Magnetic tunnel junction

Abstract

Provided in the present invention is a magnetic tunnel junction. The magnetic tunnel junction comprises a reference layer, a barrier layer and a free layer, which are sequentially stacked, wherein the free layer comprises: a first magnetic layer, which is adjacent to the barrier layer, an interface between the first magnetic layer and the barrier layer having interfacial perpendicular magnetic anisotropy; a second magnetic layer, which is located on the side of the first magnetic layer away from the barrier layer, the second magnetic layer having bulk perpendicular magnetic anisotropy; and a first spacer layer, which is located between the first magnetic layer and the second magnetic layer. The present invention can prolong the data retention time of small-sized magnetic tunnel junctions at high temperatures.

Description

Magnetic tunnel junction

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410033300.3 filed on January 9, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of magnetic memory, and in particular to a magnetic tunnel junction. Background Art

[0004] Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM) offers advantages such as simple circuit design, fast read and write speeds, and non-volatility. The core component of STT-MRAM is the magnetic tunnel junction (MTJ), which primarily consists of a free layer, a reference layer, and a barrier layer sandwiched between them. The reference layer has a fixed magnetization direction, while the free layer has a variable magnetization direction. By utilizing the spin torque of electrons, the magnetization direction of the free layer is flipped, making the magnetization directions of the reference and free layers parallel (lower resistance) or antiparallel (higher resistance), thereby enabling the writing of a "0" or "1."

[0005] With the development of MRAM, the critical dimensions of MTJ are getting smaller and smaller. The miniaturization of dimensions has brought about new technical problems: the data retention time at high temperatures drops sharply. Summary of the Invention

[0006] To solve the above problems, the present invention provides a magnetic tunnel junction, which can improve the data retention time of a small-sized magnetic tunnel junction at high temperature.

[0007] The present invention provides a magnetic tunnel junction, comprising:

[0008] Reference layer;

[0009] a barrier layer, located on one side of the reference layer;

[0010] a free layer, located on a side of the barrier layer away from the reference layer;

[0011] The free layer is a structure combining interface perpendicular magnetic anisotropy and bulk perpendicular magnetic anisotropy, including:

[0012] a first magnetic layer adjacent to the barrier layer, wherein an interface between the first magnetic layer and the barrier layer has an interface perpendicular magnetic anisotropy;

[0013] a second magnetic layer located on a side of the first magnetic layer away from the barrier layer, the second magnetic layer having a body perpendicular magnetic anisotropy;

[0014] The first spacer layer is located between the first magnetic layer and the second magnetic layer.

[0015] Optionally, a material of the first magnetic layer is selected from any one of CoB, FeB and CoFeB.

[0016] Optionally, the material of the second magnetic layer is selected from any one of CoPdB, CoPdBC, FePdB and FePdBC, wherein 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 Heusler alloy.

[0017] Optionally, the material of the first spacer layer is selected from Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x 、MgO、MgTiO x and MgAlO x Any one or combination of .

[0018] Optionally, the free layer further includes:

[0019] a third magnetic layer, located on a side of the second magnetic layer away from the first spacer layer;

[0020] The magnetic tunnel junction further comprises:

[0021] The interface enhancement layer is located on a 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.

[0022] Optionally, a material of the third magnetic layer is selected from any one of CoB, FeB and CoFeB.

[0023] Optionally, the free layer further includes:

[0024] The second spacer layer is located between the second magnetic layer and the third magnetic layer.

[0025] Optionally, the material of the second spacer layer is selected from Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x 、MgO、MgTiO x and MgAlO x Any one or combination thereof is the same as or different from the material of the first spacer layer.

[0026] Optionally, the second magnetic layer adopts [A / X] n / A multilayer structure, 1≤n≤6, where A represents a magnetic layer with bulk perpendicular magnetic anisotropy, and X represents a spacer layer between two magnetic layers.

[0027] 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:

[0028] The seed layer is located below the second magnetic layer and is used to assist the growth of the second magnetic layer.

[0029] The magnetic tunnel junction proposed by the present invention introduces interface perpendicular magnetic anisotropy and a magnetic layer with bulk perpendicular magnetic anisotropy in the free layer. The free layer's architecture, combining interface PMA and bulk PMA, enhances the perpendicular magnetic anisotropy of the free layer, thereby increasing the data retention time of small-sized magnetic tunnel junctions at high temperatures. This architecture also improves STT efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention;

[0031] FIG2 is a second structural diagram of a magnetic tunnel junction according to an embodiment of the present invention;

[0032] FIG3 is a third structural diagram of a magnetic tunnel junction according to an embodiment of the present invention;

[0033] FIG4 is a fourth structural diagram of a magnetic tunnel junction according to an embodiment of the present invention;

[0034] FIG5 is a fifth structural diagram of a magnetic tunnel junction according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present disclosure. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0036] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments of the present disclosure. These figures are not drawn to scale, and for the purpose of clarity, certain details are exaggerated and certain details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0037] In the context of the present disclosure, when a layer / element is referred to as being "on" another layer / element, it can be directly on the other layer / element or an intervening layer / element may be present therebetween. In addition, if a layer / element is "on" another layer / element in one orientation, it may be "below" the other layer / element when the orientation is reversed.

