CN113594364A - Multi-vortex ferroelectric domain multi-logic-state storage unit and power regulation method - Google Patents
Multi-vortex ferroelectric domain multi-logic-state storage unit and power regulation method Download PDFInfo
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Abstract
The invention discloses a multi-logic-state storage unit with multiple vortex ferroelectric domains and an electric power regulation method. And determining the state of the multi-logic-state memory cell of the multi-vortex ferroelectric domain according to the polarization directions of the residual ferroelectric layer, the dielectric layer and the ferroelectric periodic multilayer composite film layer and the force applied to the substrate. The power and electricity regulation and control method determines the logic state in the storage unit by utilizing the conductivity of the multi-logic-state storage unit of the multi-vortex ferroelectric domain after the electric power is applied, effectively improves the storage density of the ferroelectric memory, can identify the stored logic state based on the magnitude of the reading current, does not influence the stored data in the process of reading the logic state, realizes the nondestructive reading, and is beneficial to realizing the miniaturization of the ferroelectric memory due to the nanoscale size of the ferroelectric vortex domain.
Description
Technical Field
The invention relates to the field of information storage, in particular to a multi-logic-state storage unit with multi-vortex ferroelectric domains and an electric power regulation method.
Background
The ferroelectric memory based on the capacitor structure utilizes the spontaneous polarization characteristic of the ferroelectric material to store data, has the advantages of radiation resistance, fatigue resistance, good retentivity and the like, and has important application in the aspects of aircrafts, airplane black boxes, high-speed rails and the like. However, in the process of reading data, the ferroelectric memory based on the capacitor structure often involves a phenomenon of polarization reversal in a part of the memory cells, which destroys the data already written in the memory cells, and needs to perform a rewriting operation to ensure the readability of the data again. This mode greatly increases the volume and circuit complexity of the device unit, is not beneficial to miniaturization and high-density storage of the device, and also limits the improvement of the storage and reading speed. In fact, the ferroelectric material can utilize the special domain structure in the ferroelectric material for data storage, besides utilizing the remanent polarization of the material itself for data storage. The domains are regions of consistent spontaneous polarization orientation in the ferroelectric material, and the domain structure is the formation condition of the domains in the ferroelectric material. In ferroelectric materials there is a particular electric domain structure, in which the domains within the electric domain structure are not uniform in spontaneous polarization but form a particular structure resembling a vortex, which is called a ferroelectric vortex domain. Since the discovery of ferroelectric vortex domains, how to use them for data storage has become an important scientific problem. The erasing and writing of ferroelectric vortex domains is considered to be a very useful way, but practical research results show that the formation of ferroelectric vortex domains is caused by various reasons, such as stress, strain and the fact that the system reduces its own energy to reach a steady state. So far, complete erasing/writing of ferroelectric vortex domains and maintaining this state has not been achieved. Although researchers have found that applying force perpendicular to the axial direction of the ferroelectric vortex domain can temporarily erase the ferroelectric vortex domain, this state cannot be preserved after the force is removed and the ferroelectric vortex domain will return to its original state. In order to promote the application of the ferroelectric vortex domain in the aspect of information storage, the realization of the external field to regulate and control the conductivity of the ferroelectric vortex domain is a very effective way.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a multi-logic-state memory cell with multi-vortex ferroelectric domains and a power control method, which can realize at least 4 logic-state memories in a novel ferroelectric memory device that stores information based on a ferroelectric vortex domain structure by the power control method, thereby effectively increasing the storage density of the ferroelectric memory.
The technical scheme of the invention is as follows:
a multi-vortex ferroelectric domain multi-logic state storage unit comprises a substrate, a transition layer, a lower electrode, a ferroelectric layer, a dielectric and ferroelectric periodic multilayer composite film layer and an upper electrode which are sequentially arranged from bottom to top.
The multi-logic state storage unit of the multi-vortex ferroelectric domain is characterized in that a transition layer, a lower electrode, a ferroelectric layer, a dielectric and ferroelectric periodic multilayer composite film layer are epitaxially grown;
the thickness of the transition layer is 1 to 200 nm, the thickness of the bottom electrode is 1 to 30 nm, and the ratio of the thickness of the transition layer to the thickness of the bottom electrode is 1:1 to 10: 1.
The multi-vortex ferroelectric domain multi-logic-state storage unit is characterized in that the thicknesses of the lower electrode and the ferroelectric layer are 1: 1-20: 1.
The multi-logic-state storage unit of the multi-vortex ferroelectric domain is characterized in that the thickness ratio of an upper electrode to a lower electrode is 1: 1-10: 1.
The multi-logic state memory unit with the multi-vortex ferroelectric domains is characterized in that the dielectric and ferroelectric periodic multilayer composite film layer is formed by compounding n groups of composite films, wherein n is greater than or equal to 3; each group of combination films is a dielectric film and a ferroelectric film which are arranged from bottom to top.
