Magnetic tunnel junction

Abstract

The invention provides a magnetic tunnel junction, which comprises a reference layer, a barrier layer and a free layer which are stacked in sequence, and is characterized in that the free layer comprises a first magnetic layer which is adjacent to the barrier layer, and the interface of the first magnetic layer and the barrier layer has interface perpendicular magnetic anisotropy; the second magnetic layer is located on the side, away from the barrier layer, of the first magnetic layer, and the second magnetic layer has body perpendicular magnetic anisotropy; and a first spacer layer between the first magnetic layer and the second magnetic layer. According to the invention, the data retention time of the small-size magnetic tunnel junction at a high temperature can be prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic memories, and in particular, to a magnetic tunnel junction. Background Art

[0002] Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM) has the advantages of simple circuit design, fast read and write speed, and non-volatility. The core device of STT-MRAM is a magnetic tunnel junction (MTJ), which mainly includes a free layer, a reference layer, and a barrier layer sandwiched between the two. Among them, the magnetization direction of the reference layer is fixed, and the magnetization direction of the free layer is variable. By using the spin torque of electrons, the magnetization direction of the free layer is flipped to achieve parallel (lower resistance) or anti-parallel (higher resistance) magnetization directions of the reference layer and the free layer, thereby realizing writing "0" or "1".

[0003] With the development of MRAM, the key size of the MTJ has become smaller and smaller, and the size reduction has brought new technical problems: the data retention time at high temperatures has decreased sharply. Summary of the Invention

[0004] To solve the above problems, the present invention provides a magnetic tunnel junction that can improve the data retention time of small-size magnetic tunnel junctions at high temperatures.

[0005] The present invention provides a magnetic tunnel junction, comprising:

[0006] A reference layer;

[0007] A barrier layer located on one side of the reference layer;

[0008] A free layer located on the side of the barrier layer away from the reference layer;

[0009] The free layer has a structure combining interface perpendicular magnetic anisotropy and bulk perpendicular magnetic anisotropy, and includes:

[0010] A first magnetic layer adjacent to the barrier layer, and the interface between the first magnetic layer and the barrier layer has interface perpendicular magnetic anisotropy;

[0011] A second magnetic layer located on the side of the first magnetic layer away from the barrier layer, and the second magnetic layer has bulk perpendicular magnetic anisotropy;

[0012] A first spacer layer located between the first magnetic layer and the second magnetic layer.

[0013] Optionally, the material of the first magnetic layer is selected from any one of CoB, FeB, and CoFeB.

[0014] Optionally, the material of the second magnetic layer is selected from any one of CoPdB, CoPdBC, FePdB, and FePdBC, where the atomic percentage content of B ranges from 20% to 30%, and the atomic percentage content of C ranges from 1% to 5%; alternatively, the material of the second magnetic layer is a Heusler alloy.

[0015] Optionally, the material of the first spacer layer is selected from any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x , MgO, MgTiO x and MgAlO x and any combination thereof.

[0016] Optionally, the free layer further includes:

[0017] a third magnetic layer, located on a side of the second magnetic layer away from the first spacer layer;

[0018] The magnetic tunnel junction further includes:

[0019] an interface enhancement layer, located on a side of the third magnetic layer away from the second magnetic layer, and an interface between the third magnetic layer and the interface enhancement layer has interface perpendicular magnetic anisotropy.

[0020] Optionally, the material of the third magnetic layer is selected from any one of CoB, FeB, and CoFeB.

[0021] Optionally, the free layer further includes:

[0022] a second spacer layer, located between the second magnetic layer and the third magnetic layer.

[0023] Optionally, the material of the second spacer layer is selected from any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x , MgO, MgTiO x and MgAlO x and any combination thereof, which is the same as or different from the material of the first spacer layer.

[0024] Optionally, the second magnetic layer adopts a [A / X] n / A multi-layer structure, where 1 ≤ n ≤ 6, and A represents a magnetic layer with bulk perpendicular magnetic anisotropy, and X represents a spacer layer between two magnetic layers.

[0025] Optionally, if the magnetic tunnel junction is a top-pinned structure, the second magnetic layer is located at the bottom, and the magnetic tunnel junction further includes:

[0026] The seed layer, located below the second magnetic layer, is used to assist the growth of the second magnetic layer.

