High electro-strained sodium bismuth titanate-based lead-free piezoelectric thin film and method of manufacturing the same

Abstract

The application provides a high-electric-field-induced-strain sodium bismuth titanate-based lead-free piezoelectric film, which has a general chemical formula of 0.9212(Bi 0.5 Na 0.5 )TiO3-0.0588BaTiO3-0.02La 0.7 Sr 0.3 MnO3. The application also provides a preparation method of the high-electric-field-induced-strain sodium bismuth titanate-based lead-free piezoelectric film, which comprises the following steps: S1, according to the stoichiometric ratio of the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film, bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate and strontium acetate are weighed and dissolved in acetic acid to prepare a first solution; S2, according to the stoichiometric ratio of the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film, acetylacetone, tetrabutyl titanate and manganese acetate tetrahydrate are weighed and dissolved in ethylene glycol methyl ether to prepare a second solution; S3, the first solution and the second solution are mixed to obtain a mixed solution, and the concentration and the pH value of the mixed solution are adjusted to prepare a precursor solution; S4, a substrate is cleaned and dried; and S5, the precursor solution is coated on the substrate to prepare the high-electric-field-induced-strain sodium bismuth titanate-based lead-free piezoelectric film.

Description

Technical Field

[0001] The present invention belongs to the field of electronic functional materials and devices, and in particular relates to a sodium bismuth titanate-based lead-free piezoelectric film with high electro-induced strain and a preparation method thereof. Background Art

[0002] The future information society will require a variety of functional devices, such as micro-actuators and micro-ultrasonic transducers, to achieve functions such as energy conversion, driving, and sensing. Piezoelectric thin film materials have attracted much attention from researchers due to their excellent comprehensive ferroelectric, piezoelectric, and electro-optical properties. Currently, the most widely used piezoelectric films are lead-containing. However, the preparation and recycling of piezoelectric films with excessive lead content can cause serious damage to the environment and humans. Although lead bans in commercial electronic products are gradually being implemented, lead-based piezoelectric materials still have an irreplaceable position in some high-tech and aerospace fields. Therefore, achieving greater electrical strain in piezoelectric materials, especially in lead-free materials, is a key requirement for driving the application of lead-free materials.

[0003] Among the lead-free piezoelectric materials, sodium bismuth titanate (Bi 0.5 Na 0.5 )TiO3 (BNT)-based materials have attracted extensive research interest due to their large strain response and high inverse piezoelectric coefficient. For example, by introducing a second phase or a third phase to form a binary or ternary system, it has excellent electrostrain at its quasi-modular phase boundary (Adv. Mater. 2016, 28, 574–578.). In addition, most microelectronic devices are integrated on silicon substrates. In order to combine piezoelectric films with other functional materials and develop new multifunctional devices, it is very necessary to directionally grow piezoelectric films on Si substrates. For this strategy, some buffer layers must be used. Lanthanum nickelate LaNiO3 (LNO) is a very attractive buffer layer candidate with a pseudo-cubic lattice parameter (0.384nm), which matches most ferroelectric perovskite materials. Based on theoretical calculations, the (001) textured 0.94 (Bi 0.5 Na 0.5)TiO3-0.06BaTiO3 (BNTBT6) film, not only the piezoelectric performance is improved, but also the depolarization temperature Td is increased. It can be seen that the (001) texture structure and the in-plane tensile strain caused by the bottom LNO layer can stabilize the low-symmetry ferroelectric order and improve the piezoelectricity and thermal stability of the BNTBT6 film (Adv. Electron. Mater., 2018, 4, 1800351.). However, as the thickness of the film increases, the tensile effect of the bottom LNO layer will weaken, and the piezoelectric performance of the film will also weaken. However, there is no relevant report in the prior art on the thickness scale at which piezoelectric films can exhibit excellent electrostrictive properties. In addition, although the sodium bismuth titanate-barium titanate component piezoelectric film has strong ferroelectricity, its large leakage current and low Curie temperature greatly limit its application in devices. Summary of the Invention

[0004] The present invention is made to solve the above problems, and its purpose is to provide a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain and a preparation method thereof.

[0005] The present invention provides a high electrostrain sodium bismuth titanate-based lead-free piezoelectric film, which has the following characteristics: the chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film is: 0.9212 (Bi 0.5 Na 0.5 )TiO3-0.0588BaTiO3-0.02La 0.7 Sr 0.3 MnO3.

