A sodium bismuth titanate-based ferroelectric thin film and a method for preparing the same

Abstract

The application discloses a preparation method of a sodium bismuth titanate-strontium titanate-bismuth ferrite manganate ferroelectric film, and the chemical composition of the ferroelectric film is (1-x)Bi 0.35 Na 0.35 Sr 0.3 O3-xBiMnO3, and the molar component x is 0-0.10. The preparation method comprises the following steps: ①adding bismuth nitrate, sodium acetate, strontium acetate and manganese acetate into deionized water and an acetic acid solvent, stirring at 40-90 DEG C for 5-40 min, and obtaining solution A; ②adding tetrabutyl titanate into acetylacetone and ethylene glycol methyl ether solvents, stirring for 5-40 min, and obtaining solution B; ③mixing solution A with solution B, stirring for 5-40 min, and obtaining mixed solution C; and ④coating the mixed solution C on a Pt / Ti / SiO2 / Si substrate by a spin coating method, and obtaining a sodium bismuth titanate-based lead-free ferroelectric film after high-temperature treatment; the ferroelectric film is smooth and flat, has a typical perovskite structure, a very high polarization intensity and excellent piezoelectric performance, and especially, the remanent polarization intensity Pr is greatly improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electronic functional materials and devices, and relates to a sodium bismuth titanate-based lead-free ferroelectric film and a preparation method thereof, in particular to a preparation method of a sodium bismuth titanate-based lead-free ferroelectric film with excellent piezoelectric and ferroelectric properties by solid solution doping. BACKGROUND

[0002] Compared with bulk ceramic materials, ferroelectric films have the advantages of small volume, low working voltage, easy integration with semiconductor processes, etc., making them have wide application prospects in many high-tech fields such as microelectronics, optoelectronics, micro-electromechanics, etc. However, the ferroelectric films widely used in commercial applications at present are mainly lead-based ferroelectric films, such as lead titanate-based, lead magnesium niobate-based, etc. As is known, lead is a neurotoxin with strong toxicity, which brings serious harm to the ecological environment and human health. Therefore, it is urgent to develop lead-free ferroelectric film materials with excellent ferroelectric and piezoelectric properties comparable to lead-based ferroelectric films to replace lead-based ferroelectric films in the application of electronic devices.

[0003] Bi 0.5 Na 0.5 TiO3(BNT) is a typical lead-free ferroelectric material with a perovskite structure, which belongs to a trigonal phase at room temperature and has a Curie temperature of about 320℃. The excellent ferroelectric properties of BNT have attracted the scientific research interest of many researchers, and it is considered as one of the important systems that can replace lead-based ferroelectric materials. However, the pure BNT ferroelectric film has the disadvantages of small maximum polarization, small remanent polarization and small piezoelectric coefficient, which limits its wide application in the field of microelectronic devices. In recent years, researchers have added a second component strontium titanate (SrTiO3, STO) to the sodium bismuth titanate film, and the ferroelectric and piezoelectric properties of the prepared Bi 0.35 Na 0.35 Sr 0.3 TiO3(BNST) film have been greatly improved. Existing researches all take the BNST film as an energy storage material, and improve the maximum polarization and breakdown strength and reduce the remanent polarization by third phase doping. However, the core indicators of excellent ferroelectric properties of ferroelectric materials are to obtain high maximum polarization and remanent polarization and low coercive field. It can be seen that there is inconsistency between the key indicators of energy storage performance and ferroelectric performance of ferroelectric materials.

[0004] Bismuth manganate (BiMnO3, BMO) is a multiferroic film with a perovskite structure, which not only has a perovskite structure easy to deform at room temperature, but also has a low leakage current. Although some researchers add the perovskite structure BMO as a second or third component to the lead-containing and lead-free matrix materials to well regulate the electrical properties of the materials. Existing researches have found that doping BMO can indeed increase the maximum polarization P max and the remanent polarization Pr However, P r The improved amplitude is much smaller than P max Therefore, doping BMO can significantly improve the energy storage performance, but not the ferroelectric performance (Wu S, Song B, Li P, et al. Reduced leakage current and enhanced piezoelectricity of BNT-BT-BMO thin films [J]. Journal of the American Ceramic Society, 2020, 103(2): 1219-1229). However, there is no report on the preparation of (1-x) BNST-xBMO ferroelectric thin films by doping BMO in BNST. In the present patent, the 0.96BNST-0.04BMO ferroelectric thin film with the best ferroelectric performance in the BNST thin film doped with BMO has a P r Increased by 74.8%, P max Increased by 46.4%, significantly improving the ferroelectric performance of (1-x) BNST-xBMO ferroelectric thin films. SUMMARY

[0005] To solve the above problems, the present application provides a sodium bismuth titanate-based lead-free ferroelectric thin film and a preparation method thereof. The thin film has excellent ferroelectric and piezoelectric properties: P max 47.09 μC / cm 2 -128.7 μC / cm 2 , P r 25.87 μC / cm 2 -72.24 μC / cm 2 and d 33 30.3 pm / V-140.0 pm / V.

[0006] The chemical composition of the sodium bismuth titanate-based lead-free ferroelectric thin film is (1-x)(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-xBiMnO3(BNST-BMO) thin film, wherein x represents the mole percentage of added BMO, generally x is 0-0.10, preferably x=0.02-0.10, preferably x=0.06-0.1, preferably x=0.02-0.06, more preferably x=0.04-0.06, for example x=0.04, and x is the mole fraction.

[0007] The application discloses a preparation method of a sodium bismuth titanate-based ferroelectric film, and belongs to the field of electronic functional materials and devices. The preparation method provided by the application comprises the following steps: step 1, bismuth nitrate, sodium acetate, strontium acetate and manganese acetate are added into a mixed solvent of acetic acid and deionized water, acetic acid:deionized water=a:7-a (a=0-5), a is a volume capacity, and the solution A is obtained by stirring at 40-90 DEG C for 5-40 min; step 2, tetrabutyl titanate is added into a mixed solvent of acetylacetone and ethylene glycol methyl ether, and the solution B is obtained by stirring for 5-40 min; step 3, the solution A is mixed with the solution B, and the mixed solution C is obtained after pretreatment; and step 4, the mixed solution C is coated on a treated substrate by a spin coating method, and the sodium bismuth titanate-based lead-free ferroelectric film of (1-x)BNST-xBMO is obtained after high-temperature treatment.

[0008] In the preparation method of the sodium bismuth titanate-based lead-free ferroelectric film provided by the application, the mass excess of bismuth nitrate is 1-15%, and the mass excess of sodium acetate is 1-10%.

