A quaternary topological insulator heterostructure and a functional layer of a spin-orbit torque device, a preparation method and applications thereof

Abstract

The application relates to a four-element topological insulator heterostructure and a functional layer and a preparation method and application of a spin-orbit torque device, wherein the topological insulator heterostructure is expressed as: [Sb2Te3 (5-x) / Bi2Se3 (x)]d / Sb2Te3 (3 nm), Sb2Te3 and Bi2Se3 are periodically and alternately stacked, x represents the thickness of the Bi2Se3 layer in a single period, x=0-5 nm, and d represents the number of the alternating periods. The functional layer of the spin-orbit torque device is sequentially deposited with a Ti layer, a CoFeB layer, an MgO layer and a Ta layer on the TI layer. The preparation method adopts a magnetron sputtering deposition process. The functional layer needs to be subjected to annealing treatment. The functional layer of the spin-orbit torque device can be used for manufacturing a Hall bar device. The application realizes effective regulation of a topological insulator energy band structure and a carrier concentration, thereby obtaining a wide band gap, a high spin Hall angle and a low critical switching current density, and can be used for manufacturing a low-power-consumption spin electronic device.

Description

Technical Field

[0001] This invention belongs to the field of spintronic devices and relates to the structure and fabrication of spin orbital torque devices. Background Technology

[0002] With the development of spintronics, magnetic random access memory (SOT-MRAM) based on spin-orbit torque (SOT) is considered an important development direction for next-generation low-power information storage technology. SOT devices rely on the charge-to-spin conversion efficiency in the material system, which is usually determined by the material's spin Hall angle (θSH).

[0003] Traditional heavy metal materials, such as Pt, Ta, and W, can generate the spin Hall effect, but their spin Hall angles are usually low (about 0.08-0.3, with a narrow tuning range). Therefore, a large driving current is required to achieve magnetization reversal, which leads to high power consumption of the device and limits its application in low-power spintronic devices.

[0004] In recent years, topological insulators (TI) have been considered important candidate materials for realizing high-efficiency SOT devices because their surface states have spin-momentum locking properties, which can achieve charge-spin conversion efficiency far higher than that of traditional heavy metals.

[0005] However, the common binary or ternary topological insulators (such as Bi2Se3, Sb2Te3 and (Bi,Sb)2Te3) have the following problems: (1) The band gap is small (usually ≤0.3 eV), which makes it easy to generate bulk conductivity at room temperature. The serious bulk conductivity will affect the surface state transport; (2) The Fermi level is easy to enter the bulk band, so that the contribution of topological surface state is masked by bulk carriers; (3) The optimal doping range of ternary topological insulators is narrow (usually about 10%), which makes it difficult to meet the requirements of composition control precision in industrial preparation; (4) Existing topological insulator preparation methods have certain difficulties in terms of composition uniformity and industrial scale.

[0006] Quaternary topological insulator Bi2−xSb x Te3−ySe y Due to their larger band gap and lower bulk carrier concentration, quaternary topological insulators are considered an important material system for solving the aforementioned problems. However, current research on quaternary topological insulators in spin-orbit torque devices is still limited, especially in terms of wide band gap modulation and spin Hall angle tunability, which lacks systematic study.

[0007] Therefore, developing a topological insulator structure with a wide bandgap, low carrier concentration, and a wide range of tunable spin-orbit torque is of great significance for realizing low-power spintronic devices. Summary of the Invention

[0008] This invention addresses the problems of narrow bandgap, severe bulk conductivity, and limited spin-orbit torque control range in existing topological insulator materials by providing a quaternary topological insulator heterostructure and a corresponding fabrication method. It also proposes a functional layer for a spin-orbit torque device and a corresponding fabrication method.

