Tantalum-tungsten-based nanocomposite target material, thin film and application thereof

Abstract

This invention relates to the field of functional metal materials technology, and more particularly to a tantalum-tungsten-based nanocomposite target, thin film, and their applications. The tantalum-tungsten-based nanocomposite target uses tantalum as the matrix, with a tungsten content of 0.1~12 wt.% and a carbon nanophase content of 0.01~1.0 wt.%. The tantalum-tungsten-based nanocomposite target has a (001) preferred orientation in the direction perpendicular to the target surface. This invention provides a low-stress, high-conductivity tantalum-tungsten-based nanocomposite sputtering target. The target has high density, uniform composition, small local deviation in W content, and a significant (001) preferred orientation in the direction perpendicular to the target surface. It can be used to deposit low-stress, high-conductivity, and high-flexibility tantalum-tungsten thin films on flexible substrates. This target is suitable for flexible electrodes in brain-computer interfaces, and can significantly improve electrode bending life and signal stability.

Description

Technical Field

[0001] This invention relates to the field of functional metal materials, and more particularly to a tantalum-tungsten based nanocomposite target, thin film and its application. Background Technology

[0002] Flexible implantable electrodes for brain-computer interfaces typically need to be permanently attached to soft tissue surfaces such as the cerebral cortex for signal acquisition and electrical stimulation. These flexible electronic devices require metal thin-film electrode materials with high conductivity, good biocompatibility, corrosion resistance, and stable electrical performance under repeated bending conditions. Typical applications include flexible microelectrode arrays on cortical surfaces, flexible connections between deep brain stimulation electrodes, and flexible leads between implanted decoding chips and electrode arrays.

[0003] While commonly used metallic electrode materials such as gold and platinum offer good conductivity and flexibility, their long-term stability and mechanical strength in bodily fluid environments are limited. When flexible electrodes operate in vivo for extended periods, the adhesion and fatigue resistance of the metal film to the substrate and tissue interface become crucial. Au and Pt films, due to their lower Young's modulus, may crack or peel off from the substrate after prolonged bending; they may also experience stress corrosion or wear in physiological saline solutions. Tantalum-tungsten alloys (Ta-W), with their excellent biocompatibility and corrosion resistance, have been successfully used in implantable devices such as cardiovascular stents. Pure tantalum has a high resistivity (approximately 13.5 μΩ·cm), while tungsten has a relatively low resistivity (approximately 5.5 μΩ·cm). Alloying a small amount of tungsten into tantalum can effectively reduce the alloy resistivity and improve the material's strength and stability. Therefore, Ta-W alloys are considered a key conductive film layer choice for flexible brain-computer interface electrodes.

[0004] Regarding Ta-W alloy materials, existing technologies both domestically and internationally have been used to study improvements in their preparation processes and microstructures. For example, invention patent application CN119489150A proposes coating the outer surface of large-size Ta-W alloy ingots with high-temperature resistant glass powder and encasing them in a stainless steel sleeve, achieving a microstructure at 900~1400℃. Hot forging at ℃ reduces high-temperature oxidation loss and increases yield, resulting in Ta-W alloy slabs with good surface quality and large dimensions. Patent application CN117737536A discloses a comprehensive process including powder mixing, multiple vacuum electron beam melting to obtain a uniform ingot, followed by room temperature triaxial forging, multi-stage vacuum annealing, and widening cold rolling. This process achieves a tungsten segregation degree ≤8% and a grain size of 6.5~8 in high-tungsten content Ta-W alloy plates, significantly reducing material anisotropy and obtaining Ta-W plates with high isotropy, high strength, and good plasticity. Patent application CN119553161A introduces trace amounts of Sc2O3 pre-alloyed strips into Ta-W alloys, combined with double vacuum electron beam melting to refine the solidification structure, high-temperature multi-directional die forging to break columnar crystals, and steel plate cladding hot rolling and vacuum annealing, refining the grain size of high-tungsten content alloy plates such as Ta-10W to 15~30. The elongation at room temperature is increased to 28–46%, meeting the high plasticity requirements of high-temperature structural and functional materials. The aforementioned existing technologies mainly target the application of hard tantalum-tungsten thin films in high-temperature structural components, corrosion-resistant parts, or microelectronic devices, focusing on improving material purity, refining grain size, and enhancing microstructure uniformity and mechanical properties. In addition, some emerging flexible electrode material solutions, such as liquid metal electrodes, have been proposed. For example, invention patent application CN110251125A provides a stretchable neural electrode with a liquid metal conductor embedded in a flexible polymer matrix, exhibiting good biocompatibility, high conductivity, and excellent tensile properties. However, such liquid metal electrodes require complex encapsulation and structural design, posing challenges in process compatibility and long-term reliability when applied to implanted electrodes. Therefore, for metal thin film electrodes prepared using traditional sputtering processes, improving the stress and flexibility of the film at the target material level is a more direct and feasible approach.

