethylsiloxane is used as a support layer to transfer the perovskite film to another substrate. The remaining strontium titanate substrate after the perovskite film transfer is cleaned, and then etched using an ammonium fluoride-hydrofluoric acid buffer solution. This etching process directionally etches a titanium-oxygen end face with a stepped structure, followed by appropriate annealing at high temperature to remove moisture. The remaining titanium-oxygen layer forms an orderly arrangement of steps at high temperature, resulting in a regenerated single-crystal strontium titanate substrate.

[0044] According to embodiments of this disclosure, etching and annealing with ammonium fluoride-hydrofluoric acid buffer solution enable the directional etching of a single-crystal strontium titanate substrate to create a stepped titanium oxide end face, resulting in a distinct stepped surface without any corrosion pits. Compared to single-crystal strontium titanate substrates treated by other methods, the substrate surface treated by this method exhibits better quality, with no pits at the center of the steps and lower surface roughness, which is beneficial for depositing the target thin film and enabling the stable growth of high-quality functional thin films.

[0045] According to embodiments of this disclosure, when cleaning a strontium titanate substrate, it is cleaned sequentially with acetone solution, ethanol solution, and deionized water.

[0046] According to embodiments of this disclosure, when regenerating single-crystal strontium titanate substrates, the untreated strontium titanate substrates after use are first cleaned. The cleaning process begins with acetone solution for approximately 10 minutes, followed by ethanol solution for 15 minutes, and then ultrasonic cleaning with deionized water for 10 minutes. This results in a cleaned strontium titanate substrate, removing impurities from the substrate surface to avoid affecting subsequent processing. Full ultrasonic cleaning can be selected based on actual conditions, and the temperature and time during the cleaning process can be adjusted.

[0047] According to embodiments of this disclosure, the ammonium fluoride-hydrofluoric acid buffer solution is prepared by mixing ammonium fluoride and hydrofluoric acid. The molar ratio of ammonium fluoride to hydrofluoric acid in the ammonium fluoride-hydrofluoric acid buffer solution is 7:1. Under this ratio, the pH value of the ammonium fluoride-hydrofluoric acid buffer solution is about 5, which is suitable for acidity and alkalinity. It can directionally etch strontium titanate substrates without causing corrosion pits.

[0048] According to embodiments of this disclosure, the etching process is performed at room temperature for a time of 40–55 seconds, such as 40 seconds, 48 ​​seconds, 50 seconds, 52 seconds, etc., but not limited to the listed values; other unlisted values ​​within this range are also applicable. If the etching time is too short, steps will not form on the surface of the strontium titanate substrate; if the etching time is too long, the surface of the strontium titanate substrate may be corroded with holes, affecting material properties and failing to effectively guarantee the regeneration of the single-crystal strontium titanate substrate.

[0049] According to embodiments of this disclosure, the above regeneration method further includes: cleaning the etched strontium titanate substrate with deionized water, drying it with nitrogen gas, and then annealing it.

[0050] According to the embodiments of this disclosure, after etching with ammonium fluoride-hydrofluoric acid buffer, free particles in the buffer will remain on the surface of the strontium titanate substrate. After etching, washing with deionized water for 1 to 5 minutes can effectively remove the impurities remaining on the surface. After washing, blowing with nitrogen gas can prevent the ions remaining during the annealing process from reacting with the strontium titanate substrate and affecting the flatness of the steps on the surface of the single crystal strontium titanate substrate.

[0051] According to embodiments of this disclosure, the annealing treatment is carried out in an oxygen environment at a temperature of 950–1100°C, such as 950°C, 1000°C, 1050°C, 1100°C, etc., but not limited to the listed values; other unlisted values ​​within this range are also applicable. Further, the oxygen environment for the annealing treatment is a low-oxygen-pressure condition, with an oxygen pressure of 10... -5 Around Torr. Under low oxygen pressure conditions and within this temperature range, the step width formed on the surface of the strontium titanate substrate can be made more uniform and neat.

