Zero-field spin-orbit moment memory with ferromagnetic layer component gradient structure and preparation method of zero-field spin-orbit moment memory

Abstract

The invention discloses a zero-field spin-orbit moment memory with a ferromagnetic layer component gradient structure and a preparation method thereof, the core structure of the memory comprises a CoFeB ferromagnetic layer with a vertical component gradient, and magnetic moments at two sides of a domain wall generate asymmetry in amplitude or orientation by regulating and controlling gradient distribution of Co, Fe and B elements and inducing non-uniform Dzyaloshiski-Moriya interaction (DMI); furthermore, domain wall chiral characteristics are weakened, a net effective field is formed, and deterministic magnetization overturning without assistance of an external magnetic field is finally realized. In the preparation process, a magnetron sputtering technology is adopted, a heavy metal strong spin orbit coupling layer, a vertical magnetic anisotropy magnetic free layer with component gradient, a tunnel barrier layer, a magnetic vertical reference layer, an artificial antiferromagnetic pinning layer and a covering layer are stacked in sequence, and a magnetic tunnel junction (MTJ) unit is prepared through annealing and micro-nano processing technologies. The invention provides an efficient solution for the research and development of controllable magnetic memories and logic devices, and has a wide application prospect in the field of high-density magnetic memories.

Description

Technical Field

[0001] This invention relates to the fields of spintronics and magnetic memory, specifically to a zero-field spin orbital moment memory with a ferromagnetic layer composition gradient structure and its fabrication method. In particular, by controlling the concentration gradient of ferromagnetic layer elements to induce non-uniform DMI interactions, deterministic magnetization reversal without external magnetic field assistance can be achieved. It can be widely used in the design and fabrication of high-density, low-power magnetic random access memory (MRAM) and magnetic logic devices. Background Technology

[0002] Current-induced spin-orbit torque (SOT), with its significant advantages of high-speed response and low-power manipulation of magnetic states, has become a core supporting technology for the development of next-generation high-performance magnetic random access memory (MRAM). Under the action of SOT, the strong spin-orbit coupling effect in the heavy metal layer can generate spin current, which in turn drives the magnetic moment reversal of the magnetic layer, providing a key mechanism for fast read and write of magnetic storage devices. However, traditional SOT-MRAM faces insurmountable technical bottlenecks in practical applications: to achieve deterministic reversal of the magnetization state, an external auxiliary magnetic field must be used to break the system symmetry. This limitation not only significantly increases the hardware complexity of the storage system (requiring additional integration of a magnetic field generation module), but also severely restricts the high-density integration of devices (exacerbating magnetic field interference problems) and embedded applications (limited miniaturization).

[0003] Currently, academia and industry have proposed various alternatives for zero-field SOT flipping, mainly including electric field-controlled magnetic anisotropy, interlayer exchange coupling modulation, and geometrically asymmetric structure design. However, these solutions generally suffer from insurmountable drawbacks:

[0004] 1. Poor process compatibility, making it difficult to integrate with mainstream semiconductor manufacturing processes;

[0005] 2. High fabrication complexity: Some solutions have stringent requirements for the precision of micro- and nano-scale structures (such as sub-nanometer layer thickness control and nanometer linewidth uniformity), resulting in low device yield, significantly increasing production costs, and hindering large-scale production.

[0006] 3. Significant performance trade-offs: To achieve zero-field switching, the core performance of the device is often sacrificed. For example, by reducing the vertical magnetic anisotropy to improve switching sensitivity, thermal stability deteriorates (data retention capability decreases); or by introducing additional damping through complex structural design, switching energy consumption increases, which violates the original intention of low power consumption design.

[0007] Currently, two published patents have explored gradient structure optimization to some extent. Patent CN114824062A proposes a spin-orbit moment-driven gradient synthetic antiferromagnetic structure, which improves thermal stability and reduces the flipping current through a multi-layer combination of two gradient magnetic layers and an antiferromagnetic coupling layer. However, this scheme belongs to an interlayer gradient system, and the magnetization flipping depends on the antiferromagnetic coupling control, which has extremely high requirements for interface thickness and symmetry, resulting in a complex structure that fails to achieve zero-field flipping in a single-layer system. Patent CN117202765A optimizes the spin current injection efficiency and reduces the SOT critical current density by introducing thickness or concentration gradients in the metal functional layer and oxide functional layer, but its flipping still requires external field assistance and fails to achieve zero-field SOT flipping. Furthermore, it does not consider the non-uniform DMI control inside the ferromagnetic free layer, thus limiting the flipping mechanism.