[0009] The technical solution of this invention: a quaternary topological insulator heterostructure, the topological insulator heterostructure being represented as: [Sb2Te3(5- x ) / Bi2Se3( x ) ] d / Sb₂Te₃ (3 nm), Sb₂Te₃ and Bi₂Se₃ are periodically stacked alternately, where Sb₂Te₃ is a p-type topological insulator and Bi₂Se₃ is an n-type topological insulator. Parameters x This represents the thickness of the Bi₂Se₃ layer in a single period, in nanometers, with a value range of [value missing]. x = 0~5 nm, the thickness of the Sb2Te3 layer in a single period is (5- x )nm, where d represents the number of alternating periods. The preferred scheme is d = 4. x The selected numerical values ​​enable adjustment of the overall electric transport characteristics and spin-orbit torque performance of the quaternary topological insulator heterostructure, and can be specifically selected according to actual needs. x The value of .

[0010] By alternating stacking of p-type Sb₂Te₃ layers and n-type Bi₂Se₃ layers, a quaternary topological insulator heterostructure with periodic modulation characteristics can be formed, thereby achieving effective control over carrier type, carrier concentration, and Fermi level position. This structure is not a traditional homogeneous solid solution, but rather achieves the functional characteristics of a quaternary topological insulator through an artificially periodic multilayer structure, possessing advantages such as tunable composition, good reproducibility, and suitability for large-scale fabrication.

[0011] A method for fabricating quaternary topological insulator heterostructures is employed using magnetron sputtering deposition. The process conditions are as follows: thermally oxidized Si / SiO2 is used as the substrate, and the substrate vacuum is better than 5 × 10⁻⁶. -5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. - 3During the Torr deposition process, the substrate temperature was maintained at 300℃. Thin layers were deposited sequentially according to the set thickness, alternating between Sb₂Te₃ and Bi₂Se₃ to form a periodic quaternary topological insulator heterostructure. After deposition, the substrate was allowed to cool naturally to room temperature.

[0012] A functional layer of a spin-orbit torque device is represented by the structure: TI / Ti / CoFeB / MgO / Ta, where TI represents a quaternary topological insulator heterostructure layer, and Ti layer, CoFeB layer, MgO layer and Ta layer are sequentially placed on top of the TI layer. These four layers constitute a magnetic heterostructure for spin-orbit torque driving.

[0013] The preferred scheme is as follows: the thickness of the Ti layer is 5 nm, the thickness of the CoFeB layer is 1.4 nm, the thickness of the MgO layer is 3 nm, and the thickness of the Ta layer is 2 nm.

[0014] Method for fabricating the functional layer of a spin orbital torque device: 1) The Ti layer was prepared using magnetron sputtering deposition with the following conditions: thermally oxidized Si / SiO2 as the substrate, and a substrate vacuum better than 5 × 10⁻⁶. -5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. -3 During the deposition process, the substrate temperature is maintained at 300℃. Sb2Te3 and Bi2Se3 are deposited layer by layer according to the set thickness to obtain the TI layer. 2) The multilayer structure was prepared using magnetron sputtering deposition with the following process conditions: substrate vacuum better than 5 × 10⁻⁶. - 5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. -3 During the deposition process, the temperature of the substrate and the TI layer is maintained at 300℃. The TI layer is deposited layer by layer according to the set thickness to form a thin layer. The Ti layer, CoFeB layer, MgO layer and Ta layer are deposited on the TI layer to obtain a multilayer structure. 3) The multilayer structure deposited in step 2) is annealed in a magnetron sputtering deposition apparatus at a temperature of 240-260℃ for 0.8-1.1 hours to obtain the functional layer of the spin-orbit torque device. After annealing, the functional layer acquires perpendicular magnetic anisotropy, thereby meeting the requirements for magnetization reversal of the spin-orbit torque and facilitating its application in low-power spin-orbit torque devices.

[0015] Furthermore, when fabricating the functional layer of the spin-orbit torque device, before deposition, the TI layer is etched by reverse sputtering to remove 4 nm of the Sb2Te3 layer thickness on the surface, thus removing the surface oxide layer and ensuring a clean interface to reduce the impact of surface oxidation of the TI layer.

