Spin memory based on quantum well resonant enhancement of out-of-plane spin polarization

Abstract

The application discloses a spin memory based on quantum well resonance enhancement of out-of-plane spin polarization, which comprises a seed layer, an anti-ferromagnetic layer, a non-magnetic layer, an interface regulation layer, a quantum well metal layer, a reflection regulation layer, a free layer, a barrier layer and a protection layer which are sequentially stacked. The anti-ferromagnetic layer is grown under an in-situ magnetic field, and the interface formed by the anti-ferromagnetic layer and the non-magnetic layer directly generates an out-of-plane polarized spin current through spin-orbit filtering and precession effect; the interface regulation layer, the quantum well metal layer and the reflection regulation layer form a metal quantum confinement structure, the thickness of the quantum well metal layer matches the quantum well resonance condition, so that the out-of-plane polarized spin current is resonantly transmitted, and spin enhancement is realized. The enhanced out-of-plane polarized spin current is injected into the vertically magnetized free layer, and the magnetic moment can be flipped without an external magnetic field; the barrier layer is used for reading a magnetoresistance signal. The application does not need an additional auxiliary magnetic field, and is expected to be used for a low-power-consumption, high-speed and high-reliability nonvolatile memory device.

Description

Technical Field

[0001] This invention belongs to the field of spintronics and information storage technology, specifically relating to a spin memory structure based on the coordinated control of quantum confinement and interface spin-orbit coupling, which can be applied to low-power, high-speed, and high-reliability non-volatile memories. Background Technology

[0002] As VLSI process technology continues to approach the nanoscale, and with the rapid iteration of artificial intelligence, big data, and edge computing technologies, traditional semiconductor memories based on charge storage mechanisms are gradually reaching their physical limits in terms of core performance indicators such as power consumption, read / write speed, storage density, and device durability. Traditional memories rely on the accumulation and release of charge to read and write information, which has inherent defects such as high leakage power consumption, large read / write latency, and susceptibility to aging due to repeated erasures and writes. They cannot meet the application requirements of next-generation high-speed, low-power, and long-life computing devices.

[0003] Spintronic memory technology, based on the control of electron spin degrees of freedom, has become a core research direction for next-generation information storage technology due to its outstanding advantages such as non-volatility, ultra-high-speed read / write, ultra-low power consumption, radiation resistance, and high integration. Currently, the mainstream spin memories in industrialization and research mainly include two types: Spin-TransferTorque Magnetoresistive Random Access Memory (STT-MRAM) and Spin-Orbit Torque Magnetoresistive Random Access Memory (SOT-MRAM). Among them, SOT-MRAM has significant technical advantages over traditional STT-MRAM: it adopts a three-terminal independent structure to achieve read / write path separation, completely avoiding the barrier layer breakdown and aging failure problems caused by the direct passage of read / write current through the tunnel junction in STT-MRAM, and significantly improving the device's cycle durability; it also features faster read / write speeds, lower switching power consumption, and stronger thermal stability, making it more suitable for high-frequency, high-speed storage scenarios. However, existing commercial and traditional research-oriented SOT-MRAM still have core technological bottlenecks: they mainly rely on the heavy metal spin Hall effect to generate spin current, and the generated spin polarization current is in-plane polarization, which cannot directly realize the magnetic moment reversal of the vertically magnetized free layer. They must rely on an external auxiliary magnetic field to complete the vertical magnetic moment reversal and data writing.

[0004] The introduction of an external magnetic field not only increases the overall size of the device and raises the cost of fabrication and packaging, but also causes problems such as magnetic field crosstalk, increased power consumption, and greater integration difficulty, severely restricting the miniaturization, high-density integration, and large-scale mass production of SOT-MRAM. External field-free vertical magnetic moment reversal technology has become a core challenge urgently needing to be overcome for the commercialization of SOT-MRAM. Existing technologies cannot simultaneously meet the application requirements of low power consumption and high write efficiency. Based on this, this invention proposes a spin memory structure based on quantum well resonance-enhanced out-of-plane spin polarization. Through a technical solution combining interface spin manipulation and quantum confined resonant transport, it is expected to provide an optional technical solution for realizing high-performance SOT-MRAM. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a spin memory based on quantum well resonance-enhanced out-of-plane spin polarization. Building upon the external field-free vertical magnetic moment reversal achieved by the out-of-plane component spin current, the invention utilizes the resonance effect of quantum well states (QWS) to enhance spin transport efficiency in the z-direction, thereby improving the write efficiency of the vertically magnetized device and reducing power consumption.

