Field-free flipping spin memory based on double-wedge-shaped structure

Abstract

The invention discloses a field-free flip spin memory based on a double-wedge-shaped structure. Comprising a cross Hall rod structure and four electrodes. The cross Hall rod structure sequentially comprises a substrate layer, a buffer layer, a thin film layer and a protective layer from bottom to top. The thin film layer comprises a lower Pt layer, a Co layer and an upper Pt layer from bottom to top, and the lower Pt layer is of a double-wedge-shaped splicing structure and comprises two attached wedge-shaped Pt layers. On one hand, the double-wedge-shaped Pt structure provides spin current for the Co layer, and on the other hand, the double-wedge-shaped Pt structure has the characteristic of interface symmetry breaking and can generate an in-plane equivalent magnetic field. The upper layer Pt further enhances the perpendicular anisotropy of the thin film layer. Pulse current is introduced along the direction perpendicular to the wedge-shaped tangent plane, and the resistance values of the device are detected at the other two ends. The problem that the thickness of a thin film layer of a single wedge-shaped device is not uniform is solved, and the stability of the device is improved while magnetic-field-free overturning is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of spin material magnetic random access memory, and in particular relates to a field-free flip spin memory based on a double wedge structure. Technical Background Magnetic Random Access Memory (MRAM) is a new non-volatile storage technology based on the magnetoresistive effect. It offers advantages such as data non-volatility, near-infinite erase / write cycles, long lifespan, and low power consumption. It combines the high read / write speed of SRAM with the high integration density of DRAM. Currently, achieving low power consumption and improving device reliability are key challenges in the development of MRAM. Recent advances in spin-orbit torque (SOT) have provided new technical solutions for MRAM.

[0002] The mechanism of SOT magnetization reversal is that heavy metals with spin-orbit coupling (SOC) exert torque on the magnetic material's magnetic moment by converting charge flow into spin current, thereby controlling magnetization reversal. Spin-transfer torque (STT) uses spin-polarized current to directly manipulate the magnetization direction of a magnetic material. Both SOT and STT technologies are based on the magnetization reversal mechanism and can serve as core driving technologies for MRAM. However, STT technology suffers from higher power consumption and insufficient device durability compared to SOT technology. In contrast, SOT technology exhibits significant advantages by generating a stronger magnetic torque driving force through the SOC effect.

[0003] Currently, one of the key research focuses on SOT-MRAM devices is whether they can be flipped without an external auxiliary magnetic field. The SOT effect exists in the Pt / Co structure. To achieve field-free flipping, the Pt layer can be transformed into a wedge-shaped state. To achieve field-free flipping, an asymmetric memory cell formed by a single wedge structure is designed. The tilted anisotropy and out-of-plane effective field generated by the spatial asymmetry of the single wedge asymmetric memory cell enable field-free flipping. However, the single wedge structure has an inherent flaw: the growth of the wedge-shaped Pt layer results in a significant thickness difference between the two ends of the device, resulting in uneven thickness of the film layer, which in turn leads to uneven device performance, making it impossible to truly implement the device and apply it to large-scale production. To address the problem of uneven thickness during the growth of the single wedge Pt layer, the present invention proposes a field-free flipping spin memory based on a double wedge structure. The Pt layer is deposited in a double wedge shape. By introducing a wedge structure gradient at the device interface to break its symmetry, this gradient generates an in-plane effective magnetic field under the action of spin-orbit coupling of the heavy metal layer, thereby driving the magnetization to achieve field-free flipping. Compared to single-wedge devices, dual-wedge devices offer the following advantages: The film layer maintains consistent thickness at all locations, enabling more efficient non-magnetic field switching. This maintains the wedge structure's ability to break spatial symmetry while also resolving the challenges of device thickness variations that hinder practical applications. While achieving non-magnetic field switching, the device maintains uniform thickness, lowers current consumption, and is therefore suitable for large-scale manufacturing applications. Summary of the Invention

[0004] In order to address the shortcomings of the current single-wedge device, the present invention proposes and prepares a field-free reversal spin memory based on a double-wedge structure, which solves the problem of uneven thickness of the thin film layer of the single-wedge device, realizes reversal without a magnetic field, and improves the stability of the device.