[0016] The functional layer of the spin-orbit torque device is applied by processing the functional layer of the spin-orbit torque device into a Hall strip device through standard photolithography and ion etching processes.

[0017] Compared with the prior art, the present invention has the following significant advantages: 1. This invention employs a periodic alternating stacking structure of Sb2Te3 and Bi2Se3. Through the complementary thickness design of p-type and n-type topological insulators, the functional characteristics of the quaternary topological insulator system are realized without the need for the complex four-element co-doping control in traditional quaternary solid solutions, thereby significantly improving the reproducibility of material preparation.

[0018] 2. By adjusting the Bi2Se3 layer thickness parameters x It can effectively control the Fermi level position of the material system, making it close to the Dirac point of the topological surface state, thereby obtaining a lower carrier concentration and enhancing the transport contribution of the topological surface state.

[0019] 3. This structure can achieve an effective band gap of about 0.45 to 0.5 eV, which is larger than that of traditional binary or ternary topological insulators, and helps to suppress bulk conductivity.

[0020] 4. A high spin Hall angle (approximately 0.4–0.99) can be obtained in this material system and remains stable over a wide composition range, thereby significantly improving the spin orbital torque efficiency.

[0021] 5. In spin-orbit torque devices, this material system can achieve a low critical magnetization reversal current density, approximately 10. -5 The power consumption is on the order of A / cm², which is about two orders of magnitude lower than that of traditional heavy metal systems, thus significantly reducing device power consumption.

[0022] 6. This invention uses magnetron sputtering technology for preparation, which has better industrial scalability compared to molecular beam epitaxy. Attached Figure Description

[0023] Figure 1 The experimental characterization results of the structural composition and the quaternary topological insulator heterostructure are used to demonstrate the following: (a) is a schematic diagram of the band structure of the traditional binary topological insulator and the quaternary topological insulator heterostructure of the present invention; (b) is a schematic diagram of the quaternary topological insulator heterostructure with d = 4; (c) are the X-ray diffraction (XRD) test results of the samples of the quaternary topological insulator heterostructure under different Bi2Se3 layer thicknesses; (d) is the relationship curve of the diffraction peak position and out-of-plane lattice constant of the quaternary topological insulator heterostructure (0 0 15) with the Bi2Se3 thickness; (e) is the relationship curve of the quaternary topological insulator heterostructure when... xAtomic force microscopy (AFM) images of the sample surface morphology at d = 1.5 nm and d = 4; (f) shows the root mean square roughness of the quaternary topological insulator heterostructure thin film surface. R a. Relationship between a and the thickness of Bi2Se3; Figure 2 The electrical transport properties and bandgap modulation characteristics of the quaternary topological insulator heterostructure of the present invention are characterized, wherein (a) is the resistivity of the sample with temperature under different Bi2Se3 layer thicknesses of the quaternary topological insulator heterostructure; (b) is the relationship between the magnetic field and the Hall coefficient under different Bi2Se3 layer thicknesses of the quaternary topological insulator heterostructure; and (c) is the relationship between the carrier concentration |n| and mobility μ of the quaternary topological insulator heterostructure with respect to the Bi2Se3 layer thickness parameter. x The graph shows the relationship between the changes, where the red curve represents the change in mobility and the black curve represents the change in carrier concentration; (d) is a schematic diagram of the regulation of the Fermi level of the quaternary topological insulator heterostructure with the change in Bi2Se3 layer thickness; (e) is the temperature-dependent resistivity curve of the sample under different Bi2Se3 layer thicknesses of the quaternary topological insulator heterostructure. Figure 3 The spin-orbit torque characteristics and magnetic properties of the quaternary topological insulator heterostructure of this invention are characterized, wherein (a) is the coercivity extracted from the hysteresis loop. H c shows the relationship between the thickness of the Bi2Se3 layer and the magnetic hysteresis loops of different compositions of the quaternary topological insulator heterostructure obtained by magneto-optical Kerr effect (MOKE); (b) shows the longitudinal scanning magnetic field of the quaternary topological insulator heterostructure. H The second harmonic Hall resistance signal measured under condition x, where the inset is the corresponding first harmonic Hall resistance curve; (c) is the effective field of the damped spin-orbit torque of the quaternary topological insulator heterostructure. H DL With current density J The relationship curve; (d) is the spin Hall angle of the quaternary topological insulator heterostructure. θ SH With Bi2Se3 layer thickness parameters x A diagram showing the changing relationships; Figure 4 Performance characterization of devices containing the quaternary topological insulator heterostructure of the present invention, wherein (a) is the relationship curve between the critical magnetization reversal current density of the Hall bar device and the applied auxiliary magnetic field, and the inset is the pulse current density of different applied auxiliary magnetic fields; (b) is the relationship between the critical current density in the topological insulator layer of the Hall bar device and the thickness parameter of the Bi2Se3 layer; (c) is the result of the stability test of the Hall bar device after multiple read-write cycles; and (d) is the relationship between the critical reversal current density of the Hall bar device and the pulse width. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the implementation of the present invention is not limited to the following.