[0005] Current technologies do not consider the specific service conditions required for flexible brain-computer interface electronics. For example, when depositing Ta-W films on flexible polymer substrates, the films are prone to high internal stress (measured values ​​can reach 200-300 MPa) due to the flexibility of the substrate and the lack of rigid support. Repeated bending (>10) with a curvature radius ≤1 mm further exacerbates this issue. 4 After several uses, cracks, detachment, or resistance drift failures are likely to occur. Existing Ta-W targets are mainly used for rigid silicon-based chip interconnects, and there is a lack of dedicated Ta-W-based nanocomposite targets and their supporting preparation technologies for flexible electrodes in brain-computer interfaces.

[0006] In summary, there is currently a lack of Ta-W-based nanocomposite sputtering targets specifically designed for flexible electrodes in brain-computer interfaces. To address the issues of high internal stress, poor bending life, and poor conductivity associated with traditional Ta-W targets in flexible electronics applications, innovative designs for the target composition and microstructure are necessary to provide a tantalum-tungsten-based thin film material solution that can balance low internal stress, high flexibility, and good conductivity. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a tantalum-tungsten-based nanocomposite target, thin film, and their applications. This invention introduces a nano-carbon reinforcing phase into a Ta matrix and controls crystal orientation, resulting in stable and uniform deposition. This significantly reduces the internal stress of the sputtered film, improves its stability under bending conditions, and maintains good conductivity and biocompatibility. This target, while ensuring high purity and high density, imparts low internal stress (≤100 MPa) and excellent flexibility and durability to the deposited film (withstanding 10 cycles of bending under a radius of curvature ≤1 mm). 4 The subsequent rate of change in thin film resistivity ΔR / R (0≤5%), thus meeting the requirements for long-term reliable and safe operation of brain-computer interface implanted electrodes.

[0008] In a first aspect, the present invention provides a tantalum-tungsten-based nanocomposite target, wherein tantalum is used as the matrix, the tungsten content is 0.1~12 wt.%, and the carbon nanophase content is 0.01~1.0 wt.%; the tantalum-tungsten-based nanocomposite target has a (001) preferred orientation in the direction perpendicular to the target surface. The low-stress, high-conductivity tantalum-tungsten-based nanocomposite sputtering target provided by the present invention uses tantalum as the matrix, with added tungsten and carbon nanophase. The target has high density, uniform composition, small local deviation in tungsten content, and a significant (001) preferred orientation in the direction perpendicular to the target surface. It can be used to deposit low-stress, high-conductivity, and high-flexibility tantalum-tungsten thin films on flexible substrates. This target is suitable for flexible electrode applications in brain-computer interfaces, and can significantly improve electrode bending life and signal stability.

[0009] Preferably, using a region with a diameter of 30 μm as the statistical unit, the deviation of tungsten content within any region is ≤3%. Preferably, the relative density of the tantalum-tungsten based nanocomposite target is ≥99%; the diameter of the tantalum-tungsten based nanocomposite target is preferably 50~500 mm, and the thickness is preferably 3~30 mm. In this invention, the target can be prepared as a disc-shaped target with a diameter of 50~500 mm and a thickness of 3~30 mm, and has a density of ≥99% to meet the requirements of large-size deposition processes.

[0010] Preferably, the tantalum-tungsten based nanocomposite target material provided by the present invention has a specially designed composition and structure. This target material uses high-purity tantalum as a matrix, containing 0.1~12 wt.% tungsten and 0.01~1.0 wt.% carbon nanophase, with the remainder being tantalum and unavoidable impurities. The target material can be prepared by powder metallurgy sintering to form a (001) preferred orientation fiber texture, thereby ensuring that the grain orientation in the normal direction (i.e., perpendicular to the target surface) is mainly (001) oriented. <001> Crystal orientation. The resulting target material exhibits highly uniform internal microstructure and composition. Statistically, within a circular region of any diameter of 30 μm, the tungsten content deviation at each location does not exceed 3%. This tantalum-tungsten based nanocomposite target material effectively reduces the resistivity of the tantalum-tungsten alloy, improves conductivity while enhancing stress buffering, further reducing the internal stress of the deposited film, and improving the film's performance under brain-computer interface flexible electrode conditions.

[0011] Preferably, the tantalum-tungsten based nanocomposite target contains 2-10 wt.% tungsten, 0.2-0.8 wt.% carbon nanophase, with the balance being tantalum and unavoidable impurities. This is more conducive to balancing alloy conductivity and thin film stress control.

[0012] According to the present invention, the tantalum-tungsten based nanocomposite target uses tantalum as a matrix, adds 2-10 wt.% tungsten and 0.2-0.8 wt.% carbon nanophase, and forms a (001) texture orientation by powder metallurgy sintering with a strong magnetic field during the sintering process. The preferred composition ratio and texture design can better balance high density and compositional uniformity, and further improve the comprehensive performance of the deposited film in terms of low internal stress, high flexibility and conductivity, thus better meeting the stringent requirements of flexible electrodes for brain-computer interfaces.

