A magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency

Abstract

The application discloses a magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency, comprising spin orbit coupling layer, free layer, barrier layer and reference layer which are stacked in sequence, the spin orbit coupling layer comprises a first heavy metal layer and a second heavy metal layer, the second heavy metal layer is located between the first heavy metal layer and the free layer, and the first heavy metal layer and the second heavy metal layer are selected from different materials and used for cooperating to improve the contribution of the electron orbital coupling term to the perpendicular magnetic anisotropy. The magnetic tunnel junction adopts the double-layer heavy metal layer with different materials in the spin orbit coupling layer, can improve the contribution of the electron orbital coupling term to the perpendicular magnetic anisotropy, realizes the improvement of the perpendicular magnetic anisotropy and the switching efficiency, is helpful to improve the thermal stability of the magnetic memory in the miniaturization process, reduces the power consumption, and is simple in structure and convenient to process and manufacture.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of spin electronics, and particularly relates to a magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency. BACKGROUND

[0002] Magnetic Random Access Memory (MRAM) has the advantages of non-volatility, high-speed reading and writing, low power consumption, unlimited times of erasing, etc., and has attracted extensive attention. The core device of MRAM is a magnetic tunnel junction (MTJ). The MTJ is a sandwich-like film layer structure, including a reference layer, a barrier layer and a free layer. In the MTJ, the storage of information depends on the retention ability of the magnetization state in the free layer, that is, the thermal stability. The thermal stability of the free layer is measured by a thermal stability factor, which can be generally expressed as Δ=KV / K B T, wherein K is an effective magnetic anisotropy constant, V is the volume of the free layer, K B is the Boltzmann constant, and T is the temperature.

[0003] The thermal stability factor of the MTJ is generally required to be higher than 60, and when it is reduced to below 60, the requirement for long-term reliable storage of data cannot be met, so it is very important to improve the thermal stability of the MTJ. At the same time, due to the effect of the in-plane demagnetizing field, the in-plane magnetic anisotropy of the MTJ has a too large write current density, which is difficult to meet the requirement of low power consumption. Therefore, a magnetic tunnel junction with perpendicular magnetic anisotropy is usually used to reduce the power consumption and to increase the perpendicular magnetic anisotropy to improve the thermal stability. However, the existing technology often increases the interface between the free layer and the magnesium oxide layer (such as forming a multi-interface structure of free layer / magnesium oxide layer / free layer / magnesium oxide layer) to improve the thermal stability of the magnetic tunnel junction, thereby increasing the number of film layers, and further existing the disadvantages of complex structure, increased difficulty in preparation, increased resistance, reduced tunnel magnetoresistance (TMR), etc. Therefore, it is urgent to study a magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency. SUMMARY

[0004] The application aims to solve the above problems, and provides a magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency. The magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency helps to improve the thermal stability of the magnetic tunnel junction and reduce the power consumption, and has a simple structure and is convenient for processing and manufacturing.

[0005] To achieve the above object, the technical scheme adopted by the application is as follows:

[0006] The application provides a magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency, which comprises a spin-orbit coupling layer, a free layer, a barrier layer and a reference layer which are sequentially stacked, the spin-orbit coupling layer comprises a first heavy metal layer and a second heavy metal layer, the second heavy metal layer is located between the first heavy metal layer and the free layer, and the first heavy metal layer and the second heavy metal layer are made of different materials and are used to improve the contribution of the electron orbital coupling term to the perpendicular magnetic anisotropy.

[0007] Preferably, the thickness of the first heavy metal layer is 0.5-5 nm, the thickness of the second heavy metal layer is 0.2-2 nm, the thickness of the free layer is 0.5-1 nm, the thickness of the barrier layer is 0.5-2 nm, and the thickness of the reference layer is 1.5-2.5 nm.

[0008] Preferably, the thickness of the first heavy metal layer and the thickness of the second heavy metal layer are both four atomic layers, the thickness of the reference layer is five atomic layers, and the thickness of the barrier layer is three atomic layers.

[0009] Preferably, the material of the first heavy metal layer is selected from one of Hf, Os and Bi.

[0010] Preferably, the material of the second heavy metal layer is selected from one of Ta, Ru, Mo, Nb and W.

[0011] Preferably, the material of the reference layer is selected from one of Co, Fe, CoFe, CoFeB, CoFeAl, Hulser alloy and MnGa.

[0012] Preferably, the material of the barrier layer is selected from one of MgO, HfO and Al2O3.

[0013] Preferably, the material of the free layer is selected from one of Co, Fe, CoFe, CoFeB, Heusler alloy, MnGa.