[0006] A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization is proposed. This is achieved by constructing an Hf / Cu / Ru multilayer quantum confinement structure between a PtMn / Ti spin source layer and a free layer, thereby enhancing and controlling the spin polarization current in the z-direction, thus reducing write power consumption and improving magnetization reversal efficiency. The structure comprises, from bottom to top, a Ta seed layer, a PtMn antiferromagnetic layer, a Ti nonmagnetic layer, an Hf interface control layer, a Cu quantum well metal layer, a Ru reflection control layer, a CoFeB free layer, an MgO barrier layer, and a Ta protective layer.

[0007] The Ta seed layer is used to improve the film growth quality and crystal orientation; the interface between the PtMn antiferromagnetic layer and the Ti nonmagnetic layer is used to generate out-of-plane polarized spin current in the z-direction, which is used to adjust the interface orbital coupling and electron transport characteristics; the Cu layer is a quantum well metal layer; the Hf layer / Cu layer interface and the Cu layer / Ru layer interface together form an electron reflection boundary; electrons form thickness-dependent quantum well states in the Cu quantum well metal layer, which are used to form an electron reflection boundary and adjust interface transport. The quantum well resonance condition can enhance the spin transport efficiency in the z-direction. The CoFeB layer is a vertically magnetized free layer used to receive spin current to achieve magnetic moment reversal, i.e., data storage; the MgO barrier layer is used to form a magnetic tunnel junction to achieve TMR readout; the Ta protective layer can prevent oxidation and facilitate electrode contact and etching.

[0008] The PtMn antiferromagnetic layer is grown under an in-situ magnetic field (65mT). The antiferromagnetic PtMn interface has uncompensated magnetic moments due to atomic coordination asymmetry. The in-situ magnetic field applied during the deposition process will orient these disordered uncompensated magnetic moments along the magnetic field direction. When current flows through the interface, it generates out-of-plane (z-direction) polarized spin current at the PtMn / Ti interface through spin orbit filtering and precession effect.

[0009] The Cu quantum well metal layer is a single-crystal Cu (001). When the thickness of the Cu quantum well metal layer reaches the range of electronic coherence length, electrons are constrained in the vertical direction by the potential barriers formed by the Hf / Cu interface and the Cu / Ru interface, and their vertical motion is quantized, thus forming a discrete QWS. The Hf interface control layer and the Ru reflection control layer serve as the lower and upper reflection boundaries of the quantum well structure, respectively, causing the electron wave function to undergo multiple reflections and interferences within the Cu quantum well metal layer. When the electron Fermi level and the quantum well level satisfy the resonance condition, the electron transmission probability increases significantly, forming quantum well resonant transport.

[0010] Because the spin current generated at the PtMn / Ti interface has a z-axis polarization component, the reflection phase and resonance conditions of electrons with different spin directions in the Cu quantum well are different. ,,in: For discrete energy levels in a quantum well; The wave vector that satisfies the boundary conditions; For the effective mass of electrons, This is Planck's constant. Due to the influence of spin-orbit coupling and exchange interactions, different spin states correspond to different resonance conditions, thus forming spin-selective resonance transmission. At a specific Cu quantum well metal layer thickness, the transmittance of z-polarized spin electrons is higher than that of other spin components, thus enhancing out-of-plane spin polarization. After the enhanced z-polarized spin current is injected into the CoFeB free layer, a spin-orbit torque is applied to the free layer: μ , where μ is the direction of free layer magnetization; is the out-of-plane spin polarization vector.

[0011] Since the PtMn / Ti interface itself can generate out-of-plane spin polarization, vertical magnetic moment reversal can be achieved without an external auxiliary magnetic field. Quantum well resonance further enhances the spin current intensity in the z-direction, thereby reducing the critical switching current of the device and improving the writing efficiency.