[0006] The sodium bismuth titanate-based lead-free piezoelectric film with high electro-strain provided by the present invention may also have the following characteristics: wherein the sodium bismuth titanate-based lead-free piezoelectric film has a thickness ranging from 50 nm to 500 nm.

[0007] The present invention also provides a method for preparing a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain, which has the following characteristics: Step S1, weighing bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate in acetic acid according to the stoichiometric ratio of the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film to prepare a first solution;

[0008] Step S2, weighing acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate in a stoichiometric ratio according to the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film and dissolving them in ethylene glycol methyl ether to prepare a second solution;

[0009] Step S3, mixing the first solution and the second solution to obtain a mixed solution, and adjusting the concentration and pH of the mixed solution to obtain a precursor solution;

[0010] Step S4, cleaning the substrate and drying the substrate;

[0011] Step S5: coating the precursor solution on the substrate to prepare a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0012] In the preparation method of the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention, it can also have the following characteristics: in step S1, bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate are dissolved in acetic acid, stirred and heated to boiling, and maintained for 20 minutes to 30 minutes to obtain a first solution.

[0013] In the preparation method of the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention, it can also have the following characteristics: in step S2, acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate are dissolved in ethylene glycol methyl ether, stirred and heated to 40°C to 60°C, and stirring is maintained for 20 minutes to 30 minutes to obtain a second solution.

[0014] In the preparation method of the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention, it can also have the following characteristics: in step S3, the concentration of the mixed solution is adjusted using acetic acid, and the pH of the mixed solution is adjusted using ammonia water. After the adjustment is completed, the mixed solution is stirred at 40°C to 60°C for 200 minutes to 400 minutes to obtain a precursor solution.

[0015] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention may also have the following characteristics: in step S3, the concentration of the mixed solution is adjusted to 0.1 mol / L to 0.4 mol / L, and the pH of the mixed solution is adjusted to a pH value of 4 to 6.

[0016] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention may also have the following feature: the substrate is a LaNiO3 / Pt / Ti / SiO2 / Si substrate.

[0017] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention may also have the following characteristics: in step S4, the substrate is ultrasonically cleaned for 20 minutes using acetone, deionized water and ethanol respectively, and then the substrate is blown dry using high-purity nitrogen.

[0018] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain provided by the present invention may also have the following characteristics: step S5 further includes the following sub-steps:

[0019] Step S5-1, spin-coating a layer of the precursor solution on the substrate at a speed of 4000 rpm for 30 seconds to obtain a thin film;

[0020] Step S5-2, placing the film in a tube furnace and treating it at 200°C for 5 minutes, 450°C for 5 minutes, and 700°C for 5 minutes in sequence;

[0021] Step S5-3, repeating steps S5-1 and S5-2 until a film of desired thickness is obtained, and finally annealing at 600°C to 750°C for 30 minutes to 60 minutes to obtain a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0022] Functions and effects of the invention

[0023] According to the present invention, the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain is prepared by doping lanthanum strontium manganate into the sodium bismuth titanate-barium titanate film, thereby reducing the leakage current of the sodium bismuth titanate-barium titanate film and weakening domain pinning, thereby increasing the polarization strength of the film and enhancing the electrostrain characteristics. Furthermore, the preparation method of the present invention is not only simple in process, but also capable of controlling the thickness of the prepared sodium bismuth titanate-based lead-free piezoelectric film by repeated spin coating and heat treatment, thereby achieving control of the film structure by the lanthanum nickelate substrate, and further improving the electrostrain performance of the sodium bismuth titanate-based lead-free piezoelectric film. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Flowchart of a method for preparing a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain in an embodiment of the present invention;

[0025] Figure 2 is a cross-sectional scanning electron microscope image of the sodium bismuth titanate-based lead-free piezoelectric film prepared in Example 1 of the present invention;

[0026] Figure 3 The X-ray diffraction patterns of sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 of the present invention and the comparative example are shown;

[0027] Figure 4 The displacement generated by the electrostriction of the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 of the present invention and the comparative example;

[0028] Figure 5 These are the electric field-strain curves of the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 of the present invention and the comparative example. DETAILED DESCRIPTION

[0029] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the following examples and accompanying drawings specifically illustrate the high electrostrain sodium bismuth titanate-based lead-free piezoelectric film and its preparation method of the present invention.

