A magnetic tunnel junction with high thermal stability

Abstract

The application discloses a magnetic tunnel junction with high thermal stability, comprising a reference layer, a barrier layer, a first free layer, a magnesium oxide layer and a cover layer which are sequentially stacked, wherein the reference layer has direction-fixed vertical magnetization; the barrier layer is used for generating a tunneling effect; the first free layer has direction-variable vertical magnetization and changes atomic magnetic moment by doping a nonmetallic element, so as to reduce saturation magnetization and enhance vertical magnetic anisotropy; the magnesium oxide layer is used for enhancing the vertical magnetic anisotropy with the first free layer; and the cover layer is used for reducing a damping coefficient, so as to reduce a critical current. The magnetic tunnel junction changes atomic magnetic moment by doping a nonmetallic element in a magnetic metal layer, so as to reduce saturation magnetization and enhance vertical magnetic anisotropy, thereby significantly improving the thermal stability of the magnetic tunnel junction, realizing miniaturization of a magnetic memory while ensuring the thermal stability, and being simple in structure and convenient for production and manufacturing.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of spin electronics, and particularly relates to a magnetic tunnel junction with high thermal stability. 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 capability 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 (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] Generally, the thermal stability factor of the MTJ is required to be higher than 60 in the industry, 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. Meanwhile, 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 generally 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. Especially, with the miniaturization of the device size, the volume of the free layer is reduced, and the thermal stability is insufficient to keep the stored data for a long enough time. Therefore, it is particularly important to improve the thermal stability and the perpendicular magnetic anisotropy of the magnetic tunnel junction without increasing the interface. SUMMARY

[0004] The application aims to solve the above problems, and provides a magnetic tunnel junction with high thermal stability. By doping a non-metallic element in a magnetic metal layer to change the atomic magnetic moment, the saturation magnetization is reduced and the perpendicular magnetic anisotropy is enhanced, so that the thermal stability of the magnetic tunnel junction is significantly improved. The miniaturization of the magnetic memory is realized while the thermal stability is ensured, and the structure is simple and convenient for production and manufacturing.

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

[0006] The present application provides a magnetic tunnel junction with high thermal stability, comprising a reference layer, a barrier layer, a first free layer, a magnesium oxide layer and a cover layer which are sequentially stacked, wherein:

[0007] The reference layer has a fixed direction of vertical magnetization;

[0008] The barrier layer is used to generate a tunneling effect;

[0009] The first free layer has a variable direction of vertical magnetization, and the atomic magnetic moment is changed by doping a non-metallic element to reduce the saturation magnetization and enhance the vertical magnetic anisotropy;

[0010] The magnesium oxide layer is used to enhance the vertical magnetic anisotropy with the first free layer;

[0011] The cover layer is used to reduce the damping coefficient, thereby reducing the critical current.

[0012] Preferably, the magnetic tunnel junction with high thermal stability further comprises a spacer layer and a second free layer, the spacer layer is located between the first free layer and the second free layer and is used for interlayer exchange coupling of the first free layer and the second free layer, and the second free layer is located between the barrier layer and the spacer layer and has a variable direction of vertical magnetization.

[0013] Preferably, the reference layer and the second free layer are both doped with a non-metallic element, the thickness of the reference layer is 1.2-2nm, and the thickness of the first free layer and the second free layer is both 0.6-1nm.

[0014] Preferably, the material of the spacer layer is one of W, Ta, Ru and Mo, and the thickness is 0.2-0.6nm.

[0015] Preferably, the doping content of the non-metallic element is 2%-20%.

[0016] Preferably, the non-metallic element is one of nitrogen, phosphorus and sulfur.

[0017] Preferably, the non-metallic element is doped in at least one of the edge position, the gap position, the face center position and the body center position of the corresponding layer.

[0018] Preferably, the material of the reference layer and each free layer is one of Co, Fe, CoFe, CoFeB, CoFeAl, Hulser alloy and MnGa.

[0019] Preferably, the material of the barrier layer is one of MgO, HfO and Al2O3, and the thickness is 1-1.5nm.

