Preparation method and application of LaNiO3 film based on monoethanolamine regulation and control

Abstract

The invention relates to the technical field of functional oxide thin film materials, in particular to a preparation method and application of a LaNiO3 thin film based on monoethanolamine regulation and control, and the preparation method comprises the following steps: S1, dissolving a lanthanum source and a nickel source in an organic solvent to prepare a LaNiO3 precursor solution; and S2, adding monoethanolamine into the precursor solution to serve as a stabilizer, wherein the molar ratio of the monoethanolamine to the LaNiO3 is 0.50-1.50. According to the preparation method, the monoethanolamine modified precursor is added in the chemical solution deposition process, and the temperature and time of the rapid thermal annealing process are controlled, so that collaborative optimization of film orientation, thickness and conductivity is realized, and the LaNiO3 film with high c-axis orientation, large thickness and low resistivity can be prepared on the silicon substrate; the produced film can be used as a bottom electrode to induce preferred orientation growth of functional layers such as BiFeO3 and the like, shows strong ferroelectric performance, is suitable for silicon-based integrated devices, and has the characteristics of low cost, simple process and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of functional oxide thin film materials technology, specifically to a method for preparing LaNiO3 thin films based on monoethanolamine and its application. Background Technology

[0002] LaNiO3, a conductive oxide with a pseudo-cubic perovskite structure, is widely considered an ideal electrode material for functional devices due to its excellent crystallinity compatibility, high-temperature chemical stability, and strong adhesion to silicon substrates. Two common methods are used to prepare LaNiO3 thin films: high-temperature solid-state reaction and chemical solution deposition.

[0003] In chemical solution deposition technology, in order to prevent La³ + and Ni³ + Hydrolysis occurs in water or alcohol to form hydroxide precipitates, which must be stabilized by adding complexing agents. Commonly available stabilizers include monoethanolamine, acetylacetone, and acetic acid.

[0004] However, when using chemical solution deposition technology to prepare LaNiO3 films, the preferred orientation of (00l) depends on the rapid thermal annealing process. After the addition of stabilizers, the orientation, the thickness of the film after a single coating, and the room temperature resistivity of the LaNiO3 film will have a synergistic effect. In particular, the metering of stabilizers and the temperature and time control of the rapid thermal annealing process will jointly affect the LaNiO3 film.

[0005] Therefore, developing a method to synergistically optimize the orientation, thickness, and conductivity of LaNiO3 thin films by controlling the composition of precursors is of great significance for promoting the integration of silicon-based functional devices. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing LaNiO3 thin films based on monoethanolamine and its application, which solves the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing LaNiO3 thin films based on monoethanolamine regulation includes the following steps: S1. Dissolve lanthanum source and nickel source in an organic solvent to prepare LaNiO3 precursor solution; S2. Add monoethanolamine as a stabilizer to the precursor solution, wherein the molar ratio of monoethanolamine to LaNiO3 is 0.50-1.50; S3. Spin-coat the precursor solution onto a silicon substrate to prepare a LaNiO3 wet film; S4. The LaNiO3 wet film is baked, pyrolyzed and annealed to form a crystallized LaNiO3 thin film; S5. Repeat S3-S4 several times until the film thickness is ≥300nm; Wherein, the baking temperature in S4 is 145-160℃, the pyrolysis temperature is 390-420℃, the annealing temperature is 700-720℃, and the baking, pyrolysis and annealing times are all 10-12 minutes.

[0008] Preferably, the molar ratio of monoethanolamine to LaNiO3 in S2 is 1.00.

[0009] Preferably, the lanthanum source in S1 is lanthanum nitrate, the nickel source is nickel acetate, and the organic solvent is 2-methoxyethanol.

[0010] Preferably, the concentration of the LaNiO3 precursor solution in S1 is 0.3 mol / L.

[0011] Preferably, in step S2, after mixing monoethanolamine with the LaNiO3 precursor solution, the mixture is further stirred for 5-6 hours and then allowed to stand for 8-14 hours.

[0012] Preferably, before spin coating in step S3, the silicon substrate is ultrasonically cleaned with acetone, ethanol and deionized water. The spin coating speed in step S3 is 4800-5200 rpm and the spin coating time is 13-18 s.

[0013] Preferably, in step S5, the silicon substrate is repeatedly spin-coated, baked, pyrolyzed, and annealed six times, and then annealed at 700-720°C for 30-35 minutes.