[0005] The present invention includes a cross Hall bar structure and four electrodes; the cross Hall bar structure is composed of a substrate layer, a buffer layer, a thin film layer, and a protective layer from bottom to top. The buffer layer is used to provide an interface for the growth of the upper thin film; the protective layer is used to isolate the air; the thin film layers are respectively a lower Pt layer, a Co layer, and an upper Pt layer from bottom to top, wherein the lower Pt layer is a double wedge splicing structure, which is two bonded wedge-shaped Pt layers. The Co layer is used to form the magnetic perpendicular anisotropy of the spin memory. On the one hand, the double wedge-shaped Pt structure provides a spin current for the Co layer. On the other hand, the double wedge structure has the characteristic of broken interface symmetry and can generate an in-plane equivalent magnetic field. The upper Pt layer further strengthens the perpendicular anisotropy of the thin film layer.

[0006] Preferably, the buffer layer is a Ta film with a thickness of 1 nm, and the protective layer is a Ta film with a thickness of 2 nm.

[0007] Preferably, the thicknesses of the lower Pt layer, the Co layer, and the upper Pt layer are 3nm-5nm, 1.2nm-1.6nm, and 0.3nm, respectively.

[0008] Preferably, the substrate layer is made of Si or SiO2 material.

[0009] Preferably, the electrode is a Cr / Cu / Pt composite electrode.

[0010] The fabrication method for a field-free spin-flip memory involves the following steps: A buffer layer, a thin film layer, and a protective layer are grown sequentially on a substrate from bottom to top. To ensure precise growth of the double-wedge Pt layer beneath the thin film layer, a two-step approach is employed: First, the tray is stopped while the first layer of Pt wedges is grown. Then, when the second layer is grown, the tray is rotated 180° and the growth of complementary wedges continues, creating two aligned double-wedge structures. Following growth, the substrate layer is micro-nanomachined perpendicularly and parallel to the double-wedge cross-sections to form a cross-Hall bar structure, surrounded by four electrodes.

[0011] Furthermore, electrodes are arranged around the Hall bar using overlay and magnetron sputtering. While growing the buffer layer, protective layer, and remaining thin film layers, the tray holding the silicon wafer rotates at a constant speed to ensure uniform film growth.

[0012] The field-free flip spin memory based on a double-wedge structure uses a pulsed current applied to two electrodes perpendicular to the wedge's tangential direction. The output signals from the other two electrodes reflect the change in the memory device's resistance. This resistance change enables the writing and storage of information. When the current intensity reaches the flip threshold of the spin memory, the spin memory undergoes a magnetic domain flip without a magnetic field.

[0013] The beneficial effects of the present invention are as follows: Compared to traditional spin magnetic memories, 1. The present invention achieves magnetization reversal without magnetic field through a double-wedge structure, resulting in a low device process difficulty and a wide range of applications. 2. The present invention employs a double-wedge structure design to break the device symmetry, thereby significantly improving the magnetization reversal efficiency. 3. The proposed double-wedge-based field-free reversal spin memory has a high spin-orbit moment efficiency, which helps improve device stability and storage density. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the test use based on the double-wedge spin memory device; Figure 2 is a schematic cross-sectional view of the double-wedge device structure; Figure 3 This is a schematic diagram of the device after micro-nano processing; Figure 4This is a graph showing the resistance change of the device after a pulse current is applied; Figure 5 is a schematic cross-sectional view of a single wedge device structure; Figure 6 This is a comparison chart of spin Hall efficiency. DETAILED DESCRIPTION

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] like Figure 1 and 2 A field-free spin memory based on a double-wedge structure is shown. It includes a cross-Hall bar structure and four electrodes. From bottom to top, the cross-Hall bar structure consists of a substrate layer, a buffer layer, a thin film layer, and a protective layer. The buffer layer provides a good interface for the growth of the upper thin film, improving the smoothness of the device's thin film interface, enhancing the connection with the substrate, and improving device quality. The protective layer is used to isolate the device from the air.

