Room-temperature multi-resistance-state magnetic memory based on ferromagnetic / semiconductor / ferromagnetic Van der Waals heterojunction

Abstract

The invention discloses a room-temperature multi-resistance-state magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic Van der Waals heterojunction, and belongs to the field of magnetic memories. The invention aims to solve the problems of low working temperature, limited resistance state number, complex process and poor controllability of a two-dimensional magnetoresistive device. Fe3GaTe2 is used as an upper electrode and a lower electrode, InSe is used as a middle tunnel barrier layer, and the sandwich Van der Waals heterojunction is constructed. The magnetization direction of the electrode is regulated and controlled, and the tunneling magnetoresistance effect is utilized to realize the antisymmetric magnetoresistance behavior of a three-resistance state or a four-resistance state at room temperature. The performance of the device is excellent. The working temperature reaches 320K, and the signal amplitude of a 4-320K wide temperature zone is stable. The function is stable in a wide current range of 0.1-1000 [mu] A; the method has universal stability for an external magnetic field in a vertical plane. The preparation method of transferring after electrode is adopted, the process is simple, complicated thickness or folding modulation is avoided, controllable preparation of the multi-resistance-state magnetic memory is realized, and a brand new technical path is provided for developing a nonvolatile memory with high storage density and low power consumption.

Description

Technical Field

[0001] This invention relates to the intersection of spintronics and novel information storage technologies, and more particularly to a room-temperature multi-resistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction and its fabrication method. Furthermore, it relates to a non-volatile magnetic memory cell employing a Fe3GaTe2 / InSe / Fe3GaTe2 sandwich van der Waals heterojunction, capable of stable switching between three or four resistance states at room temperature. Background Technology

[0002] Electrons possess two intrinsic degrees of freedom: charge and spin. Traditional semiconductor devices primarily utilize the charge property of electrons, while spintronic devices aim to simultaneously manipulate both charge and spin, thus giving rise to a new generation of information devices with superior characteristics such as non-volatility, high speed, low power consumption, and high integration, such as magnetoresistive random access memory (MRAM) and spin logic devices. Among them, magnetic multistate memory (MMM), capable of storing multiple bits of information in a single cell (i.e., multi-value storage), can significantly improve storage density and reduce the cost per bit, showing great application potential in fields such as artificial intelligence, big data, and cloud computing. The antisymmetric magnetoresistive effect is an important physical mechanism for realizing multi-value storage. In recent years, with the rise of two-dimensional van der Waals materials, especially the discovery of intrinsic two-dimensional ferromagnetic materials, it has become possible to construct novel spintronic devices at atomic-level thicknesses. In 2022, researchers used thickness-modulated Fe3GaTe2 material to achieve the three-resistance state phenomenon in a two-dimensional system for the first time by measuring the magnetoresistive properties of its thickness-thin interface region. However, the Curie temperature of Fe3GaTe2 is far below room temperature, severely limiting its practical applications. Subsequently, the emergence of room-temperature ferromagnetic Fe3GaTe2 materials propelled the development of room-temperature devices. Between 2024 and 2025, researchers achieved room-temperature operating tri-resistivity devices in Fe3GaTe2 using thickness modulation or fold modulation methods. However, existing technologies suffer from the following inherent drawbacks, severely hindering their large-scale integration and application:

[0003] 1. Complex and uncontrollable fabrication processes: Both "thickness modulation" and "folding modulation" rely on creating regions with non-uniform structures (such as steep steps or specific folding angles) on a single material sheet. These processes have low repeatability and poor controllability, making it difficult to achieve uniform and reliable manufacturing at the wafer scale.

[0004] 2. Limited number of resistive states: Existing schemes are based on structural modulation using a single ferromagnetic material, and their physical mechanism inherently limits the number of achievable resistive states, typically only three. Achieving four or more resistive states to further increase storage density presents fundamental difficulties for the aforementioned schemes.

[0005] 3. Limited device performance and design flexibility: Device structures based on a single material have limited electrical transport characteristics (such as tunneling barrier height and interface quality) that are difficult to effectively control, thus limiting the optimization space for device performance.