[0014] Preferably, a method for preparing a LaNiO3 thin film based on monoethanolamine regulation, wherein the LaNiO3 thin film prepared by the method has an (00l) orientation degree ≥98%, a thickness ≥340nm, and a room temperature resistivity ≤0.7mΩ·cm.

[0015] This invention also provides an application of LaNiO3 thin films prepared by a method based on monoethanolamine regulation in silicon-based compatible functional devices. By employing the above technical solution, the method for preparing LaNiO3 thin films based on monoethanolamine regulation provided by the present invention has at least the following beneficial effects: This invention achieves synergistic optimization of film orientation, thickness, and conductivity by controlling the addition of monoethanolamine to modify the precursor during chemical solution deposition and by controlling the temperature and time of rapid thermal annealing. It can prepare LaNiO3 films with high c-axis orientation, large thickness, and low resistivity on silicon substrates. The produced films can be used as bottom electrodes to induce the preferential orientation growth of functional layers such as BiFeO3 and exhibit strong ferroelectric properties. They are suitable for silicon-based integrated devices and have the characteristics of low cost, simple process, and excellent performance. Attached Figure Description

[0016] The accompanying drawings, which are provided to further illustrate the invention, constitute a part of this application: Figure 1 Photographs of the precursor pH and solutions with different amounts of monoethanolamine used in this invention; Figure 2 The XRD pattern of the LaNiO3 thin film of the present invention and the changes in (00l) orientation degree and grain size with the amount of monoethanolamine; Figure 3 Here is a typical SEM image of the surface of a LaNiO3 thin film of the present invention; Figure 4 Here is a cross-sectional SEM image of a typical LaNiO3 thin film of the present invention; Figure 5 The resistivity-temperature curve of the LaNiO3 thin film of the present invention and the change of room temperature resistivity with the amount of monoethanolamine are shown. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1 This invention provides a method for preparing LaNiO3 thin films based on monoethanolamine regulation, comprising the following steps: S1. Precursor preparation: Lanthanum nitrate and nickel acetate were used as raw materials, dissolved in 2-methoxyethanol solvent to prepare a 0.3 mol / L LaNiO3 precursor solution. The specific operation is as follows: 1.1 Weighing: Weigh 1.291g of lanthanum nitrate hexahydrate using an analytical balance; weigh 0.742g of nickel acetate tetrahydrate using an analytical balance, and record the actual weighing values, accurate to 0.0001g. 1.2 Dissolving and preparing: Transfer the weighed medicine to a 50mL beaker, add 8mL of 2-methoxyethanol, place the beaker on a magnetic stirrer, and stir magnetically until completely dissolved at a speed of 300rpm. Transfer the solution to a 25 mL volumetric flask. Rinse the beaker three times with a small amount of 2-methoxyethanol and add the washings to the volumetric flask. Dilute to the 10 mL mark with 2-methoxyethanol. Shake well and pour back into the original beaker.

[0019] S2. Add 180 μL of monoethanolamine to the precursor solution. The molar ratio of monoethanolamine to LaNiO3 is 1.00. Stir the mixture for 5 hours and then let it stand for at least 8 hours. The specific operation is as follows: 2.1 Place the precursor solution prepared in S1 on a magnetic stirrer and stir at a speed of 100 rpm; 2.2. Accurately pipette 180 μL of monoethanolamine and slowly add it dropwise to the precursor solution while stirring; 2.3 After adding the ingredients, gradually increase the stirring speed of the magnetic stirrer to 400 rpm and stir continuously at room temperature for 5 hours. 2.4 After stirring, transfer the precursor solution in the beaker to a 15mL sealed glass bottle and let it stand at room temperature in the dark for 8-14 hours to complete the aging process. The precursor solution should eventually be transparent, homogeneous, and free of precipitate.