The multi-vortex ferroelectric domain multi-logic state memory cell comprises a dielectric film with a thickness of 1 nm to 100 nm, a ferroelectric film with a thickness of 1 nm to 5 nm, and a ratio of the dielectric film to the ferroelectric film with a thickness of 1:10 to 20: 1.
The multi-vortex ferroelectric domain multi-logic state storage unit is characterized in that the transition layer is any one of strontium titanate, barium strontium titanate, strontium zirconate titanate and neodymium-doped strontium titanate;
the lower electrode is any one of strontium ruthenate, neodymium-doped strontium titanate and lanthanum strontium manganese oxide;
the ferroelectric layer is any one of lead titanate, zirconium-doped lead titanate, barium titanate and strontium-doped barium titanate;
the upper electrode is any one of strontium ruthenate, neodymium-doped strontium titanate, lanthanum strontium manganese oxide, gold, silver, platinum, copper, aluminum, copper alloy, aluminum alloy, gold alloy, platinum alloy, graphene, carbon nano tube, molybdenum disulfide, tin sulfide, stannous sulfide and tungsten selenide;
the dielectric film is any one of strontium titanate, zirconium-doped strontium titanate, neodymium-doped strontium titanate, bismuth-doped strontium titanate and lanthanum-doped strontium titanate;
the ferroelectric film is any one of lead titanate, zirconium-doped lead titanate, barium titanate, and strontium-doped barium titanate.
An electric power regulation method for a multi-logical-state memory cell with multi-vortex ferroelectric domains as described above, comprising the following steps:
electric regulation and control: applying voltage between the lower electrode and the upper electrode, and regulating and controlling the ferroelectric layer, the dielectric layer and the ferroelectric periodic multilayer composite film layer to show upward or downward residual polarization so that the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted into other stable logic states;
force regulation and control: and applying a force vertical to the substrate on the upper electrode while applying a voltage between the lower electrode and the upper electrode, and removing the force to enable the multi-logic-state memory cell of the multi-vortex ferroelectric domain to be converted into other stable logic states.
The electric power regulation and control method of the multi-logic-state storage unit of the multi-vortex ferroelectric domain further comprises the following steps:
applying a fixed electric field between the lower electrode and the upper electrode, and recording the current magnitude in different logic states as reference current;
the voltage of the fixed electric field is 0.001V-3.0V.
The electric power regulation and control method of the multi-logic-state storage unit of the multi-vortex ferroelectric domain further comprises the following steps:
and applying a fixed electric field between the lower electrode and the upper electrode to obtain the current of the multi-logic-state storage unit of the multi-vortex ferroelectric domain, comparing the current with a reference current, and identifying the logic state of the multi-logic-state storage unit of the multi-vortex ferroelectric domain according to the read current.
Has the advantages that: the multi-logic-state storage unit of the multi-vortex ferroelectric domain can be applied to a novel ferroelectric memory device for storing information based on a ferroelectric vortex domain structure, at least 4 logic states can be stored in the novel ferroelectric memory device for storing information based on the ferroelectric vortex domain structure through an electric and electric regulation method, and the storage density of the ferroelectric memory is effectively improved. In addition, the stored logic state can be identified based on the magnitude of the reading current, the stored data cannot be influenced in the process of reading the logic state, nondestructive reading is achieved, and the nanoscale size of the ferroelectric vortex domain is beneficial to achieving miniaturization of the ferroelectric memory.
Drawings
FIG. 1 is a schematic structural diagram of a multi-logical-state memory cell with multi-vortex ferroelectric domains according to the present invention.
Fig. 2 is a schematic diagram of an internal structure of an intermediate and ferroelectric periodic multilayer composite thin film layer in a multi-logical-state memory cell with multiple vortex ferroelectric domains, where n = 3.
FIG. 3 is a model diagram of the ferroelectric layer, dielectric layer and ferroelectric periodic multi-layer composite thin film layer with remnant polarization upward as a whole when voltage is applied to a multi-logical-state memory cell with multi-vortex ferroelectric domains according to the present invention, wherein arrows indicate the direction of remnant polarization p.
FIG. 4 is a schematic diagram of a multi-logical-state memory cell with multi-vortex ferroelectric domains according to the present invention, wherein the ferroelectric layer, the dielectric layer and the ferroelectric periodic multi-layer composite thin film layer have a remnant polarization downward as a whole, and arrows indicate the directions of remnant polarization p.
FIG. 5 is a model diagram of the force applied by a multi-logical-state memory cell of a multi-vortex ferroelectric domain according to the present invention, wherein the arrows indicate the direction of remanent polarization p.
FIG. 6 shows a multi-vortex ferroelectric domain multi-logic state memory cell ferroelectric layer PbZr according to the present invention0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3Piezoelectric mode test results of atomic force microscopy of stacked structures.
