A spintronic device with polymorphism and synapse-like properties and its preparation method

Abstract

The present invention provides a spintronic device with polymorphism and synapse-like properties, including a substrate layer and a magnetic layer on the substrate layer. The material used for the magnetic layer is ferrimagnetic, and the magnetic layer has an anisotropy gradient or a DMI gradient through a ferrimagnetic composition gradient. Its advantages are as follows: enabling the spintronic device to achieve the magnetic moment reversal of a ferrimagnetic with perpendicular magnetic anisotropy driven by the spin-orbit torque under zero magnetic field at room temperature, laying a foundation for the realization of next-generation high-performance and high-stability spintronic information storage and logic devices.

Description

Technical Field

[0001] The present invention relates to the technical field of information storage, and more particularly to a spin electronic device with polymorphism and synapse-like functions and a preparation method thereof. Background Art

[0002] All-electrically driven magnetic moment reversal based on the spin orbit torque (SOT) effect has advantages such as fast writing speed, strong durability, long service life, and low power consumption, and shows great application potential in new spin electronic memories and logic devices.

[0003] Ferromagnetic materials have the property of antiferromagnetic coupling in magnetic moment arrangement, and their spins are composed of magnetic sublattices with antiferromagnetic exchange coupling. They are natural candidates for realizing magnetic materials with low net angular momentum. In addition to increasing the domain wall reversal speed, the lower magnetization intensity of ferromagnetic materials also has the additional advantage of a smaller stray field, which avoids the occurrence of magnetic dipole coupling between adjacent devices, resulting in a higher device density. Materials with antiferromagnetic coupling have the advantage of being relatively stable against external magnetic fields.

[0004] Spin orbit torque-driven perpendicular magnetic moment reversal usually requires applying an in-plane auxiliary magnetic field in the direction parallel to the current to break the symmetry of the perpendicular system. For practical applications, this not only increases the additional power consumption but also makes the circuit design more complex, which is obviously not conducive to the practical application of spin electronic devices. Summary of the Invention

[0005] The present invention provides a spin electronic device with polymorphism and synapse-like functions and a preparation method thereof, aiming to at least overcome the above-mentioned technical defects and enable the prepared spin electronic device to have a full-electrically polymorphic storage function.

[0006] In a first aspect of the present invention, a spin electronic device with polymorphism and synapse-like functions is provided, including a substrate layer and a magnetic layer on the substrate layer, and the material of the magnetic layer is ferromagnetic, so that the magnetic layer has an anisotropy gradient or a DMI gradient.

[0007] Preferably, the material of the magnetic layer is obtained by co-sputtering of Co, Gd, and W or co-sputtering of Co, Gd, and Pt or co-sputtering of Co, Gd, and Ta, and the magnetic layer has a DMI gradient in the vertical direction, as Figure 1 shown.

[0008] Preferably, a spin source layer is further provided between the substrate layer and the magnetic layer, so that the magnetic layer has an anisotropy gradient in the vertical direction or in-plane direction through the ferromagnetic component gradient, as Figure 2 shown.

[0009] Preferably, the material used for the spin source layer is a heavy metal or a two-dimensional semimetal material, and the magnetic layer is obtained by co-sputtering of Co and Gd, as Figure 3 shown.

[0010] In the second aspect of the present invention, a method for preparing the spin electronic device described in the first aspect is provided. The ferromagnetic is deposited on the substrate by magnetron sputtering, and then a Hall target device is prepared as Figure 4 shown;

[0011] Among them, the magnetic layer composed of ferromagnetic has an anisotropy gradient or a DMI gradient.

[0012] Preferably, a method for preparing a spin electronic device with multiple states and synaptic-like properties is as follows:

[0013] S1. Clean and dry the silicon wafer for use as a substrate.

[0014] S2. Deposit a ferromagnetic material doped with a heavy metal on the substrate prepared in step S1 by magnetron sputtering;

[0015] Among them, the sputtering power of the ferromagnetic material is fixed, and the sputtering power of the heavy metal gradually decreases or increases so that a DMI gradient is formed on the magnetic layer;

[0016] S3. Prepare a Hall target device and grow electrodes to obtain a spin electronic device.

