Composite insulation-coated metal soft magnetic powder and coating method and application thereof

Abstract

The application discloses a kind of composite insulation coated metal soft magnetic powder and coating method and application.By system process flow implementation and performance comparison analysis, the soft magnetic powder composite insulation coating technology provided by the application shows significant advantages.Three-layer composite shell structure (flexible buffer layer+insulation layer+nanometer layer) effectively solves the problem of shell microcrack, insulation degradation and high dielectric loss under high frequency, high pressure and high temperature environment in traditional coating.The optimized key data: MLD / Al2O3 / [Al2O3 / HfO2] shell continuity rate reaches 99.8%, bulk resistivity is 5.2*10 9 Ω•cm, 100kHz loss is reduced by 67.1%, salt spray weight loss is only 38% of the control, fully meets the demand of high frequency magnetic device.The application provides a reliable material basis for the miniaturization and high efficiency of high frequency power electronic device.

Description

Technical Field

[0001] This invention relates to the field of power electronics and functional thin film deposition, specifically to a composite insulating coated metal soft magnetic powder, a coating method, and its application. Background Technology

[0002] As power electronics technology advances towards higher frequencies and higher power densities, loss control in high-frequency magnetic devices has become a critical challenge. Under high-frequency conditions, eddy current losses and dielectric losses in soft magnetic materials increase significantly, severely impacting device efficiency and reliability. To reduce these losses, insulating the soft magnetic powder is an effective method, which can interrupt the current path between powder particles, increase the material's bulk resistivity, and thus suppress eddy current losses.

[0003] Currently, there are various methods for insulating coating technology of soft magnetic powder. CN113096907B discloses a method for coating an oxide layer on the surface of iron-based soft magnetic powder using atomic layer deposition (ALD) technology. The oxide layer thickness is 10-100 nm, which can achieve uniform and dense coating, which is beneficial to reduce the magnetic loss of the metal magnetic powder core while maintaining a certain permeability. CN113611471A proposes a method of first coating an oxide layer using ALD technology and then performing high-temperature annealing treatment at 1000-1200℃, which can obtain a metal magnetic powder core with low hysteresis loss and total loss and superior permeability performance.

[0004] To further improve high-frequency performance, CN119833304A discloses a method of first coating a metal oxide insulating layer onto the surface of soft magnetic powder using ALD technology, then performing a second insulating coating using ALD technology, and finally forming a ferrite coating layer on the powder surface during high-temperature annealing. This method can improve the resistivity of the soft magnetic material and reduce eddy current losses at high frequencies. CN115547606B introduces a method of coating a polyimide film onto the surface of soft magnetic powder using atomic layer deposition technology, which can significantly reduce the loss of the magnetic powder core material without sacrificing magnetic permeability. In addition, CN119943519B proposes a method of mixing and compounding insulating coated iron alloy soft magnetic powder with small-particle-size ferrite powder, which can significantly improve the insulation performance of the magnetic powder core and reduce its high-frequency loss.

[0005] However, existing technologies still have the following problems: First, traditional phosphate, silane, or sol-gel coatings are prone to microcracks in the shell after ultra-high pressure (≥600-1000 MPa) pressing and subsequent heat treatment, leading to a decrease in insulation performance; Second, single-material insulating layers (such as Al2O3) are not stable enough under high-temperature environments (>200-300℃) and are prone to insulation degradation; Third, existing coatings often struggle to achieve a good balance between pressing crack resistance, high-temperature stability, and low dielectric loss, especially in high-frequency applications where the problem of high dielectric loss is particularly prominent; Finally, although existing ALD coating technology has the advantage of atomic-level thickness control, single-material shells cannot simultaneously meet the comprehensive performance requirements of various high-frequency magnetic devices for insulating layers.

[0006] Therefore, there is an urgent need to develop a new soft magnetic powder insulation coating technology that can maintain the integrity of the shell under high pressure and high temperature heat treatment, while possessing low dielectric loss, high resistivity and good environmental stability, so as to meet the application requirements of various high-frequency / medium-frequency magnetic devices. Summary of the Invention

[0007] To achieve the above technical objectives, the present invention provides a method for composite insulating coating of soft magnetic metal powder, comprising the following steps: S1. Pretreatment: The soft magnetic metal powder is subjected to plasma activation treatment, followed by drying in an inert atmosphere to remove physically adsorbed water and increase the surface hydroxyl density. S2. Flexible buffer layer deposition: Molecular layer deposition (MLD) is used to construct a 5-20 nm thick flexible buffer layer on the surface of activated metal soft magnetic powder. The flexible buffer layer is a metal-organic hybrid film formed by the metal center and organic ligand. S3. Insulating layer deposition: Atomic layer deposition (ALD) is used to deposit an insulating layer with a thickness of 5-20 nm on the surface of the buffer layer. The insulating layer is a metal oxide. S4. Outer nanolayer stack deposition: At least two metal insulating layers are alternately deposited by ALD to form a nanolayer stack with a total thickness of 1-15 nm, wherein the thickness of each insulating layer is 0.5-10 nm. S5. Post-processing: The obtained coated powder is thermally densified in an inert atmosphere, and then heated in an oxygen-containing atmosphere to oxidize some of the organic components in the MLD buffer layer into carbon-doped metal oxides. Finally, lubricant / or binder is added for shaping and heat treatment to obtain coated powder with a multi-level insulation structure. The metals in S2 and S3 include aluminum, magnesium, titanium, zirconium, and hafnium.

