CN110473959A - The bismuth sodium titanate base leadless piezoelectricity film and preparation method thereof of high inverse piezoelectric modulus - Google Patents

Abstract

The present invention relates to the bismuth sodium titanate base leadless piezoelectricity film and preparation method thereof of high inverse piezoelectric modulus, which is (0.94-x) Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xBiInO₃, wherein x be molar fraction, x=0~0.015, and not be 0, preparation method is metallo-organic decomposition process, i.e., first configure precursor solution, solution is then dropped to clean Pt/TiO_x/SiO₂Rotary coating is carried out on/Si substrate, is successively heat-treated at different temperatures, above-mentioned rotary coating and heat treatment process are repeated, until film thickness reaches 300-500 nanometers.Compared with prior art, the bismuth sodium titanate base leadless piezoelectricity film prepared by the present invention with high inverse piezoelectric modulus has excellent piezoelectric property, against piezoelectric modulus up to 76.6 micromicrons/volt.

Description

Bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient and preparation method thereof

technical field

The invention belongs to the field of electronic functional materials and devices, in particular to a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient and a preparation method thereof.

Background technique

Piezoelectric film refers to a film material with piezoelectric properties and a thickness ranging from a few nanometers to tens of nanometers. Compared with bulk materials, piezoelectric thin films not only have similar mechanical, thermal, acoustic, optical and electrical properties, but also have the advantages of small size, low operating voltage, and integration with semiconductor processes, which makes them widely used in microelectronics. , optoelectronics, microelectromechanical and many other high-tech fields have broad application prospects.

However, the piezoelectric films that are widely used commercially at present are lead-containing piezoelectric films without exception, such as lead titanate-based and lead magnesium niobate-based piezoelectric films. As we all know, lead is a highly toxic neurotoxin, and the preparation and recycling of these piezoelectric films with excessive lead content will cause serious damage to the environment and human beings. Both the European Union and my country have issued a series of laws and regulations to limit the application of lead-containing piezoelectric films. In this regard, researchers from all over the world have developed a series of lead-free piezoelectric materials, among which sodium bismuth titanate is undoubtedly the one that has attracted the most attention from researchers. This material has a perovskite structure, which is a trigonal phase at room temperature, has good piezoelectricity and ferroelectricity, and has a Curie temperature of about 320°C (Ferroelectrics, 1982, 40(1):75–77). The high coercive field and large hysteresis limit its application in piezoelectric materials to a certain extent.

A series of related studies have shown that bismuth-sodium titanate-based piezoelectric thin films have excellent ferroelectric and piezoelectric properties at their quasi-isotropic phase boundaries after adding the second or third component. Among them, a binary system film with better performance is the Bi _0.5 Na _0.5 TiO ₃ -BaTiO ₃ binary system film, which has been proved that when the molar ratio of Bi _0.5 Na _0.5 TiO ₃ and BaTiO ₃ is 47:3, the piezoelectric performance Best (J. Alloy. Compd., 2010, 504(1): 129–133). In addition, studies have shown that adding BiInO ₃ , which also has a typical perovskite structure, as the second or third component to lead-containing and lead-free matrix materials can well regulate the electrical properties of the material (Chem.Mater. , 2006, 18(7): 1964–1968; J. Mater. Res., 2004, 19(7): 2185–2193). However, these studies mainly focus on ceramic materials, and the relevant reports on thin film materials are still extremely scarce. As for the effect of adding BiInO ₃ in the Bi _0.5 Na _0.5 TiO ₃ –BaTiO ₃ binary system thin film on the material properties is more important. No one has ever done research on this.

Contents of the invention

The purpose of the present invention is exactly to provide a kind of bismuth sodium titanate base lead-free piezoelectric thin film with high inverse piezoelectric coefficient and preparation method thereof in order to overcome the defective that above-mentioned prior art exists, because adding _BiInO in the binary system thin film will What kind of impact on material properties has never been studied. Based on this background, we prepared (0.94-x)Bi _0.5 Na _0.5 TiO ₃ –0.06BaTiO ₃ –xBiInO ₃ ternary thin films, and found that when x was taken to its preferred value of 0.005, the prepared piezoelectric thin films had excellent Piezoelectric properties, the inverse piezoelectric coefficient reaches 76.6 picometers/volt.

