A Preparation Method of Flexible Self-Polarized Bismuth Ferrite-Based Thin Films

Abstract

The present invention belongs to the technical field of new microelectronic materials, and particularly relates to a method for preparing a flexible self-polarized bismuth ferrite-based thin film. In this method, heat-resistant flexible mica is used as the substrate material, and a metal thin film or an oxide thin film is used as the bottom electrode material. After pretreatment of the bottom electrode, the bismuth ferrite-based thin film is grown. The present invention directly grows a bismuth ferrite-based thin film with a self-polarization effect at high temperature on a flexible substrate for the first time, and its chemical composition is Bi(Fe 1‑x‑y Mn x Ti y )O3, where 0 < x ≤ 0.05 and 0 < y ≤ 0.05. The process of the present invention is simple and effective. The prepared bismuth ferrite-based thin film is resistant to bending, has excellent electrode polarization characteristics, strong charge retention force, good anti-fatigue performance, and exhibits good piezoelectric performance without artificial polarization, and has great application potential in technical fields such as flexible ferroelectric storage and flexible piezoelectric sensing.

Description

Technical Field

[0001] The present invention belongs to the technical field of new microelectronic materials, and particularly relates to a method for preparing a flexible self-polarized bismuth ferrite-based thin film. Background Art

[0002] Ferroelectric materials are an important class of functional materials, which have excellent ferroelectric, piezoelectric, pyroelectric, dielectric and other properties, and can be widely used in non-volatile ferroelectric random access memories, piezoelectric sensors, piezoelectric transducers, pyroelectric infrared sensors, capacitors, etc., and have important application values in technical fields such as microelectronics. With the development of a new generation of intelligent electronics, the rise of flexible electronic technologies such as wearable electronic fabrics, flexible displays, and deformable sensors has put forward requirements for semiconductor functional devices based on ferroelectric materials such as being light, portable, bendable, and stretchable. Common flexible ferroelectric thin films are mostly ferroelectric polymer thin film materials such as polyvinylidene fluoride (PVDF) deposited on organic polymer flexible substrates. Although they have good flexibility, compared with inorganic ferroelectric thin film materials, their electrical properties are not ideal enough, and there are defects such as small polarization intensity and poor anti-fatigue performance. Recently, two-dimensional mica has been considered an ideal flexible substrate material for growing inorganic ferroelectric thin films at high temperatures because of its good flexibility and thermal stability (~1000 °C), which is sufficient to withstand the high crystallization temperature (usually ≥500 °C) required for inorganic functional thin films. At present, most of the inorganic ferroelectric piezoelectric devices prepared using high-temperature-resistant flexible mica substrates use lead zirconate titanate (PZT) as the functional layer (Reference: J. Jiang, Y. Bitla, C.-W. Huang, T.H. Do, H.-J. Liu, Y.-H. Hsieh, C.-H. Ma, C.-Y. Jang, Y.-H. Lai, P.-W. Chiu, W.-W. Wu, Y.-C. Chen, Y.-C. Zhou, Y.-H. Chu, Flexible ferroelectric element based on van der Waals heteroepitaxy, Science Advances, 2017, 3, e1700121.), but the lead pollution during the production, use, and post-disposal processes will seriously endanger human health and the natural environment.

[0003] Bismuth ferrite (BiFeO 3 ) is a typical perovskite-type ferroelectric, which is lead-free and environmentally friendly, has a high Curie temperature ( T c ~830 °C), and has a large ferroelectric polarization intensity ( P s ~100 μC / cm 2), is a hot material that ferroelectric materials researchers are concerned about (References: J. Wang, J. B. Neaton, H. Zheng, V. Nagarajan, S. B. Ogale, B. Liu, D. Viehland, V. Vaithyanathan, D. G. Schlom, U. V. Waghmare, N. A. Spaldin, K. M. Rabe, M. Wuttig and R. Ramesh, Epitaxial BiFeO 3 multiferroic thin film heterostructures, Science, 2003, 299 (5613), 1719 - 1722.). However, currently, all electronic devices prepared using the excellent ferroelectric and piezoelectric properties of BiFeO 3 -based thin films use hard materials as substrates, and flexible ferroelectric and piezoelectric devices based on BiFeO 3 -based thin films have not been reported. Therefore, combining the excellent ferroelectric and piezoelectric properties of BiFeO 3 -based thin films with flexible electronics technology is an urgent need to promote the industrialization of BiFeO 3 -based thin film devices.

