Magnetic tunnel junction storage cell based on magnetic skyrmions and method of operation thereof

Abstract

This invention relates to a magnetic tunnel junction memory cell based on magnetic skyrmions and its operation method. A magnetic tunnel junction memory cell may include: a reference magnetic layer and a free magnetic layer separated by a barrier layer; a skyrmion carrier layer separated from the free magnetic layer by a spacer layer, the spacer layer inducing ferromagnetic coupling or antiferromagnetic coupling between the skyrmion carrier layer and the free magnetic layer; and a cap layer formed on the skyrmion carrier layer, the cap layer applying a bias magnetic field to the skyrmion carrier layer by an exchange bias, such that the skyrmion carrier layer is in the skyrmion phase, wherein the cap layer generates a spin current when an in-plane write current is applied, the spin current being vertically injected into the skyrmion carrier layer to write skyrmions, and the skyrmions being coupled to the free magnetic layer through ferromagnetic coupling or antiferromagnetic coupling induced by the spacer layer.

Description

Technical Field

[0001] This invention belongs to the field of magnetic random access memory, and more specifically, relates to a magnetic tunnel junction memory cell that uses magnetic skyrmions as information storage carriers and its operation method. Background Technology

[0002] With the advent of the Internet of Things and the era of big data, people's demand for massive data storage, high-efficiency, and high-speed functional devices is increasing daily. Improving the storage density of traditional hard drives faces a series of physical problems, such as thermal stability and the superparamagnetic critical limit. Magnetic skyrmions, or simply skyrmions, are chiral spin structures with vortex configurations that are topologically nontrivial. Currently, skyrmions are generally classified into two types: Bloch-type skyrmions, which exist in bulk materials due to the breaking of structural noncentrosymmetry, and Neel-type skyrmions, which exist in thin film materials due to the breaking of interface inversion symmetry. Figure 1 Schematic diagrams of a Bloch-type skyrmion (see small figure (a) on the left) and a Nell-type skyrmion (see small figure (b) on the right) are shown, where the magnetization direction at the center of the skyrmion is vertically downward, while the magnetization direction around the skyrmion is vertically upward. However, the opposite can also be true, where the magnetization direction at the center of the skyrmion is vertically upward, while the magnetization direction around the skyrmion is vertically downward.

[0003] Skyrmions possess a rich material base, existing in ferromagnetic, hypoferromagnetic, and antiferromagnetic materials. They also exhibit characteristics such as small size, high stability, low critical drive current density, low energy consumption, and topological nonvolatility. Given these properties, the application of skyrmions in next-generation ultra-high-density magnetic storage devices has been a subject of ongoing research. Several prototype devices have been proposed, such as skyrmion spin nanooscillators, skyrmion shift registers, and skyrmion racetrack memories. However, due to limitations in the generation, manipulation, deletion, and retrieval of skyrmions, their successful application in magnetic tunnel junctions (MTJs) remains unresolved. MTJs, as classic spintronic devices, are widely used in magnetic storage and magnetic logic devices; therefore, understanding how to more effectively manipulate and retrieve skyrmions using MTJs is crucial for realizing skyrmion-based device applications. Summary of the Invention

[0004] To address the aforementioned problems, this invention is proposed. This invention provides a novel magnetic tunnel junction structure in which a magnetic free layer and a skyrmion carrier layer are coupled to each other, and the skyrmion information in the carrier layer is determined by reading the magnetoresistance of the magnetic tunnel junction. The magnetic tunnel junction of this invention can conveniently implement multi-bit storage in a single memory cell and can also be used to perform in-memory computations.

[0005] According to an exemplary embodiment, a magnetic tunnel junction memory cell is provided, comprising: a reference magnetic layer and a free magnetic layer separated by a barrier layer; a skyrmion carrier layer separated from the free magnetic layer by a spacer layer, the spacer layer inducing ferromagnetic coupling or antiferromagnetic coupling between the skyrmion carrier layer and the free magnetic layer; and a cap layer formed on the skyrmion carrier layer, the cap layer applying a bias magnetic field to the skyrmion carrier layer by an exchange bias, such that the skyrmion carrier layer is in the skyrmion phase, wherein the cap layer generates a spin current when an in-plane write current is applied, the spin current being vertically injected into the skyrmion carrier layer to write skyrmions, and the skyrmions being coupled to the free magnetic layer by the ferromagnetic coupling or antiferromagnetic coupling induced by the spacer layer.

[0006] In some embodiments, the reference magnetic layer, the free magnetic layer, and the skyrmion carrier layer have perpendicular magnetic anisotropy, and the initial magnetization direction of the free magnetic layer is parallel to or antiparallel to the magnetization direction of the reference magnetic layer.

[0007] In some embodiments, the spacer layer comprises one or more of Cu, Ta, W, Pt, Ru, Hf, Ir, and Au.

[0008] In some embodiments, the skyrmion carrier layer comprises one or more of MnNiGa, MnSi, FeCoSi, Pt / Co / Ta multilayer film, Pd / Co / Ta multilayer film, Pt / Co multilayer film, and Pd / Co multilayer film.

[0009] In some embodiments, the cap layer comprises an antiferromagnetic material PtMn, IrMn, or AuMn. In some embodiments, the cap layer comprises a ferromagnetic material layer and an antiferromagnetic coupling layer located between the ferromagnetic material layer and the skyrmion carrier layer, thereby forming an artificial antiferromagnetic structure between the cap layer and the skyrmion carrier layer. The ferromagnetic material layer comprises Co, Fe, CoFeB, Pt / Co multilayer film, Pt / CoFeB multilayer film, Pd / Co multilayer film, or Pd / CoFeB multilayer film, and the antiferromagnetic coupling layer comprises Ta, W, Pt, Ru, Hf, Ir, or Au.

[0010] In some embodiments, the cap layer includes an artificial antiferromagnetic structure comprising a first ferromagnetic layer and a second ferromagnetic layer separated by an antiferromagnetic coupling layer, wherein the first ferromagnetic layer contacts the skyrmion carrier layer, the first ferromagnetic layer comprises a Pt / Co multilayer film or a Pt / CoFeB multilayer film, and the layer in contact with the skyrmion carrier layer is a Pt layer, the second ferromagnetic layer comprises Co, Fe, CoFeB, Pt / Co multilayer film, Pt / CoFeB multilayer film, Pd / Co multilayer film, or Pd / CoFeB multilayer film, and the antiferromagnetic coupling layer comprises Cu, Ta, W, Pt, Ru, Hf, Ir, or Au.