[0013] Further preferably, the enhancement factor of the (001) crystal plane diffraction peak intensity of the tantalum-tungsten based nanocomposite target relative to random polycrystalline is ≥2; and there are no continuous tungsten-rich or tungsten-poor segregation areas inside the tantalum-tungsten based nanocomposite target. In this invention, the enhancement factor of the X-ray diffraction peak intensity of the (001) crystal plane of the target relative to random polycrystalline is not less than 2, and there are no continuous tungsten-rich or tungsten-poor macroscopic segregation regions inside the target, ensuring the high uniformity of the target composition and structure.

[0014] Further preferably, the carbon nanophase is mainly distributed at the grain boundaries and intergranular spaces of the target material, forming a continuous or semi-continuous three-dimensional disordered mesh structure. Figure 1 In this invention, the nano-carbon phase (black part) is mainly distributed at the grain boundaries of the tantalum-tungsten matrix (white grains), forming a continuous network structure.

[0015] Preferably, the carbon nanophase includes one or more of amorphous carbon nanotubes, multi-walled carbon nanotubes, and graphene.

[0016] Preferably, the amorphous carbon nanotubes have a particle size of 50-200 nm; the multi-walled carbon nanotubes have an outer diameter of 10-50 nm and a length of 0.5-5 μm; and the graphene has a sheet diameter of 0.5-5 μm and a thickness of 1-10 layers. In this invention, the carbon nanophase can be amorphous carbon nanotubes with a particle size of 50-200 nm, multi-walled carbon nanotubes (MWCNTs) with an outer diameter of 10-50 nm and a length of 0.5-5 μm, graphene and / or graphene nanosheets with a sheet diameter of 0.5-5 μm and a thickness of several layers. This carbon nanophase is mainly distributed at the grain boundaries and intergranular spaces of the tantalum-tungsten matrix, forming a continuous or semi-continuous three-dimensional disordered network structure, acting as a stress buffer and conductive network without significantly reducing the purity of the matrix.

[0017] Further preferably, the surface of the carbon nanophase is coated with a two-dimensional material layer.

[0018] Preferably, the two-dimensional material layer is boron nitride.

[0019] In this invention, the carbon nanophase undergoes surface functionalization treatment before being added to the alloy matrix. Preferably, the surface is coated with a two-dimensional material, boron nitride, which can further improve the stability of the nano-carbon material and its bonding force with the tantalum-tungsten matrix interface.

[0020] Secondly, the present invention also provides a tantalum-tungsten based thin film, which is obtained by depositing the tantalum-tungsten based nanocomposite target on a flexible polymer substrate.

[0021] Preferably, the internal stress of the tantalum-tungsten based film is ≤100MPa; the tantalum-tungsten based film is subjected to a bending radius of ≤1mm for 10... 4 After repeated bending, the change rate of thin film resistivity ΔR / R 0 ≤ 5%.

[0022] Thirdly, the present invention provides the application of the tantalum-tungsten based nanocomposite target or the tantalum-tungsten based film in flexible electrodes for brain-computer interfaces.

[0023] The beneficial effects of this invention are at least as follows: 1) Precisely controlled grain structure and texture orientation: The target material exhibits a highly oriented (001) fiber texture in the direction perpendicular to the target surface. This texture helps improve the sputtering uniformity of the target material, reduce internal stress during film deposition, and minimize the risk of particle detachment during use. Simultaneously, by strictly controlling the raw material ratio and process parameters, the tungsten content deviation in a local area (30 μm diameter scale) can be ≤3%, significantly improving the uniformity of the composition and thickness of the deposited film.

[0024] 2) Nano-carbon reinforced phase provides flexible conductive network and stress buffer: Introducing a small amount of nano-carbon (secondary phase), such as nano-amorphous carbon, carbon nanotubes, or graphene, into the traditional Ta-W alloy can optimize film performance without significantly affecting alloy purity. Nano-carbon particles are uniformly dispersed during powder mixing and, after sintering, are mainly enriched at grain boundaries and intergranular spaces, forming a disordered, three-dimensional network structure. On one hand, the carbon nanonetwork can hinder grain growth and migration, acting as grain boundary pinning, thereby refining the target material grains and reducing thermal stress concentration. On the other hand, due to the high surface energy and low elastic modulus of carbon materials, the carbon phase can absorb some of the incident particle energy during deposition, acting as a stress buffer layer and inhibiting crack initiation and propagation. Furthermore, the Fermi level of carbon matches well with the Ta-W matrix, forming low-barrier conductive channels at grain boundaries, reducing electron scattering loss at grain boundaries, and thus improving the overall conductivity of the film.