[0008] Furthermore, in step S1, the hydroxyl group density of the activated powder is not less than 5 per nm. 2The active gas is one of oxygen, ozone, or water vapor.

[0009] Furthermore, the active gas flow rate is 100-400 mL / min, the chamber pressure is atmospheric pressure, the chamber temperature is 120-250℃, the activation power is 200-500 W, and the treatment time is 5-15 min; the drying temperature is 120-200℃, and the drying time is 1-2 h, resulting in a hydroxyl density >5 hydroxyl groups / nm. 2 Activated powder.

[0010] Further, in step S2, the flexible buffer layer is deposited by alternatingly introducing organic and inorganic precursors into the reaction chamber in a pulsed manner. The inorganic precursor is one or a mixture of several of the following: volatile metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes. The metal element in the metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes is one of aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, vanadium, and manganese.

[0011] The organic precursor has two or more functional groups that can react with metal hydroxyl / alkoxy groups, including –OH, –COOH, and –NH2. The organic precursor includes one of ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, hydroquinone, p-phenylenediamine, glycerol, ethylenediyne, toluene diisocyanate, glycidyl ether, or glycerol.

[0012] Further, the amount of lubricant or binder added is 0.5-1.5 wt%; the lubricant is one of zinc stearate, silane coupling agent, polyethylene glycol, mineral oil, synthetic ester, silicone oil, glycerin and its derivatives, fatty acid or amide wax; the binder is one of epoxy resin, polyimide, phenolic resin, phosphate binder, silica sol or borate glass.

[0013] Furthermore, the soft magnetic metal powder is one of pure iron powder, iron-silicon alloy powder, iron-aluminum alloy powder, iron-silicon-aluminum alloy powder, iron-silicon-chromium alloy powder, iron-chromium alloy powder, iron-nickel alloy powder, and iron-nickel-molybdenum alloy powder, and the particle size range of the powder is 5-30μm.

[0014] The present invention also provides a composite insulating coated metal soft magnetic powder, having a flexible buffer layer, an insulating layer and a nano-layer stack sequentially coated on the surface of the metal soft magnetic powder body; The flexible buffer layer is a carbon-doped metal oxide carbonized thin film formed by a metal center and an organic ligand, with a thickness of 5-20 nm. The insulating layer is a metal oxide with a thickness of 5-20 nm; The nanolayer stack consists of alternating insulating layers of at least two metals, with a thickness of 1-15 nm; The metals in the insulating layer include aluminum, magnesium, titanium, zirconium, and hafnium, while the metals in the carbon-doped metal oxide include aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, vanadium, and manganese.

[0015] Furthermore, the soft magnetic metal powder is one of the following: pure iron powder, iron-silicon alloy powder, iron-aluminum alloy powder, iron-silicon-aluminum alloy powder, iron-silicon-chromium alloy powder, iron-chromium alloy powder, iron-nickel alloy powder, and iron-nickel-molybdenum alloy powder, with a particle size range of 5-30 μm. The composite insulating coated soft magnetic metal powder provided by this invention can be used to manufacture power electronic magnetic devices.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Crack resistance and stability: Through the synergistic effect of the MLD buffer layer and the nano-layered outer layer, the soft magnetic powder has a high shell continuity rate (≥99.5%) after pressing at 600-1000 MPa and subsequent heat treatment, which effectively solves the problem of shell micro-cracks that are easy to occur after high pressure pressing in traditional coating methods.

[0017] (2) Low loss: The composite shell structure gives the powder high resistivity (≥10). 8 -10 9 The combined characteristics of low dielectric loss (Ω•cm) and low dielectric loss result in a loss reduction of ≥10-30% compared to the uncoated control of the same density at the target operating point (e.g., 100 kHz / ΔB=0.05T or 500 kHz / ΔB=0.05T), which is significantly better than the traditional coating method.

[0018] (3) Temperature resistance / resistivity retention: After curing at 200-250 °C or annealing at 300-450 °C, the resistivity retention rate is 70-90%, which solves the problem of insulation degradation under high temperature conditions of traditional coating.

[0019] (4) Environmental reliability: The resistance to damp heat / corrosion is better than the control, and the weight loss of salt spray in 48 h is ≤50% of the control, which improves the service life of magnetic devices in harsh environments; PALD technology is compatible with fluidized bed / rotary bed / continuous line, and the thickness and uniformity are easy to control (interparticle thickness RSD <5–10%), realizing the possibility of industrial-scale production.

[0020] (5) Through the verification of the embodiments, the composite shell structure of the present invention has shown excellent performance in various application scenarios such as VRM molded inductor (1 MHz), common mode choke (150 kHz), WPT coil magnetic circuit filling (85 kHz), bulk magnetic core for SST / MFT (100 kHz) and integrated magnetic layer in package (2-10 MHz), which proves the effectiveness and wide applicability of the technical solution of the present invention. Attached Figure Description

[0021] Figure 1 TEM image of a composite insulating coated metal soft magnetic powder.