[0009] In the preparation method of the sodium bismuth titanate-based lead-free ferroelectric film provided by the application, the concentration of the mixed solution C is adjusted to 0.1-0.60 mol / L.

[0010] In the preparation method of the sodium bismuth titanate-based lead-free ferroelectric film provided by the application, the substrate is a Pt / Ti / SiO2 / Si substrate.

[0011] In the preparation method of the sodium bismuth titanate-based lead-free ferroelectric film provided by the application, the treatment process of the substrate is as follows: step 1, the substrate is ultrasonically cleaned with a solvent to obtain a cleaned substrate, and the ultrasonic cleaning solvent is selected from one or more of acetone, nitric acid, hydrogen peroxide, deionized water and anhydrous ethanol; and step 2, the cleaned substrate is dried with nitrogen to obtain a treated substrate.

[0012] In the preparation method of the sodium bismuth titanate-based lead-free ferroelectric film provided by the application, the process parameters for preparing the film are as follows: the spin coating process: the rotation speed is 3000-5000 r / min, and the glue uniformizing time is 20-60 s; the high-temperature treatment process: heat treatment is carried out at 100-250 DEG C for 3-5 min, heat treatment is carried out at 300-500 DEG C for 5-10 min, the above heat treatment operation is repeated, the number of repetitions is consistent with the number of film layers, the number of film layers is controlled to be 4-10, the thickness of the film is controlled to be 300-700 nm, and finally annealing treatment is carried out at 600-900 DEG C for 3-20 min to complete coating.

[0013] The piezoelectric coefficient of the sodium bismuth titanate-based lead-free ferroelectric film prepared by the application is 130.0 pm / V-140.0 pm / V, the P max r is 128.7 muC / cm 2 , the P r r is 72.24 muC / cm2 , thickness is 300-700nm.

[0014] The present application adjusts the dissolving speed and PH value of the solute in the solution by using deionized water as the main solvent, and the dissolving speed and PH value of the solute in the solution are the key factors to determine whether the preparation of the sodium bismuth titanate-based precursor solution is successful. When the dissolving speed of the solute in the solution is too fast and the PH value is too low, the solute will react to form a precipitate during the preparation of the solution, so the solution will fail to be prepared and cannot be used to prepare a thin film. When the dissolving speed of the solute in the solution is too slow and the PH value is too high, the solution will take too long to be prepared or cannot be dissolved, and the solution will also fail to be prepared. The basic principle of the sol-gel method is that the metal compound (inorganic salt or metal alkoxide) which is easy to hydrolyze reacts with water in a certain solvent, and gradually gels through the hydrolysis and polycondensation process. Therefore, the present application adjusts the dissolving speed and PH value of the solute in the solution by using deionized water as the main solvent, so as to adjust the hydrolysis and polycondensation reaction speed of the solution, and make the hydrolysis and polycondensation reaction reach a dynamic balance, thereby obtaining a sodium bismuth titanate-based precursor solution which is mixed uniformly. The present inventors have found that the content of the added deionized water plays a decisive role in whether the sodium bismuth titanate-based precursor solution can be prepared successfully and the quality of the prepared BNST-BMO thin film. If the amount of the added deionized water is too much, the contact angle of the solution with the substrate will be too small, so that the thin film cannot be spin-coated uniformly on the substrate or cannot be spin-coated on the substrate, thereby failing the experiment. If the amount of the added deionized water is too low, the PH value of the solution will be too high, the dynamic balance of the hydrolysis and polycondensation reaction of the solution will be destroyed, the solute will react to form a precipitate, and the sodium bismuth titanate-based solution cannot be prepared successfully.

[0015] It is worth noting that the sodium bismuth titanate-strontium titanate-bismuth manganate ternary solid solution thin film prepared by the present application has a high P max and a low P r , compared with the high P max and P r of the binary or ternary solid solution thin film prepared by other researchers by dissolving bismuth manganate in other materials. max The reason why the present application has a high P max is that the lattice parameter of the solvent lattice (BNT-STO) gradually increases with the entry of the solute lattice (BMO), and the stretching effect of the lattice enhances the polarization strength of the material, thereby increasing the P max of the material. With the gradual increase of the doping amount of BMO, the stretching effect reaches a limit at the solubility limit, and when the doping amount of BMO is 0.04, the P 2 increases to a limit value of 128.7 μC / cm rThe different reasons are: compared with the process of preparing one layer of thin film and annealing once, the process of preparing multiple layers of thin film and annealing once has more defects in the growth process of the thin film, for example, the thickness is thicker when annealing, which leads to uneven grain growth, Bi 3+ and Na + The amount of volatilization increases, the internal oxygen vacancies and holes increase, and the domain pinning effect occurs, so that after the electric field is removed, the dipole in the thin film is difficult to flip, and the thin film prepared by the process of preparing multiple layers of thin film and annealing once has high P r .

[0016] The prepared sodium bismuth titanate-based lead-free ferroelectric thin film can be applied in the field of non-volatile ferroelectric memory, brake and energy collector. Whether it is the sodium bismuth titanate-based lead-free ferroelectric thin film introduced above or the non-volatile ferroelectric memory obtained by the method for preparing the sodium bismuth titanate-based lead-free ferroelectric thin film, the ferroelectric and piezoelectric properties of the ferroelectric material can be significantly improved. Compared with the prior art, the present application overcomes the harm of lead-based ferroelectric thin film to human beings and ecological environment in the production, use and disposal process, and provides a preparation method of ferroelectric thin film with simple production process and repeatability. The ferroelectric thin film has excellent ferroelectric and piezoelectric properties.

