Method for preparing high self-polarization piezoelectric performance bismuth ferrite-based thin film through multi-element isometric solid solution

Abstract

The application discloses a method for preparing a high self-polarization piezoelectric performance bismuth ferrite-based film through multi-element isometric solid solution. The method comprises the following steps: configuring sols of more than three different cations which are solid-solved at B positions of bismuth ferrite, then dropping the sols on a substrate, uniformly coating the sols, solidifying, drying, pyrolyzing and annealing, repeating the dropping, uniformly coating, solidifying, drying, pyrolyzing and annealing processes, and obtaining a bismuth ferrite-based ferroelectric polycrystal film with a required thickness. The sol-gel method is adopted to prepare the multi-element isometric solid solution ferroelectric film, so that accurate component control can be realized, the growth of the material on a large-area substrate is suitable, the equipment and synthesis steps are simple, the material is saved, the cost is low, industrialized production is easy to realize, and the prepared ferroelectric polycrystal film has excellent self-polarization characteristics and a high piezoelectric coefficient, so that the ferroelectric polycrystal film has a wide application prospect in the field of electronic material technology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of piezoelectric thin film materials, and relates to a method for preparing a high self-polarization piezoelectric performance bismuth ferrite-based thin film through a multiple-element isometric solid solution. BACKGROUND

[0002] Piezoelectric materials are the key medium for realizing the mutual conversion of electrical energy and mechanical energy, and play a crucial role in the realization of electromechanical integration and intelligentization of structural components. With the development of nanotechnology, materials are developing towards low dimension, small size and multi-function. Microelectromechanical systems (MEMS) based on piezoelectric thin films are widely used in various fields such as radar, transducer, sonar and loudspeaker.

[0003] As the core functional unit of MEMS, the development of piezoelectric thin films is crucial. ScAlN piezoelectric thin films with a wurtzite structure occupy a significant market share due to their stability and compatibility with semiconductor Si processes. However, their piezoelectric coefficient is usually less than 30 pC / N, which greatly limits the further improvement of the signal sensitivity of related devices. Therefore, it is urgent to explore more piezoelectric thin films with different structures, excellent piezoelectric performance and alternatives.

[0004] Perovskite ferroelectric materials are being widely studied due to their simple structural characteristics and excellent piezoelectric performance. Lead zirconate titanate, Pb(Zr,Ti)O3 (PZT), is the most commonly used perovskite ferroelectric material in the current commercial market. PZT ferroelectric thin films have excellent piezoelectric performance, with a piezoelectric coefficient as high as 200 pC / N. However, compared with ScAlN thin films, the piezoelectric coefficient of PZT thin films is usually obtained by applying a sufficient direct current field for polarization for about 30 min. However, the semiconductor industry based on Si substrates usually requires processes such as solder packaging with a temperature exceeding 260℃ before obtaining the final device. Under such high-temperature operation, PZT and other ferroelectric thin films are easily depolarized and fail. Therefore, compared with piezoelectric materials such as ScAlN that do not require polarization, although they have more excellent piezoelectric performance, their application has not made a significant breakthrough. In addition, due to the lead content of PZT, it is harmful to the human body and the environment, so it is also extremely important to seek alternative lead-free materials.

[0005] In summary, breaking through the polarization process limitation of PZT and other ferroelectric thin films, obtaining an environmentally friendly perovskite ferroelectric thin film that can spontaneously polarize and has a piezoelectric coefficient superior to ScAlN thin films, is one of the bottlenecks in the development of the current MEMS field. SUMMARY

[0006] The application provides a method for preparing a high self-polarization piezoelectric performance bismuth ferrite (BiFeO3) based film through a multiple element isometric solid solution.

[0007] The technical scheme of the application is as follows:

[0008] The method for preparing a high self-polarization piezoelectric performance bismuth ferrite based film through a multiple element isometric solid solution comprises the following steps:

[0009] (1) preparing a sol: according to the stoichiometric ratio of the multiple element isometric solid solution BiFeO3, raw materials are dissolved in an organic solvent, then a chemical chelating stabilizer is added, stirring is performed until mixing is uniform, filtration is performed, sealing is performed, and the obtained clear and transparent, uniform and stable multiple element isometric solid solution BiFeO3 precursor sol is aged at room temperature, wherein the multiple element isometric solid solution BiFeO3 is a BiFeO3 based compound in which the B site (i.e. the Fe site) is replaced by three or more cations, and the replacement mode is that all the replacement cations are replaced at an equal ratio or are replaced according to a weight stoichiometric ratio, and the replacement cations are selected from three or more of Fe 3+ , Sc 3+ , Ga 3+ , Al 3+ , Mn 3+ , Ni 2+ and Ti 4+ ;

