Graphene spintronic device, method of constructing the same, and method of measuring non-local signal

Abstract

This invention relates to a graphene spin device, its construction method, and a method for measuring nonlocal signals. The construction method of the graphene spin device includes the step of setting electrodes on the graphene surface; wherein, the electrodes are set by magnetron sputtering, using a direct current, and the magnetron sputtering power is 200±10W. This invention creates defects at the contact point between the graphene and the electrodes through magnetron sputtering under specific conditions, forming serrated graphene edges. Then, it utilizes the unique magnetism of graphene to construct a spin device. This spin device has high spin polarization and long spin transport distance. More importantly, this spin device relies solely on the magnetism of the graphene itself for spin injection and spin detection, providing a new approach for the development of graphene spin devices. It can be used for nonlocal measurements at room temperature, has low requirements for experimental environmental conditions, and is beneficial for exploring some nontrivial electrical mechanisms.

Description

Technical Field

[0001] This invention relates to the fields of information technology and microelectronic devices, and in particular to a graphene spin device, a method for constructing the same, and a method for measuring nonlocal signals. Background Technology

[0002] Since its discovery in 2004, graphene spin microelectronic devices have been a hot research topic. Due to its excellent electrical properties, ultra-high carrier concentration, ultra-long spin relaxation time, weak spin-orbit interaction, and long spin diffusion distance, graphene is an ideal spin transport material.

[0003] Nonlocal measurement methods are often used to detect some special physical properties of micro and nano devices that are difficult to detect, and have gradually become one of the research hotspots of spintronics in recent years.

[0004] Currently, the main devices for nonlocal measurement of graphene include four-terminal structures, H-shaped structures, and Hall structures. However, these devices have complex structures, demanding measurement conditions, low measurement efficiency, and cannot be effectively measured at room temperature, which is not conducive to device integration and application. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a graphene spin device, its construction method, and a non-local measurement method. The graphene spin device of this invention is a five-terminal device that effectively utilizes the edge magnetism of graphene to realize the transport and detection of spin current.

[0006] In a first aspect, the present invention provides a method for constructing a graphene spin device, including the step of setting electrodes on the graphene surface;

[0007] The electrodes are set by magnetron sputtering, a direct current is selected, and the power of the magnetron sputtering is 200±10W.

[0008] This invention employs magnetron sputtering under certain conditions to bombard the graphene surface with high-energy atoms, thereby creating defects at the contact points between the graphene and the electrode. This results in serrated graphene edges (only at the electrode contact points; other locations are not serrated), which possess unique magnetism, unlike the ferromagnetism of traditional paramagnetic metals. By utilizing the unique magnetism of graphene, a spin injection end can be constructed to obtain a spin device. This spin device has high spin polarization and long spin transport distance. More importantly, this spin device relies solely on the magnetism of graphene itself for spin injection and spin detection, providing a new approach for the development of graphene spin devices.

[0009] Existing technologies using magnetron sputtering to deposit metals employ relatively low power to avoid damaging the structure of the two-dimensional material (graphene). This invention, however, takes the opposite approach, causing some damage, but not complete destruction (affecting the graphene's conductivity), resulting in a serrated edge at the electrode-graphene contact point. Experiments have shown that this invention can only achieve the desired serrated edge under the aforementioned conditions; changes in power or DC current will prevent the formation of the desired edge.

[0010] According to the method for constructing a graphene spin device provided by the present invention, the number of electrodes is 5, wherein one electrode is located in the middle of the graphene and penetrates the surface of the graphene, and the other 4 electrodes are in contact with the edge of the graphene and are distributed in pairs on both sides of the middle electrode.

[0011] This invention, with its five electrodes, allows for measurement using the five-terminal method. Traditional four-terminal and Hall structure measurement structures employ a tunnel junction approach to achieve spin injection (a "sandwich" structure: ferromagnetic electrode + 0.5–0.8 nm oxide layer (Al₂O₃) + graphene). In contrast, the device structure of this invention lacks an intermediate oxide layer, simplifying the device fabrication process. From a measurement perspective, the structure is unique. While others typically mimic four-terminal spin valve structures or Hall structures to study graphene spin devices, this invention, using this structure, allows for the study of nonlocal transport of spin signals and the spin Hall effect through the arrangement and combination of electrodes.

[0012] According to the method for constructing graphene spin devices provided by the present invention, the spacing between each electrode is 0.5-1 μm.