[0027] For the magnetic tunnel junction provided by the present invention, an interfacial perpendicular magnetic anisotropy and a magnetic layer with bulk perpendicular magnetic anisotropy are introduced into the free layer. The free layer adopting the architecture combining interfacial PMA and bulk (Bulk) PMA can enhance the perpendicular magnetic anisotropy of the free layer, thereby improving the data retention time of small-size magnetic tunnel junctions at high temperatures. At the same time, this architecture can also improve the STT efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention Figure One ;

[0029] Figure 2 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention Figure Two ;

[0030] Figure 3 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention Figure Three ;

[0031] Figure 4 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention Figure Four ;

[0032] Figure 5 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention Figure Five 。 DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0034] Various schematic structural diagrams according to embodiments of the present disclosure are shown in the drawings. These figures are not drawn to scale, where for the purpose of clear expression, some details are enlarged and some details may be omitted. The shapes of various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary. In practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art can design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0035] In the context of the present disclosure, when a layer / component is referred to as being "on" another layer / component, the layer / component can be directly on the other layer / component, or there can be an intermediate layer / component therebetween. Additionally, if a layer / component is "on" another layer / component in one orientation, then when the orientation is reversed, the layer / component can be "under" the other layer / component.

[0036] The following will describe in detail some embodiments of the present invention with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0037] An embodiment of the present invention provides a magnetic tunnel junction, as Figure 1 shown, the magnetic tunnel junction is a bottom-pinned structure, including a reference layer 101, a barrier layer 102, and a free layer 103 stacked from bottom to top. The free layer 103 is a structure combining interface perpendicular magnetic anisotropy and bulk perpendicular magnetic anisotropy, and can include a first magnetic layer 1031, a first spacer layer 1032, and a second magnetic layer 1033. The first magnetic layer 1031 is adjacent to the barrier layer 102, and the interface between the first magnetic layer 1031 and the barrier layer 102 has interface perpendicular magnetic anisotropy (interface PMA); the second magnetic layer 1033 is located on the side of the first magnetic layer 1031 away from the barrier layer 102, and the second magnetic layer 1033 has bulk perpendicular magnetic anisotropy (Bulk PMA); the first spacer layer 1032 is located between the first magnetic layer 1031 and the second magnetic layer 1033.

[0038] As an embodiment, the material of the first magnetic layer 1031 is selected from any one of CoB, FeB, and CoFeB.

[0039] In this embodiment, the second magnetic layer 1033 has bulk perpendicular magnetic anisotropy (Bulk PMA), and its material system satisfies the following requirements:

[0040] 1) The thin film has a high K u value, where K u represents the perpendicular magnetic anisotropy energy of the thin film and needs to be greater than the K u value (2 - 5 Merg / cm 3 ) of the CoFeB / MgO interface. For example, the K u value needs to be greater than 5 Merg / cm 3 to have a high data retention ability.

[0041] 2) The thin film has low damping, which needs to be less than or equal to the CoFeB / MgO system. For example, the damping coefficient ranges from 0.002 to 0.006, so it has a low switching current and is convenient for improving the STT efficiency.

[0042] As an implementation, the material of the second magnetic layer 1033 is selected from any one of CoPdB, CoPdBC, FePdB, and FePdBC, where the atomic percentage content of B ranges from 20% to 30%, and the atomic percentage content of C ranges from 1% to 5%; alternatively, the material of the second magnetic layer 1033 can also be a Heusler alloy, such as MnGa, Fe2CrCoSi.

[0043] For the bottom-pinned magnetic tunnel junction, referring to the MgO / CoFeB system, a suitable first spacer layer 1032 is introduced to obtain the first spacer layer / FePdB (or CoPdB, etc.) system to achieve a lower crystallization temperature. The first spacer layer 1032 can be used as a growth template layer for the second magnetic layer 1033.

[0044] As an implementation, the material of the first spacer layer 1032 is selected from any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x 、MgO、MgTiO x and MgAlO x and any combination thereof.

[0045] Further referring to Figure 1 ,the magnetic tunnel junction further includes: a capping layer 105, which plays a protective role.

[0046] Furthermore, Figure 2 shows a schematic structural diagram of a magnetic tunnel junction of another embodiment. As shown in Figure 2 ,on the basis of the magnetic tunnel junction shown in Figure 1 ,the free layer 103 further includes a third magnetic layer 1034, which is located on the side of the second magnetic layer 1033 away from the first spacer layer 1032;

[0047] Correspondingly, the magnetic tunnel junction further includes: an interface enhancement layer 104, which is located on the side of the third magnetic layer 1034 away from the second magnetic layer 1033, and the interface between the third magnetic layer 1034 and the interface enhancement layer 104 has interface perpendicular magnetic anisotropy.