[0010] (2) spinning the glue to form a film: the multiple element isometric solid solution BiFeO3 precursor sol is spin-coated on a substrate to form a film, and then the substrate coated with the multiple element isometric solid solution BiFeO3 precursor sol is initially solidified at 150±5 ℃ to obtain a multiple element isometric solid solution BiFeO3 precursor sol film;

[0011] (3) heat treatment: the substrate coated with the multiple element isometric solid solution BiFeO3 precursor sol film in step (3) is subjected to heat treatment, is dried at 120 ℃-300 ℃ for 30 s-2 min, is pyrolyzed at 200 ℃-500 ℃ for 1-5 min, and is finally annealed at 500 ℃-900 ℃ for 1-15 min, so that a multiple element isometric solid solution BiFeO3 based piezoelectric film is obtained after cooling.

[0012] Preferably, in step (1), the organic solvent is selected from one or a combination of ethylene glycol methyl ether, acetic acid and ethylene glycol. In the specific embodiment of the application, ethylene glycol methyl ether is used as an example.

[0013] Preferably, in step (1), the chemical chelate stabilizer is one or a combination of acetylacetone and citric acid, and the molar ratio of the chemical chelate stabilizer to the cations in the multi-element isomorphically solid-solution BiFeO3 is 1:1. In the specific embodiment of the present application, acetylacetone is used as an example.

[0014] Preferably, in step (1), the stirring temperature is 25-80℃, and the stirring time is 0.5-1h.

[0015] Preferably, in step (1), the concentration of the multi-element isomorphically solid-solution BiFeO3 precursor sol is 0.01-0.5mol / L.

[0016] Preferably, in step (1), the multi-element isomorphically solid-solution BiFeO3 is BiFe 1 / 3 Sc 1 / 3 Ga 1 / 3 O3, Bi(Fe 1 / 3 Sc 1 / 3Ga 1 / 3 ) 0.99 Al 0.01 O3, Bi(Fe 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 O3, BiFe 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3, BiFe 1 / 4 Sc 1 / 4Ga 1 / 4 Al 1 / 4 O3, or BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3.

[0017] Preferably, in step (1), the raw materials are a combination of three or more of bismuth nitrate, iron nitrate, scandium nitrate, acetylacetone gallium, aluminum nitrate, manganese acetate, nickel nitrate, and titanium isopropoxide.

[0018] Preferably, in step (2), the spin coating method is first spin coating at a low rotation speed of 200-800r / min for 5s-20s, and then spin coating at a high rotation speed of 2000-8000r / min for 20-40s.

[0019] Preferably, in step (2), the initial curing time is 10s-2min.

[0020] Preferably, in step (3), the heating rate is 10-150℃ / s, the cooling rate is 0.5-3℃ / s, and the heat treatment atmosphere is air, oxygen or nitrogen.

[0021] Preferably, the thickness of the multi-element eutectic solid solution BiFeO3-based piezoelectric film is regulated by controlling the number of repetitions of step (2) and step (3), preferably 2-50 times.

[0022] Compared with the prior art, the present application has the following advantages:

[0023] (1) The present application realizes excellent self-polarization piezoelectric performance by preparing a multi-element eutectic solid solution BiFeO3-based ferroelectric film by a sol-gel method, and the preparation method is simple, and can realize precise control of stoichiometric ratio synthesis of oxides at room temperature, and fine multi-element eutectic solid solution modification of the film; (2) The multi-element eutectic solid solution BiFeO3-based piezoelectric film of the present application has excellent self-polarization piezoelectric coefficient (d 33 ), avoids depolarization in the high-temperature packaging process of MEMS, and can be used for the manufacture of piezoelectric microsensors, actuators, transducers, etc., and has very broad application prospects in the field of electronic material technology; (3) The method of the present application requires simple equipment, is easy to use, has high production efficiency, and is easy to realize industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a flowchart of the preparation method of the multi-element eutectic solid solution BiFeO3-based sol.

[0025] Figure 2 It is a flowchart of the preparation method of the multi-element eutectic solid solution BiFeO3-based film.

[0026] Figure 3 It is an X-ray diffraction pattern (a) of the multi-element eutectic solid solution BiFeO3-based film obtained in Examples 1-6 and a transmission electron microscope morphology stress analysis diagram (b) of the Bi(Fe 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 O3 film obtained in Example 3.