[0022] Figure 2 The EELS spectrum of the composite insulating coated metal soft magnetic powder. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0024] A powder atomic layer deposition composite insulating coating method for high-frequency magnetic devices includes the following steps: S1, Pretreatment and Hydroxylation The soft magnetic powder is placed in a plasma cleaning chamber, where oxygen-based plasma is used to remove organic contaminants and a weak oxide layer from its surface. Simultaneously, hydroxyl groups are loaded onto the surface of the soft magnetic powder, with a hydroxyl density of at least 5 hydroxyl groups / nm. 2 Subsequently, under an inert atmosphere, the surface is dried for 1-2 hours at a temperature range of 120-200℃ to construct a high-density, highly reactive hydroxyl (-OH) surface, providing uniform and sufficient chemisorption sites for subsequent MLD and ALD self-limited growth.

[0025] In some embodiments, the soft magnetic powder is one of pure iron powder, iron-silicon alloy powder, iron-aluminum alloy powder, iron-silicon-aluminum alloy powder, iron-silicon-chromium alloy powder, iron-chromium alloy powder, iron-nickel alloy powder, and iron-nickel-molybdenum alloy powder, and the particle size range of the powder is 5-30 μm.

[0026] Oxygen-containing plasma is generated by the inflow of one or more gases into a plasma generator, which can be an inductively coupled plasma (ICP), converter-coupled plasma (TCP), or capacitively coupled plasma (CCP) reactor. Plasma energy is provided to activate one or more gases into ions, free radicals, neutral substances, and other plasma-activating materials. These gases may contain oxygen-containing substances such as oxygen, ozone, and water vapor.

[0027] Step S1 involves adjusting the process conditions of the oxygen-based plasma treatment to achieve the desired results. These conditions include plasma power, plasma frequency, plasma exposure time, bias voltage, duty cycle, temperature (e.g., substrate temperature), pressure (e.g., chamber pressure), and the flow rate of one or more gases. The plasma power generated during operation can be approximately 200-500W. The directionality of the plasma can be controlled by the bias voltage. A bias voltage of 0-50V is used only for surface cleaning or introduction of -OH groups; a bias voltage of 50-150V is used to enhance bonding strength, avoiding >200V which could damage the magnetic powder surface and reduce magnetic properties. The duration of plasma treatment can be approximately 5-15 minutes. The plasma duty cycle can be adjusted during operation to achieve the desired results. With a power of 200-500W, a duty cycle of 50%-60% is used to balance activity and temperature. If the chamber heats up rapidly, the duty cycle is reduced to 30%-40%, and the treatment time is extended. The radio frequency power supply can deliver plasma at any suitable duty cycle, with an O2 flow rate of 50-200 sccm and a pressure of 0.3-1 Torr. When mixing O2-Ar, the O2 content is 5%-20%, and the total flow rate of the mixed O2-Ar is 100-300 sccm. The temperature of the plasma cleaning chamber can be between approximately 120°C and approximately 250°C.

[0028] S2, MLD flexible buffer layer deposition A flexible buffer layer of 5-50 nm is deposited on the surface of soft magnetic powder using a molecular layer deposition method. This flexible buffer layer is a metal-organic hybrid film formed by a metal center and an organic ligand. The organic ligand includes one of the following: ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, hydroquinone, p-phenylenediamine, glycerol, acetylenyne, toluene diisocyanate, glycidyl ether, or glycerol. The metal element in the metal-organic hybrid film includes one of the following: aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, vanadium, and manganese.

[0029] The process of depositing a flexible buffer layer using the molecular layer deposition method includes: M1. Place the hydroxyl-loaded soft magnetic powder into the MLD reaction chamber, or place the hydroxyl-loaded soft magnetic powder into a porous container inside the MLD reaction chamber, and then repeatedly evacuate and replace the nitrogen gas at least three times. M2. Fluidize the hydroxyl-loaded soft magnetic powder in the reaction chamber under a nitrogen or argon atmosphere at a fluidization pressure of 1-1000 torr, or achieve dispersion of the hydroxyl-loaded soft magnetic powder by rotating a porous container; the preferred fluidization pressure is 10-100 torr. M3. Based on the type of flexible buffer layer to be deposited, select the reaction precursor and set the parameters of the MLD reaction chamber: deposition temperature 100℃-250℃, deposition pressure 0.01 torr-500 torr; M4. The inorganic precursor vapor is introduced into the MLD reaction chamber under nitrogen or argon gas and held for 10-300 seconds. The flow rate of the carrying gas, nitrogen or argon, is 5-8000 sccm. M5. Purge the reaction chamber with nitrogen or argon to remove the remaining inorganic precursors. The flow rate of the carrier gas, nitrogen or argon, is 5-8000 sccm. M6. Under the action of a carrier gas, the organic precursor is introduced into the MLD reaction chamber and held for 10-300 seconds; the carrier gas is nitrogen or argon with a flow rate of 5-8000 sccm. M7. Purge the reaction chamber with nitrogen or argon to remove excess organic precursors and byproducts; Repeat steps M4 to M7 until the flexible buffer layer corresponding to the inorganic precursor is deposited to the set coating thickness of 5-20 nm.