[0020] S3. Thin film deposition: After ultrasonically cleaning the silicon substrate with acetone, ethanol, and deionized water, the precursor is coated onto the substrate surface using spin coating. The spin coating speed is 5000 rpm, and the spin coating time is 15 seconds. The specific operation is as follows: 3.1. A p-type monocrystalline silicon substrate with dimensions of 10mm×10mm×0.5mm was selected. 3.2 Cleaning 3.2.1 Place the silicon substrate in a small beaker containing 20 mL of acetone, ensuring the silicon substrate is completely submerged in the acetone. Place the beaker in an ultrasonic cleaner and clean it at an ultrasonic frequency of 40 kHz for ten minutes. After cleaning, remove the silicon substrate with tweezers and dry it with nitrogen gas. 3.2.2 Place the silicon substrate, which has been cleaned and dried with acetone, into a small beaker containing 20 mL of anhydrous ethanol. The silicon substrate is completely immersed in the anhydrous ethanol. Place the beaker in an ultrasonic cleaner and clean it at an ultrasonic frequency of 40 kHz for ten minutes. After cleaning, remove the silicon substrate with tweezers and dry it with nitrogen gas. 3.2.3 Place the silicon substrate, which has been cleaned and dried with acetone and anhydrous ethanol, into a small beaker containing 20 mL of deionized water. The silicon substrate is completely immersed in the deionized water. Place the beaker in an ultrasonic cleaner and clean it at an ultrasonic frequency of 40 kHz for ten minutes. After cleaning, use tweezers to remove the silicon substrate and dry it with nitrogen gas to complete the cleaning of the silicon substrate. 3.3 Spin coating 3.3.1 Add the precursor solution. Mount the silicon substrate on the hollow adsorption seat of the spin coater, use a pipette to draw 100 μL of the precursor solution, and drop it onto the center of the silicon wafer. Let it stand for 15 seconds. 3.3.2 Start the spin coater. The spin coating program is divided into two stages. The first stage has a rotation speed of 500 rpm, a spin coating time of 5 s, and an acceleration time of 3 s. The second stage has a rotation speed of 5000 rpm, a spin coating time of 15 s, and an acceleration time of 2 s. The thin film on the surface of the spin-coated silicon substrate should be uniform, free of color spots, and without edge shrinkage; S4. The coated silicon substrate is sequentially baked at 150℃, pyrolyzed at 400℃, and annealed at 700℃. Each baking, pyrolysis, and annealing session lasts 10 minutes. The specific operation is as follows: 4.1 After removing the spin-coated silicon substrate from the spin coater, use tweezers to place it into the heat treatment furnace with the film side facing up; 4.1.1 Baking: Heat the precursor solution to 150℃ for 10 minutes at a rate of 5-8℃ / min, allowing for natural air convection. This process gently and uniformly removes most of the solvent, forming a uniform gel film and preventing the "coffee ring" effect or cracking. A heating rate of 5-8℃ / min avoids rapid solvent evaporation, which can lead to premature hardening of the film surface and subsequent bubble or pinhole formation due to internal solvent vaporization. This method also ensures production efficiency and film quality. 4.1.2 Pyrolysis: After baking, the heat treatment furnace is heated at a rate of 1-2℃ / min to 400℃ and held for 10min. Clean air is actively introduced for convection at a flow rate of 0.5-1L / min to fully decompose, oxidize and discharge organic substances such as nitrates, acetates and monoethanolamine, forming a pure inorganic amorphous framework. At the same time, it prevents the film from pulverizing or peeling off due to violent gas generation.

[0021] The low heating rate of 1-2℃ / min is used because the pyrolysis stage involves a violent chemical reaction that releases a large amount of gas, such as NO2, CO2, and H2O. The heating rate must be slow enough to allow sufficient time for the gas to escape gradually, rather than a sudden burst that could damage the film structure. A low heating rate is the most critical step in preventing film cracking and improving density during the pyrolysis stage.

[0022] 4.1.3 Annealing: After pyrolysis, the heat treatment furnace is heated at a rate of 10℃ / min to 700℃ and then held for 10 minutes. Oxygen is continuously and stably introduced for convection at a flow rate of 0.1-0.3 L / min. The oxygen atmosphere helps ensure sufficient oxygen in the crystal lattice and repairs oxygen vacancies, which is crucial for obtaining high conductivity. The oxygen atmosphere can also remove possible trace impurity gases, such as water vapor, from the furnace tube, which is beneficial for forming the correct perovskite crystal structure.

[0023] 4.1.4 Cooling: After annealing, allow the temperature inside the heat treatment furnace to cool naturally to 300°C, then remove the silicon substrate and allow it to cool naturally to room temperature.

[0024] S5. Repeat S3 and S4 a total of 6 times. After 6 times, anneal at 700℃ for an additional 30 minutes. The specific operation is as follows: 5.1 After the silicon substrate cooled to room temperature, the surface of the LaNiO3 film on the silicon substrate was inspected using a microscope. The surface was uniform with no obvious defects and no shrinkage at the edges. 5.2 Observe after spin coating, baking, pyrolysis and annealing. The temperature and time of each spin coating, baking, pyrolysis and annealing operation should be consistent with S3 and S4. 5.3 Final Annealing: During the final annealing, the temperature is raised to 700℃ and held for 40 minutes, followed by an additional 30 minutes of annealing. This provides sufficient reaction time for grains to migrate across grain boundaries and for small grains to be absorbed by larger grains. This can significantly increase the average grain size, reduce the number of grain boundaries, and thus lower the room temperature resistivity. It can also eliminate the stress between layers during the six repeated thin film deposition processes, which is beneficial to improving the mechanical stability and adhesion of the thin film.