[0013] According to the method for constructing a graphene spin device provided by the present invention, the electrode is made of ferromagnetic metal cobalt, or paramagnetic metal, such as molybdenum or tantalum. When these metals are used as the electrode, the target material during magnetron sputtering is also made of these metals.

[0014] According to the method for constructing a graphene spin device provided by the present invention, the thickness of the electrode is 60±10 nm.

[0015] According to the method for constructing a graphene spin device provided by the present invention, the method specifically includes the following steps:

[0016] S1. Transfer graphene onto a silicon wafer substrate;

[0017] S2. Perform micro / nano fabrication;

[0018] S3. Electrodes are placed on the graphene surface.

[0019] Specifically, in step S1, the silicon wafer needs to be pre-cleaned to ensure that there are no impurities on the surface. The cleaning process can be as follows: place the silicon wafer in acetone and clean it ultrasonically, then clean it ultrasonically with isopropanol, and finally clean it with a plasma cleaner.

[0020] The graphene is either single-layer or double-layer graphene. Graphene can be prepared using methods known in the art.

[0021] In a specific embodiment of the present invention, the graphene preparation method is as follows: using highly oriented pyrolytic graphite, 3M tape is used as the release material, and graphene is obtained on the tape by micromechanical exfoliation. The graphene is then transferred to a 300nm SiO2 substrate by heating at 85 degrees Celsius for 5 minutes on a hot stage.

[0022] In step S2, the micro-nano fabrication employs a double-layer photoresist process. Specifically, this includes: spin coating, where two layers of photoresist are spin-coated onto a silicon wafer substrate; and photolithography, where a pre-designed device layout is prepared using photolithography, accurately locating the graphene, followed by exposure and development.

[0023] Furthermore, the spin coating conditions are controlled as follows: first spin coating at 4000r for 60s, then heating for 1min, then spin coating at 2000r for 60s, then heating for 2min, with the hot plate temperature being a constant 115℃.

[0024] In step S3, the electrode is deposited using the magnetron sputtering method described above. After the electrode is deposited, excess metal needs to be stripped off. The sample after metal deposition can be placed in an acetone solution or further heated at 80°C on a hot stage to accelerate the stripping process, thereby removing excess metal and completing the fabrication of the graphene spin device.

[0025] In a preferred embodiment of the present invention, the electrode is prepared as follows:

[0026] Using a magnetron sputtering instrument, the target material is Mo metal, the power is 200W, the current is DC, and the electrode thickness is 60nm.

[0027] Secondly, the present invention provides a graphene spin device obtained by any of the above-described construction methods.

[0028] Thirdly, the present invention provides a method for measuring nonlocal signals using the aforementioned graphene spin device. The graphene spin device enables room temperature measurement.

[0029] The method for measuring nonlocal signals provided by the present invention includes the following steps:

[0030] The graphene spin device is used as a spin injection terminal and a voltage is applied to one electrode on one side to form a current loop. The two electrodes on the other side are used as spin detection terminals. By changing the gate voltage, a curve of the nonlocal signal changing with the gate voltage is obtained.

[0031] Specifically, according to the above wiring method, there are four different measurement methods using the graphene spin device described in this invention, as detailed in the specific implementation section.

[0032] According to the nonlocal signal measurement method provided by the present invention, the measurement method is applicable to any scenario including no magnetic field, presence of an x-level magnetic field, and presence of a y-level magnetic field.

[0033] This invention provides a graphene spin device, its construction method, and a nonlocal measurement method. The invention utilizes magnetron sputtering under specific conditions to create defects at the contact point between graphene and the electrode, forming serrated graphene edges. Then, it leverages the unique magnetic properties of graphene to construct a spin device. This spin device exhibits high spin polarization and long spin transport distance. More importantly, it relies solely on the inherent magnetism of graphene for spin injection and spin detection, providing a new approach to the development of graphene spin devices. This spin device can be used for nonlocal measurements at room temperature, has low requirements for experimental conditions, and is beneficial for exploring nontrivial electrical mechanisms. Furthermore, the construction method of this invention is simple to operate and easy to promote. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. It should be noted that the dimensions of the parts in the schematic diagrams are not drawn according to actual scale. The accompanying drawings described below are some embodiments of the present invention.