[0020] Preferably, the material of the covering layer is one of W, Ta, Hf, Mo, Nb, Ru, and the thickness is 3-8nm.

[0021] Compared with the prior art, the application has the following advantages:

[0022] 1) The magnetic tunnel junction can reduce the atomic magnetic moment of the adjacent or similar magnetic atoms of the doping atoms by doping non-metallic elements in the magnetic metal layer (such as the reference layer and the free layer), thereby reducing the saturation magnetization of the magnetic metal layer, and also improving the perpendicular magnetic anisotropy of the magnetic tunnel junction, and achieving the improvement of the thermal stability of the magnetic tunnel junction.

[0023] 2) By adjusting the type, position and content of the doping elements, the thermal stability of the magnetic tunnel junction can be significantly improved compared with the prior art, which helps to solve the problem of insufficient thermal stability of the magnetic memory in the miniaturization process, and the structure is simple and easy to produce. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of the magnetic tunnel junction of the first embodiment of the application.

[0025] Figure 2 It is a schematic diagram of the material composition of the magnetic tunnel junction of the first embodiment of the application.

[0026] Figure 3 It is a graph of the relationship between the N element content and the perpendicular magnetic anisotropy of the magnetic tunnel junction of the first embodiment of the application.

[0027] Figure 4 It is a schematic diagram of the overall structure of the magnetic tunnel junction of the second embodiment of the application.

[0028] Figure 5 It is a schematic diagram of the material composition of the magnetic tunnel junction of the second embodiment of the application.

[0029] Figure 6 It is a schematic diagram of the material composition of the magnetic tunnel junction of the third embodiment of the application.

[0030] Reference signs: 1, reference layer; 2, barrier layer; 3, first free layer; 4, magnesium oxide layer; 5, covering layer; 6, spacer layer; 7, second free layer. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0032] It should be noted that unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application.

[0033] Embodiment 1

[0034] As shown in the drawings, a magnetic tunnel junction with high thermal stability includes a reference layer 1, a barrier layer 2, a first free layer 3, a magnesium oxide layer 4 and a capping layer 5 which are sequentially stacked, wherein: the reference layer 1 has a direction-fixed perpendicular magnetization; the barrier layer 2 is used to generate a tunneling effect; the first free layer 3 has a direction-variable perpendicular magnetization, and the atomic magnetic moment is changed by doping a non-metallic element to reduce the saturation magnetization and enhance the perpendicular magnetic anisotropy; the magnesium oxide layer 4 is used to enhance the perpendicular magnetic anisotropy with the first free layer 3; and the capping layer 5 is used to reduce the damping coefficient, thereby reducing the critical current. Figures 1-3 The reference layer 1 has a direction-fixed perpendicular magnetization, where "direction-fixed" does not mean absolute fixation, but refers to the difficulty of changing the magnetization direction of the free layer 3, i.e., the coercivity of the material selected for the reference layer 1 is relatively large, and the magnetization direction is difficult to change, while the coercivity of the material selected for the free layer 3 is relatively small, and the magnetization direction is easy to change.

[0035] In an embodiment, the doping content of the non-metallic element is 2% to 20%. The doping content of the non-metallic element in the corresponding layer within this range helps to obtain a higher perpendicular magnetic anisotropy.

[0036] In an embodiment, the non-metallic element is one of nitrogen, phosphorus and sulfur.

[0037] In an embodiment, the non-metallic element is doped in at least one of the edge position, the gap position, the face center position and the body center position of the corresponding layer.

[0038] In an embodiment, the materials of the reference layer 1 and each free layer are one of Co, Fe, CoFe, CoFeB, CoFeAl, Hulser alloy and MnGa. The materials selected for the reference layer 1 and the first free layer 3 can be the same or different, and the selected materials are relatively easy to obtain and can effectively ensure that the magnetic tunnel junction has good performance.