[0008] In summary, existing technologies have not yet proposed a spin-orbit moment storage structure that can form an effective internal field and achieve deterministic zero-field reversal within a single ferromagnetic layer. Addressing these technical limitations, this invention proposes an innovative solution based on a ferromagnetic layer composition gradient structure. By constructing a tunable element concentration gradient perpendicular to the magnetization layer, non-uniform DMI interactions are directly induced, thereby achieving deterministic magnetization reversal without the need for an external magnetic field. This solution is based on mature magnetron sputtering technology and the traditional CoFeB material system, possessing advantages such as strong process compatibility, simple fabrication process, and stable performance, providing a feasible path for the industrialization of high-density, embedded magnetic storage and logic devices. Summary of the Invention

[0009] To address the issues of requiring external magnetic field assistance or complex interface design in existing technologies, this invention proposes a zero-field spin orbital moment memory based on ferromagnetic layer composition gradient and its fabrication method.

[0010] This invention achieves deterministic magnetic moment reversal based on spin-orbit torque under zero magnetic field by introducing a vertical compositional gradient within the ferromagnetic free layer. Specifically, through various processes such as sequential sputtering of CoFeB targets with different compositions, the concentrations of Co, Fe, and B atoms in different depth regions are continuously varied, thereby forming a vertical compositional gradient distribution of the three elements in the vertically magnetized layer. This gradient structure induces non-uniform Dzyaloshinskii-Moriya interaction (DMI), leading to asymmetry in the amplitude or orientation of the magnetic moments on both sides of the domain walls, thus weakening the domain wall chirality and generating a net effective field. Based on this, without the need for an external auxiliary magnetic field, the spin-orbit torque of the heavy metal layer alone can drive the magnetic free layer to achieve deterministic magnetic moment reversal, changing its relative magnetization direction with the magnetic reference layer, completing data writing, and ultimately achieving all-electric magnetic storage without external magnetic field assistance.

[0011] To achieve the above objectives, the technical solution of the present invention is as follows: A zero-field spin-orbit moment memory with a ferromagnetic layer composition gradient structure, characterized in that it comprises, from bottom to top, the following layers stacked sequentially: a substrate, a heavy metal strong spin-orbit coupling layer, a vertically magnetically anisotropic magnetic free layer with a composition gradient, a tunnel barrier layer, a magnetic reference layer, an artificial antiferromagnetic pinning layer, and a capping layer; wherein, the heavy metal strong spin-orbit coupling layer is composed of a metal or alloy with a high spin Hall angle, the material including one or more of Ta, W, Pt, and Ir, used to generate a spin polarization current when a write current is applied; the magnetic free layer is composed of CoFeB material and has a polarization current perpendicular to the film surface. The concentration distribution of Co, Fe, and B elements changes continuously in the direction, wherein the atomic concentrations of Co and Fe increase in the direction away from the heavy metal layer, and the atomic concentration of B decreases; the elemental composition gradient induces non-uniform Dzyaloshinskii-Moriya interaction (DMI) in the magnetic free layer, causing the magnetic moments on both sides of the magnetic domain wall to be asymmetrically distributed in amplitude or orientation, thereby generating a net effective field in the magnetic free layer; when a write current is applied to the heavy metal layer, through the synergistic effect of spin-orbit torque and net effective field, a deterministic reversal of the magnetization direction of the magnetic free layer can be achieved without an external magnetic field, and its zero-field reversal ratio is greater than 95%. The significant advantages of this invention are: (1) It achieves zero-field all-electric operation, and the magnetic free layer can complete the magnetic moment orientation reversal through spin-orbit torque without an additional auxiliary magnetic field, ensuring stable data writing; (2) It has high storage density, non-volatility and excellent thermal stability, and its performance meets the requirements of high-performance storage; (3) The composition gradient is controlled based on standard sputtering process, the preparation process is simple, it has strong compatibility with existing semiconductor processes, and excellent scalability.