The purpose of the present invention can be achieved through the following technical solutions:

Bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient, the chemical composition of the lead-free piezoelectric film is (0.94-x)Bi _0.5 Na _0.5 TiO ₃ –0.06BaTiO ₃ –xBiInO ₃ , where x is the mole fraction , x=0～0.015, and not 0.

The value of x is preferably 0.005.

The bismuth sodium titanate-based lead-free piezoelectric thin film has a thickness of 300-500 nanometers.

The preparation method of bismuth sodium titanate-based lead-free piezoelectric film with high converse piezoelectric coefficient is as follows:

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the general chemical formula (0.94-x)Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -xBiInO ₃ and dissolve it in ethylene glycol methyl ether, Among them, acetylacetone plays the role of complexing titanium n-tetrabutoxide, and then the above solution is stirred at room temperature on a magnetic stirrer for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate or its hydrate, sodium acetate or its hydrate, barium acetate and nitric acid according to the stoichiometric ratio of the general chemical composition formula (0.94-x)Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -xBiInO ₃ Indium or its hydrate, because bismuth and sodium elements volatilize violently at high temperature, bismuth nitrate or its hydrate, sodium acetate or its hydrate can be weighed in a slight excess, and then the weighed medicine is dissolved in acetic acid, at 20 ~ Stirring at 70°C for 60-80 minutes to obtain precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.1-0.4 mol/liter, and then stir at room temperature for 4-5 hours. Obtain precursor solution;

(4) Cut the Pt/TiO _x /SiO ₂ /Si substrate into squares or rectangles with a side length between 0.8 and 1.5 cm. Afterwards, the silicon wafer is first ultrasonically cleaned in acetone for 10-20 minutes, then ultrasonically cleaned in distilled water for 10-20 minutes, and finally ultrasonically cleaned in ethanol for 15-30 minutes. After cleaning, blow dry with high-purity nitrogen or spin dry at high speed with a homogenizer;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 2000-4000 rpm, and the coating time is 20-60 seconds;

(b) heat-treat the film obtained after step (a) in a tube furnace at 100-250°C for 3-5 minutes, at 350-450°C for 3-5 minutes, and at 700-750°C for 5 minutes ~10 minutes;

(c) Repeat step (b) several times until the film thickness reaches the expectation. Finally, the annealing treatment is performed at 700-750° C. for 30-60 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with a high inverse piezoelectric coefficient.

(6) A circular metal top electrode with a diameter of 0.3-1.0 mm is sputtered on the surface of the piezoelectric film by using a sputtering apparatus.

The existing studies on adding BiMeO ₃ type (Me represents a certain trivalent metal ion) third component to the binary ferroelectric film with perovskite structure to improve the physical properties of the film mainly focus on BiFeO ₃ , On the third component such as BiMnO ₃ and BiAlO ₃ , however, due to the presence of various valences of Fe and Mn and the violent decomposition and volatilization of Al organic salts at high temperatures, slight changes in raw materials and process parameters may affect the final properties of the film. greater impact. However, BiInO ₃ has a typical perovskite structure, and has been used as the second or third component in both lead-containing and lead-free dielectric ceramics to regulate the electrical properties of the material, and In ³⁺ ions do not have the possibility of changing valence and The organic salt does not volatilize violently at high temperature, so compared with the existing film preparation technology, the production process of the present invention is stable and has good repeatability. In this patent, by adjusting the content of BiInO ₃ , a quasi-isomorphic phase boundary can be formed in the 0.94Bi _0.5 Na _0.5 TiO ₃ –0.06BaTiO ₃ binary material, thereby increasing the dielectric constant and polarization strength of the piezoelectric film, and improving the piezoelectric film The inverse piezoelectric coefficient of .