[0027] Figure 4 It is a cross-sectional morphology scanning diagram of the Bi(Fe 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 O3 film obtained in Example 3.

[0028] Figure 5The self-polarizing piezoelectric coefficient (d) of the multi-element equiproportional solid solution BiFeO3-based ferroelectric thin films obtained in Examples 1-6 is shown. 33 The curves (a)-(f) correspond to Examples 1-6, respectively.

[0029] Figure 6 XRD patterns and self-polarization piezoelectric coefficients (d) of the pure-phase BiFeO3 ferroelectric thin film obtained in Comparative Example 1 are shown. 33 ).

[0030] Figure 7 XRD patterns and self-polarization piezoelectric coefficients (di) of ordinary Sc-doped (non-multi-element equiproportional solid solution) BiFeO3-based ferroelectric thin films obtained in Comparative Example 2 are shown. 33 ). Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0032] This invention prepares a BiFeO3-based precursor sol by selectively adding three or more elements from Sc, Ga, Al, Mn, Ni, and Ti to the Fe sites of BiFeO3 through solid solution treatment. This precursor sol is then spin-coated and initially cured, and finally heat-treated to form a BFO-based thin film. With an increase in the number of elements in the solid solution, an Arrhenius phase appears in the BiFeO3-based thin film prepared by this method. This phase exists in the form of dislocations and can unidirectionally pin the electric dipoles in the film through dislocation stress, thereby causing excellent self-polarization properties in the obtained film. Furthermore, the solid solution of multiple elements increases the structural inhomogeneity and complicates the phase coexistence, allowing for precise control of a high piezoelectric coefficient d. 33 It can provide MEMS devices with ferroelectric thin films that have self-polarization characteristics, high voltage coefficient, and good reliability.

[0033] Example 1

[0034] Bismuth ferrite-based BiFe was prepared by solid solution treatment of Fe, Sc, and Ga in equal proportions at the B site. 1 / 3 Sc 1 / 3 Ga 1 / 3 The method for producing O3 ferroelectric thin films includes the following steps:

[0035] (1)BiFe 1 / 3 Sc 1 / 3 Ga 1 / 3Preparation of O3 precursor sol: 1.0673 g of bismuth nitrate (Bi(NO3)3.5H2O) was added to a beaker A containing 6 ml of ethylene glycol methyl ether (C3H8O2, 2 mole) and stirring was started at room temperature (25 °C) at a speed of 500 r / min; after complete dissolution, 0.2694 g of iron nitrate (Fe(NO3)3.9H2O) and 0.1660 g of scandium nitrate (Sc(NO3)3.xH2O) were added in sequence and stirring was continued until complete dissolution. Separately, 0.2447 g of gallium acetylacetonate (C 15 H 21 O6Ga) was added to a beaker B containing 4 ml of ethylene glycol methyl ether, the heating temperature was set at 45-70 °C and stirring was continued for 10 min until complete dissolution. After complete dissolution in beakers A and B and stirring for 30 min respectively, the two were mixed and 0.4025 ml of acetylacetone was added, stirring was continued at room temperature for 4 h, the solution was filtered and stored in a reagent bottle, and was left to stand at room temperature for aging for 48 h, to obtain a uniform and stable BiFe 1 / 3Sc 1 / 3 Ga 1 / 3 O3 precursor sol, with a sol concentration of 0.2 M and an excess of 10% of Bi element.

[0036] (2) Substrate thermal activation treatment: first, the Pt / Ti / SiO2 / Si substrate was washed and dried, and then was placed in a rapid annealing furnace for annealing treatment: the heating rate was 37.5 °C / s, annealing at 400 °C for 1 min, and then furnace cooling to room temperature.

[0037] (3) The BiFe 1 / 3 Sc 1 / 3 Ga 1 / 3 O3 precursor sol obtained in step (1) was spin-coated on the Pt / Ti / SiO2 / Si substrate of step (2) by using a spin coater, and the spin coating program was set as low speed 600 r / min, time 10 s, high speed 4000 r / min, spin coating time 30 s, to obtain a BiFe 1 / 3 Sc 1 / 3 Ga 1 / 3 O3 precursor sol film.

[0038] (4) The BiFe 1 / 3 Sc 1 / 3 Ga 1 / 3 O3 precursor sol film was placed in a rapid annealing furnace for heat treatment: the heating rate was 17.5 °C / s, drying at 200 °C for 2 min, pyrolysis at 400 °C for 5 min, and annealing at 550 °C for 5 min.