[0011] In some embodiments, the magnetic tunnel junction storage unit is implemented as a polymorphic storage unit, with different storage states corresponding to different numbers of skyrmions written into the skyrmion carrier layer.

[0012] According to another exemplary embodiment, a method for operating the above-described magnetic tunnel junction memory cell is provided, comprising: a writing step, including applying an in-plane writing current to the cap layer such that the cap layer generates a spin current through a spin Hall effect, the spin current being vertically injected into the skyrmion carrier layer to write skyrmions, and the skyrmions being coupled to the free magnetic layer through ferromagnetic coupling or antiferromagnetic coupling generated by the spacer layer; and a reading step, including applying a vertical reading current to the magnetic tunnel junction memory cell to read the resistance of the magnetic tunnel junction memory cell, the resistance of the magnetic tunnel junction memory cell being associated with the number of skyrmions written into the skyrmion carrier layer.

[0013] In some embodiments, during the writing step, the number of skyrmions written into the skyrmion carrier layer is controlled by controlling the pulse width, pulse amplitude, and / or pulse number of the in-plane writing current.

[0014] In some embodiments, the writing step further includes applying an in-plane reset current to the cap layer before applying the in-plane write current, the in-plane reset current being opposite in direction to the in-plane write current, so as to reset the skyrmion carrier layer to the initial magnetization direction.

[0015] In some embodiments, the magnetic tunnel junction memory cell is configured to perform in-memory computation operations, including: applying a first in-plane write current to the cap layer to write a first number of skyrmions to the skyrmion carrier layer; applying a second in-plane write current to the cap layer to write a second number of skyrmions to the skyrmion carrier layer; and applying a vertical read current to the magnetic tunnel junction memory cell to read the resistance of the magnetic tunnel junction memory cell, the read resistance corresponding to a third number of skyrmions, the third number being equal to the sum of the first number and the second number.

[0016] The above and other features and advantages of the present invention will become apparent from the following description of exemplary embodiments taken in conjunction with the accompanying drawings. Attached Figure Description

[0017] Figure 1 Schematic diagrams of Bloch-type and Nell-type magnetic skyrmions are shown.

[0018] Figure 2 A schematic diagram of a magnetic tunnel junction memory cell based on magnetic skyrmions according to an embodiment of the present invention is shown.

[0019] Figure 3A and Figure 3B The figures before and after writing magnetic skyrmions are shown according to an embodiment of the present invention. Figure 2 The diagram shows the magnetization direction in a magnetic tunnel junction storage cell.

[0020] Figure 4A and Figure 4B The following diagrams illustrate the process before and after writing magnetic skyrmions according to another embodiment of the invention. Figure 2 The diagram shows the magnetization direction in a magnetic tunnel junction storage cell.

[0021] Figure 5 A schematic diagram of the structure of a test sample of a magnetic tunnel junction storage cell based on magnetic skyrmions according to an embodiment of the present invention is shown.

[0022] Figure 6 Show Figure 5 The normalized hysteresis loop in the direction perpendicular to the film surface of the magnetic tunnel junction memory cell test sample is shown.

[0023] Figure 7 An embodiment of the present invention is shown including Figure 5 A schematic diagram of the test device for skyrmion magnetic storage cells.

[0024] Figure 8 The resistance of a 4μm junction test sample according to an embodiment of the present invention is shown as a function of magnetic field.

[0025] Figure 9 A micrograph showing the variation of magnetic domains in a skyrmion carrier layer with a magnetic field in a 2μm junction test sample according to an embodiment of the present invention.

[0026] Figure 10 The diagram shows the synchronous measurement results of the magnetic domains and tunnel junction resistance of the skyrmion carrier layer in a 3μm junction region according to an embodiment of the present invention as a function of magnetic field.

[0027] Figure 11A flowchart illustrating a method for performing in-memory computation using a skyminzi magnetic storage unit according to an embodiment of the present invention is shown. Detailed Implementation

[0028] Exemplary embodiments of the present invention are described below with reference to the accompanying drawings.

[0029] Figure 2 A schematic diagram of a magnetic tunnel junction storage cell 100 based on magnetic skyrmions according to an embodiment of the present invention is shown. Figure 2 As shown, the magnetic tunnel junction storage cell 100 includes a seed layer 120, a pinning layer 130, a reference layer 140, a barrier layer 150, a free layer 160, a spacer layer 170, a skyrmion carrier layer 180, and a cap layer 190 sequentially formed on a substrate 110.

[0030] The substrate 110 can be selected as an insulating substrate or a conductive (including semiconductor) substrate according to actual needs. Examples of commonly used substrate materials include, but are not limited to, SiO2, MgO, Al2O3, Si, SiC, and plastics.

[0031] The seed layer 120, also known as a buffer layer, provides lattice matching between the substrate 110 and the overlying magnetic material layer, offering a favorable growth interface for the magnetic material layer. In some embodiments, such as when the substrate 110 is an insulating substrate, the seed layer 120 can also serve as a bottom electrode layer. The seed layer 120 can be formed from a single-layer or multi-layer composite film of a non-magnetic metallic material with good conductivity and tight bonding to the substrate 110. The material of the seed layer 120 can be selected based on the materials of the substrate 110 and the overlying magnetic layer, and the thickness of the seed layer 120 can be selected within a wide range, generally from 1 nm to 100 nm, preferably from 2 nm to 20 nm.