[0035] Figure 1 A method for forming edge defects at the contact points between graphene and electrodes;

[0036] Figure 2 This is a front view of the graphene spin device obtained in Example 1;

[0037] Figure 3 This is a top view of the graphene spin device obtained in Example 1;

[0038] Figure 4 Raman characterization of graphene in Example 1;

[0039] Figure 5 Four nonlocal measurement methods;

[0040] Figure 6 The results are from the non-local measurement in Example 3. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Unless otherwise specified, all raw materials involved in the embodiments of this invention can be obtained commercially.

[0043] Example 1

[0044] This embodiment provides a method for constructing a graphene spin device, the steps of which are as follows:

[0045] Substrate cleaning: Place the silicon wafer (300nm) in acetone and clean it ultrasonically, then clean it ultrasonically with isopropanol, and finally clean it with a plasma machine to ensure that there are no impurities on the surface of the silicon wafer.

[0046] Graphene preparation: Using highly oriented pyrolytic graphite and 3M tape as the release material, graphene (single layer) was obtained on the tape using micromechanical exfoliation. The graphene was then transferred to a clean silicon wafer by heating at 85°C for 5 minutes on a hot stage.

[0047] Spin coating: Spin coat two layers of photoresist (S1813) onto the silicon wafer substrate. First, spin coat at 4000r for 60s and heat for 1min. Then spin coat at 2000r for 60s and heat for 2min. The hot stage temperature is constant at 115℃.

[0048] Photolithography: Accurately positioning the designed device layout onto the graphene, exposing it, and developing it.

[0049] Evaporated electrode: Using a magnetron sputtering system, with Mo as the target material, a power of 200W, and DC current, the electrode thickness is 60nm. High-energy atoms from magnetron sputtering bombard the graphene surface to create defects at the graphene-electrode contact point, forming serrated edges and constructing a spin-injection end. Figure 1 As shown;

[0050] Peeling: Finally, a lift-off operation is performed. The sample after metal vapor deposition is placed in an acetone solution and heated on a hot stage at 80°C to accelerate the peeling speed and complete the fabrication of the graphene spin device.

[0051] A schematic diagram of the obtained graphene spin device is shown below. Figure 2 and Figure 3 As shown, Figure 2 Main view, Figure 3The top view shows that the device has five electrodes. Electrode 1 is located in the middle of the graphene and penetrates the graphene surface. Electrodes 2, 3, 4, and 5 only contact the edges of the graphene. Electrodes 2 and 4 are on one side of electrode 1, and electrodes 3 and 5 are on the other side of electrode 1. It should be noted that the numbering of electrodes 1, 2, 3, 4, and 5 here is only for ease of description and differentiation and does not refer to the deposition order or connection order.

[0052] Electrode 1 is the spin input terminal. Electrode 1 can form a current loop with any other electrode, while the two electrodes on the other side are used as nonlocal signal measurement terminals. Electrode 1 has a width of 2μm, and the other electrodes have a width of 1μm. The spin transport material is graphene, and the substrate is SiO2 / Si, which serves as the dielectric layer and back gate.

[0053] In addition, the Raman characterization of the graphene obtained in the graphene preparation step is as follows: Figure 4 As shown. It can be seen that 1350cm -1 The peak at 1600 cm⁻¹ represents the D peak of graphene. -1 The peak at 2700 cm⁻¹ represents the G peak of graphene. -1 The value at point G represents the 2D peak of graphene, where the D peak is very weak. The ratio of the 2D peak to the G peak indicates that this is a single-layer graphene.

[0054] Example 2

[0055] This embodiment provides a method for measuring nonlocal signals using the graphene spin device of Embodiment 1. Since the spin device has five electrodes, a current loop is formed by applying a voltage to one electrode on one side as the spin injection terminal, and the two electrodes on the other side as the detection terminals. A total of four measurement methods are provided, such as... Figure 5 As shown, the details are as follows:

[0056] Method 1: Apply a constant voltage between electrodes 1 and 3, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 2 and 4;

[0057] Method 2: Apply a constant voltage between electrodes 1 and 5, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 2 and 4;

[0058] Method 3: Apply a constant voltage between electrodes 1 and 2, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 3 and 5;

[0059] Method 4: Apply a constant voltage between electrodes 1 and 4, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 3 and 5.