[0030] <Example 1>

[0031] Figure 1 This is a flow chart of the method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain in Example 1 of the present invention.

[0032] like Figure 1 As shown, the method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain in this embodiment includes the following steps:

[0033] Step S1, according to the stoichiometric ratio of the general chemical formula of sodium bismuth titanate-based lead-free piezoelectric film, bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate are weighed and dissolved in acetic acid to prepare a first solution, and the specific operation is as follows:

[0034] According to the stoichiometric ratio of the chemical formula of sodium bismuth titanate-based lead-free piezoelectric film, bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate and strontium acetate are weighed. Since bismuth and sodium elements evaporate more violently at high temperatures, bismuth nitrate and sodium acetate are weighed in excess of 5%. The weighed drugs are dissolved in acetic acid, stirred and heated to boiling for 20 minutes to prepare a first solution.

[0035] Step S2, according to the stoichiometric ratio of the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film, acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate are weighed and dissolved in ethylene glycol methyl ether to prepare a second solution, and the specific operation is as follows:

[0036] Acetylacetone, tetrabutyl titanate and manganese acetate tetrahydrate were weighed and dissolved in ethylene glycol methyl ether in a stoichiometric ratio according to the general chemical formula of sodium bismuth titanate-based lead-free piezoelectric film. The mixture was stirred and heated to 50° C. for 20 minutes to prepare a second solution.

[0037] Step S3, mixing the first solution and the second solution to obtain a mixed solution, adjusting the concentration and pH of the mixed solution to obtain a precursor solution, the specific operation is as follows:

[0038] The first solution and the second solution were mixed to obtain a mixed solution, ammonia water was added to adjust the pH value until the solute was completely dissolved, acetic acid was added to adjust the concentration to 0.15 mol / L, and the mixture was stirred at 50° C. for 300 minutes to obtain a precursor solution.

[0039] Step S4: cleaning the substrate and drying it. The specific operations are as follows:

[0040] The LaNiO3 / Pt / Ti / SiO2 / Si substrate was cut into squares with a side length of 10 mm, cleaned with acetone, deionized water and ethanol for 20 minutes respectively, and then blown dry with high-purity nitrogen gas.

[0041] Step S5: coating the precursor solution on the substrate to prepare a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0042] Step S5 also includes the following sub-steps:

[0043] Step S5-1, spin-coating a layer of precursor solution on the substrate at a rotation speed of 4000 rpm for 30 seconds to obtain a thin film.

[0044] Step S5-2: placing the film in a tube furnace and treating it at 200°C for 5 minutes, 450°C for 5 minutes, and 700°C for 5 minutes.

[0045] In step S5-3, steps S5-1 and S5-2 are repeated 13 times to obtain a film with a thickness of 250 nm, and finally annealed at 700° C. for 45 minutes to obtain a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0046] In this embodiment, spin coating was repeated 13 times to prepare a 250 nm thick sodium bismuth titanate-based lead-free piezoelectric film. After the preparation was completed, an electrode with a diameter of 1 mm was plated on the surface of the sodium bismuth titanate-based lead-free piezoelectric film using a sputtering apparatus.

[0047] Figure 2 This is a cross-sectional scanning electron microscope image of the sodium bismuth titanate-based lead-free piezoelectric film prepared in Example 1 of the present invention.

[0048] like Figure 2 As shown, the surface of the sodium bismuth titanate-based lead-free piezoelectric film prepared in this embodiment is flat and smooth, without obvious pores, and has a thickness of about 250 nanometers, indicating that the preparation method of the present invention has good operability. Not only is the process simple, but the thickness of the sodium bismuth titanate-based lead-free piezoelectric film can also be controlled by repeated spin coating and heat treatment.

[0049] <Example 2>

[0050] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain in this embodiment comprises the following steps:

[0051] Step S1, weighing bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate according to the stoichiometric ratio of the chemical formula of sodium bismuth titanate-based lead-free piezoelectric film. Since bismuth and sodium elements evaporate more violently at high temperatures, bismuth nitrate and sodium acetate are weighed in excess of 5%, and the weighed drugs are dissolved in acetic acid, stirred and heated to boiling for 20 minutes to obtain a first solution.

