Iron oxide nickel sputtering target material, method for preparing the same, and use thereof

Abstract

This invention belongs to the field of sputtering target technology, and specifically relates to a nickel-iron oxide sputtering target, its preparation method, and its application. The raw materials for preparing the nickel-iron oxide sputtering target of this invention include NiO, Fe2O3, MgO, and TiO2; in NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:(2±0.1%). This invention refines the grain size, suppresses the formation of impurity phases (NiO, Fe2O3), and stabilizes the stoichiometry by adding MgO; and enhances the diffusion kinetics by adding TiO2, achieving rapid densification at low temperatures while reducing oxygen content and improving sputtering quality. Furthermore, by combining composite molding, gradient pre-firing, and sintering processes, the stoichiometry deviation of the nickel-iron oxide sputtering target is ≤±0.1%, the density is ≥99.6%, the oxygen content is ≤30ppm, and it possesses equiaxed crystals with a grain size of 30-60μm.

Description

Technical Field

[0001] This invention belongs to the field of sputtering target technology, and specifically relates to an iron-nickel oxide sputtering target, its preparation method, and its application. Background Technology

[0002] Nickel iron oxide (NiFe2O4) spinel material combines high resistivity, excellent ferromagnetism, and thermal stability, making it a core material for preparing high-frequency insulating magnetic thin films. It is widely used in high-end applications such as 5G millimeter-wave devices, magnetoresistive random access memory (MRAM) barrier layers, and precision sensors. As devices evolve towards higher frequencies, smaller sizes, and higher precision, stringent requirements are placed on NiFe2O4 targets, such as: 1) precise stoichiometry (Ni:Fe atomic ratio must be strictly controlled within 1:2 ± 0.1%); 2) density ≥ 99.5% to avoid sputtering particle contamination; 3) fine and uniform grains, 30-60 μm equiaxed crystals; and 4) high purity and low oxygen, O ≤ 30 ppm.

[0003] Currently, existing nickel-iron oxide sputtering targets have the following problems: 1) Large deviation in stoichiometry: The Ni:Fe atomic ratio often deviates from 1:2 (deviation ≥ ±2%), easily resulting in NiO and Fe2O3 impurities, leading to fluctuations in film permeability and resistivity ≥ 10%; 2) Low density: Traditional sintering density is usually < 98.5%, with many internal pores and microcracks, resulting in severe particle contamination during sputtering and reducing device yield; 3) Coarse and uneven grains: Conventional sintering easily forms coarse grains > 150 μm, leading to uneven sputtering rates and high film stress; 4) Dependence on hot isostatic pressing (HIP) process: Although it can improve density, the equipment is expensive and easily induces abnormal grain growth, resulting in high mass production costs, long cycle time (≥ 24 h), and yield < 85%.

[0004] Furthermore, many current studies only optimize a single step and rely heavily on HIP or high-temperature sintering, lacking a systematic solution of "low-temperature densification + fine grains + low oxygen". There are still significant technological gaps in the synergistic control of atomic-level segregation suppression, precise oxygen control and grain homogenization, making it difficult to meet the needs of high-end scenarios such as 5G and MRAM.

[0005] Therefore, it is of great significance to provide an iron-nickel oxide sputtering target with small stoichiometric deviation, fine grains, low oxygen content, and high density. Summary of the Invention

[0006] The present invention aims to solve one or more technical problems existing in the prior art, and at least provide a beneficial alternative. Specifically, the present invention provides an iron-nickel oxide sputtering target with a Ni to Fe atomic ratio deviation ≤ ±0.1%; fine grains, with equiaxed crystals of 30-60 μm, and no columnar crystals or coarse grains; oxygen content ≤ 30 ppm and density ≥ 99.6%.

[0007] The inventive concept of this invention: The raw materials for preparing the nickel oxide sputtering target of this invention include NiO, Fe2O3, MgO, and TiO2; In the NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:(2±0.1%).