[0017] Preferably, a heavy metal material or a two-dimensional semimetal material is sputtered on the substrate as the spin source layer by sputtering, and then a ferromagnetic is sputtered on the spin source layer by sputtering so that the magnetic layer has an anisotropy gradient in the vertical direction or the in-plane direction, and then a Hall target device is prepared and electrodes are grown to obtain a spin electronic device.

[0018] Preferably, during the sputtering of the ferromagnetic, the substrate is kept fixed so that the magnetic layer has an anisotropy gradient in the in-plane direction.

[0019] A spin electronic device with multiple states and synaptic-like properties and a method for preparing the same according to the present invention have the following advantages: In the spin electronic device with the structure of the present invention, since there is a magnetic thin film (i.e., the magnetic layer in the present invention) that can exhibit different saturation magnetization intensities, DM interactions, and magnetic anisotropies at room temperature, the spin electronic device can achieve the magnetic moment reversal of the ferromagnetic with perpendicular magnetic anisotropy driven by the spin-orbit torque under zero magnetic field at room temperature, laying a foundation for the realization of the next generation of high-performance and high-stability spin information storage and logic devices. Description of the Drawings

[0020] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification for explaining the present invention together, and do not constitute a limitation to the present invention. In the drawings:

[0021] Figure 1 Schematic diagram of the NM / FM bilayer film structure with gradient anisotropy in the vertical direction in Embodiment 1 of the present invention;

[0022] Figure 2 Schematic diagram of the FM single-layer film structure with gradient anisotropy in the vertical direction in Embodiment 2 of the present invention;

[0023] Figure 3 Schematic diagram of the NM / FM bilayer film structure with gradient anisotropy in the in-plane direction in Embodiment 3 of the present invention;

[0024] Figure 4 Test diagrams of electrical devices in Embodiments 1, 2, and 3 of the present invention;

[0025] Figure 5 Spin-orbit torque-driven magnetic moment reversal of the Hall device provided in Embodiment 1 of the present invention under full electrical action;

[0026] Figure 6 Multi-state storage of the Hall device provided in Embodiment 2 of the present invention under full electrical action;

[0027] Figure 7 Synaptic simulation of the Hall device provided in Embodiment 3 of the present invention under full electrical action. Detailed implementation manners

[0028] To better understand the above technical solutions, the technical solutions of the present application will be described in detail through specific embodiments below. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations on the technical solutions of the present application. Without conflict, the technical features in the embodiments of the present application and the embodiments can be combined with each other. It should be understood that the term "and / or" used herein includes any and all combinations of one or more of the listed related items.

[0029] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0030] The principle of the present invention is: using the rich element ratio of ferromagnetic materials to achieve gradient anisotropy and DMI interaction of the magnetic layer in the vertical direction and in-plane direction, and then realizing full electrical reversal to obtain a spin electronic device with multi-state and synaptic-like characteristics.

[0031] In the present invention, a traditional double-layer film heterostructure of NM / FM is adopted. The materials used for the non-magnetic layer (NM) include Ta, Pt, W, WTe2, Bi2Te3, etc., and the ferromagnetic layer materials adopt ferrimagnets including Co x Gd 1-x (where X = 0.65 - 0.85), Co x Tb 1-x (where X = 0.65 - 0.85) with special structure and growth design, and the functions of a multi-state and synapse-like spin electronic device capable of full electrical control can be realized under DMI longitudinal gradient, DMI transverse gradient, and DMI longitudinal and transverse multi-dimensional gradients.

[0032] In the process of preparing a spin electronic device with multi-state and synapse-like functions, the single layer of the magnetic layer is obtained by doping the CoGd ferrimagnetic material with heavy metals Pt, W, Ta. The spin source layer of the spin source layer / magnetic layer heterojunction is selected from heavy metal materials such as Pt, W, Ta; two-dimensional semimetal materials such as WTe2, MoTe2, Bi2Te3 can also be used; the materials of the electrodes are selected from Pt, Cu.