[0052] Step S2: according to the stoichiometric ratio of the general chemical formula of sodium bismuth titanate-based lead-free piezoelectric film, acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate are weighed and dissolved in ethylene glycol methyl ether, stirred and heated to 50° C., and stirred for 20 minutes to prepare a second solution.

[0053] In step S3, the first solution and the second solution are mixed to obtain a mixed solution, aqueous ammonia is added to adjust the pH value until the solute is completely dissolved, acetic acid is added to adjust the concentration to 0.15 mol / L, and the mixture is stirred at 50° C. for 300 minutes to obtain a precursor solution.

[0054] Step S4: Cut the LaNiO3 / Pt / Ti / SiO2 / Si substrate into squares with a side length of 10 mm, wash them with acetone, deionized water and ethanol for 20 minutes respectively, and then blow dry the substrate with high-purity nitrogen gas.

[0055] Step S5: coating the precursor solution on the substrate to prepare a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0056] Step S5 also includes the following sub-steps:

[0057] Step S5-1, spin-coating a layer of precursor solution on the substrate at a rotation speed of 4000 rpm for 30 seconds to obtain a thin film.

[0058] Step S5-2: placing the film in a tube furnace and treating it at 200°C for 5 minutes, 450°C for 5 minutes, and 700°C for 5 minutes.

[0059] In step S5-3, steps S5-1 and S5-2 are repeated three times to obtain a film with a thickness of 60 nm, and finally annealed at 700° C. for 45 minutes to obtain a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0060] In this embodiment, spin coating was repeated three times to prepare a sodium bismuth titanate-based lead-free piezoelectric film with a thickness of 60 nanometers. After the preparation was completed, an electrode with a diameter of 1 mm was plated on the surface of the sodium bismuth titanate-based lead-free piezoelectric film using a sputtering device.

[0061] <Example 3>

[0062] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain in this embodiment comprises the following steps:

[0063] Step S1, weighing bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate according to the stoichiometric ratio of the chemical formula of sodium bismuth titanate-based lead-free piezoelectric film. Since bismuth and sodium elements evaporate more violently at high temperatures, bismuth nitrate and sodium acetate are weighed in excess of 5%, and the weighed drugs are dissolved in acetic acid, stirred and heated to boiling for 20 minutes to obtain a first solution.

[0064] Step S2: according to the stoichiometric ratio of the general chemical formula of sodium bismuth titanate-based lead-free piezoelectric film, acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate are weighed and dissolved in ethylene glycol methyl ether, stirred and heated to 50° C., and stirred for 20 minutes to prepare a second solution.

[0065] In step S3, the first solution and the second solution are mixed to obtain a mixed solution, aqueous ammonia is added to adjust the pH value until the solute is completely dissolved, acetic acid is added to adjust the concentration to 0.15 mol / L, and the mixture is stirred at 50° C. for 300 minutes to obtain a precursor solution.

[0066] Step S4: Cut the LaNiO3 / Pt / Ti / SiO2 / Si substrate into squares with a side length of 10 mm, wash them with acetone, deionized water and ethanol for 20 minutes respectively, and then blow dry the substrate with high-purity nitrogen gas.

[0067] Step S5: coating the precursor solution on the substrate to prepare a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0068] Step S5 also includes the following sub-steps:

[0069] Step S5-1, spin-coating a layer of precursor solution on the substrate at a rotation speed of 4000 rpm for 30 seconds to obtain a thin film.

[0070] Step S5-2: placing the film in a tube furnace and treating it at 200°C for 5 minutes, 450°C for 5 minutes, and 700°C for 5 minutes.

[0071] In step S5-3, steps S5-1 and S5-2 are repeated 7 times to obtain a film with a thickness of 134 nm, and finally annealed at 700° C. for 45 minutes to obtain a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0072] In this embodiment, spin coating was repeated seven times to prepare a sodium bismuth titanate-based lead-free piezoelectric film with a thickness of 134 nanometers. After the preparation was completed, an electrode with a diameter of 1 millimeter was plated on the surface of the sodium bismuth titanate-based lead-free piezoelectric film using a sputtering device.