[0008] In this invention, MgO can enter the spinel lattice to suppress Fe. 2+ The process generates and refines grains, suppresses the formation of impurity phases (NiO, Fe2O3), and stabilizes the stoichiometric ratio. TiO2 can enhance diffusion kinetics, enabling rapid densification at low temperatures, while reducing oxygen content and improving sputtering quality. Simultaneously, by limiting the Ni / Fe atomic ratio fluctuation to ≤±0.1%, the permeability of 5G RF devices is ensured to be stable (fluctuation ≤3%).

[0009] Therefore, a first aspect of the present invention provides an iron-nickel oxide sputtering target.

[0010] Specifically, the raw materials for preparing the nickel-iron oxide sputtering target include NiO, Fe2O3, MgO, and TiO2; In the NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:(2±0.1%).

[0011] Preferably, based on the total mass of the nickel oxide sputtering target, the mass percentages of MgO and TiO2 are 0.02-0.08 wt% and 0.01-0.05 wt%, respectively.

[0012] Preferably, the iron-nickel oxide sputtering target also contains impurities, and the content of the impurities, based on the total mass of the iron-nickel oxide sputtering target, is C≤8ppm, O≤30ppm, N≤4ppm, S≤1ppm, and total metal impurities≤40ppm.

[0013] Preferably, the purity of the iron-nickel oxide sputtering target is ≥4N5 grade.

[0014] Preferably, the nickel oxide sputtering target has equiaxed crystals with a grain size of 30-60 μm.

[0015] A second aspect of the present invention provides a method for preparing the nickel oxide sputtering target described in the first aspect of the present invention.

[0016] Specifically, the preparation method of the iron-nickel oxide sputtering target includes the following steps: The raw materials are mixed, and then composite molding, gradient pre-firing, and sintering are carried out to obtain the final product.

[0017] The composite molding process includes cold isostatic pressing and compression molding.

[0018] Specifically, this invention, through the combination of composite molding, gradient pre-firing, and sintering processes, can suppress the formation of impurity phases, ensure that the Ni:Fe atomic ratio fluctuation is ≤±0.1%, and refine the grains, avoiding the formation of columnar crystals and coarse grains. Simultaneously, it can improve density, thereby increasing device yield; and reduce or eliminate internal stress, thereby reducing thin film stress.

[0019] Preferably, the raw materials are mixed after pretreatment, which includes vacuum annealing, ultrasonic cleaning and vacuum drying performed sequentially.

[0020] Preferably, the purity of each of the raw materials used in the preparation is ≥5N.

[0021] Preferably, the vacuum degree of the vacuum annealing is 1×10⁻⁶. -5 -1×10 -4 Pa, temperature 650-750℃, time 1-2h; to remove surface-adsorbed water and impurities.

[0022] Preferably, anhydrous ethanol is used for ultrasonic cleaning.

[0023] Preferably, the vacuum drying temperature is 60-80℃, ultimately obtaining a dry and pure raw material powder.

[0024] Preferably, the mixture is first ball-milled and then composite molded.

[0025] Preferably, the ball mill is a high-energy ball mill.

[0026] Preferably, anhydrous ethanol is used as a dispersant for high-energy ball milling.

[0027] Preferably, the ball-to-material ratio during ball milling is (8-12):1.

[0028] Specifically, the ball-to-material ratio refers to the mass ratio of grinding balls to raw material powder.

[0029] Preferably, the solid-liquid ratio during ball milling is 1:(0.7-1.0).

[0030] Specifically, the solid-liquid ratio refers to the ratio of the mass of the solid raw material (i.e., the mass of the raw material powder) to the volume of the dispersant.

[0031] Preferably, the ball milling speed is 250-350 r / min, and the ball milling time is 6-10 h; after ball milling, vacuum drying is performed to obtain a uniformly mixed powder.

[0032] Preferably, during the preparation of ingredients, the atomic ratio of Ni to Fe in NiO and Fe2O3 is 1:(2±0.1%); that is, the ingredients are precisely prepared according to the atomic ratio of Ni to Fe of 1:(2±0.1%).

[0033] Preferably, the deviation of the amount of MgO and TiO2 added during the preparation is ≤ ±0.005wt%.

[0034] Preferably, the pressure of the cold isostatic pressing is 180-220 MPa, and the holding time is 20-40 min.