[0014] Compared with the prior art, the application has the following beneficial effects:

[0015] 1) The magnetic tunnel junction uses double-layer heavy metal layers with different materials in the spin-orbit coupling layer, which can increase the interface interaction between the heavy metal layers and the free layer and between the heavy metal layers, change the distribution of Bloch electron states near the Fermi level, further improve the contribution of the electron orbital coupling term to the perpendicular magnetic anisotropy, realize the improvement of the perpendicular magnetic anisotropy, and help to improve the thermal stability of the magnetic tunnel junction.

[0016] 2) by the heavy metal layer material and thickness reasonable configuration, compared with the prior art can significantly improve the thermal stability of magnetic tunnel junction, solve the thermal stability problem encountered in the miniaturization process of magnetic memory, at the same time can improve the flip efficiency of magnetic tunnel junction, without using multi-layer MgO interface, can reduce the RA to a certain extent, reduce power consumption, and the structure is simple, easy to process and manufacture. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic diagram of the structure of the magnetic tunnel junction of the present application;

[0018] Figure 2 is a comparison diagram of the atomic structure of the prior art magnetic tunnel junction (a) and the atomic structure of the magnetic tunnel junction of the present application (b);

[0019] Figure 3 is a comparison diagram of the relationship between the number of atomic layers and the magnetic anisotropy of the prior art magnetic tunnel junction (a) and the relationship between the number of atomic layers and the magnetic anisotropy of the magnetic tunnel junction of the present application (b).

[0020] Reference signs: 1, spin orbit coupling layer; 11, first heavy metal layer; 12, second heavy metal layer; 2, free layer; 3, barrier layer; 4, reference layer. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments of the present application, not for limiting the present application.

[0023] As Figure 1 shown, a magnetic tunnel junction with strong perpendicular magnetic anisotropy and high flip efficiency, comprising spin orbit coupling layer, free layer, barrier layer and reference layer stacked in turn, the spin orbit coupling layer comprises a first heavy metal layer and a second heavy metal layer, the second heavy metal layer is located between the first heavy metal layer and the free layer, and the first heavy metal layer and the second heavy metal layer are selected to be different in material and used to cooperate to improve the contribution of the electron orbit coupling term to the perpendicular magnetic anisotropy.

[0024] The magnetic tunnel junction is based on interface effect, and the double-layer heavy metal layer with different materials in the spin orbit coupling layer 1 can increase the interface interaction between the heavy metal layer and the free layer 2 and between the heavy metal layers, change the distribution of Bloch electron state near the Fermi level, further improve the contribution of the electron orbit coupling effect term to the perpendicular magnetic anisotropy, and realize the improvement of the perpendicular magnetic anisotropy, which is helpful to improve the thermal stability of the magnetic tunnel junction. Compared with the prior art, the thermal stability of the magnetic tunnel junction can be significantly improved by reasonably configuring the heavy metal layer material and thickness, the thermal stability problem encountered in the miniaturization process of the magnetic memory can be solved, the flip efficiency of the magnetic tunnel junction can be improved, the multi-layer MgO interface does not need to be used, the RA value (the product of the resistance value and the cross-sectional area of the magnetic tunnel junction) can be reduced to some extent, the reading speed can be improved by reducing the RA value, the power consumption can be reduced, and the structure is simple and convenient for processing and manufacturing.

[0025] It should be noted that the layer structure of the magnetic tunnel junction is not limited to this, when a film layer is said to be stacked with another film layer, it can be directly stacked on another film layer or there can be a central film layer, which can be other magnetic tunnel junction structures commonly used in the prior art. In addition, the magnetic tunnel junction flip working principle of the present application is the prior art, and those skilled in the art can obtain it by referring to relevant materials, which will not be described here.

[0026] In an embodiment, the thickness of the first heavy metal layer is 0.5-5 nm, the thickness of the second heavy metal layer is 0.2-2 nm, the thickness of the free layer is 0.5-1 nm, the thickness of the barrier layer is 0.5-2 nm, and the thickness of the reference layer is 1.5-2.5 nm. By limiting the thickness of each layer, the reliability of reading can be improved, and low-power flip can be realized.

[0027] In an embodiment, the material of the first heavy metal layer is selected from one of Hf, Os and Bi.

[0028] In an embodiment, the material of the second heavy metal layer is selected from one of Ta, Ru, Mo, Nb and W.