[0025] In this embodiment, a thermally oxidized Si / SiO2 substrate is first selected as the substrate material. A quaternary topological insulator thin film is prepared on the substrate using magnetron sputtering. During the deposition process, the system substrate vacuum is better than 5 × 10⁻⁶. -5 Pa, using Ar gas as the sputtering working gas, with the working gas pressure controlled at approximately 3 × 10 Pa. -3 During the deposition process, the substrate temperature is controlled at approximately 300°C to ensure good crystallinity of the film.

[0026] Under the above conditions, a periodic multilayer structure was constructed by alternately depositing Sb₂Te₃ and Bi₂Se₃ thin layers, thereby obtaining a topological insulator thin film with the following structural form: [Sb₂Te₃(5- x ) / Bi2Se3( x ) ]4 / Sb2Te3(3 nm) Where parameters x The thickness of the Bi₂Se₃ layer in a single period is represented, with values ​​ranging from greater than 0 to less than or equal to 5 nm. Experimental values ​​included 0 (for reference), 0.2 nm, 0.5 nm, 1 nm, 1.5 nm, 2.5 nm, 4 nm, and 5 nm. By changing this thickness parameter, different values ​​of electrical transport properties and spin-orbit torque performance can be obtained. After film deposition, the sample was allowed to cool naturally to room temperature.

[0027] To fabricate the functional layer of the spin-orbit torque device, a magnetic multilayer structure can be further deposited on the surface of the aforementioned quaternary topological insulator heterostructure thin film. Prior to depositing the magnetic multilayer structure, a reverse sputtering etching process is preferably used to remove approximately 4 nm of the surface Sb₂Te₃ layer to remove the surface oxide layer and obtain a clean interface. Subsequently, a Ti layer, a CoFeB layer, a MgO layer, and a Ta layer are deposited sequentially using a magnetron sputtering deposition process under the following conditions: substrate vacuum better than 5 × 10⁻⁶. -5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. -3 During the deposition process, the temperature of the substrate and the Ti layer is maintained at 300°C, thereby forming a functional layer for the spin-orbit torque device. The preferred thicknesses of each layer are: approximately 5 nm for the Ti layer, approximately 1.4 nm for the CoFeB layer, approximately 3 nm for the MgO layer, and approximately 2 nm for the Ta layer.

[0028] After deposition, the heterostructure was subjected to in-situ annealing at approximately 250°C for about 1 hour to induce vertical magnetic anisotropy in the CoFeB layer, thereby forming a functional layer structure suitable for spin-orbit torque-driven magnetization reversal.

[0029] The functional layer of the spin-orbit torque device was further processed and fabricated into a Hall strip device using standard photolithography and ion etching processes. The current channel length was approximately 60 μm and the width was approximately 10 μm. Subsequently, the spin-orbit torque performance of the Hall strip device was tested using harmonic Hall measurement. Experimental results show that, under appropriate auxiliary magnetic field conditions, this functional layer system can achieve a large spin Hall angle and a low magnetization reversal critical current density, while maintaining good read / write cycle stability.