[0039]

[0040] ​In one embodiment, the barrier layer 2 is made of one of MgO, HfO, and Al2O3, with a thickness of 1 to 1.5 nm. This material exhibits excellent insulation properties, further ensuring good performance of the magnetic tunnel junction. To achieve a suitable RA value (the product of the resistance and cross-sectional area of ​​the magnetic tunnel junction), the barrier layer 2 is preferably between 1 and 1.5 nm thick.

[0041] In one embodiment, the cover layer 5 is made of one of W, Ta, Hf, Mo, Nb, and Ru, and has a thickness of 3 to 8 nm. The cover layer 5 is a metal cover layer, and the damping coefficient is reduced by properly selecting the material, thereby reducing the critical current and achieving low power consumption.

[0042] Specifically, if Figure 2 As shown, the magnetic tunnel junction comprises a reference layer 1, a barrier layer 2, a first free layer 3, a magnesium oxide layer 4, and a capping layer 5. The reference layer 1 has a fixed perpendicular magnetization and is made of CoFe with a thickness of 1.5 nm. The barrier layer 2, located above the reference layer 1, is made of MgO with a thickness of 1.5 nm and is used to provide a tunneling effect. The first free layer 3, located above the barrier layer 2, has a variable perpendicular magnetization and is made of CoFeN (i.e., the corresponding doped non-metallic element is nitrogen) with a thickness of 1 nm. Nitrogen is doped into the magnetic layer through ion implantation or gas flow. The doped atoms are located in the interstitial regions of the magnetic layer crystals, which reduces the saturation magnetization of the magnetic layer and changes the crystal structure and electronic density of states of the magnetic layer, thereby increasing its perpendicular magnetic anisotropy. The magnesium oxide layer 4, located above the first free layer 3, is used to enhance the perpendicular magnetic anisotropy with respect to the first free layer 3 and has a thickness of 1 nm. The capping layer 5, located above the magnesium oxide layer 4, is made of Ta with a thickness of 5 nm.

[0043] like Figure 3 As shown, when the N doping content is zero (i.e., a magnetic tunnel junction in the prior art without non-metallic doping), the perpendicular magnetic anisotropy energy is 1.08 meV. When the N doping content is 4.7%, the perpendicular magnetic anisotropy energy increases to 1.74 meV, an increase of approximately 61%. At 9.1% N doping, the perpendicular magnetic anisotropy energy increases to 1.46 meV, an increase of approximately 35%. N doping increases the perpendicular magnetic anisotropy energy, especially when the N doping content is between 3% and 8%, which essentially guarantees an increase of more than 50%.

[0044] It should be noted that the materials for the various layers of the magnetic tunnel junction (except the magnesium oxide layer) of the present application are not limited to the materials listed above, and can also be selected from any material that meets the performance requirements in the prior art. Persons skilled in the art can select materials based on actual conditions. Furthermore, the operating principle of the magnetic tunnel junction flipping of the present application is prior art, and those skilled in the art can obtain information from relevant literature, so this will not be elaborated here.

[0045] The magnetic tunnel junction can reduce and dope atomic magnetic moments of adjacent or similar magnetic atoms of the doped atoms in the magnetic metal layer (such as the free layer) by doping non-metallic elements in the magnetic metal layer, thereby reducing the saturation magnetization of the magnetic metal layer, and can also improve the perpendicular magnetic anisotropy of the magnetic tunnel junction. The reduction of the saturation magnetization of the magnetic tunnel junction and the improvement of the perpendicular magnetic anisotropy are both conducive to solving the problem of insufficient thermal stability of the magnetic memory, achieving the improvement of the thermal stability of the magnetic tunnel junction, and meeting the requirement of data storage time in actual application; and by adjusting the type, doping position and doping content of the doped elements, the thermal stability of the magnetic tunnel junction can be significantly improved compared with the prior art, which is helpful to solve the problem of insufficient thermal stability encountered in the miniaturization process of the magnetic memory, and will not affect the resistance and tunneling magnetoresistance, and the structure is simple and convenient for production and manufacturing.