[0025] 3) Improved service life and signal quality of flexible electrodes: The Ta-W-based nanocomposite film obtained by sputtering deposition using the target material of this invention possesses low internal stress, high flexibility, good conductivity, and excellent corrosion resistance. Compared with traditional tantalum or tantalum alloy films, this film is less prone to cracking or peeling from the substrate during repeated bending, significantly reducing the failure probability of flexible electrodes. Simultaneously, the interfacial impedance between the electrode and tissue is reduced, improving signal transmission quality and meeting the requirements for long-term stability and low noise, high signal-to-noise ratio in various brain-computer interface applications such as EEG signal recording and electrical stimulation. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the microstructure of the tantalum-tungsten-based nanocomposite target provided by the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0030] Unless otherwise specified, the techniques or conditions described in the embodiments of this invention shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Devices, instruments, reagents, etc., without specified manufacturers, are all conventional products that can be purchased through legitimate channels. All experimental reagents and raw materials involved are commercially available products, and all reagents are analytical grade products.

[0031] Unless otherwise specified, the target materials obtained in the embodiments and comparative examples of the present invention are all processed into disc-shaped target materials by subsequent machining. The sample specifications used for structural and performance verification are 100 mm in diameter and 6 mm in thickness. Based on the same powder mixing, forming, densification and machining processes, the target materials of the present invention can be stably prepared into engineering specifications with a diameter of 50~500 mm and a thickness of 3~30 mm.

[0032] Example 1 This embodiment provides a Ta-8 wt.%W / 0.8 wt.% nano-carbon (001) textured tantalum-tungsten-based nanocomposite target: I. Target Composition and Structure This embodiment provides a tantalum-tungsten based nanocomposite target material, which uses high-purity Ta as the matrix, has a W content of 8 wt.%, and introduces a nano-carbon reinforcing phase with a total amount of 0.8 wt.%. The nano-carbon reinforcing phase consists of amorphous carbon nanotubes with a particle size of 150 nm and multi-walled carbon nanotubes (MWCNTs) with an outer diameter of 20 nm and a length of 2 μm, with a mass ratio of 1:1. Before adding alloy powder, the nano-carbon is first subjected to surface chemical vapor deposition (CVD) to coat it with a layer of two-dimensional boron nitride (h-BN). A clear (001) preferred orientation is formed in the direction perpendicular to the target surface, and the W content deviation within the 30 μm diameter circular region is used as the statistical unit, with a deviation of ≤3%.

[0033] II. Methods of Obtaining Targets In this embodiment, the target material can be prepared by powder metallurgy hot pressing sintering. During the densification process, a unidirectional static magnetic field is applied along the direction perpendicular to the target surface to induce the target material to form an enhanced (001) fiber texture (8T). Nano-carbon is introduced during the powder mixing process and preferentially distributed in the grain boundaries and grain gaps after sintering to form a disordered network structure, thus serving as both a stress buffer and a conductive channel.

[0034] III. Characterization of Structure and Homogeneity The target material of this embodiment was subjected to microstructure and compositional uniformity testing. EBSD pole figures showed a significant enhancement of the (001) orientation perpendicular to the target surface, with the (001) texture intensity being approximately 2.5 times that of random polycrystalline materials. Multiple locations on the target surface were selected, and EDS lattice scanning was performed using a 30 μm diameter circle as the statistical region. The W content deviation at each point was less than 2.5%, meeting the requirement of W element deviation ≤3%. Cross-sectional high-resolution TEM revealed that nano-carbon and carbon nanotubes formed continuous or semi-continuous network enrichment regions at grain boundaries, verifying that the carbon phase is mainly located at grain boundaries and intergranular spaces. The relative density of the target material was approximately 99.5%, and the Vickers hardness was approximately 240 HV, with minimal differences at different locations, indicating uniform microstructure.

[0035] The target material obtained in this embodiment was machined into a disc-shaped target with a diameter of 100 mm and a thickness of 6 mm. Further surface and line scan analysis of multiple regions of the target surface and cross-section was performed using SEM-BSE combined with EDS. No continuous band-like, mesh-like, sheet-like, or penetrating tungsten-rich or tungsten-poor regions were observed, indicating that the W element distribution within the target material of this embodiment is uniform, and there is no continuous tungsten-rich or tungsten-poor segregation.

[0036] Application verification showed that the target material of this embodiment was used for thin film deposition to deposit Ta-WC conductive films on flexible polymer substrates. Test results showed that the deposited film could achieve an internal stress of 100 MPa and withstand bending radii of 1 mm and 10 bending cycles. 4 Thin film resistivity change rate under subcondition ΔR / R The accuracy is 0.05%, meeting the long-term reliability requirements of flexible electrodes for brain-computer interfaces. In contrast, when depositing films using traditional Ta-W targets that do not contain nano-carbon and lack design for flexible film tissues, the internal stress of the film can reach 250 MPa, and cracks, detachment, or resistance drift failures are prone to occur under the same bending conditions.