[0035] Preferably, the molding pressure is 280-320 MPa, and the holding time is 15-25 min.

[0036] A green body with a density ≥90% of the theoretical density can be obtained through a composite molding process of cold isostatic pressing and molding, without delamination or cracks.

[0037] Preferably, the gradient preheating process includes first heating to 350-450°C at a heating rate of 4-6°C / min and holding at that temperature for 0.5-1.5h; then heating to 550-650°C at a heating rate of 2-4°C / min and holding at that temperature for 1.5-2.5h; and then heating to 750-850°C at a heating rate of 1-3°C / min and holding at that temperature for 2.5-3.5h.

[0038] Specifically, the first stage of pre-firing removes moisture and dispersant and is gently preheated; the second stage of pre-firing eliminates internal forming stress and initially activates the powder particles; and the third stage of pre-firing initially forms the NiFe2O4 spinel phase and suppresses the formation of impurity phases (NiO, Fe2O3), thereby initially densifying the green body.

[0039] Preferably, the pre-fired green body is first placed in a vacuum sintering furnace and evacuated to a vacuum level of ≤5×10⁻⁶. -6 Pa, pressurize with protective gas to 0.03-0.05 MPa; then sinter.

[0040] Preferably, the sintering process includes first heating to 650-750℃ at a heating rate of 4-6℃ / min and holding at that temperature for 30-60min; then heating to 950-1050℃ at a heating rate of 3-5℃ / min and holding at that temperature for 30-60min; and then heating to 1100-1200℃ at a heating rate of 2-4℃ / min and holding at that temperature for 4.5-5.5h.

[0041] Preferably, the protective gas includes at least one of high-purity nitrogen, high-purity argon (Ar), and high-purity helium (He).

[0042] Specifically, the protective atmosphere must be oxygen-free, carbon-free, and non-reducing to avoid affecting the phase structure and purity of the target material.

[0043] Preferably, after sintering, the temperature is reduced to 850-950°C at a rate of 1-3°C / min, held at that temperature for 1.5-2.5 hours, and then allowed to cool naturally to room temperature.

[0044] Specifically, a target blank with a density of ≥99.6% can be obtained through sintering.

[0045] Preferably, the sintering process further includes machining and surface treatment.

[0046] Preferably, the machining includes CNC turning and grinding.

[0047] Preferably, the flatness after machining is ≤0.02mm and the roughness Ra is ≤0.3μm.

[0048] Preferably, the surface treatment includes chemical polishing, ultrasonic cleaning, and vacuum drying.

[0049] Preferably, the chemical polishing reagents include HNO3, HF, and CH3COOH.

[0050] Preferably, the volume ratio of HNO3, HF and CH3COOH is 1:(0.4-0.6):(2.5-3.5).

[0051] Preferably, the chemical polishing time is 30-120 seconds.

[0052] Preferably, ultrasonic cleaning is performed using water.

[0053] Preferably, the ultrasonic cleaning is performed 1-3 times, each time for 3-8 minutes.

[0054] Preferably, the vacuum drying temperature is 60-90℃, the vacuum degree is ≤100Pa, and the time is 2-4h.

[0055] Specifically, the surface treatment process removes the deteriorated layer from the processing, reducing the risk of particulate contamination.

[0056] The third aspect of the present invention provides an application of the nickel oxide sputtering target described in the first aspect of the present invention in 5G radio frequency devices, MRAM, and precision sensors.

[0057] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows: (1) Extremely precise stoichiometry: By adding MgO, this invention can suppress impurities, refine grains, suppress impurity generation, and reduce stoichiometry deviation. At the same time, combined with the three-stage gradient pre-sintering process, the Ni:Fe atomic ratio fluctuation is ≤ ±0.1%, ensuring the stability of the permeability of 5G radio frequency devices (fluctuation ≤ 3%).

[0058] (2) High density and extremely low defects: By adding TiO2, this invention can achieve rapid densification at low temperature, and the addition of MgO can suppress impurity phases, further improving the density. At the same time, by combining composite molding, gradient pre-firing and sintering processes, a density of ≥99.6% can be achieved without hot isostatic pressing (HIP) process. The target material is free of pores, microcracks and impurity phases. The number of particles in the sputtering process is reduced to ≤5, which significantly reduces the risk of device short circuit, leakage and failure, and improves the yield of downstream devices by 8-17%.