[0039] (5) Steps (3) and (4) were repeated 15 times, to obtain a BiFe 1 / 3 Sc 1 / 3 Ga1 / 3 O3 thin film.

[0040] Example 2

[0041] A BiFeO3 thin film was prepared by using Fe, Sc, Ga and Al four elements in equal proportion solid solution in B site, and the preparation method was substantially same as that of Example 1, except that 1% of aluminum nitrate (Al (NO3) 3·9H2O) was added in beaker A in step (1), and BiFeO3 thin film was prepared. 1 / 3 Sc 1 / 3Ga 1 / 3 ) 0.99 Al 0.01 O3 ferroelectric thin film. 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Al 0.01 O3 thin film.

[0042] Example 3

[0043] A BiFeO3 thin film was prepared by using Fe, Sc, Ga and Mn four elements in equal proportion solid solution in B site, and the preparation method was substantially same as that of Example 1, except that 1% of manganese acetate (MnC4H6O4·4H2O) was added in beaker A in step (1), and BiFeO3 thin film was prepared. 1 / 3 Sc 1 / 3Ga 1 / 3 ) 0.99 Mn 0.01 O3 ferroelectric thin film. 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 O3 thin film.

[0044] Example 4

[0045] A BiFeO3 thin film was prepared by using Fe, Sc, Ni and Ti four elements in equal proportion solid solution in B site, and the preparation method was substantially same as that of Example 1, except that 1% of aluminum nitrate (Al (NO3) 3·9H2O) was added in beaker A in step (1), and BiFeO3 thin film was prepared. 1 / 3 Sc 1 / 3 Ni 1 / 6 Ti 1 / 6O3 ferroelectric thin film.

[0046] (1) BiFeO3 thin film was prepared by using Fe, Sc, Ni and Ti four elements in equal proportion solid solution in B site, and the preparation method was substantially same as that of Example 1, except that 1% of aluminum nitrate (Al (NO3) 3·9H2O) was added in beaker A in step (1), and BiFeO3 thin film was prepared. 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3Preparation of O3 precursor sol: 1.0673 g of bismuth nitrate (Bi(NO3)3.5H2O) was added to a beaker A containing 6 ml of ethylene glycol methyl ether (C3H8O2, 2 mole) and stirring was started at room temperature (25 °C) at a speed of 500 r / min. After complete dissolution, 0.2694 g of iron nitrate (Fe(NO3)3.9H2O) and 0.1660 g of scandium nitrate (Sc(NO3)3.xH2O) were added successively and stirring was continued until complete dissolution. Separately, 0.0989 g of nickel nitrate (Ni(NO3)2.6H2O) was added to a beaker B containing 4 ml of ethylene glycol methyl ether, followed by maintaining the temperature at 25 °C and stirring for 2 min until complete dissolution, after which 0.1 ml of titanium isopropoxide (Ti[OCH(CH3)2]4) was added. After complete dissolution in beakers A and B and stirring for 30 min each, both were mixed and 0.4025 ml of acetylacetone was added. The solution was continuously stirred for 4 h at room temperature and then filtered and stored in a reagent bottle, which was kept at room temperature for aging for 48 h, to obtain a uniform and stable BiFe 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 precursor sol.

[0047] (2) Substrate thermal activation treatment: The Pt / Ti / SiO2 / Si substrate was first cleaned and dried, and then placed in a rapid annealing furnace for annealing treatment: the heating rate was 37.5 °C / s, annealing at 400 °C for 1 min, and then furnace cooling to room temperature.

[0048] (3) The BiFe 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 precursor sol obtained in step (1) was spin-coated on the Pt / Ti / SiO2 / Si substrate of step (2) using a spin coater, and the spin coating program was set as low speed 600 r / min, time 10 s, high speed 4000 r / min, spin coating time 30 s, to obtain a BiFe 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 precursor sol film.

[0049] (4) The BiFe 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3The O3 precursor sol film is placed in a rapid annealing furnace for heat treatment: heating rate 17.5°C / s, drying at 200°C for 2 minutes, pyrolysis at 400°C for 5 minutes, annealing at 550°C for 5 minutes.

[0050] (5) Repeat steps (3) and (4) 15 times to obtain a BiFe 1 / 3 Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 film with a thickness of about 250 nm.