[0030] In summary, this invention achieves multiple technical effects, such as enhanced topological surface state transport, improved spin-orbit torque efficiency, and reduced device power consumption, by constructing a periodic multilayer quaternary topological insulator heterostructure, thus providing a new material and structural solution for low-power spintronic devices.

Claims

1. A quaternary topological insulator heterostructure, characterized by: topological... The insulator heterostructure is represented as: [Sb2Te3(5- x ) / Bi2Se3( x ) ] d / Sb₂Te₃ (3 nm), Sb₂Te₃ and Bi₂Se₃ are periodically stacked alternately, where Sb₂Te₃ is a p-type topological insulator and Bi₂Se₃ is an n-type topological insulator. Parameters x This represents the thickness of the Bi₂Se₃ layer in a single period, in nanometers, with a value range of [value missing]. x = 0~5 nm, the thickness of the Sb2Te3 layer in a single period is (5- x )nm, where d represents the number of alternating periods.

2. The quaternary topological insulator heterostructure as described in claim 1, characterized in that: d = 4。 3. A functional layer of a spin-orbit torque device, characterized in that, The functional layer structure is represented as: TI / Ti / CoFeB / MgO / Ta, where TI represents the quaternary topological insulator heterostructure layer of claim 1, and Ti layer, CoFeB layer, MgO layer and Ta layer are sequentially arranged above the TI layer.

4. The functional layer of a spin-orbit torque device as described in claim 3, characterized in that: The thickness of the Ti layer is 5 nm, the thickness of the CoFeB layer is 1.4 nm, the thickness of the MgO layer is 3 nm, and the thickness of the Ta layer is 2 nm.

5. The method for preparing the quaternary topological insulator heterostructure according to claim 1 or 2, characterized in that: The magnetron sputtering deposition process was employed, with the following process conditions: thermally oxidized Si / SiO2 as the substrate, and a substrate vacuum better than 5 × 10⁻⁶. -5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. -3 During the deposition process, the substrate temperature is maintained at 300℃, and Sb2Te3 and Bi2Se3 are deposited layer by layer into thin layers according to the set thickness.

6. A method for preparing the functional layer of the spin-orbit torque device according to claim 3 or 4, characterized in that: 1) The Ti layer was prepared using magnetron sputtering deposition with the following conditions: thermally oxidized Si / SiO2 as the substrate, and a substrate vacuum better than 5 × 10⁻⁶. -5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. -3 During the deposition process, the substrate temperature is maintained at 300℃. Sb2Te3 and Bi2Se3 are deposited layer by layer according to the set thickness to obtain the TI layer. 2) The multilayer structure was prepared using magnetron sputtering deposition with the following process conditions: substrate vacuum better than 5 × 10⁻⁶. -5 Pa, the working gas is Ar, and the working gas pressure is controlled at 3×10 Pa. -3 During the deposition process, the temperature of the substrate and the TI layer is maintained at 300℃. The TI layer is deposited layer by layer according to the set thickness to form a thin layer. The Ti layer, CoFeB layer, MgO layer and Ta layer are deposited on the TI layer to obtain a multilayer structure. 3) The multilayer structure deposited in step 2) is annealed in a magnetron sputtering deposition apparatus at a temperature of 240-260°C for 0.8-1.1 hours to obtain the functional layer of the spin-orbit torque device.

7. The method for fabricating the functional layer of the spin-orbit torque device as described in claim 6, characterized in that: When fabricating the functional layer of the spin-orbit torque device, before deposition, the TI layer is etched by reverse sputtering to remove 4 nm of the Sb2Te3 layer thickness on the surface.

8. The application of the functional layer of the spin-orbit torque device according to claim 3 or 4, characterized in that: The functional layer of the spin orbital torque device is fabricated into a Hall strip device using standard photolithography and ion etching processes.

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