[0059] (3) Microstructure optimization: By adding MgO, the grains can be refined and combined with gradient pre-sintering process, a uniform equiaxed grain structure of 30-60μm can be obtained. Compared with the coarse grains of traditional target materials (>100μm), the sputtering particle deposition energy is more uniform and the film density is significantly improved. Accordingly, the internal stress of the film can be controlled below 40MPa. Compared with traditional sintered target materials, the film adhesion is improved by about 30%, which effectively improves the problems of film cracking and peeling and improves the reliability of the device.

[0060] (4) High purity and low oxygen: By adding TiO2, the oxygen content can be reduced. Combined with the addition of MgO and gradient pre-calcination, the oxygen content can be ≤30ppm and the total metal impurities can be ≤40ppm, which meets the stringent requirements of semiconductor-grade applications.

[0061] (5) Strong feasibility for mass production: The preparation cycle is shortened to about 30 hours, the device yield can reach >97%, the production cost is reduced, and it is more suitable for large-scale industrial production. Attached Figure Description

[0062] Figure 1 This is a metallographic image of the iron-nickel oxide sputtering target of Embodiment 1 of the present invention; Figure 2 The image shows the metallographic structure of the iron oxide nickel sputtering target for Comparative Example 5 of this invention. Detailed Implementation

[0063] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0064] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0065] Example 1: Standard 5G RF Grade Iron-Nickel Oxide Sputtering Target This embodiment provides an iron-nickel oxide sputtering target, which is prepared from NiO, Fe2O3, MgO and TiO2. In NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:2. Based on the total mass of the iron-nickel oxide sputtering target, the mass percentages of MgO and TiO2 are 0.05wt% and 0.03wt%, respectively.

[0066] In the iron-nickel oxide sputtering target prepared in this embodiment, the impurity content, based on the total mass of the iron-nickel oxide sputtering target, is: C 5ppm, O 26ppm, N 2ppm, S 0.5ppm; the main metallic impurities are Al 8ppm, Ca 5ppm, Cr 3ppm, Cu 2ppm, Pb 1ppm, and other metallic impurities were not detected, with total metallic impurities ≤20ppm.

[0067] This embodiment also provides a method for preparing the above-mentioned iron-nickel oxide sputtering target, the specific steps of which are as follows: (1) Raw material pretreatment Each raw material was placed separately in a vacuum furnace at a temperature of 1×10⁻⁶. -5 Vacuum annealing at 700℃ for 1.5 h under vacuum to remove surface adsorbed water and impurities; then ultrasonic cleaning with anhydrous ethanol and vacuum drying at 70℃ to obtain dry and pure raw material powder. (2) Precise ingredient proportioning and high-energy mixing Ingredients: Using an electronic balance with an accuracy of ≤0.0001g, ingredients are precisely dispensed according to a Ni:Fe atomic ratio of 1:2, with the addition deviation of MgO and TiO2 ≤±0.005wt%; Mixing: Using anhydrous ethanol as a dispersant, high-energy ball milling was performed at a ball-to-material ratio of 10:1, a solid-to-liquid ratio of 1:0.9, a ball milling speed of 300 r / min, and a ball milling time of 8 h; after ball milling, vacuum drying was performed to obtain a uniformly mixed powder. (3) Composite molding First, cold isostatic pressing is performed on the material in step (2) at a pressure of 200 MPa and a holding time of 30 min; then molding is performed at a pressure of 300 MPa and a holding time of 20 min; after molding, a green body with a density ≥ 90% of the theoretical density is obtained, without delamination or cracks. (4) Gradient pre-firing The green body obtained in step (3) was placed in a vacuum furnace for gradient heating pre-firing. In the first stage, the temperature was increased to 400°C at 5°C / min and held for 1 hour to remove moisture and dispersant. In the second stage, the temperature was increased to 600°C at 3°C / min and held for 2 hours to eliminate internal stress. In the third stage, the temperature was increased to 800°C at 2°C / min and held for 3 hours to form the initial phase and suppress the formation of impurity phase. After the holding period, the green body was naturally cooled to room temperature with the furnace. (5) Low-temperature densification sintering The pre-fired green body was placed in a vacuum sintering furnace and evacuated to a vacuum level of ≤5×10⁻⁶. -6 The pressure was increased to 0.04 MPa by filling with high-purity Ar; then sintering was carried out using a gradient sintering process. First, the temperature was increased to 700℃ at a heating rate of 5℃ / min and held for 45 min; then the temperature was increased to 1000℃ at a heating rate of 4℃ / min and held for 45 min; then the temperature was increased to 1150℃ at a heating rate of 3℃ / min and held for 5 h; after sintering, the temperature was decreased to 900℃ at a heating rate of 2℃ / min and held for 2 h to eliminate internal stress, and then the furnace was naturally cooled to room temperature to obtain a target blank with a density ≥99.6%; (6) Precision machining and surface treatment Precision machining: The target blank is machined to the target size by CNC turning and grinding, with flatness controlled to ≤0.02mm and surface roughness Ra≤0.3μm; Surface treatment: Chemical polishing was performed using HNO3, HF and CH3COOH in a volume ratio of 1:0.5:3 for 75 seconds. Then, ultrasonic cleaning was performed three times with deionized water for 6 minutes each time. Finally, vacuum drying was carried out at 75°C and 100 Pa for 3 hours to remove the processing-modified layer, reduce the risk of particulate contamination, and obtain the iron-nickel oxide sputtering target.