[0012] As an improvement of the present invention, the magnetic free layer is a CoFeB layer with a compositional gradient and a thickness of 0.8-1.2 nm; the magnetic reference layer is a CoFeB layer without a compositional gradient and a thickness of 1-1.4 nm, and its perpendicular magnetic anisotropy intensity is greater than that of the magnetic free layer.

[0013] As an improvement of the present invention, the composition gradient of the magnetic free layer is achieved by any of the following methods:

[0014] (1) Sputtering CoFeB target material with at least two component ratios in sequence;

[0015] (2) Co, Fe and B single targets were co-sputtered and the sputtering rate was controlled separately;

[0016] (3) Insert a pure B element layer of a certain thickness during the CoFeB sputtering process;

[0017] (4) Adjust the process parameters of sputtering gas pressure or DC voltage to induce element diffusion and form a composition gradient;

[0018] Thus, a gradient CoFeB magnetic free layer with perpendicular magnetic anisotropy was prepared.

[0019] When using CoFeB targets with different composition ratios for sequential sputtering, the target material includes Co 30 Fe 30 B 40 With Co 40 Fe 40 B 20 The CoFeB layer formed by sequentially sputtering the above two target materials has a continuous concentration distribution of increasing Co and Fe elements and decreasing B element in the vertical direction.

[0020] As an improvement of the present invention, the thickness difference between the magnetic free layer and the magnetic reference layer is not less than 0.2 nm, and the perpendicular magnetic anisotropy intensities of the two are different, so as to form a stable magnetization read / write window.

[0021] The substrate is a silicon wafer, an aluminum oxide substrate, or a magnesium oxide substrate.

[0022] The memory includes at least one magnetic tunnel junction unit whose resistance state is defined by the relative magnetization direction between the magnetic free layer and the reference layer; during write operations, the magnetization reversal of the free layer is driven solely by the spin-orbit torque of the heavy metal layer, without the need for external magnetic field assistance.

[0023] The compositional gradient of the magnetic free layer induces non-uniform Dzyaloshinskii-Moriya interaction (DMI), resulting in asymmetry in the magnitude or orientation of magnetic moments on both sides of the domain wall, weakening the domain wall chirality and generating a net effective field. The net effective field drives the magnetic domain reversal, realizing a zero-field deterministic reversal of the relative magnetization direction between the magnetic free layer and the reference layer, thus completing the data writing.

[0024] The memory structure and fabrication method are detailed below:

[0025] The multilayer film stacked structure is formed by using magnetron sputtering technology to sputter high-purity metal targets with argon gas and stacking them sequentially on a substrate to form the following structure (from the substrate to the top layer): the substrate is a silicon wafer (with a silicon oxide layer of not less than 300nm on the surface), an aluminum oxide substrate, or a magnesium oxide substrate.

[0026] Heavy metal strong spin-orbit coupling (SOC) layer: with a thickness of 2-10nm, preferably Ta or W material, used to generate strong spin-orbit coupling effect and provide a basis for spin-orbit torque;

[0027] Vertically anisotropic magnetic free layers with compositional gradients: Compositional gradients can be achieved in various ways, including sequential sputtering of Co. 30 Fe 30 B40 and Co 40 Fe 40 B 20 The process involves using a target material, co-sputtering a single Co, Fe, and B target, and adjusting process parameters such as rate control of composition, insertion of a pure B layer during CoFeB sputtering, or adjustment of sputtering gas pressure and DC voltage. The total thickness of the CoFeB ferromagnetic layer is 0.8-1.2 nm—too thin will affect magnetic moment stability, while too thick will easily lead to degradation of perpendicular magnetic anisotropy, both of which will weaken the magnetic anisotropy strength.

