Spin torque nano-oscillator and method of making the same

Abstract

The application discloses a manufacturing method of a spin-torque nano-oscillator, which comprises the following steps: forming a magnetic multi-layer film on a substrate with a bottom electrode; sequentially spin-coating a polymethyl methacrylate layer and a nano-imprint adhesive layer on the magnetic multi-layer film; using a nano-imprint method to imprint the nano-imprint adhesive layer, so that the nano-imprint adhesive layer is imprinted into a nano-pillar; taking the nano-pillar as a mask layer, and sequentially etching the polymethyl methacrylate layer and the magnetic multi-layer film, so that the etched magnetic multi-layer film forms a magnetic multi-layer film nano-junction; depositing a passivation layer on the bottom electrode and the nano-pillar; stripping the polymethyl methacrylate layer, the nano-imprint adhesive layer on the polymethyl methacrylate layer and the passivation layer, so as to expose the magnetic multi-layer film nano-junction; etching the passivation layer on both sides of the magnetic multi-layer film nano-junction, so as to expose the bottom electrode, depositing a leading electrode on the bottom electrode, and depositing a top electrode on the magnetic multi-layer film nano-junction. The application also provides a plurality of spin-torque nano-oscillators arranged in an array on the same substrate.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to an oscillator, and more particularly to a spin torque nano-oscillator and a method for fabricating the same. Background Technology

[0002] Spin Torque Nano Oscillators (STNOs) are emerging microwave devices in the field of spintronics. They are extremely small, only a few hundred nanometers in size, consume less than 1mW, are compatible with CMOS processes, and can oscillate at frequencies ranging from 100MHz to 65GHz. This frequency band essentially covers most frequencies currently used in communication, making STNOs highly promising for applications in emerging wireless communication fields such as on-chip interconnects, micro base stations, and the Internet of Things (IoT). When a signal close to its oscillation frequency is applied to an STNO, a DC voltage difference can be detected across the oscillator. The sensitivity of microwave detection using STNOs is higher than that of traditional Schottky diodes. The detected DC signal can also be used to power a load, making it a promising method of wireless energy harvesting in IoT, on-chip interconnects, and autonomous driving. Beyond these applications related to microwave emission characteristics, STNOs have also been used in recent years as fundamental computing components in emerging computing architectures such as reservoir computing and neuromorphic computing, demonstrating superior performance compared to traditional von Neumann architecture calculators for specific computational problems. In summary, STNO is an emerging nanoelectronic device with great potential in the field of spintronics. Summary of the Invention

[0003] In view of this, in order to obtain a spin torque nano-oscillator with lower cost and higher repeatability, the present invention provides a spin torque nano-oscillator and a method for fabricating the same.

[0004] As one aspect of the present invention, a method for fabricating a spin-torque nanooscillator is provided, comprising: forming a magnetic multilayer film on a substrate having a bottom electrode; sequentially spin-coating a polymethyl methacrylate layer and a nanoimprint adhesive layer on the magnetic multilayer film; imprinting the nanoimprint adhesive layer using a nanoimprinting method to imprint the nanoimprint adhesive layer into a nanopillar; using the nanopillar as a mask layer, sequentially etching the polymethyl methacrylate layer and the magnetic multilayer film, such that the etched magnetic multilayer film forms a magnetic multilayer film nanojunction; depositing a passivation layer on the bottom electrode and the nanopillar; peeling off the polymethyl methacrylate layer, the nanoimprint adhesive layer and the passivation layer on the polymethyl methacrylate layer to expose the magnetic multilayer film nanojunction; and etching the passivation layers on both sides of the magnetic multilayer film nanojunction to expose the bottom electrode, depositing an lead electrode on the bottom electrode, and depositing a top electrode on the magnetic multilayer film nanojunction.

[0005] As another aspect of the present invention, the present invention provides a spin torque nano-oscillator obtained by the above-described fabrication method.

[0006] According to an embodiment of the present invention, multiple spin-torque nano-oscillators are arranged in an array on the same substrate.

[0007] The method for fabricating spin-torque nanooscillators according to the above embodiments of the present invention utilizes nanoimprinting to rapidly and accurately form high-resolution magnetic multilayer nanostructures, reducing fabrication costs and greatly facilitating the fabrication of large-scale spin-torque nanooscillator arrays. Simultaneously, it overcomes the problem of poor device fabrication repeatability caused by electron beam lithography. Attached Figure Description

[0008] Figure 1 This is a three-dimensional schematic diagram of a magnetic multilayer nanostructure.