[0051] Example 5

[0052] A BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4O3 ferroelectric thin film is prepared by equimolar solid solution of Fe, Sc, Ga and Al at B site, comprising the following steps:

[0053] (1) BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3 precursor sol preparation: 1.0673 g of bismuth nitrate (Bi(NO3)3·5H2O) is added to beaker A containing 6 ml of ethylene glycol methyl ether (C3H8O2, 2moe), stirring at room temperature (25°C) at a speed of 500 r / min, after complete dissolution, 0.2020 g of iron nitrate (Fe(NO3)3·9H2O), 0.1245 g of scandium nitrate (Sc(NO3)3·xH2O) and 0.1876 g of aluminum nitrate (Al(NO3)3·9H2O) are added in turn, and continue to stir until complete dissolution. In addition, 0.1835 g of gallium acetylacetonate (C 15 H 21 O6Ga) is added to beaker B containing 4 ml of ethylene glycol methyl ether, the heating temperature is set at 45-70°C and stirred for 10 min until complete dissolution. After complete dissolution in beakers A and B and stirring for 30 min respectively, mix the two and add 0.4025 ml of acetylacetone, continue to stir at room temperature for 4 h, filter the solution and seal in a reagent bottle, and let it stand at room temperature for 48 hours to obtain a uniform and stable BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3 precursor sol, wherein the sol concentration is 0.2M and the Bi element is 10% excess.

[0054] (2) Substrate thermal activation treatment: first clean and dry the Pt / Ti / SiO2 / Si substrate, then place it in a rapid annealing furnace for annealing treatment: heating rate 37.5°C / s, 400°C annealing for 1 minute, then furnace cooling to room temperature.

[0055] (3) Spin-coat the BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3 precursor sol on the Pt / Ti / SiO2 / Si substrate of step (2), set the spin-coat program as low speed 600 r / min, time 10 s, high speed 4000 r / min, spin-coat time 30 s, to obtain a BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3 precursor sol film.

[0056] (4) Place the BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3 precursor sol film in a rapid annealing furnace for thermal treatment: heating rate 17.5°C / s, 200°C drying for 2 minutes, 400°C pyrolysis for 5 minutes, 550°C annealing for 5 minutes.

[0057] (5) Repeat steps (3) and (4) 15 times to obtain a BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3 film with a thickness of about 250 nm.

[0058] Example 6

[0059] A method for preparing a bismuth ferrite-based BiFe 1 / 3 Ga 1 / 3 Ni 1 / 6 Ti 1 / 6O3 ferroelectric film by equimolar solid solution of four elements Fe, Ga, Ni and Ti at B site, comprising the following steps:

[0060] (1) BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3Preparation of O3 precursor sol: 1.0673 g of bismuth nitrate (Bi(NO3)3.5H2O) was added to a beaker A containing 6 ml of ethylene glycol methyl ether (C3H8O2, 2 mole) and stirring was started at room temperature (25 °C) at a speed of 500 r / min. After complete dissolution, 0.2694 g of iron nitrate (Fe(NO3)3.9H2O) and 0.0989 g of nickel nitrate (Ni(NO3)2.6H2O) were added in succession and stirring was continued until complete dissolution. Separately, 0.2447 g of gallium acetylacetonate (C 15 H 21 O6Ga) was added to a beaker B containing 4 ml of ethylene glycol methyl ether. The heating temperature was set at 45-70 °C and stirring was continued for 10 min until complete dissolution. Then, 0.1 ml of titanium isopropoxide (Ti[OCH(CH3)2]4) was added. After complete dissolution in beakers A and B and stirring for 30 min each, the two were mixed and 0.4025 ml of acetylacetone was added. Stirring was continued at room temperature for 4 h, after which the solution was filtered and stored in a reagent bottle, sealed and allowed to stand at room temperature for 48 h for aging. A uniform and stable BiFe 1 / 3 Ga 1 / 3 Ni 1 / 6 Ti 1 / 6 O3 precursor sol was obtained.

[0061] (2) Substrate thermal activation treatment: The Pt / Ti / SiO2 / Si substrate was first washed and dried, and then placed in a rapid annealing furnace for annealing treatment: the heating rate was 37.5 °C / s, annealing at 400 °C for 1 min, and then furnace cooling to room temperature.

[0062] (3) The BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 precursor sol obtained in step (1) was spin-coated on the Pt / Ti / SiO2 / Si substrate of step (2) using a spin coater, and the spin coating program was set as low speed 600 r / min, time 10 s, high speed 4000 r / min, spin coating time 30 s, to obtain a BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 precursor sol film.

[0063] (4) The BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3The O3 precursor sol film is placed in a rapid annealing furnace for heat treatment: heating rate 17.5℃ / s, drying at 200℃ for 2 minutes, pyrolysis at 400℃ for 5 minutes, annealing at 550℃ for 5 minutes.