[0006] Therefore, there is an urgent need in this field for a new technological solution that can overcome the aforementioned shortcomings. This solution should possess the characteristics of simple and controllable fabrication process, the ability to achieve storage functions with more than three resistance states, and excellent stability at room temperature, thereby laying the foundation for the practical application of high-density, low-power memories. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide a multi-resistivity magnetic memory with a simple and controllable fabrication process, an adjustable number of resistive states (three or four states), and stable performance at room temperature and over a wide temperature range, as well as a controllable fabrication method thereof.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction, comprising:

[0010] Substrate;

[0011] Multiple electrodes disposed on the substrate, the electrodes including a source electrode, a drain electrode and multiple probe electrodes;

[0012] The device also includes a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction structure located on the electrode. The ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction structure comprises a bottom ferromagnetic layer, a semiconductor intermediate layer, and a top ferromagnetic layer stacked sequentially. The bottom and top ferromagnetic layers are both made of room-temperature van der Waals ferromagnetic materials with perpendicular magnetic anisotropy, and the semiconductor intermediate layer is made of two-dimensional van der Waals semiconductor material. By applying an external magnetic field perpendicular to the device plane, the relative state of the magnetization directions of the bottom and top ferromagnetic layers is controlled, so that the device exhibits multiple non-volatile resistive states under the measurement of the probe electrode, and these multiple non-volatile resistive states are maintained at a temperature of 320K.

[0013] The room-temperature van der Waals ferromagnetic material is Fe3GaTe2.

[0014] The two-dimensional van der Waals semiconductor material is InSe.

[0015] The detection electrode includes two detection electrodes located on the same side of the heterojunction structure. When measurement is performed through the two detection electrodes on the same side, the device exhibits three resistance states: high, medium, and low, depending on the change of the external magnetic field.

[0016] The detection electrode includes four detection electrodes located on opposite sides of the heterojunction structure, forming a cross-measurement configuration; when cross-measurement is performed through the detection electrodes on opposite sides, the device exhibits four resistance states: high, medium-high, medium-low, and low, depending on the change of the external magnetic field.

[0017] In this invention, the signal amplitude of the multi-resistivity characteristic remains stable within a temperature range of 4K to 320K.

[0018] When the applied injection current varies in the range of 0.1μA to 1000μA, the signal amplitude of the multi-resistivity characteristic remains stable.

[0019] When the direction of the external magnetic field varies from 0° to 360° relative to the normal of the device plane, the signal amplitude of the multi-resistivity characteristic remains stable.

[0020] The present invention also includes an encapsulation layer covering the heterojunction structure, wherein the encapsulation layer is hexagonal boron nitride.

[0021] A method for fabricating the magnetic storage device includes the following steps:

[0022] 1) Clean the substrate;

[0023] 2) The source electrode, drain electrode, and probe electrode are formed on the cleaned substrate by photolithography and metal deposition processes;

[0024] 3) By mechanical stripping and van der Waals transfer technology, the bottom ferromagnetic layer, the semiconductor intermediate layer and the top ferromagnetic layer are sequentially aligned and transferred to the electrode to form a sandwich heterojunction structure, wherein the bottom ferromagnetic layer is in contact with the source electrode and part of the probe electrode, the top ferromagnetic layer is in contact with the drain electrode and the remaining probe electrode, and the semiconductor intermediate layer is sandwiched between the two ferromagnetic layers.

[0025] 4) The transfer encapsulation layer covers the heterojunction structure;

[0026] 5) Anneal the device to enhance the interfacial bonding of the heterojunction.

[0027] The detection electrode is provided with four electrodes. The bottom ferromagnetic layer and the top ferromagnetic layer have different thicknesses. The bottom ferromagnetic layer is in contact with the source electrode and two of the detection electrodes. The top ferromagnetic layer is in contact with the drain electrode and the other two detection electrodes. The semiconductor intermediate layer is located between the bottom ferromagnetic layer and the top ferromagnetic layer and is in direct contact with both of them, but is not in direct contact with the detection electrodes.

[0028] The physical basis for the multi-resistivity storage of this invention is the tunneling magnetoresistance effect. Its working principle is that by applying an external magnetic field perpendicular to the device plane, the magnetization direction (upward or downward) of the top and bottom ferromagnetic electrodes can be independently controlled.

[0029] 1. When the magnetization directions of the two ferromagnetic electrodes are parallel (both upward or downward), the probability of electrons tunneling through the InSe barrier layer is relatively high, and the device exhibits a low tunneling resistance (low resistance state).

[0030] 2. When the magnetization directions of the two ferromagnetic electrodes are antiparallel (one upward and the other downward), the electron tunneling probability is significantly reduced, and the device exhibits high tunneling resistance (high resistance state).