[0009] Figure 2 This is a flowchart illustrating a method for fabricating a spin-torque nano-oscillator according to an embodiment of the present invention;

[0010] Figures 3A to 3J A schematic diagram illustrating the fabrication process of a spin-torque nano-oscillator according to an embodiment of the present invention; and

[0011] Figure 4 This is a cross-sectional view of a spin torque nano-oscillator according to an embodiment of the present invention.

[0012] [Explanation of Labels in the Attached Image]

[0013] 1-Substrate;

[0014] 2- Bottom electrode;

[0015] 3-Magnetic multilayer film;

[0016] 3'-Magnetic multilayer nanostructure;

[0017] 31-Magnetic reference layer;

[0018] 32 - Isolation layer;

[0019] 33-Magnetic Free Layer;

[0020] 4-Polymethyl methacrylate layer;

[0021] 5-nanometer imprinted adhesive layer;

[0022] 6-Passivation layer;

[0023] 7-Top electrode;

[0024] 8-Lead electrode. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. However, this invention can be implemented in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make the invention thorough and complete, and to fully convey the scope of the invention to those skilled in the art. In the accompanying drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated, and the same reference numerals denote the same elements throughout.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0027] The core structure reference of the self-rotation torque nano-oscillator Figure 1 As shown, the main components include nanostructures formed by magnetic multilayer thin films. These magnetic multilayer thin films can be the spin valve (SV) structure commonly found in giant magnetoresistive devices, using metals such as Cu and Ag as intermediate layers, or they can be tunneling magnetoresistive devices using MgO and AlO. X MgAlO x A magnetic tunnel junction (MTJ) structure consisting of a ferromagnetic layer / barrier layer / ferromagnetic layer with oxide as the barrier layer.

[0028] Patterning nanojunctions has always been a technical challenge in STNO fabrication. To achieve the spin-transfer torque effect, the length and width of STNO nanojunctions are typically less than 500 nm, which is difficult to achieve with traditional photolithography. Electron beam lithography is commonly used to pattern nanojunctions, but it is expensive and, due to its direct-write method, suffers from poor repeatability between devices, hindering large-scale applications.

[0029] In view of this, this invention employs nanoimprinting to pattern the most critical nanostructure in the STNO process, and utilizes pre-spin-coated PPMA combined with a lift-off method to fabricate electrode vias, reducing the number of patterning steps. Compared to electron beam lithography, the nanoimprinting process for STNO fabrication can significantly reduce costs, as the cost of a single nanoimprinting operation is much lower than that of electron beam lithography. Furthermore, the obtained nanostructures exhibit better repeatability and consistency, which is highly beneficial for fabricating large-scale spin-torque nanooscillator arrays, thereby facilitating the large-scale fabrication and application of STNOs.

[0030] Figure 2 This is a flowchart illustrating a method for fabricating a spin-torque nano-oscillator according to an embodiment of the present invention.

[0031] Figures 3A to 3J This is a schematic diagram illustrating the fabrication process of a spin-torque nano-oscillator according to an embodiment of the present invention.

[0032] According to an exemplary embodiment of the present invention, the present invention provides a method for fabricating a spin-torque nano-oscillator, with reference to... Figure 1 , Figure 2 , Figures 3A to 3J As shown, it includes steps S01 to S07.

[0033] In step S01, a magnetic multilayer film 3 is formed on a substrate 1 on which the bottom electrode 2 is formed.

[0034] According to an embodiment of the present invention, the substrate 1 can be a Si / SiO2 substrate. A bottom electrode 2 is formed on the Si / SiO2 substrate 1, and a magnetic multilayer film 3 is deposited on the bottom electrode 2 by magnetron sputtering. The vacuum level during the magnetron sputtering deposition of the magnetic multilayer film 3 is maintained below 10. -6 Pa.

[0035] According to an embodiment of the present invention, the magnetic multilayer film 3 can be a giant magnetoresistive film or a tunneling magnetoresistive film. The magnetic multilayer film 3 includes, in sequence, a magnetic reference layer 31, an isolation layer 32, and a magnetic free layer 33 in the direction away from the bottom electrode 2.

[0036] According to an embodiment of the present invention, the magnetic reference layer 31, the isolation layer 32, and the magnetic free layer 33 are formed into a magnetic tunnel junction structure comprising a ferromagnetic layer, a barrier layer, and a ferromagnetic layer, respectively. That is, the magnetic reference layer 31 includes a first ferromagnetic layer, the isolation layer 32 includes a barrier layer, and the magnetic free layer 33 includes a second ferromagnetic layer; the first ferromagnetic layer, the intermediate layer, and the second ferromagnetic layer constitute a spin valve structure. The barrier layer can be MgO or AlO. X MgAlO x The oxide layer has a barrier layer thickness of less than 1.2 nm.

