Strontium-doped bismuth titanate-based ferroelectric film and preparation method thereof

Abstract

The invention discloses a strontium-doped bismuth titanate-based ferroelectric film and a preparation method thereof, and belongs to the technical field of dielectric energy storage materials. The chemical composition of the film is Ba < 1-x > Sr < x > Bi < 4 > Ti < 4 > O < 15 >, wherein x ranges from 0.025 to 0.1. The preparation method comprises the following steps: mixing ethylene glycol monomethyl ether and ethylene glycol, adding bismuth nitrate, barium acetate, strontium acetate and butyl titanate, fully stirring and filtering to obtain a precursor solution, aging, dripping to the center of a substrate for spin coating, heating a spin-coated sample to obtain a dry film, and annealing to obtain the ferroelectric film. The method is low in technological condition requirement, and the thin film obtains the optimal energy storage density by changing the doping proportion of Sr. According to the ferroelectric film, when x is equal to 0.075, the leakage current density of Ba0. 925Sr0. 075Bi4Ti4O15 (BBST75) is only 1.59 * 10 <-7 > A / cm < 2 >, the breakdown field strength is as high as 3.22 MV / cm, and at the moment, the film has the energy storage density of 28.2 J / cm < 3 > and the energy storage efficiency of 80.36%.

Description

Technical Field

[0001] The present invention belongs to the technical field of dielectric energy storage materials, and in particular relates to a strontium-doped bismuth titanate-based lead-free ferroelectric thin film and a preparation method thereof. Background Art

[0002] A dielectric capacitor is a device that achieves energy storage based on the polarization phenomenon of dielectric materials. It has high power density, ultra-fast charge and discharge speed, and long cycle life. It is widely used in many fields such as pulse power storage systems, consumer electronics, and new energy vehicle power supplies. The energy storage performance of a dielectric capacitor is affected by the dielectric constant (ε), polarization difference (ΔP), and breakdown field strength (BDS). ε reflects the ability of the material to store electrical energy in an electric field and is an important parameter for measuring the insulation strength of the material; ΔP is the saturation polarization value (P max ) and the residual polarization value (P r ). Higher ΔP and BDS (Bonferroni-Derivatives) values ​​are beneficial for improving the energy storage density of dielectric capacitors. With the trend toward miniaturization and lightweighting of electronic products, dielectric capacitors are becoming increasingly miniaturized, requiring dielectric materials with higher energy storage density. Ferroelectric materials possess high spontaneous polarization, but their low breakdown field limits their application as dielectric energy storage materials. Therefore, achieving high-performance ferroelectric energy storage films by increasing BDS is of great practical significance.

[0003] BaBi4Ti4O 15 (BBT) is a ferroelectric material with an Aurivillius structure, the chemical expression of which is Bi2A m-1 B m O 3m+3 , composed of fluorite structure layer (Bi2O2) 2+ With perovskite-like layer (A m1 B m O 3m+1 ) 2- Among them, the A position in the perovskite layer is composed of Ba ions and Bi ions, and the B position is occupied by Ti ions. This layer plays a role in providing polarization; the fluorite structure (Bi2O2) 2+ As a high-resistance unit, it can provide charge compensation and insulation without any modification. However, pure BBT systems are prone to the generation of intrinsic oxygen vacancies, which increases its leakage current and reduces its breakdown field strength. This limits the high-voltage performance of the BBT system and, in turn, affects its energy storage performance. Therefore, how to further improve the polarization value and breakdown field strength of BBT films to obtain ferroelectric energy storage films with better energy storage performance to meet the development trend of miniaturization of dielectric capacitors is an urgent problem that needs to be solved. Summary of the Invention

[0004] The purpose of the present invention is to address the problems in the background technology, propose a doped modified bismuth titanate-based ferroelectric film, and also provide a preparation method of the ferroelectric film.

[0005] The present invention is achieved through the following technical solutions: A high energy storage density ferroelectric film based on ferroelectric effect is a strontium-doped bismuth titanate-based ferroelectric film with a chemical composition of Ba 1-x Sr x Bi4Ti4O 15 , x range is 0.025-0.1, the substrate is a Pt(111) / Ti / SiO2 / Si composite substrate, the substrate from top to bottom are Pt(150nm), Ti(20nm), SiO2 and Si, and the thickness of the ferroelectric film is 200-400nm.