[0048] In this embodiment, the material of the third magnetic layer 1034 is selected from any one of CoB, FeB, and CoFeB. The interface enhancement layer 104 can be MgO.

[0049] Furthermore, Figure 3The schematic structural diagram of a magnetic tunnel junction according to yet another embodiment is shown, as Figure 3 shown. Based on the magnetic tunnel junction shown in Figure 2 , the free layer 103 further includes a second spacer layer 1035, which is located between the second magnetic layer 1033 and the third magnetic layer 1034. The material of the second spacer layer 1035 is selected from any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x , MgO, MgTiO x and MgAlO x and any combination thereof. It should be noted here that the material of the second spacer layer 1035 can be the same as or different from that of the first spacer layer 1032.

[0050] Furthermore, Figure 4 The schematic structural diagram of a magnetic tunnel junction according to yet another embodiment is shown, as Figure 4 shown. Based on the magnetic tunnel junction shown in Figure 3 , the second magnetic layer 1033 adopts a multi-layer structure of A / X / A, where A represents a magnetic layer with bulk perpendicular magnetic anisotropy, and X represents a spacer layer between two magnetic layers. As for the materials of A and X, reference can be made to the description of the previous embodiments. The material of A can be any one of CoPdB, CoPdBC, FePdB, and FePdBC, where the atomic percentage content of B ranges from 20% to 30%, and the atomic percentage content of C ranges from 1% to 5%; alternatively, the material of A can also be a Heusler alloy, such as MnGa, Fe2CrCoSi. The material of X can be any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x , MgO, MgTiO x and MgAlO x and any combination thereof.

[0051] It should be noted that Figure 4 only the multi-layer structure of A / X / A adopted by the second magnetic layer 1033 is used for exemplary illustration. In practical applications, the second magnetic layer can adopt a multi-layer structure of [A / X] n / A, where 1 ≤ n ≤ 6, where A represents a magnetic layer with bulk perpendicular magnetic anisotropy, and X represents a spacer layer between two magnetic layers.

[0052] In addition, it should also be noted that Figure 1 and Figure 2 the second magnetic layer 1033 in can also adopt a multi-layer structure of [A / X] n / A, where 1 ≤ n ≤ 6, and will not be elaborated here.

[0053] Figures 1 to 4Enumerates different combinations of the free layer of the bottom-pinned magnetic tunnel junction adopting a combined architecture of interfacial PMA and bulk PMA, and realizes its ordered phase formation at a lower temperature through methods such as inserting a spacer layer, doping with bulk PMA materials B, C, etc., and post-annealing (≤400 °C), to match its process compatibility with the front-end CMOS and MTJ.

[0054] On the other hand, the stacked structure of the magnetic tunnel junction proposed in this application is also applicable to the top-pinned magnetic tunnel junction. In one embodiment, Figure 5 The schematic structural diagram of the top-pinned magnetic tunnel junction is shown, as Figure 5 shown, the magnetic tunnel junction includes a free layer 501, a barrier layer 502, and a reference layer 503 stacked from bottom to top, wherein the free layer 501 includes a first magnetic layer 5011, a first spacer layer 5012, and a second magnetic layer 5013. The first magnetic layer 5011 is adjacent to the barrier layer 502, and the interface between the first magnetic layer 5011 and the barrier layer 502 has interfacial perpendicular magnetic anisotropy (interfacial PMA); the second magnetic layer 5013 is located on the side of the first magnetic layer 5011 away from the barrier layer 502, and the second magnetic layer 5013 has bulk perpendicular magnetic anisotropy (Bulk PMA); the first spacer layer 5012 is located between the first magnetic layer 5011 and the second magnetic layer 5013.

[0055] The stacked structure of the magnetic tunnel junction in this embodiment can be regarded as Figure 1 inverting the up-and-down symmetry of the reference layer, barrier layer, and free layer, and at this time, the second magnetic layer 5013 far from the barrier layer 502 is located at the bottom. For the top-pinned magnetic tunnel junction, in order to assist the growth of the second magnetic layer 5013, as Figure 5 shown, the top-pinned magnetic tunnel junction further includes a seed layer 500. The seed layer 500 is located below the second magnetic layer 5013 and is used to assist the growth of the second magnetic layer 5013. The materials of the seed layer 500 include but are not limited to Ru, Cr, CrRu, Mo, W, TiO x 、MgTiO x , etc., to further promote lattice growth.