[0012] Compared to existing traditional SOT-MRAM technology, this invention overcomes the core bottlenecks of existing technologies, such as reliance on external field assistance, low spin transport efficiency, high power consumption, and poor stability, through a synergistic innovative design of interface spin modulation and multilayer quantum well resonant transport. It possesses certain technical advantages, specifically manifested in the following ways: This invention regulates the ordered arrangement of uncompensated magnetic moments at the PtMn / Ti interface using an in-situ magnetic field. Relying on the asymmetric spin-orbit coupling effect at the interface, it directly generates a stable intrinsic z-direction out-of-plane polarized spin current. It can achieve precise magnetic moment reversal of the vertically magnetized free layer without the need for an external auxiliary magnetic field, completely eliminating the dependence of traditional SOT-MRAM on external magnetic fields. This effectively solves the problems of large device size, low integration density, circuit crosstalk, and high manufacturing cost caused by external magnetic fields, significantly improving the device's miniaturization and high-density integration capabilities, and fully adapting to the requirements of chip mass production processes.

[0013] Simultaneously, an innovative Hf / Cu / Ru multilayer quantum confinement structure is introduced. Utilizing the spin-selective resonant transmission characteristics of single-crystal Cu quantum wells, the transmission efficiency of out-of-plane spin components in the z-direction is specifically enhanced, while suppressing in-plane spin loss and stray spin interference. This effectively solves the defects of weak interface spin polarization and high spin transport loss in traditional devices. By matching the quantum well resonance conditions, a significant improvement in spin polarization and spin injection efficiency can be achieved, accelerating the free-layer magnetic moment reversal rate and effectively improving the high-frequency read / write performance of the device. Furthermore, the quantum well resonance effect can significantly increase the transmission probability of out-of-plane spin electrons. Under the premise of achieving the same magnetic moment reversal effect, the critical reversal current of the device is significantly reduced, effectively reducing Joule heat loss and drive power consumption during the read / write process. Compared with traditional SOT memory devices without external fields, it can further reduce the device's operating power consumption, meeting the stringent requirements of low power consumption and long battery life for artificial intelligence terminals, IoT devices, embedded chips, and wearable devices. Furthermore, this invention employs a three-terminal SOT structure with separate read and write paths, avoiding repeated impacts of read and write currents on the MgO barrier layer. This effectively eliminates tunnel layer aging and breakdown failure issues, significantly improving the device's cycle write / erase durability. Simultaneously, the multilayer thin-film structure combined with a Ta protective layer effectively resists oxidation and isolates external interference. The annealing process optimizes the interface structure, significantly reducing interface defects and lattice mismatch issues, improving device operational stability, thermal stability, and lifespan. This meets the long-term stable operation requirements under complex conditions. Moreover, the Ta, PtMn, Ti, Hf, Cu, Ru, CoFeB, and MgO materials used in this invention are all existing MRAM and CM materials. OS semiconductor process adaptable materials are compatible with existing mature semiconductor processing lines for the preparation processes of thin film deposition, magnetic field growth, and annealing of each functional layer. No new special equipment or complex processes are required. The preparation process is simple, highly controllable, and has low production costs, making it highly promising for industrialization and promotion. At the same time, by precisely controlling the thickness of the Ti non-magnetic layer, Cu quantum well metal layer, and Ru reflection control layer, different quantum well resonance conditions can be flexibly matched, and the spin orbital torque efficiency and spin polarization intensity in the z-direction can be precisely controlled. Different performance indicators such as low power consumption, high speed, and high integration can be adapted to meet the needs of different scenarios, thus covering a wider range of application scenarios. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of the invented device; Figure 2 Test results of magnetic moment reversal without magnetic field assistance achieved by out-of-plane spin flow at an antiferromagnetic / nonmagnetic interface; Appendix Figure 1 Labeling explanations: 1. Ta seed layer; 2. PtMn antiferromagnetic layer; 3. Ti nonmagnetic layer; 4. Hf interface control layer; 5. Cu quantum well metal layer; 6. Ru reflection control layer; 7. CoFeB free layer; 8. MgO barrier layer; 9. Ta protective layer. Detailed Implementation