[0004] However, for BiFeO 3 thin films, the material itself has a high leakage current and a large coercive field, making it difficult to be polarized (i.e., single-domain) when applied to piezoelectric microelectromechanical systems and pyroelectric infrared sensors. Even if it can be polarized, it will bring very high energy consumption. If the BiFeO 3 -based thin film has a certain degree of self-polarization effect after preparation, that is, it spontaneously forms the polarization of a ferroelectric without any external excitation, then the problem of difficult polarization of the thin film can be solved when developing flexible integrated piezoelectric chips, laying a good foundation for the preparation of high-performance flexible BiFeO 3 -based thin film piezoelectric devices. SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide a preparation method of a flexible self-polarized bismuth ferrite-based thin film for the problems that the bismuth ferrite-based thin film material on a conventional hard substrate cannot be bent and the bismuth ferrite-based thin film is difficult to be polarized. The present invention directly grows BiFeO 3 -based thin films on a flexible mica substrate with high temperature resistance by using chemical solution deposition technology, and the prepared BiFeO 3The matrix film has excellent bending resistance, polarization characteristics, charge retention ability, and fatigue resistance, and exhibits good piezoelectric properties without artificial polarization. It can be used as a key material for information collection and data storage in a new generation of flexible electronic devices, and has great application potential in technical fields such as flexible ferroelectric storage and flexible piezoelectric sensing.

[0006] The present invention is achieved through the following technical solutions:

[0007] A preparation method of a flexible self-polarized bismuth ferrite-based film, the method comprising: using high-temperature-resistant flexible mica as a substrate material and a metal film or an oxide film as a bottom electrode material, and growing a bismuth ferrite-based film after pre-treating the bottom electrode. Among them, the pre-treatment process of the bottom electrode is annealing in an N 2 atmosphere at 300-650 °C for 5-20 min, and the heat treatment process of the bismuth ferrite-based film is annealing at 250-325 °C for 2-5 minutes and annealing at 480-540 °C for 5-10 minutes.

[0008] In the above preparation method of the flexible self-polarized bismuth ferrite-based film, the bottom electrode material can be Pt, SrRuO 3 or LaNiO 3 film. When the bottom electrode is a metal Pt film, it is prepared by magnetron sputtering and has a thickness of 30-150 nm; when the bottom electrode material is an oxide SrRuO 3 film, it is prepared by magnetron sputtering and has a thickness of 10-50 nm; when the bottom electrode material is an oxide LaNiO 3 film, it is prepared by chemical solution deposition technology and has a thickness of 20-60 nm.

[0009] In the above preparation method of the flexible self-polarized bismuth ferrite-based film, the chemical composition of the film is Bi(Fe 1-x- y Mn x Ti y )O 3 , where 0 < x ≤ 0.05, 0 < y ≤ 0.05; the film thickness is 300-800 nm to maintain a single spontaneous polarization orientation.

[0010] Preferably, the process of growing a bismuth ferrite-based film after pre-treating the bottom electrode is: preparing Bi(Fe 1-x-y Mn x Ti y )O 3The precursor solution was deposited on the pretreated bottom electrode by spin coating. Then, the material was dried and annealed. The process of "spin coating - drying - heat treatment" was repeated until the film thickness reached 300 - 800 nm. The rotation speed during spin coating was 3000 - 4000 revolutions per minute, and the time was 20 - 40 seconds. The drying conditions were drying at 200 - 350 °C for 2 - 5 minutes. The heat treatment conditions were pre - treating at 250 - 325 °C for 2 - 5 minutes and annealing at 480 - 540 °C for 5 - 10 minutes.

