阅读说明：本技术 一种基于磁致伸缩实现BaTiO3薄膜铁电极化转动的使用方法 (Implementation of BaTiO based on magnetostriction3Method for using ferroelectric polarization rotation of thin film ) 是由 仲崇贵 顾小伟 朱森杰 杨民民 李祥彪 周朋霞 于 2020-03-20 设计创作，主要内容包括：本发明公开了一种基于磁致伸缩实现BaTiO<Sub>3</Sub>薄膜铁电极化转动的使用方法,包括衬底和BaTiO<Sub>3</Sub>薄膜,BaTiO<Sub>3</Sub>薄膜沿着[001]方向外延生长在衬底上,对薄膜需进行单畴化处理,将该生长于衬底上的薄膜放置在垂直于薄膜表面且不断加大的外加电场中,测量薄膜c方向的极化强度,至极化强度不再增加,撤去外电场；将金属导线卷绕在金属芯上,固定在衬底的两侧,导线通过可调电阻连接于直流稳压电源；以初始极化方向作为起始方向,逐渐加大电压,记录铁电极化方向的改变,至铁电极化翻转到平行于薄膜平面；重新接通电源,可通过调控电压进行10进制编码的信息存储或读取。本发明通过磁致伸缩和应变耦合,使得薄膜产生双轴等效应变而驱动铁电薄膜自发极化转动,实现多态存储。(The invention discloses a method for realizing BaTiO based on magnetostriction 3 The method for using ferroelectric polarization rotation of thin film comprises a substrate and BaTiO 3 Film, BaTiO 3 Film is along [001 ]]Directionally epitaxially growing on a substrate, performing single domain processing on the film, placing the film grown on the substrate in an external electric field which is vertical to the surface of the film and is continuously increased, measuring the polarization strength of the film in the c direction until the polarization strength is not increased any more, and removing the external electric field; winding a metal lead on the metal core, fixing the metal lead on two sides of the substrate, and connecting the lead to a direct current stabilized voltage power supply through an adjustable resistor; gradually increasing voltage by taking the initial polarization direction as an initial direction, and recording the change of the ferroelectric polarization direction until the ferroelectric polarization is turned over to be parallel to the plane of the film; the power supply is switched on again and the power supply is switched on again,the 10-system coded information can be stored or read by regulating and controlling the voltage. The invention enables the film to generate biaxial equivalent strain to drive the ferroelectric film to rotate in spontaneous polarization through magnetostriction and strain coupling, thereby realizing multi-state storage.)

1. Implementation of BaTiO based on magnetostriction₃The use method of the ferroelectric polarization rotation of the thin film is characterized in that: comprises a substrate and BaTiO₃Film of said BaTiO₃The film is grown and fixed above the substrate, and the specific operation is as follows: film is along [001 ]]Directional epitaxial growth, wherein the lattice constant of the film is larger than that of the substrate; the film is subjected to the compressive strain of the substrate, so that ferroelectric polarization has the tendency of being arranged along the c-axis direction; performing single domain treatment on the film, placing the film grown on the substrate in an external electric field perpendicular to the surface of the film, and then continuously applyingMeasuring the polarization strength of the film in the c direction in a large electric field until the ferroelectric polarization strength of the BaTiO3 film is not increased any more, and removing the external electric field; winding a metal wire on the metal core, fixing the metal wire on two sides of the substrate, connecting the wire to a direct current stabilized voltage power supply through an adjustable resistor, and enabling the electromotive force of a power supply to meet a magnetic field excited by current in a circuit so as to enable the magnetostrictive strain of the substrate material to be greater than or equal to 2% to become a reference standard; switching on a power supply by taking the initial polarization direction as an initial direction, gradually increasing voltage, recording the change of the ferroelectric polarization direction until the ferroelectric polarization is turned over to be parallel to the plane of the thin film, switching off the power supply, and judging the relation between the rotation of the polarization direction and the voltage change; and switching on the power supply again, rotating the ferroelectric polarization by regulating and controlling the voltage, storing or reading the information of the 10-system code, and determining the corresponding relation between the external voltage and the ferroelectric polarization direction.

2. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: the BaTiO₃The film is grown on [001 ] by epitaxial method]On the square substrate in the direction, in order to ensure that the crystal lattice between the substrate and the film has good adaptation, ensure the stoichiometric proportion of the film material and reduce the loss of strain transfer, the film should grow in an ultra-vacuum environment, and the thickness of the film is less than or equal to 10 um.

3. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: the substrate is made of a material with magnetostriction, and the following specific requirements are as follows: (1) polarization flip 90^oThe required biaxial strain range is 1.5%, and the magnetostriction coefficient of the substrate material is 1 x 10^-2-3*10^-2Part of rare earth metal oxide can be taken; (2) selecting isotropic bulk magnetostrictive materials as a substrate, wherein the isotropic bulk magnetostrictive materials have equivalent positive transverse and longitudinal magnetostrictive coefficients; (3) selecting tetragonal system and BaTiO with lattice constant ratio₃The material with the lattice constant of the film being 1.5% smaller is used as the substrate.

4. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: and placing the film obtained by epitaxial growth in a strong constant external electric field for initial polarization, and ensuring that the direction of the initial polarization is set to be vertical to the surface direction of the film so as to ensure that the obtained film is a single-phase single-crystal single-domain film, wherein the direction of the external electric field is vertical to the surface of the film.

5. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: a magnetic field is excited to the substrate through current in a closed loop, large strain expansion and contraction are generated in the substrate due to magnetostriction, then the large strain expansion and contraction are coupled to the ferroelectric thin film through strain, biaxial equivalent strain is generated in the thin film due to biaxial equal strain in the substrate, and therefore phase change and polarization rotation of the thin film are driven.

6. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: in the whole strain range, BaTiO₃The film has three phase changes and undergoes four phases, wherein two tetragonal phases, one trigonal phase and one cubic phase are adopted, and when external stress drives polarization to turn over, even if BaTiO is under the action of interface strain₃These structural transformations occur in the film, but since the transformations are sequential second order transformations, the polarization is in the plane perpendicular to abWhen the polarization is turned in the plane, the change of the polarization P is continuous and no jump occurs.

7. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: to BaTiO₃First principle calculation was performed on the film to determine the polarization P-stress F relationship, and when the tensile strain was about 0.75%, Pz =0, Px = Py, and the polarization reached in the ab planeMaximum, and as the tensile strain decreases, Px = Py =0 and Pz reaches a maximum, i.e., the polarization completely flips to the c-axis direction, by the time the compressive strain increases to 0.01, i.e., 1%.

8. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: the area of the side face of the metal chip is slightly larger than that of the side face of the substrate, and the centers of the two side faces are flush.

9. The use method of realizing ferroelectric polarization rotation of BaTiO3 thin film based on magnetostriction as claimed in claim 1, wherein: the polarization rotation angle is defined by taking the polarization strength P as an initial direction along the c-axis direction and the included angle between the polarization strength and the c-axis, and is specifically as follows: when the voltage is zero, theta is 0 degrees when the polarization is along the c axis, the voltage is gradually increased, and when the polarization direction starts to rotate, the voltage value is recorded; then, it is polarized in ferroelectric modeRecording a voltage value every time the plane rotates 10 degrees as an interval until the included angle theta between the ferroelectric polarization and the c axis is 90 degrees, recording 10 voltage values in total, and making a voltage-ferroelectric polarization turning angle relation curve; the above process is repeated, and the average value of the voltage is measured for a plurality of times.

10. The use method of magnetostrictive based BaTiO3 thin film ferroelectric polarization rotation according to claim 9, characterized in that: because different angles correspond to different polarization states, the corresponding relation between the ferroelectric polarization state and the voltage magnitude is established through the measurement, and the required polarization quantum state can be obtained by modulating the applied voltage; if the change of 10 degrees is used as a quantum state conversion according to the measured data, 10 quantum states can be obtained within a 90-degree rotation range, and the ferroelectric polarization is rotated by regulating and controlling the voltage, so that the information of the 10-system code can be stored or read.