[0032] Pinning layer 130 is used to pin the magnetic moment of reference layer 140 in a predetermined direction, so that the direction of the magnetic moment of reference layer 140 does not change with the change of external magnetic field during normal operation. Commonly used pinning layers include antiferromagnetic pinning layers and artificial antiferromagnetic (SAF) structures. Antiferromagnetic pinning layers can be formed of antiferromagnetic (AFM) materials such as IrMn, PtMn, FeMn, etc., and their thickness can be in the range of 1 to 30 nm. Artificial antiferromagnetic (SAF) structures include multiple ferromagnetic metal layers (FM) separated by non-magnetic metal layers (NM), which can be represented as FM / NM / FM. The non-magnetic metal layers induce antiferromagnetic (or antiparallel) coupling between the two ferromagnetic metal layers. The ferromagnetic metal layers can include magnetic single-layer or multi-layer film structures. Commonly used materials include, but are not limited to, Pt / Co, Pt / CoFeB, Pd / Co, Pd / CoFeB, Co, Fe, CoFeB, etc., and the thickness is generally in the range of 1 to 20 nm. Common materials for the non-magnetic metal layer may include Cu, Cr, Nb, Ru, Pd, Ta, W, Pt, Mo, Au, or alloys thereof, with a thickness typically ranging from 0.2 to 6 nm. Alternatively, the pinning layer 130 may also be made of a ferromagnetic material with high coercivity, such as a permanent magnet, with a thickness ranging from 1 to 30 nm. In some embodiments, the pinning layer 130 may be omitted, in which case the reference layer 140 may have a self-pinning structure, which will be described in detail below.

[0033] The reference layer 140 may comprise a single layer of ferromagnetic metal material, such as Co, Fe, CoFe, NiFe, CoFeB, etc., or a multilayer structure comprising non-magnetic metal layers and ferromagnetic metal layers, such as Pt / Co, Pd / Co, Ta / CoFeB, W / CoFeB, Ir / CoFeB, Pt / CoFeB, etc. The thickness of the reference layer 140 may be in the range of 1–20 nm, preferably in the range of 2–10 nm. As mentioned above, the magnetization direction of the reference layer 140 may be fixed in a predetermined direction by the pinning layer 130; when the pinning layer 130 is omitted, the reference layer 140 may have a self-pinning structure, for example, the reference layer 140 may be formed of a ferromagnetic material with high coercivity, or the reference layer 140 may comprise the aforementioned multilayer structure of non-magnetic metal layers and ferromagnetic metal layers, wherein the non-magnetic metal layers can cause the ferromagnetic metal layers to be antiparallel coupled to each other, which can reduce the net magnetic moment of the entire reference layer 140, thereby making the reference layer 140 less susceptible to the influence of external magnetic fields.

[0034] The barrier layer 150, also known as the tunneling layer, is formed of a non-magnetic insulating material, creating an electron barrier. Electrons then tunnel through the barrier layer 150, and the tunneling resistance depends on the magnetization directions of the adjacent ferromagnetic layers. Generally, the tunneling resistance is lowest when the magnetization directions of the adjacent ferromagnetic layers are parallel to each other, and highest when the magnetization directions are antiparallel. Commonly used barrier layer materials include metal oxides, such as MgO and AlO. x MgAlO x The thickness of the barrier layer 150 can be 0.5–6 nm, preferably 1–4 nm.

[0035] The free layer 160 may include a ferromagnetic metallic material, such as a single layer of ferromagnetic metallic material, or a multilayer structure of ferromagnetic metallic layers and non-magnetic metallic layers. The free layer 160 generally includes a ferromagnetic material with low coercivity, such as, but not limited to, CoFeB, Co, CoFe, etc., and its thickness may be 0.5 to 15 nm, preferably 1 to 10 nm.

[0036] Layers 110-160 described above, especially core layers 140-160, constitute a conventional magnetic tunnel junction structure, the operating principle of which is known and will not be elaborated here. It is understood that layers 110-160 are not limited to the embodiments described above, but can employ other implementations commonly used in conventional magnetic tunnel junction structures.

[0037] The spacer layer 170 may comprise a non-magnetic metallic material, such as a single-layer or multi-layer film structure comprising a non-magnetic metallic material. Examples of non-magnetic metallic materials that may be used for the spacer layer 170 include, but are not limited to, Cu, Ta, W, Pt, Ru, Hf, Ir, Au, etc., and the thickness of the spacer layer 170 may be 0.1–10 nm. The thickness of the spacer layer 170 may be used to modulate the RKKY interaction or magnetic dipole interaction between adjacent free layers 160 and skyrmion carrier layers 180, inducing ferromagnetic (parallel) or antiferromagnetic (antiparallel) coupling between free layers 160 and skyrmion carrier layers 180.

[0038] Skyrmion carrier layer 180 (or simply carrier layer), as the name suggests, can be used to carry (i.e. store) magnetic skyrmions. Skyrmion carrier layer 180 may include magnetic materials capable of storing skyrmions, such as a single layer of magnetic metal or a multilayer film structure of magnetic metal and non-magnetic metal, examples of which include, but are not limited to, MnNiGa, MnSi, FeCoSi, Pt / Co / Ta multilayer films, Pd / Co / Ta multilayer films, Pt / Co multilayer films, and Pd / Co multilayer films. The thickness of skyrmion carrier layer 180 can be 1–100 nm, preferably 4–50 nm.

[0039] The cap layer 190 formed above the skyrmion carrier layer 180 has multiple functions. Firstly, the cap layer 190 serves as a top electrode to apply a vertical current flowing through the magnetic tunnel junction. Secondly, it functions as a spin injection layer, writing or erasing skyrmions in the carrier layer 180 by injecting a spin current into it. Thirdly, it also functions as a magnetic bias layer, applying a bias magnetic field to the skyrmion carrier layer 180 to bias it into the skyrmion phase, i.e., a state capable of writing skyrmions. The material and structure of the cap layer 190 can be designed based on these functional requirements.

[0040] In some embodiments, the cap layer 190 may include an antiferromagnetic material exhibiting a spin Hall effect, such as PtMn, IrMn, or AuMn. The antiferromagnetic material can be used to apply a desired bias magnetic field to the skyrmion carrier layer 180 by exchanging the bias. Alternatively, these antiferromagnetic materials exhibit a spin Hall effect, generating a spin current when an in-plane current is applied. This spin current is injected perpendicularly into the adjacent skyrmion carrier layer 180, perturbing the magnetic moment of the skyrmion carrier layer 180 and thereby reversing the magnetization direction of a local region, forming skyrmions.