FIG. 7 shows the I-V test results of the multi-logical state memory cell of the multi-vortex ferroelectric domain after applying different forces.
Description of reference numerals: 1. a substrate; 2. a transition layer; 3. a lower electrode; 4. a ferroelectric layer; 5. dielectric and ferroelectric periodic multilayer composite thin film layers; 6. an upper electrode; 51. a dielectric film; 52 a ferroelectric film.
Detailed Description
The invention provides a multi-vortex ferroelectric domain multi-logic state memory cell and an electric power regulation method, and the invention is further detailed below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.
The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.
The invention aims to provide a multi-logic-state storage unit of a multi-vortex ferroelectric domain and an electric power regulation and control method thereof, which can be applied to a novel ferroelectric memory device for storing information based on a ferroelectric vortex domain structure, at least 4 logic states can be stored in the novel ferroelectric memory device for storing information by utilizing the ferroelectric vortex domain structure through the electric power regulation and control method, the storage density of the ferroelectric memory is effectively improved, the stored logic states can be identified based on the magnitude of reading current, the stored data cannot be influenced in the process of reading the logic states, nondestructive reading is realized, and the nanoscale size of the ferroelectric vortex domain is beneficial to realizing miniaturization of the ferroelectric memory.
Specifically, the multi-logic-state memory cell of the multi-vortex ferroelectric domain, as shown in fig. 1, includes, from bottom to top, a substrate 1, a transition layer 2, a lower electrode 3, a ferroelectric layer 4, a dielectric and ferroelectric periodic multilayer composite thin film layer 5, and an upper electrode 6, which are sequentially disposed.
After the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite thin film layer 5 are prepared, a ferroelectric vortex domain structure is spontaneously formed in the system, and the central axis of the ferroelectric vortex domain is parallel to the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite thin film layer 5.
The interior of the structure of the simple dielectric and ferroelectric periodic multilayer composite film layer can form a stable ferroelectric vortex domain state, the ferroelectric vortex domain can be reconstructed under the action of an applied electric field, but the ferroelectric vortex domain structure can be restored after the electric field is removed. In the invention, the stacked structure of the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is adopted, so that the inhibition effect of the ferroelectric vortex domain structure on the out-of-plane polarization can be reduced, and the integral ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 can show upward or downward residual polarization after the electric field is applied.
The multi-logic-state storage unit of the multi-vortex ferroelectric domain can store at least 4 logic states.
The transition layer 2 and the lower electrode 3 are epitaxially grown, the thickness of the transition layer 2 is 1-200 nm, the thickness of the lower electrode 3 is 1-30 nm, and the ratio of the thicknesses of the transition layer 2 and the lower electrode 3 is 1: 1-10: 1.
The transition layer 2 is any one of strontium titanate, barium strontium titanate, strontium zirconate titanate and neodymium-doped strontium titanate, and the lower electrode 3 is any one of strontium ruthenate, neodymium-doped strontium titanate and lanthanum strontium manganese oxide.
When the material and the thickness of the transition layer 2 are different, the lattice constant of the lower electrode 3 is affected, and the strain state of the lower electrode 3 is further affected, so that the strain of the lower electrode 3 can be controlled by controlling the material type and the thickness of the transition layer 2, and the conductivity of the lower electrode 3 is improved. The thickness of the lower electrode 3 is controlled below the transition layer 2, so that the fluctuation of the lower electrode 3 can be controlled, the flatness of the lower electrode 3 is guaranteed, and the quality of the lower electrode 3 is improved.
The thickness of the ferroelectric layer 4 is smaller than that of the lower electrode 3, and the ratio of the thicknesses of the lower electrode 3 and the ferroelectric layer 4 ranges from 1:1 to 20: 1. The material of the ferroelectric layer 4 is any one of lead titanate, zirconium-doped lead titanate, barium titanate, and strontium-doped barium titanate.
The strain of the dielectric and ferroelectric periodic multilayer composite thin film layer 5 can be controlled by controlling the material type and thickness of the ferroelectric layer 4, and the thickness of the lower electrode 3 is larger than that of the ferroelectric layer 4, so that the strain of the ferroelectric layer 4 can be prevented from being released, and the formation of vortex domains in the dielectric and ferroelectric periodic multilayer composite thin film layer 5 can be ensured. The thickness of the ferroelectric layer 4 is controlled under the lower electrode 3, and the fluctuation of the ferroelectric layer 4 can also be controlled, thereby ensuring the flatness of the dielectric and ferroelectric periodic multilayer composite thin film layer 5 and improving the quality of the dielectric and ferroelectric periodic multilayer composite thin film layer 5.