Technical Field

The invention relates to the field of dielectric material application, in particular to a method for realizing BaTiO based on magnetostriction₃The method for using the ferroelectric polarization rotation of the thin film.

Background

The ferroelectric material has spontaneous ferroelectric polarization and larger piezoelectric and electrostrictive properties, so the ferroelectric material has extremely wide application prospect in the fields of modern information storage, photoelectric sensing and the like. It can be seen from the hysteresis curve of the ferroelectric medium that under the action of the electric field, the polarization can be reversed upwards and downwards, and according to the basic theory of electrical storage, if the polarization is taken upwards as the "0" state, the polarization is taken downwards to form the "1" state, which is also the basic basis for binary data storage.

With the rapid development of modern society, the integration level of large data-requiring components is higher and higher, and the functions are more and more, while the information storage technology based on binary system can not meet the social development requirement gradually, so the development of the polymorphic storage technology is imperative. Recently, the group of the Masu good subjects of the institute of metals of the Chinese academy of sciences has been ultra-thin PbZr_0.52Ti_0.48O₃The phenomenon of interfacial oxygen octahedron coupling regulation polarization rotation is found in the ferroelectric, and an effective mechanism is provided for regulating polarization rotation in the ferroelectric medium. And meanwhile, the continuous rotation of polarization also provides a support carrier for realizing multi-state storage.

Through theoretical research, we found BaTiO₃The ferroelectric thin film has polarization rotation characteristics driven by biaxial equivalent strain. That is, by adding BaTiO₃The ferroelectric film is applied with biaxial strain, and the method can realize the similar effect to that of ultrathin PbZr_0.52Ti_0.48O₃The phenomenon of interfacial oxygen octahedron coupling regulation polarization rotation is found in the ferroelectric, so that BaTiO is realized₃The possibility of multi-state storage in thin films. And for an ultra-thin film, biaxial, etcThe strain-effective application can be by a variety of methods, either simple mechanical stretching, or by strain transmission between the film and the substrate.

Disclosure of Invention

The invention aims to provide a method for realizing BaTiO based on magnetostriction₃The use method of the ferroelectric polarization rotation of the film is an effective method for realizing the multi-state storage by enabling the film to generate biaxial equivalent strain through magnetostriction and strain coupling so as to drive the ferroelectric film to rotate in a spontaneous polarization manner.

In order to realize the purpose of the invention, the invention adopts the following technical scheme: implementation of BaTiO based on magnetostriction₃The method for using ferroelectric polarization rotation of thin film comprises a substrate and BaTiO₃Film of said BaTiO₃The film is grown and fixed above the substrate, and the specific operation is as follows: film is along [001 ]]Directional epitaxial growth, wherein the lattice constant of the film is larger than that of the substrate; the film is subjected to the compressive strain of the substrate, so that ferroelectric polarization has the tendency of being arranged along the c-axis direction; performing single domain treatment on the film, placing the film grown on the substrate in an external electric field vertical to the surface of the film, then increasing the electric field continuously, measuring the polarization strength of the film in the c direction until the ferroelectric polarization strength of the BaTiO3 film is not increased any more, and removing the external electric field; winding a metal wire on the metal core, fixing the metal wire on two sides of the substrate, connecting the wire to a direct current stabilized voltage power supply through an adjustable resistor, and enabling the electromotive force of a power supply to meet a magnetic field excited by current in a circuit so as to enable the magnetostrictive strain of the substrate material to be greater than or equal to 2% to become a reference standard; switching on a power supply by taking the initial polarization direction as an initial direction, gradually increasing voltage, recording the change of the ferroelectric polarization direction until the ferroelectric polarization is turned over to be parallel to the plane of the thin film, switching off the power supply, and judging the relation between the rotation of the polarization direction and the voltage change; and switching on the power supply again, rotating the ferroelectric polarization by regulating and controlling the voltage, storing or reading the information of the 10-system code, and determining the corresponding relation between the external voltage and the ferroelectric polarization direction.