[0017] The ferroelectric thin film prepared by the present application has a smooth surface, a typical perovskite structure, a very high polarization strength and good piezoelectric properties, and the P max is 47.09 mu C / cm 2 -128.7 mu C / cm 2 , the P r is 25.87 mu C / cm 2 -72.24 mu C / cm 2 and the d 33 is 30.3 pm / V-140.0 pm / V. It has very important significance for the development of high-performance lead-free ferroelectric thin film. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the grazing incidence X-ray diffraction pattern of the sodium bismuth titanate-based lead-free ferroelectric thin film obtained by the comparative example 1 and examples 1-3 of the present application;

[0019] Figure 2 is the surface and cross-section scanning electron microscope image and scanning electron microscope energy spectrum of the sodium bismuth titanate-based lead-free ferroelectric thin film obtained by the example 2 of the present application;

[0020] Figure 3 is the electric hysteresis loop diagram of the sodium bismuth titanate-based lead-free ferroelectric thin film obtained by the comparative example 1 and examples 1-3 of the present application under the same voltage;

[0021] Figure 4 The hysteresis loop graph of 0.96BNST-0.04BMO lead-free ferroelectric thin film at different voltages obtained in Comparative Example 1 and Examples 1-3 of the present application;

[0022] Figure 5 The butterfly curve and phase-voltage curve graph of sodium bismuth titanate-based lead-free ferroelectric thin film obtained in Comparative Example 1 and Examples 1-3 of the present application;

[0023] Figure 6 The d 33 curve graph of sodium bismuth titanate-based lead-free ferroelectric thin film obtained in Comparative Example 1 and Examples 1-3 of the present application. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described in more detail below with reference to the drawings in the present application.

[0025] I. 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 thin film with different molar concentration ratios

[0026] Example 1:

[0027] A preparation method of a solution of sodium bismuth titanate-based lead-free ferroelectric thin film (0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) with a molar concentration of 0.1 mol / L, comprising the following steps:

[0028] Step 1, dissolve 1.8864 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.2894 grams of sodium acetate (CH3COONa), 0.5985 grams of strontium acetate (C4H6O4Sr) and 0.099 grams of manganese acetate (MnC4H6O4·4H2O) in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and stir at 80°C for 20 min to obtain solution A.

[0029] Step 2, dissolve 3.3 grams of tetrabutyl titanate (C 16 H 36 O4Ti) in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and stir for 20 min to obtain solution B.

[0030] Step 3, mix solution A and solution B, adjust the concentration to 0.1 mol / L, and then stir at 50°C for 8 h to obtain mixed solution C.

[0031] Step 4, coating the mixed solution C on the treated substrate by spin coating method, and obtaining the sodium bismuth titanate-based lead-free ferroelectric thin film after high temperature treatment.

[0032] In the present embodiment 1, the treatment process of the substrate is as follows: cutting the Pt / Ti / SiO2 / Si substrate into a square with a side length of 10 mm, cleaning with acetone, deionized water and ethanol for 20 min respectively, and then blowing the substrate dry with high-purity nitrogen to obtain the treated substrate.

[0033] In the present embodiment 1, the high temperature treatment process includes the following steps:

[0034] Step 1, spin coating a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate by spin coating method at a speed of 4000 r / s for 30 s to obtain a thin film.

[0035] Step 2, treating the thin film on a low temperature heating table at 180°C for 5 min and on a high temperature heating table at 400°C for 5 min.

[0036] Step 3, repeating step 2 until a thin film with 6 layers is obtained, and then annealing the thin film in a rapid annealing furnace at 750°C for 5 min to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric thin film.

[0037] Embodiment 2:

[0038] A solution with a molar concentration of 0.2 mol / L of a sodium bismuth titanate-based lead-free ferroelectric thin film (0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO 3) The preparation method comprises the following steps:

[0039] Step 1, dissolving 3.7728 g of bismuth nitrate (Bi(NO3)3·5H2O), 0.5788 g of sodium acetate (CH3COONa), 1.197 g of strontium acetate (C4H6O4Sr) and 0.198 g of manganese acetate (MnC4H6O4·4H2O) in 30 ml of deionized water (H2O) and 40 ml of acetic acid (CH3COOH), and stirring at 80°C for 20 min to obtain solution A.

[0040] Step 2, dissolving 6.6 g of tetrabutyl titanate (C 16 H 36O4Ti) was dissolved in 10 ml of ethylene glycol methyl ether (C3H8O2) and 10 ml of acetylacetone (C5H8O2) mixed solution, stirred for 20 min to prepare solution B.

[0041] Step 3, solution A was mixed with solution B, and after the concentration was adjusted to 0.2 mol / L, solution C was prepared by stirring at 60°C for 7 h.

[0042] Step 4, solution C was coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric film was obtained.

[0043] In this embodiment 2, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate was cut into a square with a side length of 10 mm, washed with acetone, deionized water and ethanol for 20 min respectively, and then dried with high-purity nitrogen, to obtain a treated substrate.

[0044] In this embodiment 2, the high temperature treatment process includes the following steps:

[0045] Step 1, spin coating a layer of solution C on the Pt / Ti / SiO2 / Si substrate by spin coating, at a speed of 4000 r / s for 30 s, to obtain a thin film.

[0046] Step 2, the thin film was treated on a low temperature heating table at 180°C for 5 min, and on a high temperature heating table at 400°C for 5 min.

[0047] Step 3, repeat step 2 until a thin film with 6 layers is obtained, and then anneal it in a rapid annealing furnace at 800°C for 4 min, to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric film.

[0048] Embodiment 3:

[0049] A method for preparing a solution with a mole concentration of 0.4 mol / L of a sodium bismuth titanate-based lead-free ferroelectric film (0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3), including the following steps:

[0050] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3.5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr) and 0.2971 grams of manganese acetate (MnC4H6O4.4H2O) were dissolved in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH) to prepare solution A, which was stirred at 80°C for 20 min.

[0051] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) to prepare solution B, which was stirred for 20 min.

[0052] Step 3, solution A was mixed with solution B, and after adjusting the concentration to 0.4 moles / liter, solution C was prepared by stirring at 50°C for 8 h.

[0053] Step 4, solution C was coated on the treated substrate by spin coating, and after high-temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric film was obtained.

[0054] In this example 3, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate was cut into a square with a side length of 10 mm, and then sequentially cleaned with acetone, deionized water and ethanol for 20 min, and then dried with high-purity nitrogen to obtain a treated substrate.

[0055] In this example 3, the high-temperature treatment process includes the following steps:

[0056] Step 1, a thin film was obtained by spin coating a layer of solution C on the Pt / Ti / SiO2 / Si substrate at a speed of 4000 r / s for 30 s.

[0057] Step 2, the thin film was sequentially treated at 180°C for 5 min on a low-temperature heating table and at 400°C for 5 min on a high-temperature heating table.

[0058] Step 3, step 2 was repeated until a thin film with 6 layers was obtained, which was annealed at 750°C for 5 min in a rapid annealing furnace to obtain a 0.96(Bi0.35Na0.35Sr0.3TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric film.