[0064] (5) Repeat steps (3) and (4) 15 times to obtain a BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3 film.

[0065] Comparative Example 1

[0066] A method for preparing a pure-phase BiFeO3 polycrystalline piezoelectric film without self-polarization characteristics by using Fe as a single element at the B site, comprising the following steps:

[0067] (1) Preparation of BiFeO3 precursor solution: 1.0673 g of bismuth nitrate (Bi(NO3)3·5H2O) is added to a beaker containing 10 ml of ethylene glycol methyl ether (C3H8O2, 2moe), stirring at a speed of 500 r / min at room temperature (25℃), and after complete dissolution, 0.8081 g of iron nitrate (Fe(NO3)3·9H2O) is added, and stirring is continued until complete dissolution. 0.8406 g of citric acid is added, and after stirring at room temperature for 4 h, the solution is filtered and sealed in a reagent bottle for storage, and left to stand at room temperature for aging for 48 hours, to obtain a uniform and stable BiFeO3 precursor sol, with a sol concentration of 0.2 M and an excess of 10% Bi element.

[0068] (2) Heat activation treatment of the substrate: first wash and dry the Pt / Ti / SiO2 / Si substrate, and then perform annealing treatment in a rapid annealing furnace: heating rate 37.5℃ / s, annealing at 400℃ for 1 minute, and then cooling to room temperature with the furnace.

[0069] (3) The BiFeO3 precursor sol obtained in step (1) is spin-coated on the Pt / Ti / SiO2 / Si substrate of step (2), and the spin-coating program is set as low speed 600 r / min, time 10 s, high speed 4000 r / min, spin-coating time 30 s, to obtain a BiFeO3 precursor sol film.

[0070] (4) The obtained BiFeO3 precursor sol film is placed in a rapid annealing furnace for heat treatment: heating rate 17.5℃ / s, drying at 200℃ for 2 minutes, pyrolysis at 400℃ for 5 minutes, annealing at 550℃ for 5 minutes.

[0071] (5) Repeat step (4) 15 times to obtain a BiFeO3 film with a thickness of about 250 nm.

[0072] Comparative Example 2

[0073] BiFe2+ ferrite-based materials with non-self-polarizing properties were prepared by using Fe and Sc at the B site. 0.8 Sc 0.2 The method for producing O3 polycrystalline piezoelectric thin films includes the following steps:

[0074] (1)BiFe 0.8 Sc 0.2 Preparation of O3 precursor sol: 1.0673 g of bismuth nitrate (Bi(NO3)3·5H2O) was added to a beaker containing 10 ml of ethylene glycol methyl ether (C3H8O2, 2 mol). The mixture was stirred at 500 r / min at room temperature (25 °C) until completely dissolved. Then, 0.6465 g of ferric nitrate (Fe(NO3)3·9H2O) and 0.0997 g of scandium nitrate (Sc(NO3)3·xH2O) were added successively, and stirring continued until completely dissolved. Subsequently, 0.8826 g of citric acid was added, and the mixture was stirred at room temperature for 4 h. The solution was then filtered and sealed in a reagent bottle. After aging at room temperature for 48 h, a homogeneous and stable BiFe2O3 precursor sol was obtained. 0.8 Sc 0.2 O3 precursor sol, with a sol concentration of 0.2 M and Bi element in excess of 10%.

[0075] (2) Substrate thermal activation treatment: First, the Pt / Ti / SiO2 / Si substrate is washed and dried, and then placed in a rapid annealing furnace for annealing treatment: the heating rate is 37.5℃ / s, annealing at 400℃ for 1 minute, and then cooled to room temperature with the furnace.

[0076] (3) Take the BiFe obtained in step (1) 0.8 Sc 0.2 In step (2), the O3 precursor sol was spin-coated onto the Pt / Ti / SiO2 / Si substrate. The spin-coating program was set to a low spin speed of 600 r / min for 10 s and a high spin speed of 4000 r / min for 30 s, resulting in BiFe. 0.8 Sc 0.2 O3 precursor sol film.

[0077] (4) The obtained BiFe 0.8 Sc 0.2 The O3 precursor sol film was annealed in a rapid annealing furnace: heating rate 17.5℃ / s, drying at 200℃ for 2 minutes, pyrolysis at 400℃ for 5 minutes, and annealing at 550℃ for 5 minutes.

[0078] (5) Repeat step (4) 15 times to obtain BiFe with a thickness of approximately 250 nm. 0.8 Sc 0.2 O3 thin film.