Preferably, the BaTiO₃The film is grown on [001 ] by epitaxial method]On a square substrate of direction, isThe lattice between the substrate and the film is well adapted, the ideal chemical proportion of the film material is ensured, the loss of strain transfer is reduced, the film is required to grow in an ultra-vacuum environment, and the thickness of the film is less than or equal to 10 um.

Preferably, the substrate is made of a material with magnetostriction, and the following requirements are specifically required: (1) polarization flip 90^oThe required biaxial strain range is 1.5%, and the magnetostriction coefficient of the substrate material is 1 x 10^-2-3*10^-2Part of rare earth metal oxide can be taken; (2) selecting isotropic bulk magnetostrictive materials as a substrate, wherein the isotropic bulk magnetostrictive materials have equivalent positive transverse and longitudinal magnetostrictive coefficients; (3) selecting tetragonal system and BaTiO with lattice constant ratio₃The material with the lattice constant of the film being 1.5% smaller is used as the substrate.

Preferably, the film obtained by epitaxial growth is subjected to initial polarization in a strong constant external electric field, and in order to ensure that the direction of the initial polarization is set to be vertical to the surface of the film, the obtained film is a single-phase single-crystal single-domain film, and the direction of the external electric field is vertical to the surface of the film.

Preferably, a magnetic field is excited to the substrate by a current in a closed loop, large strain expansion and contraction are generated in the substrate due to magnetostriction of the substrate, and then the large strain expansion and contraction are coupled to the ferroelectric thin film through strain, so that biaxial equivalent strain is also generated in the thin film due to biaxial equal strain in the substrate, and phase change and polarization rotation of the thin film are driven.

Preferably, BaTiO is present over the entire strain range₃The film has three phase changes and undergoes four phases, wherein two tetragonal phases, one trigonal phase and one cubic phase are adopted, and when external stress drives polarization to turn over, even if BaTiO is under the action of interface strain₃These structural phase transitions occur in the film, but since the phase transition is a continuous second-order phase transition, the polarization is perpendicular to the first-order phase transitionabThe change in the magnitude of polarization P is always continuous and no jump occurs when the substrate is turned in-plane.

Preferably, for BaTiO₃The film is subjected to first principle calculation, and the relation of polarization P-stress F is measured, and when the tensile strain is about 0.75%, Pz =0, Px = Py, polarization reaches a maximum in the ab-plane, and as tensile strain decreases, by the time compressive strain increases to 0.01, i.e., 1%, Px = Py =0, Pz reaches a maximum, and polarization completely flips to the c-axis direction.

Preferably, the area of the side surface of the metal chip is slightly larger than that of the side surface of the substrate, and the centers of the two side surfaces are flush.

Preferably, the polarization rotation angle is defined by an angle between the polarization intensity and the c axis, taking the polarization intensity P along the c axis as an initial direction, and specifically as follows: when the voltage is zero, theta is 0 degrees when the polarization is along the c axis, the voltage is gradually increased, and when the polarization direction starts to rotate, the voltage value is recorded; then, it is polarized in ferroelectric modeRecording a voltage value at each interval of 10 degrees of rotation in the plane until the included angle theta between the ferroelectric polarization and the c axis is 90 degrees, recording 10 voltage values in total, and making a voltage-ferroelectric polarization turning angle relation curve; the above process is repeated, and the average value of the voltage is measured for a plurality of times.

Preferably, because different angles correspond to different polarization states, the corresponding relation between the ferroelectric polarization state and the voltage magnitude is established through the measurement, and the required quantum state can be obtained by modulating the external voltage; if the change of 10 degrees is used as a quantum state conversion according to the measured data, 10 quantum states can be obtained within a 90-degree rotation range, and the ferroelectric polarization is rotated by regulating and controlling the voltage, so that the information of the 10-system code can be stored or read.