[0015] The following specific embodiments further illustrate the essential features and significant advancements of the present invention, but the scope of the present invention is not limited to the following embodiments: Detailed implementation methods: such as Figure 1As shown, the spin memory based on quantum well resonance-enhanced out-of-plane spin polarization described in this embodiment includes a Ta seed layer 1, a PtMn antiferromagnetic layer 2, a Ti nonmagnetic layer 3, an Hf interface control layer 4, a Cu quantum well metal layer 5, a Ru reflection control layer 6, a CoFeB free layer 7, an MgO barrier layer 8, and a Ta protective layer 9. The stacked structure from bottom to top is: Ta (3 nm) / PtMn (3 nm) / Ti (0.8 nm–3.0 nm) / Hf (0.4 nm) / Cu (1 nm–4 nm) / Ru (0.8 nm–1.2 nm) / CoFeB (1 nm) / MgO (5 nm) / Ta (2 nm).

[0016] The device fabrication process steps in this embodiment are as follows: Step 1, Substrate Pretreatment: Select a high-purity silicon substrate or a SiO2 / Si substrate, and ultrasonically clean it sequentially with acetone, ethanol, and deionized water to remove surface oil, impurities, and dust. Dry it for later use to ensure that the substrate surface is clean and flat.

[0017] Step 2, Thin Film Deposition: Multilayer thin films are deposited sequentially using a magnetron sputtering system. First, a 3nm Ta seed layer 1 is deposited to optimize the crystal orientation of the substrate surface. Then, a 3nm PtMn antiferromagnetic layer 2 is deposited under a constant in-situ magnetic field of 65mT to achieve the directional and ordered arrangement of the uncompensated magnetic moment at the interface. The following layers are deposited: a Ti nonmagnetic layer 3 of the corresponding thickness, a 0.4nm Hf interface control layer 4, a 1~4nm single-crystal Cu quantum well metal layer 5, a 0.8nm~1.2nm Ru reflection control layer 6, a 1nm CoFeB vertical magnetization free layer 7, a 5nm MgO barrier layer 8, and finally a 2nm Ta protective layer 9 to complete the thin film stacking.

[0018] Step 3, Vacuum Annealing: Place the deposited device sample in a vacuum annealing furnace and anneal it at a constant temperature of 200~350℃ for 60 minutes in a vacuum environment. Then, allow it to cool naturally to room temperature to repair thin film interface defects, optimize lattice structure and interface coupling characteristics, and improve spin transport stability.

[0019] Step 4, Device micro / nano fabrication: Device electrodes and memory cell arrays are fabricated through photolithography, ion beam etching, metal evaporation, and lift-off processes to complete device packaging.

[0020] When current flows through the PtMn antiferromagnetic layer 2 / Ti nonmagnetic layer 3, a spin current with a z-direction component is generated. The Hf interface control layer 4, Cu quantum well metal layer 5, and Ru reflection control layer 6 constitute a quantum confinement structure. When the resonance condition is met, the spin current passing through the quantum confinement structure forms quantum well resonant transport in the Cu quantum well metal layer 5, enhancing spin-selective transmission and thus improving the z-direction spin injection efficiency. The enhanced spin current is injected into the vertically magnetized CoFeB free layer 7, achieving vertical magnetic moment reversal under no external magnetic field conditions. The MgO barrier layer 8 is used for magnetoresistance readout; the uppermost Ta protective layer 9 prevents oxidation and facilitates electrode contact and etching.

[0021] In this embodiment, performance optimization can be achieved by adjusting the thickness of the core functional layer: the quantum well resonance condition and interface spin transport efficiency can be adjusted by changing the thickness of the Ti nonmagnetic layer, the Cu quantum well layer, and the Ru reflection control layer. The thickness of the Ti nonmagnetic layer can be selected between 0.8 nm and 3.0 nm, the thickness of the Cu quantum well metal layer can be selected between 1 nm and 4 nm, and the thickness of the Ru reflection control layer can be selected between 0.8 nm and 1.2 nm. Different Cu quantum well metal layer thicknesses correspond to different quantum well resonance conditions and exhibit different z-direction spin-orbit torque efficiencies. Through harmonic Hall measurements and critical flip current measurements, non-monotonic changes or oscillatory enhancement characteristics resulting from variations in the Cu quantum well metal layer thickness can be observed, thereby verifying the quantum well resonance enhancement effect.