[0031] 3. Obtaining the three resistance states: By measuring the voltage between the two probe electrodes on the same side, the resistance of the device exhibits a three-state switching of high resistance, intermediate resistance and low resistance under the scanning of an external magnetic field.

[0032] 4. Obtaining the four resistance states: By measuring the configuration with electrodes on opposite sides, two different antiparallel magnetization configurations (such as top layer up / bottom layer down, and top layer down / bottom layer up) can be further distinguished, thus exhibiting the switching of four states: high resistance state, medium-high resistance state, medium-low resistance state and low resistance state.

[0033] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0034] 1. Achieved a breakthrough in the number of resistance states and controllable design: For the first time, stable three- or four-resistance state storage can be achieved in a single device by simply selecting the electrode measurement configuration. This breaks through the limitation of existing two-dimensional magnetoresistive devices that can only achieve three resistance states, and provides a new path for improving storage density.

[0035] 2. Stable operation at room temperature: The device is based on Fe3GaTe2 material with a Curie temperature higher than room temperature, which enables the multi-resistivity characteristics to be maintained in a wide temperature range of 4K to 320K, and the signal amplitude to be stable, meeting the basic requirements of practical applications.

[0036] 3. Simple and controllable fabrication process with high repeatability: The standard van der Waals dry transfer technology is adopted, which completely avoids the complex "thickness modulation" or "folding modulation". The process is simple, intuitive and highly controllable, which is conducive to the large-scale and highly uniform device fabrication and solves the core problem of uncontrollable fabrication in existing technologies.

[0037] 4. The device exhibits extremely strong robustness: The multi-resistivity characteristics show excellent stability over a wide current range of 0.1 μA to 1000 μA and under different external magnetic field directions, indicating that the device has strong anti-interference capabilities and high practical value. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the overall three-dimensional structure of an embodiment of the present invention.

[0039] Figure 2This is a graph showing the antisymmetric magnetoresistive signal curves of the three-resistance state measured at different temperatures according to an embodiment of the present invention.

[0040] Figure 3 The graphs show the antisymmetric magnetoresistive signal curves of the four-resistance state obtained at different temperatures according to embodiments of the present invention.

[0041] Figure 4 This is a graph showing the antisymmetric magnetoresistive signal curves of the three-resistance state measured under fixed temperature and different injection current conditions according to an embodiment of the present invention.

[0042] Figure 5 This is a graph showing the relationship between the amplitude of the three-resistance signal and the injected current in an embodiment of the present invention.

[0043] Figure 6 This is a graph of the antisymmetric magnetoresistive signal in three states measured under a fixed current and different directions (angles) of the applied magnetic field in an embodiment of the present invention.

[0044] Figure 7 This is a graph showing the relationship between the amplitude of the three-resistance and four-resistance signals and the direction (angle) of the applied magnetic field in an embodiment of the present invention. Detailed Implementation

[0045] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] Example 1

[0047] like Figure 1 As shown in the figure, a room temperature multiresistivity magnetic memory based on Fe3GaTe2 / InSe / Fe3GaTe2 van der Waals heterojunction described in this embodiment includes: probe electrodes 1, 2, 3 and 4, source electrode 5, bottom layer Fe3GaTe2 6, middle layer InSe 7, top layer Fe3GaTe2 8, drain electrode 9, SiO2 substrate 10 and Si substrate 11;

[0048] The SiO2 substrate 10 is located above the Si substrate 11, and the two together form a SiO2 / Si substrate; the aforementioned multiple electrodes are disposed on the SiO2 / Si substrate; the bottom Fe3GaTe2 and the top Fe3GaTe2 have different thicknesses;

[0049] The bottom Fe3GaTe2 layer 6 is located above and in contact with the source electrode 5 and the probe electrodes 4 and 2. The intermediate InSe layer is located above the bottom Fe3GaTe2 layer and does not contact the probe electrodes 1, 2, 3, and 4. The top Fe3GaTe2 layer 8 is located above the intermediate InSe layer. The top Fe3GaTe2 layer, the intermediate InSe layer, and the bottom Fe3GaTe2 layer have overlapping areas, but the top Fe3GaTe2 layer is not in direct contact with the bottom Fe3GaTe2 layer. The top Fe3GaTe2 layer is in direct contact with the drain electrode 9 and the probe electrodes 1 and 3. All the probe electrodes, source electrodes, drain electrodes, Fe3GaTe2 layer, and InSe layer are located above the SiO2 substrate 10.