[0028] Tunnel barrier layer: Located between the magnetic free layer and the reference layer, it serves as an insulating layer to achieve the tunnel magnetoresistance effect;

[0029] Magnetic vertical reference layer: A CoFeB layer with no compositional gradient is used, exhibiting strong vertical magnetic anisotropy, with a thickness of 1-1.4 nm. It is necessary to ensure that the thickness difference between this layer and the free layer is ≥0.2 nm, and that there is a difference in vertical anisotropy intensity, to guarantee the stability of read / write operations.

[0030] Artificial antiferromagnetic nailing: Fixes the magnetization direction of the reference layer by exchanging bias, improving read reliability;

[0031] Cover layer: Used to protect devices from oxidation and improve the long-term stability of memory.

[0032] Key preparation processes include:

[0033] (1) Annealing treatment: After the multilayer film stacking is completed, high-temperature annealing is performed to promote thin film crystallization, enhance vertical magnetic anisotropy, and improve the thermal stability of the device.

[0034] (2) Micro / nano fabrication: After sputtering to form a vertical multilayer film with exchange bias, magnetic tunnel junction (MTJ) cells are fabricated through micro / nano fabrication steps such as electron beam lithography, ion beam etching, resist removal, and photoelectron beam evaporation. The memory contains at least one MTJ cell, and data is written by applying a specific current to drive the magnetic moment of the free layer to flip, based on its relative direction with the magnetic moment of the reference layer.

[0035] This invention introduces a vertical compositional gradient into a CoFeB ferromagnetic layer, causing a non-uniform distribution of Co, Fe, and B elements along the thickness direction. This results in a non-uniform Dzyaloshinskii-Moriya interaction (DMI) within the layer, achieving asymmetry in the amplitude or orientation of magnetic moments on both sides of the domain walls and inducing a net effective field. Compared to CN114824062A and CN117202765A mentioned above, this invention achieves true zero-external-field spin-orbit moment deterministic magnetization reversal without requiring an additional antiferromagnetic coupling layer or thickness gradient structure. This structure not only simplifies the device hierarchy, facilitating fabrication and CMOS compatibility, but also overcomes the limitations of previous "interface symmetry manipulation" in terms of physical mechanism, significantly improving the controllability and stability of the device. It possesses outstanding novelty, inventiveness, and application prospects.

[0036] Compared with the prior art, the present invention has the following outstanding advantages:

[0037] 1. Simplified structure: Zero-field flipping can be achieved without the need for double heavy metal layers or antiferromagnetic layers, reducing interface complexity.

[0038] 2. High zero-field reversal efficiency: Deterministic magnetic domain reversal is driven by the intrinsic net effective field induced by the composition gradient, without the need for an external auxiliary magnetic field. The measured zero-field reversal rate is greater than 95%, truly achieving all-electric control.

[0039] 3. Good process compatibility: Based on standard magnetron sputtering technology and traditional CoFeB material system, the composition gradient can be directly controlled by sputtering process parameters without the need for the introduction of additional material system. It is suitable for standard CMOS compatible processes and has good industrialization prospects.

[0040] 4. Excellent performance: While achieving zero-field operation, it also maintains high thermal stability and low energy consumption characteristics, meeting the requirements of next-generation high-performance applications.

[0041] The application requirements of high-performance magnetic storage devices have broad application potential in the field of spintronic storage and logic devices. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the stacked structure of the zero-field spin orbital moment memory of the present invention;

[0043] Figure 2 This is a schematic diagram of the current-induced spin orbit moment magnetization switching circuit under different auxiliary magnetic fields in this invention;

[0044] Figure 3 This is a flowchart illustrating the workflow of the zero-field spin magnetic memory based on the composition gradient of the ferromagnetic layer according to the present invention. Detailed Implementation

[0045] To make the technical solution of the present invention clearer and easier to understand, the zero-field spin magnetic memory and its fabrication method of the present invention will be described in detail below with reference to specific embodiments. These embodiments are merely illustrative and are not intended to limit the scope of protection of the present invention.

[0046] I. Device Structure Parameter Design

[0047] The zero-field spin magnetic memory in this embodiment adopts a vertical magnetic tunnel junction (MTJ) structure, and the multilayer film stack structure and parameters from the substrate to the top layer are as follows:

[0048] 1. Substrate: Select a monocrystalline silicon substrate with a 300nm silicon oxide layer on the surface. Remove surface impurities by standard cleaning process (ultrasonic cleaning with acetone, ethanol, and deionized water for 10 minutes in sequence), and dry it for later use.