[0079] Test case

[0080] (1) Characterization of phase structure and morphology of multi-element equal-proportion solid solution BiFeO3-based polycrystalline thin film

[0081] The crystal structure and cross-sectional morphology of the multi-element, equal-proportion solid-solution BiFeO3-based ferroelectric thin films prepared in Examples 1-6 were characterized. Specifically, X-ray diffraction analysis was performed on the BiFeO3-based thin films, and the results are as follows: Figure 3 As shown in Figure a, the labels in the figure represent the chemical formulas of each component, corresponding to Examples 1-6. Figure 3 The crystallization and phase information of the BiFeO3-based polycrystalline thin films in the examples are known. XRD results show that all samples are predominantly perovskite-type structures. In the perovskite phase, 100, 110, and 200 diffraction peaks are present. Meanwhile, the single 200 diffraction peak of pure BiFeO3 theoretically splits into multiple peaks, indicating the characteristic of localized multiphase coexistence. This experimental design method is currently a better way to optimize piezoelectric performance. In addition, XRD shows that these films have a distinct Arrhenius phase diffraction peak, along with a small amount of Si peaks and a strong (111) oriented Pt peak.

[0082] Bi(Fe) prepared in Example 3 was examined using transmission electron microscopy. 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 The cross-sectional analysis of O3 ferroelectric thin films is carried out by using a focused, narrow high-energy electron beam to scan the sample. Through the interaction between the beam and the material, various physical information is excited. This information is collected, amplified, and re-imaged to characterize the microscopic morphology and atomic arrangement of the material. Figure 3 Figure b shows the atomic image and superimposed stress distribution in a certain region. As can be seen from the figure, there are a large number of dislocation prestress concentration regions in the grown polycrystalline thin film and the multi-element equiproportional solid solution BiFeO3-based thin film. These dislocations and stresses have a pinning effect on the electric dipoles, which is the reason why these films have self-polarization characteristics. These dislocations correspond to the Arrhenius phase diffraction peaks shown in the XRD above.

[0083] Furthermore, the Bi(Fe) prepared in Example 3 was examined using a low-magnification transmission electron microscope. 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 Cross-sectional analysis of the O3 ferroelectric thin film revealed that the grown polycrystalline film had granular grains, and the thickness of the 15-layer multi-element, proportionally balanced BFO-based thin film was approximately 250 nm. The results are as follows...Figure 4 As shown.

[0084] (2) Self-polarizing piezoelectric properties of multi-element equiproportional solid solution BiFeO3-based polycrystalline thin films

[0085] Use d 33 The self-polarizing piezoelectric coefficient of the thin films prepared in Examples 1-6 was determined using a testing instrument. Specifically, the sample was placed on a stable testing platform, and a test metal column was continuously brought into contact with the sample at a linearly constant force (20g, 40g, 60g…). The mechanical stress on the sample film caused a piezoelectric effect, resulting in changes in the surface charge distribution of the piezoelectric material. By recording the charge changes detected on the surface, a charge change curve could be generated, and the piezoelectric coefficient d could be fitted. 33 The result is as follows Figure 5 As shown, the films prepared in Examples 1-6 exhibit similar characteristics, all possessing good self-polarization properties. The film corresponding to Example 3 has the largest amplitude, indicating that this Bi(Fe) composition... 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 O3 thin films exhibit the best piezoelectric properties, reaching 236 pC / N. Figure 5 It can be seen that, compared with commercial ScAlN (approximately 30 pC / N), the piezoelectric coefficients of the films prepared in Examples 1-6 are all improved to varying degrees, ensuring their good performance in sensor applications using piezoelectricity for both transmission and reception, enabling MEMS to utilize this excellent self-polarizing piezoelectric property for actuation or sensing functions.

[0086] (3) Characterization of phase composition and self-polarized piezoelectric properties of BiFeO3 polycrystalline thin films controlled by pure phase and conventional doping

[0087] Compared with Examples 1-6, Comparative Examples 1 and 2 prepared pure-phase BiFeO3 polycrystalline thin films and ordinary Sc-doped (non-multi-element equiproportional solid solution) BiFeO3-based ferroelectric thin films, and characterized their crystal structures and self-polarizing piezoelectric properties. The results are as follows: Figures 6-7 As shown, from Figure 6 As can be seen from samples a and 7a, both comparative samples are primarily perovskite-type structures. Within the perovskite phase, diffraction peaks at 100, 110, and 200 are all present. However, unlike multi-element, proportionally dissolved BiFeO3-based ferroelectric films, the 200 diffraction peak is a theoretical single peak of the R phase, lacking the characteristic of phase coexistence. Furthermore, due to the absence of Arrhenius phase faults, this type of film does not possess self-polarizing properties. 33 No valid signal was detected during the test.