[0068] Example 2: MRAM high-purity low-oxygen iron-nickel oxide target This embodiment provides an iron-nickel oxide sputtering target, which is prepared from NiO, Fe2O3, MgO and TiO2. In NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:1.999. Based on the total mass of the iron-nickel oxide sputtering target, the mass percentages of MgO and TiO2 are 0.08wt% and 0.05wt%, respectively.

[0069] In the iron-nickel oxide sputtering target prepared in this embodiment, the impurity content, based on the total mass of the iron-nickel oxide sputtering target, is: C 5ppm, O 26ppm, N 2ppm, S 0.5ppm; the main metallic impurities are Al 8ppm, Ca 5ppm, Cr 3ppm, Cu 2ppm, Pb 1ppm, and other metallic impurities were not detected, with total metallic impurities ≤20ppm.

[0070] The preparation method of the iron-nickel oxide sputtering target in Example 2 differs from that in Example 1 only in that the vacuum annealing temperature of the raw material is increased to 750°C, and the sintering holding time is extended to 5.5 hours after the temperature is raised to 1150°C during the sintering process. The other preparation methods are the same as those in Example 1.

[0071] Example 3: Sensor-grade low-stress, high-adhesion iron-nickel oxide sputtering target This embodiment provides an iron-nickel oxide sputtering target, which is prepared from NiO, Fe2O3, MgO and TiO2. In NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:2.001. Based on the total mass of the iron-nickel oxide sputtering target, the mass percentages of MgO and TiO2 are 0.02wt% and 0.01wt%, respectively.

[0072] In the iron-nickel oxide sputtering target prepared in this embodiment, the impurity content, based on the total mass of the iron-nickel oxide sputtering target, is: C 5ppm, O 26ppm, N 2ppm, S 0.5ppm; the main metallic impurities are Al 8ppm, Ca 5ppm, Cr 3ppm, Cu 2ppm, Pb 1ppm, and other metallic impurities were not detected, with total metallic impurities ≤20ppm.