[0041] In other embodiments, the cap layer 190 may include a ferromagnetic material layer and an antiferromagnetic coupling layer, with the antiferromagnetic coupling layer located between the ferromagnetic material layer and the skyrmion carrier layer 180. Thus, the cap layer 190 (i.e., the ferromagnetic material layer and the antiferromagnetic coupling layer) together with the skyrmion carrier layer 180 form an artificial antiferromagnetic structure, wherein the ferromagnetic material layer provides the required bias magnetic field to the skyrmion carrier layer 180 through antiferromagnetic coupling. Such a ferromagnetic material layer may include Co, Fe, CoFeB, Pt / Co multilayer films, Pt / CoFeB multilayer films, Pd / Co multilayer films, or Pd / CoFeB multilayer films, etc., and the antiferromagnetic coupling layer may include heavy metal materials with spin Hall effect, such as Ta, W, Pt, Ru, Hf, Ir, or Au, etc. In this way, when an in-plane current is applied to the cap layer 190, the heavy metal material layer will generate a spin current. The spin current is injected vertically into the adjacent skyrmion carrier layer 180, which can disturb the magnetic moment of the skyrmion carrier layer 180, thereby writing skyrmions.

[0042] In some embodiments, the cap layer 190 itself can form an artificial antiferromagnetic structure. For example, the cap layer 190 may include a first ferromagnetic layer and a second ferromagnetic layer separated by an antiferromagnetic coupling layer. The first and second ferromagnetic layers may be the same or different. For ease of description, the first ferromagnetic layer may contact the skyrmion carrier layer 180. The first ferromagnetic layer may include a Pt / Co multilayer film or a Pt / CoFeB multilayer film, and the layer in contact with the skyrmion carrier layer 180 is a Pt layer because Pt is a heavy metal material with a spin Hall effect, which can provide spin flow injection to the skyrmion carrier layer 180. The second ferromagnetic layer may include Co, Fe, CoFeB, Pt / Co multilayer film, Pt / CoFeB multilayer film, Pd / Co multilayer film, or Pd / CoFeB multilayer film, etc., and the antiferromagnetic coupling layer may include Cu, Ta, W, Pt, Ru, Hf, Ir, or Au, etc. In this way, the artificial antiferromagnetic structure can bias the magnetization direction of the skyrmion carrier layer 180 through exchange coupling; on the other hand, when an in-plane current is applied to the artificial antiferromagnetic structure, the heavy metal material layer (e.g., the Pt layer) in contact with the skyrmion carrier layer 180 will generate a spin current. The spin current is injected vertically into the skyrmion carrier layer 180, which can perturb the magnetic moment of the skyrmion carrier layer 180, thereby writing skyrmions.

[0043] In the above embodiments, the heavy metal materials included in the cap layer 190, such as Pt, Ta, Au, and W, have good oxidation resistance and conductivity, thereby ensuring that the underlying layers are not easily oxidized or corroded by moisture. The cap layer 190 can also serve as the top electrode of the magnetic storage cell, used to apply write and read currents, as will be described in detail below. The thickness of the cap layer 190 can be selected within a wide range depending on its structure, generally from 1 nm to 100 nm, preferably from 1 nm to 20 nm. Besides writing skyrmions into the skyrmion carrier layer 180 using the cap layer 190, the skyrmion carrier layer 180 can also be erased by applying a spin current in the opposite direction to the skyrmion carrier layer 180 by controlling the direction of the in-plane current applied to the cap layer 190. The operations of writing and erasing skyrmions will be further described in detail below in conjunction with the magnetization direction configuration of each layer.

[0044] Figure 3A and Figure 3BSchematic diagrams are shown of the magnetization directions of the various magnetic layers in the magnetic tunnel junction storage cell 100 before and after the writing of magnetic skyrmions. In this embodiment, the pinned layer 130, reference layer 140, free layer 160, and skyrmion carrier layer 180 have perpendicular magnetic anisotropy, i.e., the easy magnetization axis is in the vertical direction, rather than in the in-plane direction. It should be understood that these magnetization directions are merely examples, and the various magnetic layers may also be configured to have different magnetization directions without departing from the principles of the invention.

[0045] First refer to Figure 3A The pinning layer 130 employs an artificial antiferromagnetic (SAF) structure, comprising a first ferromagnetic layer 132 and a second ferromagnetic layer 136 separated by a non-magnetic metal layer 134, and the first ferromagnetic layer 132 and the second ferromagnetic layer 136 are antiferromagnetically coupled to each other. In this example, the first ferromagnetic layer 132 has a vertically downward magnetization direction, and the second ferromagnetic layer 136 has a vertically upward magnetization direction, but other configurations are also possible, such as the first ferromagnetic layer 132 having a vertically upward magnetization direction and the second ferromagnetic layer 136 having a vertically downward magnetization direction.

[0046] The reference layer 140 can be ferromagnetically coupled to the second ferromagnetic layer 136 in the artificial antiferromagnetic structure 130, thus also having a vertically upward magnetization direction in this example.

[0047] The initial magnetization direction of the free layer 160 (the magnetization direction before skyrmions are written) can be oriented parallel or antiparallel to the reference layer 140, thus minimizing (corresponding to the parallel state) or maximizing (corresponding to the antiparallel state) the resistance of the magnetic tunnel junction 100. Figure 3A In the example shown, the initial magnetization direction of the free layer 160 is antiparallel to the reference layer 140, i.e., vertically downward. It can be understood that because the spacer layer 170 ferromagnetically couples or antiferromagnetically couples the free layer 160 with the skyrmion carrier layer 180, the magnetization direction of the free layer 160 can change in response to changes in the magnetic moment in the skyrmion carrier layer 180. However, it can resist changes in the external magnetic field to a certain extent (depending on the coupling strength induced by the spacer layer 170). Therefore, the magnetic tunnel junction memory cell of the present invention also has improved magnetic stability.

[0048] Skyrmion carrier layer 180 can be ferromagnetically or antiferromagnetically coupled to free layer 160 through spacer layer 170. Figure 3A In the example shown, ferromagnetic coupling is used, and the magnetization direction of the skyrmion carrier layer 180 is parallel to the magnetization direction of the free layer 160, i.e., vertically downward. When it is antiferromagnetic coupling, the magnetization direction of the skyrmion carrier layer 180 is antiparallel to the magnetization direction of the free layer 160, i.e., vertically upward.

[0049] It is understandable that the resistance of the magnetic tunnel junction 100 mainly depends on the magnetization directions of the reference layer 140 and the free layer 160 on both sides of the barrier layer 150. The resistance is minimal when they are parallel coupled and maximum when they are antiparallel coupled. Since the spacer layer 170 and the non-magnetic metal layer 134 are both formed of conductive metal material, although the ferromagnetic and antiferromagnetic coupling of the magnetization directions of the ferromagnetic layers on both sides will also affect the resistance of the magnetic tunnel junction 100 due to the giant magnetoresistance (GMR) effect, this effect is very small and negligible for the vertical readout current.

