A preparation method of high-quality lead zirconate titanate crystal thin film

Abstract

The present invention relates to a method for preparing a high-quality lead zirconate titanate crystal thin film, and relates to the technical field of functional materials. The preparation process of the present invention includes the following steps: mixing a lead source with a solvent, heating and reacting, then cooling, and then adding a zirconium source and a titanium source for reaction to obtain a PZT precursor solution; using a lanthanide substance as a target, preparing a seed layer by magnetron sputtering; then coating the PZT precursor solution on the surface of the seed layer, and obtaining a lead zirconate titanate crystal thin film after pyrolysis and annealing treatments. The present invention prepares a stable PZT precursor solution by the sol-gel method, and uses the seed layer to prepare a high-quality PZT crystal thin film that is smooth and crack-free and has a (100) preferred orientation, and has the characteristics of simple preparation process, convenient operation, easy availability of raw materials, and low preparation cost.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and particularly to a method for preparing a high-quality lead zirconate titanate crystal thin film. Background Art

[0002] Lead zirconate titanate (PZT) thin film is a metal oxide with a perovskite structure, possessing excellent piezoelectric, ferroelectric, dielectric, and optoelectronic properties. It is widely used in the field of microelectromechanical systems (MEMS) and has become a popular field in the research of functional materials.

[0003] There are various methods for preparing PZT thin films, and the quality of the thin film is closely related to the selected method. Currently, there are mainly radio frequency sputtering method, metal organic chemical vapor deposition (MOCVD) method, pulsed laser deposition (PLD) method, sol-gel method, etc. Among them, the sol-gel method has received extensive attention due to its advantages such as simple process, large-area film formation, low cost, and easy control of stoichiometry.

[0004] Although the sol-gel method for preparing PZT thin films has relatively prominent advantages, it also faces huge challenges. Among them, the stability of the PZT precursor solution, the smoothness and crack-free of the thin film, and the crystallization quality are still the biggest obstacles to the practical application of this thin film. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a high-quality lead zirconate titanate crystal thin film to solve the problems existing in the above-mentioned prior art, and to achieve high stability of the PZT precursor solution, smooth and crack-free thin film, and excellent crystallization quality.

[0006] To achieve the above purpose, the present invention provides the following scheme:

[0007] The present invention provides a method for preparing a lead zirconate titanate crystal thin film, comprising the following steps:

[0008] Preparation of PZT precursor solution:

[0009] Mix a lead source with a solvent, heat and react, then cool, and then sequentially add a zirconium source and a titanium source for reaction to obtain the PZT precursor solution;

[0010] Preparation of seed layer: Use a lanthanide substance as a target and prepare the seed layer by magnetron sputtering process;

[0011] Pyrolysis and annealing treatment: Coat the PZT precursor solution on the surface of the seed layer, and obtain the lead zirconate titanate crystal thin film after pyrolysis and annealing treatment.

[0012] During the preparation of the PZT precursor solution, by adopting the addition sequence of the lead source, zirconium source, and titanium source of the present invention above, excellent stability of the PZT precursor solution can be achieved, and it will not deteriorate after being stored at 8°C for one year. If the above addition sequence of the lead source, zirconium source, and titanium source of the present invention is not adopted, the stability of the PZT precursor solution will be seriously affected.

[0013] As a further preference of the present invention, the temperature of the heating reaction is 100 - 150°C, and the time is 0.5 - 3.0 h; the temperature of the cooling is 25 - 90°C; the temperature of the reaction is 25 - 90°C, and the time is 0.5 - 3.0 h.

[0014] As a further preference of the present invention, the lead source includes but is not limited to metal lead sources such as lead acetate, lead acetate trihydrate, and lead halide; the zirconium source includes but is not limited to metal zirconium sources such as zirconium acetate, zirconium n-propoxide, zirconium isopropoxide, zirconium halide, or zirconium sulfate; the titanium source includes but is not limited to metal titanium sources such as titanium n-propoxide, titanium isopropoxide, tetraisopropyl titanate, or tetramethanol titanium.

[0015] As a further preference of the present invention, the solvent includes but is not limited to solvents such as acetic acid or ethylene glycol monomethyl ether.

[0016] As a further preference of the present invention, after the reaction ends, it further includes the step of adjusting the concentration of the PZT precursor solution by using one or several of acetic acid, water, and alcohol compounds. The stirring time for adjusting the concentration of the PZT precursor solution by adding the above substances is preferably 12 h.

[0017] Among them, the alcohol compounds include but are not limited to alcohol compounds such as n-propanol, isopropanol, ethylene glycol, n-octanol, and ethanol.