[0033] Example 1

[0034] A preparation method of a spin electronic device with multi-state and synapse-like functions according to the present invention includes the following specific steps:

[0035] (1) Clean the silicon wafer: The substrate is a silicon wafer. The silicon wafer used is a single-sided polished high-resistance silicon with a resistivity of 4000 Ω / cm, ensuring that the resistance of the silicon wafer itself is extremely different from that of the device and it has no conductivity, which can be used as an ideal substrate material;

[0036] (2) Deposit the heavy metal layer and the magnetic layer on the silicon wafer by magnetron sputtering: Deposit the heavy metal layer material on the silicon wafer by magnetron sputtering. Magnetron sputtering means that under the action of an electrostatic field, gas molecules are ionized into plasma and electrons. The plasma bombards the target surface under the action of the electric field, causing the bombarded particles to deposit on the substrate, and the generated electrons move in a spiral in the magnetic field, generating more plasma to accelerate the sputtering of the target material, and the above steps are repeated. The method selected in the embodiment of the present invention is magnetron sputtering. The thickness of the heavy metal layer Pt is 5 nm, which is suitable for magnetron sputtering. The thickness of the thin film prepared by this method is easy to control, the thin film has good repeatability, strong bonding ability between the thin film and the substrate, a wide range of preparation materials, and high purity and smooth surface. Among them, the sputtering target is a Pt target, the working gas pressure is 3×10 -4 Torr, the sputtering power is 30 W, and the sputtering time is 210 s.

[0037] Subsequently, the magnetic layer material is deposited on the heavy metal by magnetron sputtering. The magnetic layer material is obtained by co-sputtering from two magnetron targets, where the two targets are Co and Gd. In order to achieve all-electric switching, a CoGd alloy thin film is co-sputtered in the vertical direction. The specific sputtering scheme is that the total thickness of the co-sputtered magnetic layer is 7 nm, the sputtering time is 88 s, the working pressure is 3×10 -4 Torr, the sputtering power slowly decreases from 100 W to 80 W for Co and slowly increases from 30 W to 40 W for Gd, so that the sputtered CoGd magnetic layer has a composition gradient in the vertical direction, further generating a thin film with a DMI interaction gradient.

[0038] (3) Perform micro-nano processing to prepare Hall target devices or strip devices: Use micro-nano processing technology to fabricate Hall target structures and strip structures on the thin film. Preferably, in the lithography process of this embodiment of the present invention, a negative photoresist process is selected. First, a uniformly thick photoresist thin film is spin-coated on the thin film by a spin coater, that is, a photoresist solution is dropped on the substrate using a dropper, and then the centrifugal force is used to uniformly spin-coat the glue solution dropped on the substrate on the substrate. Then the substrate needs to be placed on a heating table for heating, the temperature is 90 °C, and the time is 1 min 30 s. The heated substrate is placed in a lithography machine, and a mask plate with Hall target structures and strip structures is placed above the substrate. The mask plate and the substrate are attached by bottom blowing, and the substrate is first exposed to ultraviolet light, the exposure time is 4 s, then the substrate is placed on the heating table again for heating, the temperature is 110 °C, and the time is 1 min 30 s. The substrate after being heated again is placed in the lithography machine, the photomask is removed, and the substrate is directly exposed to ultraviolet light, the exposure time is 20 s. The substrate after the two exposures is placed in a developer for development, the development time is 45 s, and after development, the substrate needs to be quickly placed in deionized water for cleaning to ensure the development effect, and the substrate after lithography is obtained. The substrate after lithography is placed in an ion etching machine for ion etching. During etching, the working pressure is 2×10 -2 Pa, the energy is set to 490 eV, and the beam current is 60 mA. Since long-term etching will cause the photoresist to denature, a small amount and multiple etching scheme is selected, the etching time is 30 s each time, and a total of 5 times. After etching, the substrate is placed in acetone for cleaning to obtain Hall target devices and strip devices.