[0049] 2. Heavy metal strong spin-orbit coupling (SOC) layer: Ta is used as the material, and the thickness is set to 5nm. Ta is chosen because it has a strong spin-orbit coupling effect, which generates spin polarization current when energized, can efficiently generate spin-orbit torque, and has good interface compatibility with the subsequent magnetic layer.

[0050] 3. Magnetic free layer: using Co 30 Fe 30 B 40 and Co 40 Fe 40 B 20 Two targets were sputtered sequentially to create a vertical composition gradient. The bottom layer, Co... 30 Fe 30 B 40 The thickness is 0.4 nm, and the top layer is Co. 40 Fe 40 B 20 With a thickness of 0.6 nm and a total thickness of 1.0 nm, it meets the optimization range of 0.8-1.2 nm, ensuring the vertical magnetic anisotropy intensity. Through layered sputtering, a gradient distribution of increasing Co and Fe element concentrations (decreasing B element concentration) is formed in the vertical direction.

[0051] 4. Tunnel Barrier Layer: MgO is used as the tunnel barrier material, with a thickness of 1.2 nm. MgO has high barrier height and low leakage current characteristics, which can ensure the efficient realization of the tunnel magnetoresistance (TMR) effect.

[0052] 5. Magnetic reference layer: A CoFeB layer with no compositional gradient (composition is Co) is used. 40 Fe 40 B 20The thickness is 1.2 nm. The difference between this thickness and the magnetic free layer (1.0 nm) is 0.2 nm, which meets the design requirements. Moreover, its perpendicular magnetic anisotropy intensity is higher than that of the free layer, ensuring the stability of the magnetization direction of the reference layer.

[0053] 6. Artificial antiferromagnetic anchor layer: Adopting a [Co / Pt]4 / Ru / [Pt / Co]6 structure with a total thickness of 15 nm. The magnetization direction of the magnetic reference layer is fixed through antiferromagnetic coupling, with the Ru layer having a thickness of 0.7 nm serving as the interlayer coupling medium.

[0054] 7. Covering layer: Ta is used as the covering layer with a thickness of 5nm to protect the device from oxidation and mechanical damage.

[0055] II. Preparation Process Steps

[0056] 1. Preparation of multilayer films by magnetron sputtering

[0057] ① Sputtering equipment: Employs an ultra-high vacuum magnetron sputtering system with a base vacuum level better than 4×10⁻⁶. -8 Torr.

[0058] ②Sputtering gas: Argon gas with a purity of 99.999% is used as the sputtering gas, with a flow rate controlled at 40 sccm and a working pressure maintained at 0.4 Pa.

[0059] ③ Layered sputtering process: First, a Ta layer (heavy metal SOC layer) is sputtered using a 99.99% high-purity Ta target, with a sputtering power of 30W, a deposition rate of 0.02nm / s, and a thickness controlled at 5nm; then, a magnetic free layer is sputtered sequentially: first, Co is sputtered. 30 Fe 30 B 40 The target material (15W power, 0.01nm / s) was sputtered to 0.4nm, followed by Co sputtering. 40 Fe 40 B 20 A target material (15W power, 0.01nm / s) was deposited to a total thickness of 1.0nm, forming a vertical compositional gradient. A sputtered tunnel barrier layer was formed using an MgO target at 50W RF sputtering power under an argon atmosphere, depositing a 1.2nm thick MgO layer to ensure the insulation and uniformity of the barrier layer. A sputtered magnetic reference layer was formed using a Co target. 40 Fe 40 B 20The target material was sputtered at a power of 15W to deposit a 1.2nm thick CoFeB layer without compositional gradient. An artificial antiferromagnetic pinning layer was sputtered by alternating sputtering of Co (0.4nm) and Pt (0.75nm) to form a [Co / Pt]4 sublayer, followed by sputtering of a Ru layer (0.7nm), and finally sputtering of a [Pt / Co]6 sublayer, with a total thickness of 15nm. A capping layer was sputtered using a Ta target material at a sputtering power of 30W to deposit a 5nm thick Ta layer.