[0018] As a further preference of the present invention, the molar ratio of lead, zirconium, and titanium elements in the lead source, zirconium source, and titanium source is 1.0 - 1.3:x:(1 - x), where the value of x is 0.3 - 0.7.

[0019] As a further preference of the present invention, the process of preparing the PZT precursor solution further includes the step of adding an additive. In terms of mass fraction, the addition amount of the additive is 1% - 30% of the PZT precursor solution.

[0020] The additive of the present invention includes but is not limited to surfactants such as polyethylene glycol, polyoxyethylene hydrocarbon, polyacrylate, and polyvinylpyrrolidone. For relatively thick (greater than 300 nm) PZT films, the addition of the additive can avoid defects in the film and prevent the generation of cracks and streaks.

[0021] As a further preference of the present invention, the lanthanide substance is lanthanum oxide or lanthanum carbonate.

[0022] As a further preference of the present invention, the sputtering gas pressure of the magnetron sputtering process is 0.5 to 3.5 Pa, and the sputtering atmosphere is a mixed gas of Ar and O 2 (preferably Ar / O 2 = 1:1), the sputtering temperature is 25 °C, and the time is 10 min; the pyrolysis temperature is 350 - 500 °C, and the pyrolysis time is 5 - 30 min; the annealing temperature is 550 - 800 °C, and the time is 5 min - 5 h, and the annealing atmosphere is O 2 or air.

[0023] As a further preference of the present invention, the thickness of the lead zirconate titanate crystal film is 50 nm - 2 μm, and the thickness of the seed layer is 4 nm - 20 nm.

[0024] As a further preference of the present invention, during the pyrolysis and annealing processes, the preferred coating method of the PZT precursor solution is spin coating.

[0025] The present invention discloses the following technical effects:

[0026] The present invention provides a method for preparing a PZT thin film. This method prepares a stable PZT precursor solution through the sol-gel method without adding additional stabilizers, and uses a seed layer to prepare a high-quality PZT crystal film that is smooth, crack-free, and has a (100) preferred orientation.

[0027] The preparation process of the present invention is simple, the operation is convenient, the raw materials are easy to obtain, and the preparation cost is relatively low. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a physical diagram of the PZT thin film prepared in Example 1 of the present invention;

[0030] Figure 2 It is an XRD diagram of the PZT thin film prepared in Example 1 of the present invention;

[0031] Figure 3 It is an SEM diagram of the PZT thin film prepared in Example 1 of the present invention;

[0032] Figure 4 It is a physical diagram of the PZT thin film prepared in Example 2 of the present invention;

[0033] Figure 5XRD pattern of the PZT thin film prepared in Example 2 of the present invention;

[0034] Figure 6 SEM images of the PZT thin film prepared in Example 2 of the present invention;

[0035] Figure 7 SEM images of the PZT thin film prepared in Example 3 of the present invention;

[0036] Figure 8 SEM images of the PZT thin film prepared in Example 4 of the present invention. Detailed implementation manners

[0037] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation to the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0038] It should be understood that the terms used in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0040] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0041] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0042] Example 1 A method for preparing a PZT crystal thin film

[0043] a. Preparation of the PZT precursor solution:

[0044] 1) Take lead acetate trihydrate (12 g, 31.63 mmol), dissolve it in 6 mL of acetic acid, heat it to 110 °C and stir for 3 hours (distill to remove water), and then cool it to 90 °C.

[0045] 2) Add zirconium propoxide (6.41 g, 13.71 mmol, 70 w%) to the above lead - acetic acid solution, and then add titanium isopropoxide (3.2 g, 12.65 mmol) and stir for 0.5 hour.

[0046] 3) Cool to room temperature, add 30 mL of acetic acid, stir overnight, filter to obtain a clear and transparent solution, which is the PZT precursor solution; the obtained clear and transparent PZT precursor solution can be stored in a refrigerator at 8 °C for one year without deterioration.

[0047] b. Preparation of the seed layer:

[0048] Select a lanthanum oxide target and prepare the seed layer by magnetron sputtering. The sputtering atmosphere is Ar / O 2 = 1:1, the gas pressure is 0.5 Pa, the sputtering temperature is 25 °C, and the time is 10 min.

[0049] c. Pyrolysis and annealing treatment:

[0050] Spin - coat the prepared PZT precursor solution on the seed layer (the thickness of the seed layer is 5 nm), pyrolyze at 450 °C for 10 min, and anneal at 600 °C for 1.0 hour (under air conditions) to finally obtain a high - quality PZT thin film.

