Spin-orbit torque magnetic storage unit and preparation method thereof

Abstract

The invention provides a spin-orbit torque magnetic storage unit and a preparation method thereof. The preparation method comprises the following steps: preparing a bottom electrode with at least one electrode on a substrate; transferring a magnetic Van der Waals material onto the bottom electrode to form a magnetic layer covering and in direct contact with at least a portion of each of the at least one electrode of the bottom electrode; a Van der Waals spin current material is transferred onto the magnetic layer to form a spin current layer, the spin current layer completely covering the magnetic layer, and an area of the spin current layer is larger than an area of the magnetic layer such that the spin current layer is in contact with at least a portion of each of the at least one electrode of the bottom electrode. According to the scheme, damage to the magnetic material and the self-swirling flow material caused by high-temperature heating and oxygen contact can be avoided, so that the performance of the device is improved, the working current density of the magnetic storage unit is reduced, and the efficiency of the magnetic storage unit is improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductors, specifically relating to a spin-orbit torque magnetic storage cell and its fabrication method. Background Technology

[0002] Spintronics utilizes the new degree of freedom of electron spin to construct novel device systems that surpass traditional charge-based micro / nanoelectronic devices. Among these, magnetic memories based on spin-orbit torque (SOT) have become a hot research topic in recent years due to their advantages of low power consumption, fast read / write speeds, and high durability. SOT magnetic memories are typically composed of stacked spin-current materials and magnetic materials. The magnetic moment of the magnetic material is manipulated by the spin current generated by the spin-current material to achieve information storage.

[0003] However, existing SOT magnetic memory requires more than 10 6 A / cm 2 The high operating current density and device efficiency ε below 1 of SOT magnetic memory devices significantly limit their practical applications. This problem stems from limitations inherent in the materials themselves, as well as defects in device design and fabrication processes. Therefore, there is an urgent need to develop a SOT magnetic memory device with low operating current density and high device efficiency. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a spin-orbit torque magnetic storage cell and its preparation method to overcome or at least partially solve the above problems.

[0005] One objective of this invention is to provide a method for fabricating a spin-orbit torque magnetic storage cell, which can avoid damage to the magnetic material and the self-spinning material caused by high-temperature heating and oxygen contact, thereby improving device performance, reducing the operating current density of the magnetic storage cell, and increasing the efficiency of the magnetic storage cell.

[0006] A further objective of this invention is to reduce the damage to magnetic material samples during the residual adhesive cleaning process, thereby improving the quality of the contact surface between the magnetic layer and the spin flow layer.

[0007] Another object of the present invention is to provide a spin-orbit torque magnetic storage cell prepared by the aforementioned preparation method, which has low operating current density and high device efficiency.

[0008] In particular, according to one aspect of the present invention, a method for fabricating a spin-orbit torque magnetic storage cell is provided, comprising:

[0009] A bottom electrode having at least one electrode is fabricated on a substrate;

[0010] Magnetic van der Waals material is transferred onto the bottom electrode to form a magnetic layer that covers and is in direct contact with at least a portion of each of the bottom electrodes.

[0011] A van der Waals spin flow material is transferred onto a magnetic layer to form a spin flow layer that completely covers the magnetic layer and has an area larger than that of the magnetic layer, such that the spin flow layer is in contact with at least a portion of each of at least one of the electrodes of the bottom electrode.

[0012] Optionally, the step of transferring the magnetic van der Waals material onto the bottom electrode includes:

[0013] Magnetic van der Waals materials were cleaved using adhesive tape and transfer medium to obtain magnetic van der Waals material samples with the required thickness and dimensions.

[0014] Transfer the magnetic van der Waals material sample on the transfer medium to the bottom electrode;

[0015] The transfer medium, which is a polydimethylsiloxane membrane, is peeled off without heating.

[0016] Optionally, after the magnetic layer is formed and before the van der Waals spin flow material is transferred onto the magnetic layer, the preparation method further includes:

[0017] The substrate with the magnetic layer was sequentially immersed in a first organic solvent and a second organic solvent after deoxidation for cleaning.

[0018] The first organic solvent is acetone, and the second organic solvent is propylene glycol.

[0019] The first and second organic solvents are deoxygenated in the following manner:

[0020] Place the first and second organic solvents in an oxygen-free environment for at least 24 hours.

[0021] Alternatively, the magnetic van der Waals material is a van der Waals ferromagnet with room temperature out-of-plane magnetization.

[0022] Alternatively, the van der Waals ferromagnet is Fe3GaTe2.

[0023] Optionally, the van der Waals spin flow material is a van der Waals metal with out-of-plane component spin electron flow.

[0024] Optionally, the van der Waals metal is WTe2.

[0025] Optionally, the step of transferring van der Waals spin flow material onto a magnetic layer to form a spin flow layer includes:

[0026] By using adhesive tape and transfer medium to cleave van der Waals spin flow materials, spin flow material samples with the required thickness and dimensions were obtained.

[0027] Transferring a spin-flow material sample from the transfer medium to a magnetic layer;

[0028] The transfer medium, which is a polydimethylsiloxane membrane, is peeled off without heating.

[0029] Optionally, the preparation method further includes:

[0030] An insulating layer is transferred onto the spin flow layer to form an encapsulated insulating layer that completely covers the magnetic layer and the spin flow layer.