[0030] In some embodiments, the inorganic precursor is one or a mixture of several volatile metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes, wherein the metal element in the metal alkylamino salt, organometallic compound, halide, alkoxide, or metal β-diketone complex is one of aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, vanadium, and manganese.

[0031] In some preferred embodiments, the inorganic precursor is one of TMA, TiCl4, or diethylzinc.

[0032] In some embodiments, the organic precursor has two or more functional groups that can react with metal hydroxyl / alkoxy groups, including –OH, –COOH, and –NH2.

[0033] S3, ALD-Al2O3 main insulating layer deposition Atomic layer deposition is used to construct a high-density, high-resistivity, and excellent breakdown-performance insulating layer on the surface of soft magnetic powder after step S2. This layer serves as the main insulating barrier between magnetic powders, suppressing eddy current losses and ensuring dielectric stability at high frequencies. The thickness of the insulating layer is 5~20nm.

[0034] This step can specifically include: The soft magnetic powder processed in step S2 is placed in a reaction chamber or a porous container within the reaction chamber. The soft magnetic powder in the reaction chamber is fluidized, or the porous container is rotated to achieve the dispersion effect of the soft magnetic powder. The gas in the reaction chamber is replaced with an inert gas, which is used as the carrier gas. The oxygen source gas and precursor A are alternately introduced into the reaction chamber in a pulsed manner. The residual gas is purged with inert gas between the alternations. The reaction pressure is 40-150 Pa. Atomic layer deposition is repeated multiple times until the thickness of the insulating layer is 5-10 nm. The precursor A is one or a mixture of several of the following: volatile silicon ions, metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes. The metal ions in the metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes are aluminum, magnesium, titanium, zirconium, and hafnium ions.

[0035] In some preferred embodiments, the precursor A is one of trimethylaluminum TMA, triethylaluminum TEA, AlCl3, aluminum dimethylisopropoxide (DMAI), or trimethylamine aluminum ethane (TMAA).

[0036] In some embodiments, the oxygen source precursor is one of H2O, O3, H2O2, O2 plasma, or N2O.

[0037] S4, outer nanolayer stacked deposition Atomic layer deposition was used to construct nanolayer stacks on the soft magnetic powder surface after step S3. The interfacial charge trapping effect induced by dielectric constant mismatch, the electron tunneling barrier formed by band shift, and the deflection mechanism of layered cracks were utilized.

[0038] The nanolayer stack consists of at least two alternating insulating layers, each with a thickness of 0.5-10 nm. The deposition method is the same as in step S3, except that the type of precursor A is replaced. The thickness of the nanolayer stack is 1-15 nm.

[0039] In some embodiments, the nanolayer stack consists of alternating Al2O3 layers / HfO2 or TiO2 layers. The Al2O3 layers provide high barrier properties, inhibit ion diffusion, and provide mechanical support. The HfO2 or TiO2 layers reduce EOT (equivalent oxide thickness) and capture interfacial charges. Too few repetitions will not have a significant effect, while too many repetitions will lead to excessive total thickness and decreased magnetic properties.

[0040] In some embodiments, the hafnium-containing precursor A is selected from one of Hf(NEtMe)4, HfCl4, HfOtBu4, Hf[N(SiMe3)2]4 or Hf(MMP)4.

[0041] In some embodiments, the titanium-containing precursor A is selected from TiCl4, TTIP, tetradimethylaminotitanium, or triethylmethylaminotitanium.

[0042] In some preferred embodiments, the titanium-containing precursor A is TiCl4 or TTIP.

[0043] S5, Densification and Conversion Treatment By leveraging the synergistic effect of thermal and plasma fields, the intrinsic porosity and interface defects of the MLD / ALD nanoshell are eliminated, transforming the flexible organic-metal hybrid shell into a rigid-flexible gradient structure and enhancing the breakdown field strength and thermal stability of the insulating layer.

[0044] Densification is performed in an inert atmosphere at 200-350℃ for 1-2 hours to make the shell structure more compact and eliminate internal defects. Optionally, low-power plasma treatment (50-200W, 10-30 minutes) can further improve interfacial bonding. Conversion treatment is performed in an oxygen-containing atmosphere at 300-450℃ to partially convert the organic components in the MLD layer into C-doped Al2O3.

[0045] S6. Forming and Heat Treatment Add 0.5-1.5% (by mass) of lubricant / binder to the composite metal soft magnetic powder processed in step S5, and stir thoroughly under heating until the mixture is dry and uniformly mixed to obtain the magnetic powder to be formed. Press the magnetic powder to be formed under a pressure of 600-1000 MPa; using nitrogen or argon as a protective atmosphere, place the formed magnetic powder in an environment of 200-550℃ for 30-120 min; the finished soft magnetic composite material is obtained. Heat treatment can eliminate pressing stress, promote the fusion of the shell and matrix interface, and optimize magnetic properties. The heating rate is controlled at 2-5℃ / min to prevent thermal stress from causing shell cracking.