The thickness ratio of the upper electrode to the lower electrode ranges from 1:1 to 10: 1. The thickness of the upper electrode is larger than that of the lower electrode, so that the ferroelectric layer, the dielectric and ferroelectric periodic multilayer composite film layer can be protected from being damaged when mechanical load is applied. The upper electrode is made of any one of strontium ruthenate, neodymium-doped strontium titanate, lanthanum strontium manganese oxide, gold, silver, platinum, copper, aluminum, copper alloy, aluminum alloy, gold alloy, platinum alloy, graphene, carbon nano tube, molybdenum disulfide, tin sulfide, stannous sulfide and tungsten selenide.
As shown in fig. 2, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is formed by compositing n sets of composite films, which can be expressed as (dielectric film/ferroelectric film) n, wherein each set of composite films is a dielectric film 51 and a ferroelectric film 52 arranged from bottom to top. Where n is greater than or equal to 3, the situation is shown in fig. 2 when n = 3. The ratio of the thickness of the dielectric film to the thickness of the ferroelectric film is 1:10 to 20:1, the thickness of the dielectric film is 1 nm to 100 nm, and the thickness of the ferroelectric film is 1 nm to 5 nm. The dielectric film is any one of strontium titanate, zirconium-doped strontium titanate, neodymium-doped strontium titanate, bismuth-doped strontium titanate, and lanthanum-doped strontium titanate, and the ferroelectric film is any one of lead titanate, zirconium-doped lead titanate, barium titanate, and strontium-doped barium titanate.
The dielectric and ferroelectric periodic multilayer composite thin film layer 5 has the periodic dielectric film 51 and the ferroelectric film 52 epitaxially grown, and also has the ferroelectric layer 4 epitaxially grown. The epitaxial growth of the ferroelectric layer 4, the periodic dielectric film 51, and the ferroelectric film 52 is a necessary condition for forming a ferroelectric vortex domain structure in the dielectric and ferroelectric periodic multilayer composite thin film layer 5.
As shown in fig. 3, when a downward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logical state memory cell of the multi-vortex ferroelectric domain (fig. 3a), the remanent polarization direction of the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 as a whole is downward (fig. 3 b).
As shown in fig. 4, when an upward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logical-state memory cell of the multi-vortex ferroelectric domain (fig. 4a), the remanent polarization direction of the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 as a whole is upward (fig. 4 b).
When an electric field is applied between the lower electrode 3 and the upper electrode 6, the ferroelectric vortex domain structure in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is not destroyed, the ferroelectric vortex domains in the ferroelectric layer 4, the dielectric film 51 and the ferroelectric film 52 still maintain the form of vortex domains, but the polarization direction at the edges between adjacent ferroelectric vortex domains is reconfigured in a small range, so that the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 as a whole shows upward or downward residual polarization. Since the core portion of the ferroelectric vortex domain is not changed, the internal stress and strain in the ferroelectric layer, dielectric and ferroelectric periodic multilayer composite thin film layer 5 are slightly changed after the electric field is applied, so that the whole is transited from one stable state to another stable state. Particularly, the size of the ferroelectric vortex domain is extremely small, and the size of the area with changed polarization at the edge between adjacent ferroelectric vortex domains is a few atomic layers, so that the size of the memory cell can be greatly reduced.
As shown in fig. 5, the multi-logical state memory cell of the multi-vortex ferroelectric domain exhibits upward or downward remanent polarization in the entire ferroelectric layer 4, dielectric and ferroelectric periodic multilayer composite thin film layer 5, and a downward force is applied above the upper electrode 6. By utilizing the local electric field generated by the force in the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite thin film layer 5 when the force is applied and the weak coordination strain generated when the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite thin film layer 5 are self-adaptively applied, the system reaches another stable state after the force is removed.
When the applied force is different in magnitude and the residual polarization directions shown in the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite thin film layer 5 are different, the stable states formed by the system are not completely the same, and these stable states can be respectively used for representing different logic states. Setting a weak voltage (0.001V-3.0V) which does not change a polarization system in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite film layer 5, reading the current of the multi-logic-state memory cell of the multi-vortex ferroelectric domain, comparing the current with a reference current, and determining the logic state in the memory cell according to the read current and the reference current. The different logic states are current values between the partitions, with a read current in a range corresponding to one logic state.
The memory cell can have a stable logic state at the upward remanent polarization exhibited in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5; then, a certain amount of force is applied on the upper electrode 6 and the memory cell transitions to another stable logic state. The memory cell can have a stable logic state at the downward remanent polarization exhibited in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5; then, a certain amount of force is applied on the upper electrode 6 and the memory cell transitions to another stable logic state. So that the entire memory cell can store at least 4 stable logic states.
The invention also provides some specific composition combinations of the multi-logic-state storage units of the multi-vortex ferroelectric domains, and the composition combinations of the two-dimensional homogeneous structure storage units modulated by the ferroelectric domain engineering can be specifically as follows:
(1) the substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbTiO3)3And the upper electrode 6 is Pt.
(2) The substrate 1 is SrTiO3The transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbTiO3)3And the upper electrode 6 is Pt.