[0031] The insulating layered material is hexagonal boron nitride (hBN).

[0032] According to another aspect of the present invention, a spin-orbit torque magnetic storage cell is also provided, comprising:

[0033] A bottom electrode having at least one electrode formed on a substrate;

[0034] A magnetic layer disposed on the bottom electrode and covering at least a portion of each of at least one electrode of the bottom electrode and in direct contact therewith; and

[0035] A spin flow layer is disposed on the magnetic layer, the spin flow layer completely covers the magnetic layer, and the area of ​​the spin flow layer is larger than the area of ​​the magnetic layer, such that the spin flow layer is in contact with at least a portion of each of at least one electrode of the bottom electrode.

[0036] The bottom electrode, magnetic layer, and spin flow layer are prepared using the aforementioned preparation method.

[0037] Optionally, the spin-orbit torque magnetic storage unit further includes:

[0038] An encapsulation insulating layer is disposed on the spin flow layer and completely covers the magnetic layer and the spin flow layer;

[0039] The encapsulation insulating layer is prepared by the following method:

[0040] An insulating layered material is transferred onto a spin flow layer to form an encapsulated insulating layer. The insulating layered material is hexagonal boron nitride (hBN).

[0041] The method for fabricating a spin-orbit torque magnetic storage cell and the corresponding device provided by this invention employ a bottom electrode process. By first fabricating the bottom electrode on the substrate and then stacking the magnetic material and spin-current material, damage to the magnetic material and spin-current material caused by high-temperature heating and oxygen contact, as is done with the top electrode method, is avoided, thereby improving the performance of the device. Specifically, the spin-orbit torque magnetic storage cell exhibits a significant anomalous Hall signal, sharp Hall resistance changes, and a small coercive field.

[0042] Meanwhile, by first stacking the magnetic layer on the bottom electrode to make direct contact between the magnetic layer and the bottom electrode, and then stacking a spin current layer that can completely cover the magnetic layer on the magnetic layer, and the spin current layer also making contact with all electrodes of the bottom electrode, the influence of the interface contact resistance between the magnetic layer and the spin current layer on the device signal measurement is reduced, resulting in a high signal-to-noise ratio and good Hall signal quality for the obtained spin-orbit torque magnetic storage cell.

[0043] Furthermore, by sequentially immersing and cleaning the interface between the magnetic layer and the spin flow layer with a first organic solvent and a second organic solvent (specifically, acetone with low oxygen content and isopropanol with low oxygen content), residual adhesive can be effectively removed with less damage to the sample. This results in a spin-orbit torque magnetic storage cell with a lower flip current density, higher device efficiency, and a higher signal-to-noise ratio.

[0044] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below.

[0045] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0046] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0047] Figure 1 This is a schematic diagram of the structure of a spin-orbit torque magnetic storage cell according to an embodiment of the present invention;

[0048] Figure 2 This is a schematic flowchart of a method for fabricating a spin-orbit torque magnetic storage cell according to an embodiment of the present invention;

[0049] Figure 3 This is a schematic flowchart of a method for fabricating a spin-orbit torque magnetic storage cell according to another embodiment of the present invention;

[0050] Figure 4 This is a schematic diagram of the fabrication process of the spin-orbit torque magnetic storage unit in Example 1;

[0051] Figure 5This is a schematic diagram of the fabrication process of the spin-orbit torque magnetic storage unit in Example 1;

[0052] Figure 6 This is a schematic structural design diagram of electron beam exposure in Example 1;

[0053] Figure 7 This is a schematic diagram of the fabrication process of the spin-orbit torque magnetic storage cell in Comparative Example 1.

[0054] Figure 8 This is a schematic diagram of the fabrication process of the spin-orbit torque magnetic storage cell in Comparative Example 2.

[0055] Figure 9 This is a schematic diagram of the measuring device for the spin-orbit torque magnetic storage unit used in this invention.

[0056] Figure 10a and Figure 10b The anomalous Hall signal measurement results of the spin-orbit torque magnetic storage cells prepared in Example 1 and Comparative Example 2 are respectively.

[0057] Figure 11a and Figure 11b The anomalous Hall signal measurement results of the spin-orbit torque magnetic storage cells prepared in Example 1 and Comparative Example 3 are respectively.

[0058] Figure 12a and Figure 12b The graphs show the dependence of the anomalous Hall resistance of the spin-orbit torque magnetic storage cells prepared in Example 1 and Comparative Example 1 on the magnitude and direction of the pulse current, respectively.

[0059] Figure 13a The anomalous Hall resistor of the spin-orbit torque magnetic storage cell in Example 1 The graph shows the relationship between the amplitude and direction of the pulse current, where the initial state of the spin-orbit torque magnetic storage cell is...

[0060] Figure 13b The anomalous Hall resistor of the spin-orbit torque magnetic storage cell in Example 1 The graph shows the relationship between the amplitude and direction of the pulse current, where the initial state of the spin-orbit torque magnetic storage cell is... Detailed Implementation

[0061] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0062] In recent years, the rise of two-dimensional materials research has provided ideal materials for the selection of spin current materials and magnetic materials. The transition from heavy metals to topological insulators has significantly improved spin current efficiency, while the transition from three-dimensional lattice magnetic materials to layered van der Waals materials has effectively reduced the volume of memory cells and significantly lowered interfacial contact resistance. In terms of information readout, there has been an evolution from high-power readout methods that measure tunneling resistance to low-power readout methods that measure anomalous Hall signals.