[0073] This embodiment also provides a method for preparing the above-mentioned iron-nickel oxide sputtering target, the specific steps of which are as follows: (1) Raw material pretreatment Each raw material was placed separately in a vacuum furnace at a temperature of 1×10⁻⁶. -5 Vacuum annealing at 700℃ for 1.5 h under vacuum to remove surface adsorbed water and impurities; then ultrasonic cleaning with anhydrous ethanol and vacuum drying at 70℃ to obtain dry and pure raw material powder. (2) Precise ingredient proportioning and high-energy mixing Ingredients: Using an electronic balance with an accuracy of ≤0.0001g, ingredients are precisely dispensed according to a Ni:Fe atomic ratio of 1:2.001, with the addition deviation of MgO and TiO2 ≤±0.005wt%; Mixing: Using anhydrous ethanol as a dispersant, high-energy ball milling was performed at a ball-to-material ratio of 10:1, a solid-to-liquid ratio of 1:0.9, a ball milling speed of 300 r / min, and a ball milling time of 8 h; after ball milling, vacuum drying was performed to obtain a uniformly mixed powder. (3) Composite molding First, cold isostatic pressing is performed on the material in step (2) at a pressure of 200 MPa and a holding time of 30 min; then molding is performed at a pressure of 300 MPa and a holding time of 20 min; after molding, a green body with a density ≥ 90% of the theoretical density is obtained, without delamination or cracks. (4) Gradient pre-firing The green body obtained in step (3) was placed in a vacuum furnace for gradient heating pre-firing. In the first stage, the temperature was increased to 400°C at 5°C / min and held for 1 hour to remove moisture and dispersant. In the second stage, the temperature was increased to 600°C at 3°C / min and held for 2 hours to eliminate internal stress. In the third stage, the temperature was increased to 800°C at 2°C / min and held for 3 hours to initially form phase and suppress the formation of impurity phase. (5) Low-temperature densification sintering The pre-fired green body was placed in a vacuum sintering furnace and evacuated to a vacuum level of ≤5×10⁻⁶. -6 The pressure was increased to 0.04 MPa by filling with high-purity Ar, and then sintering was carried out using a gradient sintering process. First, the temperature was increased to 700℃ at a heating rate of 5℃ / min and held for 0.5 h. Then, the temperature was increased to 1000℃ at a heating rate of 4℃ / min and held for 0.5 h. Finally, the temperature was increased to 1150℃ at a heating rate of 3℃ / min and held for 5 h to complete the gradient sintering. Finally, the temperature was decreased to 900℃ at a cooling rate of 2℃ / min and held for 2 h to relieve stress. Then, the material was naturally cooled to room temperature to obtain the target blank. (6) Precision machining and surface treatment Precision machining: The target blank is machined to the target size by CNC turning and grinding, with flatness controlled to ≤0.02mm and surface roughness Ra≤0.3μm; Surface treatment: Chemical polishing was performed for 60 seconds using HNO3, HF and CH3COOH in a volume ratio of 1:0.5:3 as polishing liquid; then ultrasonic cleaning was performed twice with deionized water for 5 minutes each time; finally, vacuum drying was carried out at 80℃ and 50Pa for 3 hours to remove the processing-modified layer, reduce the risk of particulate contamination, and obtain the iron-nickel oxide sputtering target.

[0074] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that MgO was not added to Comparative Example 1; otherwise, they are the same as in Example 1.

[0075] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 did not add TiO2; otherwise, it was the same as Example 1.

[0076] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 does not undergo gradient pre-firing and is directly sintered; otherwise, it is the same as Example 1.

[0077] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that Comparative Example 4 only undergoes one stage of pre-firing, instead of three-stage gradient pre-firing, i.e., it is kept at 700℃ for 3 hours without gradient heating, while the rest is the same as Example 1.

[0078] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that Comparative Example 5 uses conventional high-temperature sintering (not low-temperature, non-gradient), that is, the sintering process is to directly heat to 1300°C, hold for 3 hours, and then cool naturally, while the rest is the same as Example 1.

[0079] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that Comparative Example 6 uses low-temperature but gradient-free sintering (one-step isothermal sintering), that is, the sintering process is to directly heat to 1150°C and hold for 5 hours, which is low-temperature sintering, but without gradient heating and without gradient holding. The rest is the same as Example 1.