Compared with the prior art, the technical scheme for realizing BaTiO based on magnetostriction₃The use method of the ferroelectric polarization rotation of the thin film has the following beneficial effects: the implementation of BaTiO based on magnetostriction by adopting the invention₃The use method of the ferroelectric polarization rotation of the thin film realizes the possibility of multi-state storage of data by driving the polarization rotation, because the polarization continuously rotates in the plane, the continuous rotation actually corresponds to infinite states, and each angle can be a storage state; and the storage state (polarization orientation) can be regulated and controlled by strain and an external magnetic field,the magnetic writing and electric reading are realized, the relationship between the magnitude of an external magnetic field (or the magnitude of external voltage) and a polarization turnover angle can be determined according to the strain coupling condition between the film and the substrate, namely, the polarized quantum state is determined according to the magnitude of the external magnetic field (or the external voltage); the invention has simple structure and convenient operation, can greatly improve the integration level, is easy to process, and realizes the exponential increase of the information storage data volume.

Drawings

FIG. 1 shows the implementation of BaTiO based on magnetostriction in the invention₃The structure schematic diagram of an embodiment of the using method of the thin film ferroelectric polarization rotation;

FIG. 2 shows the implementation of BaTiO based on magnetostriction in this embodiment₃Structural phase change diagram of the using method of the ferroelectric polarization rotation of the thin film;

FIG. 3 shows the implementation of BaTiO based on magnetostriction in this embodiment₃The principle of the method for using the rotation of the ferroelectric polarization of the thin film is shown schematically.

Reference numerals: 1. a film; 2. a substrate.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

FIG. 1 shows the implementation of BaTiO based on magnetostriction₃The structural schematic diagram of the using method of the ferroelectric polarization rotation of the thin film comprises a substrate 2 and BaTiO₃Film 1 of said BaTiO₃The membrane 1 is fixed above the substrate 2, the specific operation is as follows: BaTiO 2₃The film 1 is grown on [001 ] by epitaxy]On the square substrate of direction, in order to make substrate 2 and film 1 have good adaptation of lattice, guarantee the stoichiometric proportion of film 1 material, reduce the loss of strain transfer, film 1 should grow in the super vacuum environment, the thick end of film 1 is less than or equal to 10um, and the area is littleer more easily to obtain the single crystal thinner the thickness. For information storage applications, the film 1 is as thin as possible, or even as few atomic layers.

The substrate 2 is made of a material with magnetostriction, and the lattice constant of the film 1 is larger than that of the substrate 2; the method comprises the following specific steps: (1) polarization flip 90^oThe required biaxial strain range is 1.5%, linerThe material of the base 2 has a magnetostriction coefficient of 1 x 10^-2-3*10^-2Part of rare earth metal oxide can be taken; (2) isotropic bulk magnetostrictive materials are selected as the substrate 2, and have equivalent positive transverse and longitudinal magnetostrictive coefficients, so that an external magnetic field induces equal strain elongation in two vertical directions of the substrate 2, and thus, the magnetic field in one direction can be reduced; (3) selecting tetragonal system and BaTiO with lattice constant ratio₃The material with the lattice constant of the film 1 being 1.5% smaller is used as the substrate 2, the difference between the two lattice constants is not large, the mismatch strain of the film 1 is small, and the effective transmission of the strain between the film 1 and the substrate 2 can be realized.

The film 1 obtained by epitaxial growth is placed in a strong constant external electric field for initial polarization, the film 1 is subjected to the action of the compressive strain of the substrate 2 to enable ferroelectric polarization to have the tendency of being arranged along the c-axis direction, in order to ensure that the direction of the initial polarization is set to be vertical to the surface direction of the film 1, the direction of an external electric field is vertical to the surface of the film 1, and single domain processing is carried out on the film 1, so that the obtained film 1 is the single-phase single-crystal single-domain film 1. The thin film 1 grown on the substrate 2 is placed in an external electric field vertical to the surface of the thin film 1, then the electric field is continuously increased, and the polarization strength of the thin film 1c direction is measured until the BaTiO₃Until the ferroelectric polarization of the thin film 1 no longer increases, the external electric field is removed.