[0037] According to an embodiment of the present invention, the magnetic reference layer 31, the isolation layer 32, and the magnetic free layer 33 are formed into a spin valve structure comprising a ferromagnetic layer, an intermediate layer, and a ferromagnetic layer, respectively. The magnetic reference layer 31 includes a first ferromagnetic layer, the isolation layer 32 includes an intermediate layer, and the magnetic free layer 33 includes a second ferromagnetic layer. The first ferromagnetic layer, the intermediate layer, and the second ferromagnetic layer constitute a spin valve structure. The intermediate layer can be a metal such as Cu or Ag.

[0038] In step S02, a polymethyl methacrylate layer 4 and a nanoimprint adhesive layer 5 are sequentially spin-coated onto the magnetic multilayer film 3.

[0039] According to an embodiment of the present invention, a polymethyl methacrylate layer 4 is spin-coated onto a magnetic multilayer film 3 and then dried. After drying, a nanoimprint adhesive layer 5 is spin-coated onto the polymethyl methacrylate layer 4. The thickness of the polymethyl methacrylate layer (PMMA layer) 4 is less than 300 nm.

[0040] According to an embodiment of the present invention, the resolution of the nanoimprint adhesive layer 5 is better than 100 nm.

[0041] In step S03, the nanoimprint adhesive layer 5 is imprinted using a nanoimprinting method to imprint the nanoimprint adhesive layer 5 into nanopillars.

[0042] According to an embodiment of the present invention, the above-mentioned nanoimprint adhesive layer 5 is imprinted using an imprinting device having an imprinting template, so as to remove the nanoimprint adhesive layer imprinted by the imprinting template and retain the nanoimprint adhesive layer not imprinted by the imprinting template, so as to imprint the nanoimprint adhesive layer 5 into nanopillars.

[0043] It should be noted that the embossing shape and size of the embossing template can be made according to actual needs.

[0044] In step S04, using nanopillars as a mask layer, the methyl methacrylate layer 4 and the magnetic multilayer film 3 are etched sequentially, so that the etched magnetic multilayer film 3 forms a magnetic multilayer film nanostructure 3'.

[0045] According to an embodiment of the present invention, reactive ion etching (RIE) is used to etch the polymethyl methacrylate layer 4 to remove the methyl methacrylate layer not covered by the nanopillars, while retaining the methyl methacrylate layer covered by the nanopillars. The etching gas used is O2.

[0046] According to an embodiment of the present invention, the magnetic multilayer film 3 is etched using ion beam etching (IBE) to the bottom electrode 2.

[0047] In step S05, a passivation layer 6 is deposited on the bottom electrode 2 and the nanopillar.

[0048] According to an embodiment of the present invention, the passivation layer 6 is made of silicon oxide or silicon nitride.

[0049] In step S06, the methyl methacrylate layer 4, the nanoimprint adhesive layer 5 and the passivation layer 6 on the methyl methacrylate layer 4 are peeled off to expose the magnetic multilayer nanostructure 3'.

[0050] According to an embodiment of the present invention, an acetone solution is used to peel off the methyl methacrylate layer 4, the nanoimprint adhesive layer 5 and the passivation layer 6 on the methyl methacrylate layer 4.

[0051] It should be noted that nanoimprint enamel is insoluble in common organic solvents, making it difficult to remove directly using a stripping process. Before forming the nanoimprint enamel layer, pre-spin-coating PMMA eliminates the need for additional patterning steps to bring out the top electrode on the nanojunction, simplifying the process and reducing costs.

[0052] In step S07, the passivation layers 6 on both sides of the magnetic multilayer nanostructure 3' are etched to expose the bottom electrode 2, and the lead electrode 8 is deposited on the bottom electrode 2, and the top electrode 7 is deposited on the magnetic multilayer nanostructure 3'.

[0053] According to an embodiment of the present invention, photolithography and RIE etching are used to etch the passivation layer 6 on both sides of the magnetic multilayer nanostructure 3' to etch through holes in the passivation layer 6, thereby exposing the bottom electrode 2.

[0054] The method for fabricating spin-torque nanooscillators according to the above embodiments of the present invention utilizes nanoimprinting to rapidly and accurately form high-resolution magnetic multilayer nanostructures, reducing fabrication costs and greatly facilitating the fabrication of large-scale spin-torque nanooscillator arrays. Simultaneously, it overcomes the problem of poor device fabrication repeatability caused by electron beam lithography.