[0011] Beneficial effects

[0012] For the first time, the present invention combines the excellent ferroelectric and piezoelectric properties of bismuth ferrite - based thin films with flexible electronic technology, directly growing bismuth ferrite - based thin films with self - polarization effect on a flexible mica substrate at high temperature, solving the problems that bismuth ferrite - based thin film materials on existing rigid substrates cannot be bent and it is difficult to polarize bismuth ferrite - based thin films. The preparation method of the present invention is simple and effective. The prepared bismuth ferrite - based thin films are resistant to bending, have excellent electrode polarization characteristics, strong charge retention force, good anti - fatigue performance, and exhibit good piezoelectric properties without artificial polarization, showing good practical prospects in the technical fields such as flexible ferroelectric storage and flexible piezoelectric sensing. Description of the drawings

[0013] Figure 1 It is a schematic structural diagram of the flexible self - polarized bismuth ferrite - based thin film prepared by the present invention.

[0014] Figure 2 It is the X - ray diffraction pattern of the Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 thin film deposited on the Mica / Pt electrode prepared in Example 1.

[0015] Figure 3 (a) It is the atomic force microscope surface topography map of the Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 thin film deposited on the Mica / Pt electrode prepared in Example 2, Figure 3 (b) It is the scanning electron microscope cross - sectional topography map of the Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 thin film deposited on the Mica / Pt electrode prepared in Example 2.

[0016] Figure 4 (a) It is the Bi(Fe 0.93 Mn 0.05 Ti0.02 )O 3 Out-of-plane phase image of the piezoelectric force microscopy of the thin film Figure 4 (b) Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 Piezoelectric amplitude curve of the thin film

[0017] Figure 5 (a) Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 Hysteresis loop diagrams of the thin film under different bending degrees Figure 5 (b) Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 Variation curves of the polarization intensity and coercive field of the thin film with the bending radius

[0018] Figure 6 For the Bi(Fe 3 deposited on the Mica / SrRuO 0.93 Mn 0.02 Ti 0.05 )O 3 X-ray energy spectrum analysis spectrogram of the thin film

[0019] Figure 7 For the Bi(Fe 3 deposited on the Mica / SrRuO 0.90 Mn 0.05 Ti 0.05 )O 3 Variation curve of the leakage current density of the thin film with the electric field in the flat state

[0020] Figure 8 For the Bi(Fe 3 deposited on the Mica / SrRuO 0.93 Mn 0.05 Ti 0.02 )O 3 Retention characteristic curves of the thin film before and after bending

[0021] Figure 9 For the Bi(Fe 3 deposited on the Mica / LaNiO 0.93 Mn 0.02Ti 0.05 )O 3 Electric hysteresis loop diagram of the film in a flat state.

[0022] Figure 10 Deposited on Mica / LaNiO for Example 9 3 electrode of Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 Fatigue characteristic curve of the film in a flat state.

[0023] Figure 11 Deposited on Mica / LaNiO for Example 10 3 electrode of Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 Retention characteristic curve of the film under different bending times. Detailed implementation manners

[0024] The present invention will be further described below in conjunction with specific embodiments. It should be noted that the following description is only for explaining the present invention and does not limit its content.

[0025] Example 1

[0026] Deposit a Pt bottom electrode on a mica substrate with a thickness < 50 μm to prepare Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 film. The specific process is as follows:

[0027] (1) Substrate treatment: Select a surface-flat fluorophlogopite sheet and gradually thin it layer by layer with double-sided tape to a thickness < 50 μm.

[0028] (2) Preparation of the bottom electrode material: Deposit a Pt thin film bottom electrode on the flexible mica substrate by magnetron sputtering, with a thickness of about 150 nm. Then place it in a rapid annealing furnace and pre-burn it in an N 2 atmosphere at 350 °C for 10 min.

[0029] (3) Preparation of the Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 )3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O was dissolved in 30 ml of ethylene glycol by stirring at room temperature, and then tetrabutyl titanate was dropped in according to the molar ratio. 2 ml of acetylacetone was added as a stabilizer, and acetic acid was used as a regulator for the pH of the solution to prepare a precursor solution with a concentration of 0.3 mol / L and a pH of about 5.

[0030] (4) Preparation of Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 Film preparation: The prepared precursor solution was allowed to stand and age for 2 days, and the precursor solution was deposited on the pretreated Mica / Pt electrode by spin coating at a rotation speed of 3000 rpm for 30 s; then the material was dried on a hot plate at 250 °C for 2 min, and the dried film was placed in a rapid annealing furnace. It was pretreated at 300 °C for 5 min and then heated to 480 °C for annealing for 8 min. The process of "spin coating - drying - heat treatment" was repeated until the film thickness was about 400 nm.