[0006] The present invention also provides a method for preparing a strontium-doped bismuth titanate-based ferroelectric thin film, which comprises the following steps: S01, liquid preparation, take ethylene glycol methyl ether and ethylene glycol in a volume ratio of 1:1 as a solvent, after fully mixing, add bismuth nitrate, barium acetate, strontium acetate, and butyl titanate in succession, wherein the volume ratio of butyl titanate to solvent is 1:6, the above solvent and solute are fully stirred and filtered to obtain a precursor solution; S02. Filtering: Filter the solution using a molecular sieve filter.

[0007] S03, aging, leaving the precursor solution at low temperature for 3 days.

[0008] S04, substrate cleaning: clean the substrate with acetone, then place the substrate in an ultrasonic cleaner and clean it with alcohol and ultrapure water for 5 minutes each.

[0009] S05, substrate pretreatment, placing the substrate in a plasma cleaning machine for cleaning for 3 minutes.

[0010] S06. Spin coating: absorb an appropriate amount of precursor solution, drop it to the center of the substrate, and spin coat at a speed of 5000-6000 rpm for 30-40 seconds.

[0011] S07. Prepare a dry film. Heat the spin-coated sample to obtain a dry film. The preset temperature is 350-400° C. and the heating time is 5-6 minutes.

[0012] S08, annealing, placing the dry film in a high-temperature tube furnace for annealing at a temperature of 575-675°C, layer-by-layer annealing for 3-5 minutes, and final annealing for 30-40 minutes.

[0013] Preferably, the molar ratio of bismuth nitrate, barium acetate, strontium acetate and butyl titanate in the solution is: (4-4.4): (0.9-0.975): (0.025-0.1):4.

[0014] The S01 precursor solution forms a stable and clear solution through processes such as hydrolysis and polycondensation. When a significant Tyndall effect occurs, it indicates that the precursor of the target substance has been formed.

[0015] Preferably, the aging process is carried out at 14°C.

[0016] Preferably, in the S06 spin coating process, the preset condition of the coater is 6000 rpm for 30 seconds.

[0017] Preferably, the preset heating temperature in process S07 is 350° C. and the baking time is 5 minutes.

[0018] Preferably, the layer-by-layer annealing time in process S08 is 3 minutes.

[0019] The advantages and beneficial effects of the present invention are: The present invention uses the sol-gel method and high-temperature tube furnace annealing to prepare a Sr-doped modified high energy storage density ferroelectric thin film Ba 1-x Sr x Bi4Ti4O 15 The method has low process requirements and can achieve the optimal energy storage density by changing the Sr doping ratio. The ferroelectric film has good dielectric, ferroelectric and voltage resistance properties at room temperature. When x=0.075, Ba 0.925 Sr 0.075 Bi4Ti4O 15 (BBST75) leakage current density is only 1.59×10 -7 A / cm 2 The breakdown field strength is as high as 3.22 MV / cm. At this time, the film has a breakdown field strength of 28.2 J / cm 3 energy storage density and 80.36% energy storage efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of the ferroelectric thin film in the embodiment.

[0021] Figure 2 XRD analysis of the embodiment shows that they all have (109), (110), (11 10 ) and (219) characteristic peaks.

[0022] Figure 3 Graph showing dielectric constant and dielectric loss for an example.

[0023] Figure 4The actual breakdown field strength of the embodiment and the theoretical breakdown field strength obtained by Weibull statistical distribution.

[0024] Figure 5 (a), (b), (c), (d), and (e) are hysteresis loop diagrams of Examples 1, 2, 3, 4, and Comparative Example 1, respectively.

[0025] Figure 6 Graph showing energy storage density and energy storage efficiency for an embodiment. DETAILED DESCRIPTION

[0026] The present invention prepares a Sr-doped modified ferroelectric thin film Ba with high energy storage density by sol-gel method and high temperature tube furnace annealing. 1-x Sr x Bi4Ti4O 15 , x range is 0.025-0.1, the specific embodiment is as follows: Example