[0059] II. (0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) films prepared by different ratios of deionized water and acetic acid

[0060] Example 4:

[0061] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric thin film 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3, comprising the following steps:

[0062] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr) and 0.2971 grams of manganese acetate (MnC4H6O4·4H2O) are dissolved in 20 milliliters of deionized water (H2O) and 50 milliliters of acetic acid (CH3COOH), and a solution A is prepared by stirring at 80°C for 20 min.

[0063] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) is dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and a solution B is prepared by stirring for 20 min.

[0064] Step 3, solution A is mixed with solution B, and after adjusting the concentration to 0.3 moles / liter, a mixed solution C is prepared by stirring at 50°C for 8h.

[0065] Step 4, the mixed solution C is coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric thin film is obtained.

[0066] In this example 4, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate is cut into a square with a side length of 10 millimeters, and then sequentially cleaned with acetone, deionized water and ethanol for 20 min respectively, and then the substrate is blown dry with high-purity nitrogen, thereby obtaining a treated substrate.

[0067] In this example 4, the high temperature treatment process includes the following steps:

[0068] Step 1, a layer of mixed solution C is spin-coated on the Pt / Ti / SiO2 / Si substrate by spin coating at a speed of 4000r / s for 30s, thereby obtaining a thin film.

[0069] Step 2, the thin film is sequentially treated at 180°C for 5 min on a low-temperature heating table and at 400°C for 5 min on a high-temperature heating table.

[0070] Step 3, step 2 is repeated until a thin film with 6 layers is obtained, which is annealed at 750°C for 5 min in a rapid annealing furnace, thereby obtaining (0.96(Bi 0.35 Na 0.35 Sr0.3 Na0.96(Bi0.5Na0.5)TiO3)-0.04BiMnO3) sodium bismuth titanate-based lead-free ferroelectric thin film.

[0071] Example 5:

[0072] A sodium bismuth titanate-based lead-free ferroelectric thin film 0.96(Bi 0.35 Na 0.35 Sr 0.3 A method for preparing Na0.96(Bi0.5Na0.5)TiO3)-0.04BiMnO3, comprising the following steps:

[0073] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr) and 0.2971 grams of manganese acetate (MnC4H6O4·4H2O) are dissolved in 50 milliliters of deionized water (H2O) and 20 milliliters of acetic acid (CH3COOH), and a solution A is prepared by stirring at 80°C for 20 min.

[0074] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) is dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and a solution B is prepared by stirring for 20 min.

[0075] Step 3, solution A is mixed with solution B, and after adjusting the concentration to 0.3 moles / liter, a mixed solution C is prepared by stirring at 50°C for 8h.

[0076] Step 4, the mixed solution C is coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric thin film is obtained.

[0077] In this example 5, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate is cut into a square with a side length of 10 millimeters, and then sequentially cleaned with acetone, deionized water and ethanol for 20 min respectively, and then dried with high-purity nitrogen gas to obtain a treated substrate.

[0078] In this example 5, the high temperature treatment process includes the following steps:

[0079] Step 1, a layer of mixed solution C is spin-coated on the Pt / Ti / SiO2 / Si substrate by spin coating at a speed of 4000r / s for 30s to obtain a thin film.

[0080] Step 2, the thin film is sequentially treated at 180°C for 5 min on a low-temperature heating table and at 400°C for 5 min on a high-temperature heating table.

[0081] Step 3, repeat Step 2 until a thin film with 6 layers is obtained, anneal the thin film in a rapid annealing furnace at 750°C for 5 min to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) sodium bismuth titanate-based lead-free ferroelectric thin film.

[0082] Example 6:

[0083] A method for preparing a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) sodium bismuth titanate-based lead-free ferroelectric thin film, comprising the following steps:

[0084] Step 1, dissolve 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr) and 0.2971 grams of manganese acetate (MnC4H6O4·4H2O) in 70 milliliters of deionized water (H2O), and stir at 80°C for 20 min to obtain solution A.

[0085] Step 2, dissolve 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and stir for 20 min to obtain solution B.

[0086] Step 3, mix solution A with solution B, adjust the concentration to 0.3 moles / liter, and stir at 50°C for 8h to obtain mixed solution C.

[0087] Step 4, use spin coating method to coat mixed solution C on the treated substrate, and after high temperature treatment, a 0.96(Bi

[0088] In this example 6, the treatment process of the substrate is as follows: cut the Pt / Ti / SiO2 / Si substrate into a square with a side length of 10 millimeters, wash with acetone, deionized water and ethanol for 20 min respectively, and then blow dry the substrate with high-purity nitrogen to obtain a treated substrate.

[0089] In this example 6, the high temperature treatment process includes the following steps:

[0090] Step 1, use spin coating method to spin coat a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate, the rotation speed is 4000r / s, and the time is 30s to obtain a thin film.

[0091] Step 2, the film is treated on the low temperature heating station at 180°C for 5 min and on the high temperature heating station at 400°C for 5 min.

[0092] Step 3, repeat Step 2 until the film with 6 layers is obtained, and then the film is annealed in a rapid annealing furnace at 750°C for 5 min to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) sodium bismuth titanate-based lead-free ferroelectric film.

[0093] III. 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) films prepared by different ratios of ethylene glycol methyl ether and acetylacetone

[0094] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric film (0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3) includes the following steps:

[0095] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr), and 0.2971 grams of manganese acetate (MnC4H6O4·4H2O) are dissolved in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and a solution A is prepared by stirring at 80°C for 20 min.

[0096] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) is dissolved in 20 milliliters of acetylacetone (C5H8O2) solution, and a solution B is prepared by stirring for 20 min.

[0097] Step 3, solution A and solution B are mixed, the concentration is adjusted to 0.3 moles / liter, and then a mixed solution C is prepared by stirring at 50°C for 8 h.

[0098] Step 4, the mixed solution C is coated on the treated substrate by spin coating, and a sodium bismuth titanate-based lead-free ferroelectric film is obtained after high-temperature treatment.

[0099] In this embodiment 7, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate is cut into a square with a side length of 10 mm, and then cleaned with acetone, deionized water and ethanol for 20 min respectively, and then the substrate is blown dry with high-purity nitrogen to obtain a treated substrate.

[0100] In this Example 7, the high temperature processing procedure includes the following steps:

[0101] Step 1. A thin film was prepared by spin-coating a mixture C on a Pt / Ti / SiO2 / Si substrate at 4000 r / s for 30 s.

[0102] Step 2. The thin film was sequentially treated at 180 °C for 5 min on a low temperature heating stage and at 400 °C for 5 min on a high temperature heating stage.