[0052] According to embodiments of this disclosure, the annealing process takes no less than 30 minutes to obtain a single-crystal strontium titanate substrate with an atomically stepped structure. The processing time can be, for example, 30 minutes, 50 minutes, 80 minutes, 100 minutes, 150 minutes, etc. If the annealing time is too short, the steps formed on the surface of the strontium titanate substrate will be uneven, affecting its flatness. The annealing time should be adjusted according to the actual situation, but excessive processing time should also be avoided. If the annealing time is too long, the surface of the single-crystal strontium titanate substrate will be over-reconstructed, potentially forming other structural surface shapes, affecting the formation of atomically stepped structures on the surface of the single-crystal strontium titanate.

[0053] According to embodiments of this disclosure, pulsed laser deposition technology is used to deposit strontium aluminate thin films and perovskite thin films epitaxially on a single-crystal strontium titanate substrate. The temperature for depositing the strontium aluminate thin film is 700–750°C, for example, 700°C, 710°C, 720°C, 730°C, 740°C, etc.; the temperature for epitaxially depositing the perovskite thin film is 600–1000°C, for example, 600°C, 720°C, 850°C, 960°C, 1000°C, etc. However, the methods are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0054] According to embodiments of this disclosure, a strontium titanate substrate etched with ammonium fluoride-hydrofluoric acid buffer is placed in a pulsed laser deposition (PLD) apparatus, and approximately 10 μL of ion exchange rate is introduced into the apparatus. -5 Oxygen at Torr pressure was annealed at 950°C to obtain a strontium titanate substrate with a stepped titanium-oxygen termination surface exhibiting atomically smoothness. Subsequently, the equipment temperature was adjusted, and a strontium aluminate film was deposited on the strontium titanate substrate at 700°C. Then, the temperature was adjusted to 750°C to epitaxially grow a target perovskite-type film on the surface with deposited strontium aluminate.

[0055] To make the objectives, technical solutions, and advantages of this disclosure clearer, the technical solutions and principles of this disclosure are further illustrated below with reference to specific embodiments and accompanying drawings. It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this disclosure is not limited thereto.

[0056] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available. Methods not specifically described in the examples are conventional and can be performed according to the techniques or conditions described in the literature or the product instructions.

[0057] Example 1

[0058] Simulation of the preparation of strontium titanate substrates to be regenerated:

[0059] First, clean the brand-new, polished strontium titanate substrate by rinsing it with acetone solution for 10 minutes, then with ethanol solution for 10 minutes, and finally with deionized water by ultrasonic cleaning for 10 minutes. Prepare an ammonium fluoride-hydrofluoric acid buffer solution with a molar ratio of ammonium fluoride and hydrofluoric acid of 7:1. Immerse the cleaned strontium titanate substrate in the ammonium fluoride-hydrofluoric acid buffer solution at room temperature for 45 seconds for etching. After etching, remove the substrate, rinse it with deionized water for 1 minute, and then dry it with nitrogen gas.

[0060] Then, the etched strontium titanate substrate is placed in the vacuum chamber of a pulsed laser deposition (PLD) device, and 10 μL of gas is introduced. -5 Oxygen at Torr pressure was subjected to high-temperature annealing at 950℃ for 30 min to obtain a single-crystal strontium titanate substrate with a stepped titanium-oxygen termination surface exhibiting atomically smoothness. The resulting surface is as follows... Figure 1 As shown, the high-energy electron diffraction pattern is as follows: Figure 2 As shown, Figure 1 This is an atomic force microscope image of the single-crystal strontium titanate substrate in Embodiment 1 of this disclosure. Figure 2 This is a high-energy electron diffraction pattern of the single-crystal strontium titanate substrate in Embodiment 1 of this disclosure.

[0061] Subsequently, the temperature of the pulsed laser deposition (PLD) equipment was adjusted to 700°C and the oxygen pressure to 10. -5 Under Torr conditions, an 8 nm strontium aluminate film was deposited and grown as a sacrificial layer on a single-crystal strontium titanate substrate. The temperature was then increased to 750 °C, and the oxygen pressure was adjusted to 10. -4 Torr, under these conditions, epitaxially grows a 20 nm barium titanate film on a strontium aluminate film.

