Multiferroic tunnel junction based on Janus ferroelectric material, device and method

Abstract

The invention discloses a multiferroic tunnel junction based on a Janus ferroelectric material, a device and a method. The magnetic tunnel junction comprises a polarization layer; a first ferromagnetic conductive layer is superposed on the upper surface of the polarization layer; a second ferromagnetic conductive layer is arranged on the lower surface of the polarization layer; a first electrode layer is superposed on the upper surface of the first ferromagnetic conductive layer; a second electrode layer is arranged on the lower surface of the second ferromagnetic conductive layer; wherein the polarization layer is made of a Janus ferroelectric material. The method has the advantages of low energy consumption and high storage density.

Description

Technical Field

[0001] The present invention relates to the technical field of multiferroic tunnel junctions, and in particular to a multiferroic tunnel junction, a device and a method based on Janus ferroelectric materials. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The amount of data that can be stored per unit volume of a storage medium and its stability are important factors in evaluating the quality of a storage medium. Storage media usually include tunnel junctions.

[0004] The current mainstream tunnel junction is based on perovskite (such as calcium titanate). Although it has a large TMR and TER, it is based on insulating perovskite. Therefore, in order to achieve the conditions for the quantum tunneling effect, a large voltage needs to be applied to both ends of the tunnel junction, resulting in high overall energy consumption of the tunnel junction and a large amount of heat, resulting in unstable performance. In addition, its single unit cell lattice constant and RA are large, resulting in low storage density. At the same time, because its binding force is not van der Waals force, diffusion will occur over time, causing the overall structure of the tunnel junction to be destroyed, resulting in data loss. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a multiferroic tunnel junction, a device and a method based on Janus ferroelectric materials, which have the characteristics of low power consumption and high storage density.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] In the first aspect, a multiferroic tunnel junction based on Janus ferroelectric materials is proposed, including a polarization layer;

[0008] The first ferromagnetic conductive layer is stacked on the upper surface of the polarization layer

[0009] A second ferromagnetic conductive layer is disposed on the lower surface of the polarization layer;

[0010] A first electrode layer is stacked on the upper surface of the first ferromagnetic conductive layer;

[0011] A second electrode layer is disposed on the lower surface of the second ferromagnetic conductive layer;

[0012] Among them, the polarization layer adopts Janus ferroelectric material.

[0013] Furthermore, different elements are used on the two surfaces of the Janus ferroelectric material.

[0014] Furthermore, the Janus ferroelectric material is a ferroelectric material with different elements on the upper surface and the lower surface.

[0015] Furthermore, the first ferromagnetic conductive layer and the second ferromagnetic conductive layer are made of ferromagnetic materials.

[0016] Furthermore, the first electrode layer and the second electrode layer are made of electrode materials.

[0017] Furthermore, the first electrode layer and the second electrode layer are both multi-layered.

[0018] Furthermore, the lattice constants of the first electrode layer, the first ferromagnetic conductive layer, the polarization layer, the second ferromagnetic conductive layer and the second electrode layer are matched.

[0019] Furthermore, the first ferromagnetic conductive layer, the polarization layer and the second ferromagnetic conductive layer are all made of high Curie temperature materials.

[0020] In a second aspect, a device is proposed, including a multiferroic tunnel junction based on Janus ferroelectric material proposed in the first aspect.

[0021] In the third aspect, a method for preparing a multiferroic tunnel junction based on a Janus ferroelectric material proposed in the first aspect is proposed, comprising:

[0022] preparing a second electrode layer;

[0023] preparing a second ferromagnetic conductive layer on the second electrode layer;

[0024] On the second ferromagnetic conductive layer, a polarization layer is prepared by using a Janus ferroelectric material;

[0025] preparing a first ferromagnetic conductive layer on the polarization layer;