[0031] The X-ray diffraction pattern of the film is as Figure 2 shown. Among them, the abscissa is the diffraction angle 2θ, and the ordinate is the diffraction intensity. It can be seen that a pure-phase BiFeO 3 -based film was prepared on the Mica / Pt electrode without impurity peaks.

[0032] Example 2

[0033] A Pt bottom electrode was deposited on a mica substrate with a thickness < 50 μm to prepare a Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 film, and the specific process is as follows:

[0034] (1) Substrate treatment: A fluorophlogopite sheet with a flat surface was selected and thinned layer by layer with double-sided tape to a thickness < 50 μm.

[0035] (2) Preparation of the bottom electrode material: A Pt thin film bottom electrode with a thickness of about 30 nm was deposited on the flexible mica substrate by magnetron sputtering. Then it was placed in a rapid annealing furnace and pre-burned in an N 2 atmosphere at 480 °C for 8 min.

[0036] (3) Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3Preparation of thin film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O according to the molar ratio, stir and dissolve them in 30 ml of ethylene glycol at room temperature, then drop tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as a regulator for the pH of the solution to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 5.

[0037] (4) Preparation of Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 thin film: Let the prepared precursor solution stand and age for 3 days, deposit the precursor solution on the pretreated Mica / Pt electrode by spin coating method, with a rotation speed of 4000 rpm and a time of 30 s; then place the material on a hot plate at 300 °C and dry for 2 min, put the dried thin film in a rapid annealing furnace, first pretreat at 325 °C for 5 min, and then heat up to 500 °C and anneal for 10 min. Repeat the process of "spin coating - drying - heat treatment" until the thickness of the thin film is about 700 nm.

[0038] The atomic force microscope surface topography of this thin film is shown in Figure 3 (a). It can be seen that the surface roughness of the Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 thin film prepared on the Mica / Pt electrode is relatively large. The scanning electron microscope cross-section topography of this thin film is shown in Figure 3 (b). It can be seen that the interface between the thin film and the Pt electrode is clear and the combination is good.

[0039] Example 3

[0040] Deposit a Pt bottom electrode on a mica substrate with a thickness < 50 μm to prepare a Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film. The specific process is as follows:

[0041] (1) Substrate treatment: Select a fluorophlogopite sheet with a flat surface and gradually thin it layer by layer with double-sided tape to a thickness < 50 μm.

[0042] (2) Preparation of the bottom electrode material: A Pt thin film bottom electrode with a thickness of about 50 nm was deposited on a flexible mica substrate by magnetron sputtering. Then it was placed in a rapid annealing furnace and pre-burned for 8 min in an N 2 atmosphere at 450 °C.

[0043] (3) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film precursor solution: Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O were accurately weighed according to the molar ratio, stirred at room temperature and dissolved in 30 ml of ethylene glycol. Then tetrabutyl titanate was dropped in according to the molar ratio, and 2 ml of acetylacetone was added as a stabilizer. Acetic acid was used as a regulator for the solution pH to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 4.5.

[0044] (4) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film: The prepared precursor solution was allowed to stand and age for 2 days. The precursor solution was deposited on the pretreated Mica / Pt electrode by spin coating at a speed of 4000 rpm for 30 s. Then the material was dried on a hot plate at 300 °C for 2 min. The dried thin film was placed in a rapid annealing furnace, pre-treated at 300 °C for 5 min first, and then heated to 500 °C and annealed for 8 min. The process of "spin coating - drying - heat treatment" was repeated until the thin film thickness was about 500 nm.

[0045] The out-of-plane phase image of the piezoresponse force microscopy of this thin film is as shown in Figure 4 (a), and the piezoelectric amplitude curve is as shown in Figure 4 (b). It can be seen that the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film prepared on the Mica / Pt electrode shows a consistent upward spontaneous polarization orientation. The piezoelectric coefficient d 33 of this thin film is calculated to be 313 pm / V.