[0037] Example 2 This embodiment provides a Ta-10 wt.%W / 1.0 wt.%graphene (001) textured tantalum-tungsten-based nanocomposite target: I. Target Composition and Structure This embodiment provides another tantalum-tungsten-based nanocomposite target, which uses high-purity Ta as the matrix, has a W content of 10 wt.%, and introduces 1.0 wt.% nano-carbon reinforcing phase; the nano-carbon reinforcing phase is graphene (sheet diameter 0.5~5 μm, thickness ≤1.7 nm), and can also be further compounded with a small amount of nano-amorphous carbon to enhance the continuous conductive network at the grain boundaries (graphene:amorphous carbon mass ratio is 7:3). Before adding alloy powder, the nano-carbon is first subjected to surface chemical vapor deposition (CVD) to coat a layer of two-dimensional boron nitride (h-BN). The target material also meets the following requirements: (001) preferred orientation in the direction perpendicular to the target surface, and W content deviation ≤3% in a statistical region with a diameter of 30 μm.

[0038] II. Methods of Obtaining Targets In this embodiment, the target material can also be obtained through powder metallurgy densification. During the densification stage, a unidirectional static magnetic field is applied along the direction perpendicular to the target surface to induce (001) texture growth (8T), thereby forming a (001) fiber texture with enhanced normal direction of the target material. Under the action of the magnetic field, graphene tends to align along the magnetic field lines and forms a synergy with the three-dimensional network at the grain boundaries, which is beneficial to suppressing macroscopic component segregation and promoting texture formation.

[0039] III. Characterization of Structure and Homogeneity The target material in this embodiment was tested, and EBSD showed enhanced (001) orientation and a significantly increased texture intensity (2 times) compared to random polycrystalline materials, indicating that the target material possesses controllable texture characteristics. EDS statistics for a 30 μm diameter region showed that the W content deviation met the requirement of ≤3%, thus ensuring the compositional consistency of the sputtered deposition. Cross-sectional observation showed that nano-carbon was distributed in a lamellar / network pattern at the grain boundaries, forming a continuous or semi-continuous conductive-buffered network. The relative density of the target material reached 99.8%, satisfying the structural stability requirements of the large-size sputtering process.

[0040] The target material obtained in this embodiment was machined into a disc-shaped target with a diameter of 100 mm and a thickness of 6 mm, falling within the range of 50-500 mm in diameter and 3-30 mm in thickness defined in this invention. SEM-BSE observation of the target surface and cross-section, combined with EDS surface and line scanning analysis, revealed no continuous banded or sheet-like tungsten-rich or tungsten-poor regions, indicating that there is no continuous tungsten-rich or tungsten-poor segregation within the target material of this embodiment, and that the composition is highly uniform.

[0041] Application verification shows that using the target material of this embodiment to deposit flexible Ta-WC thin films results in films with internal stress ≤100MPa, and bending radius ≤1 mm and bending cycles ≥10. 4 Under these conditions, the rate of change of thin film resistivity ΔR / R 0 ≤ 5%.

[0042] Example 3 This embodiment provides a Ta-4 wt.%W / 0.30 wt.% nano-carbon (001) textured tantalum-tungsten-based nanocomposite target: I. Target Composition and Structure This embodiment provides a tantalum-tungsten based nanocomposite target material, which uses high-purity Ta as the matrix, has a W element content of 4 wt.%, and introduces a total of 0.30 wt.% nano-carbon reinforcing phase; the nano-carbon reinforcing phase is composed of amorphous nano-carbon with a particle size of 50~150 nm and multi-walled carbon nanotubes, with a mass ratio of 3:1.

[0043] Before adding alloy powder, the nano-carbon reinforcing phase is first surface-coated, and a two-dimensional boron nitride protective layer is formed on its surface by chemical vapor deposition. The resulting target material forms a clear (001) preferred orientation in the direction perpendicular to the target surface, and the W content deviation within the 30 μm diameter circular region is ≤3%.

[0044] II. Methods of Obtaining Targets In this embodiment, the target material can be prepared by powder metallurgy hot pressing sintering. High-purity Ta powder, W powder, and a boron nitride-coated nano-carbon reinforcing phase are mixed uniformly, pressed into shape, and then densified and sintered under high vacuum or a protective atmosphere. During the densification process, a unidirectional static magnetic field with a strength of 4 T is applied along the direction perpendicular to the target surface to induce the formation of a reinforced (001) fiber texture. After sintering, the nano-carbon reinforcing phase is mainly distributed at grain boundaries and intergranular spaces, forming a continuous network buffer structure.

[0045] III. Characterization of Structure and Homogeneity The target material of this embodiment was tested, and the EBSD pole figure and XRD results showed that there was an obvious (001) preferred orientation in the direction perpendicular to the target surface. The enhancement factor of the (001) crystal plane diffraction peak intensity relative to the random polycrystalline was about 2.1.

[0046] EDS statistics were performed on circular regions with a diameter of 30 μm at multiple locations on the target surface, and the W content deviation was approximately 2.8%. The relative density of the target material was approximately 99.2%, and cross-sectional observation showed that the nano-carbon reinforcing phase was mainly located at grain boundaries and intergranular spaces.

[0047] The target material obtained in this embodiment was machined into a disc-shaped target with a diameter of 100 mm and a thickness of 6 mm. SEM-BSE combined with EDS was used to analyze the W element distribution inside the target material. The results showed that no continuous banded, network-like, or multi-grain-penetrating tungsten-rich or tungsten-poor segregation regions were observed within the detected area, indicating that there is no continuous tungsten-rich or tungsten-poor segregation inside the target material of this embodiment.