(3) The substrate 1 is SrTiO3The transition layer 2 is Ba0.5Sr0.5TiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbTiO3)3And the upper electrode 6 is Pt.
(4) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is La0.3Sr0.7MnO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbTiO3)3And the upper electrode 6 is Pt.
(5) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbZr0.2Ti0.8O3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbTiO3)3And the upper electrode 6 is Pt.
(6) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbZr0.2Ti0.8O3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/ PbZr0.2Ti0.8O3)3And the upper electrode 6 is Pt.
(7) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbZr0.2Ti0.8O3)3And the upper electrode 6 is Pt.
(8) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is La0.3Sr0.7MnO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbZr0.2Ti0.8O3)3And the upper electrode 6 is Pt.
(10) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbTiO3)3And the upper electrode 6 is Au.
(11) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbZr0.2Ti0.8O3)3And the upper electrode 6 isAu。
(12) The substrate 1 is SrTiO3The transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbZr0.2Ti0.8O3)3And the upper electrode 6 is Au.
(13) The substrate 1 is Si and the transition layer 2 is Ba0.5Sr0.5TiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbZr0.2Ti0.8O3)3And the upper electrode 6 is Pt.
(14) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (Ba)0.5Sr0.5TiO3/PbTiO3)3And the upper electrode 6 is Pt.
(15) The substrate 1 is Si and the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbTiO3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (Ba)0.5Sr0.5TiO3/PbTiO3)3And the upper electrode 6 is Au.
As shown in fig. 3, 4 and 5, the present invention further provides an electric power regulating method for a multi-logical-state memory cell with multi-vortex ferroelectric domains, which includes the following steps:
(1) electrical regulation and control;
(2) and (5) force regulation and control.
The memory cell can have a stable logic state at the upward remanent polarization exhibited in the ferroelectric, dielectric and ferroelectric periodic multilayer composite thin film layers; then, a force of a certain magnitude is applied to the upper electrode and the memory cell transitions to another stable logic state. The memory cell can have a stable logic state at the downward remanent polarization exhibited in the ferroelectric, dielectric and ferroelectric periodic multilayer composite thin film layers; then, a force of a certain magnitude is applied to the upper electrode and the memory cell transitions to another stable logic state. So that the entire memory cell can store at least 4 stable logic states as shown in fig. 6.
Further, the electrical regulation comprises the steps of:
and applying a voltage between the lower electrode 3 and the upper electrode 6, and regulating and controlling the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 to show upward or downward remanent polarization, so that the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted into other stable logic states.
Specifically, an upward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain, and upward remanent polarization is expressed in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5, so that the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A1; and applying a downward electric field between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain, and regulating and controlling the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite film layer 5 to show downward remanent polarization, so that the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A2.
Further, the force modulation comprises the steps of:
and applying a force vertical to the substrate on the upper electrode 6 while applying a voltage between the lower electrode 3 and the upper electrode 6, and removing the force to enable the multi-logic-state memory cell of the multi-vortex ferroelectric domain to be converted into other stable logic states.
Specifically, when an upward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain and a certain force is applied, the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A3 after the force is removed; and the applied force varies in magnitude and also transitions to different stable logic states a31, a32, etc. When a downward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain and a certain force is applied, the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A4 after the force is removed; and the applied force varies in magnitude and also transitions to different stable logic states a41, a42, etc.
Further, the electric power regulation method of the multi-logical-state memory cell of the multi-vortex ferroelectric domain further comprises the following steps:
a fixed electric field is applied between the lower electrode 3 and the upper electrode 6, and the current magnitude in different logic states is recorded as a reference current.
Specifically, a weak voltage which does not change a polarization system in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is set, a fixed electric field is applied between the lower electrode 3 and the upper electrode 6, an upward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain, upward residual polarization is expressed in the ferroelectric layer 4, the dielectric and ferroelectric periodic multilayer composite thin film layer 5, so that the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A1, and the current magnitude at the time is recorded as a reference current;
applying a downward electric field between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory unit of the multi-vortex ferroelectric domain, regulating and controlling the ferroelectric layer 4 and the dielectric and ferroelectric periodic multilayer composite film layer 5 to show downward remanent polarization, so that the multi-logic-state memory unit of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A2, and recording the current magnitude at the moment as a reference current;
when an upward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain and a certain force is applied, the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A3 after the force is removed; and the applied force is different in magnitude and can be converted into different stable logic states A31, A32 and the like, and the current magnitude at different force is recorded as the reference current;
when a downward electric field is applied between the lower electrode 3 and the upper electrode 6 of the multi-logic-state memory cell of the multi-vortex ferroelectric domain and a certain force is applied, the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted from one stable logic state to another stable logic state A4 after the force is removed; and the applied force with different magnitudes can be converted into different stable logic states A41, A42 and the like, and the magnitude of the current with different magnitudes is recorded as the reference current.