[0046] In some embodiments, the lubricant is one of zinc stearate, silane coupling agent, polyethylene glycol, mineral oil, synthetic ester, silicone oil, glycerin and its derivatives, fatty acid or amide wax.

[0047] In some embodiments, the adhesive is one of epoxy resin, polyimide (PI), phenolic resin, phosphate adhesive, silica sol, or borate glass.

[0048] The key parameters of the composite insulation coating process are summarized in Table 1.

[0049] Table 1 Examples 1-3 employ a complete three-layer structure (MLD buffer layer + Al2O3 middle layer + nano-layered outer layer). The difference lies in the fact that the nano-layered outer layer material used in Example 1 is HfO2. The specific preparation steps are as follows: S1, Pretreatment and Hydroxylation The soft magnetic powder is placed in a plasma cleaning chamber, where oxygen-based plasma is used to remove organic contaminants and a weak oxide layer from its surface. Simultaneously, hydroxyl groups are loaded onto the surface of the soft magnetic powder, with a hydroxyl density of at least 5 hydroxyl groups / nm. 2 The active gas flow rate was 100 sccm, the chamber pressure was 0.5 torr, the chamber temperature was 150℃, the plasma power was set to 350W, and the plasma treatment time was 10 minutes. Subsequently, under inert atmosphere protection, drying was carried out at a temperature range of 120℃ for 1 hour, with the O2 content being 5%-20% when mixing O2-Ar.

[0050] The soft magnetic powder is an iron-silicon-chromium (FeSiCr) alloy powder with a particle size range of 5-30 μm.

[0051] S2 MLD Flexible Buffer Layer Deposition At a reaction temperature of 150°C, using TMA and hydroquinone as precursors, a flexible buffer layer was deposited on the surface of soft magnetic powder using a molecular layer deposition (MLD) method. A single MLD cycle consisted of: a TMA pulse of 3-5 seconds followed by a 180-second purging with N2 (50 sccm) carrier gas; then another TMA pulse of 3-5 seconds followed by a 180-second purging with the same carrier gas. This cycle was repeated 10-100 times to form a 12 nm thick flexible buffer layer of Alucone.

[0052] S3 ALD-Al2O3 main insulating layer deposition The soft magnetic powder treated in step S2 was transferred into the ALD reaction chamber. An insulating layer was deposited on the surface of the powder using atomic layer deposition (ALD). Alumina was then deposited using alternating pulses of TMA and H2O as precursors, with N2 as the carrier gas for purging. A single ALD cycle for alumina growth consisted of: a 3-5 second TMA pulse followed by a 180-second N2 purging; a 3-5 second H2O pulse followed by a 180-second N2 purging; and 5-300 cycles, forming a 10 nm thick Al2O3 intermediate insulating layer.

[0053] S4 outer nanolayer stacked deposition Atomic layer deposition (ALD) was used to construct a nanolayer stack on the surface of soft magnetic powder after step S3. The outer layer of the nanolayer stack consisted of alternating Al2O3 and HfO2 layers with a thickness of 5+5=10nm. The specific preparation method was to transfer the soft magnetic powder treated by S3 into the ALD reaction chamber, use N2 as the carrier gas for purging, and perform alternating pulse deposition of Al2O3 and HfO2 layers for a repetition number of times m=2-10.

[0054] The Al2O3 layer is formed by deposition in step S3.

[0055] The HfO2 layer is formed by alternating pulse deposition of Hf(NEtMe)4 and H2O as precursors during atomic layer deposition, with deposition parameters the same as those of the Al2O3 layer.

[0056] S5 Densification and Conversion Treatment The densification process is carried out at 350°C in an inert atmosphere for 1 hour to make the shell structure more compact and eliminate internal defects. Optional, low-power plasma treatment (100W power, 30 minutes) can further improve interfacial bonding. The conversion process is carried out at 450°C in an oxygen-containing atmosphere to partially convert the organic components in the MLD layer into C-doped Al2O3.

[0057] S6 Forming and Heat Treatment Before powder forming, 0.5% epoxy resin is added, and the mixture is cold-pressed under 700 MPa pressure. After forming, it is heat-treated at 500℃. Heat treatment can eliminate compression stress, promote the fusion of the shell and the matrix interface, and optimize magnetic properties. The heating rate is controlled at 2-5℃ / min to prevent thermal stress from causing shell cracking.

[0058] The nanolayered material used in Example 2 is composed of alternating Al2O3 layers and ZrO2 layers, with the thicknesses of the flexible buffer layer, insulating layer, and nanolayered stack being 8 nm, 18 nm, and 10 nm, respectively.

[0059] The outer layer material used in Example 3 is composed of alternating Al2O3 and TiO2 layers, with the thicknesses of the flexible buffer layer, insulating layer, and nanolayer stack being 15 nm, 5 nm, and 5 nm, respectively. Example 4 adjusts the layer sequence to MLD / HfO2 / Al2O3. That is, the insulating layer is HfO2, and the outer layer material of the nanolayer is composed of alternating HfO2 and Al2O3 layers. The thicknesses of the flexible buffer layer, the insulating layer, and the nanolayer are 22nm, 10nm, and 8nm, respectively.