[0063] Furthermore, the inventors discovered that if the magnetic material of the SOT device has out-of-plane ferromagnetism at room temperature and the spin electrons of the spin current material have out-of-plane spin components, then an SOT magnetic memory that operates at room temperature and under no magnetic field conditions can be fabricated, which has broad application prospects.

[0064] Typically, the stacked structure of SOT magnetic storage cells from bottom to top is a metallic magnetic layer / spin flow layer / measuring electrode. The magnetic layer stores bit information through the magnetization direction. The large pulse current flowing through the spin flow layer accumulates spin-polarized charge at the interface of the magnetic layer / spin flow layer. This spin-polarized charge couples with the magnetic moment of the magnetic layer to generate spin-orbit torque (SOT), which flips the direction of the magnetic moment, achieving the effect of current controlling the magnetic storage cell through spin.

[0065] However, the stacked structure of SOT magnetic memory cells—metallic magnetic layer / spin flow layer / measurement electrode—usually has defects in actual fabrication.

[0066] First, the measuring electrode is located above the magnetic layer and the spin flow layer. Before fabricating the electrode, the magnetic material and the spin flow material need to be stacked on the substrate. Then, processes such as spin coating, exposure, development and coating are performed to fabricate the electrode. These electrode fabrication processes usually require high temperature heating (e.g., baking the adhesive at 120 degrees Celsius, electron beam coating thermal radiation) and contact with oxygen (even in a nitrogen environment, the developing solution contains dissolved oxygen). These processes can damage the magnetic material and spin flow material already on the substrate, such as causing lattice defects and oxide material surfaces due to high temperature.

[0067] Secondly, typical metal magnetic layer / spin flux layer / measuring electrode structures do not directly contact the metal magnetic layer and the measuring electrode. Although theoretically the metallicity of the spin flux layer allows the anomalous Hall signal of the metal magnetic layer to be detected by the electrode, there is usually contact resistance in the metal magnetic layer / spin flux layer. This contact resistance reduces the magnitude of the measured Hall signal, exacerbates measurement noise, and may even render the electrode unable to detect the Hall signal at all. After repeated use, the large pulse current inevitably damages the metal magnetic layer / spin flux layer interface, increasing its contact resistance. The Hall signal of devices with this metal magnetic layer / spin flux layer / measuring electrode structure will further deteriorate after repeated use.

[0068] Finally, the quality of the contact surface between the magnetic layer and the spin flux layer directly determines the operating efficiency of the SOT magnetic memory cell. This is because spin-polarized spin electrons need to pass through this contact surface to enter the magnetic layer, thereby completing the SOT flipping. However, the transfer process requires using an adhesive (such as PDMS, PC, etc.) to hold the magnetic material, inverting the material onto the electrode, and then using the fact that the van der Waals force of the substrate on the material is greater than the adhesion force of the adhesive to peel the adhesive off the material. After the transfer, in most cases, there will be residual adhesive on the upper surface of the magnetic material. This upper surface is the contact surface between the magnetic layer and the spin flux layer, and the residual adhesive will greatly affect the performance of the device. Usually, after the transfer, the upper surface of the sample is "gently rubbed" with rare gas ions (such as Ar ions). However, this "gentle rubbing" cannot guarantee that the residual adhesive is completely removed, and excessive power can damage the sample.

[0069] Based on the above, this invention provides a spin-orbit torque (SOT) magnetic storage cell and its fabrication method. This SOT magnetic storage cell can be read by measuring Hall signals. Through novel design and fabrication of the SOT magnetic storage cell, this invention optimizes the contact between the spin current and the magnetic layer, and reduces damage to the sample during fabrication.

[0070] Figure 1 This is a schematic diagram of the structure of a spin-orbit torque magnetic storage unit 100 according to an embodiment of the present invention. See also... Figure 1 As shown, the spin-orbit torque magnetic storage unit 100 of the present invention includes: a substrate 110; a bottom electrode 120 having at least one electrode formed on the substrate 110; a magnetic layer 130 disposed on the bottom electrode 120 and covering at least a portion of each of the at least one electrode of the bottom electrode 120 and in direct contact therewith; and a spin flow layer 140 disposed on the magnetic layer 130, the spin flow layer 140 completely covering the magnetic layer 130, and the area of ​​the spin flow layer 140 being larger than the area of ​​the magnetic layer 130, such that the spin flow layer 140 is in contact with at least a portion of each of the at least one electrode of the bottom electrode 120.

[0071] The spin-orbit torque magnetic storage unit 100 in this embodiment is fabricated using a bottom electrode 120 process. By first fabricating the bottom electrode 120 on the substrate 110, and then sequentially stacking magnetic materials and spin flow materials on it, the damage to the magnetic materials and spin flow materials caused by high-temperature heating and oxygen contact caused by the top electrode method is avoided, thereby improving the performance of the device.

[0072] Meanwhile, since the magnetic layer 130 is first stacked on the bottom electrode 120 and in direct contact with the bottom electrode 120, and the spin flow layer 140 is stacked on the magnetic layer 130 and completely covers the magnetic layer 130, and the spin flow layer 140 is also in contact with all electrodes of the bottom electrode 120, the influence of the interface contact resistance between the magnetic layer 130 and the spin flow layer 140 on the device signal measurement is reduced, resulting in a high signal-to-noise ratio and good Hall signal quality in the obtained spin-orbit torque magnetic storage unit 100.