[0103] Step 3. Step 2 was repeated until a 6-layer thin film was obtained, which was annealed at 750 °C for 5 min in a rapid annealing furnace to produce a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric thin film.

[0104] Example 8:

[0105] A method for preparing a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric thin film includes the following steps:

[0106] Step 1. A solution A was prepared by dissolving 5.6592 g of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 g of sodium acetate (CH3COONa), 1.7953 g of strontium acetate (C4H6O4Sr), and 0.2971 g of manganese acetate (MnC4H6O4·4H2O) in 30 ml of deionized water (H2O) and 40 ml of acetic acid (CH3COOH) and stirring at 80 °C for 20 min.

[0107] Step 2. A solution B was prepared by dissolving 9.9 g of tetrabutyl titanate (C 16 H 36 O4Ti) in 20 ml of ethylene glycol methyl ether (C3H8O2) and stirring for 20 min.

[0108] Step 3. A mixture C was prepared by mixing the solution A and the solution B, adjusting the concentration to 0.3 mol / L, and stirring at 50 °C for 8 h.

[0109] Step 4. The mixture C was coated on the treated substrate by spin-coating, and a 0.96(Bi

[0110] In this embodiment 8, the process of treating the substrate is as follows: cut the Pt / Ti / SiO2 / Si substrate into a square with a side length of 10 mm, clean it with acetone, deionized water and ethanol for 20 min respectively, and then dry the substrate with high-purity nitrogen to obtain the treated substrate.

[0111] In this embodiment 8, the process of high-temperature treatment includes the following steps:

[0112] Step 1: spin-coat a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate at a speed of 4000 r / s for 30 s to obtain a thin film.

[0113] Step 2: treat the thin film on a low-temperature heating table at 180℃ for 5 min and on a high-temperature heating table at 400℃ for 5 min.

[0114] Step 3: repeat step 2 until a thin film with 6 layers is obtained, and then anneal the thin film in a rapid annealing furnace at 750℃ for 5 min to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 bismuth sodium titanate-based lead-free ferroelectric thin film.

[0115] IV. 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 thin films prepared at different annealing temperatures

[0116] Embodiment 9:

[0117] A method for preparing a bismuth sodium titanate-based lead-free ferroelectric thin film 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3, including the following steps:

[0118] Step 1: dissolve 5.6592 g of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 g of sodium acetate (CH3COONa), 1.7953 g of strontium acetate (C4H6O4Sr) and 0.2971 g of manganese acetate (MnC4H6O4·4H2O) in 30 ml of deionized water (H2O) and 40 ml of acetic acid (CH3COOH), and stir at 80℃ for 20 min to obtain solution A.

[0119] Step 2: dissolve 9.9 g of tetrabutyl titanate (C 16 H 36O4Ti) was dissolved in 10 ml of ethylene glycol methyl ether (C3H8O2) and 10 ml of acetylacetone (C5H8O2) mixed solution, stirred for 20 min to prepare solution B.

[0120] Step 3, solution A was mixed with solution B, and after the concentration was adjusted to 0.3 mol / L, solution C was prepared by stirring at 50°C for 8 h.

[0121] Step 4, solution C was coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric film was obtained.

[0122] In this embodiment 9, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate was cut into a square with a side length of 10 mm, and then cleaned with acetone, deionized water and ethanol for 20 min, respectively, and then dried with high-purity nitrogen to obtain a treated substrate.

[0123] In this embodiment 9, the high temperature treatment process includes the following steps:

[0124] Step 1, a layer of solution C was coated on the Pt / Ti / SiO2 / Si substrate by spin coating at a speed of 4000 r / s for 30 s to obtain a thin film.

[0125] Step 2, the thin film was treated on a low temperature heating table at 180°C for 5 min and on a high temperature heating table at 400°C for 5 min.

[0126] Step 3, step 2 was repeated until a thin film with 6 layers was obtained, which was annealed at 600°C for 5 min in a rapid annealing furnace to obtain a 0.96(Bi0.35Na0.35Sr0.3TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric film.

[0127] Embodiment 10:

[0128] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric film 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 includes the following steps:

[0129] Step 1, 5.6592 g of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 g of sodium acetate (CH3COONa), 1.7953 g of strontium acetate (C4H6O4Sr) and 0.2971 g of manganese acetate (MnC4H6O4·4H2O) were dissolved in 30 ml of deionized water (H2O) and 40 ml of acetic acid (CH3COOH), and stirred at 80°C for 20 min to prepare solution A.

[0130] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, stirred for 20 min to prepare solution B.

[0131] Step 3, mixed solution A with solution B, after adjusting the concentration to 0.3 moles / liter, stirred at 50°C for 8h to prepare mixed solution C.

[0132] Step 4, mixed solution C was coated on the treated substrate by spin coating method, after high temperature treatment, the sodium bismuth titanate-based lead-free ferroelectric film was obtained.

[0133] In this embodiment 10, the treatment process of the substrate is as follows: Pt / Ti / SiO2 / Si substrate was cut into a square with a side length of 10mm, and then cleaned with acetone, deionized water and ethanol for 20min respectively, and then dried with high purity nitrogen, to obtain the treated substrate.

[0134] In this embodiment 10, the high temperature treatment process includes the following steps:

[0135] Step 1, spin coating a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate by spin coating method, the rotation speed is 4000r / s, and the time is 30s, to obtain a thin film.

[0136] Step 2, the thin film was treated on the low temperature heating table at 180°C for 5min, and on the high temperature heating table at 400°C for 5min.

[0137] Step 3, repeat step 2 until the number of layers of the thin film is 6, and then anneal it in a rapid annealing furnace at 650°C for 5min, to obtain a sodium bismuth titanate-based lead-free ferroelectric film of 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3.

[0138] Embodiment 11:

[0139] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric film of 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3, including the following steps:

[0140] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3.5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr) and 0.2971 grams of manganese acetate (MnC4H6O4.4H2O) were dissolved in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH) to prepare solution A, which was stirred at 80°C for 20 min.

[0141] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) to prepare solution B, which was stirred for 20 min.

[0142] Step 3, solution A was mixed with solution B, and after adjusting the concentration to 0.3 moles / liter, solution C was prepared by stirring at 50°C for 8 h.

[0143] Step 4, solution C was coated on the treated substrate by spin coating, and after high-temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric thin film was obtained.

[0144] In this example 11, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate was cut into a square with a side length of 10 mm, and then sequentially cleaned with acetone, deionized water and ethanol for 20 min, and then dried with high-purity nitrogen to obtain a treated substrate.