[0026] A first electrode layer is formed on the first ferromagnetic conductive layer.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] A multiferroic tunnel junction, device and method based on Janus ferroelectric material proposed by the present invention, the middle layer of the multiferroic tunnel junction is a polarization layer, and the polarization layer adopts a Janus ferroelectric material that can be polarized, which not only has a low resistance value, but also has a special energy band, resulting in a large difference in resistance value before and after polarization, and more materials can be changed from semiconductors to conductors before and after polarization changes, so that the difficulty of data reading is greatly reduced, and the voltage applied by the quantum tunneling effect does not need to be so high, which reduces energy consumption and solves the problem of high energy consumption. And because the material used is a ferroelectric material, it has polarization stability. If data needs to be copied, it is necessary to apply a reverse voltage to it. When a sufficiently large reverse voltage is not applied, its polarization situation will not change, so its polarization situation will not change when the power is off, thereby realizing the long-term storage of data. At the same time, because the material used is at the molecular level, its storage density is greatly improved, and most of the materials that can be used can work stably under conditions higher than room temperature, and fully adapt to the working environment of current computers.

[0029] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0031] Figure 1 The present invention discloses a schematic diagram of the overall structure of a multiferroic tunnel junction based on Janus ferroelectric materials;

[0032] Figure 2 A schematic diagram of the phonon spectrum of the Janus ferroelectric material disclosed in the embodiment;

[0033] Figure 3 A schematic diagram of the energy band of the Janus ferroelectric material disclosed in the embodiment;

[0034] Figure 4 A unit cell structure diagram of a multiferroic tunnel junction disclosed in an embodiment.

[0035] Among them, 1. polarization layer, 2. first ferromagnetic conductive layer, 3. second ferromagnetic conductive layer, 4. first electrode layer, 5. second electrode layer. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0037] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0038] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0039] Example 1

[0040] Terminology explanation:

[0041] Janus material: Janus material is a material with an asymmetric structure, usually composed of two or more different components. Its upper and lower surfaces are often two different elements, so it is asymmetric.

[0042] Multiferroic materials: Multiferroic materials are a class of materials that simultaneously possess two or more ferroic properties, including ferroelectricity, ferromagnetism, and ferroelasticity.

[0043] Ferroelectric materials: A class of materials that have spontaneous polarization properties, which means they can maintain a certain electric polarization even without an external electric field. The direction of their spontaneous polarization can be changed by applying an external electric field, so they can be used to make the basis of non-volatile storage media.

[0044] Tunnel junction: An electronic device of great significance in the field of quantum mechanics, whose working principle is based on the quantum tunneling effect. Tunnel junctions are usually composed of two conductive materials (such as metals or superconductors) separated by a very thin insulating layer (oxide layer or other materials).

[0045] Tunnel induced resistance (TER): refers to the rate of change of resistance caused by the change of polarization direction of the ferroelectric layer in a ferroelectric tunnel junction. It is used to evaluate the difference in resistance of a ferroelectric tunnel junction under two different polarization states. It is often used to evaluate the performance of a ferroelectric tunnel junction. The larger the value, the better the tunnel junction performance.

[0046] Tunnel magnetoresistance (TMR): refers to the rate of change of resistance caused by the change of the relative magnetization direction of the two ferromagnetic layers in a ferromagnetic tunnel junction.

[0047] Information storage technology is one of the foundations of the development of the information age. The amount of data that can be stored per unit volume of storage media and its stability are important factors in evaluating the quality of storage media. Tunnel junctions have great potential in storage due to their extremely small size and ability to store data. The current mainstream tunnel junctions are based on perovskites (such as calcium titanate). Although they have large TMR and TER, they are based on insulating perovskites, and the potential barrier of the intermediate insulating layer is large. To achieve the conditions for the quantum tunneling effect, a large voltage needs to be applied to both ends of the tunnel junction, resulting in a high overall energy consumption of the tunnel junction. According to existing public papers, the tunnel junction resistance area product (RA product) is relatively large. This indicator can be used to evaluate the overall resistance of the tunnel junction, which has reached 10Ω / μm. 2 Therefore, if it is used as an integrated circuit, the energy consumption will be large, and a large amount of heat will cause more instability. In addition, the current 25mm 2 The storage structure can only store about 2-4TB of data, and the storage density is low.

