WO2020010559A1 - Thin film with bismuth ferrite solid solution doped at b-site, preparation method therefor and use thereof - Google Patents

Abstract

Disclosed are a thin film with a bismuth ferrite solid solution doped at the B-site, a preparation method therefor and the use thereof. The preparation method comprises: preparing a bismuth ferrite solid solution sol which is to be doped at the B-site; coating the solid solution sol onto a substrate to form a sol coating; subjecting the sol coating on the substrate to a thermosetting treatment; subjecting the sol coating which has been subjected to the thermosetting treatment to an annealing treatment, wherein, in the annealing treatment, rapid temperature raising and preservation are performed for improving the surface flatness of a thin film, and controlling and improving the crystallinity of the material; and then slowly reducing the temperature to cause the film to form out-of-plane single domains. In the method of the present invention, traditional bismuth ferrite sol-gel thin film preparation technology is improved, and a morphotropic phase boundary piezoelectric enhancement effect is obtained through doping at the B-site and mixing with calcium titanate; and by adjusting an annealing process, a prepared high quality epitaxial room temperature multiferroic thin film has a good high piezoelectricity, room temperature multiferroic property, and single crystal epitaxy.

Description

B-site doped bismuth ferrite solid solution film, preparation method and application thereof Technical field

The invention relates to the technical field of preparation of magnetoelectric coupling materials, in particular to a B-site doped bismuth ferrite solid solution film, and a preparation method and application thereof.

Background technique

Multiferroic materials have both ferroelectricity and ferromagnetism. They are multifunctional magnetoelectric composite materials. They not only have a variety of single ferroelectricity (such as ferroelectricity, ferromagnetism), but also synergize through ferrous coupling and recombination. It is possible to control the polarization through the magnetic field or the magnetic pole through the electric field; therefore, it is the technical core of many electronic devices and sensors. The more common multiferroic materials such as TMO (TbMnO3, rhenium manganate) and BFO (BiFeO3, bismuth ferrite) have very good performance. At the same time, there are also their own shortcomings; for example, the temperature at which the magnetoelectric coupling phenomenon occurs in the TMO system is far below room temperature, and its novel ferroelectricity is rarely reached in strength; BFO is not in a ferromagnetic state at room temperature but in The antiferromagnetic state does not meet the needs of reading information storage materials.

Based on the above, room temperature ferroelectricity was successfully achieved in the (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ solid solution ceramic material hybridized at the B site of the perovskite structure. The coexistence of ferromagnetism, meanwhile, due to the complexity of doping, new challenges have also been raised for the development of processes from ceramic systems to high-quality thin-film systems and the preparation of microelectronic devices. Therefore, in the preparation of BFO thin film materials, hybridization can also be adopted to achieve the coexistence of room temperature ferroelectric ferromagnetism.

At present, the preparation methods of bismuth ferrite thin films are usually prepared by laser pulse deposition (PLD), atomic layer deposition (ALD), chemical vapor deposition (CVD) and other methods. They are very sensitive to experimental conditions such as temperature and oxygen pressure. And, depending on the epitaxial stress provided by a high-quality single crystal substrate, some also require expensive pulsed laser deposition (PLD) equipment; the final prepared BFO material has a single-domain structure in the out-of-plane direction, and is ferromagnetic at room temperature. insufficient. Compared with the above methods, the sol-gel method for preparing BFO thin films is a more suitable method, which has the obvious advantages of multi-doping, flexible doping, accuracy, controllability, and industrial large-scale production; and In the preparation of high-quality thin-film materials of ferroelectric ferromagnetic room temperature multi-ferrous materials, the B-site element hybridization can be flexibly adjusted, and its effects on the Curie temperature, ferromagnetism, and room-temperature magnetoelectric coupling strength of the material can be studied. However, at present, a sol-gel preparation method of a room temperature polyferrous film is used. The thin film is a bismuth ferrite polycrystalline film, which has no piezoelectric enhancement effect caused by the quasi-homogeneous phase boundary chemical ratio, or no substrate epitaxy, or the surface Unable to achieve no grain boundaries and high flatness.

Summary of the invention

The main purpose of the present invention is to provide a method for preparing a B-site doped bismuth ferrite solid solution thin film, which aims to improve the multiferrocity and single crystal epitaxial properties of the prepared bismuth ferrite solid solution thin film at room temperature, and make it have Good high-voltage electrical properties.