[0051] The physical picture of the single - layer PZT thin film prepared in Example 1 is shown in Figure 1 The XRD pattern is shown in Figure 2 The SEM image is shown in Figure 3 .

[0052] It can be seen from Figure 1 that the PZT thin film is smooth and crack - free. It can be seen from Figure 2 that the single - layer PZT thin film has good crystallinity and obvious (100) grain preferred orientation, which can indicate that the prepared PZT thin film has excellent properties. In the figure, the diffraction angles 2θ = 21.7° and 44.3° are the peaks of PZT (100) and (200) respectively. It can be seen from Figure 3 that the spin - coated single - layer PZT thin film has a uniform thickness (the thickness is 140.4 nm) and the crystals are relatively compact, indicating that the quality of the crystals in the prepared thin film is good.

[0053] Based on Example 1 of the present invention, the influence of the addition order of metal sources on the stability of the PZT precursor solution was further explored:

[0054] Adjust the preparation steps of the PZT precursor solution as follows:

[0055] 1) Take lead acetate trihydrate (12 g, 31.63 mmol), dissolve it in 6 mL of acetic acid, heat it to 110 °C and stir for 3 hours (distill to remove water), and then cool it to 90 °C.

[0056] 2) Add titanium isopropoxide (3.2 g, 12.65 mmol) to the above lead - acetic acid solution, and then add zirconium n - propoxide (6.41 g, 13.71 mmol, 70 w%) and stir for 0.5 hours.

[0057] 3) Cool to room temperature, add 30 mL of acetic acid, stir overnight, filter, and obtain a clear and transparent solution, which is the PZT precursor solution.

[0058] The obtained PZT precursor solution will deteriorate (white precipitate forms) after only half a month of storage.

[0059] Example 2 A method for preparing a PZT crystal thin film

[0060] a. Preparation of PZT precursor solution:

[0061] 1) Take lead acetate trihydrate (12 g, 31.63 mmol), dissolve it in 6 mL of acetic acid, heat it to 150 °C and stir for 0.5 hours (distill to remove water), and then cool it to 25 °C.

[0062] 2) Add zirconium n - propoxide (6.41 g, 13.71 mmol, 70 w%) to the above lead - acetic acid solution, and then add titanium isopropoxide (3.2 g, 12.65 mmol) and stir for 3 hours.

[0063] 3) Add 11 mL of acetic acid and 2 mL of polyethylene glycol 200, stir for 12 hours, filter, and obtain a clear and transparent solution, which is the PZT precursor solution. The obtained PZT precursor solution can be stored in a refrigerator (8 °C) for one year without deterioration.

[0064] b. Preparation of the seed layer:

[0065] Select a lanthanum carbonate target and use magnetron sputtering to prepare the seed layer, where the sputtering atmosphere is Ar / O 2 = 1:1, the gas pressure is 0.5 Pa, the sputtering temperature is 25 °C, and the time is 10 min.

[0066] c. Pyrolysis and annealing treatment:

[0067] Use the spin - coating method to spin - coat the prepared PZT solution on the seed layer (the seed layer thickness is 5 nm), and respectively carry out pyrolysis at 400 °C for 10 min and annealing at 700 °C for 30 min (under air conditions), and finally obtain a high - quality PZT thin film.

[0068] The physical picture of the single-layer PZT thin film prepared in Example 2 is shown in Figure 4 , and the XRD pattern is shown in Figure 5 , and the SEM image is shown in Figure 6 .

[0069] It can be seen from Figure 4 that the PZT thin film is smooth and crack-free. It can be seen from Figure 5 that the single-layer PZT thin film has good crystallinity and obvious (100) grain preferred orientation, indicating that the prepared PZT thin film has excellent properties. In the figure, the diffraction angles 2θ = 21.7° and 44.3° are the peaks of PZT (100) and (200), respectively. It can be seen from Figure 6 that the single-layer PZT thin film prepared by spin coating has a uniform thickness (thickness is 349.8 nm), and the crystals are relatively compact, indicating that the quality of the crystals of the prepared thin film is good.

[0070] Example 3 A preparation method of a PZT crystal thin film

[0071] a. Preparation of the PZT precursor solution:

[0072] 1) Take lead acetate trihydrate (10 g, 26.35 mmol), dissolve it in 6 mL of acetic acid, heat it to 110 °C and stir for 3.0 hours (distill to remove water), and then cool it to 80 °C.

[0073] 2) Add zirconium n-propoxide (6.41 g, 13.71 mmol, 70 w%) to the above lead-acetic acid solution, and then add titanium isopropoxide (3.2 g, 12.65 mmol) and stir for 3 hours.