[0073] In some embodiments, the spin-orbit torque magnetic storage cell 100 may further include an encapsulation insulating layer 150 disposed on the spin flow layer 140 and completely covering the magnetic layer 130 and the spin flow layer 140. The encapsulation insulating layer 150 may be prepared by transferring an insulating layered material onto the spin flow layer 140 to form the encapsulation insulating layer 150. The encapsulation insulating layer 150 prevents air damage to the material after the spin-orbit torque magnetic storage cell 100 is removed from the fabrication setup.

[0074] The preparation method of the spin-orbit torque magnetic storage unit 100 of the present invention will be described below.

[0075] Figure 2 This is a schematic flowchart illustrating a method for fabricating a spin-orbit torque magnetic storage unit 100 according to an embodiment of the present invention. See also... Figure 2 As shown, the method for preparing the spin-orbit torque magnetic storage unit 100 of the present invention includes at least the following steps S202 to S206:

[0076] Step S202: A bottom electrode 120 having at least one electrode is fabricated on the substrate 110.

[0077] Step S204: Transfer magnetic van der Waals material onto bottom electrode 120 to form a magnetic layer 130 that covers and is in direct contact with at least a portion of each of at least one of the electrodes of bottom electrode 120.

[0078] In step S206, van der Waals spin flow material is transferred onto magnetic layer 130 to form spin flow layer 140, which completely covers magnetic layer 130 and has an area larger than that of magnetic layer 130, such that spin flow layer 140 contacts at least a portion of each of at least one electrode of bottom electrode 120.

[0079] In the fabrication method of this embodiment, a bottom electrode 120 process is used. First, the electrode is fabricated on the substrate 110, and then magnetic materials and spin-flow materials are stacked. This method places the stacking operation of easily damaged materials at the end of the device fabrication process, and can be carried out in an oxygen-free environment (e.g., stacking materials in a nitrogen atmosphere), effectively avoiding damage to the magnetic materials and spin-flow materials during the electrode fabrication process.

[0080] Simultaneously, the magnetic metal layer 130 is first stacked on the bottom electrode 120, followed by the spin current layer 140. This direct contact between the magnetic layer 130 and the electrode effectively avoids the influence of the contact between the magnetic layer 130 and the spin current layer 140 on the measurement signal, significantly improving the signal-to-noise ratio and effectively extending the device's lifespan. Since the spin current layer 140 is responsible for controlling the magnetic layer 130, and a large current also flows through it, to avoid the influence of the magnetic layer 130 / spin current layer 140 contact on the spin current layer 140, and to achieve complete control over the magnetic layer 130, the spin current layer 140 is made larger than the magnetic layer 130, completely covering it, and has areas that directly contact all electrodes. This design minimizes the impact of interface contact resistance on device performance.

[0081] In step S202, the bottom electrode 120 can be fabricated using micro / nano fabrication techniques. The substrate 110 can be a commonly used semiconductor substrate, such as a Si / SiO2 substrate.

[0082] In some embodiments, step S204 may specifically include: first, using tape and transfer medium to cleave the magnetic van der Waals material to obtain a magnetic van der Waals material sample with the required thickness and size; then, transferring the magnetic van der Waals material sample on the transfer medium to the bottom electrode 120; and finally, peeling off the transfer medium without heating.

[0083] Specifically, the magnetic van der Waals material is repeatedly cleaved using tape and a transfer medium until a sample of suitable thickness and size is obtained, and the location of the suitable sample is marked. Then, the suitable sample on the transfer medium is transferred to the bottom electrode 120 using a transfer stage.

[0084] Optionally, the pre-prepared bottom electrode 120 can be cleaned before transferring the magnetic van der Waals material, for example, by cleaning the bottom electrode 120 with Ar ions.

[0085] The transfer medium can be a commonly used transfer medium membrane, such as a polydimethylsiloxane (PDMS) membrane or a polycarbonate membrane. In a specific embodiment, the transfer medium is a polydimethylsiloxane membrane.

[0086] In some embodiments, the magnetic van der Waals material used is a van der Waals ferromagnet with room temperature out-of-plane magnetization. Specifically, the van der Waals ferromagnet may be Fe3GaTe2.

[0087] Step S206 can employ the same transfer method as for magnetic van der Waals materials. In some embodiments, step S206 may specifically include: first, cleaving the van der Waals spin flow material using tape and a transfer medium to obtain a spin flow material sample with the required thickness and dimensions; then, transferring the spin flow material sample on the transfer medium onto the magnetic layer 130; and finally, peeling off the transfer medium without heating.

[0088] Specifically, the van der Waals spinflow material is repeatedly cleaved using adhesive tape and a transfer medium until a sample of suitable thickness and size is obtained, and the location of the suitable sample is marked. Then, the suitable sample on the transfer medium is transferred to the magnetic layer 130 using a transfer stage. The adhesive tape and transfer medium used for transferring the spinflow material can be the same as those used for the magnetic van der Waals material.

[0089] In some embodiments, the van der Waals spin-flow material used is a van der Waals metal with out-of-plane spin electron flow. Specifically, the van der Waals metal may be WTe2.