To achieve the above objective, the method for preparing a B-site doped bismuth ferrite solid solution film provided by the present invention is characterized by including the following steps:

Preparing B-doped bismuth ferrite solid solution sol;

Applying the solid solution sol on a substrate to form a sol coating;

Subjecting the sol coating on the substrate to a thermosetting treatment;

The sol coating after the thermosetting treatment is annealed; wherein the temperature of the annealed treatment is 700 to 900 ° C, and the temperature decrease rate during the temperature reduction process of the annealed treatment is 0.5 to 1 ° C / s.

The invention further proposes a B-site doped bismuth ferrite solid solution film directly prepared by the above method. And the application of the B-site doped bismuth ferrite solid solution film in a sensor or driver.

The above method of the present invention improves the traditional bismuth ferrite sol-gel thin film preparation technology, and obtains the piezoelectric enhancement effect of a quasi-homogeneous phase boundary through B-site doping and mixing with calcium titanate. High-quality epitaxial room-temperature multiferroic thin film has good high-voltage electrical properties, room-temperature multiferroic and single crystal epitaxiality.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic diagram of writing a surface voltage of a prepared thin film sample according to an embodiment of the present invention;

FIG. 2 is a diagram showing a shape detection result of a prepared thin film sample according to an embodiment of the present invention; FIG.

FIG. 3 is an amplitude test result chart of a prepared thin film sample according to an embodiment of the present invention; FIG.

FIG. 4 is a phase test result diagram of a prepared thin film sample according to an embodiment of the present invention; FIG.

5 is an XRD diffraction pattern of a prepared thin film sample according to an embodiment of the present invention;

FIG. 6 is a magnetic moment-temperature change diagram of a thin film sample measured according to an embodiment of the present invention; FIG.

7 is a schematic diagram of writing a surface voltage of a prepared thin film sample according to another embodiment of the present invention;

FIG. 8 is a diagram illustrating a shape detection result of a prepared thin film sample according to another embodiment of the present invention; FIG.

FIG. 9 is an amplitude test result chart of a prepared thin film sample according to another embodiment of the present invention; FIG.

FIG. 10 is a phase test result diagram of a prepared thin film sample according to another embodiment of the present invention; FIG.

FIG. 11 is an XRD diffraction pattern of a prepared thin film sample according to another embodiment of the present invention.

detailed description

The realization of the purpose, functional characteristics and advantages of the present invention will be further described with reference to the embodiments and the drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

The invention provides a method for preparing a B-site doped bismuth ferrite solid solution film, which is improved on the basis of the traditional method for preparing a thin film of bismuth ferrite sol-gel. The method steps include:

S10, preparing B-doped bismuth ferrite solid solution sol;

S20, applying the bismuth ferrite solid solution sol of step S10 on the substrate to form a sol coating;

S30: The sol coating is subjected to thermosetting treatment;

S40: The sol coating after the thermosetting treatment is annealed; among them, rapid heating and slow cooling are used to control the quality of the film during the annealing process;

S50. The substrate is peeled off to obtain a B-site doped bismuth ferrite solid solution film prepared by the present invention.

In the implementation of the above steps of the present invention, firstly, the piezoelectric enhancement effect of the quasi-homogeneous phase boundary is obtained through B-site doping. In step S10, the B-site doped bismuth ferrite solid solution sol is used as the material for the film preparation. Heterobismuth ferrite is (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ , where the doping amount x = 0.1 ～ 0.2 is used in the formula, y = 0.7 to 0.95. At the same time, in order to further reduce the influence on the quality of the subsequent film voids due to the volatility and compatibility of the solvent itself, the invention adds a dehydrating agent, propionic anhydride, in the preparation of the sol-gel, on the one hand, it can promote the polycondensation between the components. The reaction can also improve the properties of the sol. The amount of propionic anhydride added is 0.5 to 2 times the amount of solvent in accordance with the requirements of conventional implementation. At the same time, it is carried out using a metal-organic system in the preparation of a sol, preferably using ethylene glycol methyl ether as a solvent, and adding a chelating agent, citric acid, to the sol. For specific sol preparation process, please refer to (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ doped bismuth ferrite solid solution described in other papers or patents. The preparation method of the sol is performed, or the following detailed implementation steps are used to prepare a sol with a doping amount of x = 0.15 and y = 0.8:

S11, calculated according to 0.3mol / L 100mL of sol preparation amount, using the following table to obtain raw materials:

Drug Name	Molecular weight	Drug purity	Experimental ratio	Stoichiometry	Weighing quality
Bismuth nitrate (pentahydrate)	485.07	0.98	1.1	0.85	13.8839g
Iron nitrate (nine water)	404.02	0.985	1	0.544	8.3675g

Magnesium nitrate (hexahydrate)	256.41	0.99	1	0.085	0.6605g
Calcium acetate (monohydrate)	176.18	0.99	1	0.15	0.8008g
Titanium tetraisopropoxide	340.32	0.99	1	0.235	2.4235g
Citric acid (monohydrate)	210.14	0.995	1	1	6.3359g
Ethylene glycol monomethyl ether	76.09	> 0.99	-	-	-
Propionic anhydride	130.14	> 0.985	-	-	-

S12. Dissolve the Bi, Fe, Mg, and Ca salts in 50 mL of ethylene glycol methyl ether in sequence, and mix and stir until dissolved to obtain the first solution A;

S13, dissolving titanium tetraisopropoxide in 30 mL of ethylene glycol methyl ether, and thoroughly mixing and stirring to obtain a second solution B;

S14. Add the second solution B to the first solution A and mix thoroughly to obtain a mixed solution C;

S15. Add 0.03 mol of citric acid to the mixed solution C, and stir and mix thoroughly; continue to stir for 12 h under normal temperature and pressure environment to obtain 0.3 mol / L sol;

S16. Take 20 mL of the 0.3 mol / L sol prepared in step S15, add 20 mL of ethylene glycol methyl ether to dilute, and then add 10 mL of propionic anhydride, mix and stir well;

S17. Finally, it is transferred to a conical flask and sealed for storage. After standing for 72 hours, it can be used for subsequent preparation of the film.

Further, after the preparation of the sol is completed, in step S20, the sol of step S10 is coated on the substrate, wherein the substrate in the present invention provides epitaxial stress based on a single crystal substrate equivalent to the prepared bismuth ferrite lattice constant. Using a single crystal substrate with a controlled lattice constant in the range of 3.85 Angstroms to 3.95 Angstroms is suitable for bismuth ferrite extension to reduce film stress. In the implementation, one of NbSTO substrate (Nb-doped strontium titanate (STO) single crystal substrate), LSMO (lanthanum strontium manganese oxide), and LAO (lanthanum aluminate) can be preferably used. The doping concentration is 0.5% and the substrate crystal orientation is in the [001] direction. The size of the substrate may be selected according to the size of the thin film usually prepared.

At the same time, in the application of the sol on the substrate in step S20, a spin coating method is preferred in the present invention; compared with a coating method such as doctor blade coating, the dimensional error of the doctor blade can be prevented from reducing the uniformity and regularity of the film. Of course, when the quality requirements of the film formation quality can be achieved, other similar coating methods can also be used. At the same time, based on the requirements for the quality of thin film preparation in the present invention, the coating of the thin film is performed under vacuum conditions, and the spin coating process includes a slow process and a fast process; under vacuum conditions, slow rotation and then fast rotation. It can ensure the stability of sol dispersion during high-speed rotation, and prevent the substrate itself and the liquid sol from affecting the spin coating effect due to the centrifugal force; on the other hand, a good isolation environment can prevent other particles from interfering with the preparation process; as a whole It can improve the uniformity of the components in the film, avoid the existence of micron particles in the film, and the thickness of the film is uniform and controllable.

In implementation, the spin-coating process of step S20 is performed by a vacuum spin-coater. In specific operations, the speed control can be performed by using the following parameters:

step	Speed r / min	Time / second	Acceleration
Slow process	600 ± 20	7 ± 2	600
Fast process	5000 ± 100	15 ± 2	1200

At the same time, in order to further prevent and remove the influence of other particles on film formation before spin coating, the Nb-doped strontium titanate (STO) single crystal substrate NbSTO was cleaned with oxygen plasma before spin coating. On the one hand, oxygen plasma can be used to bombard and oxidize pollutants on the substrate surface through various active particles; on the other hand, the surface of the substrate can be micro-treated to make the surface grains smooth. , Which helps to improve the quality of the film in the future. The time of the oxygen plasma cleaning treatment is controlled from 90 to 100s; the treatment process is controlled in a relatively appropriate time to avoid atomic voids and surface damage on the substrate surface, which affects the quality of subsequent thin film preparation.