[0074] 3) Cool to room temperature, add 11 mL of acetic acid, stir for 12 hours, filter to obtain a clear and transparent solution, which is the PZT precursor solution. The obtained PZT precursor solution can be stored in a refrigerator at 8 °C for one year without deterioration.

[0075] b. Preparation of the seed layer: Select a lanthanum oxide target and use magnetron sputtering to prepare the seed layer, where the sputtering atmosphere is Ar / O 2 = 1:1, the gas pressure is 0.5 Pa, the sputtering temperature is 25 °C, and the time is 10 min.

[0076] c. Pyrolysis and annealing treatment: Spin coat the prepared PZT solution on the seed layer (seed layer thickness 5 nm) by spin coating, and pyrolyze at 450 °C for 10 min and anneal at 800 °C for 10 min (under air conditions) respectively, and finally obtain a high-quality PZT thin film.

[0077] The SEM image of the PZT thin film prepared in Example 3 is shown in Figure 7 .

[0078] From Figure 7 It can be seen that the spin-coated single-layer PZT film has a uniform thickness (130.3 nm), and the crystals are relatively compact, indicating that the quality of the crystals in the prepared film is good.

[0079] Example 4 A method for preparing a PZT crystal film

[0080] a. Preparation of PZT precursor solution:

[0081] 1) Take lead acetate trihydrate (12 g, 31.63 mmol), dissolve it in 6 mL of acetic acid, heat it to 110 °C and stir for 3.0 hours (distill to remove water), and then cool it to 80 °C.

[0082] 2) Add zirconium propoxide (3.7 g, 7.9 mmol, 70 w%) to the above lead-acetic acid solution, and then add titanium isopropoxide (4.67 g, 18.45 mmol) and stir for 3 hours.

[0083] 3) Add 1.2 mL of ethylene glycol, continue to stir at 80 °C for 3 hours, and then add 6 mL of water and stir for 12 hours.

[0084] 4) Cool to room temperature, add 11 mL of acetic acid and 2 mL of polyethylene glycol 200, stir for 12 hours, filter to obtain a clear and transparent solution, which is the PZT precursor solution. The obtained PZT precursor solution can be stored in the refrigerator (8 °C) for one year without deterioration.

[0085] b. Preparation of the seed layer: Select a lanthanum oxide target and use magnetron sputtering to prepare the seed layer, where the sputtering atmosphere is Ar / O 2 = 1:1, the gas pressure is 0.5 Pa, the sputtering temperature is 25 °C, and the time is 10 min.

[0086] c. Pyrolysis and annealing treatment: Spin-coat the prepared PZT solution on the seed layer (seed layer thickness 5 nm) by spin coating, pyrolyze at 450 °C for 10 min and anneal at 600 °C for 1 hour (under air conditions), and finally obtain a high-quality PZT film.

[0087] The SEM image of the PZT film prepared in Example 4 is shown in Figure 8 .

[0088] From Figure 8 It can be seen that the spin-coated single-layer PZT film prepared in Example 4 has a uniform thickness (326.7 nm), and the crystals are relatively compact, indicating that the quality of the crystals in the prepared film is good.

[0089] Example 5 A method for preparing a PZT crystal film

[0090] a. Preparation of PZT precursor solution:

[0091] 1) Take lead acetate trihydrate (12 g, 31.63 mmol), dissolve it in 6 mL of acetic acid, heat it to 110 °C and stir for 3.0 hours (distill to remove water), then cool it to 80 °C.

[0092] 2) Add zirconium n-propoxide (8.64 g, 18.45 mmol, 70 w%) to the above lead - acetic acid solution. Then add titanium isopropoxide (2.0 g, 7.9 mmol) and stir for 3 hours.

[0093] 3) Cool to room temperature, add 11 mL of acetic acid, stir for 12 hours, filter to obtain a clear and transparent solution, which is the PZT precursor solution. The obtained solution can be stored in a refrigerator at 8 °C for one year without deterioration.

[0094] b. Preparation of seed layer:

[0095] Select a lanthanum oxide target and prepare the seed layer by magnetron sputtering. The sputtering atmosphere is Ar / O 2 = 1:1, the gas pressure is 0.5 Pa, the sputtering temperature is 25 °C, and the time is 10 min.

[0096] c. Pyrolysis and annealing treatment:

[0097] Spin-coat the prepared PZT solution on the seed layer (the thickness of the seed layer is 5 nm), pyrolyze at 450 °C for 10 min and anneal at 600 °C for 1 hour (under air conditions) respectively, and finally obtain a high-quality PZT thin film with a thickness of 150.2 nm.