[0027] 1. Mix ethylene glycol methyl ether and ethylene glycol in a volume ratio of 1:1 and stir for 5 minutes. As the solvent, bismuth nitrate, barium acetate, strontium acetate, and butyl titanate reagent are added to the above solvent in a molar ratio of 4:0.975:0.025:4. butyl titanate is a liquid. When preparing the solution, the volume ratio of butyl titanate to solvent is 1:6. 2. Stir the mixed solution until the solute is completely dissolved to form a clear and transparent solution, and filter the solution using a 0.22 μm molecular sieve filter; 3. Aging the solution at 14°C for 3 days; 4. Select a 1 cm × 1 cm Pt / Ti / SiO2 / Si substrate and perform an initial clean using acetone. Then, place the substrate in an ultrasonic cleaner and clean it with alcohol and ultrapure water for 5 minutes each. After that, dry the substrate in a drying oven and then use a plasma cleaner for 3 minutes. 5. Place the treated substrate firmly on the center of the sample holder of the spin coater, drip the precursor solution onto the center of the substrate, set the speed to 500 rpm, and continue for 10 seconds; then set the speed to 6000 rpm, and continue for 30 seconds; 6. After each spin coating layer is completed, the sample heating plate is preset to 400 ° C and the baking time is 6 minutes. Then the sample is transferred to a tube furnace for layer-by-layer annealing at 575 ° C and annealing time for 5 minutes in an oxygen atmosphere. 7. After repeating the spin coating three times, the sample was transferred to a tube furnace for final annealing at 675°C for 40 minutes. Figure 1 The structural diagram of the ferroelectric thin film is given. Figure 2XRD analysis shows that the film has (109), (110), (11 10 ) and (219) characteristic peaks, and the straight line peak below is the BBT standard PDF card. The dielectric constant and dielectric loss are obtained as follows Figure 3 As shown, the breakdown field strength is Figure 4 As shown, the hysteresis loop is Figure 5 As shown in (a), the energy storage density and energy storage efficiency are as follows Figure 6 shown.

[0028] The relevant Sr doping contents and electrical properties of the specific examples and comparative examples are shown in Table 1. As shown in Table 1, the film has an energy storage density of 19.4 J / cm at 2.39 MV / cm. 3 The energy storage efficiency is 73%. The substitution of Sr element A for Ba causes the unit cell volume to shrink, which improves the residual polarization value and breakdown field strength of the film. Example

[0029] 1. Mix ethylene glycol methyl ether and ethylene glycol in a volume ratio of 1:1 and stir for 5 minutes. Then, add bismuth nitrate, barium acetate, strontium acetate, and butyl titanate reagent in a molar ratio of 4:0.95:0.05:4 to the mixed solution. butyl titanate is a liquid, and the volume ratio of butyl titanate to the mixed solution is 1:6. 2. Stir the mixed solution until the solute is completely dissolved to form a clear and transparent solution, and filter the solution using a 0.22 μm molecular sieve filter; 3. Aging the solution at 14°C for 3 days; 4. Select a 1 cm × 1 cm Pt / Ti / SiO2 / Si substrate and perform an initial clean using acetone. Then, place the substrate in an ultrasonic cleaner and clean it with alcohol and ultrapure water for 5 minutes each. After that, dry the substrate in a drying oven and then use a plasma cleaner for 3 minutes. 5. Place the treated substrate firmly on the center of the sample holder of the spin coater, drip the precursor solution onto the center of the substrate, set the speed to 500 rpm, and continue for 10 seconds; then set the speed to 6000 rpm, and continue for 30 seconds; 6. After each spin coating layer is completed, the sample heating plate is preset to 350 ° C and the baking time is 5 minutes. Then the sample is transferred to a tube furnace for layer-by-layer annealing at 675 ° C and annealing time for 3 minutes in an oxygen atmosphere. 7. After repeating the spin coating three times, the sample was transferred to a tube furnace for final annealing at 675°C for 30 minutes. Figure 1 The structural diagram of the ferroelectric thin film is given. Figure 2XRD analysis shows that the film has (109), (110), (11 10 ) and (219) characteristic peaks, and the straight line peak below is the BBT standard PDF card. The dielectric constant and dielectric loss are obtained as follows Figure 3 As shown, the breakdown field strength is Figure 4 As shown, the hysteresis loop is Figure 5 As shown in (b), the energy storage density and energy storage efficiency are as follows Figure 6 The Sr doping content and electrical properties of the specific embodiment and the comparative example are shown in Table 1. As shown in Table 1, the film has an energy storage density of 21.3 J / cm at 2.68 MV / cm. 3 , the energy storage efficiency is 76.7%. With the increase of Sr doping content, the energy storage density and energy storage efficiency of this embodiment are further improved, and the residual polarization value drops to 0.93 μC / cm 2 . Example