After the spin coating in step S20, the substrate coated with the sol is further subjected to thermosetting treatment in step S30, and the sol is initially dried and cured by heating; on the one hand, the volatile components in the sol can escape quickly and uniformly , To prevent the uniformity of the thin film components from decreasing due to different steam escape speeds, which affects the film formation quality; on the other hand, the thin film materials can be well combined with the substrate by heat treatment without falling off, and the occurrence of micro-cracks is also avoided , Thereby ensuring the performance of the prepared film. In addition, the heating process during the implementation includes two stages: preheating and drying, and then heating and maintaining; in the specific implementation, the sample is placed near a heating stage at 180 ° C for preheating and drying for a while, and the surface can be uniformly discolored. The hot stage temperature was adjusted to 400 ° C and held for 30 ± 2 minutes. In the present invention, preheating and drying for a while, and then heating and heating can well avoid the problem of crystallization due to temperature jump or uneven dispersion due to the thick sol of the raw material of the thin film, thereby promoting the substrate. Better combination with film raw materials can also further improve the quality of the prepared film.

On the other hand, according to different needs in actual use, there may be different film thicknesses according to the needs. Therefore, when a thicker film is needed, a new sol can be added again after each thermosetting, and the above is repeated. Steps S20 (dropwise addition of sol-spin coating) to S30 (heating and curing), gradually form a new film layer on the surface of the cured film layer until the thickness of the film reaches the required requirements.

After step S30, step S40 anneals the cured spin coating. During the annealing process, the surface smoothness of the sample is improved by rapid heating; and the crystallinity of the material is controlled and improved at a maximum crystallization temperature range of 700 to 900 ° C. When the number of layers of the film increases within the temperature range, then Corresponding to the quality requirements of the preparation, a higher range of temperature can be used for implementation; finally, the temperature is slowly reduced (the cooling rate is about 0.5 to 1 ° C./s) to promote the formation of out-of-plane single domains. Specific details The temperature control at each stage of the complete annealing process during implementation uses the following parameters:

Phase sequence	Target temperature	Rise / fall time		Holding time
1	100 ± 5 ℃	80 ± 5s	30 ± 5s
2	450 ± 10 ℃	70 ± 5s	300 ± 5s
3	700 ～ 900 ℃	70 ± 5s	600 ± 10s
4	Room temperature	700 ～ 1800s	10 ± 2s

It can be seen from the above-mentioned temperature change parameter setting of the annealing process that the main annealing process of the present invention adopts first increasing temperature (pre-annealing), and finally slowly lowering the temperature to room temperature, the temperature decreasing time is relatively long, and the rate control is 0.5 to 1 At about ℃ / s, it promotes the formation of out-of-plane single domains of the thin film.

By adopting the method for preparing the B-position doped bismuth ferrite solid solution film of the present invention, the traditional bismuth ferrite sol-gel film preparation technology is improved, and the quasi-homogeneous phase boundary is obtained by mixing with B-site doping and calcium titanate. Piezoelectric enhancement effect; using the substrate to provide epitaxial stress for film growth; through fine adjustment of annealing parameters, the prepared high-quality epitaxial room-temperature multiferroic thin film has good high-voltage electrical properties, room-temperature multiferroic, and single crystal epitaxiality.

On the basis of the above method, the present invention further proposes a B-site doped bismuth ferrite solid solution thin film material prepared by the above method; it has good high-voltage electrical properties, room temperature multiferroicity, and single crystal epitaxy.

The invention and further proposes the application of the B-site doped bismuth ferrite solid solution film material prepared above to sensors and drivers.

In order to make the details of the method for preparing the B-site doped bismuth ferrite solid solution film of the present invention more conducive to the understanding and implementation of those skilled in the art, and to verify the progressive effect of the thin film material prepared in this case, the following examples are used to illustrate The above-mentioned content of this case is exemplified.