[0039] (4) Perform lithography again: Use ultraviolet exposure lithography to perform lithography on the substrate again, and lithograph electrode patterns on the Hall devices and strip devices. In this embodiment of the present invention, a positive photoresist process is used, so that the electrode part is empty and the rest is covered with photoresist. The parameters of spin coating, heating, and bonding are the same as those in the previous step, and then ultraviolet exposure is performed, the exposure time is 20 s. After exposure, the substrate is placed in a developer for development, the development time is 45 s, and immediately after development, it is placed in deionized water for cleaning to obtain the electrode pattern.

[0040] (5) Growing the electrodes by magnetron sputtering: The electrodes are grown using magnetron sputtering. In the embodiments of the present invention, Cu is selected as the electrode. As a commonly used electrode material, Cu has the advantages of low cost, resistance to oxidation, and high conductivity. During the sputtering process, the sputtering gas pressure is 3×10 -4 Torr, the sputtering power is 30 w, and the sputtering time is 20 min. The device is obtained by using ultrasonic cleaning technology for cleaning.

[0041] In the above process, if a spintronic device with a CoGd composition gradient in the vertical direction, thus having a DMI gradient in the vertical direction, is to be obtained, then the bottom layer of the device uses the traditional heavy metal Pt as the spin source layer, and the magnetic layer is in the form of a multilayer film. The method of co-sputtering Co and Gd is adopted, where the power of Co slowly increases during the sputtering process, and the power of Gd slowly decreases.

[0042] If a spin source layer is not required and only a single magnetic layer is needed, then heavy metals (Pt, W, or Ta) are incorporated into the magnetic layer. The magnetic layer is co-sputtered with Co, Gd, and W (or Pt and Ta). The sputtering powers of Co and Gd are fixed, and the sputtering power of W (or Pt and Ta) is increased or decreased according to time. Since there is a Pt gradient in the vertical direction in the magnetic layer CoGd, there is also a DMI gradient in the vertical direction. Relevant experiments are carried out on the devices with this structure, specifically as follows:

[0043] A pulsed current (keithley6221) is applied in the x-axis direction in the Hall target structure, and a voltage measuring device (keithley2182) is connected in the y-direction as Figure 4 shown. The given pulse width is 50 us, and the current I read is 0.1 mA. The pulsed current scans from +60 mA to -60 mA at a step of 2 mA each, and then scans back to +60 mA at the same interval. The loop of the spin-orbit torque driving the perpendicular magnetic moment of its full electrical properties is as Figure 5 shown. When the charge current density is increased, due to the spin Hall effect, the spin current density with z-direction spin polarization increases, so the torque acting on the magnetic moment of the magnetic layer increases, causing the magnetic moment of the magnetic layer to flip in the easy axis direction, and the measured anomalous Hall voltage reflects the relative amount of the magnetic moment of the magnetic layer in the Z direction.

[0044] Embodiment 2

[0045] A method for preparing a spintronic device with multiple states and synapse-like functions according to the present invention, wherein the spintronic device has only a single magnetic layer.

[0046] (1)Clean the silicon wafer substrate: Since the substrate surface is in contact with the external environment during the preparation and production process, it will inevitably carry a layer of impurities. The requirements for the substrate by the thin film are very high, and even extremely small contaminants will affect the growth and performance of the thin film. Therefore, it is required that the substrate has a very high cleanliness and flatness. To obtain a thin film with good quality, the substrate must be pretreated to remove the surface impurities. The specific treatment process is as follows:

[0047] Cut the circular silicon wafer into 1 cm × 1 cm squares using a diamond pen; blow off the surface debris of the cut silicon wafer using a nitrogen gun; place the substrate in acetone and clean it with an ultrasonic cleaner for 5 minutes; ultrasonically clean it with absolute ethanol for 5 minutes; ultrasonically clean the substrate with deionized water for 8 minutes; dry its surface with a nitrogen gun and then place it in an oven set at 100 °C and dry for 3 minutes.

[0048] (2)Grow the magnetic layer on the cleaned silicon wafer using magnetron sputtering: The steps are as follows:

[0049] Sample injection: Place the cleaned silicon wafer on the tray, use vacuum tape to firmly stick the silicon wafer diagonally, place the tray in the sample injection rod in the sample chamber, and align the tray position mark with the mark on the sample injection rod during the placement process.