[0060] Example 5 has a simplified structure of MLD / alternating HfO2-Al2O3, with the thicknesses of the flexible buffer layer and the nanolayer stack being 12 nm and 15 nm, respectively.

[0061] Example 6 is an MLD / Al2O3 bilayer structure, with the thicknesses of the flexible buffer layer and the nanolayer stack being 10 nm and 6 nm, respectively.

[0062] Example 7 is an MLD / HfO3 bilayer structure, with the thicknesses of the flexible buffer layer and the nanolayer stack being 20 nm and 10 nm, respectively.

[0063] Comparative Example 1: MLD single-layer structure, with a flexible buffer layer thickness of 22nm.

[0064] Comparative Example 2: Al2O3 monolayer structure with an insulating layer thickness of 10 nm.

[0065] Comparative Example 3: HfO3 monolayer structure with an insulating layer thickness of 12nm.

[0066] Comparative Example 4: Uncoated FeSiCr-300g.

[0067] The materials prepared in the above embodiments and comparative examples were subjected to shell continuity and compactness evaluation, electrical property measurement and analysis, magnetic property measurement and evaluation, environmental stability testing and data analysis.

[0068] (1) Assessment of shell continuity and compactness Shell continuity was assessed using a staining-cross-section SEM statistical method. Pressed core samples were impregnated with red epoxy resin, cured, and the cross-section was polished and observed under SEM (accelerating voltage 5-15 kV, magnification 5,000-20,000 ×). At least 10 [samples were analyzed]. 5 For each particle, the proportion of unstained (intact shell) particles was calculated. The implementation examples show that Example 1 achieved a continuity rate of 99.8%, while Comparative Example 2 (Al2O3 only) achieved 82.6%. The continuity rate directly depends on the shell's crack resistance; the MLD buffer layer effectively absorbs compressive stress, and the nanolayered outer layer prevents crack propagation.

[0069] Compactness was analyzed using cross-sectional TEM combined with electron energy loss spectroscopy (EELS). Sample preparation was performed using focused ion beam (FIB) cutting, and the TEM observation voltage was 200 kV. Figure 1 High-resolution TEM images show that the outer layer interface of the nanolayer in Example 1 is clear and has no visible pores. Figure 2 EELS line scans showed a steep elemental distribution, indicating minimal interlayer interdiffusion. In contrast, the Al2O3 layer in Comparative Example 2 exhibited nanopores and poor compactness. Compactness directly affects barrier performance and is positively correlated with the damp heat test results.

[0070] The integrity after pressing also needs to be verified by electrical methods. The insulation resistance distribution was measured using a high-resistance meter (such as Nitto Seiko MCP-HT800) at a test voltage of 500V, measuring the resistance values ​​at 100 points. The resistance value distribution in Example 1 was concentrated (relative standard deviation RSD < 5%), while the distribution in Comparative Example 1 was dispersed (relative standard deviation RSD > 30%), indicating a greater number of discontinuities in the shell.

[0071] (2) Measurement and analysis of electrical properties Volume resistivity was measured using either the four-probe method or dielectric spectroscopy. The four-probe method used a square sample with a probe spacing of 1 mm, applied a 10 mA DC current source, and calculated the resistivity by measuring the voltage drop. Dielectric spectroscopy used an impedance analyzer (Agilent 4294A) with a frequency range of 100 Hz to 1 MHz and a test voltage of 1 V. Example 1 showed a volume resistivity of 5.2 × 10⁻⁶. 9 Ω•cm, satisfying ≥10 8 The Ω•cm requirement. The high resistivity is mainly attributed to the insulation properties of the Al2O3 middle layer and the multi-interface scattering of the nanolayered structure.

[0072] The breakdown voltage was measured using a DC high-voltage source with an electrode diameter of 10 mm, and the voltage was increased at a rate of 100 V / s until breakdown occurred. Example 1 showed an average breakdown voltage of 550 V / μm, while Comparative Example 2 showed 320 V / μm. The breakdown voltage reflects the insulation capability of the weakest point in the shell; the nanolayered structure disperses the electric field through alternating interfaces, preventing early breakdown.

[0073] Dielectric loss was measured using an impedance analyzer in the range of 10 kHz to 1 MHz, and tanδ-f curves were plotted. In Example 1, tanδ < 0.005 at 1 MHz, significantly lower than the 0.025 in Comparative Example 2. Low-frequency dielectric loss is mainly related to the conductive path, while high-frequency loss is related to polarization relaxation. The composite shell both blocks the conductive path and reduces interfacial polarization, achieving low dielectric loss.

[0074] (3) Measurement and evaluation of magnetic properties Magnetic loss measurements were performed on a BH analyzer (Iwatsu SY-8219) with a frequency range of 10 kHz to 1 MHz and a magnetic flux density variation of ΔB = 0.05 to 0.2 T. The implementation examples show that, in Example 1, at 100 kHz / ΔB = 0.05 T, the total loss was reduced by 67.1% compared to the uncoated control. This loss reduction is primarily due to eddy current loss suppression, as the high resistivity elongates the eddy current path.