[0029] The heavy metal layer has a large Hall angle, and a larger spin orbit torque can be generated by the current through the heavy metal layer, which is helpful to realize low-power flip. In addition, the materials of the first heavy metal layer and the second heavy metal layer are different, and the different properties of the two materials are used, one material is used to provide high perpendicular magnetic anisotropy, and the other material is used to provide spin orbit coupling torque, thereby further improving the thermal stability and flip efficiency of the magnetic tunnel junction. For example, the first heavy metal layer 11 is located below the second heavy metal layer 12, which is used to enhance the perpendicular magnetic anisotropy and improve the flip efficiency, and the second heavy metal layer 12 provides the spin orbit coupling effect and promotes the growth of the crystal direction of the film layer.

[0030] In an embodiment, the material of the reference layer is selected from Co, Fe, CoFe, CoFeB, Heusler alloy, and MnGa. The material of the reference layer 4 is selected from ferromagnetic material, and the magnetization direction is vertical and fixed. The material is not limited to the above, and other materials meeting the performance requirements in the prior art can also be used. The proportions of various elements can also be different. For example, the proportions of the elements in CoFe can be different, such as Co40Fe60, where the numbers represent the percentages of the corresponding elements, and the specific proportions can be adjusted according to actual requirements.

[0031] In an embodiment, the material of the barrier layer is selected from MgO, HfO, and Al2O3. The barrier layer 3 is made of metal oxide, which is used to generate the tunneling effect. Preferably, the barrier layer 3 is made of MgO, which has small lattice mismatch and few lattice defects, and is easy to synthesize.

[0032] In an embodiment, the material of the free layer is selected from Co, Fe, CoFe, CoFeB, Heusler alloy, and MnGa. The material of the free layer 2 is selected from ferromagnetic material, and the magnetization direction can be reversed. The material is not limited to the above, and other materials meeting the performance requirements in the prior art can also be used. The proportions of various elements can also be different. For example, the proportions of the elements in CoFe can be different, such as Co40Fe60, where the numbers represent the percentages of the corresponding elements, and the specific proportions can be adjusted according to actual requirements.

[0033] Specifically, the magnetic anisotropy energy is equal to the difference between the magnetization energies of the magnetic tunnel junction in different crystal directions, which is generally expressed as: MAE=E 100 -E 001 , where E 100 and E 001 are the magnetization energies of the magnetic tunnel junction in the in-plane and out-of-plane directions, respectively.

[0034] The changes in the magnetic anisotropy energy of the magnetic tunnel junction when the single-layer heavy metal (i.e., the magnetic tunnel junction in the prior art) and the double-layer heavy metal (i.e., the magnetic tunnel junction in the present application) are used as the spin-orbit coupling layer 1 are compared as follows: Figures 2-3As shown. The structure of the magnetic tunnel junction in this embodiment is, from bottom to top, a first heavy metal layer 11, a second heavy metal layer 12, a free layer 2, a barrier layer 3, and a reference layer 4. The corresponding materials are selected in order: Hf, Ta, CoFe, MgO, and CoFe. The magnetic tunnel junction can have any shape and can be adjusted according to actual needs. For example, in this embodiment, it is an inverted T-shaped structure. The first heavy metal layer 11 is located below the second heavy metal layer 12 to enhance the perpendicular magnetic anisotropy and improve the switching efficiency. The second heavy metal layer 12 provides a spin-orbit coupling effect and promotes the formation of the growth crystal direction of the film layer. The free layer 2 is Co40Fe60, where the numbers represent the percentages of the corresponding elements, and its magnetization direction can be reversed. The barrier layer 3 is made of MgO and is used to provide a tunneling effect. The reference layer 4 is Co40Fe60, where the numbers represent the percentages of the corresponding elements, and its magnetization direction is perpendicular and fixed, and is used to provide a reference.

[0035] The models used in existing technologies are as follows Figure 2 As shown in (a) (reference layer 4 is not shown), along the (001) crystal direction, there are 4 atomic layers of Ta film (spin-orbit coupling layer 1), 5 atomic layers of CoFe film (free layer 2), and 3 atomic layers of MgO film (barrier layer 3). In order to ensure the consistency of the interface structure, CoFe with a body-centered cubic lattice structure is selected as the interface matching standard, so that the other film layers produce corresponding deformations and the in-plane lattice constant is fixed at The model used in this embodiment is as follows Figure 2 As shown in (b) (reference layer 4 is not shown), along the (001) crystal direction, there are 4 atomic layers of Hf film and 4 atomic layers of Ta film, which are composed of spin-orbit coupling layer 1, 5 atomic layers of CoFe film (free layer 2), and 3 atomic layers of MgO film (barrier layer 3). In order to ensure the consistency of the interface structure, CoFe with a body-centered cubic lattice structure is selected as the interface matching standard, so that the other film layers produce corresponding deformations and the in-plane lattice constant is fixed at