[0048] In order to reduce the energy consumption of tunnel junction and improve the storage density of tunnel junction, the present embodiment proposes a multiferroic tunnel junction based on Janus ferroelectric material, wherein the interlayer is a polarization layer, and the polarization layer adopts a Janus ferroelectric material that can be polarized, which not only has a low resistance value, but also has a special energy band, resulting in a large difference in resistance value before and after polarization, and more materials can be changed from semiconductors to conductors before and after polarization changes, so that the difficulty of data reading is greatly reduced, and the voltage applied by the quantum tunneling effect does not need to be so high, which reduces energy consumption and solves the problem of high energy consumption. And because the material used is a ferroelectric material, it has polarization stability. If data needs to be copied, it is necessary to apply a reverse voltage to it. When a sufficiently large reverse voltage is not applied, its polarization situation will not change, so its polarization situation will not change when the power is off, thereby realizing the long-term storage of data. At the same time, because the material used is at the molecular level, its storage density is greatly improved, and most of the materials used can work stably under conditions higher than room temperature, and fully adapt to the working environment of current computers.

[0049] This embodiment discloses a multiferroic tunnel junction based on Janus ferroelectric materials, such as Figure 1-Figure 3 As shown, it includes a polarization layer 1;

[0050] A first ferromagnetic conductive layer 2 is stacked on the upper surface of the polarization layer 1;

[0051] A second ferromagnetic conductive layer 3 is disposed on the lower surface of the polarization layer 1;

[0052] The first electrode layer 4 is superimposed on the upper surface of the first ferromagnetic conductive layer 2;

[0053] A second electrode layer 5 is disposed on the lower surface of the second ferromagnetic conductive layer 3;

[0054] Among them, the polarization layer adopts Janus ferroelectric material.

[0055] Since the tunnel junction needs to store data, it needs different resistances when the current flows through the units storing different data, where the smaller resistance represents "1" and the other represents "0" to achieve the effect of data storage, and vice versa. Therefore, it is often necessary to create an asymmetry. Most tunnel junctions use different ferromagnetic materials for the conductive layers on both sides of the intermediate shielding layer to create an interface difference to achieve this effect. In this embodiment, the Janus material is used to prepare the polarization layer, starting with the intermediate ferroelectric material, to create an asymmetric interface to generate two different resistances.

[0056] The multiferroic tunnel junction disclosed in this embodiment adopts a sandwich structure with five layers. The middle layer is the polarization layer 1, and the polarization layer 1 adopts Janus ferroelectric material for storing data. Different elements are used on the two surfaces of the Janus ferroelectric material. The polarization layer in the middle adopts Janus ferroelectric material, which increases the asymmetry of the entire tunnel junction. Its two polarization states have two different resistance values. The change in the resistance value is caused by a large change in the energy band before and after the polarization of the material. Therefore, it can be used to represent "0" and "1" to achieve the effect of data storage (TER).

[0057] Janus ferroelectric material is a ferroelectric material with different elements on the upper and lower surfaces. It is a new type of material. It uses ferroelectric material as the substrate and replaces a layer of atoms on one surface with other atoms, thereby producing a Janus ferroelectric material that breaks the interface symmetry. The preparation process can be atomic layer deposition (ALD), chemical vapor deposition (CVD), or molecular beam epitaxy (MBE).

[0058] Among them, the ferroelectric material can be In2Se3 (indium selenide) or In2S3 (indium sulfide), etc. Taking the ferroelectric material In2S3 as an example, a layer of S (sulfur) atoms on the upper surface or lower surface of In2S3 is replaced with Se (selenium) atoms to obtain the Janus ferroelectric material In2S2Se (indium selenide sulfide).

[0059] The first ferromagnetic conductive layer and the second ferromagnetic conductive layer are made of ferromagnetic materials. The Janus ferroelectric material is wrapped by the ferromagnetic material to improve the overall stability of the multiferroic tunnel junction. At the same time, the magnetic moment direction of the first ferromagnetic conductive layer and the second ferromagnetic conductive layer can also be changed to achieve a larger tunnel resistance difference (TMR), thereby achieving the purpose of data storage.

[0060] The first electrode layer and the second electrode layer are in the outermost layer. The first electrode layer and the second electrode layer are made of electrode materials, which are used to provide electrical energy and positive and negative voltages to the multiferroic tunnel junction as a whole, so as to control the polarization direction of the polarization layer.