[0050] Example 2

[0051] This embodiment details the fabrication process of a room-temperature multiresistivity magnetic memory based on a Fe3GaTe2 / InSe / Fe3GaTe2 van der Waals heterojunction.

[0052] 1. Substrate pretreatment

[0053] A silicon wafer (SiO2 / Si) with a 285 nm thick silicon dioxide layer thermally grown on its surface was selected as the substrate. It was then placed in a reactive ion etching (RIE) machine for oxygen plasma cleaning to thoroughly remove surface organic contaminants. The process parameters were: oxygen flow rate 20 sccm, RF power 18 W, and processing time 3 minutes. This step is crucial for obtaining a clean surface and ensuring the quality of the interface for subsequent material transfer.

[0054] 2. Electrode preparation (electrode preparation)

[0055] PMMA 495 A4 electron beam photoresist was spin-coated onto a clean substrate. The spin-coating parameters were: spin speed 3000 rpm, spin time 50 s, acceleration 500 rpm / s; followed by baking on a 180°C hot plate for 2 minutes to completely remove the solvent. Next, electron beam lithography was used for exposure, followed by development with a solution of methyl isobutyl ketone and isopropanol (MIBK:IPA = 1:3) to form the desired electrode pattern (including source, drain, and probe electrodes). Subsequently, the substrate was subjected to ultra-high vacuum (reference vacuum level better than 1×10⁻⁶). -6 Under Torr conditions, a 5 nm thick titanium (Ti) adhesion layer (rate 0.8 Å / s) and a 50 nm thick gold (Au) conductive layer (rate 0.5 Å / s) were sequentially deposited using electron beam evaporation. Finally, the electrodes were stripped with acetone and ultrasonically cleaned in isopropanol to obtain a patterned and clean Ti / Au metal electrode.

[0056] 3. Dry sequential transfer (post-transfer) of van der Waals heterojunctions

[0057] This is a key step in building the core functional structure:

[0058] 3.1 Preparation and Transfer of the Substrate Ferromagnetic Electrode (b-Fe3GaTe2): First, a thin-layer sample was obtained from the Fe3GaTe2 bulk material using a mechanical exfoliation method. Specifically, blue adhesive tape was repeatedly folded and thinned, then pressed onto a pre-fabricated polydimethylsiloxane (PDMS) elastic film. After rapid peeling, the thin Fe3GaTe2 layer remained on the PDMS. Thin sheets of suitable thickness and area were identified under an optical microscope. Then, using a high-precision dry transfer system, the b-Fe3GaTe2 sheet on the PDMS was precisely aligned and brought into contact with the predetermined electrode position on the substrate. After slow lifting, the b-Fe3GaTe2 was adsorbed to the electrode surface by van der Waals forces.

[0059] 3.2 Transfer of the semiconductor barrier layer (InSe): Using the same mechanical stripping and dry transfer techniques, the thin InSe semiconductor layer is precisely transferred onto the already in place b-Fe3GaTe2, covering part of its area.

[0060] 3.3 Transfer of the top ferromagnetic electrode (t-Fe3GaTe2): Another thin layer of Fe3GaTe2 is transferred onto InSe, ensuring that it partially overlaps with the underlying b-Fe3GaTe2 region, thus ultimately forming a complete b-Fe3GaTe2 / InSe / t-Fe3GaTe2 sandwich heterojunction structure.

[0061] 4. Device packaging and annealing

[0062] Finally, a large-area thin film of hexagonal boron nitride (hBN) is transferred to completely cover the constructed heterojunction region for encapsulation and protection against environmental degradation. The fabricated device is then subjected to a vacuum level higher than 1×10⁻⁶. -5 Annealing at 200°C for 3 hours under Torr conditions. This process effectively removes interfacial residues, enhances van der Waals interactions between layers, and optimizes ohmic contacts.

[0063] The multi-resistivity properties of the devices fabricated using the above method were characterized by electrical measurements, see [link to documentation]. Figures 2-7 .

[0064] 1. Multiresistivity behavior

[0065] A scanning magnetic field perpendicular to the plane was applied to the device over a wide temperature range (4K to 320K), and the nonlocal voltage was measured. When a same-side probe electrode configuration was used, the resistance exhibited a clear switching between high, medium, and low resistance states as the magnetic field changed, and the signal remained stable in amplitude and had good repeatability at room temperature.