[0025] 5.4 Cooling: After annealing, allow the temperature inside the heat treatment furnace to cool naturally to 300°C, then remove the silicon substrate and allow it to cool naturally to room temperature.

[0026] Example 2 The difference between this embodiment and Embodiment 1 is that the amount of monoethanolamine added is modified to 90 μL, and the molar ratio of monoethanolamine to LaNiO3 is 0.50.

[0027] Example 3 The difference between this embodiment and Embodiment 1 is that the amount of monoethanolamine added is modified to 270 μL, and the molar ratio of monoethanolamine to LaNiO3 is 1.50. Comparative Example 1 The difference between this comparative example and Example 1 is that monoethanolamine is not added to the precursor solution.

[0028] Comparative Example 2 The difference between this comparative example and Comparative Example 1 is that 30 μL of monoethanolamine was added to the precursor solution, and the molar ratio of monoethanolamine to LaNiO3 was 0.17.

[0029] Comparative Example 3 The difference between this comparative example and Comparative Example 1 is that 45 μL of monoethanolamine was added to the precursor solution, and the molar ratio of monoethanolamine to LaNiO3 was 0.25.

[0030] Comparative Example 3 The difference between this comparative example and Comparative Example 1 is that 60 μL of monoethanolamine was added to the precursor solution, and the molar ratio of monoethanolamine to LaNiO3 was 0.33.

[0031] Table 1 according to Figure 1 and Figure 3 The pH value of the precursor of LaNiO3 film increases with the increase of monoethanolamine addition, and the relationship between the two is approximately positive. Too low pH value will lead to insufficient metal ion complexation in the precursor solution, resulting in unstable solution and poor crystallinity. Too high pH value will lead to premature precipitation of metal hydroxide, destroying solution homogeneity, affecting normal grain growth, resulting in decreased crystallinity or the appearance of impurities and increased surface roughness.

[0032] Refer to Table 1 and Figure 2 According to XRD results, when the molar ratio of monoethanolamine to LaNiO3 is 1, the orientation degree of (00l) reaches 98%; when the molar ratio is 0.17-0.33, the film exhibits random orientation.

[0033] Refer to Table 1 and Figure 3 The surface roughness of the LaNiO3 film showed a trend of first improving and then deteriorating with the increase of monoethanolamine dosage. In the range of monoethanolamine dosage from 0 to 60 μL, the surface roughness of the LaNiO3 film gradually became denser and smoother with the increase of monoethanolamine dosage. In the range of monoethanolamine dosage from 0 to 270 μL, the surface roughness of the LaNiO3 film gradually became rougher and the porosity increased with the increase of monoethanolamine dosage.

[0034] The surface roughness of LaNiO3 films affects their electrical properties, mechanical adhesion, and interfacial characteristics. The lower the surface roughness, the better the electrical properties, mechanical adhesion, and interfacial characteristics of the film.

[0035] Refer to Table 1 and Figure 4The thickness of the LaNiO3 film monotonically increases with increasing monoethanolamine dosage, reaching 343 nm with 180 μL of monoethanolamine and 275 nm without it. According to... Figure 4 When the amount of monoethanolamine added is less than 60 μL, the film cross-section exhibits a porous, loose sponge-like or columnar structure with extremely high porosity and weak interlayer bonding, resulting in high room temperature resistivity, poor mechanical strength, and easy peeling. When the amount of monoethanolamine added is greater than 60 μL, the film cross-section becomes extremely dense and uniform, the porosity is significantly reduced or even disappears, and it exhibits the characteristics of a flat and continuous bulk material. Moreover, when the amount of monoethanolamine added is 180 μL, there are no obvious pores in the cross-section, and the cross-section is flat and continuous as a whole.

[0036] Summary Table 1 Figure 3 and Figure 4 When the amount of monoethanolamine added is 180 μL and the molar ratio of monoethanolamine to LaNiO3 is 1.00, the overall morphology of LaNiO3 is the best. It is neither too rough on the surface to affect the adhesion during subsequent deposition, nor too loose inside to cause excessive resistivity and easy detachment.