[0050] As previously described, when an in-plane current is applied to the cap layer 190, it generates a spin current that is vertically injected into the skyrmion carrier layer 180 via the spin Hall effect. The spin polarization direction of the generated spin current can be controlled by controlling the direction of the in-plane current applied to the cap layer 190. For example, when the in-plane current (i.e., the in-plane writing current) has a first direction, the generated spin current can reverse the local magnetic moment of the skyrmion carrier layer 180, thereby writing skyrmions. Figure 3B It shows in Figure 3A The magnetic tunnel junction storage cell 100 is shown with a magnetization orientation when skyrmions are written into it. The thick arrow in the skyrmion carrier layer 180 indicates the initial magnetization direction, and the thin arrow indicates the magnetization direction of the written skyrmions (or, the magnetization direction of the central region of the skyrmions). These skyrmions are coupled to the free layer 160 through coupling induced by the spacer layer 170 (ferromagnetic coupling in the example shown), thereby changing the local magnetization direction of the free layer 160. It can be understood that initially, the magnetic moments of the free layer 160 and the reference layer 140 are antiparallel, resulting in maximum tunneling resistance. As more skyrmions are written, more of the magnetic moment of the free layer 160 is flipped to be parallel to the magnetic moment of the reference layer 140, thus reducing the tunneling resistance of the magnetic tunnel junction. By measuring the tunneling resistance of the magnetic tunnel junction, the number of skyrmions written can be determined, and thus the information stored in the magnetic tunnel junction storage cell can be determined.

[0051] On the other hand, when the direction of the in-plane current (i.e., the in-plane reset current) applied to the cap layer 190 is opposite to the direction of the aforementioned in-plane write current, the spin polarization direction of the generated spin current is opposite to the spin polarization direction generated by the write current. Therefore, skyrmions in the skyrmion carrier layer 180 can be erased, and the skyrmion carrier layer 180 can be reset to its initial magnetization direction. At the same time, through the coupling effect induced by the spacer layer 170, the free layer 160 is also reset to its initial magnetization direction, such as... Figure 3A As shown.

[0052] Figure 4A and Figure 4B Schematic diagrams are shown of the magnetization directions of the various magnetic layers in the magnetic tunnel junction storage cell 100 before and after the writing of magnetic skyrmions, according to another exemplary embodiment. Figure 4A and Figure 4B The example shown is similar to in many ways Figure 3A and Figure 3B The examples shown are the same, so repeated descriptions of the same parts will be omitted here, and only the different parts will be described.

[0053] First refer to Figure 4A ,and Figure 3A Unlike the previous example, the initial magnetization direction of the free layer 160 is parallel to that of the reference layer 140, thus the magnetic tunnel junction has minimal tunneling resistance. The spacer layer 170 induces antiferromagnetic coupling, so the magnetic moment of the skyrmion carrier layer 180 is antiparallel to the free layer 160.

[0054] Reference Figure 4B By controlling the direction of the in-plane writing current applied to the cap layer 190, skyrmions can be written into the skyrmion carrier layer 180. Figure 4B As indicated by the upward-pointing thin arrows, skyrmions are coupled to the free layer 160 through antiferromagnetic coupling induced by the spacer layer 170, as shown by the downward-pointing thin arrows in the free layer 160. It can be understood that initially, the magnetic moments of the free layer 160 and the reference layer 140 are parallel to each other, resulting in minimal tunneling resistance. As more skyrmions are written, a larger portion of the magnetic moment of the free layer 160 is flipped to be antiparallel to the magnetic moment of the reference layer 140, thus increasing the tunneling resistance of the magnetic tunnel junction. By measuring the tunneling resistance of the magnetic tunnel junction, the number of skyrmions written can be determined, and thus the information stored in the magnetic tunnel junction memory cell can be determined.

[0055] Figure 5 A schematic diagram of a magnetic tunnel junction memory cell sample based on magnetic skyrmions according to an embodiment of the present invention is shown, wherein (a) is a schematic diagram of the layered structure, and (b) is a micrograph of the cross-section. Figure 5 As shown, the sample comprises the following layer structure from the substrate 110 (not shown) upwards: Ta(2) / Ru(5) / Pt(2) / [Co(0.28) / Pt(0.16)]9 / Co(0.28) / Ru(0.4) / Co(0.28) / [Pt(0.16) / Co(0.28)]5 / Ta(0.2) / Co 40 Fe 40 B 20 (0.8) / MgO(2.5) / Co 20 Fe 60 B 20 (1.2, 1.3, 1.4 or 1.5) / Ta(2) / [Pt(3) / Co(2) / Ta(2)] 10 / Pt(2), the value in parentheses represents the thickness in nm, square brackets represent the unit structure of the multilayer film, and the subscript of the square brackets indicates the number of repetitions. It can be understood that in this sample, Ta(2) / Ru(5) is used as the seed layer 120, the pinning layer 130 includes an artificial antiferromagnetic (SAF) structure, wherein the first and second ferromagnetic layers 132 / 136 are Pt / Co multilayer films, the non-magnetic metal layer 134 is 0.4 nm thick Ru, on which a 0.2 nm thick Ta layer is used as a buffer layer to facilitate the growth of a 0.8 nm thick CoFeB layer with perpendicular magnetic anisotropy as a reference layer 140. The barrier layer 150 is 2.5 nm thick MgO, the free layer 160 is CoFeB, and multiple samples with thicknesses of 1.2 nm, 1.3 nm, 1.4 nm and 1.5 nm were prepared. The spacer layer 170 is a 2 nm thick Ta layer, and the skyrmion support layer 180 is a Pt / Co / Ta multilayer film. Here, in order to measure the magnetic domains of skyrmion carrier layer 180 to illustrate the principle of the present invention, cap layer 190 uses a 2nm Pt layer instead of a bias structure. In the following measurements, an external magnetic field generated by the measuring device can be used instead of the bias magnetic field applied by cap layer 190 to skyrmion carrier layer 180.