[0060] Example 3

[0061] This embodiment provides a nonlocal signal measurement method according to Method 1 in Embodiment 2, the steps of which are as follows:

[0062] In the absence of a magnetic field, a voltage of 100 millivolts is applied between electrodes 1 and 3, with the gate voltage swept from -30V to 30V. Electrodes 2 and 4 serve as detection terminals, and the potentials of electrodes 2 and 4 are measured. The nonlocal signal measurement results of the graphene spin device under the absence of a magnetic field are obtained, such as... Figure 6 As shown.

[0063] It can be seen that the nonlocal measured potentials of electrodes 2 and 4 change with the gate voltage Vbg. When the gate voltage is negative, the nonlocal potential increases with the increase of the gate voltage. When the gate voltage is 0, the gate voltage values ​​of electrodes 2 and 4 reach their maximum values ​​at the same time. When the gate voltage is positive, the nonlocal potential decreases with the increase of the gate voltage.

[0064] Under a horizontal magnetic field of x, the same method as in the case of no magnetic field can be used to apply a constant magnetic field and change the magnitude of the magnetic field. Apply magnetic fields of 0mT, 50mT, 100mT, 150mT, 200mT, 250mT, and 300mT to the device in sequence to obtain the curve of the nonlocal signal changing with the gate voltage under the magnetic field.

[0065] Under a horizontal magnetic field, the same method as in the absence of a magnetic field can be used: apply a constant magnetic field and change the magnitude of the magnetic field. Apply magnetic fields of 0mT, 50mT, 100mT, 150mT, 200mT, 250mT, and 300mT to the device in sequence to obtain the curve of the nonlocal signal changing with the gate voltage under the magnetic field.

[0066] Example 4

[0067] In this embodiment, the electrode deposition method in the graphene spin device fabrication process of Example 1 was changed to vacuum thermal evaporation, magnetron sputtering power of 50W, and magnetron sputtering power of 100W, respectively, to prepare the device.

[0068] The following method was used for measurement:

[0069] Method 1: Apply a constant voltage between electrodes 1 and 3, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 2 and 4;

[0070] Method 2: Apply a constant voltage between electrodes 1 and 5, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 2 and 4;

[0071] Method 3: Apply a constant voltage between electrodes 1 and 2, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 3 and 5;

[0072] Method 4: Apply a constant voltage between electrodes 1 and 4, apply a gate voltage to the back electrode, and measure the nonlocal signal at electrodes 3 and 5.

[0073] The measurements were performed using the above method. At the electrode probe end, the voltage signals measured by both electrodes were consistent, indicating that the voltage was divided by the middle electrode. This suggests that the device with this structure cannot achieve spin injection or has extremely low spin injection efficiency.

[0074] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for constructing a graphene spin device, characterized in that, This includes the step of setting electrodes on the graphene surface; The electrodes are set by magnetron sputtering with a DC current and a power of 200±10W. The magnetron sputtering creates defects at the contact point between the graphene and the electrode, forming a serrated graphene edge. The special magnetism of the graphene is then used to construct a spin device. The number of electrodes is 5, one of which is located in the middle of the graphene and penetrates the graphene surface, and the other 4 electrodes are in contact with the edge of the graphene and are distributed in pairs on both sides of the middle electrode. The middle electrode serves as the spin injection end. The spacing between each electrode is 0.5-1 μm; The electrode is made of ferromagnetic cobalt or paramagnetic molybdenum; the thickness of the electrode is 60±10 nm. The graphene is either single-layer graphene or double-layer graphene. The construction method specifically includes the following steps: S1. Transfer graphene onto a silicon wafer substrate; S2. Perform micro / nano fabrication; S3. Electrodes are placed on the graphene surface; The micro-nano fabrication employs a double-layer adhesive process.

2. A graphene spin device, characterized by, Obtained by the construction method described in claim 1.

3. A method of measuring a non-local signal, characterized by, The graphene spin device described in claim 2 is used.

4. The method of measuring a non-local signal according to claim 3, wherein, Includes the following steps: The graphene spin device is used as a spin injection terminal and a voltage is applied to one electrode on one side to form a current loop. The two electrodes on the other side are used as spin detection terminals. By changing the gate voltage, a curve of the nonlocal signal changing with the gate voltage is obtained.

5. The method of measuring a non-local signal according to claim 4, wherein, The measurement method is applicable to any scenario including no magnetic field, the presence of an x-level magnetic field, and the presence of a y-level magnetic field.

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