[0036] Compared to the prior art that uses a single-layer heavy metal 4-atomic layer Ta film as the spin-orbit coupling layer 1, the present application uses a double-layer heavy metal 4-atomic layer Ta film and a 4-atomic layer Hf film as the spin-orbit coupling layer 1. Through first-principles calculations, the changes in the magnetic anisotropy energy and interface electronic structure of the magnetic tunnel junction before and after the spin-orbit coupling layer 1 are revealed, and the influence of the element type, action position, and film thickness of the heavy metal layer on the magnetic anisotropy of the magnetic tunnel junction is obtained, thereby verifying the key factors for improving the perpendicular magnetic anisotropy and flipping efficiency of the magnetic tunnel junction. It should be noted that the first-principles pseudopotential method based on density functional theory is a technology well known to those skilled in the art and will not be repeated here.

[0037] By using two different heavy metal layers Ta and Hf in the spin orbit coupling layer 1 of the magnetic tunnel junction, the interaction between the heavy metal Ta and the interface of CoFe is increased, and the contribution of Ta and Hf to the perpendicular magnetic anisotropy energy is also increased, which changes the distribution of the Bloch electron state near the Fermi level (such as between -0.5-0.5eV), and then improves the contribution of the control electron orbital coupling term to the perpendicular magnetic anisotropy, and realizes the improvement of the perpendicular magnetic anisotropy of the magnetic tunnel junction. As shown in Figure 3 , it is a layered perpendicular magnetic anisotropy energy diagram. Figure 3 , and 3(b) are respectively Figure 2 , and 2(b) are the magnetic anisotropy energy diagrams of each layer from bottom to top. The layered magnetic anisotropy energy can also represent the strength of the spin orbit coupling of the layer and the contribution to the switching efficiency. It can be seen that when the double-layer heavy metal layer Ta and Hf are used as the spin orbit coupling layer 1, the layered magnetic anisotropy energy at the interface adjacent to the free layer 2 (such as the 8th layer in Figure 3 (b)) is increased compared with the single-layer Ta as the spin orbit coupling layer 1 (such as the 4th layer in Figure 3 (a)). After using the double-layer heavy metal Ta and Hf as the spin orbit coupling layer 1, the total perpendicular magnetic anisotropy energy of the magnetic tunnel junction is increased from 0.93meV when the single-layer Ta is used as the spin orbit coupling layer 1 to 1.92meV, and the perpendicular magnetic anisotropy energy is increased by nearly one time. Therefore, the double-layer heavy metal layer Ta and Hf as the spin orbit coupling layer 1 can improve the perpendicular magnetic anisotropy and the switching efficiency of the magnetic tunnel junction, thereby realizing the improvement of the thermal stability of the magnetic tunnel junction.

[0038] The technical features of the above-mentioned embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described, but as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the description.

[0039] The above-mentioned embodiments only express the more specific and detailed embodiments described in the present application, but should not be construed as limiting the scope of the patent application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency, characterized by: The magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency includes a spin-orbit coupling layer, a free layer, a barrier layer, and a reference layer stacked in sequence, wherein the spin-orbit coupling layer includes a first heavy metal layer and a second heavy metal layer, the second heavy metal layer is located between the first heavy metal layer and the free layer, and the first heavy metal layer and the second heavy metal layer are made of different materials and are used to cooperate to enhance the contribution of the electron orbital coupling term to the perpendicular magnetic anisotropy; The thickness of the first heavy metal layer is 0.5-5 nm, the thickness of the second heavy metal layer is 0.2-2 nm, the thickness of the free layer is 0.5-1 nm, the thickness of the barrier layer is 0.5-2 nm, and the thickness of the reference layer is 1.5-2.5 nm; The material of the first heavy metal layer is selected from one of Hf, Os and Bi; The material of the second heavy metal layer is selected from Ta, Ru, Mo, Nb, and W.

2. The magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency according to claim 1, wherein: The material of the reference layer is selected from one of Co, Fe, CoFe, CoFeB, CoFeAl, Hulsers alloy and MnGa.

3. The magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency according to claim 1, wherein: The material of the barrier layer is selected from one of MgO, HfO and Al2O3.

4. The magnetic tunnel junction with strong perpendicular magnetic anisotropy and high switching efficiency according to claim 1, wherein: The material of the free layer is selected from among Co, Fe, CoFe, CoFeB, Heusler alloy, and MnGa.

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