[0060] 2. Annealing treatment

[0061] ① Place the deposited multilayer film sample in a vacuum chamber and perform in-situ annealing.

[0062] ② Set the annealing temperature to 300℃, the holding time to 1 hour, the heating rate to 1℃ / s, and allow it to cool naturally to room temperature.

[0063] ③ This annealing process can promote the crystallization of the CoFeB layer, further enhance the vertical magnetic anisotropy and stabilize the composition gradient distribution.

[0064] ④ Annealing can enhance the pinning effect of the artificial antiferromagnetic layer and improve the thermal stability of the device.

[0065] 3. Fabrication of MTJ units using micro / nano fabrication

[0066] ① Electron beam lithography: Electron beam photoresist is coated on the surface of a multilayer film, and the MTJ unit pattern (a circular structure with a diameter of 50nm) is defined by an electron beam exposure system. After development, a photoresist mask is formed.

[0067] ② Ion beam etching: using Ar + Ion beam etching (energy 500eV, beam current 20mA) sequentially etches the capping layer, artificial antiferromagnetic nail layer, magnetic reference layer, tunnel barrier layer and magnetic free layer until the heavy metal SOC layer is exposed, forming a columnar MTJ structure.

[0068] ③ Resin Removal and Cleaning: Oxygen plasma is used for resist removal (100W power, 3 minutes) to remove residual photoresist.

[0069] Then it is ultrasonically cleaned with deionized water (5 minutes) and dried.

[0070] ④ Electrode fabrication: Ti / Au (5nm / 80nm) is deposited as electrodes by photoelectron beam evaporation to form a complete device testing structure.

[0071] III. Device Operation Verification

[0072] The zero-field spin magnetic memory prepared in this embodiment achieves data writing in the following manner:

[0073] 1. Apply current (current density 2×10⁻⁶) to the heavy metal SOC layer11 A / m 2 The spin current is generated by the spin orbital torque of the Ta layer and acts on the magnetic free layer.

[0074] 2. The magnetic free layer generates a non-uniform DMI due to the vertical compositional gradient of Co, Fe and B elements, forming a net effective field. Under the condition of no external magnetic field, the spin flow drives the free layer magnetic moment to achieve deterministic reversal (parallel to or antiparallel to the reference layer magnetic moment).

[0075] 3. Data can be read and verified by detecting the changes in the tunnel magnetoresistance of the MTJ (high and low resistance states correspond to "1" and "0").

[0076] Test results show that, under conditions without an external magnetic field, the device described in this invention achieves stable deterministic magnetization reversal under pulsed current drive, with a reversal success rate exceeding 95%, verifying the dominant role of the net effective field induced by the composition gradient in zero-field reversal.

[0077] This embodiment verifies the feasibility of a zero-field spin magnetic memory based on ferromagnetic layer composition gradient through specific material selection, structural parameters, and fabrication process. Its performance meets the design requirements of zero-field operation, high thermal stability, and low power consumption.

[0078] In summary, this invention achieves internal symmetry breaking by introducing a vertical composition gradient in the ferromagnetic free layer, forming a non-uniform DMI-driven zero-field magnetization reversal mechanism, thereby achieving high-efficiency and repeatable spin-orbit moment storage performance while maintaining structural simplicity.