In this way, the logic state of the multi-logic-state memory cell of the multi-vortex ferroelectric domain is identified by obtaining the magnitude of the current passing current of the multi-logic-state memory cell of the multi-vortex ferroelectric domain.
Further, the electric power regulation method of the multi-logical-state memory cell of the multi-vortex ferroelectric domain further comprises the following steps:
and applying a fixed electric field between the lower electrode 3 and the upper electrode 6 to obtain the current of the multi-logic-state storage unit of the multi-vortex ferroelectric domain, comparing the current with a reference current, and identifying the logic state of the multi-logic-state storage unit of the multi-vortex ferroelectric domain according to the read current.
Thus, the state of the multi-logical-state memory cell of the multi-vortex ferroelectric domain is determined according to the polarization direction remaining in the ferroelectric layer, the dielectric and ferroelectric periodic multilayer composite thin film layer, and the magnitude of the force applied perpendicular to the substrate. The power and electricity regulation and control method determines the logic state in the storage unit by utilizing the conductivity of the multi-logic-state storage unit of the multi-vortex ferroelectric domain after the electric power is applied, effectively improves the storage density of the ferroelectric memory, can identify the stored logic state based on the magnitude of the reading current, does not influence the stored data in the process of reading the logic state, realizes the nondestructive reading, and is beneficial to realizing the miniaturization of the ferroelectric memory due to the nanoscale size of the ferroelectric vortex domain.
The present invention is further illustrated by the following specific examples.
Example 1
In embodiment 1, the multi-logical state memory cell of the multi-vortex ferroelectric domainThe substrate 1 is Si, the transition layer 2 is SrTiO3The lower electrode 3 is SrRuO3The ferroelectric layer 4 is PbZr0.2Ti0.8O3And the dielectric and ferroelectric periodic multilayer composite thin film layer 5 is (SrTiO)3/PbZr0.2Ti0.8O3)3And the upper electrode 6 is Pt. The main process for realizing the method comprises the following steps:
a) preparation of 100 nm transition layer SrTiO on Si substrate by using atomic layer deposition method3。
b) SrTiO transition layer by using atomic layer deposition method3Preparation of 15 nm lower electrode SrRuO3。
c) SrRuO at lower electrode by using atomic layer deposition method3Preparation of 5 nm ferroelectric PbZr0.2Ti0.8O3。
d) SrRuO at lower electrode by using atomic layer deposition method3Alternately preparing dielectric and ferroelectric periodic multilayer composite film layer, repeating SrTiO 3 times3/PbZr0.2Ti0.8O3Film of SrTiO each layer3、PbZr0.2Ti0.8O3The thickness of the film was 5 nm.
e) Preparing a Pt electrode with the thickness of 100 nm on the dielectric and ferroelectric periodic multilayer composite film layer by using a magnetron sputtering method, and masking and etching.
The ferroelectric layer PbZr0.2Ti0.8O3And the dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3After the preparation is finished, a ferroelectric vortex domain structure is spontaneously formed in the system, and the central axis of the ferroelectric vortex domain is parallel to the ferroelectric layer PbZr0.2Ti0.8O3And the dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3。
In this example, the structure shown in FIG. 1, a transition layer SrTiO, was used3And lower electrode SrRuO3For epitaxial growth, the thickness of the transition layer is 100 nm, the thickness of the lower electrode is 15 nm, and the ratio of the thicknesses of the transition layer and the lower electrode is less than 10: 1. Tong (Chinese character of 'tong')Over-control transition layer SrTiO3Can control the lower electrode SrRuO3Increasing the lower electrode SrRuO3The electrical conductivity properties of (a). The lower electrode SrRuO3The thickness of the transition layer is controlled to be SrTiO3Under the control of the lower electrode SrRuO3To ensure the lower electrode SrRuO3The flatness of the lower electrode is improved3The quality of (c).
Ferroelectric layer PbZr0.2Ti0.8O3Is less than the lower electrode SrRuO3The lower electrode SrRuO3And the ferroelectric layer PbZr0.2Ti0.8O3Is greater than 2: 1.
In this example, the dielectric and ferroelectric periodic multilayer composite thin film layer adopts the structure shown in FIG. 2 and is composed of a periodic dielectric film SrTiO3PbZr film0.2Ti0.8O3Is a composite of (SrTiO)3/PbZr0.2Ti0.8O3)nWherein n is equal to 3.
By controlling the ferroelectric layer PbZr0.2Ti0.8O3Can control the thickness of the dielectric and ferroelectric periodic multilayer composite film layer (SrTiO)3/PbZr0.2Ti0.8O3)3Strain of (2), lower electrode SrRuO3Is thicker than the ferroelectric layer PbZr0.2Ti0.8O3The thickness of the material can ensure the ferroelectric layer PbZr0.2Ti0.8O3The strain of the film is not released, and the dielectric and ferroelectric periodic multilayer composite film layer (SrTiO) is ensured3/PbZr0.2Ti0.8O3)3Formation of the mesovortex domain. The ferroelectric layer PbZr0.2Ti0.8O3Thickness of (2) is controlled at the lower electrode SrRuO3In addition, the ferroelectric layer PbZr can be controlled0.2Ti0.8O3To ensure dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3The flatness of the dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO) is improved3/PbZr0.2Ti0.8O3)3The quality of (c).