[0056] Figure 6 Show Figure 5 The normalized hysteresis loop perpendicular to the film surface of the magnetic tunnel junction storage cell sample is shown, where the horizontal axis represents the external magnetic field H, and the vertical axis represents the normalized magnetic moment M with respect to the saturation magnetic moment (Ms). In the test sample, the thickness of the free layer 160 is 1.2 nm, and the skyrmion carrier layer 180 (Pt / Co / Ta) is ferromagnetically coupled to the free layer 160 (CoFeB). Skyrmions in each magnetic layer are coupled together through interlayer coupling. Figure 6 The magnetic moment distribution of the magnetic layer in different magnetic field ranges within the hysteresis loop is represented by three vertical arrows, which correspond to... Figure 5 The three arrows in the left figure (a).

[0057] Reference Figure 6When the external magnetic field H is approximately zero, the magnetic moments of the two ferromagnetic layers of the artificial antiferromagnetic nailing layer 130 are antiparallel to each other, with the magnetic moment of the first ferromagnetic layer 132 pointing vertically downwards and the magnetic moment of the second ferromagnetic layer 136 pointing vertically upwards. The skyrmion carrier layer 180 exhibits a multi-domain phase, possessing both upward and downward magnetic moments. As the external magnetic field H gradually increases (in either the positive or negative direction), the magnetic domains of the skyrmion carrier layer 180 are gradually oriented towards the direction of the external magnetic field H, so the total magnetic moment M gradually increases with the external magnetic field H. Near H = ±2 kOe, the magnetic domains of the skyrmion carrier layer 180 are all oriented towards the direction of the external magnetic field H. When the external magnetic field H increases from approximately ±2 kOe to approximately ±6 kOe, the external magnetic field H is insufficient to overcome the antiferromagnetic coupling induced by the non-magnetic metal layer 134. The magnetic moments of the first ferromagnetic layer 132 and the second ferromagnetic layer 134 remain unchanged, therefore the total magnetic moment M remains essentially constant within the range of this external magnetic field H. As the external magnetic field H continues to increase, it overcomes the antiferromagnetic coupling induced by the non-magnetic metal layer 134, gradually aligning the magnetic moments of the first ferromagnetic layer 132 or the second ferromagnetic layer 134 to the same direction as the external magnetic field H. At this point, the total magnetic moment M gradually increases. When the external magnetic field H reaches approximately ±8 kOe, the magnetic moments of the first ferromagnetic layer 132, the second ferromagnetic layer 134, and the skyrmion carrier layer 180 are all aligned to the same direction as the external magnetic field H. At this point, the total magnetic moment M reaches the saturation magnetic moment Ms, which remains unchanged even if the external magnetic field H continues to increase.

[0058] Figure 7 A schematic diagram of a test device for a skyminzir magnetic storage cell according to an embodiment of the present invention is shown. Figure 7 In this design, the transverse electrode is the bottom electrode, and the longitudinal electrode is the top electrode. The width of the current channel is 50 μm. The region where the transverse and longitudinal current channels intersect contains a single magnetic tunnel junction. The junction size (e.g., the diameter of a circular junction) can be fabricated to vary from 0.1 μm to 10 μm. Reference numerals 1-12 correspond to electrode numbers, e.g., V 13 I represents the voltage measured on electrodes 1 and 3. 24 This indicates the current applied to electrodes 2 and 4, through V. 13 and I 24 This allows for the measurement of the tunneling resistance of the magnetic tunnel junction at the intersection of the current channels connecting electrodes 1, 2 and 3, 4.

[0059] Figure 8 This is a curve showing the tunneling resistance R of a magnetic tunnel junction sample with a junction region size of 4 μm as a function of an external magnetic field H perpendicular to the film surface. Figure 8 The left figure shows that the tunneling resistance R changes with the external magnetic field H as previously discussed. Figure 6The described hysteresis loops correspond to each other, with the high and low resistance states corresponding to the antiparallel and parallel magnetic moments of the ferromagnetic layers on both sides of the barrier layer, respectively. The magnetic moment of the reference layer 140 is parallel to the magnetic moment of the second ferromagnetic layer 136 in the artificial antiferromagnetic structure 130, and the magnetic moment of the free layer 160 is parallel to the magnetic moment of the skyrmion carrier layer 180.

[0060] Figure 8 The right figure shows the tunneling resistance R loop measured under a vertical magnetic field H of -1T until saturation magnetization was achieved. The external magnetic field H was then reduced to -2kOe, and the loop was measured within the external magnetic field range of -2kOe to +2kOe. From this, the tunneling magnetoresistance (TMR) was calculated to be approximately 18.5%. Figure 8 The right figure also shows the three states (i.e. "phases") of skyminton carrier layer 180: multi-domain state, skyminton state, and single-domain state, which will be described in further detail below.

[0061] Figure 9 This is a micrograph showing the variation of magnetic domains in the skyrmion carrier layer 180 of a magnetic tunnel junction with a vertical external magnetic field H, where the magnetic domains were measured using a magnetic force microscope. (Reference) Figure 9 When the external magnetic field H is zero, the skyrmion carrier layer 180 exhibits a multi-domain state. When the external magnetic field H increases to 1082 Oe, a clear coexistence of multi-domain and skyrmions appears. As the external magnetic field H continues to increase, for example at 1236 Oe and 1623 Oe, the skyrmion carrier layer 180 exhibits a skyrmion state (or skyrmion phase), stably storing multiple skyrmions. With further increases in the external magnetic field H, the skyrmions in the skyrmion carrier layer 180 gradually disappear. When the external magnetic field H reaches 1700 Oe, the skyrmions completely disappear, and the skyrmion carrier layer 180 exhibits a single-domain state. Figure 9 The measurement results show that when a predetermined bias magnetic field is applied, the skyrmion carrier layer 180 can be in a state capable of stably storing skyrmions. Although the measurement data for this sample indicate that [Pt(3) / Co(2) / Ta(2)]... 10 The magnitude of the bias magnetic field of the skyrmion carrier layer 180 in the skyrmion phase is approximately in the range of 1150 Oe to 1650 Oe. However, further theoretical analysis and experimental data show that the required magnitude of the bias magnetic field varies depending on factors such as the material selection, thickness, and magnetocrystalline anisotropy of the skyrmion carrier layer 180. Therefore, this invention does not impose any special limitations on this, but rather, under the guidance of this invention, those skilled in the art can determine it according to actual needs.