[0037] Refer to Table 1 and Figure 5 All films exhibited metallic conductivity, with room temperature resistivity initially decreasing and then increasing with the amount of monoethanolamine added. The lowest resistivity, approximately 0.7 mΩ·cm, was observed when the volume of monoethanolamine was 30-60 μL; the resistivity was 1.41 mΩ·cm without the addition of monoethanolamine.

[0038] In summary, by adding monoethanolamine to the precursor during chemical solution deposition, synergistic optimization of film orientation, thickness, and conductivity was achieved, enabling precise control of the preferred orientation of LaNiO3 films (00l), with an orientation degree exceeding 98%. Furthermore, the addition of monoethanolamine increased the thickness of a single coating pass, reducing the number of coating passes and lowering preparation costs. Simultaneously, the resistivity of the monoethanolamine-modified film was reduced by approximately 50% compared to the unmodified sample, meeting the conductivity requirements of the electrode material.

[0039] Example 4 This invention also provides an application of LaNiO3 thin films prepared by a method based on monoethanolamine regulation in silicon-based compatible functional devices: The LaNiO3 film prepared in Example 1 was used as the bottom electrode to induce the (00l) orientation growth of functional layers such as BiFeO3. The BiFeO3 film was deposited by chemical solution deposition. XRD showed that BiFeO3 inherited the (00l) orientation of LaNiO3. Ferroelectric testing showed that it has strong ferroelectric properties, with a remanent polarization (2Pr) of 30 μC / cm².

[0040] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing LaNiO3 thin films based on monoethanolamine regulation, characterized in that, Includes the following steps: S1. Dissolve lanthanum source and nickel source in an organic solvent to prepare LaNiO3 precursor solution; S2. Add monoethanolamine as a stabilizer to the precursor solution, wherein the molar ratio of monoethanolamine to LaNiO3 is 0.50-1.50; S3. Spin-coat the precursor solution onto a silicon substrate to prepare a LaNiO3 wet film; S4. The LaNiO3 wet film is baked, pyrolyzed and annealed to form a crystallized LaNiO3 thin film; S5. Repeat S3-S4 several times until the film thickness is ≥300nm; Wherein, the baking temperature in S4 is 145-160℃, the pyrolysis temperature is 390-420℃, the annealing temperature is 700-720℃, and the baking, pyrolysis and annealing times are all 10-12 minutes.

2. The method for preparing LaNiO3 thin films based on monoethanolamine regulation according to claim 1, characterized in that, The molar ratio of monoethanolamine to LaNiO3 in S2 is 1.

00.

3. The method for preparing LaNiO3 thin films based on monoethanolamine regulation according to claim 1, characterized in that, The lanthanum source in S1 is lanthanum nitrate, the nickel source is nickel acetate, and the organic solvent is 2-methoxyethanol.

4. The method for preparing LaNiO3 thin films based on monoethanolamine regulation according to claim 1, characterized in that, The concentration of the LaNiO3 precursor solution in S1 is 0.3 mol / L.

5. The method for preparing LaNiO3 thin films based on monoethanolamine regulation according to claim 1, characterized in that, The step S2, after mixing monoethanolamine with the LaNiO3 precursor solution, further includes stirring the mixture for 5-6 hours and then letting it stand for 8-14 hours.

6. The method for preparing LaNiO3 thin films based on monoethanolamine regulation according to claim 1, characterized in that, Before spin coating, the silicon substrate in step S3 is ultrasonically cleaned with acetone, ethanol and deionized water. The spin coating speed in step S3 is 4800-5200 rpm and the spin coating time is 13-18 s.

7. The method for preparing LaNiO3 thin films based on monoethanolamine regulation according to claim 1, characterized in that, In step S5, the silicon substrate is repeatedly spin-coated, baked, pyrolyzed, and annealed six times, and then annealed at 700-720℃ for 30-35 minutes.

8. A method for preparing LaNiO3 thin films based on monoethanolamine regulation according to any one of claims 1-8, characterized in that, The LaNiO3 thin film prepared by the method has an (00l) orientation degree of ≥98%, a thickness of ≥340nm, and a room temperature resistivity of ≤0.7mΩ·cm.

9. The application of the LaNiO3 thin film prepared by the method for preparing LaNiO3 thin films based on monoethanolamine regulation according to any one of claims 1-8 in silicon-based compatible functional devices.

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