[0066] When using a cross-probe electrode configuration, the antisymmetric magnetoresistive signals of four resistance states—high, medium-high, medium-low, and low—can be further distinguished. This result fully demonstrates the breakthrough of this invention in terms of the number of resistance states.

[0067] 2. Stability of operating current range

[0068] Tests show that when the injected current varies over a wide range from 0.1 μA to 1000 μA, the amplitude of the device's three-resistance signal remains highly stable, demonstrating excellent electrical robustness and meeting the requirements of practical circuit driving.

[0069] 3. Magnetic field angle dependence

[0070] The device is insensitive to the direction of the external magnetic field. When the direction of the magnetic field changes within the range of 0° to 360° relative to the plane normal (except for the direction parallel to the plane), the amplitude of the multi-resistance signal changes very little, indicating that the device has perpendicular magnetic anisotropy, is easy to control, and has strong anti-interference ability.

[0071] In summary, this specific embodiment fully demonstrates the effectiveness and superiority of the solution provided by the present invention in realizing high-performance, high-reliability multi-resistance magnetic memory.

Claims

1. A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction, characterized in that, include: Substrate; Multiple electrodes disposed on the substrate, the electrodes including a source electrode, a drain electrode and multiple probe electrodes; The device also includes a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction structure located on the electrode. The ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction structure comprises a bottom ferromagnetic layer, a semiconductor intermediate layer, and a top ferromagnetic layer stacked sequentially. The bottom and top ferromagnetic layers are both made of room-temperature van der Waals ferromagnetic materials with perpendicular magnetic anisotropy, and the semiconductor intermediate layer is made of two-dimensional van der Waals semiconductor material. By applying an external magnetic field perpendicular to the device plane, the relative state of the magnetization directions of the bottom and top ferromagnetic layers is controlled, so that the device exhibits multiple non-volatile resistive states under the measurement of the probe electrode, and these multiple non-volatile resistive states are maintained at a temperature of 320K.

2. The room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in claim 1, characterized in that: The room-temperature van der Waals ferromagnetic material is Fe3GaTe2.

3. The room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in claim 1, characterized in that: The two-dimensional van der Waals semiconductor material is InSe.

4. The room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in claim 1, characterized in that: The detection electrode includes two detection electrodes located on the same side of the heterojunction structure. When measurement is performed through the two detection electrodes on the same side, the device exhibits three resistance states: high, medium, and low, depending on the change of the external magnetic field.

5. A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in claim 1, characterized in that: The detection electrode includes four detection electrodes located on opposite sides of the heterojunction structure, forming a cross-measurement configuration; when cross-measurement is performed through the detection electrodes on opposite sides, the device exhibits four resistance states: high, medium-high, medium-low, and low, depending on the change of the external magnetic field.

6. A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in any one of claims 1 to 5, characterized in that: The signal amplitude of the multi-resistivity characteristic remains stable in the temperature range of 4K to 320K.

7. A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in any one of claims 1 to 5, characterized in that: When the applied injection current varies in the range of 0.1μA to 1000μA, the signal amplitude of the multi-resistivity characteristic remains stable.

8. A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in any one of claims 1 to 5, characterized in that: When the direction of the external magnetic field varies from 0° to 360° relative to the normal of the device plane, the signal amplitude of the multi-resistivity characteristic remains stable.

9. A room-temperature multiresistivity magnetic memory based on a ferromagnetic / semiconductor / ferromagnetic van der Waals heterojunction as described in any one of claims 1 to 5, characterized in that: It also includes an encapsulation layer covering the heterojunction structure, wherein the encapsulation layer is hexagonal boron nitride.

10. A method for preparing the magnetic storage device according to any one of claims 1 to 9, characterized in that, Includes the following steps: 1) Clean the substrate; 2) The source electrode, drain electrode, and probe electrode are formed on the cleaned substrate by photolithography and metal deposition processes; 3) By mechanical stripping and van der Waals transfer technology, the bottom ferromagnetic layer, the semiconductor intermediate layer and the top ferromagnetic layer are sequentially aligned and transferred to the electrode to form a sandwich heterojunction structure, wherein the bottom ferromagnetic layer is in contact with the source electrode and part of the probe electrode, the top ferromagnetic layer is in contact with the drain electrode and the remaining probe electrode, and the semiconductor intermediate layer is sandwiched between the two ferromagnetic layers. 4) The transfer encapsulation layer covers the heterojunction structure; 5) Anneal the device to enhance the interfacial bonding of the heterojunction.

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