[0030] 1. Mix ethylene glycol methyl ether and ethylene glycol in a volume ratio of 1:1 and stir for 5 minutes. As the solvent, bismuth nitrate, barium acetate, strontium acetate, and butyl titanate reagent are added to the above solvent in a molar ratio of 4.4:0.925:0.075:4. butyl titanate is a liquid. When preparing the solution, the volume ratio of butyl titanate to solvent is 1:6. 2. Stir the mixed solution until the solute is completely dissolved to form a clear and transparent solution, and filter the solution using a 0.22 μm molecular sieve filter; 3. Aging the solution at 14°C for 3 days; 4. Select a 1 cm × 1 cm Pt / Ti / SiO2 / Si substrate and perform an initial clean using acetone. Then, place the substrate in an ultrasonic cleaner and clean it with alcohol and ultrapure water for 5 minutes each. After that, dry the substrate in a drying oven and then use a plasma cleaner for 3 minutes. 5. Place the treated substrate firmly on the center of the sample holder of the spin coater, drip the precursor solution onto the center of the substrate, set the speed to 500 rpm, and continue for 10 seconds; then set the speed to 6000 rpm, and continue for 30 seconds; 6. After each spin coating layer is completed, the sample heating plate is preset to 350 ° C and the baking time is 5 minutes. Then the sample is transferred to a tube furnace for layer-by-layer annealing at 675 ° C and annealing time for 3 minutes in an oxygen atmosphere. 7. After repeating the spin coating three times, the sample was transferred to a tube furnace for final annealing at 675°C for 30 minutes. Figure 1 The structural diagram of the ferroelectric thin film is given. Figure 2XRD analysis shows that the film has (109), (110), (11 10 ) and (219) characteristic peaks, and the straight line peak below is the BBT standard PDF card. The dielectric constant and dielectric loss are obtained as follows Figure 3 As shown, the breakdown field strength is Figure 4 As shown, the hysteresis loop is Figure 5 As shown in (c), the energy storage density and energy storage efficiency are as follows Figure 6 The Sr doping content and electrical properties of the specific embodiment and the comparative example are shown in Table 1. As shown in Table 1, the film has an energy storage density of 28.2 J / cm at 3.22 MV / cm. 3 , the energy storage efficiency is 80.36%. When the Sr doping content is 0.075, the film obtains the highest breakdown field strength and the largest energy storage density among all the examples at room temperature. At this time, due to the substitution of Ba ions by Sr doping, the internal domain size becomes smaller, and P r Down to 0.73μC / cm 2 At the same time, the reduction in grain size increases the bonding strength between cations and oxygen ions. This bonding strength inhibits the dissociation of oxygen ions from the crystal lattice, thereby reducing oxygen vacancies within the film and resulting in a higher breakdown field strength. Taking into account both energy storage density and efficiency, this film exhibits the best energy storage performance among all examples. Example

[0031] 1. Mix ethylene glycol methyl ether and ethylene glycol in a volume ratio of 1:1 and stir for 5 minutes. As the solvent, bismuth nitrate, barium acetate, strontium acetate, and butyl titanate reagent are added to the above solvent in a molar ratio of 4:0.9:0.1:4. butyl titanate is a liquid. When preparing the solution, the volume ratio of butyl titanate to solvent is 1:6. 2. Stir the mixed solution until the solute is completely dissolved to form a clear and transparent solution, and filter the solution using a 0.22 μm molecular sieve filter; 3. Aging the solution at 14°C for 3 days; 4. Select a 1 cm × 1 cm Pt / Ti / SiO2 / Si substrate and perform an initial clean using acetone. Then, place the substrate in an ultrasonic cleaner and clean it with alcohol and ultrapure water for 5 minutes each. After that, dry the substrate in a drying oven and then use a plasma cleaner for 3 minutes. 5. Place the treated substrate firmly on the center of the sample holder of the spin coater, drip the precursor solution onto the center of the substrate, set the speed to 500 rpm and continue for 10 seconds; then set the speed to 5000 rpm and continue for 40 seconds; 6. After each spin coating layer is completed, the sample heating plate is preset to 350 ° C and the baking time is 5 minutes. Then the sample is transferred to a tube furnace for layer-by-layer annealing at 675 ° C and annealing time for 3 minutes in an oxygen atmosphere. 7. After repeating the spin coating three times, the sample was transferred to a tube furnace for final annealing at 675°C for 30 minutes. Figure 1 The structural diagram of the ferroelectric thin film is given. Figure 2 XRD analysis shows that the film has (109), (110), (11 10 ) and (219) characteristic peaks, and the straight line peak below is the BBT standard PDF card. The dielectric constant and dielectric loss are obtained as follows Figure 3 As shown, the breakdown field strength is Figure 4 As shown, the hysteresis loop is Figure 5 As shown in (d), the energy storage density and energy storage efficiency are as follows Figure 6 The Sr doping content and electrical properties of the specific embodiment and the comparative example are shown in Table 1. As shown in Table 1, the film has an energy storage density of 19.82 J / cm at 2.49 MV / cm. 3 , the energy storage efficiency is 81.1%. When the Sr doping content is 0.1, the film energy storage efficiency is improved, but the energy storage density is severely reduced. This is due to the decrease in breakdown field strength. When the doping content is too high, the Sr ion concentration is too high and the agglomeration phenomenon increases. This will cause Sr ions to enter the bismuth oxide layer, reducing the insulation of the film. Overall, the film energy storage performance is reduced compared to Example 3.