Example 1

In this embodiment 1, the following detailed steps are used to prepare a thin film:

S11, calculated according to the sol preparation amount of 0.3mol / L 100mL (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ (x = 0.15, y = 0.8) Use the following table to obtain raw materials:

Drug Name	Molecular weight	Drug purity	Experimental ratio	Stoichiometry	Weighing quality
Bismuth nitrate (pentahydrate)	485.07	0.98	1.1	0.85	13.8839g
Iron nitrate (nine water)	404.02	0.985	1	0.544	8.3675g
Magnesium nitrate (hexahydrate)	256.41	0.99	1	0.085	0.6605g
Calcium acetate (monohydrate)	176.18	0.99	1	0.15	0.8008g
Titanium tetraisopropoxide	340.32	0.99	1	0.235	2.4235g
Citric acid (monohydrate)	210.14	0.995	1	1	6.3359g
Ethylene glycol monomethyl ether	76.09	> 0.99	-	-	-
Propionic anhydride	130.14	> 0.985	-	-	-

S12. Dissolve the Bi, Fe, Mg, and Ca salts in 50 mL of ethylene glycol methyl ether in sequence, and mix and stir until dissolved to obtain the first solution A;

S13, dissolving titanium tetraisopropoxide in 30 mL of ethylene glycol methyl ether, and thoroughly mixing and stirring to obtain a second solution B;

S14. Add the second solution B to the first solution A and mix thoroughly to obtain a mixed solution C;

S15. Add 0.03 mol of citric acid to the mixed solution C, and stir and mix thoroughly; continue to stir for 12 h under normal temperature and pressure environment to obtain 0.3 mol / L sol;

S16. Take 20 mL of the 0.3 mol / L sol prepared in step S15, add 20 mL of ethylene glycol methyl ether to dilute, and then add 10 mL of propionic anhydride, mix and stir well;

S17. Finally, it is transferred to a conical flask and sealed for storage. After standing for 72 hours, it can be used for subsequent preparation of the film.

S21, a Nb-doped strontium titanate (STO) single crystal substrate is selected, the crystal orientation is in the [001] direction, the doping concentration is 0.5%, and the substrate size is 5 * 5 * 1mm;

S22. The substrate of step S21 is cleaned in an oxygen plasma cleaning machine for 100s;

S23: The substrate cleaned in step S22 is placed on a homogenizer, and then the substrate is evacuated and fixed;

S24. Add the sol prepared in step S17 to the substrate in a static dropwise manner;

S25, press the program start key of the homogenizer to start spin coating; the spin coating process is set to:

step

Speed r / min

Time / second

Acceleration

Slow process	600	7	600
Fast process	5000	15	1200

S26. After the homogenization process of the homogenizer stops, release the vacuum and remove the sample.

In step S31, the substrate sample coated with the sol in step S26 is transferred to a constant temperature heating table, and it is dried for a while near the heating table (180 ° C). After the surface is uniformly discolored, it is placed in the center of the heating table;

In step S32, the temperature of the heating table is further adjusted to 400 ° C, and heating is continued for 30 minutes.

The above steps S24 to S32 are cured to form a single coating layer. Generally, the thickness of the single film layer formed after spin coating is controlled by the amount of sol to be added is about tens of nanometers; therefore, according to the required film thickness of different products, technicians In the implementation, the above steps S24 to S32 can be repeated, and a multilayer film can be formed until the thickness of the film layer reaches the required thickness, and then it can be stopped; in this embodiment 1, the above steps are repeated until the thickness of the film layer is about 10 μm and then stopped. ;

S40. The substrate coated with the cured multilayer film layer is annealed. The annealing parameters are as follows:

Phase sequence	Target temperature	Rise / fall time		Holding time
1	100 ℃	80s		30s
2	450 ℃	70s		300s
3	800 ℃	70s	600s
4	30 ℃	1600s	10s

S50: Take out the thin film sample after the annealing treatment in step S40, and then peel off the substrate, that is, the B-site doped bismuth ferrite solid solution thin film prepared in this embodiment 1.

Example 2

In this embodiment 2, the following detailed steps are used to prepare a thin film:

S10. Calculate and obtain the amount of each material according to (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ (x = 0.1, y = 0.7). Step 2 of Example 2 prepared a 0.3 mol / L 100 mL sol.

S21, select LSMO substrate, size is 5 * 5 * 1mm;

S22. The substrate in step S21 is cleaned in an oxygen plasma cleaner for 90 seconds.

S23. Place the substrate cleaned in step S22 on a homogenizer, and then vacuum-fix the substrate;

S24. Add the sol prepared in step S10 to the substrate in a static dropwise manner;

S25, press the program start button of the homogenizer to start spin coating; the spin coating process is set to:

step

Speed r / min

Time / second

Acceleration

Slow process	580	5	600
Fast process	4900	13	1200

S26. After the homogenization process of the homogenizer stops, release the vacuum and remove the sample.