[0046] Example 4

[0047] Deposit a Pt bottom electrode on a mica substrate with a thickness < 50 μm to prepare a Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film. The specific process is as follows:

[0048] (1) Substrate treatment: Select a fluorophlogopite mica sheet with a flat surface and gradually thin it layer by layer with double-sided tape to a thickness < 50 μm.

[0049] (2) Preparation of the bottom electrode material: Deposit a Pt thin film bottom electrode on a flexible mica substrate by magnetron sputtering, with a thickness of about 30 nm. Then place it in a rapid annealing furnace and pre-bake it in an N 2 atmosphere at 480 °C for 8 min.

[0050] (3) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O, stir and dissolve them in 30 ml of ethylene glycol at room temperature, then drop in tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as a regulator for the solution pH to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 5.

[0051] (4) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film: Let the prepared precursor solution stand and age for 2 days. Deposit the precursor solution on the pretreated Mica / Pt electrode by spin coating at a speed of 4000 rpm for 30 s; then place the material on a hot plate at 300 °C and dry it for 2 min. Place the dried thin film in a rapid annealing furnace, first pre-treat it at 300 °C for 5 min, and then heat it up to 500 °C and anneal it for 8 min. Repeat the process of "spin coating - drying - heat treatment" until the thin film thickness is about 300 nm.

[0052] The ferroelectric hysteresis loop diagrams of the thin film under different bending degrees are as shown in Figure 5(a), the curves of polarization intensity and coercive field varying with the bending radius are as shown in Figure 5 (b). It can be seen that for the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film prepared on the Mica / Pt electrode, there are no obvious changes in both the polarization intensity and the coercive field under various deformation and bending conditions.

[0053] Example 5

[0054] Deposit SrRuO 3 bottom electrode on a mica substrate with a thickness < 50 μm, and prepare Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 thin film. The specific process is as follows:

[0055] (1) Substrate treatment: Select a fluorophlogopite mica sheet with a flat surface, and gradually thin it layer by layer with double-sided tape to a thickness < 50 μm.

[0056] (2) Preparation of the bottom electrode material: Deposit the SrRuO 3 thin film bottom electrode on the flexible mica substrate by magnetron sputtering, with a thickness of about 30 nm. Then place it in a rapid annealing furnace and pre-bake it in an N 2 atmosphere at 600 °C for 10 min.

[0057] (3) Preparation of the Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 thin film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O, stir and dissolve them in 30 ml of ethylene glycol at room temperature, then drop in tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as a regulator for the solution pH to prepare a precursor solution with a concentration of 0.3 mol / L and a pH of about 5.

[0058] (4) Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3Preparation of the thin film: The prepared precursor solution was allowed to stand for aging for 2 days, and the precursor solution was deposited on the pretreated Mica / SrRuO 3 electrode by spin coating at a rotation speed of 3000 rpm for 30 s; then the material was dried on a hot plate at 250 °C for 2 min, and the dried thin film was placed in a rapid annealing furnace, pre-treated at 300 °C for 5 min, and then heated to 480 °C for annealing for 8 min. The process of "spin coating - drying - heat treatment" was repeated until the thickness of the thin film was about 400 nm.

[0059] The X-ray energy spectrum analysis spectrum of this thin film is as Figure 6 shown.

[0060] Example 6

[0061] Deposit SrRuO 3 bottom electrode on a mica substrate with a thickness < 50 μm, and prepare Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 thin film. The specific process is as follows:

[0062] (1) Substrate treatment: Select a fluorophlogopite mica sheet with a flat surface, and gradually thin it layer by layer with double-sided tape to a thickness < 50 μm.

[0063] (2) Preparation of the bottom electrode material: Deposit the SrRuO 3 thin film bottom electrode on the flexible mica substrate by magnetron sputtering, with a thickness of about 20 nm. Then place it in a rapid annealing furnace and pre-burn it in an N 2 atmosphere at 600 °C for 10 min.

[0064] (3) Preparation of the Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 thin film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O, stir and dissolve at room temperature in 30 ml of ethylene glycol, then drop in tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as a regulator for the solution pH to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 5.