Description of drawings

Fig. 1 is the X-ray diffraction spectrum of the bismuth sodium titanate base lead-free piezoelectric thin film that comparative example 1 and embodiment 1, 2 gain;

Fig. 2 is the dielectric spectrum of the bismuth sodium titanate-based lead-free piezoelectric film obtained in Comparative Example 1 and Examples 1-3;

Fig. 3 is the dielectric temperature spectrum of the bismuth sodium titanate-based lead-free piezoelectric film obtained in Comparative Example 1 and Examples 1-3;

Fig. 4 is the hysteresis loop of the bismuth sodium titanate-based lead-free piezoelectric film obtained in Comparative Example 1 and Examples 1 and 2;

Figures 5-1 to 5-6 show the piezoelectric response phase-voltage curve, displacement-voltage curve and inverse piezoelectric coefficient- voltage curve.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient, the chemical composition of the lead-free piezoelectric film is (0.94-x)Bi _0.5 Na _0.5 TiO ₃ –0.06BaTiO ₃ –xBiInO ₃ , where x is the mole fraction , x=0～0.015, and not 0. When the value of x is 0.005, the best technical effect can be obtained. The prepared bismuth sodium titanate-based lead-free piezoelectric thin film has a thickness of 300-500 nanometers.

The preparation method of bismuth sodium titanate-based lead-free piezoelectric film with high converse piezoelectric coefficient is as follows:

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the general chemical formula (0.94-x)Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -xBiInO ₃ and dissolve it in ethylene glycol methyl ether, Among them, acetylacetone plays the role of complexing titanium n-tetrabutoxide, and then the above solution is stirred at room temperature on a magnetic stirrer for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate or its hydrate, sodium acetate or its hydrate, barium acetate and nitric acid according to the stoichiometric ratio of the general chemical composition formula (0.94-x)Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -xBiInO ₃ Indium or its hydrate, because bismuth and sodium elements volatilize violently at high temperature, bismuth nitrate or its hydrate, sodium acetate or its hydrate can be weighed in a slight excess, and then the weighed medicine is dissolved in acetic acid, at 20 ~ Stirring at 70°C for 60-80 minutes to obtain precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.1-0.4 mol/liter, and then stir at room temperature for 4-5 hours. Obtain precursor solution;

(4) Cut the Pt/TiO _x /SiO ₂ /Si substrate into squares or rectangles with a side length between 0.8 and 1.5 cm. Afterwards, the silicon wafer is first ultrasonically cleaned in acetone for 10-20 minutes, then ultrasonically cleaned in distilled water for 10-20 minutes, and finally ultrasonically cleaned in ethanol for 15-30 minutes. After cleaning, blow dry with high-purity nitrogen or spin dry at high speed with a homogenizer;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 2000-4000 rpm, and the coating time is 20-60 seconds;

(b) heat-treat the film obtained after step (a) in a tube furnace at 100-250°C for 3-5 minutes, at 350-450°C for 3-5 minutes, and at 700-750°C for 5 minutes ~10 minutes;

(c) Repeat step (b) several times until the film thickness reaches the expectation. Finally, the annealing treatment is performed at 700-750° C. for 30-60 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with a high inverse piezoelectric coefficient.

(6) A circular metal top electrode with a diameter of 0.3-1.0 mm is sputtered on the surface of the piezoelectric film by using a sputtering apparatus.

The following are more detailed implementation examples, through which the technical solutions of the present invention and the technical effects that can be obtained are further described.

Comparative example 1

(1) According to the stoichiometric ratio of the chemical composition general formula 0.94Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ , weigh n-tetrabutoxide titanium and acetylacetone and dissolve them in ethylene glycol methyl ether, where acetylacetone acts as a complex The effect of titanium butoxide, then the above solution was stirred at room temperature on a magnetic stirrer for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate pentahydrate, sodium acetate trihydrate, barium acetate and indium nitrate hydrate according to the stoichiometric ratio of the chemical composition general formula 0.94Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ . The volatilization is relatively severe at high temperature, and 10% of bismuth nitrate pentahydrate and sodium acetate trihydrate are weighed in excess, and then the weighed medicine is dissolved in acetic acid, and stirred at 45 ° C for 1 hour to obtain the precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.25 mol/liter, and stir at room temperature for 5 hours to obtain a precursor solution ;