[0017] The film layers, from bottom to top, are a lower Pt layer, a Co layer, and an upper Pt layer. The lower Pt layer has a double-wedge structure, consisting of two laminated wedge-shaped Pt layers. The Co layer contributes to the perpendicular magnetic anisotropy of the spin memory. The double-wedge Pt structure not only provides spin current for the Co layer, but also breaks the interface symmetry, generating an in-plane equivalent magnetic field. The upper Pt layer further enhances the perpendicular anisotropy of the film layer.

[0018] In this embodiment, the substrate layer is Si / SiO2; the buffer layer is a 1nm Ta layer; the protective layer is a 2nm Ta layer; the thicknesses of the lower Pt layer, Co layer, and upper Pt layer are 5nm, 1.2nm, and 0.3nm, respectively.

[0019] The preparation process of the above field-free spin memory is as follows: Ta, Pt, Co, Pt, Ta are sputtered on the substrate from bottom to top in sequence using the magnetron sputtering method to make a Figure 1 The cross Hall bar structure shown in Figure 1 is shown in Figure 2. Figure 3 As shown, the center is a spin Hall bar storage structure, and four electrodes are arranged around it for applying current signals and testing the resistance change of the storage structure. In this embodiment, the electrodes are Cr / Cu / Pt composite electrodes.

[0020] To ensure the precise growth of the lower double-wedge Pt layer of the thin film layer, a two-step method is adopted: first, the tray stops rotating when growing the first layer of wedge-shaped Pt, and when growing the second layer of wedge-shaped Pt, the tray is turned 180° and continues to grow complementary wedges to achieve the preparation of the double-wedge structure.

[0021] To ensure that the lower Pt layer is a double wedge, the tray is stopped when the first layer of wedge-shaped Pt is sputtered. After half of the predetermined value has been grown, the motor is controlled to rotate the tray 180° to continue depositing the second layer of wedge-shaped Pt. The angle formed by the target and the substrate allows the preparation of two overlapping double wedges. When growing the buffer layer, the protective layer and the remaining layers of the thin film, the tray holding the silicon wafer rotates at a constant speed to ensure uniform growth of the thin film.

[0022] After the growth is completed, a cross Hall bar structure with a width of 10 microns is formed through photolithography and etching technology, and then the electrodes are arranged at the pin position of the cross through overlay and magnetron sputtering.

[0023] During operation, a pulsed current is applied to two electrodes in the y-direction. As the current intensity changes, the output signals from the other two electrodes reflect the changes in the memory's resistance. When the current intensity reaches the flip threshold of the spin memory, the spin memory undergoes a magnetic domain flip in the absence of a magnetic field. This change in resistance is key to information storage. By defining high resistance as 1 and low resistance as 0, information is written and stored.

[0024] The flip threshold of the spin memory is a measured value. By gradually increasing the pulse current intensity of the two electrodes in the y-direction, the resistance value changes under the action of the pulse current. Pt is a heavy metal. When a current is applied, the double-wedge Pt layer provides a spin current to the Co layer, driving the magnetic domain flipping of the Co layer. Due to the double-wedge structure of the Pt layer, the wedge interface produces symmetry breaking, generating an in-plane equivalent magnetic field, achieving magnetic domain flipping in the absence of a magnetic field. This change in magnetic domain causes a corresponding change in resistance. The magnetic domain flip also occurs after the opposite pulse current is applied, indicating that the resistance returns to its initial value.

[0025] For ease of understanding, in this embodiment, Figure 1 The three-dimensional coordinates x, y, and z shown in the figure are used as references. When a pulse current is applied to the device along the y direction, the device resistance value can be collected at the other two electrodes. As the pulse current changes, the corresponding resistance change can be collected at the other two electrodes. Figure 4 As shown, the flip threshold of the spin memory in this embodiment is 25 mA.