[0065] (4) Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 Preparation of the thin film: The prepared precursor solution was allowed to stand and age for 3 days. The precursor solution was deposited on the pretreated Mica / SrRuO 3 electrode by spin coating at a rotation speed of 4000 rpm for 30 s; then the material was dried on a hot plate at 300 °C for 2 min, and the dried thin film was placed in a rapid annealing furnace, pretreated at 325 °C for 5 min, and then heated to 500 °C and annealed for 10 min. The process of "spin coating - drying - heat treatment" was repeated until the thickness of the thin film was about 400 nm.

[0066] The curve of the leakage current density of the thin film in the flat state as a function of the electric field is as Figure 7 shown. It can be seen that when the electric field is 400 kV / cm, the leakage current density of the Bi(Fe 3 prepared on the Mica / SrRuO 0.90 Mn 0.05 Ti 0.05 )O 3 thin film is about 1×10 -4 A / cm 2 .

[0067] Example 7

[0068] Deposit SrRuO 3 bottom electrode on a mica substrate with a thickness < 50 μm, and prepare Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film. The specific process is as follows:

[0069] (1) Substrate treatment: Select a fluorophlogopite mica sheet with a flat surface, and gradually thin it layer by layer with double-sided tape to a thickness < 50 μm.

[0070] (2) Preparation of the bottom electrode material: Deposit the SrRuO 3 thin film bottom electrode on the flexible mica substrate by magnetron sputtering, with a thickness of about 20 nm. Then place it in a rapid annealing furnace and pre-burn it in N 2 atmosphere at 600 °C for 10 min.

[0071] (3) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film precursor solution: Weigh accurately Bi(NO 3 )3 ·5H 2 O (5% excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O were dissolved in 30 ml of ethylene glycol with stirring at room temperature. Then, tetrabutyl titanate was dropped in according to the molar ratio, and 2 ml of acetylacetone was added as a stabilizer. Acetic acid was used as a pH regulator for the solution to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 5.

[0072] (4) Preparation of Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film: The prepared precursor solution was left to age for 2 days, and then the precursor solution was deposited on the pretreated Mica / SrRuO 3 electrode by spin coating at a rotation speed of 4000 rpm for 30 s. Then, the material was dried on a hot plate at 300 °C for 2 min. The dried thin film was placed in a rapid annealing furnace, pretreated at 300 °C for 5 min, and then heated to 500 °C and annealed for 8 min. The process of "spin coating - drying - heat treatment" was repeated until the thin film thickness was about 400 nm.

[0073] The retention characteristic curves of the thin film before and after bending are as Figure 8 shown. It can be seen that the Bi(Fe 3 thin film prepared on the SrRuO 0.93 Mn 0.05 Ti 0.02 )O 3 thin film has a high charge retention ability.

[0074] Example 8

[0075] A LaNiO 3 bottom electrode was deposited on a mica substrate with a thickness < 50 μm to prepare a Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 thin film. The specific process is as follows:

[0076] (1) Substrate treatment: Fluorophlogopite mica sheets with a flat surface were selected and thinned layer by layer with double-sided tape to a thickness < 50 μm.

[0077] (2) Preparation of the bottom electrode material:

[0078] a. Using the chemical solution deposition method, accurately weigh La(NO 3 ) 3 ·6H 2 O and Ni(NO 3 ) 3 ·6H 2 O according to the molar ratio of 1:1, dissolve them in ethylene glycol methyl ether, and prepare a precursor solution with a concentration of 0.1 mol / L;

[0079] b. Deposit the LaNiO 3 thin film bottom electrode on a flexible mica substrate by spin coating combined with layer-by-layer annealing. The rotation speed during spin coating is 3000 rpm and the time is 30 s; then place the material on a hot plate at 300 °C and dry it for 5 min, and put the dried film in a rapid annealing furnace and anneal it at 620 °C in an N 2 atmosphere for 15 min. Repeat the process of "spin coating - drying - heat treatment" until the thickness of the LaNiO 3 thin film is about 60 nm.

[0080] (3) Preparation of the Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 thin film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O, stir and dissolve them in 30 ml of ethylene glycol at room temperature, then drop in tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as a regulator for the solution pH, and prepare a precursor solution with a concentration of 0.3 mol / L and a pH of about 5.