[0032] Comparative Example 1: In this example, there is no Sr doping, the molar ratio of bismuth nitrate, barium acetate, and butyl titanate is 4:1:4, and the other steps and parameters are the same as those in Example 1.

[0033] Figure 1 The structural diagram of the ferroelectric thin film is given. Figure 2 XRD analysis shows that the film has (109), (110), (11 10 ) and (219) characteristic peaks, and the straight line peak below is the BBT standard PDF card. The dielectric constant and dielectric loss are obtained as follows Figure 3 As shown, the breakdown field strength is Figure 4 As shown, the hysteresis loop is Figure 5 As shown in (e), the energy storage density and energy storage efficiency are as follows Figure 6 shown.

[0034] The relevant Sr doping contents and electrical properties of the specific examples and comparative examples are shown in Table 1. As shown in Table 1, the film has an energy storage density of 18.4 J / cm at 2.13 MV / cm. 3, with an energy storage efficiency of 67.34%. This comparative example demonstrates the energy storage performance of a pure-phase BBT film at room temperature. In Comparative Example 1, the Sr doping content is zero, resulting in a low breakdown field strength of only 2.13 MV / cm for the ferroelectric film. Both the energy storage density and efficiency are lower than those of Example 1.

[0035] The relevant Sr doping contents and electrical properties of the specific embodiments and comparative examples are shown in Table 1.

[0036] Table 1

Claims

1. A strontium-doped bismuth titanate-based ferroelectric film, the chemical composition of which is Ba 1-x Sr x Bi4Ti4O 15 , the x range is 0.025-0.

1.

2. The strontium-doped bismuth titanate-based ferroelectric thin film according to claim 1, characterized in that The thin film substrate is a Pt(111) / Ti / SiO2 / Si composite substrate, and the substrate comprises Pt, Ti, SiO2 and Si from top to bottom respectively; the thickness of the ferroelectric film is 200-400nm.

3. The method for preparing the strontium-doped bismuth titanate-based ferroelectric thin film according to claim 1, comprising the following steps: Step 1: preparing a liquid by mixing ethylene glycol methyl ether and ethylene glycol in a volume ratio of 1:1 as a solvent. After thorough mixing, bismuth nitrate, barium acetate, strontium acetate, and butyl titanate are added successively, wherein the volume ratio of butyl titanate to solvent is 1:

6. The above-mentioned solvent and solute are thoroughly stirred and filtered to obtain a precursor solution. Step 2: Aging: leaving the precursor solution at low temperature for 3 days; Step 3: Spin coating: drop the precursor solution onto the center of the cleaned and pretreated substrate and spin coat at a speed of 5000-6000 rpm for 30-40 seconds. Step 4: Prepare a dry film by heating the spin-coated sample to obtain a dry film. The preset temperature is 350-400°C and the heating time is 5-6 minutes. Step 5: annealing. Place the dry film in a high-temperature tube furnace for annealing at a temperature of 575-675°C. The layer-by-layer annealing lasts for 3-5 minutes, and the final annealing lasts for 30-40 minutes.

4. The preparation method according to claim 3, characterized in that The molar ratio of bismuth nitrate, barium acetate, strontium acetate and butyl titanate in step 1 is: (4-4.4): (0.9-0.975): (0.025-0.1):

4.

5. The preparation method according to claim 3, characterized in that The aging temperature in step 2 is preferably below 14°C.

6. The preparation method according to claim 3, characterized in that The cleaning and pretreatment of the substrate in step 3 include: substrate cleaning, cleaning the substrate with acetone, then placing the substrate in an ultrasonic cleaner and cleaning it with alcohol and ultrapure water for 5 minutes each; substrate pretreatment, placing the substrate in a plasma cleaner for cleaning for 3 minutes.

7. The preparation method according to claim 3, characterized in that The speed of the glue roller in step 3 is preferably 6000 rpm for 30 seconds.

8. The preparation method according to claim 3, characterized in that The preset temperature in step 4 is preferably 350° C., and the heating is performed for 5 minutes.

9. The preparation method according to claim 3, characterized in that The layer-by-layer annealing time in step 5 is preferably 3 minutes.

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