[0088] The above merely describes the preferred embodiments of the present application, and the present application is not limited to the above embodiments. It can be understood that other improvements and changes directly derived or thought by those skilled in the art without departing from the spirit and concept of the present application shall be considered to be within the protection scope of the present application.

Claims

1. A method for preparing high self-polarization piezoelectric performance bismuth ferrite-based thin films by multi-element isometric solid solution, characterized in that, The method comprises the following steps: (1) preparing sol: according to the stoichiometric ratio of multi-element isomorphous BiFeO3, raw materials are dissolved in organic solvent, then chemical chelating stabilizer is added, stirring until mixed uniformly, filtering, sealing, standing at room temperature, obtaining clear and transparent, uniform and stable multi-element isomorphous BiFeO3 precursor sol, the multi-element isomorphous BiFeO3 is BiFeO3-based compound in which B site is replaced by three or more than three kinds of cations, the replacement mode is that all replacement cations are replaced in equal proportion or according to the weight stoichiometric ratio, and the replacement cations are selected from three or more than three kinds of cations of Fe 3+ , Sc 3+ , Ga 3+ , Al 3+ , Mn 3+ , Ni 2+ and Ti 4+ ; (2) glue spinning film: spin coating the multi-element eutectic BiFeO3 precursor sol on the substrate to form a film, and then the substrate coated with the multi-element eutectic BiFeO3 precursor sol is initially solidified at 150±5℃ to obtain a multi-element eutectic BiFeO3 precursor sol film; (3) heat treatment: the substrate coated with the multi-element eutectic BiFeO3 precursor sol film in step (3) is heat treated, first dried at 120℃~300℃ for 30s~2min, then pyrolyzed at 200℃~500℃ for 1~5min, and finally annealed at 500℃~900℃ for 1~15min, and the multi-element eutectic BiFeO3-based piezoelectric thin film is obtained after cooling.

2. The method of claim 1, wherein, In step (1), the organic solvent is selected from one or a combination of ethylene glycol methyl ether, acetic acid and ethylene glycol, the chemical chelating stabilizer is one or a combination of acetylacetone and citric acid, and the molar ratio of the chemical chelating stabilizer to the cation in the multi-element eutectic BiFeO3 is 1:

1.

3. The method of claim 1, wherein, In step (1), the stirring temperature is 25~80℃, the stirring time is 0.5~1h, and the concentration of the multi-element eutectic BiFeO3 precursor sol is 0.01~0.5 mol / L.

4. The method of claim 1, wherein, In step (1), the multi-element isomorphically solid-solved BiFeO3 is BiFe 1 / 3 Sc 1 / 3 Ga 1 / 3 O3, Bi(Fe 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Al 0.01 O3, Bi(Fe 1 / 3 Sc 1 / 3 Ga 1 / 3 ) 0.99 Mn 0.01 O3, BiFe 1 / 3Sc 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3, BiFe 1 / 4 Sc 1 / 4 Ga 1 / 4 Al 1 / 4 O3, or BiFe 1 / 3 Ga 1 / 3 (Ni 0.5 Ti 0.5 ) 1 / 3 O3.

5. The method of claim 1, wherein, In step (1), the raw materials are a combination of three or more of bismuth nitrate, iron nitrate, scandium nitrate, gallium acetylacetate, aluminum nitrate, manganese acetate, nickel nitrate and titanium isopropoxide.

6. The method of claim 1, wherein, In step (2), the spin coating method is first spin coating at a low speed of 200~800r / min for 5s~20s, and then spin coating at a high speed of 2000~8000r / min for 20~40s.

7. The method of claim 1, wherein, In step (2), the initial solidification time is 10s~2min.

8. The method of claim 1, wherein, In step (3), the heating rate is 10~150℃ / s, the cooling rate is 0.5~3℃ / s, and the heat treatment atmosphere is air, oxygen or nitrogen.

9. The method of claim 1, wherein, The thickness of the multi-element eutectic BiFeO3-based piezoelectric thin film is controlled by controlling the number of repetitions of steps (2) and (3), and the number of repetitions is 2~50 times.

10. A high self-polarization piezoelectric performance bismuth ferrite-based thin film prepared by the method of any one of claims 1~9.

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