[0056] In addition, for the top-pinned magnetic tunnel junction, the second magnetic layer 5013 preferably has a material with a high K u value, low damping, and a relatively low annealing temperature, such as Fe2CrCoSi. After the deposition of the seed layer 500 and the second magnetic layer 5013, in-situ rapid-thermal-anneal rapid annealing or high-temperature deposition (T≤450 °C) is performed, and then the subsequent MTJ thin film deposition and growth are carried out normally to solve the problem of the process compatibility of the bulk PMA material with the front-end CMOS and the subsequent MTJ process.

[0057] It can be understood that for Figures 2 to 4 the bottom-pinned magnetic tunnel junction shown, by reversing the up-and-down symmetry of the reference layer, the barrier layer, and the free layer, a top-pinned magnetic tunnel junction can be correspondingly obtained.

[0058] A magnetic tunnel junction provided by an embodiment of the present invention introduces interface perpendicular magnetic anisotropy and a magnetic layer with bulk perpendicular magnetic anisotropy into the free layer. The free layer adopting an architecture combining interface PMA and bulk (Bulk) PMA can enhance the perpendicular magnetic anisotropy of the free layer, thereby improving the data retention time of small-sized magnetic tunnel junctions at high temperatures. At the same time, this architecture can also improve the STT efficiency.

[0059] In the above description, technical details such as the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. with the desired shapes. In addition, for forming the same structure, those skilled in the art can also design methods that are not exactly the same as the methods described above. In addition, although the above embodiments are described separately, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0060] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A magnetic tunnel junction, characterized in that, The magnetic tunnel junction includes: A reference layer; A barrier layer located on one side of the reference layer; A free layer located on the side of the barrier layer away from the reference layer; The free layer is a structure combining interface perpendicular magnetic anisotropy and bulk perpendicular magnetic anisotropy, and includes: A first magnetic layer adjacent to the barrier layer, and the interface between the first magnetic layer and the barrier layer has interface perpendicular magnetic anisotropy; A second magnetic layer located on the side of the first magnetic layer away from the barrier layer, and the second magnetic layer has bulk perpendicular magnetic anisotropy; A first spacer layer located between the first magnetic layer and the second magnetic layer.

2. The magnetic tunnel junction according to claim 1, wherein The material of the first magnetic layer is selected from any one of CoB, FeB, and CoFeB.

3. The magnetic tunnel junction according to claim 1, wherein The material of the second magnetic layer is selected from any one of CoPdB, CoPdBC, FePdB, and FePdBC, where the atomic percentage content of B is between 20% and 30%, and the atomic percentage content of C is between 1% and 5%; or the material of the second magnetic layer is a Heusler alloy.

4. The magnetic tunnel junction according to claim 1, wherein The material of the first spacer layer is selected from any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x , MgO, MgTiO x and MgAlO x and any combination thereof.

5. The magnetic tunnel junction according to claim 1, characterized in that, The free layer further includes: A third magnetic layer located on the side of the second magnetic layer away from the first spacer layer; The magnetic tunnel junction further includes: An interface enhancement layer located on the side of the third magnetic layer away from the second magnetic layer, and the interface between the third magnetic layer and the interface enhancement layer has interface perpendicular magnetic anisotropy.

6. The magnetic tunnel junction according to claim 5, wherein The material of the third magnetic layer is selected from any one of CoB, FeB, and CoFeB.

7. The magnetic tunnel junction according to claim 5, characterized in that The free layer further includes: A second spacer layer located between the second magnetic layer and the third magnetic layer.

8. The magnetic tunnel junction according to claim 7, characterized in that The material of the second spacer layer is selected from any one of Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x , MgO, MgTiO x and MgAlO x and combinations thereof, which may be the same as or different from the material of the first spacer layer.

9. The magnetic tunnel junction according to claim 1, wherein The second magnetic layer adopts a multi-layer structure of [A / X] n / A, where 1 ≤ n ≤ 6, and A represents a magnetic layer with bulk perpendicular magnetic anisotropy, and X represents a spacer layer between two magnetic layers.

10. The magnetic tunnel junction according to claim 1, characterized in that, If the magnetic tunnel junction is a top-pinned structure and the second magnetic layer is located at the bottom, the magnetic tunnel junction further includes: A seed layer located below the second magnetic layer for assisting the growth of the second magnetic layer.

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