The metal wire is wound on the metal core and fixed on two sides of the substrate 2, and in order to generate a uniform and adjustable magnetic field in the substrate 2, the area of the side surface of the metal chip is slightly larger than that of the side surface of the substrate 2, and the centers of the two side surfaces are flush. The wire can be connected to the DC stabilized power supply through the adjustable resistor, the ammeter and the switch, and in the embodiment, the wire can be connected to the DC stabilized power supply through the adjustable resistor. The magnitude of the electromotive force of the power supply is such that the magnetic field induced by the current in the circuit causes a 2% magnetostrictive strain in the material of the substrate 2. A magnetic field is excited to the substrate 2 through current in a closed loop, large strain expansion and contraction are generated in the substrate 2 due to magnetostriction, then the large strain expansion and contraction are coupled to the ferroelectric thin film 1 through strain, biaxial equal strain in the substrate 2 causes biaxial equivalent strain to be generated in the thin film 1, and therefore phase change and polarization rotation of the thin film 1 are driven.

Taking the polarization strength P along the c-axis direction as the initial direction, switching on the power supply, gradually increasing the voltage, recording the change of the ferroelectric polarization direction until the ferroelectric polarization is turned over to be completely parallel to the plane of the film 1, and switching off the power supply. And judging the relation between the rotation of the polarization direction and the voltage change.

FIG. 2 shows the implementation of BaTiO based on magnetostriction₃Structural phase change diagram of using method of film ferroelectric polarization rotation, BaTiO in whole strain range₃The film 1 undergoes three phase changes and undergoes four phases, two tetragonal phases, one trigonal phase and one cubic phase, as shown in fig. 2, with the presence of stable phases aa, r, t, r and c in order from tension to compression. These phases are all space-inverted symmetric failure phases, all existIn-plane spontaneous ferroelectric polarization. When external stress drives polarization to turn over, even if BaTiO acts under the action of interface strain₃These structural phase transitions occur in film 1, but since the phase transition is a continuous second-order phase transition, the polarization is in the plane perpendicular to abWhen the polarization is turned in the plane, the change of the polarization P is continuous and no jump occurs.

FIG. 3 shows the implementation of BaTiO based on magnetostriction₃The principle schematic diagram of the thin film ferroelectric polarization rotation use method is realized by applying BaTiO₃Calculating a first principle of material to obtain a quantitative relation between strain and polarization component change, measuring the relation of polarization P-stress F, when the tensile strain is about 0.75%, Px = Py,abthe in-plane polarization strength reaches the maximum, Pz =0, and as the tensile strain is reduced and the compressive strain is increased to 0.01, namely 1%, Px = Py =0, Pz reaches the maximum, the polarization is completely reversed to the c-axis direction, the structural phase change can occur during the strain change process, but the continuous reversal of the polarization in the plane is not influenced.

Switching on the power supply again, and rotating the ferroelectric polarization by regulating the voltageAnd storing or reading the 10-system coded information, and determining the corresponding relation between the applied voltage and the ferroelectric polarization direction. The rotation angle theta of polarization is defined by the included angle between the polarization intensity and the c axis, and the specific details are as follows: when the voltage is zero, theta is 0 degrees when the polarization is along the c axis, the voltage is gradually increased, and when the polarization direction starts to rotate, the voltage value is recorded; then, it is polarized in ferroelectric modeRecording a voltage value every time the plane rotates 10 degrees as an interval until the included angle theta between the ferroelectric polarization and the c axis is 90 degrees, recording 10 voltage values in total, and making a voltage-ferroelectric polarization turning angle relation curve; the above process is repeated, and the average value of the voltage is measured for a plurality of times.

Because different angles correspond to different polarization states, the corresponding relation between the ferroelectric polarization state and the voltage magnitude is established through the measurement, and the required quantum state can be obtained by modulating the applied voltage; if the change of 10 degrees is used as a quantum state conversion according to the measured data, 10 quantum states can be obtained within the 90-degree rotation range, so that the ferroelectric polarization is rotated by regulating and controlling the voltage, and the information of the 10-system code is stored or read.

The foregoing is a preferred embodiment of the present invention, and it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.