[0050] Vacuum the growth chamber and the sample chamber: Turn on the mechanical pump and let the mechanical pump vacuum the cold pump for 60 min; turn on the cold pump compressor switch and let the cold pump cool down to 13 K. During this process, use the mechanical pump and the molecular pump to control the vacuum in the growth chamber and the sample chamber at 1×10 -6 Torr; open the valve between the cold pump and the growth chamber and close the baffle between the sample chamber and the growth chamber to directly vacuum the growth chamber with the cold pump, and finally control the vacuum in the growth chamber at 1×10 -8 Torr. A higher vacuum can reduce the collision between the evaporated molecules and the residual gas molecules and reduce the contamination of the substrate surface. Therefore, the entire coating process needs to be carried out under a relatively high vacuum condition.

[0051] Perform the sample injection operation: When the vacuum difference between the sample chamber and the growth chamber is less than two orders of magnitude, open the baffle between the sample chamber and the growth chamber, and use the sample delivery arm to send the tray into the growth chamber. Considering factors such as the size of the substrate during the experiment, fix the distance between the substrate and the target at 50 mm.

[0052] Pretreat the target: Turn on the DC target power supply and the gas flowmeter, introduce argon gas and control the vacuum at 4×10 -3 Torr, sequentially turn on the DC targets required during the growth of the magnetic layer, adjust the power to 30 w to make the target glow, and pre-sputter the target for 10 min. The purpose is to remove the impurities and oxide layers on the target surface.

[0053] Finally, open the baffles of all three targets simultaneously for formal sputtering. The deposition conditions are as follows: argon is introduced as the protective gas, the deposition pressure is 3×10 -4 Torr, and the sputtering time is 88 s. The sputtering power of Co is 80 W, that of Gd is 30 W, and the power of Pt slowly increases from 10 W to 16 W during the sputtering time. After sputtering is completed, open the baffle between the sample chamber and the growth chamber, remove the tray using the sample transfer arm, send it back to the sample chamber, close the baffle, turn off the mechanical pump and the molecular pump, introduce nitrogen, restore the pressure in the sample chamber to atmospheric pressure, take out the sample, and complete the preparation of the magnetic layer.

[0054] (3)Micro-nano processing of the thin film:

[0055] Coating with glue by spin coating method: Place the sample in a spin coater, and use a dropper to drop glue on the surface; then set the spinning time, set the ACC time (the time to accelerate or decelerate to the required rotation speed) to 5 s, the rotation speed is 2000 r / min, and the spin coating time is 30 s.

[0056] Heating: Place the substrate after spin coating on a heating stage for heating, the temperature is set to 90 °C, and the time is 1 min 30 s.

[0057] Exposure: Place the substrate in a lithography machine, use a vacuum chuck to adsorb the substrate; use a mask plate holder to place the mask plate above the substrate; rotate and raise the substrate, and use bottom blowing to make the substrate fit with the mask plate; turn on the ultraviolet lamp for exposure, and the exposure time is set to 4 s.

[0058] Secondary heating: Place the substrate after the first exposure on a heating stage for heating, the heating temperature is set to 110 °C, and the time is 1 min 30 s.

[0059] Secondary exposure: Place the substrate after heating in a lithography machine, remove the mask plate, and directly use the ultraviolet lamp for exposure, and the exposure time is 20 s.

[0060] Development: Place the substrate after exposure in a developer for development, and the development time is 40 s. Immediately after the time is up, place the substrate in deionized water for cleaning, and then use a nitrogen gun to dry the substrate.

[0061] Ion etching: Place the substrate in an ion etching machine, turn on the mechanical pump and the molecular pump, evacuate the etching chamber to 5×10 -4 Pa, introduce argon, set the working pressure to 2×10 -2 Pa, set the energy to 490 eV, the beam current is 60 mA, turn on the ion source for etching, set the etching time to 30 s, and etch 5 times in total.