[0048] Using the target material of this embodiment, a Ta-WC thin film was deposited on a flexible polymer substrate, and the resulting film had an internal stress of approximately 95 MPa; after 10 days of bending with a radius of curvature ≤ 1 mm... 4 After repeated bending, the change rate of thin film resistivity ΔR / R 0 is approximately 4.8%.

[0049] The results show that when the W content and nano carbon content are lower than those in Examples 1 and 2, the overall performance of the film decreases slightly, but is still significantly better than that in Comparative Examples 1 and 2.

[0050] Example 4 This embodiment provides a Ta-8 wt.%W / 0.60 wt.% nano-carbon (001) textured tantalum-tungsten based nanocomposite target without boron nitride surface coating: I. Target Composition and Structure This embodiment provides a tantalum-tungsten based nanocomposite target material, which uses high-purity Ta as the matrix, has a W element content of 8 wt.%, and introduces a total of 0.60 wt.% of nano-carbon reinforcing phase; the nano-carbon reinforcing phase is composed of graphene and multi-walled carbon nanotubes, with a mass ratio of 2:1.

[0051] Unlike Examples 1 and 2, the nano-carbon reinforcing phase in this example is not coated with boron nitride; it is simply added to the alloy powder after conventional purification and dispersion. The resulting target material still exhibits a (001) preferred orientation in the direction perpendicular to the target surface and satisfies the requirement that the W content deviation within a statistical region of 30 μm in diameter is ≤3%.

[0052] II. Methods of Obtaining Targets After high-purity Ta powder, W powder and uncoated boron nitride nano-carbon reinforced phase are mixed evenly, they are densified by powder metallurgy hot pressing sintering or discharge plasma sintering process; during the sintering densification process, a unidirectional static magnetic field with a magnetic field strength of 6 T is applied along the direction perpendicular to the target surface to promote the formation of (001) fiber texture.

[0053] Since the nano-carbon phase is not coated with boron nitride, its tendency to locally agglomerate during powder mixing and sintering is slightly higher than that in Examples 1 and 2, but it can still form a continuous or semi-continuous conductive-buffer network at the grain boundaries.

[0054] III. Characterization of Structure and Homogeneity EBSD and XRD results show that the target material in this embodiment has a relatively obvious (001) preferred orientation in the direction perpendicular to the target surface, and the enhancement factor of the (001) crystal plane diffraction peak intensity relative to random polycrystalline is about 2.3.

[0055] EDS statistical results show that the W element deviation within a 30 μm diameter region is approximately 2.9%. The relative density of the target material is approximately 99.1%. Cross-sectional observation shows that the nano-carbon reinforcing phase is mainly located at the grain boundaries, but the uniformity is slightly lower than that of Examples 1 and 2.

[0056] The target material obtained in this embodiment was machined into a disc-shaped target with a diameter of 100 mm and a thickness of 6 mm. SEM-BSE observation and EDS surface scanning analysis were performed on the target surface and cross-section. No continuous band-like, sheet-like or mesh-like tungsten-rich or tungsten-poor regions were found. Local compositional fluctuations were observed, but no continuous segregation channels were formed, indicating that there is no continuous tungsten-rich or tungsten-poor segregation inside the target material in this embodiment.

[0057] Using the target material of this embodiment, a Ta-WC thin film was deposited on a flexible polymer substrate, and the resulting film had an internal stress of approximately 92 MPa; after 10 days of bending with a radius of curvature ≤ 1 mm... 4 After repeated bending, the change rate of thin film resistivity ΔR / R 0 is approximately 4.4%.

[0058] The results show that the performance of the target material and film obtained without boron nitride surface coating is slightly lower than that of Examples 1 and 2, but still significantly better than the comparative samples without the addition of nano-carbon phase or without (001) preferred orientation. This example further illustrates that boron nitride surface coating is a preferred solution, but it is not the only necessary condition for achieving the technical effects of this invention.

[0059] Example 5 This embodiment provides a comparative implementation scheme for Ta-8 wt.%W / 0.60 wt.% nano-carbon tantalum tungsten-based nanocomposite targets under different magnetic field strengths: I. Target Composition and Structure In this embodiment, the target material uses high-purity Ta as the matrix, with a W element content of 8 wt.% and a nano-carbon reinforcing phase content of 0.60 wt.%. The nano-carbon reinforcing phase is composed of amorphous nano-carbon and graphene in a mass ratio of 1:1. The nano-carbon reinforcing phase is first coated with boron nitride before being added to the alloy powder.

[0060] II. Methods of Obtaining Targets After the above raw materials are mixed evenly, the target material is prepared using the same powder metallurgy densification process. The only difference is that the intensity of the unidirectional static magnetic field applied along the direction perpendicular to the target surface during the sintering densification process is different, namely 2 T, 6 T and 10 T.