[0061] The ferromagnetic material may be, but is not limited to, Fe3GeTe2, Fe4GeTe2, Fe5GeTe2, Fe3GaTe2, etc., and the ferromagnetic material may be lattice-matched with the polarization layer of the Janus ferroelectric material in the middle.

[0062] The electrode material can be, but is not limited to, graphene, carbon (C), platinum (Pt), silver (Ag) or gold (Au), etc., as long as it matches the lattice of the sandwich structure in the middle.

[0063] The first electrode layer and the second electrode layer are both multi-layered.

[0064] This embodiment discloses that the lattice constants of the first electrode layer, the first ferromagnetic conductive layer, the polarization layer, the second ferromagnetic conductive layer and the second electrode layer of the multiferroic tunnel junction are matched.

[0065] The lattice constant matching means that the lattice mismatch rate among the materials selected for the first electrode layer, the first ferromagnetic conductive layer, the polarization layer, the second ferromagnetic conductive layer and the second electrode layer does not exceed 5%, preferably, does not exceed 3%.

[0066] In addition, the first ferromagnetic conductive layer, the polarization layer and the second ferromagnetic conductive layer are all made of high Curie temperature materials, which can be experimentally prepared, such as ferromagnetic materials Fe3GeTe2, Fe4GeTe2, Fe5GeTe2, Fe3GaTe2, wherein the Curie temperature of Fe3GaTe2 material is as high as 380K, 0℃=273K.

[0067] The paper "Prediction of band inversion in Janus In2XYZ (X, Y, and Z = S, Se, Te) monolayers" gives the phonon spectra of several Janus ferroelectric materials, such as Figure 2 As shown in the figure, the vertical axis represents the vibration frequency. The center of each small figure represents the Janus ferroelectric material composed of different elements. It can be seen that all frequencies are above positive values, without negative values, that is, without imaginary frequencies. This means that its vibration mode is stable and conforms to the laws of physics, thus indicating that its mechanical structure is stable.

[0068] Figure 3 The vertical axis represents energy. By comparing the positions of the conduction band and the valence band in the energy band diagram, the band gap of the material can be obtained. For semiconductors, the part above 0eV is the reverse band of the energy band diagram; the part below 0eV is the valence band; Figure 3The first and third columns are the energy band changes of the same material before and after polarization, and the fourth and sixth columns are the energy band changes of the same material before and after polarization. It can be seen that the band gap has changed greatly before and after polarization, basically one is large and the other is small. The larger the band gap, the more difficult it is for electrons to pass through the material. Therefore, this is also a basis for the TER effect. At the same time, for materials containing tellurium (Te) atoms such as tellurium sulfide (In2S2Te), there is a state without a band gap, which means that the material becomes a conductor under this polarization condition.

[0069] The performance of the multiferroic tunnel junction disclosed in this embodiment is verified by forming a multiferroic tunnel junction with three layers of PtTe2 as the first electrode layer, Fe5GeTe2 as the first ferromagnetic conductive layer, In2S2Se as the polarization layer, Fe5GeTe2 as the second ferromagnetic conductive layer, and three layers of PtTe2 as the second electrode layer. The unit cell structure of the multiferroic tunnel junction is shown in FIG. Figure 4 As shown, the electron transport properties of the multiferroic tunnel junction considering the TER effect are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] Since the material used is magnetic, it belongs to the category of spin electronics. Therefore, the electron transport of this structure is divided into two parts: spin up and spin down. The sum of the two parts is the electron transport characteristics of the entire magnetic tunnel junction. Through first-principles calculations, the electron transport characteristics under two polarization conditions can be obtained, and RA can be calculated, as shown in Table 1. The RA difference between the two conditions reaches 82.63%, that is, two completely different resistance values, which can be used to represent the two states of data respectively, and can achieve the effect of data storage.

[0074] The multiferroic tunnel junction based on Janus ferroelectric material disclosed in this embodiment has the characteristics of high operating temperature, high storage density, stability, low energy consumption and easy reading.

[0075] High operating temperature means that all materials used are high Curie temperature materials.

[0076] High storage density means that the material used to construct the multiferroic tunnel junction has a single unit cell lattice constant of 0.3nm-0.4nm, which means that only 0.09-0.16nm is needed to store each byte of data. 2 If the plane space is made into 1mm 2 The multiferroic tunnel junction can store approximately 781TB-1111TB of data.