[0098] Example 6 A method for preparing a PZT crystal thin film

[0099] a. Preparation of PZT precursor solution:

[0100] 1) Take lead acetate trihydrate (10 g, 26.36 mmol), dissolve it in 6 mL of acetic acid, heat it to 100 °C and stir for 3.0 hours (distill to remove water), then cool it to 80 °C.

[0101] 2) Add zirconium n-propoxide (6.41 g, 13.71 mmol, 70 w%) to the above lead - acetic acid solution. Then add titanium isopropoxide (3.2 g, 12.65 mmol) and stir for 3 hours.

[0102] 3) Cool to room temperature, add 11 mL of acetic acid, stir for 12 hours, filter to obtain a clear and transparent solution, which is the PZT precursor solution. The obtained PZT precursor solution can be stored in a refrigerator at 8 °C for one year without deterioration.

[0103] b. Preparation of the seed layer:

[0104] Select a lanthanum oxide target and use magnetron sputtering to prepare the seed layer (the thickness of the seed layer is 5 nm), where the sputtering atmosphere is Ar / O 2 = 1:1, the gas pressure is 0.5 Pa, the sputtering temperature is 25 °C, and the time is 10 min.

[0105] c. Pyrolysis and annealing treatment:

[0106] Spin-coat the prepared PZT solution on the seed layer by spin coating method, pyrolyze at 450 °C for 10 min, and anneal at 600 °C for 1 hour (under air conditions), and finally obtain a high-quality PZT thin film with a thickness of 146.1 nm.

[0107] In view of the shortcomings of the prior art, the present invention invented a simple method for preparing PZT thin films. This method prepares a smooth and crack-free high-quality PZT crystal thin film by preparing a stable PZT precursor solution and using the spin coating method. The method of the present invention is simple, low in cost, and the quality of the prepared PZT thin film is excellent.

[0108] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a lead zirconate titanate crystal thin film, characterized in that, it comprises the following steps: Preparation of PZT precursor solution: Mix a lead source with a solvent, heat and react, then cool, and then sequentially add a zirconium source and a titanium source for reaction to obtain the PZT precursor solution; Preparation of seed layer: Use a lanthanide substance as a target and prepare the seed layer by magnetron sputtering process; Pyrolysis and annealing treatment: Coat the PZT precursor solution on the surface of the seed layer, and obtain the lead zirconate titanate crystal thin film after pyrolysis and annealing treatment; The temperature of the heating reaction is 100 - 150 °C, and the time is 0.5 - 3.0 h; the temperature of the cooling is 25 - 90 °C; the temperature of the reaction is 25 - 90 °C, and the time is 0.5 - 3.0 h; The lead source includes lead acetate, lead acetate trihydrate or lead halide; the zirconium source includes zirconium acetate, zirconium n-propoxide, zirconium isopropoxide, zirconium halide or zirconium sulfate; the titanium source includes titanium n-propoxide, titanium isopropoxide, tetraisopropyl titanate or tetramethanol titanium; The solvent includes acetic acid or ethylene glycol monomethyl ether; The molar ratio of lead, zirconium, and titanium elements in the lead source, zirconium source, and titanium source is 1.0 - 1.3:x:(1 - x); wherein, the value of x is 0.3 - 0.7; The lanthanide substance is lanthanum oxide or lanthanum carbonate; The sputtering gas pressure of the magnetron sputtering process is 0.5 to 3.5 Pa, and the sputtering atmosphere is a mixed gas of Ar and O 2 ; the sputtering temperature is 25 °C and the time is 10 min; the pyrolysis temperature is 350 - 500 °C and the pyrolysis time is 5 - 30 min; the annealing temperature is 550 - 800 °C, the time is 5 min - 5 h, and the annealing atmosphere is O 2 or air.

2. The preparation method according to claim 1, characterized in that, after the reaction ends, it further includes a step of adjusting the concentration of the PZT precursor solution by using one or several of acetic acid, water, and alcohol compounds.

3. The preparation method according to claim 1, characterized in that, the process of preparing the PZT precursor solution further includes a step of adding an additive; the additive includes polyethylene glycol, polyoxyethylene hydrocarbon, polyacrylate or polyvinylpyrrolidone; by mass fraction, the addition amount of the additive is 1% - 30% of the PZT precursor solution.

4. The preparation method according to claim 1, characterized in that, the thickness of the lead zirconate titanate crystal thin film is 50 nm - 2 μm, and the thickness of the seed layer is 4 nm - 20 nm.

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