[0090] Figure 3 This is a schematic flowchart illustrating a method for fabricating a spin-orbit torque magnetic storage unit 100 according to another embodiment of the present invention.

[0091] See Figure 3 As shown, the method for preparing the spin-orbit torque magnetic storage unit 100 of the present invention may further include step S205:

[0092] After the magnetic layer 130 is formed and before the van der Waals spin flow material is transferred onto the magnetic layer 130, the substrate 110 with the magnetic layer 130 is sequentially immersed in a first organic solvent and a second organic solvent after deoxidation for cleaning.

[0093] In this embodiment, the interface between the magnetic layer 130 and the spin flow layer 140 is cleaned by sequentially soaking in a first organic solvent and a second organic solvent to remove residual adhesive with minimal damage to the sample. This results in a spin-orbit torque magnetic storage unit 100 with a lower flip current density, higher device efficiency, and a higher signal-to-noise ratio.

[0094] In one specific embodiment, the first organic solvent is acetone and the second organic solvent is propylene glycol.

[0095] Soaking time should be sufficient to remove residual adhesive. For example, soaking time can be 3 minutes or more.

[0096] In some alternative embodiments, the first organic solvent and the second organic solvent can be deoxygenated by placing the first organic solvent and the second organic solvent in an oxygen-free environment for at least 24 hours.

[0097] See also Figure 3 As shown, the method for preparing the spin-orbit torque magnetic storage unit 100 of the present invention may further include step S208: transferring an insulating layer material onto the spin flow layer 140 to form an encapsulation insulating layer 150, wherein the encapsulation insulating layer 150 completely covers the magnetic layer 130 and the spin flow layer 140.

[0098] Step S208 can employ the same transfer method as for magnetic van der Waals materials. The insulating layered material can be hexagonal boron nitride (hBN).

[0099] The above introduces Figure 2 and Figure 3 The embodiments shown have various implementation methods for each step. The following will describe in detail the preparation method of the spin-orbit torque magnetic storage unit 100 of the present invention and the performance improvement of the corresponding device through specific embodiments.

[0100] The reagents and instruments used in the following examples are as follows:

[0101] PMMA 950A4 adhesive and MIBK (1:3) were purchased from MicroChem; acetone and isopropanol were purchased from Sinopharm Group; PDMS was purchased from Gelpak; and cleavage tape was purchased from 3M.

[0102] The following equipment was purchased: a desktop spin coater (MODEL KW-4A) from Xinyouyan Electronic Technology (China) Co., Ltd.; an electron beam exposure system (Raith150) from Raith; a transfer stage (E1-M) from Metatronics; a wire bonding machine (7476D) from West Bond; a lock-in amplifier (LI5650) from NF Corporation, Japan; a DC power supply meter (Keithley2612B) from Keithley Instruments, USA; a 1.5K magneto-optical system from Oxford Instruments; a magnet power supply (MercuryIPS120A) from Oxford Instruments; and a temperature measurement and control system (Lakeshore350) from Lakeshore.

[0103] Example 1

[0104] Example 1 illustrates the preparation method of the SOT magnetic storage cell 100 of the present invention. Figure 4 This is a schematic diagram of the fabrication process of the spin-orbit torque magnetic storage unit 100 in Example 1. Figure 5 This is a schematic diagram illustrating the fabrication process of the spin-orbit torque magnetic storage unit 100 in Example 1. See also... Figure 4 and Figure 5 As shown, the preparation method includes the following steps.

[0105] 1. Preparation of bottom electrode 120

[0106] The fabrication steps for the bottom electrode 120 include:

[0107] (1) Coating: MicroChem's PMMA 950A4 adhesive was used to evenly coat the Si / SiO2 substrate 110 with a marked array (the array consists of 1μm wide cross marks, each 100μm apart, for a total of 40×40 marks) using a benchtop spin coater at 4000rpm for 1 minute. Then, it was baked on a hot plate at 120℃ for 1 minute.

[0108] (2) Electrode design drawings were created using CAD and imported into the Raith 150 system for electrode exposure. The aperture was 10 μm for the small electrode area and 120 μm for the large electrode area. The voltage was 20 kV for both areas, and the surface exposure dose was 100 μA / cm². 2 Develop using MIBK (1:3) for 1 minute and 30 seconds.

[0109] (3) Electron beam coating was used to deposit the following films sequentially: a 4 nm titanium (Ti) film and a 13 nm gold (Au) film. The resist was then removed by soaking the substrate in acetone for 6 hours, followed by blowing the substrate with a nitrogen gun to remove any remaining resist. Finally, the sample was cleaned with isopropanol.

[0110] (4) Repeat (1) coating, repeat (2) but do not expose the small electrode, the morphology and exposure position of the large electrode are the same as (2), repeat (3) but only plate a 40nm gold (Au) film.

[0111] Figure 6 This is a schematic structural design diagram of electron beam exposure in Embodiment 1, showing the design layout of the small and large electrodes. Measuring the out-of-plane magnetization direction of the magnetic layer 130 of the SOT magnetic memory cell 100 is accomplished by measuring the anomalous Hall signal generated by the magnetic layer 130. The out-of-plane upward (downward) magnetization direction of the magnetic layer 130 is determined by measuring the positive (negative) voltage signal of the anomalous Hall voltage. This requires the device to have source / drain electrodes providing a small current and measurement electrodes (read lines) for measuring the Hall signal. To provide a large pulse current to regulate the magnetic layer 130 of the memory cell, additional source / drain electrodes (write lines) are needed. Therefore, at least six electrodes are required in this embodiment.