In step S31, the substrate sample coated with the sol in step S26 is transferred to a constant temperature heating table, and it is dried for a while near the heating table (180 ° C). After the surface is uniformly discolored, it is placed in the center of the heating table;

In step S32, the temperature of the heating table is further adjusted to 400 ° C, and heating is continued for 28 minutes.

The above steps S24 to S32 are cured to form a single coating layer. Generally, the thickness of the single film layer formed after spin coating is controlled by the amount of sol to be added is about tens of nanometers; therefore, according to the required film thickness of different products, technicians In the implementation, the above steps S24 to S32 can be repeated, and a multilayer film can be formed until the thickness of the film layer reaches the required thickness, and then it can be stopped; in this embodiment 1, the above steps are repeated until the thickness of the film layer is about 10 μm and then stopped. ;

S40. The substrate coated with the cured multilayer film layer is annealed. The annealing parameters are as follows:

Phase sequence	Target temperature	Rise / fall time		Holding time
1	95 ℃	75s		25s
2	440 ℃	65s		295s
3	700 ℃	65s	590s
4	28 ℃	1570s	8s

In S50, the thin film sample after the annealing treatment in step S40 is taken out, and then the substrate is peeled off, that is, the B-site doped bismuth ferrite solid solution thin film prepared in this embodiment 2.

Example 3

In this embodiment 3, the following detailed steps are used to prepare a thin film:

S10. Calculate and obtain the amount of each material according to (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ (x = 0.2, y = 0.95). In Example 3, 0.3 mol / L of 100 mL of sol was prepared.

S21, select a LAO substrate, and the substrate size is 5 * 5 * 1mm;

S22. The substrate in step S21 is cleaned in an oxygen plasma cleaning machine for 95 seconds;

S23: The substrate cleaned in step S22 is placed on a homogenizer, and then the substrate is evacuated and fixed;

S24. Add the sol prepared in step S17 to the substrate in a static dropwise manner;

S25, press the program start key of the homogenizer to start spin coating; the spin coating process is set to:

step

Speed r / min

Time / second

Acceleration

Slow process	620	9	600
Fast process	5100	16	1200

S26. After the homogenization process of the homogenizer stops, release the vacuum and remove the sample.

In step S31, the substrate sample coated with the sol in step S26 is transferred to a constant temperature heating table, and it is dried for a while near the heating table (180 ° C). After the surface is uniformly discolored, it is placed in the center of the heating table;

In step S32, the temperature of the heating table is further adjusted to 400 ° C, and heating is continued for 32 minutes.

The above steps S24 to S32 are cured to form a single coating layer. Generally, the thickness of the single film layer formed after spin coating is controlled by the amount of sol to be added is about tens of nanometers; therefore, according to the required film thickness of different products, technicians In the implementation, the above steps S24 to S32 can be repeated, and a multilayer film can be formed until the thickness of the film layer reaches the required thickness, and then it can be stopped; in this embodiment 1, the above steps are repeated until the thickness of the film layer is about 10 μm and then stopped. ;

S40. The substrate coated with the cured multilayer film layer is annealed. The annealing parameters are as follows:

Phase sequence	Target temperature	Rise / fall time		Holding time
1	105 ℃	85s		35s
2	460 ℃	75s		305s
3	810 ℃	75s	610s
4	32 ℃	1630s	12s

In S50, the thin film sample after the annealing treatment in step S40 is taken out, and then the substrate is peeled off, that is, the B-site doped bismuth ferrite solid solution thin film prepared in this embodiment 3.

Further, the film prepared in the embodiment of the present invention, in order to verify the properties of the film, testing the film prepared in Example 1 includes:

(1) The voltage writing shown in Figure 1 is performed in a 4 micron area on the surface of the thin film sample, and then the piezoelectric PFM scan in the 5 micron area is performed. The results of the film morphology are shown in Figure 2 and the amplitude is shown in Figure 3 The phase is shown in Figure 4. It can be seen from the basic performance tests of FIGS. 2 to 4 that the phase after the negative voltage writing of the film prepared in Example 1 of the present invention is basically the same as the original phase of the unwritten area film, indicating that the original film has a single polarization direction. .

(2) XRD diffraction was performed on the prepared thin film sample, and the result is shown in FIG. 5. It can be seen from FIG. 5 that the sample and the substrate only have 001 and 002 diffraction peaks, and no other miscellaneous peaks, indicating that the sample is 001. Oriented single crystal epitaxial film.