[0079] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions of the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A zero-field spin-orbit moment memory with a ferromagnetic layer composition gradient structure, characterized in that, The layers stacked from bottom to top are: a substrate, a heavy metal strong spin-orbit coupling layer, a vertically magnetically anisotropic free layer with a compositional gradient, a tunnel barrier layer, a magnetic reference layer, an artificial antiferromagnetic pinning layer, and a capping layer; wherein, the heavy metal strong spin-orbit coupling layer is composed of a metal or alloy with a high spin Hall angle, and the material includes one or more of Ta, W, Pt, and Ir, used to generate a spin polarization current when a write current is applied; the magnetic free layer is composed of CoFeB material and has a continuously varying concentration distribution of Co, Fe, and B elements in the direction perpendicular to the film surface, wherein C The atomic concentrations of o and Fe increase away from the heavy metal layer, while the atomic concentration of B decreases. The elemental composition gradient induces non-uniform Dzyaloshinskii-Moriya interaction (DMI) within the magnetic free layer, causing the magnetic moments on both sides of the domain walls to be asymmetrically distributed in amplitude or orientation, thereby generating a net effective field within the magnetic free layer. When a write current is applied to the heavy metal layer, the deterministic reversal of the magnetization direction of the magnetic free layer can be achieved without an external magnetic field through the synergistic effect of spin-orbit torque and the net effective field, with a zero-field reversal ratio greater than 95%.

2. The zero-field spin orbital moment memory as described in claim 1, characterized in that: The magnetic free layer is a CoFeB layer with a compositional gradient and a thickness of 0.8-1.2 nm; the magnetic reference layer is a CoFeB layer without a compositional gradient and a thickness of 1-1.4 nm, and its perpendicular magnetic anisotropy is greater than that of the magnetic free layer.

3. The zero-field spin orbital moment memory as described in claim 1, characterized in that: The composition gradient of the magnetic free layer is achieved through any of the following methods: ① Sputter at least two different proportions of CoFeB target material sequentially; ② Co-sputter three single targets of Co, Fe and B and control the sputtering rate of each target. ③ Insert a pure boron layer of a certain thickness during the CoFeB sputtering process; ④ Adjust the process parameters of sputtering gas pressure or DC voltage to induce element diffusion and form a composition gradient; Thus, a gradient CoFeB magnetic free layer with perpendicular magnetic anisotropy was prepared.

4. The zero-field spin orbital moment memory as described in claim 1, characterized in that: When using CoFeB targets with different composition ratios for sequential sputtering, the target material includes Co 30 Fe 30 B 40 With Co 40 Fe 40 B 20 The CoFeB layer formed by sequentially sputtering the above two target materials has a continuous concentration distribution of increasing Co and Fe elements and decreasing B element in the vertical direction.

5. The zero-field spin orbital moment memory as described in claim 1, characterized in that: The thickness difference between the magnetic free layer and the magnetic reference layer is not less than 0.2 nm, and the perpendicular magnetic anisotropy intensity of the two is different, so as to form a stable magnetization read / write window.

6. The zero-field spin orbital moment memory as described in any one of claims 1 to 5, characterized in that: The substrate is a silicon wafer, an aluminum oxide substrate, or a magnesium oxide substrate.

7. The zero-field spin orbital moment memory as described in any one of claims 1 to 5, characterized in that: The memory includes at least one magnetic tunnel junction unit whose resistance state is defined by the relative magnetization direction between the magnetic free layer and the reference layer; during write operations, the magnetization reversal of the free layer is driven solely by the spin-orbit torque of the heavy metal layer, without the need for external magnetic field assistance.

8. The zero-field spin orbital moment memory as described in any one of claims 1 to 5, characterized in that: The compositional gradient of the magnetic free layer induces non-uniform Dzyaloshinskii-Moriya interaction (DMI), resulting in asymmetry in the magnitude or orientation of magnetic moments on both sides of the domain wall, weakening the domain wall chirality and generating a net effective field. The net effective field drives the magnetic domain reversal, realizing a zero-field deterministic reversal of the relative magnetization direction between the magnetic free layer and the reference layer, thus completing the data writing.

9. The method for fabricating a zero-field spin orbital moment memory as described in any one of claims 1 to 8, characterized in that, Includes the following steps: A heavy metal strong spin-orbit coupling layer, a compositional gradient magnetic free layer, a tunnel barrier layer, a magnetic vertical reference layer, an artificial antiferromagnetic nailing layer, and a capping layer are sequentially deposited on the substrate. The deposited multilayer film is annealed to enhance vertical magnetic anisotropy and promote element diffusion to form a composition gradient; magnetic tunnel junction units are formed using electron beam lithography and ion beam etching processes. Magnetic tunnel junction units are formed using electron beam lithography and ion beam etching processes.

Images