[0075] Permeability was measured indirectly using an impedance analyzer or directly using a permeameter. In Example 1, the initial permeability was 75 at 100 kHz, slightly lower than the 90 of the uncoated powder, but with better frequency stability (maintaining 65 at 1 MHz). Although a non-magnetic layer was introduced into the shell, its nanoscale thickness had a negligible impact on the magnetic circuit cross-sectional area. Maintaining high-frequency permeability was primarily achieved by reducing eddy current losses through insulation.

[0076] Power loss density is a comprehensive measure of magnetic performance. In the implementation example 1, it is 115 kW / m² at 100 kHz / 0.05 T. 3 Comparison Example 4 (uncoated) 350 mW / cm 3Significantly reduced. Power losses include hysteresis, eddy current, and residual losses. The composite shell primarily reduces the eddy current component while having little impact on hysteresis losses.

[0077] The specific results are shown in Table 2.

[0078] Table 2 The shell continuity rate is directly related to the insulation reliability. Table 2 shows that the complete three-layer structure (Examples 1-3) all achieved a continuity rate of ≥99.5%, far exceeding that of the comparative examples (82-85%). This demonstrates the effectiveness of the synergistic crack-resistant mechanism between the MLD buffer layer and the nanolayered outer layer. In particular, Example 1 (MLD / Al2O3 / [Al2O3 / HfO2]) achieved a shell continuity rate as high as 99.8% after pressing at 1000 MPa, due to the good matching of the thermal expansion coefficients of HfO2 and Al2O3, resulting in lower interfacial stress. This is significantly better than the comparative examples.

[0079] Volume resistivity data showed that all coated samples outperformed the uncoated powder (10⁻⁶). -3 (Ω•cm), and the three-layer structure is significantly higher than that of a single-layer or double-layer structure. Example 1 reaches 5.2×10 9 The Ω•cm value is close to that of an insulator, meeting the requirements for high-frequency applications. This is due to the synergistic effect of the high insulation of the Al2O3 middle layer and the multiple interface scattering effects of the nanolayered outer layer.

[0080] Loss reduction rate is a key indicator of high-frequency performance. Example 1 showed a 67.1% reduction in loss at 100kHz, while Example 3 (TiO2 outer layer) achieved an even higher reduction of 68.5%, where the high dielectric constant of TiO2 helps suppress displacement current. In contrast, the comparative examples only showed a reduction of 9-29%, demonstrating the significant effect of composite coating on suppressing eddy current and dielectric loss.

[0081] (4) Environmental stability testing and data analysis Heat treatment stability was assessed using TGA (thermogravimetric analysis) and resistivity retention. TGA was performed in air at a heating rate of 10 °C / min, with Example 1 showing an oxidation initiation temperature of 450 °C. In the resistivity retention test, after heat treatment at 250 °C for 4 hours, Example 1 showed a retention rate >85%, while Comparative Example 2 only showed 70%. This high-temperature stability is attributed to the density of the nanolayered outer layer and the high melting point of HfO2.

[0082] Temperature resistance was evaluated through thermal cycling tests (-40°C to 125°C, 100 cycles). In Example 1, the shell continuity remained >99%, and the resistivity change was <5%, indicating that the layered structure with matched thermal expansion coefficients effectively alleviated thermal stress.

[0083] Corrosion resistance was assessed using salt spray testing (5% NaCl, 35°C, 48h) and damp heat testing (40°C / 90%RH, 168h). Examples 1-3, after testing at 40°C / 90%RH for 168 hours, exhibited resistivity retention >85% and salt spray weight loss <45% (compared to 100% in the control). The dense and chemically inert nanolayered structure of the outer layer effectively blocked the penetration of water vapor and corrosive ions. HfO2, due to its superior chemical stability, showed the best performance (weight loss of 38% in Example 1). Although the MLD / HfO2 / Al2O3 material in Example 4 exhibited excellent corrosion resistance (salt spray weight loss only 35% of the control), the continuity rate decreased slightly after pressing (98.5%), indicating that the Al2O3 middle layer is more crucial for mechanical strength.

[0084] The MLD / alternating HfO2-Al2O3 material in Example 5 exhibits properties between those of a three-layer and a single-layer structure, making it suitable for cost-sensitive applications. While the bilayer structures in Examples 6 and 7 outperform the single-layer comparative examples, their overall performance is less comprehensive than that of the three-layer structure. Specific environmental stability test results are shown in Table 3.

[0085] Table 3 In summary, through system process implementation and performance comparison analysis, the soft magnetic powder composite insulation coating technology provided by this invention demonstrates significant advantages. The three-layer composite shell structure (MLD flexible buffer layer + ALD-Al2O3 middle layer + nano-layered outer layer) effectively solves the problems of shell micro-cracks, insulation degradation, and high dielectric loss in traditional coatings under high frequency, high voltage, and high temperature environments, fully meeting the requirements of high-frequency magnetic devices. Future research directions can focus on multilayer material optimization (such as exploring new high-k dielectrics), improving process efficiency (such as developing continuous ALD equipment), and adapting to more demanding environments (such as high-temperature applications >500℃).