[0081] (4) Preparation of the Bi(Fe 0.93 Mn 0.02 Ti 0.05 )O 3 thin film: Let the prepared precursor solution stand and age for 2 days, and deposit the precursor solution on the pretreated Mica / LaNiO 3On the electrode, the rotation speed was 3000 rpm and the time was 30 s; then the material was dried on a hot plate at 250 °C for 2 min. The dried film was placed in a rapid annealing furnace, pre-treated at 300 °C for 5 min, and then heated to 480 °C for annealing for 8 min. The process of "spin coating - drying - heat treatment" was repeated until the film thickness was about 500 nm.

[0082] The polarization-electric field hysteresis loop of the film in the flat state is as Figure 9 shown. It can be seen that the polarization-electric field hysteresis loop of the Bi(Fe 3 Mn 0.93 Ti 0.02 )O 0.05 film prepared on the Mica / LaNiO 3 electrode shows an obvious right shift.

[0083] Example 9

[0084] Deposit LaNiO 3 bottom electrode on a mica substrate with a thickness < 50 μm, and prepare Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 film. The specific process is as follows:

[0085] (1) Substrate treatment: Select a smooth-surface fluorophlogopite sheet, and use double-sided tape to gradually thin it to a thickness < 50 μm.

[0086] (2) Preparation of the bottom electrode material:

[0087] a. Using the chemical solution deposition method, accurately weigh La(NO 3 ) 3 ·6H 2 O and Ni(NO 3 ) 3 ·6H 2 O according to a molar ratio of 1:1, dissolve them in ethylene glycol methyl ether, and prepare a precursor solution with a concentration of 0.1 mol / L;

[0088] b. Deposit the LaNiO 3 film bottom electrode on a flexible mica substrate by spin coating combined with layer-by-layer annealing. When spin coating, the rotation speed was 3000 rpm and the time was 30 s; then the material was dried on a hot plate at 300 °C for 5 min, and the dried film was placed in a rapid annealing furnace and annealed at 620 °C in an N 2 atmosphere for 15 min. Repeat the process of "spin coating - drying - heat treatment" until the thickness of the LaNiO 3 film was about 40 nm.

[0089] (3) Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 Preparation of the thin film precursor solution: Weigh accurately Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O according to the molar ratio, stir and dissolve them in 30 ml of ethylene glycol at room temperature, then drop in tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as the regulator for the solution pH to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 5.

[0090] (4) Bi(Fe 0.90 Mn 0.05 Ti 0.05 )O 3 Preparation of the thin film: Let the prepared precursor solution stand and age for 3 days, deposit the precursor solution on the pretreated Mica / LaNiO 3 electrode by spin coating method, with a rotation speed of 4000 rpm and a time of 30 s; then place the material on a hot plate at 250 °C and dry it for 2 min, put the dried thin film in a rapid annealing furnace, first pre-treat it at 325 °C for 5 min, and then raise the temperature to 500 °C and anneal it for 10 min. Repeat the process of "spin coating - drying - heat treatment" until the thickness of the thin film is about 400 nm.

[0091] The fatigue characteristic curve of the thin film in the flat state is as Figure 10 shown. It can be seen that the Bi(Fe 3 prepared on the Mica / LaNiO 0.90 Mn 0.05 Ti 0.05 )O 3 thin film has good polarization fatigue resistance.

[0092] Example 10

[0093] Deposit a LaNiO 3 bottom electrode on a mica substrate with a thickness < 50 μm, and prepare a Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film. The specific process is as follows:

[0094] (1) Substrate treatment: Select a fluorophlogopite sheet with a flat surface and gradually thin it layer by layer with double-sided tape to a thickness <50 μm.

[0095] (2) Preparation of the bottom electrode material:

[0096] a. Using the chemical solution deposition method, accurately weigh La(NO 3 ) 3 ·6H 2 O and Ni(NO 3 ) 3 ·6H 2 O in a molar ratio of 1:1, dissolve them in ethylene glycol monomethyl ether, and prepare a precursor solution with a concentration of 0.1 mol / L;

[0097] b. Deposit the LaNiO 3 thin film bottom electrode on the flexible mica substrate by spin coating combined with layer-by-layer annealing. The rotation speed during spin coating is 3000 rpm and the time is 30 s; then place the material on a hot plate at 300 °C to dry for 5 min, and place the dried film in a rapid annealing furnace for annealing at 620 °C in an N 2 atmosphere for 15 min. Repeat the process of "spin coating - drying - heat treatment" until the thickness of the LaNiO 3 thin film is about 40 nm.