[0145] In this example 11, the high-temperature treatment process includes the following steps:

[0146] Step 1, a thin film was obtained by spin coating a layer of solution C on the Pt / Ti / SiO2 / Si substrate at a speed of 4000 r / s for 30 s.

[0147] Step 2, the thin film was sequentially treated at 180°C for 5 min on a low-temperature heating table and at 400°C for 5 min on a high-temperature heating table.

[0148] Step 3, step 2 was repeated until a thin film with 6 layers was obtained, which was annealed at 700°C for 5 min in a rapid annealing furnace to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric thin film.

[0149] Example 12:

[0150] A sodium bismuth titanate-based lead-free ferroelectric thin film 0.96(Bi 0.35 Na 0.35 Sr0.3 A method for preparing 0.96(Bi0.5Na0.5TiO3)-0.04BiMnO3, comprising the following steps:

[0151] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr) and 0.2971 grams of manganese acetate (MnC4H6O4·4H2O) were dissolved in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and a solution A was prepared by stirring at 80°C for 20 min.

[0152] Step 2, 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) was dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and a solution B was prepared by stirring for 20 min.

[0153] Step 3, solution A was mixed with solution B, and after adjusting the concentration to 0.3 moles / liter, a mixed solution C was prepared by stirring at 50°C for 8 h.

[0154] Step 4, the mixed solution C was coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric film was obtained.

[0155] In this embodiment 12, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate was cut into a square with a side length of 10 millimeters, and then sequentially cleaned with acetone, deionized water and ethanol for 20 min, and then dried with high-purity nitrogen, thereby obtaining a treated substrate.

[0156] In this embodiment 12, the high temperature treatment process comprises the following steps:

[0157] Step 1, a thin film was obtained by spin coating a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate by spin coating at a speed of 4000 r / s for 30 s.

[0158] Step 2, the thin film was sequentially treated at 180°C for 5 min on a low-temperature heating table and at 400°C for 5 min on a high-temperature heating table.

[0159] Step 3, step 2 was repeated until a thin film with 6 layers was obtained, which was annealed at 800°C for 5 min in a rapid annealing furnace, thereby obtaining a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric film.

[0160] V. BiMnO3 content of Bi 0.35 Na 0.35 Sr 0.3 TiO3 thin film

[0161] Example 13

[0162] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric thin film 0.98(Bi 0.35 N a0.35 Sr 0.3 TiO3)-0.02BiMnO3, comprising the following steps:

[0163] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8863 grams of sodium acetate (CH3COONa), 1.8327 grams of strontium acetate (C4H6O4Sr) and 0.1485 grams of manganese acetate (MnC4H6O4·4H2O) are dissolved in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and a solution A is prepared by stirring at 80°C for 20 min.

[0164] Step 2, 10.1065 grams of tetrabutyl titanate (C 16 H 36 O4Ti) is dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and a solution B is prepared by stirring for 20 min.

[0165] Step 3, solution A is mixed with solution B, and after adjusting the concentration to 0.3 moles / liter, a mixed solution C is prepared by stirring at 50°C for 8h.

[0166] Step 4, the mixed solution C is coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric thin film is obtained.

[0167] In this example 13, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate is cut into a square with a side length of 10 millimeters, and then sequentially cleaned with acetone, deionized water and ethanol for 20 min respectively, and then the substrate is blown dry with high-purity nitrogen, thereby obtaining a treated substrate.

[0168] In this example 13, the high temperature treatment process comprises the following steps:

[0169] Step 1, a layer of mixed solution C is spin-coated on the Pt / Ti / SiO2 / Si substrate by spin coating at a speed of 4000r / s for 30s, thereby obtaining a thin film.

[0170] Step 2, the thin film is sequentially treated at 180°C for 5 min on a low-temperature heating table and at 400°C for 5 min on a high-temperature heating table.

[0171] Step 3, repeat Step 2 until a 6-layer thin film is obtained, anneal the thin film in a rapid anneal furnace at 750°C for 5 min to obtain a 0.98(Bi 0.35 Na 0.35 Sr 0.3 TiO 3) -0.02BiMnO3 sodium bismuth titanate-based lead-free ferroelectric thin film.

[0172] Example 14:

[0173] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric thin film 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3, comprising the following steps:

[0174] Step 1, dissolve 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8682 grams of sodium acetate (CH3COONa), 1.7953 grams of strontium acetate (C4H6O4Sr), and 0.2971 grams of manganese acetate (MnC4H6O4·4H2O) in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and stir at 80°C for 20 min to obtain solution A.

[0175] Step 2, dissolve 9.9 grams of tetrabutyl titanate (C 16 H 36 O4Ti) in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and stir for 20 min to obtain solution B.

[0176] Step 3, mix solution A with solution B, adjust the concentration to 0.3 moles / liter, and then stir at 50°C for 8h to obtain mixed solution C.

[0177] Step 4, use spin coating method to coat mixed solution C on the treated substrate, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric thin film is obtained.

[0178] In this Example 14, the treatment process of the substrate is as follows: cut the Pt / Ti / SiO2 / Si substrate into a square with a side length of 10 millimeters, wash it with acetone, deionized water and ethanol for 20 min respectively, and then blow dry the substrate with high-purity nitrogen to obtain a treated substrate.

[0179] In this Example 14, the high temperature treatment process includes the following steps:

[0180] Step 1, use spin coating method to spin coat a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate at a speed of 4000r / s for 30s to obtain a thin film.

[0181] Step 2, the film is treated on the low temperature heating stage at 180°C for 5 min and on the high temperature heating stage at 400°C for 5 min.

[0182] Step 3, repeat Step 2 until the film with 6 layers is obtained, and then the film is annealed in a rapid annealing furnace at 750°C for 5 min to obtain a 0.96(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.04BiMnO3 sodium bismuth titanate-based lead-free ferroelectric film.

[0183] Example 15:

[0184] A method for preparing a sodium bismuth titanate-based lead-free ferroelectric film 0.94(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.06BiMnO3, comprising the following steps:

[0185] Step 1, 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.8501 grams of sodium acetate (CH3COONa), 1.7579 grams of strontium acetate (C4H6O4Sr) and 0.4456 grams of manganese acetate (MnC4H6O4·4H2O) are dissolved in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and a solution A is prepared by stirring at 80°C for 20 min.

[0186] Step 2, 9.694 grams of tetrabutyl titanate (C 16 H 36 O4Ti) is dissolved in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and a solution B is prepared by stirring for 20 min.