[0038] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0039] An embodiment of the present invention provides a magnetic tunnel junction, as shown in FIG1 . 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 that combines interface perpendicular magnetic anisotropy and bulk perpendicular magnetic anisotropy, and may 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 a 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); and the first spacer layer 1032 is located between the first magnetic layer 1031 and the second magnetic layer 1033.

[0040] As an embodiment, the material of the first magnetic layer 1031 is selected from any one of CoB, FeB and CoFeB.

[0041] In this embodiment, the second magnetic layer 1033 has bulk perpendicular magnetic anisotropy (Bulk PMA), and its material system meets the following requirements:

[0042] 1) The film has a high K u Value, K u Indicates the perpendicular magnetic anisotropy of the film, which needs to be greater than the K of the CoFeB / MgO interface u Value (2~5Merg / cm 3 ), such as Ku The value must be greater than 5Merg / cm 3 , thus having higher data retention capability.

[0043] 2) The film has low damping, which needs to be less than or equal to that of the CoFeB / MgO system. For example, the damping coefficient should be between 0.002 and 0.006, resulting in a lower switching current and facilitating improved STT efficiency.

[0044] As an embodiment, the material of the second magnetic layer 1033 is selected from any one of CoPdB, CoPdBC, FePdB and FePdBC, wherein the atomic percentage content of B is between 20%-30%, and the atomic percentage content of C is between 1%-5%; alternatively, the material of the second magnetic layer 1033 can also be a Heusler alloy, such as MnGa, Fe2CrCoSi.

[0045] For bottom-pinned magnetic tunnel junctions, a suitable first spacer layer 1032 is introduced, drawing inspiration from the MgO / CoFeB system, resulting in a first spacer layer / FePdB (or CoPdB, etc.) system to achieve a lower crystallization temperature. The first spacer layer 1032 can serve as a growth template layer for the second magnetic layer 1033.

[0046] As an embodiment, the material of the first spacer layer 1032 is selected from Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x ,MgO,MgTiO x and MgAlO x Any one or combination of .

[0047] Further referring to FIG. 1 , the magnetic tunnel junction further includes a capping layer 105 for protection.

[0048] Furthermore, FIG2 shows a schematic structural diagram of a magnetic tunnel junction according to another embodiment. As shown in FIG2 , based on the magnetic tunnel junction shown in FIG1 , the free layer 103 further includes a third magnetic layer 1034 located on a side of the second magnetic layer 1033 away from the first spacer layer 1032 ;

[0049] Correspondingly, the magnetic tunnel junction further includes an interface enhancement layer 104 located on a side of the third magnetic layer 1034 away from the second magnetic layer 1033 , and an interface between the third magnetic layer 1034 and the interface enhancement layer 104 has interface perpendicular magnetic anisotropy.

[0050] 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 may be MgO.

[0051] Furthermore, FIG3 shows a schematic diagram of the structure of a magnetic tunnel junction according to another embodiment. As shown in FIG3 , based on the magnetic tunnel junction shown in FIG2 , the free layer 103 further includes a second spacer layer 1035 located between the second magnetic layer 1033 and the third magnetic layer 1034. The material of the second spacer layer 1035 is selected from Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x 、MgO、MgTiO x and MgAlO x It is explained here that the materials of the second spacer layer 1035 and the first spacer layer 1032 can be the same or different.

[0052] Furthermore, FIG4 shows a schematic structural diagram of a magnetic tunnel junction according to another embodiment. As shown in FIG4 , based on the magnetic tunnel junction shown in FIG3 , the second magnetic layer 1033 adopts a multilayer structure of A / X / A, wherein A represents a magnetic layer having a body perpendicular magnetic anisotropy, and X represents a spacer layer between the 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, wherein the atomic percentage of B is between 20% and 30%, and the atomic percentage of C is between 1% and 5%. Alternatively, the material of A can also be a Heusler alloy, such as MnGa, Fe2CrCoSi. The material of X can be Hf, Zr, Ta, Mo, W, Cr, Ir, Ru, Rh, Mg, TiO x 、MgO、MgTiO x and MgAlO x Any one or combination of .