[0062] Figure 10 This is a synchronous measurement result of the resistance of a magnetic tunnel junction in a 3μm junction region and the magnetic domains of the skyrmion carrier layer as a function of an external magnetic field. (Refer to...) Figure 10 It can be seen that when the external magnetic field H increases from zero to 1.1 kOe, the skyrmion carrier layer 180 transitions from a multi-domain state to a skyrmion state, containing 13 skyrmions. When it transitions from a skyrmion state to a single-domain state (external magnetic field H = 1.6 kOe), the resistance of the magnetic tunnel junction decreases by approximately 10%. When the external magnetic field H decreases from 1.6 kOe to 1.1 kOe, due to the lack of magnetic moment perturbation, the skyrmion carrier layer 180 remains in a single-domain state, containing no skyrmions. The external magnetic field H continues to decrease to 0.4 kOe, and the skyrmion carrier layer 180 reverts to a multi-domain state. When the external magnetic field H increases again to 1.1 kOe, the skyrmion carrier layer 180 exhibits a skyrmion state, containing 9 skyrmions. When the external magnetic field H increases to approximately 1.6 kOe, the 9 skyrmions disappear, and the skyrmion carrier layer 180 exhibits a single-domain state. Figure 10 The measurement results indicate that under the influence of a predetermined external magnetic field H, the skyrmion carrier layer 180 exhibits a state capable of stably storing skyrmions, and is consistent with the single-domain state (which has essentially constant resistance, see...). Figure 10 Compared to c, d, and g in the sample, skyrmions significantly alter the resistance of the magnetic tunnel junction (MTJ), and for this sample, the resistance change caused by a single skyrmion can be estimated to be approximately 50 Ω.

[0063] Furthermore, for the aforementioned magnetic tunnel junction samples, when the skyrmion carrier layer 180 is in the skyrmion phase, it is possible to utilize... Figure 7 As shown, for example, current I is passed through electrodes 3 and 4. 34 The spin current generated by Pt in the top cap layer 190 exerts a torque on the magnetic moment in the skyrmion carrier layer 180. By controlling the direction and magnitude of the current, a desired number of skyrmions can be written or erased.

[0064] The following describes the operation method of the skyrmion-based magnetic tunnel junction storage cell 100, mainly including the writing step and the reading step.

[0065] The writing step involves applying an in-plane write current to the cap layer 190, causing the cap layer 190 to generate a spin current through the spin Hall effect, and the spin current is injected perpendicularly into the adjacent skyrmion carrier layer 180. At this time, the skyrmion carrier layer 180 is in the skyrmion phase due to the bias magnetic field applied by the cap layer 190, so the injected spin current can write skyrmions, and the skyrmions written into the skyrmion carrier layer 180 are coupled to the free layer 160 through ferromagnetic coupling or antiferromagnetic coupling generated by the spacer layer 170. The number of skyrmions written into the skyrmion carrier layer 180 can be controlled by controlling, for example, the pulse width, pulse amplitude, and / or the number of pulses of the in-plane write current.

[0066] It is understood that skyrmions previously written may be stored in skyrmions carrier layer 180. Therefore, before applying an in-plane write current to write new skyrmions, a reset operation can be performed to apply an in-plane reset current to cap layer 190 in the opposite direction of the in-plane write current, so as to erase the skyrmions present in skyrmion carrier layer 180 and reset them to the initial magnetization direction.

[0067] The reading step may include applying a vertical read current to the magnetic tunnel junction memory cell 100 to read its resistance. As previously described, the resistance of the magnetic tunnel junction memory cell 100 is related to the number of skyrmions written into the skyrmion carrier layer 180. For example, initially, depending on whether the magnetic moments of the free layer 160 and the reference layer 140 are parallel or antiparallel, the magnetic tunnel junction memory cell 100 may have a minimum or maximum resistance. As the number of skyrmions written into the skyrmion carrier layer 180 increases, the resistance of the magnetic tunnel junction memory cell 100 may increase or decrease.

[0068] It is understood that in some embodiments, the magnetic tunnel junction storage unit 100 can be implemented as a conventional two-state memory, that is, storing data "0" and "1", where one state corresponds to the state when no skyrmions are stored, and the other state corresponds to the state when skyrmions (preferably multiple skyrmions) are stored. In other embodiments, the magnetic tunnel junction storage unit 100 can also be implemented as a multi-state memory, that is, in addition to "0" and "1", "2", "3", "4" or more data can be stored in a single magnetic tunnel junction storage unit 100, where different storage states correspond to storing different numbers (also covering a range of numbers) of skyrmions in the skyrmion carrier layer. For example, data "0" is stored when no skyrmions are present in the skyrmion carrier layer 180, data "1" is stored when Y1 (or X1 to X2) skyrmions are present, data "2" is stored when Y2 (or X3 to X4) skyrmions are present, and so on. Therefore, compared with traditional two-state memory cells, magnetic tunnel junction memory cell 100 can store more data information.

[0069] According to one embodiment, the magnetic tunnel junction storage unit 100 can also be configured to perform in-memory computation operations, where the adder can be omitted and the addition operation can be completed through read and write operations on the memory. Figure 11 A flowchart is shown for a method 200 of performing in-memory computation using a magnetic tunnel junction storage unit 100. (Refer to...) Figure 11In step 210, a first in-plane write current can be applied to the cap layer 190 to write a first number of M skyrmions into the skyrmion carrier layer 180. As previously mentioned, the number of skyrmions written into the skyrmion carrier layer 180 can be controlled by controlling, for example, the pulse width, pulse amplitude, and / or the number of pulses of the in-plane write current. In step 220, a second in-plane write current can be applied to the cap layer 190 to write a second number of N skyrmions into the skyrmion carrier layer, where M and N can be the same or different non-negative integers. At this point, since M skyrmions have already been written, there will be Q = M + N skyrmions in the skyrmion carrier layer 180. Then, a vertical read current is applied to the magnetic tunnel junction storage cell 100 to read the resistance of the magnetic tunnel junction storage cell 100, and the number Q of skyrmions stored therein can be determined based on the read resistance, thus completing the in-memory calculation of Q = M + N.

[0070] Although magnetic tunnel junction memory cells have been described above, it is understood that a memory may include an array of multiple rows and columns of magnetic tunnel junction memory cells, and this array may be configured with multiple word lines, bit lines, power lines, and switching transistors, etc. Such array arrangements of memory cells are known and will not be elaborated upon here.