[0112] 2. Transferring magnetic materials and spin-flow materials to fabricate SOT magnetic memory cells 100

[0113] All the following operations were performed in a glove box filled with nitrogen (O2 concentration <0.01ppm, H2O concentration <0.01ppm).

[0114] (1) 24 hours before the transfer, place the beaker containing acetone and the beaker containing isopropanol in a glove box filled with nitrogen (O2 concentration <0.01ppm, H2O concentration <0.01ppm) to deoxygenate and reduce the dissolved oxygen content of acetone and isopropanol.

[0115] (2) Take two pieces of 3M cleaving tape, place the Fe3GaTe2 sample of magnetic layer 130 material on one piece of tape, and stick the other piece of tape on the tape with the sample, then tear them apart, and repeat the cleaving process until the Fe3GaTe2 sample covers a large area of ​​the tape.

[0116] (3) Cut a brand new PDMS film and place the sticky side of the PDMS film onto the tape covering the sample (note that this side can only touch the tape once, otherwise it will contaminate the sample surface). Press the PDMS film lightly and then peel it off. Use an optical microscope to find a sample with appropriate thickness and size and mark the position of the appropriate sample.

[0117] (4) Clean the bottom electrode 120 prepared in step 1 with Ar ions. Use a transfer stage to transfer the appropriate Fe3GaTe2 sample on the PDMS film onto the bottom electrode 120, ensuring that the Fe3GaTe2 sample can contact all electrodes. After the sample contacts the electrodes, slowly peel off the PDMS film without heating.

[0118] (5) Immerse the substrate 110 after the magnetic material has been transferred in acetone in (1) for 3 minutes, then take out the substrate 110 and immerse it in isopropanol in (1) for 3 minutes. After taking out the substrate 110, blow the isopropanol on the substrate 110 dry with nitrogen.

[0119] (6) Use the methods of (2)(3)(4) to cleave and transfer the spin flow material WTe2 onto the magnetic layer 130, ensuring that the spin flow layer 140 completely covers the magnetic layer 130 and that the spin flow layer 140 is in contact with all electrodes.

[0120] (7) The insulating layered material hBN is cleaved and transferred using the methods in (2), (3), and (4). hBN is used to encapsulate the device and prevent air damage to the material after the device is removed. During the transfer, hBN completely covers the magnetic layer 130 and the spin flow layer 140.

[0121] (8) Take out the glove box, use the WestBond bonding machine to connect the prepared SOT magnetic storage unit 100 to the measurement sample holder, and put it into the measurement device.

[0122] Comparative Example 1

[0123] Figure 7 This is a schematic diagram of the fabrication process for the spin-orbit torque magnetic storage cell in Comparative Example 1. (Reference) Figure 7 As shown, Comparative Example 1 also uses the bottom electrode method and is prepared according to the bottom electrode / magnetic layer / spin flow layer structure. The only difference between Comparative Example 1 and Example 1 is that the substrate after the magnetic layer was transferred was not cleaned using an oxygen-free acetone treatment process.

[0124] Comparative Example 2

[0125] Figure 8 This is a schematic diagram of the fabrication process for the spin-orbit torque magnetic storage cell in Comparative Example 2. (Reference) Figure 8 As shown, the only difference between Comparative Example 2 and Example 1 is that the SOT magnetic memory cell is prepared using the existing top electrode method.

[0126] Comparative Example 3

[0127] The only difference between Comparative Example 3 and Example 1 is that the spin-orbit torque magnetic storage cell is prepared according to the structure of bottom electrode / spin flow layer / magnetic layer, wherein the magnetic layer does not directly contact the bottom electrode.

[0128] Figure 9 A schematic diagram of the measuring device for the spin-orbit torque magnetic storage cell used in this invention is shown.

[0129] pass Figure 9 The measuring device shown was used to perform performance tests on the SOT magnetic memory cells prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. The specific measurement operations are as follows:

[0130] (1) The prepared SOT device sample was placed in a 1.5K magneto-optical dewar measuring instrument. This instrument can apply a magnetic field of up to 10T within a temperature range of 1.5K-300K. The temperature was provided by a Lakeshore 350 temperature controller and a Cernox thermometer from Lakeshore Instruments, USA, and the magnetic field was provided by a Mercury IPS120A magnet current from Oxford Instruments. A microampere-level AC signal was provided to the device through an NFLI5650 lock-in amplifier, and its Hall signal was read. A milliampere-level pulse signal with a pulse width of 0.1 milliseconds was applied to the device through a Keithley 2612B.