(3) The relationship between the magnetic moment of the film and the temperature is further measured. The results are shown in Fig. 6. In Fig. 6, FC and ZFC are the heating process after cooling under the magnetic field (6000Oe) and non-magnetic field (0Oe) conditions. Variation curve of the magnetic moment of the sample measured under the conditions of the magnetic field of 200 Oe in China and Canada. It can be seen that FC and ZFC overlap at more than 380K, indicating that the Curie temperature of the sample is 380K, that is, the sample has room temperature ferromagnetism.

Similarly, the film prepared by using the LSMO substrate in Example 2 was selected for testing, including:

(1) The voltage writing shown in FIG. 7 is performed in a 4 micron area on the surface of the thin film sample, and the piezoelectric force PFM scan is performed in a 5 micron area. The film morphology results are shown in FIG. 8 and the amplitude is shown in FIG. 9 The phase is shown in Figure 10. It can be seen from the basic performance tests of FIGS. 8 to 10 that the phase after the negative voltage writing of the film prepared in Example 2 of the present invention is basically the same as the original phase of the unwritten area film, indicating that the original film has a single polarization direction. .

(2) XRD diffraction was performed on the thin film sample prepared in Example 2. The results are shown in FIG. 11. As can be seen from FIG. 11, the sample and the substrate also have only 001 and 002 diffraction peaks, and no other miscellaneous peaks. The sample is a 001-oriented single crystal epitaxial film.

From the results of the above tests, it can be known that the thin film prepared by the present invention has multiferroic and single-crystal epitaxial properties at room temperature, and has good high-voltage electrical properties; compared with the sol-gel preparation of existing room-temperature multiferroic films The method has obvious progress.

The above are only preferred embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description and drawings of the present invention, or directly or indirectly used in other related technical fields All are included in the patent protection scope of the present invention.

Claims (10)

1. A method for preparing a B-site doped bismuth ferrite solid solution film, which comprises the following steps:

   Preparing B-doped bismuth ferrite solid solution sol;

   Applying the solid solution sol on a substrate to form a sol coating;

   Subjecting the sol coating on the substrate to a thermosetting treatment;

   The sol coating after the thermosetting treatment is annealed; wherein the temperature of the annealed treatment is 700 to 900 ° C, and the temperature decrease rate during the temperature reduction process of the annealed treatment is 0.5 to 1 ° C / s.
2. The method for preparing a B-site doped bismuth ferrite solid solution film according to claim 1, wherein the B-site doped bismuth ferrite solid solution sol is

   (1-x) BiTi _{(1-y) / 2} Fe _y Mg _{(1-y) / 2} O ₃ -xCaTiO ₃ , where x = 0.1 to 0.2 and y = 0.7 to 0.95.
3. The method for preparing a B-site doped bismuth ferrite solid solution film according to claim 1 or 2, wherein the substrate has a lattice constant of 3.85 to 3.95 angstroms.
4. The method for preparing a B-doped bismuth ferrite solid solution film according to claim 3, wherein the substrate is one of NbSTO, LSMO, or LAO.
5. The method for preparing a B-site doped bismuth ferrite solid solution film according to claim 2, wherein in the step of preparing a B-site doped bismuth ferrite solid solution sol,

   A dehydrating agent, propionic anhydride, is added to the B-site doped bismuth ferrite solid solution sol.
6. The method for preparing a B-site doped bismuth ferrite solid solution film according to claim 2 or 5, wherein the solvent of the B-site doped bismuth ferrite solid solution sol is ethylene glycol methyl ether.
7. The method for preparing a B-site doped bismuth ferrite solid solution film according to claim 2 or 5, wherein a chelating agent citric acid is added to the B-site doped bismuth ferrite solid solution sol.
8. The method for preparing a B-position doped bismuth ferrite solid solution film according to claim 1 or 2, wherein in the step of applying the solid solution sol on a substrate to form a sol coating layer, the coating method is Spin coating, the spin coating process includes:

   Spin coating at a first speed and spin coating at a second speed;

   The first rotation speed is 580 to 620 r / min, and the second rotation speed is 4900 to 5100 r / min.
9. A B-site doped bismuth ferrite solid solution thin film, which is prepared by the method for preparing a B-site doped bismuth ferrite solid solution thin film according to any one of claims 1 to 8.
10. The application of the B-site doped bismuth ferrite solid solution film according to claim 9 in a sensor or a driver.

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