[0061] III. Structural and Performance Characterization The test results show that different magnetic field strengths have a significant impact on the preferred orientation of the target material (001) and the properties of the thin film: The 2 T, 6 T, and 10 T samples were machined and dimensionally inspected. All the resulting targets were fabricated into disc-shaped targets, with a diameter of 100 mm and a thickness of 6 mm. Further elemental distribution analysis of the target surface and cross-section of the three sets of samples was performed using SEM-BSE combined with EDS surface and line scanning. The results showed that no continuous banded, mesh-like, sheet-like, or penetrating tungsten-rich or tungsten-poor regions appeared inside the three sets of samples. This indicates that changes in magnetic field strength mainly affect the texture intensity and the resulting film properties, without causing continuous tungsten-rich or tungsten-poor segregation within the target material.

[0062] Under 2T conditions, the target material has formed a (001) preferred orientation in the direction perpendicular to the target surface. The enhancement factor of the (001) crystal plane diffraction peak intensity relative to random polycrystalline is approximately 2.0, and the relative density of the target material is approximately 99.0%. The internal stress of the film deposited using this target material is approximately 96 MPa. After 10... 4 After the second bend ΔR / R 0 is approximately 4.7%.

[0063] Under 6 T conditions, the preferred orientation of the target (001) was further enhanced, with an enhancement factor of approximately 2.6, and the relative density of the target was approximately 99.5%. The internal stress of the film deposited using this target was approximately 81 MPa, and after 10... 4 After the second bend ΔR / R 0 is approximately 3.2%.

[0064] Under 10 T conditions, the preferred orientation of the target (001) continues to enhance the film, with an enhancement factor of approximately 2.8 and a relative density of approximately 99.6%. The internal stress of the film deposited using this target is approximately 79 MPa. 4 After the second bend ΔR / R 0 is approximately 3.1%.

[0065] IV. Results Analysis The above results indicate that, under essentially the same process conditions, as the magnetic field strength increases from 2 T to 10 T, the (001) preferred orientation of the target material is generally enhanced, the internal stress of the deposited film decreases, and the bending stability improves; however, when the magnetic field strength increases to a higher level, the improvement in overall performance tends to plateau. Therefore, considering the overall balance between process complexity and performance improvement, a magnetic field strength of 4–8 T is more conducive to balancing texture enhancement and engineering feasibility.

[0066] Comparative Example 1 This comparative example provides a Ta-8 wt.%W conventional tantalum-tungsten alloy sputtering target without nano-carbon reinforcing phase: I. Target Composition and Structure The target material for this comparative example uses high-purity Ta as the matrix, with a W content of 8 wt.%, and no nano-carbon reinforcing phase is added. Other process conditions are kept as consistent as possible with those in Example 1.

[0067] II. Methods of Obtaining Targets After high-purity Ta powder and W powder are mixed evenly, they are densified by powder metallurgy hot pressing sintering. During the sintering densification process, a 6 T unidirectional static magnetic field is applied along the direction perpendicular to the target surface.

[0068] III. Structural and Performance Characterization The test results show that the target material has a certain (001) preferred orientation, the intensity of the (001) crystal plane diffraction peak is about 2.1 relative to the random polycrystalline, the relative density of the target material is about 99.4%, and the W element is relatively uniformly distributed.

[0069] However, due to the lack of a conductive-buffered network formed at the grain boundaries by the nano-carbon reinforcing phase, the resulting target material has insufficient stress buffering capacity during deposition. The internal stress of the Ta-W film deposited on a flexible substrate using this target material is approximately 155 MPa; under bending curvature radius ≤1 mm conditions, after 10... 4 After repeated bending, the change rate of thin film resistivity ΔR / R The resistance is approximately 11.2%, and localized cracks or resistance drift can be observed.

[0070] The target material obtained in this comparative example was machined into a disc-shaped target with a diameter of 100 mm and a thickness of 6 mm. SEM-BSE observation of multiple regions on the target surface and cross-section, combined with EDS surface and line scanning analysis, revealed no continuous banded, mesh-like, or sheet-like tungsten-rich or tungsten-poor regions. The performance difference between this and the examples mainly stems from the absence of a nano-carbon reinforcing phase.

[0071] IV. Results Analysis This comparative example illustrates that even if the target material has a certain texture orientation, it is still difficult to simultaneously achieve low internal stress and high bending stability without introducing a nano-carbon reinforcing phase, proving that nano-carbon reinforcement plays an important role in achieving the technical effect of this invention.

[0072] Comparative Example 2 This comparative example provides a tantalum-tungsten-based nanocomposite target that contains a nano-carbon reinforcing phase but does not have a significant (001) crystal plane preferred orientation: I. Target Composition and Structure The target material of this comparative example uses high-purity Ta as the matrix, with a W element content of 8 wt.% and a nano-carbon reinforcing phase content of 0.60 wt.%. The nano-carbon reinforcing phase is a mixture of amorphous nano-carbon and graphene that has been surface-coated with boron nitride. The remaining composition is basically the same as that of Example 5.