[0022] Figure 2 The test results show that the antiferromagnetic / nonmagnetic interface constructed in this invention can achieve stable reversal of electrically controlled vertical magnetic moments without an external auxiliary magnetic field, fully verifying the effectiveness of intrinsic out-of-plane spin current generation and the feasibility of writing without an external field. Compared with the prior art, this invention utilizes the PtMn / Ti interface to achieve out-of-plane spin polarization generation, utilizes the Hf / Cu / Ru multilayer structure to form quantum well resonant transport, enhances the z-direction spin injection efficiency, and reduces the critical current for vertical magnetization reversal, which is expected to provide a new technical means for low-power SOT-MRAM design.

Claims

1. A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization, characterized in that, It includes a multilayer thin film structure stacked from bottom to top: Ta seed layer (1), PtMn antiferromagnetic layer (2), Ti nonmagnetic layer (3), Hf interface control layer (4), Cu quantum well metal layer (5), Ru reflection control layer (6), CoFeB free layer (7), MgO barrier layer (8) and Ta protective layer (9); The PtMn antiferromagnetic layer (2) and the Ti nonmagnetic layer (3) form an interface spin source structure, generating out-of-plane polarized spin current in the z direction, and realizing vertical magnetic moment reversal without external magnetic field assistance; the Hf interface control layer (4), Cu quantum well metal layer (5), and Ru reflection control layer (6) together constitute a multi-layer quantum confinement structure. The Hf interface control layer (4) and Ru reflection control layer (6) respectively form electron reflection boundaries, so that thickness-dependent quantum well states are formed in the Cu quantum well metal layer (5), and the spin transport efficiency in the z direction is enhanced through the quantum well resonance effect, thereby increasing the out-of-plane spin polarization intensity; the CoFeB free layer (7) is a vertical magnetization structure, used to receive the enhanced out-of-plane polarized spin current, realize magnetic moment reversal, and complete data storage; the MgO barrier layer (8) is used to construct a magnetic tunnel junction to realize magnetoresistive signal readout.

2. A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization according to claim 1, characterized in that, The PtMn antiferromagnetic layer (2) is prepared by deposition under an in-situ magnetic field of 65mT. An uncompensated magnetic moment is formed at the interface. When the current flows through the PtMn / Ti interface, a stable out-of-plane polarized spin current in the z direction is generated through spin orbit filtering and precession effect.

3. A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization according to claim 1, characterized in that, The Cu quantum well metal layer (5) is a single-crystal Cu(001) structure with a thickness within the range of electronic coherence length. Electrons form discrete quantum well states under the barrier constraints of the Hf / Cu interface and the Cu / Ru interface. The electronic wave function is reflected and interfered multiple times inside the Cu layer. When the resonance condition between the Fermi level and the quantum well level is satisfied, spin-selective resonance transmission is achieved.

4. A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization according to claim 1, characterized in that, The PtMn antiferromagnetic layer (2) has a thickness of 3 nm, the Ti nonmagnetic layer (3) has a thickness of 0.8 nm–3.0 nm, the Hf interface control layer (4) has a thickness of 0.4 nm, the Cu quantum well metal layer (5) has a thickness of 1 nm–4 nm, and the Ru reflection control layer (6) has a thickness of 0.8 nm–1.2 nm.

5. A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization according to claim 1, characterized in that, After the spin memory is fabricated, it is annealed at 200℃~350℃ for 60 minutes to optimize the interface structure and crystal orientation of each thin film layer and improve spin transport stability.

6. A spin memory based on quantum well resonance-enhanced out-of-plane spin polarization according to claim 1, characterized in that, The spin memory adjusts the spin orbital torque efficiency in the z-direction by controlling the thickness of the Ti nonmagnetic layer (3), the Cu quantum well metal layer (5), and the Ru reflection control layer (6) to match the quantum well resonance condition and reduce the critical current for magnetic moment reversal.

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