[0026] like Figure 5 The figure shows a cross-section of a single wedge sample. Although the single wedge sample can achieve flipping without a magnetic field, its thickness is uneven and it cannot be used in large-scale devices.

[0027] In order to demonstrate the power consumption advantage of the field-free flip spin memory with double wedge structure described in the present invention, Figure 2 and Figure 5 The spin-orbit torque efficiency of the spin memory shown is ( β DL ) test;β DL It reflects the conversion efficiency of charge flow to spin flow, and its value directly characterizes the core performance indicators of spin electronic devices. β DL The higher the value, the lower the device drive current requirement and the significantly improved magnetization switching speed, which is crucial for achieving high-efficiency, high-speed non-volatile memory. Figure 6 As shown, the double wedge structure β DL The value is improved compared with the traditional single wedge structure, which verifies that the double wedge structure of the present invention has lower power consumption than the single wedge structure.

Claims

1. A field-free spin memory based on a double-wedge structure, comprising a cross Hall bar structure and four electrodes; characterized in that: The cross Hall bar structure consists of a substrate layer, a buffer layer, a thin film layer, and a protective layer from bottom to top; the buffer layer is used to provide an interface for the growth of the upper thin film; the protective layer is used to isolate the air; the thin film layers are, from bottom to top, a lower Pt layer, a Co layer, and an upper Pt layer, wherein the lower Pt layer is a double-wedge splicing structure, which is two bonded wedge-shaped Pt layers; the Co layer is used to constitute the magnetic perpendicular anisotropy of the spin memory. On the one hand, the double-wedge Pt structure provides a spin current for the Co layer, and on the other hand, the double-wedge structure has the characteristic of broken interface symmetry, which can generate an in-plane equivalent magnetic field; the upper Pt layer further enhances the perpendicular anisotropy of the thin film layer.

2. The field-free spin memory based on a double-wedge structure according to claim 1, wherein: The buffer layer is a Ta film with a thickness of 1 nm, and the protection layer is a Ta film with a thickness of 2 nm.

3. The field-free spin memory based on a double-wedge structure according to claim 1, wherein: The thicknesses of the lower Pt layer, the Co layer, and the upper Pt layer are 3nm-5nm, 1.2nm-1.6nm, and 0.3nm, respectively.

4. The field-free spin memory based on a double-wedge structure according to claim 1, wherein: The substrate layer is made of Si / SiO2 material.

5. The field-free spin memory based on a double-wedge structure according to claim 1, wherein: The electrode is a Cr / Cu / Pt composite electrode.

6. The method for preparing the field-free inversion spin memory according to claim 1, wherein: The specific process is as follows: a buffer layer, a thin film layer, and a protective layer are grown on the substrate from bottom to top in sequence; to ensure the precise growth of the double-wedge Pt layer under the thin film layer, a two-step method is adopted: first, the tray stops rotating when the first wedge-shaped Pt layer is grown, and when the second wedge-shaped Pt layer is grown, the tray is turned 180°, and complementary wedges are continued to grow to achieve the preparation of two fitted double-wedge structures; after the growth is completed, the substrate layer is micro-nano-processed along the directions perpendicular to and parallel to the double-wedge cross-section to form a cross Hall bar structure, and four electrodes are arranged around it.

7. The method for preparing a field-free inversion spin memory according to claim 6, wherein: Electrodes are arranged around the Hall bar using overlay and magnetron sputtering methods.

8. The method for preparing a field-free inversion spin memory according to claim 6, wherein: When growing the buffer layer, the protective layer and the remaining layers of the thin film, the tray holding the silicon wafer rotates at a constant speed to ensure uniform growth of the thin film.

9. The method for using the field-free flip spin memory based on the double wedge structure according to claim 1, characterized in that: When a pulse current is applied to two electrodes in a direction perpendicular to the wedge's tangential direction, the output signals of the other two electrodes will reflect the change in the resistance value of the memory device; through the resistance change, the writing and storage functions of information are completed; when the current intensity reaches the flip threshold of the spin memory, the spin memory performs magnetic domain flipping in the absence of a magnetic field.

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