[0073] <Example 4>

[0074] The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain in this embodiment comprises the following steps:

[0075] Step S1, weighing bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate according to the stoichiometric ratio of the chemical formula of sodium bismuth titanate-based lead-free piezoelectric film. Since bismuth and sodium elements evaporate more violently at high temperatures, bismuth nitrate and sodium acetate are weighed in excess of 5%, and the weighed drugs are dissolved in acetic acid, stirred and heated to boiling for 20 minutes to obtain a first solution.

[0076] Step S2: according to the stoichiometric ratio of the general chemical formula of sodium bismuth titanate-based lead-free piezoelectric film, acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate are weighed and dissolved in ethylene glycol methyl ether, stirred and heated to 50° C., and stirred for 20 minutes to prepare a second solution.

[0077] In step S3, the first solution and the second solution are mixed to obtain a mixed solution, aqueous ammonia is added to adjust the pH value until the solute is completely dissolved, acetic acid is added to adjust the concentration to 0.15 mol / L, and the mixture is stirred at 50° C. for 300 minutes to obtain a precursor solution.

[0078] Step S4: Cut the LaNiO3 / Pt / Ti / SiO2 / Si substrate into squares with a side length of 10 mm, wash them with acetone, deionized water and ethanol for 20 minutes respectively, and then blow dry the substrate with high-purity nitrogen gas.

[0079] Step S5: coating the precursor solution on the substrate to prepare a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0080] Step S5 also includes the following sub-steps:

[0081] Step S5-1, spin-coating a layer of precursor solution on the substrate at a rotation speed of 4000 rpm for 30 seconds to obtain a thin film.

[0082] Step S5-2: placing the film in a tube furnace and treating it at 200°C for 5 minutes, 450°C for 5 minutes, and 700°C for 5 minutes.

[0083] In step S5-3, steps S5-1 and S5-2 are repeated 26 times to obtain a film with a thickness of 500 nm, and finally annealed at 700° C. for 45 minutes to obtain a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0084] In this embodiment, spin coating was repeated 26 times to prepare a sodium bismuth titanate-based lead-free piezoelectric film with a thickness of 500 nanometers. After the preparation was completed, an electrode with a diameter of 1 millimeter was plated on the surface of the sodium bismuth titanate-based lead-free piezoelectric film using a sputtering device.

[0085] <Comparative Example>

[0086] In this comparative example, lanthanum manganate La was not doped 0.7 Sr 0.3 MnO3, the chemical formula of the prepared sodium bismuth titanate-based lead-free piezoelectric film is 0.94 (Bi 0.5 Na 0.5 )TiO3-0.06BaTiO3, the preparation process is as follows:

[0087] Step S1, according to the chemical formula 0.94(Bi 0.5 Na 0.5)TiO3-0.06BaTiO3 stoichiometric ratio of bismuth nitrate, sodium acetate, and barium acetate were weighed. Since bismuth and sodium elements volatilize more violently at high temperatures, bismuth nitrate and sodium acetate were weighed in excess of 5%. The weighed drugs were dissolved in acetic acid, stirred and heated to boiling for 20 minutes to prepare a first solution.

[0088] Step S2, according to the chemical formula 0.94(Bi 0.5 Na 0.5 Acetylacetone and tetrabutyl titanate were weighed and dissolved in ethylene glycol methyl ether in a stoichiometric ratio of the chemical formula of )TiO3-0.06BaTiO3, and the mixture was stirred and heated to 50°C, and stirred for 20 minutes to prepare a second solution.

[0089] In step S3, the first solution and the second solution are mixed to obtain a mixed solution, aqueous ammonia is added to adjust the pH value until the solute is completely dissolved, acetic acid is added to adjust the concentration to 0.15 mol / L, and the mixture is stirred at 50° C. for 300 minutes to obtain a precursor solution.

[0090] Step S4: Cut the LaNiO3 / Pt / Ti / SiO2 / Si substrate into squares with a side length of 10 mm, wash them with acetone, deionized water and ethanol for 20 minutes respectively, and then blow dry the substrate with high-purity nitrogen gas.

[0091] Step S5: coating the precursor solution on the substrate to prepare a sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

[0092] Step S5 also includes the following sub-steps:

[0093] Step S5-1, spin-coating a layer of precursor solution on the substrate at a rotation speed of 4000 rpm for 30 seconds to obtain a thin film.