[0062] Finally, after covering the surface of the barium hafnium titanate film on the above substrate with polydimethylsiloxane (PDMS) as a support layer, the film was immersed in deionized water for 12 hours to fully dissolve and remove the strontium aluminate film. The barium hafnium titanate film was then transferred to other substrates using PDMS. Figure 3 This is a rocking curve diagram of the barium hafnium titanate thin film prepared on a single-crystal strontium titanate substrate in Example 1 of this disclosure. The strontium titanate substrate to be processed is obtained after transfer.

[0063] The strontium titanate substrate obtained above is then subjected to a regeneration process:

[0064] First, the strontium titanate substrate was cleaned with acetone solution for 10 min, then with ethanol solution for 10 min, followed by ultrasonic cleaning with deionized water for 10 min. An ammonium fluoride-hydrofluoric acid buffer solution with a molar ratio of ammonium fluoride to hydrofluoric acid of 7:1 was prepared. The cleaned strontium titanate substrate was immersed in the ammonium fluoride-hydrofluoric acid buffer solution at room temperature for 45 seconds for etching. After etching, it was removed, rinsed with deionized water for 1 minute, and then dried with nitrogen gas. The etched strontium titanate substrate was then placed in the vacuum chamber of a pulsed laser deposition (PLD) device, and 10 μL of nitrogen gas was introduced. -5 Oxygen at Torr pressure is subjected to high-temperature annealing at 950℃ for 30 min to obtain a regenerated single-crystal strontium titanate substrate with an atomically flat stepped titanium-oxygen termination surface, which can be reused for the preparation of self-supporting oxide thin films.

[0065] The surface of the regenerated single-crystal strontium titanate substrate is as follows: Figure 4 As shown, the high-energy electron diffraction pattern is as follows: Figure 5 As shown, Figure 4 This is an atomic force microscope image of the regenerated single-crystal strontium titanate substrate in Embodiment 1 of this disclosure. Figure 5 This is a high-energy electron diffraction pattern of the regenerated single-crystal strontium titanate substrate in Embodiment 1 of this disclosure.

[0066] Depend on Figure 1 and Figure 3 A comparison shows that the method for regenerating single-crystal strontium titanate substrates provided in this disclosure can achieve the same surface quality as new single-crystal strontium titanate substrates through simple wet processing, exhibiting atomic-level flatness, relatively neat steps, and uniform width. Figure 2 and Figure 4 The dot-like diffraction spots also indicate that both the new and regenerated single-crystal strontium titanate substrates have atomically flat two-dimensional surfaces, and the regenerated single-crystal strontium titanate substrates can be reused.

[0067] A self-supporting barium titanate film is prepared by depositing strontium aluminate and barium hafnium titanate films on a regenerated single-crystal strontium titanate substrate. Figure 6 This is a rocking curve diagram of the barium hafnium titanate thin film prepared from the regenerated single-crystal strontium titanate substrate in Example 1 of this disclosure. Figure 3 and Figure 6 It can be seen that the rocking curves of barium hafnium titanate films prepared from single-crystal strontium titanate substrates before and after regeneration are similar in full width at half maximum (FWHM), indicating that the quality of barium hafnium titanate films prepared from regenerated single-crystal strontium titanate substrates is similar to that of barium hafnium titanate films prepared from new single-crystal strontium titanate substrates. The regenerated single-crystal strontium titanate substrates can be reused, and the high quality of single-crystal strontium titanate substrates can also grow high-quality perovskite oxide films.

[0068] Comparative Example 1

[0069] The same processing method as in Example 1 was used, except that the regeneration process was changed to: no treatment was performed on the strontium titanate substrate to be treated.

[0070] Figure 7 An atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 1 of this disclosure, as shown. Figure 7 As shown, the surface of the strontium titanate substrate does not have atomic-level steps, and the surface contains products from the dissolution of strontium aluminate.

[0071] Comparative Example 2

[0072] The same processing method as in Example 1 was used, except that the regeneration process was changed to: immersing the strontium titanate substrate to be treated in hot water at 90°C for 30 minutes.

[0073] Figure 8 Here is an atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 2 of this disclosure, as shown. Figure 8 As shown, the surface of the strontium titanate substrate does not have atomic-level steps, and the products of strontium aluminate dissolution still exist on the surface.