(4) Cut the Pt(111)/TiO _x /SiO ₂ /Si(100) substrate into a square with a side length of 1 cm. The wafers were then ultrasonically cleaned first in acetone for 15 minutes, then in distilled water for 15 minutes, and finally in ethanol for 20 minutes. Blow dry with high-purity nitrogen after cleaning;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 3000 rpm, and the coating time is 30 seconds;

(b) heat-treating the film obtained after step (a) in a tube furnace at 150°C for 5 minutes, at 450°C for 5 minutes, and at 720°C for 10 minutes;

(c) Repeat step (b) 6 times until the film thickness reaches the desired value. Finally, it was annealed at 720° C. for 45 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient.

(6) A circular gold top electrode with a diameter of 0.5 mm is sputtered on the surface of the piezoelectric film using a sputtering apparatus.

Example 1

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the chemical composition general formula 0.935Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.005BiInO ₃ and dissolve it in ethylene glycol methyl ether, wherein acetylacetone Play the role of complexing titanium tetrabutoxide, and then stir the above solution on a magnetic stirrer at room temperature for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate pentahydrate, sodium acetate trihydrate, barium acetate and indium nitrate hydrate according to the stoichiometric ratio of the chemical composition general formula 0.935Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.005BiInO ₃ , due to the bismuth element and The sodium element volatilizes violently at high temperature, and 10% of bismuth nitrate pentahydrate and sodium acetate trihydrate are weighed in excess, and then the weighed medicine is dissolved in acetic acid, and stirred at 45°C for 1 hour to obtain the precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.25 mol/liter, and stir at room temperature for 5 hours to obtain a precursor solution ;

(4) Cut the Pt(111)/TiO _x /SiO ₂ /Si(100) substrate into a square with a side length of 1 cm. The wafers were then ultrasonically cleaned first in acetone for 15 minutes, then in distilled water for 15 minutes, and finally in ethanol for 20 minutes. Blow dry with high-purity nitrogen after cleaning;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 3000 rpm, and the coating time is 30 seconds;

(b) heat-treating the film obtained after step (a) in a tube furnace at 150°C for 5 minutes, at 450°C for 5 minutes, and at 720°C for 10 minutes;

(c) Repeat step (b) 6 times until the film thickness reaches the desired value. Finally, it was annealed at 720° C. for 45 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient.

(6) A circular gold top electrode with a diameter of 0.5 mm is sputtered on the surface of the piezoelectric film using a sputtering apparatus.

Example 2

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the general chemical formula 0.93Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.01BiInO ₃ and dissolve it in ethylene glycol methyl ether, wherein acetylacetone Play the role of complexing titanium tetrabutoxide, and then stir the above solution on a magnetic stirrer at room temperature for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate pentahydrate, sodium acetate trihydrate, barium acetate and indium nitrate hydrate according to the stoichiometric ratio of the chemical composition general formula 0.93Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.01BiInO ₃ , due to the bismuth element and The sodium element volatilizes violently at high temperature, and 10% of bismuth nitrate pentahydrate and sodium acetate trihydrate are weighed in excess, and then the weighed medicine is dissolved in acetic acid, and stirred at 45°C for 1 hour to obtain the precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.25 mol/liter, and stir at room temperature for 5 hours to obtain a precursor solution ;

(4) Cut the Pt(111)/TiO _x /SiO ₂ /Si(100) substrate into a square with a side length of 1 cm. The wafers were then ultrasonically cleaned first in acetone for 15 minutes, then in distilled water for 15 minutes, and finally in ethanol for 20 minutes. Blow dry with high-purity nitrogen after cleaning;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 3000 rpm, and the coating time is 30 seconds;

(b) heat-treating the film obtained after step (a) in a tube furnace at 150°C for 5 minutes, at 450°C for 5 minutes, and at 720°C for 10 minutes;

(c) Repeat step (b) 6 times until the film thickness reaches the desired value. Finally, it was annealed at 720° C. for 45 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient.