[0062] Cleaning the substrate: To remove the photoresist, the etched substrate was placed in acetone for 4 h of soaking, and then ultrasonically cleaned using an ultrasonic machine for 10 s.

[0063] (4) Repeat the steps 1236 in (3), change the exposure time to 20 s, and lithograph the electrode pattern on the cross and one - character devices.

[0064] (5) Use magnetron sputtering for electrode growth. Repeat the operations 1234 described in (2), then open the baffle, use a Cu target for sputtering, the sputtering time is 20 min, the sputtering pressure is 3×10 -4 Torr, and the sputtering power is 30 w.

[0065] (6) Electrical performance characterization and measurement of multi - states of the device

[0066] For its multi - state storage of full electrical flipping: Apply a current (keithley6221) in the x - axis direction of the Hall target device, and connect a voltage measurement device (keithley2182) in the y - direction as Figure 4 shown. Given a read current I read with a time of 50 us and a magnitude of 0.1 mA. In the test preparation stage, first pass a +60 mA current to polarize the material device in the forward direction and then enter the formal test. Pass a pulsed current of - 33 mA once, and then record the corresponding R Hall , then decrease the pulsed current at intervals of 2 mA, and record R Hall once after each increase in the pulse. Finally, summarize the relationship between the pulse magnitude and R Hall and the current density J as Figure 6 shown.

[0067] Example 3

[0068] The difference between this example and Example 1 is that:

[0069] In the double - layer film heterostructure of NM / FM, the non - magnetic layer uses traditional heavy metals (Pt, Ta, W) as the spin source layer, or two - dimensional semimetal materials such as WTe2, MoTe2, Bi2Te3 can also be used. The magnetic layer uses the co - sputtering method of Co and Gd without substrate rotation to make the magnetic layer have an anisotropic gradient in the in - plane direction. Its micro - processing and lithography processes are the same as those of the previous two processes.

[0070] The electrical synaptic performance test of this device: Apply a current (keithley6221) in the x - axis direction of the Hall target device, and connect a voltage measurement device (keithley2182) in the y - direction asFigure 4 As shown, first in the preliminary test stage, a current of +60 mA is passed to forward polarize the material device, and then the formal test begins. Set the pulse current magnitude (here, for example, 33 mA), and apply ten pulses at this current, and measure the corresponding R Hall value. Then, pass -33 mA for ten pulses and also measure the corresponding R Hall value. Repeat this three times without re-polarizing in the middle. Finally, the relationship between the R Hall values of 33 mA and -33 mA and the number of pulses is as Figure 7 shown.

[0071] The structures, principles, steps, etc. not clearly described in the present invention are all obtainable by the conventional technical means of those skilled in the art, and thus will not be elaborated herein.

[0072] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A spintronic device with polymorphism and synapse-like features, characterized in that: It includes a substrate layer and a magnetic layer on the substrate layer, and the material used for the magnetic layer is ferrimagnetic, so that the magnetic layer has an anisotropy gradient or a DMI gradient; the material used for the magnetic layer is obtained by co-sputtering of Co, Gd, and W or by co-sputtering of Co, Gd, and Pt or by co-sputtering of Co, Gd, and Ta, and the magnetic layer has a DMI gradient in the vertical direction; the substrate is a silicon wafer.

2. A preparation method of a spintronic device with polymorphism and synapse-like features as described in claim 1, characterized in that: Deposit the ferrimagnetic on the substrate by magnetron sputtering, and then prepare a Hall target device and grow electrodes to obtain a spintronic device; Among them, the magnetic layer composed of ferrimagnetic has an anisotropy gradient or a DMI gradient.

3. The preparation method according to claim 2, characterized in that: It includes the following steps: S1. Clean and dry the silicon wafer for use as a substrate; S2. Deposit the ferrimagnetic material doped with heavy metals on the substrate prepared in step S1 by magnetron sputtering; Among them, the sputtering power of the ferrimagnetic material is fixed, and the sputtering power of the heavy metal gradually decreases or increases so that the magnetic layer has a DMI gradient; S3. Prepare a Hall target device and grow electrodes to obtain a spintronic device.

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