[0055] Figure 4 This is a cross-sectional view of a spin torque nano-oscillator according to an embodiment of the present invention.

[0056] According to an exemplary embodiment of the present invention, the present invention provides a spin-torque nano-oscillator obtained by the above-described fabrication method, with reference to... Figure 4 As shown, it includes: a substrate 1; a bottom electrode 2 formed on the substrate 1; a magnetic multilayer nanostructure 3' formed on the bottom electrode 2; and a top electrode 7 formed on the magnetic multilayer nanostructure 3'.

[0057] According to an embodiment of the present invention, multiple spin-torque nano-oscillators are arranged in an array on the same substrate.

[0058] According to an embodiment of the present invention, the magnetic multilayer nanostructure 3' comprises, in sequence away from the bottom electrode 2, a magnetic reference layer 31, an isolation layer 32, and a magnetic free layer 33. The magnetic reference layer 31 is adapted to receive non-spin-polarized current, convert it into spin-polarized current, and output it as spin-polarized current, wherein the polarization direction of the spin-polarized current is the same as the magnetization direction of the magnetic reference layer 31. The isolation layer 32 is adapted to separate the magnetic coupling between the magnetic reference layer 31 and the magnetic free layer 33. The magnetic free layer 33 is adapted to receive the spin-polarized current from the magnetic reference layer 31. In response to the spin-polarized current, the magnetic moment of the magnetic free layer 33 precesses, thereby outputting an oscillation signal.

[0059] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a spin-torque nano-oscillator, characterized in that, include: A magnetic multilayer film (3) is formed on a substrate (1) on which a bottom electrode (2) is formed; A polymethyl methacrylate layer (4) and a nanoimprint adhesive layer (5) are sequentially spin-coated onto the magnetic multilayer film (3), wherein the thickness of the polymethyl methacrylate layer (4) is less than 300 nm. The nanoimprint adhesive layer (5) is imprinted using a nanoimprinting method to imprint the nanoimprint adhesive layer (5) into nanopillars; Using the nanopillars as a mask layer, the methyl methacrylate layer (4) and the magnetic multilayer film (3) are etched sequentially, so that the etched magnetic multilayer film (3) forms a magnetic multilayer film nanostructure (3'); A passivation layer (6) is deposited on the bottom electrode (2) and the nanopillar; Organic solvents were used to peel off the methyl methacrylate layer (4), the nanoimprint adhesive layer (5) on the methyl methacrylate layer (4), and the passivation layer (6) to expose the magnetic multilayer film nanostructure. as well as The passivation layers (6) on both sides of the magnetic multilayer nanostructure are etched to expose the bottom electrode (2), and an lead electrode (8) is deposited on the bottom electrode (2), and a top electrode (7) is deposited on the magnetic multilayer nanostructure.

2. The manufacturing method according to claim 1, characterized in that, The magnetic multilayer film (3) includes, in sequence, a magnetic reference layer (31), an isolation layer (32), and a magnetic free layer (33) in the direction away from the bottom electrode (2).

3. The manufacturing method according to claim 2, characterized in that, The magnetic reference layer (31), isolation layer (32), and magnetic free layer (33) are formed into a spin valve structure including a ferromagnetic layer, an intermediate layer, and a ferromagnetic layer.

4. The manufacturing method according to claim 2, characterized in that, The magnetic reference layer (31), isolation layer (32), and magnetic free layer (33) are formed into a magnetic tunnel junction structure including a ferromagnetic layer, a barrier layer, and a ferromagnetic layer.

5. The manufacturing method according to claim 1, characterized in that, Imprinting the nanoimprint adhesive layer (5) into nanopillars using a nanoimprinting method includes: The nanoimprint adhesive layer (5) is imprinted using an imprinting device with an imprinting template to remove the nanoimprint adhesive layer imprinted by the imprinting template and retain the nanoimprint adhesive layer not imprinted by the imprinting template, so as to imprint the nanoimprint adhesive layer (5) into nanopillars.

6. The manufacturing method according to claim 1, characterized in that, The sequential etching of the methyl methacrylate layer (4) and the magnetic multilayer film (3) includes: The polymethyl methacrylate layer (4) was etched using reactive ion etching.

7. The manufacturing method according to claim 1, characterized in that, The sequential etching of the methyl methacrylate layer (4) and the magnetic multilayer film (3) includes: The magnetic multilayer film was etched using ion beam etching (3).

8. A spin-torque nanooscillator obtained by the fabrication method according to any one of claims 1 to 7.

9. The spin-torque nanooscillator according to claim 8, wherein a plurality of the spin-torque nanooscillators are arranged in an array on the same substrate.

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