[0098] (3) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film precursor solution: Accurately weigh Bi(NO 3 ) 3 ·5H 2 O (5% in excess), Fe(NO 3 ) 3 ·9H 2 O, (CH 3 COO) 2 Mn·4H 2 O, stir and dissolve them in 30 ml of ethylene glycol at room temperature, then drop in tetrabutyl titanate according to the molar ratio, add 2 ml of acetylacetone as a stabilizer, and use acetic acid as a regulator for the solution pH to prepare a precursor solution with a concentration of 0.4 mol / L and a pH of about 5.

[0099] (4) Preparation of the Bi(Fe 0.93 Mn 0.05 Ti 0.02 )O 3 thin film: Let the prepared precursor solution stand and age for 2 days, and deposit the precursor solution on the pretreated Mica / LaNiO 3On the electrode, the rotation speed was 4000 rpm and the time was 30 s; then the material was dried on a hot plate at 300 °C for 2 min. The dried film was placed in a rapid annealing furnace, pre-treated at 300 °C for 5 min, and then heated to 500 °C for annealing for 8 min. The process of "spin coating - drying - heat treatment" was repeated until the film thickness was about 400 nm.

[0100] The retention characteristic curves of the film under different bending times are as Figure 11 shown. It can be seen that the Bi(Fe 3 Mn 0.93 Ti 0.05 )O 0.02 film prepared on the Mica / LaNiO 3 electrode is bend-resistant and has good charge retention under different bending deformation conditions.

Claims

1. A preparation method of a flexible self-polarized bismuth ferrite-based thin film, and the molecular formula of the bismuth ferrite-based thin film is Bi(Fe 1-x- y Mn x Ti y )O 3 , where 0 < x ≤ 0.05 and 0 < y ≤ 0.

05. It is characterized in that It includes the following steps: Using high-temperature resistant flexible mica as the substrate material, Pt, SrRuO 3 or LaNiO 3 thin film as the bottom electrode material, after pre-treating the bottom electrode, grow the bismuth ferrite-based thin film; the process of growing the bismuth ferrite-based thin film on the pre-treated bottom electrode is as follows: prepare the Bi(Fe 1-x-y Mn x Ti y )O 3 precursor solution, deposit the precursor solution on the pre-treated bottom electrode by spin coating method, then dry and anneal the material, repeat the process of "spin coating - drying - heat treatment" until the film thickness is 300 - 800 nm.

2. The preparation method of a flexible self-polarized bismuth ferrite-based thin film according to claim 1, It is characterized in that The bottom electrode is a metal Pt thin film, which is prepared by magnetron sputtering and has a thickness of 30 - 150 nm.

3. The preparation method of a flexible self-polarized bismuth ferrite-based thin film according to claim 1, It is characterized in that The bottom electrode material is the oxide SrRuO 3 thin film, which is prepared by magnetron sputtering and has a thickness of 10 - 50 nm.

4. The preparation method of a flexible self-polarized bismuth ferrite-based thin film according to claim 1, It is characterized in that The bottom electrode material is the oxide LaNiO 3 thin film, which is prepared by chemical solution deposition technology and has a thickness of 20 - 60 nm.

5. The preparation method of a flexible self-polarized bismuth ferrite-based thin film according to claim 1, It is characterized in that The pretreatment process of the bottom electrode is N 2 atmosphere, annealing at 300~650 °C for 5~20 min.

6. The preparation method of a flexible self-polarized bismuth ferrite-based thin film according to claim 1, It is characterized in that The rotation speed during spin coating is 3000 - 4000 revolutions per minute, and the time is 20 - 40 seconds; the drying conditions are drying at 200 - 350 °C for 2 - 5 minutes; the heat treatment conditions are pre-treatment at 250 - 325 °C for 2 - 5 minutes and annealing at 480 - 540 °C for 5 - 10 minutes.

Images