(6) A circular gold top electrode with a diameter of 0.5 mm is sputtered on the surface of the piezoelectric film using a sputtering apparatus.

Example 3

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the general chemical formula 0.925Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.015BiInO ₃ and dissolve it in ethylene glycol methyl ether, wherein acetylacetone Play the role of complexing titanium tetrabutoxide, and then stir the above solution on a magnetic stirrer at room temperature for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate pentahydrate, sodium acetate trihydrate, barium acetate and indium nitrate hydrate according to the stoichiometric ratio of the chemical composition general formula 0.925Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.015BiInO ₃ . The sodium element volatilizes violently at high temperature, and 10% of bismuth nitrate pentahydrate and sodium acetate trihydrate are weighed in excess, and then the weighed medicine is dissolved in acetic acid, and stirred at 45°C for 1 hour to obtain the precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.25 mol/liter, and stir at room temperature for 5 hours to obtain a precursor solution ;

(4) Cut the Pt(111)/TiO _x /SiO ₂ /Si(100) substrate into a square with a side length of 1 cm. The wafers were then ultrasonically cleaned first in acetone for 15 minutes, then in distilled water for 15 minutes, and finally in ethanol for 20 minutes. Blow dry with high-purity nitrogen after cleaning;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 3000 rpm, and the coating time is 30 seconds;

(b) heat-treating the film obtained after step (a) in a tube furnace at 150°C for 5 minutes, at 450°C for 5 minutes, and at 720°C for 10 minutes;

(c) Repeat step (b) 6 times until the film thickness reaches the desired value. Finally, it was annealed at 720° C. for 45 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient.

(6) A circular gold top electrode with a diameter of 0.5 mm is sputtered on the surface of the piezoelectric film using a sputtering apparatus.

Example 4

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the general chemical formula 0.93Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.01BiInO ₃ and dissolve it in ethylene glycol methyl ether, wherein acetylacetone Play the role of complexing titanium tetrabutoxide, and then stir the above solution on a magnetic stirrer at room temperature for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate pentahydrate, sodium acetate trihydrate, barium acetate and indium nitrate hydrate according to the stoichiometric ratio of the chemical composition general formula 0.93Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.01BiInO ₃ , due to the bismuth element and The sodium element volatilizes violently at high temperature, and 10% of bismuth nitrate pentahydrate and sodium acetate trihydrate are weighed in excess, and then the weighed medicine is dissolved in acetic acid, and stirred at 20°C for 1 hour to obtain the precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.1 mol/liter, and stir at room temperature for 5 hours to prepare the precursor solution ;

(4) Cut the Pt(111)/TiO _x /SiO ₂ /Si(100) substrate into a square with a side length of 1 cm. The wafers were then ultrasonically cleaned first in acetone for 15 minutes, then in distilled water for 15 minutes, and finally in ethanol for 20 minutes. Blow dry with high-purity nitrogen after cleaning;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the spin speed is 2000 rpm, and the coating time is 60 seconds;

(b) heat-treating the film obtained after step (a) in a tube furnace at 100°C for 3 minutes, at 350°C for 4 minutes, and at 700°C for 5 minutes;

(c) Repeat step (b) 8 times until the film thickness reaches the desired value. Finally, it was annealed at 700°C for 60 minutes, and a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient was prepared.

(6) A circular gold top electrode with a diameter of 0.5 mm is sputtered on the surface of the piezoelectric film using a sputtering apparatus.