[0071] Unless the context clearly requires otherwise, throughout the specification and claims, the terms "comprising," "including," etc., shall be interpreted in a encompassing sense, contrary to the meaning of exclusivity or exhaustiveness; that is, they shall be interpreted as "including but not limited to." Furthermore, the terms "in this document," "above," "below," and similar terms, when used in this application, shall refer to the application as a whole, and not to any specific part thereof. Where the context permits, the use of singular or plural terms in the above description may also include either the plural or the singular, respectively. Regarding the term "or" when referring to a list of two or more items, the term encompasses all of the following interpretations: any item in the list, all items in the list, and any combination of items in the list.

[0072] The above detailed description of embodiments of the present invention is not intended to be exhaustive or to limit the invention to the precise forms disclosed above. While specific embodiments and examples of the invention have been described above for illustrative purposes, various equivalent modifications may be possible within the scope of the invention, as those skilled in the art will recognize. For example, although processes or blocks are presented in a given order, alternative embodiments may execute processes having these steps in a different order or employ systems having these blocks in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and / or modified. Each of these processes or blocks may be implemented in various different ways. Furthermore, although processes or blocks are sometimes shown as being executed serially, alternatively, these processes or blocks may also be executed in parallel or at different times.

[0073] The teachings of the invention provided herein can be applied to other systems, not necessarily those described above. Elements and actions of the various embodiments described above can be combined to provide other embodiments.

[0074] While some embodiments of the invention have been described, these embodiments are presented by way of example only and are not intended to limit the scope of this application. In fact, the novel methods and systems described herein can be implemented in many other forms. Furthermore, various omissions, substitutions, and changes can be made to the form of the methods and systems described herein without departing from the scope of this application.

Claims

1. A magnetic tunnel junction memory cell, comprising: The reference magnetic layer and the free magnetic layer are separated by a barrier layer; A skyminer carrier layer separated from the free magnetic layer by a spacer layer, the spacer layer inducing ferromagnetic or antiferromagnetic coupling between the skyminer carrier layer and the free magnetic layer; and A cap layer is formed on the skyrmion carrier layer, and the cap layer applies a bias magnetic field to the skyrmion carrier layer through exchange bias, so that the skyrmion carrier layer is in the skyrmion phase. In this process, the cap layer generates a spin current when an in-plane writing current is applied. This spin current is vertically injected into the skyrmion carrier layer to write skyrmions, and the skyrmions are coupled to the free magnetic layer through ferromagnetic or antiferromagnetic coupling induced by the spacer layer. The spacer layer comprises one or more of Cu, Ta, W, Pt, Ru, Hf, Ir, and Au. The skyrmion carrier layer includes one or more of MnNiGa, MnSi, FeCoSi, Pt / Co / Ta multilayer film, Pd / Co / Ta multilayer film, Pt / Co multilayer film, and Pd / Co multilayer film.

2. The magnetic tunnel junction storage unit as described in claim 1, wherein, The reference magnetic layer, the free magnetic layer, and the skyrmion carrier layer have perpendicular magnetic anisotropy, and the initial magnetization direction of the free magnetic layer is parallel to or antiparallel to the magnetization direction of the reference magnetic layer.

3. The magnetic tunnel junction storage unit as described in claim 1, wherein, The cap layer comprises an antiferromagnetic material, such as PtMn, IrMn, or AuMn, or The cap layer comprises a ferromagnetic material layer and an antiferromagnetic coupling layer located between the ferromagnetic material layer and the skyrmion carrier layer, thereby forming an artificial antiferromagnetic structure. The ferromagnetic material layer includes Co, Fe, CoFeB, Pt / Co multilayer film, Pt / CoFeB multilayer film, Pd / Co multilayer film, or Pd / CoFeB multilayer film. The antiferromagnetic coupling layer includes Ta, W, Pt, Ru, Hf, Ir, or Au, or... The cap layer includes an artificial antiferromagnetic structure, which comprises a first ferromagnetic layer and a second ferromagnetic layer separated by an antiferromagnetic coupling layer. The first ferromagnetic layer contacts the skyrmion carrier layer. The first ferromagnetic layer comprises a Pt / Co multilayer film or a Pt / CoFeB multilayer film, and the layer in contact with the skyrmion carrier layer is a Pt layer. The second ferromagnetic layer comprises Co, Fe, CoFeB, Pt / Co multilayer film, Pt / CoFeB multilayer film, Pd / Co multilayer film, or Pd / CoFeB multilayer film. The antiferromagnetic coupling layer comprises Cu, Ta, W, Pt, Ru, Hf, Ir, or Au.

4. The magnetic tunnel junction storage unit as described in claim 1, wherein, The magnetic tunnel junction storage unit is implemented as a polymorphic storage unit, with different storage states corresponding to different numbers of skyrmions written into the skyrmion carrier layer.

5. A method of operating a magnetic tunnel junction memory cell according to any one of claims 1 to 4, comprising: The writing step includes applying an in-plane writing current to the cap layer, causing the cap layer to generate a spin current through the spin Hall effect. The spin current is vertically injected into the skyrmion carrier layer to write skyrmions, and the skyrmions are coupled to the free magnetic layer through ferromagnetic coupling or antiferromagnetic coupling generated by the spacer layer. as well as The reading step includes applying a vertical read current to the magnetic tunnel junction storage cell to read the resistance of the magnetic tunnel junction storage cell, the resistance of which is related to the number of skyrmions written into the skyrmion carrier layer.

6. The method of claim 5, wherein, In the writing step, the number of skyrmions written into the skyrmion carrier layer is controlled by controlling the pulse width, pulse amplitude, and / or pulse number of the in-plane writing current.

7. The method of claim 5, wherein, The writing step further includes applying an in-plane reset current to the cap layer before applying the in-plane write current, the in-plane reset current being opposite in direction to the in-plane write current, so as to reset the skyrmion carrier layer to the initial magnetization direction.

8. The method of claim 5, wherein, The magnetic tunnel junction storage unit is configured to perform in-memory computation operations, including: A first in-plane writing current is applied to the cap layer to write a first number of skyrmions into the skyrmion carrier layer; A second in-plane writing current is applied to the cap layer to write a second number of skyrmions into the skyrmion carrier layer; and A vertical read current is applied to the magnetic tunnel junction memory cell to read the resistance of the magnetic tunnel junction memory cell. The read resistance corresponds to a third number of skyrmions, which is equal to the sum of the first number and the second number.

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