[0053] It should be noted that FIG4 is only an example of the second magnetic layer 1033 using the multi-layer structure of A / X / A. In actual applications, the second magnetic layer can be [A / X] n / A multilayer structure, 1≤n≤6, where A represents a magnetic layer with bulk perpendicular magnetic anisotropy, and X represents a spacer layer between two magnetic layers.

[0054] It should also be noted that the second magnetic layer 1033 in FIG. 1 and FIG. 2 can also be made of [A / X] n / A's multi-layer structure, 1≤n≤6, will not be described in detail.

[0055] Figures 1 to 4 list different combinations of the interface PMA and bulk PMA architectures used in the bottom-pinned magnetic tunnel junction free layer. By inserting spacer layers, doping with bulk PMA materials B and C, and post-annealing (≤400°C), the ordered phase is achieved at a relatively low temperature, matching its compatibility with the front-end CMOS and MTJ processes.

[0056] On the other hand, the stacked structure of the magnetic tunnel junction proposed in this application is also applicable to a top-pinned magnetic tunnel junction. In one embodiment, FIG5 shows a schematic diagram of the structure of a top-pinned magnetic tunnel junction. As shown in FIG5 , 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 an interface perpendicular magnetic anisotropy (interface PMA); the second magnetic layer 5013 is located on a side of the first magnetic layer 5011 away from the barrier layer 502, and the second magnetic layer 5013 has a bulk perpendicular magnetic anisotropy (bulk PMA); and the first spacer layer 5012 is located between the first magnetic layer 5011 and the second magnetic layer 5013.

[0057] The stacked structure of the magnetic tunnel junction of this embodiment can be regarded as the reference layer, barrier layer and free layer in FIG1 being symmetrically reversed. In this case, the second magnetic layer 5013 away 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 shown in FIG5 , the top-pinned magnetic tunnel junction further includes a seed layer 500. The seed layer 500 is located below the second magnetic layer 5013 to assist the growth of the second magnetic layer 5013. The material of the seed layer 500 includes but is not limited to Ru, Cr, CrRu, Mo, W, TiO x 、MgTiO x , etc., to further promote lattice growth.

[0058] In addition, for the top pinned magnetic tunnel junction, the second magnetic layer 5013 preferably has a high K u Materials with low resistance, low damping, and low annealing temperatures, such as Fe2CrCoSi, are used. After the seed layer 500 and the second magnetic layer 5013 are deposited, in-situ rapid-thermal-annealing or high-temperature deposition (T≤450°C) is performed. Subsequently, the subsequent MTJ thin film deposition and growth proceed normally to address the compatibility issues of bulk PMA materials with front-end CMOS and subsequent MTJ processes.

[0059] It can be understood that for the bottom-pinned magnetic tunnel junction shown in FIG. 2 to FIG. 4 , a top-pinned magnetic tunnel junction can be obtained by reversing the up-down symmetry of the reference layer, the barrier layer, and the free layer.

[0060] 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 in the free layer. The free layer utilizes a combination of interface PMA and bulk PMA architecture, which enhances the perpendicular magnetic anisotropy of the free layer and, in turn, improves data retention time at high temperatures in small-scale magnetic tunnel junctions. This architecture also improves STT efficiency.

[0061] While the above description does not provide detailed technical details regarding patterning and etching of each layer, those skilled in the art will appreciate that various technical means can be employed to form layers, regions, and the like in desired shapes. Furthermore, those skilled in the art may devise methods that differ from those described above to form the same structure. Furthermore, while each embodiment has been described separately, this does not mean that the measures in each embodiment cannot be advantageously combined.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

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

2. The magnetic tunnel junction according to claim 1, characterized in that, 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, wherein the atomic percentage content of B is between 20% and 30%, and the atomic percentage content of C is between 1% and 5%; alternatively, the material of the second magnetic layer is a Heusler alloy.

4. The magnetic tunnel junction according to claim 1, characterized in that, 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 disposed on a side of the second magnetic layer away from the first spacer layer; The magnetic tunnel junction further includes: an interface enhancement layer disposed on a side of the third magnetic layer away from the second magnetic layer, the interface between the third magnetic layer and the interface enhancement layer having 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 disposed between the second magnetic layer and the third magnetic layer.

8. The magnetic tunnel junction according to claim 7, wherein 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.

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, 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, with the second magnetic layer at the bottom, the magnetic tunnel junction further includes: a seed layer disposed below the second magnetic layer for assisting the growth of the second magnetic layer.

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