[0187] Step 3, the solution A and the solution B are mixed, and after the concentration is adjusted to 0.3 moles / liter, a mixed solution C is prepared by stirring at 50°C for 8 h.

[0188] Step 4, the mixed solution C is coated on the treated substrate by spin coating, and after high temperature treatment, a sodium bismuth titanate-based lead-free ferroelectric film is obtained.

[0189] In this example 15, the treatment process of the substrate is as follows: the Pt / Ti / SiO2 / Si substrate is cut into a square with a side length of 10 millimeters, and then cleaned with acetone, deionized water and ethanol for 20 min respectively, and then the substrate is blown dry with high-purity nitrogen to obtain a treated substrate.

[0190] In this example 15, the high temperature treatment process comprises the following steps:

[0191] Step 1, spin-coat a layer of mixed solution C on the Pt / Ti / SiO2 / Si substrate by spin-coating method at 4000 r / s for 30 s to obtain a thin film.

[0192] Step 2, sequentially treat the thin film on the low-temperature heating table at 180℃ for 5 min and on the high-temperature heating table at 400℃ for 5 min.

[0193] Step 3, repeat Step 2 until a thin film with 6 layers is obtained, and then anneal the thin film in a rapid annealing furnace at 750℃ for 5 min to obtain a 0.94(Bi 0.35 Na 0.35 Sr 0.3 TiO3)-0.06BiMnO3 bismuth sodium titanate-based lead-free ferroelectric thin film.

[0194] Six, comparative examples and test examples

[0195] Comparative example:

[0196] A preparation method of a bismuth sodium titanate-based lead-free ferroelectric thin film Bi 0.35 Na 0.35 Sr 0.3 TiO3, comprising the following steps:

[0197] Step 1, dissolve 5.6592 grams of bismuth nitrate (Bi(NO3)3·5H2O), 0.9044 grams of sodium acetate (CH3COONa), and 1.8701 grams of strontium acetate (C4H6O4Sr) in 30 milliliters of deionized water (H2O) and 40 milliliters of acetic acid (CH3COOH), and stir at 80℃ for 20 min to obtain solution A.

[0198] Step 2, dissolve 10.313 grams of tetrabutyl titanate (C 16 H 36 O4Ti) in 10 milliliters of ethylene glycol methyl ether (C3H8O2) and 10 milliliters of acetylacetone (C5H8O2) mixed solution, and stir for 20 min to obtain solution B.

[0199] Step 3, mix solution A and solution B, adjust the concentration to 0.3 mol / L, and then stir at 50℃ for 8 h to obtain mixed solution C.

[0200] Step 4, coat the mixed solution C on the treated substrate by spin-coating method, and obtain the bismuth sodium titanate-based lead-free ferroelectric thin film after high-temperature treatment.

[0201] In this comparative example, the treatment process of the substrate is as follows: cut the Pt / Ti / SiO2 / Si substrate into a square with a side length of 10 millimeters, sequentially clean with acetone, deionized water and ethanol for 20 min respectively, and then blow dry the substrate with high-purity nitrogen to obtain a treated substrate.

[0202] In the present comparative example, the process of high temperature treatment comprises the following steps:

[0203] Step 1, spin-coating a layer of mixed solution C on a Pt / Ti / SiO2 / Si substrate at a rotation speed of 4000 r / s for 30 s to obtain a thin film.

[0204] Step 2, treating the thin film successively on a low-temperature heating stage at 180°C for 5 min and on a high-temperature heating stage at 400°C for 5 min.

[0205] Step 3, repeating Step 2 until a thin film with 6 layers is obtained, and then annealing the thin film in a rapid annealing furnace at 750°C for 5 min to obtain a Bi 0.35 Na 0.35 Sr 0.3 TiO3-based lead-free ferroelectric thin film.

[0206] Test Example 1: Grazing incidence X-ray diffraction test

[0207] Test method: The BiNaTiO3-based lead-free ferroelectric thin films obtained in Comparative Example 1 and Examples 13-15 were tested in a grazing incidence X-ray diffraction continuous scanning mode, and the working voltage of the grazing incidence X-ray diffractometer was 40 kV, the working current was 40 mA, the test mode was grazing incidence, Ω = 1°, the scanning step Δ2θ = 0.1°, the scanning speed was 1° / s, and the scanning range 2θ was 20°-60°.

[0208] The test results are shown in Table 1. Figure 1 Table 1: Grazing incidence X-ray diffraction patterns of the BiNaTiO3-based lead-free ferroelectric thin films obtained in Comparative Example 1 and Examples 13-15. Figure 1 As can be seen from Table 1, all the thin films have a typical perovskite structure, and when the doping amount of BiMnO3 is x = 0, 0.02 and 0.04, no obvious impurity phase appears in the thin film, and when the doping amount of BiMnO3 is x = 0.06, BiMnO3 solid solution phase is precipitated. Figure 1 Test Example 2: SEM surface morphology, cross-sectional thickness and EDS test

[0209] Test method: The BiNaTiO3-based lead-free ferroelectric thin films obtained in Comparative Example 1 and Examples 13-15 were observed for surface morphology, grain distribution, density, cross-sectional thickness and other microstructure information using a field emission scanning electron microscope (SEM, S4800, Japan Hitachi Company, Germany Zeiss), and the test voltage was 10 kV.

[0210] The test results are shown in Table 2.

[0211] Table 2: SEM surface morphology, cross-sectional thickness and EDS of the BiNaTiO3-based lead-free ferroelectric thin films obtained in Comparative Example 1 and Examples 13-15. Figure 2 Figure 2 ​SEM images of the surface and cross-section of the BiNaTi-based lead-free ferroelectric thin film obtained in Example 14 and the energy dispersive spectroscopy of the scanning electron microscope; from Figure 2 (a) shows that the surface of the 0.96BNST-0.04BMO thin film is smooth, has no cracks, and has obvious fine grains, which is a polycrystalline structure, which is consistent with the structure analyzed in the XRD. Figure (b) is a SEM cross-sectional thickness image of the 0.96BNST-0.04BMO thin film with 6 layers of spin coating, which is about 440 nm. As can be seen from Figures (c)-(h), BMO is successfully doped into the BNST thin film, and the Bi, Na, Sr, Mn and Ti elements present in the thin film are uniformly distributed in the 0.96BNST-0.04BMO thin film without any element agglomeration, indicating that the prepared thin film has uniform element distribution and good quality.