The upper electrode is SrRuO3And the thickness ratio of the upper electrode to the lower electrode is more than 1: 1. The thickness of the upper electrode is larger than that of the lower electrode, so that the ferroelectric layer, the dielectric and ferroelectric periodic multilayer composite film layer can be protected from being damaged when mechanical load is applied.
Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3Middle period dielectric film SrTiO3And a ferroelectric film PbZr0.2Ti0.8O3Exhibit an epitaxial growth relationship with each other and are in contact with the ferroelectric layer PbZr0.2Ti0.8O3Also in epitaxial growth relationship. Ferroelectric layer PbZr0.2Ti0.8O3Periodic dielectric film SrTiO3And a ferroelectric film PbZr0.2Ti0.8O3The epitaxial relationship between dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3The necessary condition for forming ferroelectric vortex domain structure.
In this embodiment, a voltage loading mode is adopted as shown in fig. 3a, and SrRuO is arranged at the lower electrode3And a downward electric field is applied between the upper electrode Pt (applied voltage 10V); adopts the voltage loading mode as shown in figure 4a and adopts SrRuO as the lower electrode3And the upper electrode Pt (the applied voltage is-10V). FIG. 6 shows a ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3As a result of piezoelectric mode test of atomic force microscope of stacked structure, the black region is a region with polarization down obtained after applying a positive voltage of +10V, and the white region is a region with polarization up obtained after applying a voltage of-10V. The figure shows that the structure of a ferroelectric layer, dielectric and ferroelectric periodic multilayer composite thin film layer stack can exhibit either up or down remanent polarization upon application of electric fields in different directions.
At the lower electrode SrRuO3And an electric field is applied between the upper electrode Pt and the ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3The ferroelectric vortex domain structure in the medium can not be damaged, and PbZr in the ferroelectric layer0.2Ti0.8O3SrTiO dielectric film3And a ferroelectric film PbZr0.2Ti0.8O3The ferroelectric vortex domains in each layer still keep the form of the vortex domains, but the polarization direction at the edge between the adjacent ferroelectric vortex domains is reconstructed within a small range, so that the whole ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3Exhibiting either upward or downward remanent polarization. Since the core portion of the ferroelectric vortex domain is unchanged, the ferroelectric layer, the dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO) is formed after an electric field is applied3/PbZr0.2Ti0.8O3)3The stress and strain inside the cell change slightly so that the whole changes from one stable state to another.
In this embodiment, the force loading method shown in fig. 5 is adopted, and the multi-logic-state memory cell with multi-vortex ferroelectric domains has the whole ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3When the remanent polarization is exhibited upward or downward, a downward force (6N to 18N) is applied above the upper electrode Pt. By applying a force, the ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3Local electric field generated by medium force, and ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3Self-adaptationThe weak coordinated strain that occurs when a force is applied allows the system to reach another stable state after the force is removed.
When the force is different, the ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3When the represented remanent polarization directions are different, the stable states formed by the system are not completely the same, and the stable states can be respectively used for representing different logic states. Providing a PbZr which does not change the ferroelectric layer0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3And (3) reading the current of the multi-logic-state memory cell of the multi-vortex ferroelectric domain by using the weak voltage (0.01V-0.1V) of the medium polarization system, comparing the current with a reference current, and determining the logic state in the memory cell according to the ratio of the read current to the reference current. After applying different forces to the multi-logic-state memory cell with multi-vortex ferroelectric domains, the resulting test is performed as shown in FIG. 7I-VThe test results, more than 4 different logic states can be seen from the test results. In the test process of fig. 7a, 0N, 6N, 9N, 12N, and 18N forces are applied to the multi-logical-state memory cells of the multi-vortex ferroelectric domains, respectively, a voltage of 10V is applied to polarize the multi-logical-state memory cells of the multi-vortex ferroelectric domains downward before applying the forces, and the forces are removed and then the forces are read at weak voltages of 0.01V, 0.02V, 0.03V, 0.04V, 0.05V, 0.06V, 0.07V, 0.08V, 0.09V, and 0.1VI-VCurve line. In the test process of fig. 7b, 0N, 6N, 12N, and 18N forces are applied to the multi-logical-state memory cells of the multi-vortex ferroelectric domains, respectively, a voltage of-10V is applied to polarize the multi-logical-state memory cells of the multi-vortex ferroelectric domains in an upward direction before applying the forces, and the forces are removed and then the cells are read at weak voltages of 0.01V, 0.02V, 0.03V, 0.04V, 0.05V, 0.06V, 0.07V, 0.08V, 0.09V, and 0.1VI-VCurve line.