[0094] Step S5-2: placing the film in a tube furnace and treating it at 200°C for 5 minutes, 450°C for 5 minutes, and 700°C for 5 minutes.

[0095] In step S5-3, step S5-1 and step S5-2 are repeated 13 times to obtain a film with a thickness of 250 nm, and finally annealed at 700° C. for 45 minutes to obtain a sodium bismuth titanate-based lead-free piezoelectric film.

[0096] In this comparative example, spin coating was repeated 13 times to produce a 250-nanometer-thick, undoped lanthanum manganate-doped sodium bismuth titanate-based lead-free piezoelectric film. Following preparation, a 1-mm-diameter electrode was deposited on the surface of the sodium bismuth titanate-based lead-free piezoelectric film using a sputtering apparatus.

[0097] Figure 3It is the X-ray diffraction pattern of the sodium bismuth titanate-based lead-free piezoelectric film prepared in Examples 1 to 4 of the present invention and the comparative example.

[0098] like Figure 3 As shown, the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 and the comparative example all have a typical perovskite structure, without obvious impurity phases, and the films have a preferred orientation of (001).

[0099] An alternating electric field of 500 kV / cm was applied to the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 and the comparative example to test the displacement change caused by electrostriction. Figure 4 It is the displacement caused by electrostriction of the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 of the present invention and the comparative example.

[0100] like Figure 4 As shown, the displacement generated by the electrostriction of the sodium bismuth titanate-based lead-free piezoelectric film with a thickness of 60 nm prepared in Example 2 is slightly lower than the displacement generated by the electrostriction of the sodium bismuth titanate-based lead-free piezoelectric film prepared in the comparative example. The displacement generated by the electrostriction of the sodium bismuth titanate-based lead-free piezoelectric film prepared in Examples 1, 3, and 4 with a thickness of 2% La 0.7 Sr 0.3 MnO3 0.9212(Bi 0.5 Na 0.5 )TiO3-0.0588BaTiO3-0.02La 0.7 Sr 0.3 The displacements produced by the electrostriction of MnO3 films are significantly higher than 0.94 (Bi 0.5 Na 0.5 )The displacement caused by the electrostriction of the TiO3-0.06BaTiO3 film is significantly increased with the increase of the thickness of the sodium bismuth titanate-based lead-free piezoelectric film.

[0101] An electric field of 0 kV / cm to 500 kV / cm was applied to the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 and the comparative example, and the strain change with increasing electric field intensity was tested. Figure 5 These are the electric field-strain curves of the sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1 to 4 of the present invention and the comparative example.

[0102] like Figure 5 As shown in the figure, the electrostrain characteristics of the sodium bismuth titanate-based lead-free piezoelectric film with a thickness of 60 nanometers prepared in Example 2 are slightly lower than those of the sodium bismuth titanate-based lead-free piezoelectric film with a thickness of 250 nanometers prepared in the comparative example. 0.5 Na 0.5)TiO3-0.06BaTiO3 film electrostrain properties, the electrostrain properties of sodium bismuth titanate-based lead-free piezoelectric films prepared in Examples 1, 3, and 4 are better than those of 0.94 (Bi 0.5 Na 0.5 )Electrostrain properties of TiO3-0.06BaTiO3 thin films.

[0103] Furthermore, when the prepared sodium bismuth titanate-based lead-free piezoelectric film has a thickness of 250 nanometers, it can produce a high strain value of 0.64% under an applied electric field of 500 kV / cm. This indicates that when the film thickness is low, the strong substrate binding effect hinders the film vibration, affecting the film's electrostrain performance. In addition, when the film thickness is too high, the film's (001) preferred orientation structure is weakened, and domain pinning is enhanced, which also leads to a decrease in the film's electrostrain performance. Therefore, when preparing sodium bismuth titanate-based lead-free piezoelectric film, it is necessary to control the film thickness within an appropriate range so that the LaNiO3 / Pt / Ti / SiO2 / Si substrate as the substrate can effectively enhance the piezoelectric performance of the sodium bismuth titanate-based lead-free piezoelectric film.

[0104] Functions and Effects of the Embodiments

[0105] According to the comparison of Examples 1 to 4 with the comparative example, the high electrostrain sodium bismuth titanate-based lead-free piezoelectric film of the present invention can reduce the leakage current of the sodium bismuth titanate-barium titanate film and weaken the domain pinning by doping lanthanum strontium manganate into the sodium bismuth titanate-barium titanate film, thereby improving the polarization strength of the film and enhancing the electrostrain characteristics.