Example 5

(1) Take n-tetrabutoxide titanium and acetylacetone according to the stoichiometric ratio of the general chemical formula 0.93Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.01BiInO ₃ and dissolve it in ethylene glycol methyl ether, wherein acetylacetone Play the role of complexing titanium tetrabutoxide, and then stir the above solution on a magnetic stirrer at room temperature for 20 minutes to obtain precursor solution A;

(2) Weigh bismuth nitrate pentahydrate, sodium acetate trihydrate, barium acetate and indium nitrate hydrate according to the stoichiometric ratio of the chemical composition general formula 0.93Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.01BiInO ₃ , due to the bismuth element and The sodium element volatilizes violently at high temperature, and 10% of bismuth nitrate pentahydrate and sodium acetate trihydrate are weighed in excess, and then the weighed medicine is dissolved in acetic acid, and stirred at 70°C for 1 hour to obtain the precursor solution B;

(3) Mix precursor solution A and precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.4 mol/liter, and stir at room temperature for 5 hours to prepare the precursor solution ;

(4) Cut the Pt(111)/TiO _x /SiO ₂ /Si(100) substrate into a square with a side length of 1 cm. The wafers were then ultrasonically cleaned first in acetone for 15 minutes, then in distilled water for 15 minutes, and finally in ethanol for 20 minutes. Blow dry with high-purity nitrogen after cleaning;

(5) Preparation of thin film: Spin-coat on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, as follows:

(a) Carry out a spin coating on the Pt/TiO _x /SiO ₂ /Si substrate obtained in step (3) at room temperature, the rotation speed is 4000 rpm, and the coating time is 20 seconds;

(b) heat-treating the film obtained after step (a) in a tube furnace at 250°C for 3 minutes, at 400°C for 4 minutes, and at 750°C for 5 minutes;

(c) Repeat step (b) 8 times until the film thickness reaches the desired value. Finally, it was annealed at 750° C. for 30 minutes to prepare a bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient.

(6) A circular gold top electrode with a diameter of 0.5 mm is sputtered on the surface of the piezoelectric film using a sputtering apparatus.

Fig. 1 is the X-ray diffraction pattern of the bismuth sodium titanate-based lead-free piezoelectric film obtained in Comparative Example 1 and Examples 1 and 2. It can be seen from the figure that all films have a typical perovskite structure, and the introduction of the third component BiMnO ₃ does not lead to the appearance of obvious impurity phases in the films.

FIG. 2 is the dielectric spectrum of bismuth sodium titanate-based lead-free piezoelectric thin films obtained in Comparative Example 1 and Examples 1-3. As can be seen from the figure, with the increase of _BiMnO3 content, the dielectric constant first increases and then decreases, indicating that adding _{BiMnO3 properly} can improve the dielectric constant _{of Bi0.5Na0.5TiO3 -} BaTiO3 film, and the embodiment The film with the composition of 0.935Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.005BiInO ₃ in 1 has the highest dielectric constant (relative permittivity at room temperature reaches 1111.2 at 10 kHz frequency).

Fig. 3 is the dielectric temperature spectrum of bismuth sodium titanate-based lead-free piezoelectric thin films obtained in Comparative Example 1 and Examples 1-3. As can be seen from the figure, with the increase of _BiMnO3 content, the dielectric constant first increases and then decreases, indicating that adding _{BiMnO3 properly} can improve the dielectric constant _{of Bi0.5Na0.5TiO3 -} BaTiO3 film, and the embodiment In 1, the film with the composition of 0.935Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.005BiInO ₃ has the highest dielectric constant in the whole temperature range of 30-360 ℃ (when the dielectric constant reaches the maximum at 10 kHz frequency The relative dielectric constant reaches 1774.1 at the Curie temperature of 261.7°C).

FIG. 4 is the hysteresis loops of bismuth sodium titanate-based lead-free piezoelectric thin films obtained in Comparative Example 1 and Examples 1-3. It can be seen from the figure that with the increase of BiMnO ₃ content, the maximum polarization intensity first increases and then decreases, indicating that the proper addition of BiMnO ₃ can improve the dielectric constant of the Bi _0.5 Na _0.5 TiO ₃ -BaTiO ₃ film, and the implementation In Example 1, the film with the composition of 0.935Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.005BiInO ₃ has the highest maximum polarization intensity.