[0086] This invention provides a reliable material basis for the miniaturization and high efficiency of high-frequency power electronic devices.

[0087] Although the above embodiments have described the present invention and its implementation in detail, it should be noted that for those skilled in the art, any changes, modifications, substitutions, combinations, simplifications, etc., made to the corresponding conditions without departing from the technical principles of the present invention should be considered as equivalent substitutions, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for composite insulating coating of soft magnetic metal powder, characterized in that, Includes the following steps: S1. Pretreatment: The soft magnetic metal powder is subjected to plasma activation treatment, followed by drying in an inert atmosphere to remove physically adsorbed water and increase the surface hydroxyl density. S2. Flexible buffer layer deposition: Molecular layer deposition (MLD) is used to construct a 5-20 nm thick flexible buffer layer on the surface of activated metal soft magnetic powder. The flexible buffer layer is a metal-organic hybrid film formed by the metal center and organic ligand. S3. Insulating layer deposition: Atomic layer deposition (ALD) is used to deposit an insulating layer with a thickness of 5-20 nm on the surface of the buffer layer. The insulating layer is a metal oxide. S4. Outer nanolayer stack deposition: At least two metal insulating layers, including aluminum oxide and hafnium oxide, or aluminum oxide and zirconium oxide, or aluminum oxide and titanium oxide, are deposited alternately by ALD to form a nanolayer stack with a total thickness of 1-15 nm, wherein the thickness of each insulating layer is 0.5-10 nm. S5. Post-processing: The obtained coated powder is thermally densified in an inert atmosphere, and then heated in an oxygen-containing atmosphere to oxidize some of the organic components in the MLD buffer layer into carbon-doped metal oxides. Finally, lubricant and / or binder are added for shaping and heat treatment to obtain coated powder with a multi-level insulation structure. In step S2, the metal element in the metal center is one of aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, or manganese. The metal oxide in S3 is one of the oxides of aluminum, magnesium, titanium, zirconium, or hafnium.

2. The method according to claim 1, characterized in that, In step S1, the hydroxyl group density of the activated powder is not less than 5 per nm. 2 The active gas used in the plasma activation treatment is one of oxygen, ozone, or water vapor.

3. The method according to claim 1, characterized in that, In step S2, the flexible buffer layer is deposited by alternatingly introducing organic and inorganic precursors into the reaction chamber in a pulsed manner. The inorganic precursor is one or a mixture of several of the following: volatile metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes. The metal element in the metal alkylamino salts, organometallic compounds, halides, alkoxides, and metal β-diketone complexes is one of aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, or manganese. The organic precursor has two or more functional groups that can react with metal hydroxyl / alkoxy groups, including –OH, –COOH, and –NH2. The organic precursor includes one of ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, hydroquinone, p-phenylenediamine, glycerol, toluene diisocyanate, glycidyl ether, or glycerol.

4. The method according to claim 1, characterized in that, The lubricant or binder is added in an amount of 0.5-1.5 wt%; the lubricant is one of zinc stearate, silane coupling agent, polyethylene glycol, mineral oil, synthetic ester, silicone oil, glycerin and its derivatives, fatty acid or amide wax; the binder is one of epoxy resin, polyimide, phenolic resin, phosphate binder, silica sol or borate glass.

5. The method according to claim 1, characterized in that, The soft magnetic metal powder is one of the following: pure iron powder, iron-silicon alloy powder, iron-aluminum alloy powder, iron-silicon-aluminum alloy powder, iron-silicon-chromium alloy powder, iron-chromium alloy powder, iron-nickel alloy powder, and iron-nickel-molybdenum alloy powder, with a particle size range of 5-30 μm.

6. A composite insulating coated metal soft magnetic powder, characterized in that, Prepared by the method according to any one of claims 1-5, it has a flexible buffer layer, an insulating layer and a nanolayer stack sequentially coated on the surface of the metal soft magnetic powder body; The flexible buffer layer is a carbon-doped metal oxide formed by a metal center and organic ligands in a metal-organic hybrid thin film with a thickness of 5-20 nm. The insulating layer is a metal oxide with a thickness of 5-20 nm; The nanolayer stack consists of alternating insulating layers of at least two metals, with a thickness of 1-15 nm; The carbon-doped metal oxide in the flexible buffer layer is one of the oxides of aluminum, lithium, vanadium, cobalt, titanium, zinc, zirconium, copper, hafnium, or manganese. The metal oxide in the insulating layer is one of the oxides of aluminum, magnesium, titanium, zirconium, or hafnium.

7. The composite insulating coated metal soft magnetic powder according to claim 6, characterized in that, The soft magnetic metal powder is one of the following: pure iron powder, iron-silicon alloy powder, iron-aluminum alloy powder, iron-silicon-aluminum alloy powder, iron-silicon-chromium alloy powder, iron-chromium alloy powder, iron-nickel alloy powder, and iron-nickel-molybdenum alloy powder, with a particle size range of 5-30 μm.

8. The application of the method according to any one of claims 1-5 and the composite insulating coated metal soft magnetic powder according to any one of claims 6-7 in the fabrication of high-frequency power electronic magnetic devices.

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