[0077] Stability means that the multiferroic tunnel junction data storage proposed in this embodiment is based on the polarization state of the Janus ferroelectric material, and to achieve the reversal of the polarity of the Janus ferroelectric material, a sufficiently large reverse voltage must be applied. Therefore, after the power is disconnected, the polarization characteristics will not disappear, so that data can be stored persistently.

[0078] Low energy consumption and easy reading mean that the multiferroic tunnel junction proposed in this embodiment does not use conventional insulator materials in the middle, but uses a polarization layer made of Janus ferroelectric materials. The energy band of this material will change significantly before and after polarization, resulting in a larger TER, thereby improving readability. In addition, the Janus ferroelectric material used is a semiconductor or a semiconductor material that can be transformed into a conductor, so the voltage applied for the quantum tunneling effect does not need to be that large, thereby solving the problem of high energy consumption.

[0079] Example 2

[0080] In this embodiment, a device is disclosed, including a multiferroic tunnel junction based on Janus ferroelectric material disclosed in Embodiment 1.

[0081] Example 3

[0082] In this embodiment, a method for preparing a multiferroic tunnel junction based on a Janus ferroelectric material disclosed in Embodiment 1 is disclosed, comprising:

[0083] preparing a second electrode layer;

[0084] preparing a second ferromagnetic conductive layer on the second electrode layer;

[0085] On the second ferromagnetic conductive layer, a polarization layer is prepared by using a Janus ferroelectric material;

[0086] preparing a first ferromagnetic conductive layer on the polarization layer;

[0087] A first electrode layer is formed on the first ferromagnetic conductive layer.

[0088] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A multiferroic tunnel junction based on Janus ferroelectric material, characterized in that: including polarization layer; The first ferromagnetic conductive layer is stacked on the upper surface of the polarization layer A second ferromagnetic conductive layer is disposed on the lower surface of the polarization layer; A first electrode layer is stacked on the upper surface of the first ferromagnetic conductive layer; A second electrode layer is disposed on the lower surface of the second ferromagnetic conductive layer; Among them, the polarization layer adopts Janus ferroelectric material.

2. A multiferroic tunnel junction based on Janus ferroelectric material as claimed in claim 1, characterized in that: Janus ferroelectric materials use different elements on their two surfaces.

3. A multiferroic tunnel junction based on Janus ferroelectric material as claimed in claim 1, characterized in that: Janus ferroelectric material is a ferroelectric material with different elements on the upper and lower surfaces.

4. A multiferroic tunnel junction based on Janus ferroelectric material as claimed in claim 1, characterized in that: The first electrode layer and the second electrode layer are both multi-layered.

5. A multiferroic tunnel junction based on Janus ferroelectric material as claimed in claim 1, characterized in that: The first ferromagnetic conductive layer and the second ferromagnetic conductive layer are made of ferromagnetic materials.

6. A multiferroic tunnel junction based on Janus ferroelectric material as claimed in claim 1, characterized in that: The first electrode layer and the second electrode layer use electrode materials.

7. A multiferroic tunnel junction based on Janus ferroelectric material as claimed in claim 1, characterized in that: The lattice constants of the first electrode layer, the first ferromagnetic conductive layer, the polarization layer, the second ferromagnetic conductive layer and the second electrode layer are matched.

8. The multiferroic tunnel junction based on Janus ferroelectric material according to claim 1, characterized in that: The first ferromagnetic conductive layer, the polarization layer and the second ferromagnetic conductive layer are all made of high Curie temperature materials.

9. A device, characterized in that A multiferroic tunnel junction based on Janus ferroelectric material comprising any one of claims 1-8.

10. A method for preparing a multiferroic tunnel junction based on a Janus ferroelectric material according to any one of claims 1 to 8, characterized in that: include: preparing a second electrode layer; preparing a second ferromagnetic conductive layer on the second electrode layer; On the second ferromagnetic conductive layer, a polarization layer is prepared by using a Janus ferroelectric material; preparing a first ferromagnetic conductive layer on the polarization layer; A first electrode layer is formed on the first ferromagnetic conductive layer.

Images