Figures 5-1 to 5-6 are the piezoelectric response phase-voltage curves of the bismuth sodium titanate-based lead-free piezoelectric films obtained in Comparative Example 1 and Examples 1 and 2 (in Figures 5-1 to 5-3 solid line), displacement-voltage curve (solid point in Figure 5-4 to Figure 5-6) and inverse piezoelectric coefficient-voltage curve ((hollow point in Figure 5-4 to Figure 5-6). From It can be seen from the figure that with the increase of BiMnO ₃ content, the inverse piezoelectric coefficient first increases and then decreases, indicating that adding BiMnO ₃ properly can improve the inverse piezoelectric coefficient of Bi _0.5 Na _0.5 TiO ₃ –BaTiO ₃ film, and the implementation The film with the composition of 0.935Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -0.005BiInO ₃ in Example 1 has the highest inverse piezoelectric coefficient (the inverse piezoelectric coefficient reaches 76.6 picometer/volt when a voltage of 10 volts is applied).

In the description of this specification, descriptions with reference to the terms "one embodiment", "example", "specific example" and the like mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment of the present invention. In an embodiment or example. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above descriptions of the embodiments are for those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative efforts. Therefore, the present invention is not limited to the above-mentioned embodiments. Improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims (8)

1. Bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient, characterized in that the chemical composition of the lead-free piezoelectric film is (0.94-x)Bi _0.5 Na _0.5 TiO ₃ -0.06BaTiO ₃ -xBiInO ₃ , wherein x is the mole fraction, x=0～0.015, and is not 0. 2. The bismuth sodium titanate-based lead-free piezoelectric film with high converse piezoelectric coefficient according to claim 1, characterized in that the value of x is preferably 0.005. 3. The bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient according to claim 1 or 2, characterized in that the thickness of the bismuth sodium titanate-based lead-free piezoelectric film is 300-500 nanometers. 4. The preparation method of the bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient as claimed in any one of claims 1 to 3, characterized in that, the precursor is prepared by metal organic thermal decomposition method and Coated on substrates, including: Weighing titanium tetrabutoxide and acetylacetone and dissolving them in ethylene glycol methyl ether, stirring at room temperature to obtain precursor solution A; Weighing bismuth nitrate or its hydrate, sodium acetate or its hydrate, barium acetate and indium nitrate or its hydrate and dissolving them in acetic acid, stirring at 20-70°C to obtain precursor solution B; Mix the precursor solution A and the precursor solution B, add ammonia water to adjust the pH value until the solute is completely dissolved, add acetic acid to adjust the concentration of the mixed solution to 0.1-0.4 mol/liter, and then stir at room temperature to prepare the precursor solution; Clean the substrate and dry it; The prepared precursor solution was coated on the substrate to prepare bismuth sodium titanate-based lead-free piezoelectric film with high inverse piezoelectric coefficient. 5 . The preparation method of bismuth sodium titanate based lead-free piezoelectric thin film with high converse piezoelectric coefficient according to claim 4 , characterized in that the substrate is a Pt/TiO _x /SiO ₂ /Si substrate. 6. according to the preparation method of the bismuth sodium titanate base lead-free piezoelectric thin film of high inverse piezoelectric coefficient described in claim 4 or 5, it is characterized in that, when cleaning substrate, at first ultrasonic cleaning in acetone, then in distilled water Ultrasonic cleaning, and finally ultrasonic cleaning in ethanol. 7. according to the preparation method of the bismuth sodium titanate base lead-free piezoelectric film of the described high inverse piezoelectric coefficient of claim 4 or 5, it is characterized in that, the substrate after cleaning is blown dry with high-purity nitrogen or with glue homogenizer Spin dry on high speed. 8. according to the preparation method of the bismuth sodium titanate base lead-free piezoelectric thin film of high converse piezoelectric coefficient described in claim 4, it is characterized in that, adopt spin coating to coat precursor solution on the substrate, at room temperature after cleaning Carry out a spin coating on the dried substrate, the spin speed is 2000-4000 rpm, and the coating time is 20-60 seconds; after coating, heat treatment at 100-250°C for 3-5 minutes Heat treatment at 450°C for 3 to 5 minutes, heat treatment at 700 to 750°C for 5 to 10 minutes, and repeat the above heat treatment operation several times until the film thickness reaches the expected value, and finally anneal at 700 to 750°C for 30 to 60 minutes to complete the coating .