[0046] Embodiment 2

[0047] As shown in Figures 4-5 The magnetic tunnel junction with high thermal stability proposed in the embodiment is based on embodiment 1, and the difference lies in that the magnetic tunnel junction with high thermal stability further comprises a spacer layer 6 and a second free layer 7, the spacer layer 6 is located between the first free layer 3 and the second free layer 7, and is used for interlayer exchange coupling of the first free layer 3 and the second free layer 7, and the second free layer 7 is located between the barrier layer 2 and the spacer layer 6, and has a direction-variable perpendicular magnetization.

[0048] In an embodiment, the material of the spacer layer 6 is one of W, Ta, Ru and Mo, and the thickness is 0.2-0.6 nm.

[0049] Specifically, as shown in Figure 5As shown, the magnetic tunnel junction includes a reference layer 1, a barrier layer 2, a first free layer 3, a magnesium oxide layer 4, a capping layer 5, a spacer layer 6 and a second free layer 7, wherein the reference layer 1 has a fixed vertical magnetization, is made of CoFe and has a thickness of 1.5 nm. The barrier layer 2 is located above the reference layer 1, is made of MgO and has a thickness of 1.5 nm, and is used to provide a tunneling effect. The second free layer 7 is located above the barrier layer 2, has a variable vertical magnetization, is made of CoFe and has a thickness of 1 nm. The spacer layer 6 is located above the second free layer 7, is used for interlayer exchange coupling of the first free layer 3 and the second free layer 7, and has a thickness of 0.5 nm. The first free layer 3 is located above the spacer layer 6, has a variable vertical magnetization, is made of CoFeN (i.e., the corresponding doped non-metallic element is N), and has a thickness of 1 nm. N is doped into the magnetic layer by ion implantation or gas, and the doped atoms are located in the interstitial positions of the crystal of the magnetic layer, which reduces the saturation magnetization of the magnetic layer, changes the crystal structure and electron state density of the magnetic layer, and thus improves the perpendicular magnetic anisotropy of the magnetic layer. The magnesium oxide layer 4 is located above the first free layer 3, is used to enhance the perpendicular magnetic anisotropy of the first free layer 3, and has a thickness of 1 nm. The capping layer 5 is located above the magnesium oxide layer 4, and the capping layer 5 is made of Ta and has a thickness of 5 nm.

[0050] It should be noted that the materials of the layers of the magnetic tunnel junction of the present application (except the magnesium oxide layer) are not limited to the above-mentioned materials, but can also be selected from any material meeting the use performance in the prior art, and the materials of the reference layer 1, the first free layer 3 and the second free layer 7 can be the same or different, which can be selected by a person skilled in the art according to the actual situation. In addition, the magnetic tunnel junction flipping working principle of the present application is the prior art, which can be obtained by a person skilled in the art by referring to relevant materials, and will not be described here.

[0051] The magnetic tunnel junction can reduce and dope the atomic magnetic moment of the adjacent or similar magnetic atoms of the doping atoms by doping non-metallic elements in the magnetic metal layer (such as the free layer), thereby reducing the saturation magnetization of the magnetic metal layer, and also improving the perpendicular magnetic anisotropy of the magnetic tunnel junction. The reduction of the saturation magnetization of the magnetic tunnel junction and the improvement of the perpendicular magnetic anisotropy are both conducive to solving the problem of insufficient thermal stability of the magnetic memory, improving the thermal stability of the magnetic tunnel junction, and meeting the demand of data storage time in actual application; and by adjusting the type, doping position and doping content of the doping elements, the thermal stability of the magnetic tunnel junction can be significantly improved compared with the prior art, which is helpful to solve the problem of insufficient thermal stability encountered in the miniaturization process of the magnetic memory, and the structure is simple and convenient for production and manufacturing. Compared with embodiment 1, the embodiment adds a spacer layer 6 and a second free layer 7, provides a strong interlayer exchange coupling effect through the spacer layer 6, so that the two free layers with perpendicular anisotropy are well coupled together, which can further improve the perpendicular anisotropy of the magnetic tunnel junction and help to improve the thermal stability of the magnetic tunnel junction.