In the ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3The memory cell can have a stable logic state when exhibiting an upward remanent polarization; then, a certain amount of force is applied on the upper electrode Pt and the memory cell transitions to another stable logic state, see fig. 7 a.
In the ferroelectric layer PbZr0.2Ti0.8O3Dielectric and ferroelectric periodic multilayer composite thin film layer (SrTiO)3/PbZr0.2Ti0.8O3)3The memory cell can have a stable logic state when exhibiting a downward remanent polarization; then, a certain amount of force is applied on the upper electrode 6 and the memory cell transitions to another stable logic state. So that the entire memory cell can store more than 4 stable logic states, see fig. 7 b.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (10)
1. A multi-vortex ferroelectric domain multi-logic state storage unit is characterized by comprising a substrate, a transition layer, a lower electrode, a ferroelectric layer, a dielectric and ferroelectric periodic multilayer composite film layer and an upper electrode which are sequentially arranged from bottom to top.
2. The multi-logical state memory cell of claim 1, wherein the transition layer, the bottom electrode, the ferroelectric layer, the dielectric and ferroelectric periodic multilayer composite thin film layers are epitaxially grown;
the thickness of the transition layer is 1 to 200 nm, the thickness of the bottom electrode is 1 to 30 nm, and the ratio of the thickness of the transition layer to the thickness of the bottom electrode is 1:1 to 10: 1.
3. The multi-logical-state memory cell with multi-vortex ferroelectric domains according to claim 1, wherein the thickness of the bottom electrode and the ferroelectric layer is 1: 1-20: 1.
4. The multi-logical-state memory cell of claim 1, wherein a ratio of a thickness of the top electrode to a thickness of the bottom electrode is 1:1 to 10: 1.
5. The multi-vortex ferroelectric domain multi-logic-state memory cell of claim 1, wherein the dielectric and ferroelectric periodic multilayer composite thin film layers are compounded from n sets of composite films, n being greater than or equal to 3; each group of combination films is a dielectric film and a ferroelectric film which are arranged from bottom to top.
6. The multi-domain multi-logical state memory cell of claim 5, wherein the dielectric film has a thickness of 1 nm to 100 nm, the ferroelectric film has a thickness of 1 nm to 5 nm, and the ratio of the thicknesses of the dielectric film and the ferroelectric film is 1:10 to 20: 1.
7. The multi-vortex ferroelectric domain multi-logic state memory cell of claim 6, wherein the transition layer is any one of strontium titanate, barium strontium titanate, strontium zirconate titanate, neodymium doped strontium titanate;
the lower electrode is any one of strontium ruthenate, neodymium-doped strontium titanate and lanthanum strontium manganese oxide;
the ferroelectric layer is any one of lead titanate, zirconium-doped lead titanate, barium titanate and strontium-doped barium titanate;
the upper electrode is any one of strontium ruthenate, neodymium-doped strontium titanate, lanthanum strontium manganese oxide, gold, silver, platinum, copper, aluminum, copper alloy, aluminum alloy, gold alloy, platinum alloy, graphene, carbon nano tube, molybdenum disulfide, tin sulfide, stannous sulfide and tungsten selenide;
the dielectric film is any one of strontium titanate, zirconium-doped strontium titanate, neodymium-doped strontium titanate, bismuth-doped strontium titanate and lanthanum-doped strontium titanate;
the ferroelectric film is any one of lead titanate, zirconium-doped lead titanate, barium titanate, and strontium-doped barium titanate.
8. An electric power control method for a multi-logical state memory cell with multi-vortex ferroelectric domains as claimed in any of claims 1 to 7, comprising the steps of:
electric regulation and control: applying voltage between the lower electrode and the upper electrode, and regulating and controlling the ferroelectric layer, the dielectric layer and the ferroelectric periodic multilayer composite film layer to show upward or downward residual polarization so that the multi-logic-state memory cell of the multi-vortex ferroelectric domain is converted into other stable logic states;
force regulation and control: and applying a force vertical to the substrate on the upper electrode while applying a voltage between the lower electrode and the upper electrode, and removing the force to enable the multi-logic-state memory cell of the multi-vortex ferroelectric domain to be converted into other stable logic states.
9. The method of claim 8, further comprising the steps of:
applying a fixed electric field between the lower electrode and the upper electrode, and recording the current magnitude in different logic states as reference current;
the voltage of the fixed electric field is 0.001V-3.0V.
10. The method of claim 9, further comprising the steps of:
and applying a fixed electric field between the lower electrode 3 and the upper electrode 6 to obtain the current of the multi-logic-state storage unit of the multi-vortex ferroelectric domain, comparing the current with a reference current, and identifying the logic state of the multi-logic-state storage unit of the multi-vortex ferroelectric domain according to the read current.
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