[0073] II. Methods of Obtaining Targets After the above raw materials are mixed evenly, the target material is prepared using the same powder metallurgy densification process as in Example 5. However, no magnetic field is applied during the sintering densification process, or only a weak magnetic field that is insufficient to induce significant texture formation is applied, so that the obtained target material does not have a significant (001) crystal plane preferred orientation in the direction perpendicular to the target surface.

[0074] III. Structural and Performance Characterization The test results show that the relative density of the target material is about 99.3%, and the W element distribution is basically uniform. However, XRD and EBSD results show that no significant (001) preferred orientation was observed in the direction perpendicular to the target surface, and the enhancement factor of the (001) crystal plane diffraction peak intensity relative to random polycrystalline is only about 1.1.

[0075] The target material obtained in this comparative example was machined into a disc-shaped target with a diameter of 100 mm and a thickness of 6 mm. Further analysis of the elemental distribution inside the target material was performed using SEM-BSE combined with EDS. The results showed that although there was no obvious continuous enrichment or depletion of W element, and no continuous band-like, network-like or sheet-like segregation regions were formed, the internal stress control and bending stability of the resulting film were still significantly worse than those of the example sample due to the lack of a significant (001) crystal plane preferred orientation.

[0076] The internal stress of the Ta-WC film deposited on a flexible polymer substrate using this target is approximately 132 MPa; under bending curvature radius ≤ 1 mm, after 10... 4 After repeated bending, the change rate of thin film resistivity ΔR / R 0 is approximately 8.3%.

[0077] IV. Results Analysis The comparative example illustrates that even with the introduction of nano-carbon reinforcing phase, if the target material does not have a significant (001) crystal plane preferred orientation in the direction perpendicular to the target surface, it is still difficult to fully utilize the advantages of low-stress deposition and high bending stability, proving that (001) texture design is also an important factor in achieving the technical effect of this invention.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tantalum-tungsten-based nanocomposite target, characterized in that, In the tantalum-tungsten based nanocomposite target, tantalum is used as the matrix, the tungsten content is 0.1~12 wt.%, and the carbon nanophase content is 0.01~1.0 wt.%; the tantalum-tungsten based nanocomposite target has a preferred orientation of (001) crystal plane in the direction perpendicular to the target surface.

2. The tantalum-tungsten based nanocomposite target according to claim 1, characterized in that, Using a region with a diameter of 30 μm as the statistical unit, the deviation of tungsten content within any of the stated regions is ≤3%; Preferably, the relative density of the tantalum-tungsten based nanocomposite target is ≥99%; the diameter of the tantalum-tungsten based nanocomposite target is 50~500 mm and the thickness is 3~30 mm.

3. The tantalum-tungsten based nanocomposite target according to claim 1 or 2, characterized in that, The tantalum-tungsten based nanocomposite target contains 2-10 wt.% tungsten, 0.2-0.8 wt.% carbon nanophase, and the remainder is tantalum and unavoidable impurities.

4. The tantalum-tungsten based nanocomposite target according to any one of claims 1-3, characterized in that, The intensity of the (001) crystal plane diffraction peak of the tantalum-tungsten based nanocomposite target has an enhancement factor of ≥2 relative to random polycrystalline; the tantalum-tungsten based nanocomposite target has no continuous tungsten-rich or tungsten-poor segregation inside the target.

5. The tantalum-tungsten based nanocomposite target according to any one of claims 1-4, characterized in that, The carbon nanophase is mainly distributed at the grain boundaries and intergranular spaces of the target material, forming a continuous or semi-continuous three-dimensional disordered mesh structure.

6. The tantalum-tungsten based nanocomposite target according to any one of claims 1-5, characterized in that, The carbon nanophase includes one or more of amorphous carbon nanotubes, multi-walled carbon nanotubes, and graphene. Preferably, the amorphous carbon nanotubes have a particle size of 50-200 nm; the multi-walled carbon nanotubes have an outer diameter of 10-50 nm and a length of 0.5-5 μm; and the graphene sheets have a diameter of 0.5-5 μm and a thickness of 1-10 layers.

7. The tantalum-tungsten based nanocomposite target according to any one of claims 1-6, characterized in that, The surface of the carbon nanophase is coated with a two-dimensional material layer; Preferably, the two-dimensional material layer is boron nitride.

8. A tantalum-tungsten based thin film, characterized in that, The tantalum-tungsten based nanocomposite target as described in any one of claims 1-7 is deposited on a flexible polymer substrate.

9. The tantalum-tungsten based thin film according to claim 8, characterized in that, The internal stress of the tantalum-tungsten based film is ≤100MPa; the tantalum-tungsten based film is subjected to a bending radius of ≤1 mm for 10... 4 After repeated bending, the change rate of thin film resistivity ΔR / R 0 ≤ 5%.

10. The application of the tantalum-tungsten based nanocomposite target according to any one of claims 1-7 or the tantalum-tungsten based thin film according to claim 8 or 9 in flexible electrodes for brain-computer interfaces.

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