[0131] (2) Under the condition of device temperature of 300K, a magnetic field of ±1T is swept to measure the anomalous Hall signal of the device and determine its coercive field H. c The size. Under zero magnetic field conditions at 300K, a periodic program for control and measurement was run: within one cycle, a 0.1 ms pulse current I was applied via a Keithley 2612B.pulse 28 seconds after the pulse ends, an AC signal is provided through a lock-in amplifier to measure the Hall voltage of the device. Two seconds after the measurement is completed, the next cycle begins. For the initial state where the Hall voltage is negative, I in each cycle... pulse Constantly changing, starting from 0.2 mA, each cycle I pulse Increase the current by 0.2 mA until it reaches 5 mA, then scan to -5 mA with the same pulse interval, and finally scan to 0 mA with the same pulse interval. For the initial state where the Hall voltage is positive, the scan interval remains unchanged, and the direction of the scan current is opposite to the direction of the negative voltage. The final result is... Figure 12a and Figure 12b ,as well as Figure 13a and Figure 13b By observing the magnitude of the pulse current when the Hall signal begins to reverse, the reversal current I at which the magnetic moment of the magnetic layer reverses can be obtained. c .in, Figure 13a The anomalous Hall resistor of the spin-orbit torque magnetic storage cell in Example 1 The graph shows the relationship between the amplitude and direction of the pulse current, where the initial state of the spin-orbit torque magnetic storage cell is... Figure 13b The anomalous Hall resistor of the spin-orbit torque magnetic storage cell in Example 1 The graph shows the relationship between the amplitude and direction of the pulse current, where the initial state of the spin-orbit torque magnetic storage cell is... It should be pointed out that, Figure 13a and Figure 13b The curved black arrow in the middle indicates the scanning direction of the pulse current, that is... Figure 13a and Figure 13b The counterclockwise scanning chirality in the middle.

[0132] (3) Measure the thickness t of the magnetic layer using an atomic force microscope. FM The thickness t of the device. The saturation magnetization M of Fe3GaTe2 was measured using SQUID-VSM. s The damping coefficient α of Fe3GaTe2 was found through relevant literature. According to the formula J... c =I c / S obtains the reversal current density J c According to the SOT device efficiency formula, The efficiency ε is obtained.

[0133] Figure 10a and Figure 10b The results show the anomalous Hall signal measurement results of the spin-orbit torque magnetic storage cells prepared in Example 1 and Comparative Example 2, respectively.

[0134] In Example 1, an electrode was fabricated on a substrate first, and then magnetic and spin-flow materials were stacked. This method places the stacking of easily damaged materials at the end of the device fabrication process and can be carried out in an oxygen-free environment (e.g., stacking materials in a nitrogen atmosphere), effectively avoiding damage to the magnetic and spin-flow materials during electrode fabrication. Figure 10a and Figure 10b The anomalous Hall signals of the WTe2 / Fe3GaTe2-SOT devices prepared by the bottom electrode process in Example 1 and the top electrode process in Comparative Example 2 are shown respectively. It can be seen that the anomalous Hall signal of the SOT magnetic memory cell prepared by the bottom electrode process is obvious, the Hall resistance change is sharp, and the coercive field is small. In contrast, the anomalous Hall signal of the SOT magnetic memory cell prepared by the top electrode process is weak, the magnetization curve is elliptical, and the coercive field cannot even be distinguished. This indicates that the magnetic layer is damaged by the processing when preparing the top electrode.

[0135] Figure 11a and Figure 11b The results show the anomalous Hall signal measurement results of the spin-orbit torque magnetic storage cells prepared in Example 1 and Comparative Example 3, respectively.

[0136] In Example 1, a metallic magnetic layer is first stacked on the bottom electrode, followed by a spin current layer. This direct contact between the magnetic layer and the bottom electrode effectively avoids the influence of the contact between the magnetic layer and the spin current layer on the measurement signal, significantly improving the signal-to-noise ratio and effectively extending the device's lifespan. Since the spin current layer is responsible for controlling the magnetic layer and also carries a large current, to avoid the influence of the magnetic layer / spin current layer contact on the spin current layer and to achieve complete control over the magnetic layer, the spin current layer is made larger than the magnetic layer, completely covering it, and has areas that directly contact all electrodes of the bottom electrode. This design minimizes the impact of interface contact resistance on device performance. Figure 11a and Figure 11b The images show Hall effect diagrams of the SOT magnetic memory cell with a bottom electrode / magnetic layer / spin flux layer structure prepared in Example 1 and the SOT magnetic memory cell with a bottom electrode / spin flux layer / magnetic layer structure prepared in Comparative Example 3, respectively. It can be seen that... Figure 11a The signal-to-noise ratio is very high, while Figure 11b The noise signal is obvious, indicating that direct contact between the magnetic layer and the electrode can improve the signal quality of the device.

[0137] Figure 12a and Figure 12b The graphs show the dependence of the anomalous Hall resistance of the spin-orbit torque magnetic storage cells prepared in Example 1 and Comparative Example 1 on the magnitude and direction of the pulse current.