[0052] Embodiment 3:

[0053] As shown in Figure 6 , the magnetic tunnel junction with high thermal stability proposed in the embodiment is based on embodiment 2, and the difference lies in that the reference layer 1 and the second free layer 7 are both doped with non-metallic elements, the thickness of the reference layer 1 is 1.2-2nm, and the thickness of the first free layer 3 and the second free layer 7 is both 0.6-1nm.

[0054] Compared with embodiment 2, the reference layer 1 and the second free layer 7 are also doped in the embodiment, such as CoFeN, CoFeP, CoFeS, so that the saturation magnetization of all the magnetic layers in the magnetic tunnel junction is reduced, which is more conducive to improving the thermal stability of the magnetic tunnel junction.

[0055] The technical features of the above-mentioned embodiments can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-mentioned embodiments are not described, however, as long as the combination of these technical features does not exist contradictory, it should be considered as the scope of the description.

[0056] The above-mentioned embodiments only express the more specific and detailed embodiments described in the application, but it should not be interpreted as a limitation on the scope of the patent application. It should be pointed out that for ordinary skilled persons in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are all within the scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A magnetic tunnel junction with high thermal stability, characterized in that: The magnetic tunnel junction with high thermal stability comprises a reference layer (1), a barrier layer (2), a first free layer (3), a magnesium oxide layer (4), and a cover layer (5) stacked in sequence, wherein: The reference layer (1) has a perpendicular magnetization with a fixed direction; The barrier layer (2) is used to generate a tunneling effect; The first free layer (3) has a directionally variable perpendicular magnetization, and the atomic magnetic moment is changed by doping non-metallic elements to reduce the saturation magnetization intensity and enhance the perpendicular magnetic anisotropy, and the doping content of the non-metallic elements is 2% to 20%; The magnesium oxide layer (4) is used to enhance perpendicular magnetic anisotropy with respect to the first free layer (3); The covering layer (5) is used to reduce the damping coefficient, thereby reducing the critical current; The materials of the reference layer (1) and the first free layer (3) are each one of Co, Fe, CoFe, CoFeB, CoFeAl, Hulsers alloy and MnGa; The material of the covering layer (5) is one of W, Ta, Hf, Mo, Nb, and Ru, and the thickness is 3-8 nm.

2. The magnetic tunnel junction with high thermal stability according to claim 1, wherein: The magnetic tunnel junction with high thermal stability further comprises a spacer layer (6) and a second free layer (7), wherein the spacer layer (6) is located between the first free layer (3) and the second free layer (7) and is used for interlayer exchange coupling between the first free layer (3) and the second free layer (7), and the second free layer (7) is located between the barrier layer (2) and the spacer layer (6) and has a direction-variable perpendicular magnetization.

3. The magnetic tunnel junction with high thermal stability according to claim 2, wherein: The reference layer (1) and the second free layer (7) are both doped with non-metallic elements, the thickness of the reference layer (1) is 1.2-2 nm, and the thickness of the first free layer (3) and the second free layer (7) are both 0.6-1 nm.

4. The magnetic tunnel junction with high thermal stability according to claim 2, wherein: The material of the spacer layer (6) is one of W, Ta, Ru, and Mo, and the thickness is 0.2~0.6nm.

5. The magnetic tunnel junction with high thermal stability according to any one of claims 1 to 4, characterized in that: The non-metallic element is one of nitrogen, phosphorus and sulfur.

6. The magnetic tunnel junction with high thermal stability according to any one of claims 1 to 4, characterized in that: The non-metallic element is doped in at least one of the edge position, interstitial position, face center position and body center position of the corresponding layer.

7. The magnetic tunnel junction with high thermal stability according to any one of claims 2 to 4, characterized in that: The material of the second free layer (7) is one of Co, Fe, CoFe, CoFeB, CoFeAl, Hulsers alloy and MnGa.

8. The magnetic tunnel junction with high thermal stability according to claim 1, wherein: The material of the barrier layer (2) is one of MgO, HfO, and Al2O3, and the thickness is 1-1.5 nm.

Images