[0074] Comparative Example 3

[0075] The same processing method as in Example 1 was used, except that the regeneration process was changed to: the strontium titanate substrate to be treated was immersed in concentrated hydrochloric acid solution for 10 minutes.

[0076] Figure 9 An atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 3 of this disclosure, as shown. Figure 9 As shown, the strontium titanate substrate has no atomic-level steps, has a high surface roughness, and contains many impurities.

[0077] Comparative Example 4

[0078] The same processing method as in Example 1 was used, except that the regeneration process was changed to: the strontium titanate substrate to be treated was immersed in concentrated hydrochloric acid solution for 10 minutes, and then immersed in ammonium fluoride-hydrofluoric acid buffer solution for 55 seconds.

[0079] Figure 10 Here is an atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 4 of this disclosure, as shown. Figure 10 As shown, the surface of the strontium titanate substrate has atomic-level steps, but etch pits appear on the surface.

[0080] Comparative Example 5

[0081] The same processing method as in Example 1 was used, except that the regeneration process was changed to: the strontium titanate substrate to be treated was immersed in concentrated hydrochloric acid solution for 10 minutes, then immersed in ammonium fluoride-hydrofluoric acid buffer solution for 55 seconds, and then subjected to the same high-temperature annealing process as in Example 1.

[0082] Figure 11 An atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 5 of this disclosure, as shown. Figure 11 As shown, no atomic-level steps appeared on the surface of the strontium titanate substrate after high-temperature annealing, and etching pits still existed on its surface.

[0083] Comparative Example 6

[0084] The same processing method as in Example 1 was used, except that the regeneration process was changed to: the strontium titanate substrate to be treated was immersed in a dilute hydrochloric acid solution for 1 hour.

[0085] Figure 12 An atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 6 of this disclosure, as shown. Figure 12 As shown, the surface of the strontium titanate substrate exhibits blurred step boundaries and contains a small amount of impurities.

[0086] Comparative Example 7

[0087] The same processing method as in Example 1 was used, except that the regeneration process was changed to: the strontium titanate substrate to be treated was immersed in a dilute hydrochloric acid solution for 20 hours.

[0088] Figure 13 An atomic force microscopy image of the regenerated strontium titanate substrate in Comparative Example 7 of this disclosure, as shown. Figure 13 As shown, the surface of the strontium titanate substrate is etched with holes and is rough.

[0089] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of this disclosure. It should be understood that the above are only specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for regenerating a single-crystal strontium titanate substrate, comprising: First, a strontium aluminate thin film is deposited on a single-crystal strontium titanate substrate, and then the perovskite thin film is epitaxially grown. The epitaxial sample was placed in water to dissolve the strontium aluminate film, and the perovskite film was transferred to obtain a strontium titanate substrate. After cleaning the strontium titanate substrate, it is etched with ammonium fluoride-hydrofluoric acid buffer for 48-55 seconds. The etched strontium titanate substrate is then cleaned with deionized water, dried with nitrogen, and then annealed to regenerate the single crystal strontium titanate. The ammonium fluoride-hydrofluoric acid buffer solution is prepared by mixing ammonium fluoride and hydrofluoric acid in a molar ratio of 7:1; the annealing treatment is carried out at an oxygen pressure of 10. -5 The process is carried out under Torr conditions at a temperature of 950-1100℃ for a processing time of not less than 30 minutes to obtain a single-crystal strontium titanate substrate with an atomic-level stepped structure.

2. The regeneration method according to claim 1, wherein, The strontium titanate substrate was cleaned sequentially with acetone solution, ethanol solution, and deionized water.

3. The regeneration method according to claim 1, wherein, Epitaxial growth of strontium aluminate thin films and perovskite thin films was deposited on the single-crystal strontium titanate substrate using pulsed laser deposition technology.

4. The regeneration method according to claim 3, wherein, The temperature for depositing the strontium aluminate thin film is 700~750℃; The temperature for epitaxial growth of the perovskite thin film is 600~1000℃.

5. The regeneration method according to claim 1, wherein, The perovskite-type thin film was transferred using polydimethylsiloxane as a support layer.

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