[0138] Example 1 employed an acetone treatment method. After transferring the magnetic material sample, the substrate containing the sample was immersed in acetone for 3 minutes. Because acetone has a high dissolved oxygen content, the acetone solution was placed in an oxygen-free environment for at least 24 hours before immersion to prevent the oxygen in the acetone from oxidizing the material. The substrate was then immersed in isopropanol for 3 minutes to clean the acetone. Finally, the substrate was removed and dried with nitrogen to remove the isopropanol. All of the above processes were performed in an oxygen-free environment. The low-oxygen acetone treatment method in Example 1 is an immersion method, which is superior to the rare gas ion cleaning method in cleaning residual adhesive, and the low-oxygen acetone used causes less damage to the sample. Figure 12a and Figure 12b The figures show the relationship between the anomalous Hall resistance of WTe2 / Fe3GaTe2-SOT devices prepared by the low-oxygen acetone treatment method and the Ar ion cleaning method, respectively, and the magnitude of the pulse current. Figure 12a and Figure 12b The measurement results, after calculation, indicate that the device J treated with acetone... c =9.33·10 5 A / cm 2 ε = 5.12, while the untreated device J c =1.57·10 6 A / cm 2 ε = 2.15. That is, the switching current density of the device treated with acetone is lower than that of the device cleaned with Ar ions, the calculated efficiency of the SOT device is higher than that of the device cleaned with Ar ions, and the signal-to-noise ratio of the device after acetone treatment is higher. It can be seen that the acetone treatment method is superior to the Ar ion cleaning method.

[0139] The above data demonstrates that, in this embodiment of the invention, using room-temperature out-of-plane magnetized van der Waals ferromagnetic material (Fe3GaTe2) as the magnetic material and van der Waals metal (WTe2) with out-of-plane spin electron flow as the spin current material, a SOT memory cell capable of operating at room temperature without a magnetic field is fabricated. This SOT memory cell exhibits low operating current density and high device efficiency.

[0140] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0141] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A method for fabricating a spin-orbit torque magnetic storage cell, comprising: A bottom electrode having at least one electrode is fabricated on a substrate; Magnetic van der Waals material is transferred onto the bottom electrode to form a magnetic layer that covers and is in direct contact with at least a portion of each of the at least one electrode of the bottom electrode. A van der Waals spin flow material is transferred onto the magnetic layer to form a spin flow layer that completely covers the magnetic layer and has an area larger than that of the magnetic layer, such that the spin flow layer contacts at least a portion of each of the at least one electrode of the bottom electrode.

2. The method for preparing the spin-orbit torque magnetic storage unit according to claim 1, wherein, The step of transferring the magnetic van der Waals material onto the bottom electrode includes: The magnetic van der Waals material was cleaved using adhesive tape and a transfer medium to obtain a magnetic van der Waals material sample with the required thickness and dimensions. The magnetic van der Waals material sample on the transfer medium is transferred to the bottom electrode; The transfer medium, which is a polydimethylsiloxane film, is peeled off without heating.

3. The method for preparing the spin-orbit torque magnetic storage unit according to claim 1, wherein, After the magnetic layer is formed and before the van der Waals spin flow material is transferred onto the magnetic layer, the preparation method further includes: The substrate with the magnetic layer is sequentially immersed in a first organic solvent and a second organic solvent after deoxidation for cleaning; Wherein, the first organic solvent is acetone, and the second organic solvent is propylene glycol; The first organic solvent and the second organic solvent are deoxygenated in the following manner: The first organic solvent and the second organic solvent are placed in an oxygen-free environment for at least 24 hours.

4. The method for preparing the spin-orbit torque magnetic storage cell according to any one of claims 1 to 3, wherein, The magnetic van der Waals material is a van der Waals ferromagnet with room temperature out-of-plane magnetization.

5. The method for preparing the spin-orbit torque magnetic storage unit according to claim 4, wherein, The van der Waals ferromagnet is Fe3GaTe2.

6. The method for preparing the spin-orbit torque magnetic storage cell according to any one of claims 1 to 3, wherein, The van der Waals spin flow material is a van der Waals metal with out-of-plane component spin electron flow.

7. The method for preparing the spin-orbit torque magnetic storage unit according to claim 6, wherein, The van der Waals metal is WTe2.

8. The method for preparing the spin-orbit torque magnetic storage unit according to claim 1, wherein, The step of transferring van der Waals spin flow material onto the magnetic layer to form a spin flow layer includes: The van der Waals spin flow material was cleaved using adhesive tape and a transfer medium to obtain a spin flow material sample with the required thickness and dimensions. The spin-flow material sample on the transfer medium is transferred onto the magnetic layer; The transfer medium, which is a polydimethylsiloxane film, is peeled off without heating.

9. The method for preparing the spin-orbit torque magnetic storage unit according to claim 1 further includes: An insulating layer material is transferred onto the spin flow layer to form an encapsulation insulating layer that completely covers the magnetic layer and the spin flow layer. The insulating layered material is hexagonal boron nitride (hBN).

10. A spin-orbit torque magnetic storage cell, comprising: A bottom electrode having at least one electrode formed on a substrate; A magnetic layer disposed on the bottom electrode and covering at least a portion of each of the at least one electrode of the bottom electrode and in direct contact therewith; as well as A spin flow layer disposed on the magnetic layer, the spin flow layer completely covering the magnetic layer, and the area of ​​the spin flow layer being larger than the area of ​​the magnetic layer, such that the spin flow layer is in contact with at least a portion of each of the at least one electrode of the bottom electrode; The bottom electrode, the magnetic layer, and the spin flow layer are prepared by the preparation method according to any one of claims 1-8.

11. The spin-orbit torque magnetic storage unit according to claim 10, further comprising: An encapsulation insulating layer disposed on the spin flow layer and completely covering the magnetic layer and the spin flow layer; The encapsulation insulating layer is prepared by the following method: An insulating layered material is transferred onto the spin flow layer to form the encapsulation insulating layer, wherein the insulating layered material is hexagonal boron nitride (hBN).

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