[0080] Performance testing The performance of the iron-nickel oxide sputtering targets prepared in Examples 1-3 and Comparative Examples 1-6 was tested. The test items and test methods are as follows: Density: The Archimedes displacement method was used, and the test was conducted in accordance with GB / T 3850-2015. Grain size: Tested using the metallographic cross-section method and in accordance with GB / T 6394-2017; Ni:Fe atomic ratio: Tested using inductively coupled plasma optical emission spectrometry (ICP-OES) in accordance with GB / T 20125-2006; Oxygen content: Tested using pulse heating inert gas melting-infrared method, in accordance with GB / T 11261-2022; Thin film stress: The substrate bending method (curvature method) was used, and the test was conducted in accordance with GB / T 44517-2024 "Micro-electromechanical Systems (MEMS) Technology: Test Method for Residual Stress of MEMS Films by Wafer Curvature and Cantilever Beam Deflection". Film adhesion: Tested using the scratch / cross-cut method, in accordance with GB / T 9286-2021; Sputtered particle count: After the film is formed by sputtering the target material, the defects of large particles on the film surface are counted and the size distribution is statistically analyzed using an optical microscope or a surface defect scanner (SSIS) (a surface defect scanner is used in this test); Device yield: The batch electrical testing method for RF inductors / MRAM devices is adopted to test the permeability, resistivity, breakdown voltage and leakage current, and the percentage of qualified devices is statistically analyzed.

[0081] The performance test results of the iron-nickel oxide sputtering targets prepared in Examples 1-3 and Comparative Examples 1-6 are shown in Table 1.

[0082] Example 1, Comparative Example 5: Metallographic image of iron oxide nickel sputtering target as shown below. Figure 1 and 2 As shown.

[0083] Table 1: Performance test results of the iron-nickel oxide sputtering targets prepared in Examples 1-3 and Comparative Examples 1-6

[0084] The improvement in film adhesion is a result calculated compared to traditional sintered targets.

[0085] As shown in Table 1, the sputtering target of Example 1 has a density of 99.7%, a grain size of 40-50 μm, an oxygen content of 26 ppm, a Ni:Fe atomic ratio deviation of 0.05%, and no impurities, fully meeting the requirements for high-end MRAM and 5G RF targets. Example 2 has a density of 99.8%, a grain size of 35-45 μm, an oxygen content of 22 ppm, and a particle count of 2 / cm². 2 , adapted for the fabrication of magnetic thin films for MRAM memory cells.

[0086] Comparative Example 1, without the addition of MgO, resulted in coarse grains, impurity phase formation, large stoichiometric deviation, and increased oxygen content in the sputtering target, leading to a significant decrease in performance. This demonstrates that MgO plays a crucial role in suppressing impurity phases, refining grains, and stabilizing stoichiometry.

[0087] In Comparative Example 2, the addition of TiO2 decreased the density of the sputtering target, resulted in closed pores with high oxygen content, and increased sputtering defects. This demonstrates that TiO2 is crucial for low-temperature densification, reducing oxygen content, and improving sputtering quality.

[0088] Comparative Example 3, which did not undergo gradient pre-firing, resulted in low density, high cracking rate, high stress, and numerous impurity phases in the sputtering target, leading to substandard performance. This demonstrates that gradient pre-firing plays a crucial role in impurity removal, phase stabilization, increasing density, and eliminating internal stress.

[0089] The four comparative examples underwent single-stage pre-firing, which resulted in coarse and uneven grains, large stoichiometric deviation, and high stress in the sputtering target. This indicates that three-stage gradient pre-firing is superior to single-stage pre-firing. Single-stage pre-firing cannot fully remove impurities, stabilize the phase, and homogenize the microstructure, and its performance is significantly inferior to that of gradient pre-firing.

[0090] Comparative Example 5 uses conventional high-temperature sintering (non-low-temperature, non-gradient), while Comparative Example 6 uses low-temperature but non-gradient sintering (one-step isothermal sintering). This results in Comparative Example 5 having coarse target grains, large stoichiometric deviation, high stress, increased oxygen content, poor adhesion, and more sputtered particles, leading to low device yield. Comparative Example 6 also has coarse and uneven target grains, large stoichiometric deviation, high stress, increased oxygen content, and more sputtered particles, resulting in low device yield. This demonstrates that the low-temperature gradient sintering used in this invention is a core and essential process for achieving high density, fine grains, and low defects. Non-low-temperature, non-gradient sintering significantly reduces performance and fails to achieve the technical effects of this invention.