[0212] Test Example 3: hysteresis loop test

[0213] Test method: The BiNaTi-based lead-free ferroelectric thin film obtained in Comparative Example 1 and Examples 13-15 was subjected to hysteresis loop test.

[0214] The test results are shown in Figure 3 and Figure 4 . Figure 3 and Figure 4 are the hysteresis loops of the BiNaTi-based lead-free ferroelectric thin film obtained in Comparative Example 1 and Examples 13-15. As can be seen from Figure 3 and Figure 4 , with the increase of BiMnO3 content, the maximum polarization intensity of Comparative Example 1 first increases and then decreases, indicating that the appropriate addition of BiMnO3 can improve the polarization intensity of Bi 0.35 Na 0.35 Sr 0.3 TiO3 thin film, and the hysteresis loop gradually becomes thin, and the thin film with a composition of 0.96Bi 0.35 Na 0.35 Sr 0.3 TiO3-0.04BiMnO3 in Example 14 has the highest maximum polarization intensity and remanent polarization intensity, up to 128.7 μC / cm 2 and 72.24 μC / cm 2 .

[0215] Test Example 4: piezoelectric force microscope test

[0216] Test method: The BiNaTi-based lead-free ferroelectric thin film obtained in Comparative Example 1 and Examples 13-15 was subjected to butterfly curve-voltage and phase-voltage test, respectively.

[0217] The test results are shown in Figure 5 and Figure 6 . Figure 5 andFigure 6 Butterfly curves-voltage vs. phase-voltage curves of the BiNaTiO3-based lead-free ferroelectric thin films obtained from Comparative Example 1 and Examples 13-15, respectively.

[0218] From the above data, it can be seen that with the increase of BiMnO3 content, the inverse piezoelectric coefficients of the ferroelectric thin films first increase and then decrease, which indicates that the appropriate addition of BiMnO3 can improve the inverse piezoelectric effect of BiNaSrTiO3 thin films. Figure 5 and Figure 6 It can be seen from the above data that with the increase of BiMnO3 content, the inverse piezoelectric coefficients of the ferroelectric thin films first increase and then decrease, which indicates that the appropriate addition of BiMnO3 can improve the inverse piezoelectric effect of BiNaSrTiO3 thin films. 0.35 Na 0.35 Sr 0.3 TiO3 thin films, the electric field required for phase reversal gradually decreases, the piezoelectric hysteresis decreases, and the thin film with the composition of 0.96BiNaSrTiO3-0.04BiMnO3 in Example 14 has the highest inverse piezoelectric coefficient (the inverse piezoelectric coefficient reaches 137.67 pm / V when a voltage of 18 volts is applied). 0.35 Na 0.35 Sr 0.3 TiO3-0.04BiMnO3 has the highest inverse piezoelectric coefficient (the inverse piezoelectric coefficient reaches 137.67 pm / V when a voltage of 18 volts is applied).

[0219] Effects of the embodiments: The ferroelectric thin films prepared in the embodiments have smooth surfaces, typical perovskite structures, very high polarization strengths, and excellent piezoelectric properties, and the P max is 47.09 μC / cm 2 -128.7 μC / cm 2 , the P r is 25.87 μC / cm 2 -72.24 μC / cm 2 , and the d 33 is 30.3 pm / V-137.67 pm / V. This is of great significance for the development of high-performance lead-free ferroelectric thin films.

[0220] The above embodiments are preferred cases of the present application and are not intended to limit the protection scope of the present application.

Claims

1. A sodium bismuth titanate-based lead-free ferroelectric thin film, the ferroelectric thin film having a chemical composition of (1-x)Bi 0.35 Na 0.35 Sr 0.3 TiO3 - xBiMnO3, where x = 0.02 - 0.04, x being a molar fraction, the ferroelectric thin film being prepared using a process of one-time annealing of a multilayer thin film.

2. The method of claim 1, wherein the preparation process is as follows: ① adding bismuth nitrate, sodium acetate, strontium acetate and manganese acetate into solvent A, stirring at 40-90 ℃ for 5-40 min to obtain solution A, wherein the volume ratio of acetic acid to deionized water in solution A is a:7-a (a=0-5), and a is the volume capacity; ② dissolving tetrabutyl titanate in a mixed solvent of ethylene glycol methyl ether and acetylacetone, stirring for 5-40 min to obtain solution B, wherein the volume ratio of ethylene glycol methyl ether to acetylacetone in solution B is b:2-b (b=0-2), and b is the volume capacity; ③ mixing solution A and solution B, stirring for 2-10 h to obtain mixed solution C, and aging mixed solution C for 2-10 days; ④ coating mixed solution C on a treated substrate by spin coating, and performing high-temperature treatment to obtain the sodium bismuth titanate-based lead-free ferroelectric thin film, wherein the process parameters for preparing the thin film are as follows: spin coating process: the rotation speed is 3000-5000 r / min, and the uniform coating time is 20-60 s; high-temperature treatment process: heat treatment at 100-250 ℃ for 3-5 min, heat treatment at 300-500 ℃ for 5-10 min, repeating the above heat treatment operation, the number of repetitions is consistent with the number of thin film layers, the number of thin film layers is controlled to be 4-10, the thickness of the thin film is controlled to be 300-700 nm, and finally annealing treatment at 600-900 ℃ for 3-20 min is performed to complete coating. The mass excess of bismuth nitrate is 1-15%, and the mass excess of sodium acetate is 1-10%. The concentration of mixed solution C in step ④ is adjusted to 0.1-0.6 mol / L. The substrate in step ④ is a Pt / Ti / SiO2 / Si substrate. The treatment process of the substrate is as follows: ① ultrasonic cleaning the substrate with a solvent to obtain a cleaned substrate, wherein the ultrasonic cleaning solvent is selected from one or more of acetone, nitric acid, hydrogen peroxide, deionized water and anhydrous ethanol; ② blowing the cleaned substrate with nitrogen to obtain the treated substrate. The treatment process of the substrate is as follows: ① ultrasonic cleaning the substrate with a solvent to obtain a cleaned substrate, wherein the ultrasonic cleaning solvent is selected from one or more of acetone, nitric acid, hydrogen peroxide, deionized water and anhydrous ethanol; ② blowing the cleaned substrate with nitrogen to obtain the treated substrate. ​ 3. The method of claim 2, wherein the method further comprises the step of: ​ 4. The method of claim 2 or 3, wherein the method is characterized by, ​ 5. The method of any of claims 2-4, wherein the method further comprises: ​ 6. The method of any of claims 2-5, wherein the method further comprises: ​ ​ ​

Images