[0106] According to the comparison of Examples 1 to 4, it can be seen that the thickness of the sodium bismuth titanate-based lead-free piezoelectric film of the present invention is related to the electrostrain performance. The preparation method of the present invention can control the thickness of the sodium bismuth titanate-based lead-free piezoelectric film, and realize the control of the film structure by the lanthanum nickelate substrate. Good electrostrain performance can be obtained when the film thickness is 50 nanometers to 500 nanometers, especially when the film thickness is 250 nanometers, the most excellent electrostrain performance can be obtained.

Claims

1. A high electrostrain sodium bismuth titanate-based lead-free piezoelectric film, characterized in that: The general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film is: 0.9212(Bi 0.5 Na 0.5 )TiO3-0.0588BaTiO3-0.02La 0.7 Sr 0.3 MnO3, When the thickness of the sodium bismuth titanate-based lead-free piezoelectric film reaches 250 nm, the strain value of the sodium bismuth titanate-based lead-free piezoelectric film tested under an electric field of 500 kV / cm is 0.64%. The method for preparing the sodium bismuth titanate-based lead-free piezoelectric film comprises the following steps: Step S1, weighing bismuth nitrate, sodium acetate, barium acetate, lanthanum acetate, and strontium acetate in acetic acid according to the stoichiometric ratio of the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film to prepare a first solution; Step S2, weighing acetylacetone, tetrabutyl titanate, and manganese acetate tetrahydrate in a stoichiometric ratio according to the general chemical formula of the sodium bismuth titanate-based lead-free piezoelectric film and dissolving them in ethylene glycol methyl ether to prepare a second solution; Step S3, mixing the first solution and the second solution to obtain a mixed solution, and adjusting the concentration and pH of the mixed solution to obtain a precursor solution; Step S4, cleaning the substrate and drying the substrate; Step S5: coating the precursor solution on the substrate to prepare the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

2. The high electrostrain sodium bismuth titanate-based lead-free piezoelectric film according to claim 1, characterized in that: in, In step S1, the bismuth nitrate, the sodium acetate, the barium acetate, the lanthanum acetate, and the strontium acetate are dissolved in the acetic acid, stirred, and heated to boiling for 20 to 30 minutes to prepare the first solution.

3. The sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain according to claim 1, characterized in that: in, In step S2, the acetylacetone, the tetrabutyl titanate, and the manganese acetate tetrahydrate are dissolved in the ethylene glycol methyl ether, stirred and heated to 40° C. to 60° C., and stirred for 20 minutes to 30 minutes to prepare the second solution.

4. The sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain according to claim 1, wherein: in, In step S3, the concentration of the mixed solution is adjusted using acetic acid, and the pH of the mixed solution is adjusted using ammonia water. After the adjustment, the mixed solution is stirred at 40° C. to 60° C. for 200 minutes to 400 minutes to prepare the precursor solution.

5. The sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain according to claim 1, wherein: in, In step S3, the concentration of the mixed solution is adjusted to 0.1 mol / L to 0.4 mol / L, and the pH of the mixed solution is adjusted to a pH value of 4 to 6.

6. The sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain according to claim 1, wherein: in, The substrate is a LaNiO3 / Pt / Ti / SiO2 / Si substrate.

7. The sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain according to claim 1, characterized in that: in, In step S4, the substrate is ultrasonically cleaned with acetone, deionized water and ethanol for 20 minutes respectively, and then the substrate is blown dry with high-purity nitrogen.

8. The sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain according to claim 1, characterized in that: in, Step S5 also includes the following sub-steps: Step S5-1, spin-coating a layer of the precursor solution on the substrate at a rotation speed of 4000 rpm for 30 seconds to obtain a thin film; Step S5-2, placing the film in a tube furnace and treating it at 200° C. for 5 minutes, 450° C. for 5 minutes, and 700° C. for 5 minutes in sequence; Step S5-3, repeating steps S5-1 and S5-2 until the film of the desired thickness is obtained, and finally annealing at 600°C to 750°C for 30 minutes to 60 minutes to obtain the sodium bismuth titanate-based lead-free piezoelectric film with high electrostrain.

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