[0091] Furthermore, among the sputtering targets currently available in the technology, the Ni:Fe stoichiometric ratio has a large deviation (±1~2%), and NiO and Fe2O3 impurities are easily formed; the density is low (usually <98.5%), and high density cannot be achieved without the use of HIP; the grains are coarse and uneven (>100μm), resulting in large fluctuations in sputtering rate; the oxygen content is high (50-100ppm), affecting the magnetic properties and insulation of the thin film; the film stress is high (80-150MPa), resulting in poor adhesion; and there are many sputtered particles, leading to low device yield.

[0092] In summary, this invention refines grain size, suppresses impurity phase (NiO, Fe2O3) formation, and stabilizes the stoichiometry by adding MgO; and enhances diffusion kinetics by adding TiO2, enabling rapid densification at low temperatures while reducing oxygen content and improving sputtering quality. Furthermore, the combination of composite molding, gradient pre-firing, and sintering processes results in a small stoichiometric deviation (≤±0.1%), high density (≥99.6%), and low oxygen content (≤30ppm) in the iron-nickel oxide sputtering target, along with fine equiaxed grains (grain size 30-60μm).

[0093] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A nickel oxide sputtering target, characterized in that, The raw materials for preparing the nickel oxide sputtering target include NiO, Fe2O3, MgO and TiO2; In the NiO and Fe2O3, the atomic ratio of Ni to Fe is 1:2 (±0.1%).

2. The iron-nickel oxide sputtering target according to claim 1, characterized in that, Based on the total mass of the nickel oxide sputtering target, the mass percentages of MgO and TiO2 are 0.02-0.08 wt% and 0.01-0.05 wt%, respectively.

3. The iron-nickel oxide sputtering target according to claim 1, characterized in that, The iron-nickel oxide sputtering target also contains impurities, and based on the total mass of the iron-nickel oxide sputtering target, the content of the impurities is: C≤8ppm, O≤30ppm, N≤4ppm, S≤1ppm, and total metal impurities≤40ppm.

4. The iron-nickel oxide sputtering target according to claim 1, characterized in that, The iron-nickel oxide sputtering target has equiaxed crystals with a grain size of 30-60 μm.

5. The method for preparing the iron-nickel oxide sputtering target according to any one of claims 1-4, characterized in that, The preparation method includes the following steps: The raw materials are mixed, and then composite molding, gradient pre-firing, and sintering are carried out to obtain the product. The composite molding process includes cold isostatic pressing and compression molding.

6. The preparation method according to claim 5, characterized in that, The raw materials are mixed after pretreatment, which includes vacuum annealing, ultrasonic cleaning and vacuum drying performed sequentially. And / or, the mixture is first ball-milled and then compounded.

7. The preparation method according to claim 5, characterized in that, The pressure of the cold isostatic pressing is 180-220 MPa, and the holding time is 20-40 min; And / or, the molding pressure is 280-320 MPa, and the holding time is 15-25 min.

8. The preparation method according to claim 5, characterized in that, The gradient preheating process includes first heating to 350-450℃ at a heating rate of 4-6℃ / min and holding at that temperature for 0.5-1.5h; then heating to 550-650℃ at a heating rate of 2-4℃ / min and holding at that temperature for 1.5-2.5h; and then heating to 750-850℃ at a heating rate of 1-3℃ / min and holding at that temperature for 2.5-3.5h.

9. The preparation method according to claim 5, characterized in that, The sintering process includes first heating to 650-750℃ at a heating rate of 4-6℃ / min and holding at that temperature for 30-60min; then heating to 950-1050℃ at a heating rate of 3-5℃ / min and holding at that temperature for 30-60min; and then heating to 1100-1200℃ at a heating rate of 2-4℃ / min and holding at that temperature for 4.5-5.5h. And / or, after sintering, the temperature is lowered to 850-950°C at a rate of 1-3°C / min, held at that temperature for 1.5-2.5 hours, and then allowed to cool naturally to room temperature; And / or, the sintering process may further include machining and surface treatment.

10. The application of the nickel oxide sputtering target according to any one of claims 1-4 in 5G radio frequency devices, magnetoresistive random access memory, and precision sensors.

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